Frequently Asked Questions

FAQ

Solar Applications

I’m new to AE’s solar offerings. What does AE bring to the table for PV manufacturing?
Our company is just starting out and needs to order a large volume of equipment at once. Can AE provide all the equipment I need within a tight timeframe?
Why should I choose a vacuum-based manufacturing process? What advantages does that technique offer over other available PV manufacturing methods, such as printing and evaporation?
I’m doing a CIGS process and my last layer is a TCO. Do you have any suggestions for controlling the temperature of my TCO process to avoid degrading the active layer underneath it?
I’m starting a new solar line. What are the major TCO types I should consider?
Which of these is the highest performing?
Which TCO materials typically pose the most problems?
Which TCO material is the most cost efficient?
Are there any additional manufacturing techniques I should consider for TCOs?

Sputtering Applications

Flat Panel Display Applications

Solar Applications

I’m new to AE’s solar offerings. What does AE bring to the table for PV manufacturing?
Answer: Where do we start? AE offers solutions for crystalline silicon, wafer-based solar photovoltaics, as well as for the major thin-film technologies, including amorphous and microcrystalline silicon, CIGS, and CdTe. We have one of the most comprehensive product lines in the industry, which enables us to offer effective solutions for every phase of PV production: power supplies from DC up to 60 MHz, thermal instrumentation, an array of gas, vapor, and pressure control products, and more. These products feature highly developed designs and technologies based on our 25 years of innovating solutions that increase precision, prevent defects, and improve throughput. In fact, for more than 20 years, companies developing and manufacturing photovoltaics have chosen our products. However, what we offer goes beyond our products and technologies. It also includes expert applications support, world-class manufacturing facilities, an established global sales and support infrastructure, and more.

Please see AE’s solar market web page for further details.

Table 1. AE products for solar PV manufacturing

PV Subsystem Category	Suggested Products	Examples of Solar Applications	AE Product Features
RF Power Supplies	Cesar^® RF Power Supplies Apex^® RF Power-Delivery Systems Navigator^® Digital Matching Networks	PECVD for a-Si	Advanced power-delivery technology Wide variety of frequencies, power levels, and functionality Sophisticated arc management
Low/ Mid-Frequency Power Supplies	PEII Low-Frequency Power Supplies PDX^® Mid-Frequency Power Supplies Crystal^® Mid-Frequency Power Supplies	PVD for SiO₂
DC Power Supplies	Pinnacle^® DC Power Supplies Pinnacle^® Plus+ DC/Pulsed-DC Power Supplies Pulsar^™ DC Pulsing Accessory	PVD for metal back contact PVD for TCO front contact
Gas, Vapor, and Pressure Control Products	Aera^® FC-7700 Series MFCs Aera^® PI-980^® Pressure-Insensitive MFCs Aera^® Transformer^™ Digital MFCs Aera^® FC-D770 Industrial MFCs Aera^® AS and GS Series Thermal Vaporizers Aera^® RS Series Vaporizer Refill Systems	All manufacturing phases	Extreme precision for enhanced process repeatability, throughput, and resource usage efficiency Wide variety of flow ranges and functionality
Instrumentation	Sekidenko Optical Fiber Thermometers and Emissometers	All manufacturing phases	Unique insight into process parameters for advanced development of breakthrough processes

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Our company is just starting out and needs to order a large volume of equipment at once. Can AE provide all the equipment I need within a tight timeframe?
Answer: It’s an exciting time because it’s been many years since a new thin-film process has emerged. One nice thing for the emerging solar market is that it can take advantage of all of the development that has happened for existing, adjacent markets. This development includes technology, as well as the infrastructure for equipment manufacturing and support. AE’s work in markets such as semiconductor, FPD, and industrial coatings has enabled us to develop substantial manufacturing capacity. We already have the processes, facilities, vendors, and other necessary resources in place at our world-class facility in Shenzhen, China in order to efficiently turn around an order of any size, such as a 30 megawatt or larger order for a new solar manufacturing operation.

In addition to equipment, we provide the support you need for the success of your new manufacturing operation. AE application engineers are on call to assist you with process development, setup, optimization, and troubleshooting. They offer valuable insight and expertise based on long-term experience with a host of markets, manufacturing techniques, and process conditions.

With sales and service offices in the major worldwide manufacturing centers, AE also has the global infrastructure to efficiently serve a worldwide industry such as solar. For example, if you are located in Europe, our local office can assist you from a convenient, nearby location. Likewise, if your customer is located in Asia, we have many offices you can work with throughout that continent, as well.

Figure 2. AE’s world-class manufacturing facility in Shenzhen, China can be rapidly scaled to meet the considerable equipment needs of a new solar manufacturing operation
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Why should I choose a vacuum-based manufacturing process? What advantages does that technique offer over other available PV manufacturing methods, such as printing and evaporation?
Answer: Today’s methods for PV manufacturing include sputtering (PVD), PECVD, printing, evaporation, and more. However, vacuum-based processes such as PVD and PECVD offer definite benefits that the other methods simply can’t deliver. Specifically, PVD and PECVD provide atomic-level control that enables you to more precisely determine film characteristics, such as stoichiometry, crystallinity, and uniformity across the substrate. PVD and PECVD also produce fewer defects than other methods. This high level of control culminates in two critical benefits for today’s solar panel manufacturers: greater PV efficiency and increased throughput.

Figure 3. Simplified representation of a sputtering (PVD) process—Other PV manufacturing methods can’t match the precision of vacuum-based processes, which work on the atomic level

Figure 3 illustrates the atomic-level behavior of a sputtering process. In the first step of this process (left), argon atoms are ionized. An accelerated electron strikes an atom in an inelastic collision that removes an electron from the atom, creating an Ar+ ion. Next, during the sputtering step (middle), the Ar+ ion is accelerated toward the negative cathode surface. It strikes with enough energy to remove target material. In the final phase (right), the target material reaches the substrate surface, where it is deposited as a thin film. For more information on sputtering, please see our Sputter Spotlight^® E-newsletter.

