Optical non-chromatic-aberration focusing system

Abstract

The invention relates to the field of optical measurement, in particular to an optical non-chromatic-aberration focusing system which comprises a first curve surface reflection component, a second curve surface reflection component and a third curve surface reflection component. The first curve surface reflection component receives light beams emitted by a point light source and converts the light beams into parallel beams; the second curve surface reflection component receives the parallel beams reflected by the first curve surface reflection component; the third curve surface reflection component receives the parallel light beams reflected by the second curve surface reflection component, converts the parallel light beams into a convergent light beam and vertically emits the convergent light beam to the surface of a sample to be measured; and the first curve surface reflection component, the second curve surface reflection component and the third curve surface reflection component form a crossed Czerny-Turner structure. The optical non-chromatic-aberration focusing system is simple in structure and low in price, does not cause chromatic aberration in optical measurement and can reasonably change the propagation direction of incident light so that the incident light can be focused on the surface of the sample, and meanwhile a relatively proper work distance can be obtained.

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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