Manufacturability Considerations in Designing Optical Monitoring Methods for Control of Plasma Etch Processes

摘要

Robustness and reliability are among the most important requirements of semiconductor manufacturing processes. Their importance grows with the need to continuously improve yield and contribute to reduced cost of ownership. This necessitates including manufacturability considerations in the fundamental design of methods and instruments for in situ control of plasma etch processes. Optical monitoring methods and equipment for broadband (UV-VIS-IR) reflectometry have been developed to meet these advanced needs. The hardware is optimized for sufficiently accurate in situ metrology capabilities in a harsh plasma processing environment with minimal maintenance requirements. Novel model-based approaches are used to determine the absolute wafer state in real time. This facilitates compensating for incoming material variation with minimal reliance on operator input and interpretation. No special test structures on the wafer are required while the process chamber is only minimally modified for diagnostic equipment access. The methods facilitate development of fault detection schemes that help prevent misprocessing of wafers. Thus, demanding process control requirements are met on a wafer-to-wafer basis. The applicability of the technique has been successfully demonstrated for critical silicon-based etch applications such as shallow trench isolation (STI), recess for DRAM and embedded DRAM (eDRAM), and polysilicon gate.