Another benefit of using a vacuum-based process is the fact that within the areas of PVD and PECVD, a great deal of expertise and technological development has been amassed that can be applied directly to PV manufacturing. AE offers over 25 years of experience, as well as a comprehensive and highly developed product portfolio that enables an exceptional level of control over film properties compared to other subsystem manufacturers. For example, our products enable a lower defect rate, which not only increases solar cell efficiency, but allows higher-power operation as well, resulting in increased throughput. Higher-power operation also enables successful coating of large-area substrates. Our Crystal^® AC power supply has a long track record of success in achieving the power levels required for architectural glass applications (including low-E coatings for the passive solar market), which also makes it ideal for the increasing substrate sizes in the PV industry. Please see our Design Aspects of Large-Area Coating Supplies white paper for more information.

In fact, AE’s expertise in large-area coating for industries such as FPD and architectural glass has direct application to large-area PV manufacturing. We’ve honed our products, technologies, and expertise in these adjacent markets, as well as the semiconductor industry, which, of course, is the original silicon-wafer application. You could say that AE cut its teeth in the semiconductor industry, an industry that requires extreme manufacturing precision and allows little or no margin for error. In fact, semi has the smallest process window of any industry. Therefore, our products and technologies are designed around the concept of precision, a fact that benefits solar in the form of increased cell efficiency and process throughput.
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I’m doing a CIGS process and my last layer is a TCO. Do you have any suggestions for controlling the temperature of my TCO process to avoid degrading the active layer underneath it?
Answer: Absolutely! Thermal budgeting is a pressing issue for many manufacturing applications today. A little background for our readers: most PV manufacturing processes deposit the TCO layer first, before any other layers. However, for CIGS (and some thin-film Si) solar cells, the TCO is the last to go down. Unlike metal layers, which can be deposited with cold processes because their electrical conductivity is relatively unaffected by temperature, the conductivity of TCOs is highly affected by heat. To produce sufficient electrical conductivity, conventional TCO processes are performed at high temperatures. The problem is that for CIGS processes, which deposit the TCO last, this may exceed the thermal budget of all preceding layers. Excessive temperature can cause diffusion of the dopant within the active layers underneath the TCO, resulting in significant PV performance degradation. Further, if the substrate is temperature-sensitive, it can actually melt under the temperatures of conventional TCO deposition processes. This is a particular issue for flexible polymer substrates.

Figure 4. For a CIGS solar panel, the last layer deposited is the TCO, while on a-Si and CdTe panels, the first layer deposited is the TCO. This poses special heat-related challenges for CIGS manufacturing

So, what is the answer to this seemingly dire situation? Power methods exist that can be performed in a temperature range that will not cause diffusion of the active layers or substrate melting, while producing good TCO conductivity. These are standard methods with records of success for other processes requiring temperature control, such as for electrodes for FPD color filters, and transparent conductors for touch panel processes. Please contact us for details on an effective solution for your temperature-sensitive process.
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I’m starting a new solar line. What are the major TCO types I should consider?
Answer: Congratulations and good luck with your new endeavor! To provide a little background for our other readers, the transparent conductive oxide (TCO) layer is the first deposited for multi-junction amorphous silicon and CdTe (cadmium-telluride) cells. For most CIGS cells, the TCO is deposited last. This layer is transparent to allow sunlight to enter the solar cell, and also must be electrically conductive.

Figure 3. For most CIGS solar panels, the last layer deposited is the TCO, while for multi-junction amorphous silicon and CdTe panels, the first layer deposited is the TCO (Click graphic to enlarge.)

There are five major types of TCO: ITO, IZO, AZO, SnO, and Cd₂SnO₄. It’s also possible to use a very thin layer of metal, such as silver, to serve the same function as a TCO. Each option has its own advantages and disadvantages, so when deciding what type of TCO is best for your manufacturing operation, it’s important to weigh your particular priorities for such issues as layer performance, cost, preferred deposition method, and ease of manufacturing.
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Which of these is the highest performing?
Answer: There is no clear winner in terms of TCO performance. It depends on your requirements for a number of parameters, including:
- Sheet resistance (Ω/□)
- Cost
- Light transmission (T%)
- Chemical Stability
- Diffusion
Table 1 below shows how four of the five major types of TCO generally compare to each other. All TCO types can be sensitive to sodium diffusion. Also, Cd₂SnO₄ provides good chemical stability, light transmission, and sheet resistance, but is very expensive and poses certain health hazards. It’s interesting to note that ITO is specifically used for TCOs in flat panel display manufacturing because that application requires low resistance and high light transmission.

Table 1. TCO properties comparison

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Which TCO materials typically pose the most problems?
Answer: There are a number of potential challenges related to TCO manufacturing, but generally, reasonable solutions exist.

Certain challenges are associated with conditions created by the TCO material itself. For example, cadmium is a heavy metal and therefore toxic, making it difficult and hazardous to deposit Cd₂SnO₄. Also, bonded ITO tends to produce nodules on the target that prevent complete target utilization, necessitating frequent process shutdowns for target replacement. However, DC pulsing lowers the probability of nodule formation, helping to maintain target quality over time so that you can utilize the target more fully. Although DC pulsing is quite effective here, the best process power option for alleviating this problem seems to be RF-superimposed DC. Higher target surface temperature also reduces or eliminates nodules. Please see Maintaining Target Quality in the Q4 2007 edition of AE’s Flat Panel Focus^®newsletter for more details about nodule formation.

Another challenge inherent to the TCO material itself is AZO’s tendency to arc. It can produce hundreds or even thousands of arcs per second. Solar panel manufacturing can tolerate this level of arcing, especially if certain measures are employed during manufacturing. The use of a high-quality DC power supply with effective arc management capabilities is absolutely vital to processes depositing AZO. Pulsing provides an additional benefit by reducing the number or rate of arcs. In addition, correct output cable selection is critical. Improper selection may prevent the power supply from detecting and thus extinguishing arcs. Output cables must be shielded and have low inductance to prevent noise, high stored energy, and other problems. Please see What kind of output cables should I use for my power supply? in the Q4 2008 edition of Flat Panel Focus for more information.

