Monitoring strategies for yield enhancement

Semiconductor manufacturing is driven by the necessity to increase productivity. Higher productivity can be achieved by an increase in throughput, by an increase in yield per wafer, by improvements in equipment utilization, by a reduction in wafer flow, and by increase of wafer size. Associated with these requirements is the introduction of advanced monitoring strategies. Measurement steps are non-productive by nature. They slow down process flow, they require cleanroom space, and they use a significant number of monitoring wafers. Monitoring strategies will involve more and more integrated metrology, resulting in better equipment performance control and in a reduction of monitoring wafers. This will be achieved by either an integration of in situ sensors or integrated in-line measurement and analytical instrumentation. Several examples for the integration of different sensors are discussed in this paper. Here, monitoring strategies involving in situ measurements, integrated in-line me trology steps and attached measurement modules could be studied with respect to improvements in time and costs. An estimation of the percentage of additionally processed wafers was made. The potential advantage was calculated for ramp-up phase as well as for continuous production conditions. A distinction was made for the case of high volume mass production fab and a small volume ASIC fab, indicating for both cases a high potential for an increase in productivity.