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This paper presents a scheme for deposition time and temperature control of low pressure chemical vapor deposition silicon nitride off product wafers. A Kalman filter based estimation scheme is presented for deposition time control. Deposition temperature control is treated in additional detail, including the impact of sampling the furnace load. Furthermore, stability metrics are also derived capturing the allowable modeling error for ensuring closed-loop stability. This is important for enabling the same model to be used across multiple tools and processes. A two-step iterative scheme is presented for implementing a "batch as you go" controller. Finally, the controller is applied in high-volume production.