The problems described above are caused by properties of the TCO materials themselves. Other TCO-related problems are associated with the particular conditions of a given manufacturing operation. For example, TCO deposition traditionally is done at high temperatures in order to achieve sufficient layer conductivity. Deposition temperature is a concern for processes using flexible polymer substrates, which melt at high heat. Temperature is also an issue for the manufacturing of certain CIGS solar cells, in which the TCO layer is deposited last. Underlying doped layers may suffer from diffusion at the high temperatures required. Please see the Q2 2008 edition of PV Sun Times for more information on this phenomenon.

An excellent solution exists for temperature-sensitive processes: RF-superimposed-DC or RF-superimposed-pulsed DC. These process power methods enable the deposition of a high-conductivity TCO while keeping temperatures low enough that diffusion does not occur. Please see AE’s Arc Handling in RF-Superimposed DC Processes application note for more information on these methods.
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Which TCO material is the most cost efficient?
Answer: Table 1 shows that as TCO sheet resistance decreases, materials cost increases. However, straight material cost doesn’t necessarily tell you which material will be most cost efficient in your manufacturing operation. Cost efficiency is a fairly complicated issue related to TCOs because each material has its own unique properties, and each process has its own requirements.

For example, ITO is one of the most expensive TCO materials, but you don’t need to deposit as much compared to, for example, AZO, in order to achieve a comparable level of conductivity. Another benefit of a thinner TCO layer is that it transmits light better than a thicker layer and thus increases cell efficiency. However, ITO is also known to have problems with nodule growth on the target, which reduces target utilization and necessitates more frequent target replacement. This increases cost and downtime. Nevertheless, after all is said and done, because you don’t need as much material, your net cost for ITO may be comparable to that for a less expensive material. Also, the possible cell efficiency improvements it offers may outweigh the cost.

Figure 4. AZO vs. ITO comparison—ITO’s higher material cost may be offset by the fact that you can deposit less and still achieve the same level of resistance as less expensive materials, such as AZO. A thinner TCO layer also leads to better light transmission and thus improved cell efficiency

* In terms of material properties alone, the resistance of ITO is approximately ten times lower than that of AZO. Therefore, you can deposit much less ITO and produce a layer that performs comparably to a much thicker AZO layer. If a given ITO layer is five times thinner than the typical AZO layer, the resistance of the ITO layer is still approximately two times better (lower) than the AZO layer.

All in all, figuring TCO cost efficiency has many variables. Please contact us if you’d like assistance determining the best TCO choice for your process.
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Are there any additional manufacturing techniques to consider for TCOs?
Answer: Yes, you might consider chemical etching, which can be performed on AZO and possibly other TCO materials to increase internal light reflection. This enhances quantum efficiency by creating a faceted surface that reflects light back into the solar cell. Without this faceting, the likelihood is greater that reflected photons would escape the cell without creating a useful collision with an electron. TCO texturing for internal light reflection increases quantum efficiency. (See Figure 5.) This means that more of the photons that enter the cell are used to actually generate electricity.

Figure 5. Chemical etching creates a faceted surface on the TCO layer. This faceting increases internal light reflection and quantum efficiency by reflecting light back into the cell that otherwise would have escaped (Click graphic to enlarge.)

Also consider adding barrier layers to your solar cell. Depending on where they are deposited within the solar stack, they can provide any of the following benefits:
- Protection from external environment
- Control of sodium diffusion (when SLG is used)
- Shielding of underlying layers from laser scribing
For barrier layers, the most common deposition method is AC dual-magnetron sputtering. However, PECVD is another viable option. It’s important to deposit a thick barrier layer (> 1 micron) that is pinhole-free. Depending on the purpose of your barrier, pinholes or insufficient thickness may allow contaminants to enter the solar cell, sodium to leach out, or laser scribing to damage underlying layers. Figure 6 shows a barrier layer deposited to curb sodium diffusion.

Figure 6. The barrier layer between the soda lime glass and TCO in this solar cell curbs sodium diffusion (Click graphic to enlarge.)
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Sputtering Applications

I have a specific target material. How do I determine which type of process power supply to use: an RF power supply or an AC or DC supply?
Answer: It’s certainly straightforward to determine if you need to use RF; you will need a simple ohm meter. Place both ohm meter leads anywhere on the target surface. If your meter reads infinity (for example, a pure alumina target will read infinity), your process requires RF power. On the other hand, if your ohm meter has a reading other than infinity, use an AC or DC power supply.
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OK, then, how do I choose between AC and DC power?
Answer: This is a tricky one. If your process is a batch process, you can probably get by with DC or pulsed DC. We are concerned, here, with losing the anode during the process. If you are reactively sputtering SiO₂ using DC, the anode (floating or chamber) will eventually build up with the insulator SiO₂. This insulating layer impedes the electrons from flowing back to the power supply (the + return). The process voltage will rise, and the process will get ill and eventually die horribly with major arcing and reduced power. The key is to know just how long your process is and how much material you want to lay down. You really need to know and understand your chamber geometry and sputter process intimately. There are interesting little tricks to keep the anode cleaner longer. Pulsed DC is one of these. (Others are for another discussion.)

