Light scattering methods for semiconductor process monitoring and control

ABSTRACT Light scattering methods are being used in semiconductor device fabrication for such diverse purposes as particulatemonitoring and linewidth control. In this overview, we focus on applications of light scattering for monitoring reactivelyion etched trench profiles and plasma passivation ofIII-V materials. 1. INTRODUCTION Light scattering methods have long been useful for process control and monitoring because they are relatively simple toimplement and are inherently non-intrusive. Here, we distinguish between light scattering and microscopy in that the latterentails the generation of an image. Similarly, we distinguish between light scattering and interferometry as the latter entailsthe use of either a transmitted or specularly reflected beam. By contrast, light scattering methods make use of visible, nearir, and near-uv radiation impinging on a sample and detection of inelastically and/or elastically scattered light at an angle orangles different from either the incident or specular angles. For semiconductor device fabrication, light scattering is usedfor detecting and counting particles in the processing medium (gas or liquid) and on wafer surfaces.' It has been used formonitoring surface roughness after sputter deposition of metal films,2 and for detecting latent images in photoresist as ameans of optimizing lithographic exposure equipment settings and controlling exposure and development processes.3 For