In-situ measurement & control of photoresist development in microlithography

Abstract

Microlithography is the key enabling technology in semi-conductor manufacturing that continued to advance in order to reduce line width, feature size and critical dimension (CD) to meet the ever-growing demand for more devices to be built on an IC Chip. Due to various non-uniformities arises from previous steps, the time to reach endpoint for a develop step may vary. This paper presents a novel approach to control photoresist development process by controlling develop temperature. It has been known that develop temperature has direct influence over the develop rate. Thin photoresist film thickness can be estimated by using a Lookup Table Referencing Technique, which involves analyzing reflected light intensities acquired using commercial available optical spectrometry system. With these, a simple Proportional-Integral (PI) controller is designed to eradicate any non-uniformities that may exist prior develop step. From the experimental results, it was found that tracking of a reference develop trend is feasible. In addition to that, the standard deviation for the time to reach endpoint has also been reduced by 4 times, from 18.87 to 4.68 when the PI controller is used. © 2005 IEEE.