An inline process that requires the insulating material to be sputtered for days and weeks is pretty straightforward. AC is a very good way to go here. The down side is that a second cathode will need to be purchased, installed, and maintained. AC will provide improved film quality, including flatness, reduced pinholes, and better packing density.
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How do I determine whether straight DC or pulsed-DC power is the better fit for my process?
Answer: You’ll almost always see better film quality with pulsed DC, but straight DC is somewhat less expensive. That said, using pulsed DC lets you avoid buying another, expensive cathode. With pulsed DC, you will see improved film flatness, packing density, transmission, and a reduction of pinholes.
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What sputtering rates can I achieve?
Answer: If I could answer that easily, I’d be rich and famous! The answer depends on each, individual configuration—which can be dynamic. Sputtering rate depends on:
- Chamber geometry and cathode/anode design
- Operating pressure
- Gas mix
- Target thickness
- Magnetic strength
- Operating power
- Target-to-substrate distance
That said, you’ll probably see rates between 2 to 10 Å per second. The real message here is that optimizing your sputtering system is both an art and a science—a balance among cost, sputtering rate, and film quality. The real key is to know and understand your chamber and sputtering process intimately. You should do initial rate runs at longer times than your actual process run so you learn the personality of your chamber and process. Do initial rate runs at lower powers, and slowly raise the power each time so you will know what to expect during the real process.
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What arc set points should I dial into my sputtering equipment menu system?
Answer: Another answer that could make me rich and famous. Again, it depends on several variables:
- Target material and thickness
- Cathode size
- Operating voltage, which is affected by gas mix, magnet strength, and chamber pressure
Typically, I recommend setting the arc trip point at 10% of operating voltage. However, larger targets need longer off times, as it takes a longer time to totally dissipate the arc energy on these big guys. The bigger the target surface, the longer the arc handling off time.
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My sputtering rate had been holding steady. Why did it change suddenly today?
Answer: OK, my first response is: what is the last thing you did to your system? About 90% of the time, this gives you the answer. If that doesn’t give you the answer, here are other ways to investigate:
- Are you seeing more arcs?
- Did the plasma color change?
- Did the voltage and current on the power supply change?
- Can you go to the same base pressure?
- Is the same gas flow needed to obtain the same process pressure?
- Do you have the same time for the rate of rise test?
All of the above seem to point toward a leak in the chamber somewhere. It can also have to do with chamber cleanliness. Both of these can be dealt with in deeper discussions.
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What is the difference in utilization between planar and rotatable targets?
Answer: You typically get about 35% utilization out of a planar target and about 85% out of a rotatable. These numbers are independent of the process power method or target material you are using. Please note, however, that rotatable cathodes are not compatible with RF power. Generally, they are best used in AC, DC, or pulsed-DC powered processes.
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How do the different erosion patterns of planar and rotatable targets affect the process over the course of the target’s lifetime?
Answer: Although planar and rotatable targets do erode differently, there is actually little difference in how you should handle your process power over the course of the target’s lifetime. For rotatables, target thickness decreases in a uniform manner, causing the magnets to move closer to the target surface. This results in an increase in current and a decrease in voltage. Although planar targets erode in a non-uniform manner, you will see a decrease in current and an increase in voltage.
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You’ve mentioned before that generally, pulsed-DC and AC power produce better films than straight DC. What is the actual difference in film quality?
Answer: The photos below show that the difference in film quality is quite significant.

Film quality produced by straight-DC power (above) vs. pulsed-DC power (below)
Source: Centre for Advanced Materials and Surface Engineering, University of Salford, U.K.

Film quality produced by straight-DC power (above) vs. AC power (below)

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How can I optimize my sputter rate?
Answer: The general rule of thumb is that the lower the pressure, the better your rate and film quality because there are fewer molecular collisions in the plasma and a longer plasma throw distance (the ability of the sputtered particles to reach the substrate from the target). So, sputter at the lowest pressure you can, but of course, avoid going into gas starvation conditions, which can cause problems for your power supply. (See Evaluating Power Supply Quality above.)

The second thing you can do is use a gauss meter to check the balance of your magnetrons. Unbalanced magnetrons widen plasma throw distance and create excess electrons, which affects substrate heat and film quality. Balanced magnetrons focus throw distance, which helps your sputter rate especially when the distance is great between the cathode and substrate.

Unbalanced magnetrons (above) vs. balanced magnetrons (below)

Third, check the strength of your magnets. As you increase magnet strength, your plasma throw distance increases. One thing to note is that although this results in greater sputter rate and film packing density, stronger magnets deepen the groove in your target, which decreases utilization.

All of that said, sputter rate is a complex and multi-faceted issue. Please feel free to contact me at sputtering@aei.com for advice on your specific situation.
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I’ve heard that an upcoming technology called HPPMS produces extremely flat, uniform films, but is not yet widely available. Are there any alternatives that produce similar results using readily available equipment?
Answer: You’re in luck! There is an existing and easily accessible technique that will give you a similar degree of flatness as HPPMS (high-power, pulsed magnetron sputtering) technology. This technique combines two process power methods: RF and pulsed DC. An added bonus is that, although it is a relatively new method itself, RF-superimposed pulsed DC has been around long enough that a certain amount of information has been developed and made available about it. Please see AE’s power supply selection matrix, as well as our Arc Handling in RF-Superimposed DC Processes application note for details on this method.
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I am setting up a process and have a question regarding an RF power supply. What are the advantages and disadvantages of running a process in voltage or power mode? Will I get the same film properties running the process in fixed power that I will get running it in fixed voltage mode?—Anonymous
Answer: I personally would run your supplies in power control mode. The supply will "see" the load and adjust the V and I accordingly so there is room on both for any anomalies in the process. If the supply is run in voltage control mode, then it will adjust the P and I accordingly. This is OK if you have strict control of your load. If the load changes any, the P and I will also change; therefore the process can go out of spec quite easily. Good luck!
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We are researching TiO₂ films for an optical application using a single magnetron cathode. The target would be TiO₂ using a pulsed-DC power supply. The substrate would be heated up to 350°C max, and we would use O₂ and Ar as process gases. Can you recommend a pulsed-DC power supply and the best process parameters to get a good, dense film and high deposition rate? What is the maximum deposition rate possible for TiO₂? Give me the same information for SiO₂.—Atul Nagras
Answer: I would use a Pinnacle^® Plus DC/Pulsed DC Power Supply. AE offers 5 kW and 10 kW versions. The version you choose would depend on the size of your target. My general rule is 100 W per in² inch max, 70 W per in² nominal for decent cooling overhead. This is for continuous operation.

TiO₂ in the fully oxide mode is quite slow. The rate will depend on lots of things in your chamber: distance from target to substrate, pressure, magnet strength, etc.—you know the drill. A good guess would be 3 to 5 Å per sec. SiO₂ would use the same supply and you will probably get 5 to 8 Å per sec.

