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?

Flat Panel Display Applications

7. How do I determine if pulsed DC is a good fit for my FPD process?
8. With pulsed DC, does the lack of sputtering during the voltage reversal affect my sputter rate?
9. Are there any technologies that can extend OLED lifetime by improving the quality of the encapsulation layer?
10. Where can I get help developing OLED and other advanced processes?
11. What existing product technologies can benefit FPD?

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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Flat Panel Display Applications

7. 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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8. 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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9. 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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10. 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 over 25 years. 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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11. 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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