Full-field film thickness measurement method based on reflection spectrum using AOTF

Abstract

Thin films are widely used in the semiconductor and MEMS industry. Film thickness is an important parameter to evaluate the quality of the film. Traditional measuring methods, including reflectometry, ellipsometry, etc. are considered reliable methods for measuring film thickness. Most of these methods use point-to-point measurements that requires lateral scanning in x-y directions to obtain the film thickness at different locations, which is inefficient to measure a large area and susceptible to environmental influence. Herein, a full-field film thickness measuring method based on acousto-optic tunable filter (AOTF) and reflection spectrum is proposed. The control drive frequency interval is 0.07MHz and the AOTF is driven to select narrowband wavelengths from 520 nm to 680 nm. At the same time, as driving the wavelength scanning, the camera is controlled to capture the images synchronously corresponding to each wavelength. A standard silicon wafer with known reflectivity is used to calibrate the non-uniformity intensity of the light source at the sample surface. The reflection spectrum signal at each point of the film can be reconstructed by the image sequence. The film thickness can be calculated by using the nonlinear fitting between the theoretical and experimental data. Different thickness films are measured to verify the system performance.