Please see What sputtering rates can I achieve? and How can I optimize my sputter rate? for more information about the factors involved in sputter rate. And feel free to contact me at sputtering@aei.com for further advice.
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I don’t have enough space in my chamber to use DC in my dual-magnetron system. Are there any good alternatives?
Answer: There are two main choices: RAS or RF superimposed DC (RF/DC). I wouldn’t recommend using RAS in this case because it would require drilling holes in the vacuum chamber in order to add high-voltage anodes, which is extremely complicated and labor intensive. On the other hand, RF/DC is less complicated to add than RAS and requires less space than plain DC, since only one cathode is required. Cost-wise, there is a bit of a tradeoff. RF/DC is more expensive initially because you have to buy two power supplies (an RF unit and a DC or pulsed-DC unit), but you’ll save on consumables because you have only one cathode to buy.
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I’ve heard that setup for RF superimposed DC is complicated. What are the main pitfalls to avoid?
Answer: Proper arc handling setup is key to success with RF/DC because two different types of power are working simultaneously.

The DC or pulsed-DC power supply can more accurately identify and respond to arcs than the RF power supply. Therefore, your DC power supply must be able to control your RF unit to shut off both DC and RF power when an arc occurs. It must also be able to quickly return power once the arc is extinguished. DC power supplies on the market today vary in this regard. While some offer no built-in DC/RF control method whatsoever, others offer powerful control. For example, Arc-Sync™ technology enables Pinnacle^® Plus+ DC power supplies to easily and effectively control a connected Cesar^® RF unit in order to handle arcs.

There are additional issues to keep in mind when setting up RF/DC, such as cabling and the use of a filter/combiner. For more information, please see our Arc Handling in RF-Superimposed DC Processes application note.
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I have a question concerning the Pinnacle^® Plus+ 5 kW (325 to 650 VDC). We are using it with a small 3" molybdenum target (in DC mode) with a magnetron for sputtering moly films. However, our current process runs only at 300 W (at about 400 VDC; 0.75 A), which is well below the specified repeatability ("0.1% from 10% to 100% of rated power"). I'm a bit concerned about the overall process stability. Do you have any idea on the output accuracy and repeatability of the 5 kW power supply, operating at only 300 W? Would it be better to use a 500 W DC model? –Jeorg Winkler
Answer: Yes, you do have a problem there. While Pinnacle power supplies and their Pinnacle Plus+ cousins can indeed run “down in the weeds,” I would advise against it. AE supplies are current sources and need some sort of amperage to lock their control circuits onto. I have had a couple of other folks try to turn the Pinnacle Plus+ on at this low power who are having some strange and wonderful things happen to their processes. The current is too low for the control circuits, and accuracy will go out into the 5% range at this low power. Repeatability might not be sufficient either, as the supply might be thinking it is in a constant arc.

I agree that you should run with a Pinnacle 3 kW or an MDX 1.5 kW with a Sparc-le^® V. We know that the Sparc-le V needs about 110 to 150 W just to “heat its innards.” Knowing this, you can make the appropriate adjustments and get much better repeatability.
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How far apart do the magnetrons need to be when you are using an AC supply and a dual-magnetron system (DMS)?
Answer: This is a really good question. When you are using planar magnetrons, they can be as close as 2.5 cm (1″) and as far as 1 m (3'). The key is that you need a good path for electron flow between the magnetrons. Nothing other than the darkspace shields should be in the way of the electron flow. If you are using planar magnetrons side by side (facing the same direction or even slightly tilted toward each other), you will need to “rotate the tires”—swap target faces or even rotate them on the same magnetron, because the racetrack that is closest to the other magnetron will wear very fast, which reduces the target utilization.
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What rate can I expect from a dual-magnetron system and AC supply compared to a DC supply and one magnetron?
Answer: If we say that DC is always on and therefore we will get 100% rate of deposition, then an AC supply with a DMS will have about 80 to 85% of this because it crosses zero when it changes sputtering magnetrons. Due to the constantly changing AC signal, it cannot give a consistent signal to the magnetrons for sputtering. When it nears zero, the sputtering decreases, and when it actually hits zero, sputtering ceases. The other magnetron must re-light the fire, so there is a lag in current here.
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Flat Panel Display Applications

How do I determine if pulsed DC is a good fit for my FPD process?
Answer: If you have processes that are very sensitive to damaging arc events, then pulsed DC can surely help. Charge buildup on dielectric surfaces is inherent to every target. Pulsed DC serves to prevent damaging arcs from happening in PVD processes by periodically reversing the voltage and neutralizing this buildup.

Pulsed DC almost always creates better film quality, cost savings, yield, and throughput than straight DC. It reduces the occurrence of pinhole defects and improves electrical properties by reducing resistivity. It can also reduce material costs by both improving target utilization and enabling the use of less expensive targets, with no negative effects on film quality. This dramatically increases process productivity and throughput.

For existing DC-powered PVD processes, it’s relatively easy to add this valuable pulsing feature by integrating an accessory, such as AE’s Pulsar®, into your system.
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With pulsed DC, does the lack of sputtering during the voltage reversal affect my sputter rate?
Answer: Only slightly. AE’s unique pulsed-DC topology allows for energy storage during the voltage reversal step. This energy is then released during the subsequent sputter step. In essence, the average power delivered is therefore equal to similar DC-sputtering processes.

That said, sputtering rate is complex and influenced by many variables, including:
- Chamber geometry and cathode/anode design
- Operating pressure
- Gas mix
- Target cooling
- Target thickness
- Magnetic strength
- Operating power
- Target-to-substrate distance
Optimizing your sputtering system is both an art and a science—a balance among cost, sputtering rate, and film quality. The real key is to know and understand your chamber and sputtering process intimately. To fully understand how pulsed DC affects your process, perform initial rate runs at longer times than your actual process run to learn the personality of your chamber and process. To learn what to expect during the real process, you can try these initial runs at lower powers, and slowly raise the power each time as a method of system characterization.
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Are there any technologies that can extend OLED lifetime by improving the quality of the encapsulation layer?
Answer: Thin-film encapsulation significantly improves OLED lifetime sustainability by creating a barrier against air and moisture. This layer may be especially beneficial to flexible displays because the various substrates being considered, such as flexible polymers, can be penetrated by liquids and gases. Poor film quality can allow water and air to contaminate the organic layers by diffusion through the substrate.

