|   |   |   |

To receive the next issue by e-mail, visit My Account and confirm you have opted-in to receive e-mail from AE.

AE’s Q4 2007 flat panel newsletter describes process challenges and solutions related to an essential component of your process: your targets. The following sections describe specific target-related process strategies and their effects on critical objectives such as film quality, throughput, and profitability.

One way to significantly decrease costs in your manufacturing operation, as well as to increase process throughput, is to get more use out of your targets. Increasing target lifetime and utilization decreases the number of targets you have to buy, and also allows you to extend productive manufacturing time between process shutdowns for target cleaning or replacement.

A complete target-extending strategy involves two main tactics: maintaining good target quality for as long as possible, and, once target quality degrades, preventing any negative effect on film quality for as long as possible.

Maintaining Target Quality

In a typical magnetron sputtering process with a planar target, sputtering is concentrated in the “racetrack,” which is the region on the target surface where the tangential magnetic field is maximum (Figures 1 and 2).

Figure 1. Planar target showing racetrack erosion pattern

Figure 2. Cross-section illustration of racetrack erosion pattern on a planar target

Outside the racetrack, the sputter rate is much lower and may allow the formation of oxides (Figure 3). In the sputtering of ceramic targets such as ITO, oxides can easily form because oxygen is in the target material and typically is also introduced into the chamber. In metal sputtering, the presence of oxygen may be the result of a chamber leak or water vapor created by the outgassing of the substrate and carrier. The oxide regions that form are commonly referred to as nodules. These oxide regions are insulating and allow for a charge buildup. Because the films are extremely thin, the electric fields are extraordinarily high, even at “low” voltages. Once the electric field is sufficient, there is a breakdown (arc) on the target surface. These arcs eject particles that damage the substrate. In severe cases, when the arc is not extinguished or continues to burn due to inadequate or nonexistent power supply arc handling, there can also be damage to the target material.

Figure 3. In a typical magnetron process using planar targets, small explosions in areas of lower sputter rate on the target surface release particles that make it necessary to replace your targets long before they are fully utilized (click graphic to view animation)

DC pulsing lowers the probability of nodule formation, helping to maintain target quality over time so that you can utilize the target more fully. This process power method reduces dielectric formation and arcing by periodically reversing polarity and thus discharging the target surface. As frequency increases, the dielectric surfaces are discharged more often, lowering the possibility of nodule formation. This not only increases target life, but may also reduce damage to the substrate.

So, if you are using straight DC, consider adding a DC pulsing product, such as AE’s Pulsar^® accessory. If you are setting up a new process, consider a pulsed-DC power supply, such as AE’s Pinnacle^® Plus+ product. Please see How do I determine if pulsed DC is a good fit for my FPD process? in our Q2 2007 FP Focus newsletter for details on the advantages of pulsed DC.

Neutralizing the Negative Effects of a Degraded Target

The other major component of extending target lifetime relates to neutralizing the negative effects of poor target conditions toward the end of the target’s life. A high-quality power supply with low stored energy and effective arc management enables you to run an aging target, even with nodules, with little or no negative effects caused by the phenomenon shown in Figure 3.

Effective arc management and low stored energy can reduce the damage when a nodule explodes by limiting the power delivered to the arc. These features enable you to run an older target that may include nodules, while reducing arc energy to a level that maintains film quality. Without these features, when nodule formation increases, you have to stop your process to discard and replace your target, even though it might be only partially consumed. This increases your costs by requiring you to use a brand new target, even though the old one may be only partially utilized. It also damages throughput by requiring a complete system shut down. (Please see Arc Synch^TM below for more information about arc-management technologies.)

Using a Rotatable Target

If target utilization is particularly critical to your manufacturing cost of operation, and you want to avoid the phenomenon shown in Figure 3, you may derive benefits from using rotatable targets. Although they are more expensive than planar targets, you typically get about 85% utilization out of a rotatable, versus about 35 to 50% out of a planar target. These numbers are independent of the process power method or target material you are using.

