Resist uniformity evaluation through swing curve phenomena

Abstract

In fabrication of Micro/ Nano structure, alignment and exposure are the most critical steps in photolithography process, the resolution requirements and precise alignment are vital; each mask needs to be precisely aligned with original alignment mark. Otherwise, it can't successfully transfer the original pattern to the wafer surface causing device and circuit failure and the photo resist must be very sensitive to the exposure light to achieve reasonable throughput and the standard thickness should be 1.2μm. 24 wafers are used in this study, the wafers are separated into 2 sets, and each set which consists of 12 wafers. The first set is coated, exposed and development and the second set is also exposed and developed after being coated. after the wafer went through the standard cleaning procedure, the wafers were then coated using standard recipes which the spin speed ranging from 6500 to 7600 rpm in 100 rpm incremental Subsequently, the photoresist thickness of each wafer is measured using elipsometer. The study revealed that the minima for the dose-to-clear are at 7200 rpm where the thickness is 1.21 μm. Though, the result is slightly thicker than the expected 1.2 μm. This may be due to some unavoidable experimental errors and may due to the changing k' of the coater because coater is a bit old.