Sputtering Applications

1. 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?
2. OK, then, how do I choose between AC and DC power?
3. How do I determine whether straight DC or pulsed-DC power is the better fit for my process?
4. What sputtering rates can I achieve?
5. What arc set points should I dial into my sputtering equipment menu system? 
6. My sputtering rate had been holding steady. Why did it change suddenly today?
7. What is the difference in utilization between planar and rotatable targets?
   
   
8. How do the different erosion patterns of planar and rotatable targets affect the process over the course of the target's lifetime?
9. 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?
10. How can I optimize my sputter rate?
11. 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? 
12. 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?
13. 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.
14. I don’t have enough space in my chamber to use DC in my dual-magnetron system. Are there any good alternatives?
15. I’ve heard that setup for RF superimposed DC is complicated. What are the main pitfalls to avoid?

Flat Panel Display Applications

16. How do I determine if pulsed DC is a good fit for my FPD process?
17. With pulsed DC, does the lack of sputtering during the voltage reversal affect my sputter rate?
18. Are there any technologies that can extend OLED lifetime by improving the quality of the encapsulation layer?
19. Where can I get help developing OLED and other advanced processes?
20. What existing product technologies can benefit FPD?
21. 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?
22. I use AE’s VFP (Virtual Front Panel) to control and monitor my power supply, but can VFP help with process development?
23. In your experience, have you encountered any simple and inexpensive fixes that can create significant process improvements?
24. I’m working hard to create and maintain the best productivity possible for my PVD process. Where can I get help?
25. Do you have insight into the industry drivers that need to change in order to make FPD manufacturing more profitable?  

Sputtering Applications

1. 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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2. 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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3. 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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4. 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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5. 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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6. 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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7. 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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8. 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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9. 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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10. 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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11. 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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12. 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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13. 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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14. 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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15. 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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Flat Panel Display Applications

16. 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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17. 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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18. 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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19. 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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20. 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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17. 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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18. 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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19. 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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20. 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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21. 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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