In order to create this barrier, it’s critical to have the appropriate film properties for your application, including an absence of pinholes, as well as your desired level of film density and crystallinity. Various plasma processes allow you to control energy to enable the improved film characteristics that effective encapsulation requires.

AE has products that can attain the appropriate energy levels, as well as the arc-management capabilities that prevent arc-caused pinholes. AE’s diverse portfolio features DC, pulsed DC, and RF products that are designed to solve the challenges posed by such leading-edge applications. Please contact us at FPDapplications@aei.com for additional information.
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Where can I get help developing OLED and other advanced processes?
Answer: Expertise in adjacent thin-film markets is extremely useful to FPD process innovation. The push for better luminous efficiency, and the introduction of new devices such as flexible displays (OLEDs) and digital signage, create the need for more advanced manufacturing processes that enable end-product cost reduction. The following table draws general parallels between tomorrow’s FPD manufacturing and today’s adjacent thin-film processes.

FPD Application	Adjacent Thin-Film Application	Commonalities
All next-generation FPD devices	Semiconductors	Extremely precise processes
Flexible displays	Web coating	Flexible substrates Very high throughput Low-temperature processes
Large-scale displays	Architectural glass	Large-area substrates Equipment sourcing strategies Increasing power requirements
OLEDs	Photovoltaics	Manufacturing operation design^[1]Technology innovation

[1] Photovoltaics convert light to electricity, while OLEDs perform a reverse operation, converting electricity to light. Therefore, the two applications have extremely similar materials, equipment, processes, and procedures. Some examples of these commonalities include transparent conductive oxide, conductor, and encapsulation layers. See Question 3 above for details on encapsulation.

So, where can you find expertise that encompasses all of these thin-film industries? AE has been innovating technologies that enable precise plasma processes for decades. With experience in all of the adjacent thin-film applications listed above, we can be a valuable partner in your process development efforts^[2].

Once process design is complete, AE can assist with on-site system integration. We can also perform extensive in-situ tests to help ensure the success of your new design. This can become critical, given the trend of limiting initial acceptance testing (IAT) and performing only final acceptance testing (FAT) at the end-user site^[2].

If you have questions about your specific application development efforts, we’d be happy to answer. Please contact us at FPDapplications@aei.com.

[2] Please check with your equipment supplier to see what AE support options apply to you.

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What existing product technologies can benefit FPD?
Answer: In terms of manufacturing technology, today’s FPD market actually has an advantage over the early semiconductor industry. While semiconductor development had no technology base to start from, FPD was derived from semiconductor equipment and methods. Therefore, it started out with strong, highly developed manufacturing techniques. This has also enabled more rapid advancements compared to other industries. As the FPD market matures, existing technologies from other markets will continue to offer benefits.

Technologies that offer benefits to FPD manufacturing include:

Technology	Benefits
Arc management	Reduces substrate damage (pinholes) Improves yield Allows higher power levels for increased throughput
Flow control	Increases process stability Enables faster process transitions and shorter process steps
Match network technology	Improves power-delivery accuracy and efficiency, for better film quality and yield
Precise power delivery	Improves yield
Precise subsystem control and monitoring functions	Eases process manipulation and innovation Enhances process productivity and yield Increases uptime
Pulsed DC	Improves film quality and yield Reduces material cost

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The benefits of pulsed DC sound great, but I’m concerned about my sputter rate. Does pulsed DC remove sputtering energy during the reverse pulse?
Answer: It depends on the quality of your power supply. Lower-quality power supplies do reduce your sputter rate because they dissipate sputtering energy during the reverse pulse. However, AE power supplies store sputtering energy during the reverse pulse. This energy is then utilized during the pulse, which maintains your sputter rate and throughput.
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I use AE’s VFP (Virtual Front Panel) to control and monitor my power supply, but can VFP help with process development?
Answer: Yes! VFP allows you to manipulate your process and observe the results through your PC. In fact, you don’t even need to be near the production tool in order to test new recipes. You can control or monitor remotely through Ethernet on your network. During system startup or R&D mode, you can write new recipes while emulating specific process conditions on a specific tool. This is extremely convenient and versatile, and reduces expensive tool use. A number of AE power supplies offer VFP. Please contact us for more information.
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In your experience, have you encountered any simple and inexpensive fixes that can create significant process improvements?
Answer: There are a few that come to mind, but let’s focus on a common one: cable length and quality. One way to reduce arcing and arc damage is to check your power supply-cathode cable. Energy is stored inductively in cabling, and cables have a certain amount of inductance per meter. Decreasing cable length and using a low-inductance cable reduce the stored energy in the power supply cable-cathode system. This reduces the amount of power potentially delivered to arcs when they occur. Therefore, use the shortest, lowest-inductance cable possible between the power supply and cathode.
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I’m working hard to create and maintain the best productivity possible for my PVD process. Where can I get help?
Answer: With today’s FPD industry so focused on throughput and yield, it’s absolutely essential to make the most of your PVD processes. As applications and processes develop, AE can team up with OEMs to optimize your advanced technologies. Choosing equipment suppliers that provide comprehensive, responsive support enables your systems to grow as new technologies become available.

Your equipment suppliers’ support should include the following:
- Applications support^[1]—AE employs experts from our served industries to assist with process-related opportunities. The customer benefits from this activity both immediately and in the future as the experience gained is brought back to AE’s design teams for further product development.
- Process improvement products^[1]—Are your processes living up to their full potential for throughput, yield, and cost efficiency? Having full access to AE’s diverse product portfolio allows customized optimization opportunities. This ensures that you’ll receive the ideal products for your processes.
- Product repair services^[1]—AE offers convenient full service centers in all of the major manufacturing regions worldwide. Our knowledgeable employees ensure a rapid and professional service experience.
- Product upgrade services^[1]—Continuous product improvement is key to the success of AE and our customers. We provide such improvements to extend the lifetime and performance of your products.
[1] Please check with your equipment supplier to see which AE support options apply to you.
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Do you have insight into the industry drivers that need to change in order to make FPD manufacturing more profitable?
Answer: Current market conditions are certainly frustrating. You may feel like you’re in a bit of a holding pattern with less-than-satisfying profits until consumers start buying more FPDs or until manufacturing costs significantly decrease. But there’s good reason for optimism. First of all, there is strong consumer interest in FPD technology and therefore great potential for growth. Still, at least a few things need to happen to turn this potential into real profit.

