PSE Relevant Issues in Semiconductor Manufacturing: Application to Rapid Thermal Processing

Abstract

The quality control of the wafer is becoming more and more important as the wafer becomes larger and the feature size shrinks. An advanced IC fabrication process consists of 300+ steps with scarce and usually difficult quality measurements. Thus product yield may not be realized until months into production while in-line measurements are available on the order of a millisecond. The series production nature and measurement setup lead to a unique process control problem. In this work, typical disturbances are explained and possibility for inferential control is explored. This leads to a control architecture with multiple layers in a cascade structure. Next, rapid thermal processing (RTP) is used to illustrate recipe generation and control structure design at the tool level. The resultant multivariable controller gives satisfactory setpoint tracking for a triangular-like temperature program. In order to reduce downtime, process trend monitoring of a tool is essential. Instead of using entire batch data, a key process variable is identified and an index is computed to capture the dynamic behavior of the tool. An RTP example is used to illustrate this approach and results clearly indicate that process trend is well predicted using the index-based time-series model.