Development of positive optical photoresists: Adaptive control

• Published in: Chemical engineering science 1993, Vol.48 (12), p.2239-2250
• Main Authors: Carroll, Thomas A., Fred Ramirez, W.
• Format: Article
• Language: English
• Subjects: Applied sciences; Electronics; Exact sciences and technology; Microelectronic fabrication (materials and surfaces technology); Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices
• ISSN: 0009-2509; 1873-4405
• DOI: 10.1016/0009-2509(93)80240-Q

The microlithographic process is a series of irreversible steps. The final important step, resist development, has one useful available on-line process measurement. Interferometry was used to measure the penetration depth of the developer solution into the resist film and the rate of development. A mathematical model describing development was simplified for identification purposes and combined with a Kalman filter algorithm to determine the best possible estimate of penetration depth. A combined state and parameter estimation scheme, based on the steady-state Kalman filter estimator, was derived and installed for on-line estimation. The estimator was particularly useful in calculating the time for the development to break through to the substrate, while the parameter identification yielded an accurate model which aided in determining the total process time. the optimal development control policy was shown to be singly switched bang—bang between development and rinse solutions. A model describing post-breakthrough dissolution was used to determine the total development time, based on knowledge of the development rate parameter. Experimental results indicated that the control policy and identification algorithm provide tight adaptive control on the desired line width, despite continually changing environmental conditions.