Latent image characterization of postexposure bake process in chemically amplified resists

Abstract

The demand of smaller device dimensions drives the need to improve the lithographic and the metrology tools to produce them. Characterization of the image formation during the lithography process is key to any process control effort. Scanning probe microscopy (SPM) on exposed, unbaked and baked, undeveloped photoresist shows morphological details of the image formation process unachievable with other techniques. The use of micro-Fourier transform infrared (μ-FTIR) spectroscopy will be investigated for latent image chemical analysis. Both of these techniques will be used in the study of the dependence of the latent image of a negative novolac-based chemically amplified resist, SAL 605 (Shipley), with postexposure bake (PEB) conditions. The objective of the experiment is to understand how the thermal properties of the resist and the linking reaction taking place are related to each other during PEB. Experimental results indicate that resist from unexposed regions diffuse into the exposed resist during PEB. SPM results show that this diffusion increases as the PEB temperature rises above the glass transition temperature of the unexposed resist. μ-FTIR results show that the linker component of the resist, hexamethoxymethylmelamine, has been identified as one of the resist components that diffuses into the exposed regions during PEB.