Basic film thickness measurement system using modular spectrometer

How to Measure Film Thickness by Modular Spectrometer

Posted By : Susan

Aug 30, 2021

Category: Spectroscopy Blog

Comments: 0

Modular spectrometers are widely favored in the semiconductor industry due to their fast, non-destructive, and in-situ measurement characteristics. As the manufacturer of the miniature modular spectrometer, Optosky has also 20-year experience in this field. From plasma etching to wafer film thickness measurement, modular spectrometers have certain applications. Explain below, how to use Optosky modular spectrometer to measure film thickness?

The below picture is the principle diagram of measuring the film thickness using a spectrometer. The light beam is incident on the surface of the film at θ₁, part of which is directly reflected, and the other part is refracted at θ₂. The refracted light is reflected by the lower surface of the film and then refracted by the upper surface. The reflected light 1 and the reflected light 2 interfere coherently. The use of modular spectrometers to measure the thickness of the film is mainly based on its reflection interference spectrum.

When measuring, the entire optical path is mainly composed of reflection probes. The probe part is placed perpendicular to the wafer downwards. One part of the fiber end is connected to the light source to form incident light, and the other part is connected to the spectrometer to receive the reflection spectrum. The appearance of interference peaks in the reflectance spectrum curve is the result of film interference.
In fact, the wavelengths corresponding to multiple sets of peaks and troughs can be obtained from the reflection spectrum, and multiple film thickness values can be calculated, and then averaged to reduce measurement errors.