The beginning of the semiconductor industry was very similar to today’s FPD market. Consumer interest was high, but sales lagged. How did semi overcome this predicament and achieve the increased sales volumes that finally drove the industry into sustained profitability? There were a number of factors, including improvements in manufacturing productivity and material affordability—leading to end-product cost reductions that allowed improved market penetration and increased consumer demand.

There are already signs that the FPD industry is following in the footsteps of the semiconductor industry. Entertainment enthusiasts are consistently buying FPDs to replace CRT technology, which they now see as inadequate. Major computer manufacturers no longer treat FPDs as a luxury item, and most include them as standard equipment for new systems. Additional cost reductions through industry alliances are creating improved usage and distribution channels. These are signs that things are changing for the better and will continue to do so.
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You talked about CEX in the Q4 2007 edition of FP Focus. What exactly is it for?
Answer: CEX stands for common exciter oscillator and is used to connect multiple power supplies together that are connected to multiple electrodes or cathodes in the same chamber. The use of CEX serves to efficiently contain the plasma and alleviate the potentially debilitating effects of crosstalk between the electrodes or cathodes. This type of crosstalk can lead to target damage, substrate arcing, and substrate damage. It may also lead to eventual power supply damage. In addition, crosstalk may prevent you from reaching the desired power level, which decreases throughput.

Larger substrates, such as those frequently used in FPD and architectural glass manufacturing, and more commonly being used in solar applications, can require a dozen or more cathodes per chamber. In order to fit into a single chamber, the space between cathodes must shrink. When closely-spaced targets are not synchronized using a feature such as the PEII power supply’s CEX, they can be at different potentials, causing them to interfere with one another. This interference is called crosstalk and can lead to the serious process, film, and equipment problems described above.

Please see our Enhanced Plasma Containment for Inline Sputtering Systems application note for instructions on using the PEII low-frequency power supply’s unique CEX capability to create an alternating cathode arrangement that significantly improves process control, film quality, and uptime.
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Why is it that some AC power supplies feature CEX and others do not?
Answer: AC power supplies are either fixed or variable frequency. In order to use CEX to synchronize multiple AC power supplies, the output of all of those power supplies must be at the same frequency. Therefore, it’s fairly straightforward to use CEX to synchronize fixed-frequency AC power supplies, such as AE’s PEII power supply. However, the output of variable-frequency power supplies, such as AE’s Crystal^® power supply, depends on the load impedance, and this varies based on process conditions. This means that each power supply in the chamber will likely produce a unique frequency based on the unique impedance. Therefore, by definition, it is impossible to synchronize multiple variable-frequency power supplies with CEX or any other phase synchronization feature.

Please note that the benefits of CEX aren’t limited to processes using fixed-frequency AC power supplies. The Pinnacle^® Plus+ pulsed-DC power supply, as well as the Pulsar^® and Sparc-le^® V DC pulsing accessories, feature CEX to synchronize the output of multiple pulsed-DC units. This delivers the same plasma-containment and crosstalk-alleviation benefits to pulsed-DC power arrangements as described above for AC power supply arrangements. CEX is also available on certain AE RF power supplies.
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My power supply features CEX. How do I set it up properly?
Answer: CEX setup involves simple connections from the CEX/Drive Out port of one unit to the CEX/Drive In port of another, as shown in the illustration below. Please note that it’s also necessary to insert a CEX termination plug in the CEX/Drive Out connector on the last unit.

The following illustration shows the back panels of multiple PEII power supplies that are properly connected in a CEX arrangement. Please also see your power supply’s user manual for further instructions, or contact us and we’d be happy to answer questions about CEX setup for your specific system. Please also see our Enhanced Plasma Containment for Inline Sputtering Systems application note for more information on CEX benefits and setup.

Figure 1. Proper CEX setup for connected PEII power supplies
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My power supply won’t reach set point. Why is this happening, and what can I do about it?
Answer: In an integrated system, below-set-point power delivery triggers an alarm, but in a lab environment, it actually causes thinning of the deposited film. As to the cause of the power-delivery problems you are experiencing, there are a couple of possibilities. First, your power supply simply may not be able to deliver the power you need because of a voltage or current limit that is due to impedance mismatch. The solution is to find a more appropriate power supply for your needs. To minimize this problem, AE power supplies have extremely wide impedance ranges, and some are offered in specific impedance configurations to meet your particular needs, such as the Pinnacle^® Plus DC/Pulsed-DC power supply, which is available in a high-Z and low-Z configuration.

Another possibility is that your arc rate is too high. In order to extinguish an arc, the power supply shuts down for a very short period of time and then turns on again. Usually, after it turns back on, its output returns to set point. However, if there are too many arcs, the power supply may be shutting down so often that the amount of actual delivered power is falling below set point. For this possibility, the solution is to check your arc parameters and make sure they are set up appropriately for your process. Also evaluate your process parameters and contact Ken for further assistance.
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How do determine the best arc-management settings for my process?
Answer: Understanding and correctly setting up your power supply’s arc management enables you to prevent a number of process and film quality problems. This can also help you troubleshoot if arcing-related process or film problems arise. If you’re asking this question, you probably already know that the potential effects of excessive arcing can range from occasional process interruptions to devastating film damage and complete process shutdown. Therefore, it’s important to take full advantage of your power supply’s arc-management capabilities.

The table below defines key arc-management parameters. Understanding the effects of increasing or decreasing these parameters helps you make the best decision for your particular situation. High-quality power supplies have arc-management software that is easy to adjust. Once you understand the parameters and determine the best settings for your specific process, the procedure for implementing them should be easy and intuitive. Please contact us if you need further assistance determining and implementing the ideal arc-management settings for your power supply.