Please note, however, that rotatable targets have limited application. They are not easily compatible with RF power. Generally, they are best used in AC, DC, or pulsed-DC powered processes. Also, due to manufacturing considerations, not all target materials are available.

In addition to increasing utilization, another major benefit of rotatable targets is that they are not as susceptible to the exploding nodule problem shown in Figure 3. Unlike planar targets, which erode in a racetrack pattern, rotatable targets erode uniformly over their entire surfaces. Therefore, there are no “edges” to the erosion pattern, except at the very ends of the target, which typically are located beyond the ends of the substrate and therefore do not affect film quality. On a planar target, these edges create conditions that promote oxide formation, leading to nodules, arcing, and substrate damage problems.

Utilization is not the only issue at hand when considering the topic of targets. Target crosstalk is a potentially debilitating phenomenon that can lead to substrate arcing, substrate and target damage, and possible eventual power supply damage. Crosstalk may also prevent you from reaching the desired power level, which decreases throughput.

What is target crosstalk? Larger substrates, such as those frequently used in FPD manufacturing, can require a dozen or more targets per chamber. In order to fit into a single chamber, the space between targets must shrink. When closely-spaced targets are at different potentials, they can interfere with one another, causing the serious problems described above.

CEX or Phase Synchronization

CEX, a feature of most AE power supplies, alleviates crosstalk and eliminates the problems associated with it. Commonly referred to as phase synchronization, CEX stands for common exciter. This feature coordinates all of the power supplies on your system, matching their waveforms so that all cathodes are always at the same phase. Figure 4 shows the high potential difference between cathodes that can occur when CEX is not used.

Figure 4. Scope trace showing poor synchronization and high potential difference between cathodes

The benefits of CEX are significant. First, it protects your equipment investment. It also helps preserve film quality and reduces potential process downtime by lowering the risk of power supply, substrate, and target damage. Further, it increases process stability, and may facilitate the increased power levels required for larger substrates. Many AE products offer CEX and its related benefits.

Arc Synch^TM Technology

Arc Synch technology works well with CEX to create a comprehensive strategy to manage the arcing that results from target crosstalk and other conditions. Like CEX, arc synch coordinates all of the power supplies in a system, enabling all units respond to an arc, even if only one unit has detected it. Without arc synch, only the unit that detects an arc responds to it, allowing all other power supplies to continue operating normally. This can cause the cathodes to interfere with one another, which can lead to substrate arcing, substrate and target damage, and possible eventual power supply damage. With arc synch, when an arc is detected, a simultaneous response in all system power supplies is triggered to extinguish the arc. This prevents cathode re-ignition and arc suppression from causing the cathodes to interfere with one another.

For more information on Arc Synch and arc management, please see AE’s Arc Reduction in Magnetron Sputtering of Metallic Materials white paper. If you’d like to discuss how arc management, CEX, Arc Synch, or other power-management technologies can improve your process, please e-mail us at FPDapplications@aei.com.

Are you struggling to squeeze more profit out of your FPD process?

Bruce Fries, AE's FPD strategic marketing specialist, and Ken Nauman, AE’s FPD strategic marketing engineer, answer some of your difficult questions. Submit your question or comment to FPDapplications@aei.com. To contact Ken Nauman directly, please call +1.970.214.6280 or e-mail Ken.Nauman@aei.com.

1. 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?
2. I use AE’s VFP (Virtual Front Panel) to control and monitor my power supply, but can VFP help with process development?
3. In your experience, have you encountered any simple and inexpensive fixes that can create significant process improvements?
4. I’m working hard to create and maintain the best productivity possible for my PVD process. Where can I get help?
5. Do you have insight into the industry drivers that need to change in order to make FPD manufacturing more profitable?

1. 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.
   
   
2. 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.
   
   
3. 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.
   
   
4. 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.
   
   
5. 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.