Optical Achromatic Focusing System

Abstract

The present application relates to the field of optical measurement, in particular to an optical achromatic focusing system. Including: a first curved surface reflective element, a second curved surface reflective element and a third curved surface reflective element; the first curved surface reflective element receives the light beam emitted by the point light source and turns the light beam into a parallel light beam; the second curved surface reflective element The element receives the parallel light beam reflected by the first curved surface reflective element; the third curved surface reflective element receives the parallel light beam reflected by the second curved surface reflective element, turns it into a converging light beam and is perpendicularly incident on the The surface of the sample; the first curved reflective element, the second curved reflective element and the third curved reflective element form a crossed Czerny-Turner structure. The optical achromatic focusing system provided by the application is simple in structure and low in price, does not produce chromatic aberration during optical measurement, and can reasonably change the propagation direction of incident light so that it can be focused on the sample surface while obtaining a more suitable working distance.

Description

technical field [0001] The present application relates to the field of optical measurement, in particular to an optical achromatic focusing system. Background technique [0002] In general, a critical step in optical measurement techniques is focusing the probe beam onto the sample. With the rapid development of the semiconductor industry, it is very important to use optical measurement technology to accurately measure the critical dimension (CD, Critical Dimension), spatial morphology and material properties of the three-dimensional structure formed by single-layer or multi-layer thin films on the wafer. Moreover, it is known to those skilled in the art that it is advantageous to focus the broadband probe beam into a relatively small-sized spot on the sample surface, because the small-sized spot can measure microstructure patterns, and the broadband probe beam can improve measurement accuracy. Since the refractive index of the lens material is generally different at differ...

AI Technical Summary

Problems solved by technology

Since the refractive index of the lens material is generally different at different wavelengths, in this case, when using a lens to focus a wide-spectrum beam, there will be the following problems: the lens usually has chromatic aberration, and such chromatic aberration will cause light of different wavelengths The focus position is different, increasing the error and reducing the measurement accuracy

Because the focus adjustment range of the spherical mirror is very limited, and the general sample is usually large in size, hundreds of millimeters, it is not easy to focus the wide-spectrum beam on the sample surface only by using the spherical mirror

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