Design and control of an optical fast-scanning system for silicon wafer feature measurement

Abstract

Modem semiconductor manufacturing requires great precision for fabricating features on the surface of silicon wafers. However, testing of these wafers currently consists of selecting a subset of manufactured wafers and analyzing them with a scanning electron microscope. That process is slow and destructive to the tested wafers, and does not allow for examination of every wafer produced. This project seeks to develop an optical fast-scanning system for in-situ optical nanostructure measurement. This would be able to process many silicon wafers in a short amount of time, without destruction of the measured wafers. One key requirement for the project is thus the ability to scan a laser over the entire area of a silicon wafer in a short amount of time. Additional requirements include high precision, for accurate measurement, and adaptability to a variety of sample sizes. This thesis centers on the design and control of devices to attain these goals. Different options for design of the system are explored, with approximate scanning speed and accuracy calculated for different configurations. From these, one layout is explored in detail. The design of this system as it would be constructed is described. Driving voltage waveforms that allow for galvanometer scanning of the entire wafer area are also specified. A geometric and programmatic model of the system shows that it would be capable of detection of features greater than 1.5 mm in size in the span of 5 minutes, with speed that is easily increased.