CONTROL OF PHOTORESIST PROPERTIES - A KALMAN FILTER BASED APPROACH

The photolithography step in the semiconductor manufacturing process b ecomes increasingly critical as linewidths decrease for the next gener ation of integrated electronics. It therefore becomes necessary to red uce variations in photoresist parameters such as resist film thickness and photoactive compound concentration during manufacture, In this pa per, we present a simple feedback scheme for accurately regulating the se parameters, Our approach involves obtaining a simple, static proces s model the coefficients of which are recursively adjusted based on pr evious wafer measurements, We use this adaptive model to determine app ropriate input setpoints for the next wafer, The effectiveness of this scheme in reducing process drift is exhibited by experimental data, O ur results supports the widespread contention that modern feedback con trol offers the promise of improving the semiconductor manufacturing p rocesses, often with relative ease and minimal capital cost.