8.5 Portfolio overview
The dose concept leads to the measures which must be taken to avoid defect generation by AMC:
- Decrease the pressure
- Increase the temperature
- Reduce the time of exposure
As the queue time is a requirement of manufacturing which is needed to assure flexibility in wafer processing, an outgassing of FOUPs and wafers in vacuum at elevated temperatures is the right measure to reduce defects and thus to increase yield. To get control of AMC it is vital to monitor it inside FOUPs and as it is governed by dynamic processes monitoring must be done in the production environment. Pfeiffer Vacuum offers the APA 302 Pod Analyser as the appropriate tool for the analysis of AMC. The APA 302 gives information on total acids, total amines, total volatile organic compounds and water vapour on the ppbv level within two minutes. Measurements can be done with empty FOUPs or FOUPs loaded with wafers.
Once AMC has been analysed and its impact on yield identified, appropriate measures have to be taken to improve the situation. To this end Pfeiffer vacuum offers the APR 4300 Pod Regenerator as an efficient tool to decontaminate up to four FOUPs in a single run. This patented machine is based on the insights of physical and chemical gas-surface interaction as presented in this chapter. The pod analyser follows a vacuum process as described by figure 8.11. In a first vacuum conditioning step of about five minutes the working pressure is reached. The subsequent purge process desorbs AMC which has built-up on the surfaces and in the last step the FOUP is returned to atmospheric pressure.
Figure 8.11: Pod regenerator process cycle
The APR 4300 Pod Regenerator has proved its efficiency by yield enhancements up to 7%. New challenges will emerge for semiconductor manufacturing and the dose of airborne molecular contamination will become increasingly important. Therefore alternatives to atmospheric pressure transport between critical production steps have to be developed. Vacuum will surly play an increasing role in future solutions.