Table 2. Key arc-management parameters

Parameter	Definition	Effect of Increasing	Effect of Decreasing
Detect Time	The length of time the power supply puts output energy into the arc	Cleans surface	Reduces particles
Shutdown Time	The length of time the power supply remains off before re-igniting the plasma	Cools arcing area Allows plasma to extinguish	Increases rate Lowers re-ignition energy
Voltage Level	The voltage at which the power supply determines that there is an arc event	Increases sensitivity to arcs	Decreases sensitivity to arcs

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I’m having problems with banding across my film. What could be causing this and how can I fix it?
Answer: Banding is a type of film defect that typically extends across the substrate from top to bottom. It can be an area where deposition is too thick, too thin, or simply has the wrong film properties. There are a number of possible causes for this problem, including the following:

Drive System Malfunction
In a dynamic system, banding may result if the glass is not moving through the process smoothly. Any sudden stops, starts, or changes in speed can cause the deposition of bands of overly thick or thin film. Check the drive system and make repairs to ensure that the substrate is moving through the process at a uniform speed.

Chamber Leaks and Outgassing
The accidental addition of oxygen to the process through a chamber leak or outgassing can dramatically reduce sputter rate and result in banding. Perform a leak check on your chamber. To reduce outgassing, select vacuum-compatible materials and condition system surfaces by baking out heat-resistant materials and wiping down surfaces with anhydrous alcohol. In some cases, the “leak” may actually be an inadvertent result of process design. For example, if a chamber door opens at the end of a certain deposition phase, changes in pressure or stoichiometry may occur for a short period. Adjust your process to prevent accidental introduction of oxygen. This may involve timing the process transition precisely so that deposition is completely done before the chamber door is opened. Balancing the gas pressure and stoichiometry of adjacent chambers also may solve this problem. In addition, it’s critical to completely base out your system before starting to back fill. Pumping to high vacuum before process startup ensures that no water vapor or other substances remain that may contaminate subsequent processes.

Cathode Failure
If you are using a static deposition process, one of your cathodes may have stopped sputtering. This prevents deposition on an entire region of the substrate because each cathode is “responsible” for a given zone (See Figure 11 below).

Figure 11. Cathode failure can cause extreme banding in a static deposition process

The loss of one cathode is not as much of a problem for a dynamic process as it is for a static process. In a dynamic process, turning up the power on the remaining cathodes can compensate, with no negative effect on film quality. (Please see the Q2 2007 edition of Flat Panel Focus for a detailed discussion of this phenomenon.) However, dynamic processes are still susceptible to banding due to the particular methods of this manufacturing technique. Read below for more information.

Arcing-Related Phenomena
A variety of phenomena related to arcing can cause banding. In a dynamic process, power levels to one or more cathodes may fluctuate when excessive arcing triggers frequent power supply shutdown for arc handling. If power is shut off too often, delivered power may drop below set point. Fluctuating power levels cause corresponding fluctuations in sputter rate. As the substrate moves in front of one or more affected cathodes, bands of thinner deposition result that correspond with these dips in delivered power. Please click on the graphic below to watch an animation of this phenomenon.

Figure 12. Click the graphic above to view an animation of arc-related banding in a dynamic deposition process

A number of conditions can cause arcing at rates high enough to cause this phenomenon. Excessive arcing may simply be the result of the inherent qualities of the target material. For example, AZO is known to arc hundreds or even thousands of times per second. Furthermore, in addition to the problems described in Chamber Leaks and Outgassing above, chamber leaks, outgassing, and the failure to base out your system can introduce contaminants that cause high rates of arcing.

However, arc-related phenomena may be the cause of banding even when your arc rate isn’t high enough to cause excessive shutdown times. For example, improper arc-management setup may be at fault. If your shutdown time (see Table 2 above) is too long, power may be interrupted and deposition therefore suspended long enough to produce banding. Likewise, if shutdown time is too brief, the power supply may turn back on before the arc is extinguished, which immediately initiates another power supply shutdown. Cumulatively, power may be suspended long enough to cause a great reduction in sputter rate. Another arc-related phenomenon that may cause banding is film buildup with poor adhesion that condenses on the chamber walls, fixtures inside the chamber, or edges of the target. This buildup may flake. The flakes may short out a cathode, which the power supply will likely interpret as a constant arc and shut down power for a lengthy period. This may cause banding.

To solve any of these arc-related phenomena, the following measures are recommended:
- Choose a power supply with effective, easy-to-set arc-management capabilities. This is especially important for processes using materials that are arc-prone, such as AZO.
- Select vacuum-compatible materials to reduce outgassing. Also condition system surfaces by baking out heat-resistant materials and wiping down surfaces with anhydrous alcohol.
- Fully base out your system before backfilling to prevent contamination.
- Clean your chamber to prevent flaking from initiating inappropriate arc responses from your power supply. Implement regular cleaning to prevent excessive buildup in the first place.
- Check for and repair leaks.
- Perform a few trials to determine the optimal shutdown time setting so that a given arc is fully extinguished, but power is not suspended so long that film quality is negatively affected. Your power supply should offer effective arc-management software that enables you to easily adjust these parameters.
- Consider adding pulsing if you are using DC power and arcing is a particular problem. Pulsing periodically discharges dielectric surfaces that otherwise would likely build up a charge and eventually arc. This may be especially useful for arc-prone target materials.
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What type of output cables should I use for my power supply?
Answer: I always recommend shielded cable. Make sure it has the lowest inductance per meter possible, and ground the shield at both ends. For power usage of the magnitude used in industrial sputtering applications, grounding at one end is not sufficient and may be dangerous. The use of a cable that is well shielded and well grounded helps prevent noise, even for DC power supplies, where arcing can lead to the same noise issues commonly experienced with AC, RF, and pulsed DC. Some materials, such as AZO, may have hundreds, or even thousands of arcs per second, making the use of shielded cable absolutely vital.

DC power supplies may experience noise issues due to arcing.

Figure 13. Properly grounded power lines between a low-frequency power supply and cathodes in a coater; the power supply output cable is surrounded by a ground shield that is itself grounded at both ends

For more information about proper grounding practices, please see the Q1 2008 edition of AE’s Sputter Spotlight e-newsletter.
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