INDUSTRY GaAs MANUFACTURING
indexing to the same placement position; and wafer breakage, due to misplacement because of loss of home position. A further upgrade improved overall reliability, but intermittent faults persisted; primarily misplacement of wafers loaded onto the indexer was caused by inaccurate indexer positioning.
RFMD has installed several LAPECVD tools at its facility in Greensboro, NC
RFMD received a beta version of this tool in 2000, and following installation, engineers qualified the reactor for process and production. This system fulfilled its promise of higher manufacturing throughput, but it had some problems; most of which were minor and quite typical for any beta tool. These issues were successfully addressed in partnership with Plasma-Therm, creating a strong bond of trust between the two firms that continues to this day, and has led to further orders of LAPECVD tools.
Assistance to RFMD by Plasma-Therm through its Customer Improvement Program (CIP) did not stop with the delivery of the tools. Although the process worked as specified, there were intermittent issues, primarily handling, which Plasma Therm helped to investigate and address. Each issue was eventually resolved (see table 1, p51), and one of the outcomes of this investigation was for RFMD to establish a ‘standard’ process used for production that differs from the high rate process used for testing and qualification.
Upgrading the indexer One of the issues that required resolution relates to the indexer. This integral part of the processing chamber is a rotating fixture that is loaded with wafers. After one is added, the indexer subsequently lifts and rotates to the next position and the next wafer is loaded. Once completely populated, the load lock is isolated by a slot valve and the chamber is pumped and processing of all the wafers is initiated.
There were lingering, intermittent problem associated with the indexer, and both companies tried to come to a plausible, workable solution. Returning to the original design yielded a better overall replacement, but several intermittent indexing problems remained: Losing home position;
Plasma-Therm’s large-area plasma-enhanced CVD tool is a parallel plate design utilizing a 13.56 MHz power source to generate the plasma. Wafer temperature can be controlled from 100°C to 350°C
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www.compoundsemiconductor.net June 2013
Engineers at both firms strived to get to the bottom of this, and through continuous investigations and testing, they were able to implement a final, very robust solution. This involved installing a drive and higher resolution encoding system at RFMD. Initially three systems were retrofitted in exactly the same way. When fully loaded the indexer was seen to have a minor issue with increased load (weight), which affected the sensitivity of the encoding mechanism. The approach taken in this effort was to normalize the load across all three tools and set the corresponding sensitivity for optimal operating conditions under load and teach each load position (see Figure 1). After several months of running with zero faults on these first three systems, RFMD’s engineers upgraded their remaining tools with the drive and encoding package.
Improving the indexer led to an increase in wafer throughput. Addressing this issue propelled average wafer uptime from 91 percent to more than 97 percent, which equates to a productivity increase of over 10,000 wafers per year per tool (see Figure 2).
Showerhead improvements Working together, Plasma Therm and RFMD have also improved the across wafer and wafer-to-wafer thickness uniformity of SiNx
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