SU1374043A1 - Device for measuring thickness of optically transparent films - Google Patents

Abstract

The invention relates to a measurement technique, namely, devices for monitoring the thickness of eiitaxial films. The purpose of the invention is to improve the accuracy and speed of measurement — this is achieved by ensuring the operation of the interferometer in converging beams, which makes it possible to reduce the dimensions of the optical parts of the interferometer. The sample to be measured is placed on the object table 7. From the source of IR radiation, a light beam, deflected by a flat mirror 5, is directed to a spherical mirror 3, which focuses the IR radiation in the plane of the sample to be measured. Reflected from the sample, the rays of the diverging beams fall on the mirror 4 and further, reflected from the flat mirror 6., are focused in the plane of the beam splitter 9. When moving the movable mirror 1I of the interferometer 8, the path difference between the interfering beams changes, which leads to a change interference pattern in the plane of the receiver 16. Receiver 16 converts optical radiation into an electrical signal carrying information about the thickness of the measured film. 1 hp f-ly. 2 Il. a (C (L

Description

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figure 1

The invention relates to a measurement technique, namely, devices for controlling the thickness of epitaxial films.

The purpose of the invention is to increase the accuracy and speed of measurement, which is achieved by ensuring the operation of the interferometer in converging beams, which makes it possible to reduce the size of the optical details of the interferometer.

Fig. 1 shows an optical diagram of a device for measuring the thickness of optically transparent films; Fig. 2 shows the course of the rays incident on reflected from the measured sample.

The device contains an illuminator 1, consisting of a source of 2 IR radiation, two spherical concave mirrors 3,4 and deflecting flat mirrors 5,6, an object table 7 for placing the measured sample, an interferometer 8 consisting of a splitter 9 and two spherical concave mirrors 10, 11, one of which, for example, mirror 11, is mounted on movable rod 12 in aerostatic guides 13, IR radiation receiver 14 consisting of focusing element 15 and assembly

receiver 16, block 17 is measured along its optical axis. Concave

Spherical mirrors 10, 11 have one illuminator 1 designed for: radii of curvature, broadcasting of the sample to be measured, the receiver 14 IR radiation serves

on the stage 7, after the conversion of the optical output, as well as the formation of the reflection reflected from the jj structure, obtained by adding the radiation into the sample. Source 2 serves

the divider 9 of the interfering beams into an electrical signal proportional to the intensity of IR radiation, while the lens 15 serves to focus the IR radiation in the plane of its own receiver 16. The structurally focusing lens 15 is made of germanium, the lens diameter is 20 mm. A cyro electric bolometer was used as the receiver 16 itself.

to produce polychromatic radiation in the infrared spectrum. As a source of 2 IR radiation, a heated up to 800 ° C spiral was used. The spherical mirror 3 serves to focus the radiation of the source 2 in the plane of the sample being measured, and the spherical mirror 4 to focus the radiation reflected from the sample in the plane of the beam splitter 9 of the interferometer 8.

Flat mirrors 5.6 serve to deflect the path of the rays in the illuminator. -1

The stage 7 for placing the sample to be measured is in the center of the curvature of the spherical concave mirrors 3.4 of the illuminator 1,

Interferometer 8 is designed to determine the distance L between two

interfering wave fronts formed by a measured sample of thickness d with a refractive index n of the measured semitaxial

with

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layer (see figure 2). The beam splitter 9 is designed to divide IR radiation in the direction of the mirrors 10.11 with a ratio of transmission to reflection of 1: 1, as well as to combine (add) beams reflected from the mirrors 10.11 to obtain an interferometric pattern. The splitter 9 is located at a distance from each of the mirrors 10.11 of the interferometer (i5

0

five

This means the average or zero position of the movable mirror 11) and the mirror 4 of the illuminator 1, which is equal to the radius of curvature of the corresponding mirror. Structurally, the beam splitter 9 consists of two parts of the beam splitter itself with a reflective coating applied, and the compensator, made in the form of discs. Cesium iodide (CsJ) was used as a material, germanium (Ce) was used as a reflective coating.

A spherical concave mirror 11 fixed on the movable brush 12 in aerostatic guides 13 serves to change the optical difference of two interfering 1x wavefronts by moving the mirror 11

obtained by adding

the divider 9 of the interfering beams into an electrical signal proportional to the intensity of IR radiation, while the lens 15 serves to focus the IR radiation in the plane of its own receiver 16. The structurally focusing lens 15 is made of germanium, the lens diameter is 20 mm. A cyro electric bolometer was used as the receiver 16 itself.

Measurement unit 17 serves to control the movement of the movable mirror 11 of the interferometer 8, as well as to analyze the interferogram and calculate the thickness of the epitaxial layer being measured according to the positions of the lateral peaks of the interferogram.

The device works as follows.

The measured sample is placed on the stage 7. From the source 2 of the infrared radiation, a light beam deflected by a flat mirror 5 directs 3

with a spherical concave mirror 3, which focuses IR radiation in the plane of the sample being measured. The rays reflected from the sample from the air-epitaxial boundary layer and the substrate layer (see Fig. 2) with divergent beams fall onto the mirror 4. and then, reflected from the flat mirror 6, are focused in the plane of the beam splitter 9, which splits the reflected light. from the sample, the radiation on two coherent diverging psgchka, directly on the fixed and mobile

mirrors 10, 11 respectively. Reflected from mirrors 10, 11, the beams again fall on the beam splitter 9 by converging beams and then by diverging beams (one — passing through the beam splitter 9, the other — reflected from it) are fed to the focusing lens 15, through which they focus and interfere in the plane of the receiver 16 infrared radiation. When moving the movable mirror 11 along the optical axis by the magnitude + d relative to the mean zero position, a change in the path difference L between the interfering rods occurs, which leads to a change in the interference pattern in the plane of the receiver 16, and, as can be seen in FIG.

. d (1)

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but

1. A device for measuring the thickness of optically transparent films containing successively located illuminator, irradiated as a source of IR radiation and sequentially arranged along the radiation of a flat mirror, the first and second spherically concave mirrors and the second flat mirror, the object table, installed in the center of curvature of the first a concave mirror, an interferometer of two mirrors, one of which is driven and installed with the possibility of reciprocating movement along the interferometer axis, and a beam splitter installed at the intersection of the optical axes of the interferometer mirrors and the second spherically concave mirror, the focusing element, the IR radiation receiver and the measuring unit, the input of which r is electrically connected with the drive of the movable mirror, is distinguished. by the magnitude of the stroke and the mirror 11, equal to half the difference of the stroke L between the interfering beams, it was determined that, in order to increase, the thickness d of the epitaxial film and the measurement speed were measured.

The receiver 16 transforms the optical mirror of the interferometer and the radiation radiation obtained in the resultantly concave from the same two wavefront firing, the visual table is set into an electrical signal, the proportional radiation intensity is measured by the template. The information processing of this signal is carried out in block 17

the measurement, which analyzes the illumination interglasses equal to the radius of the cryferogram, determines its lateral visibility of the corresponding mirrors. peaks (maxima) and by their positions 2. The device is pop.1, differs by a value of 2 and further, taking into account that spherical

The volume of expression (2), calculates the value of the mirror of the illuminator, is made from the single thickness of the opticial film on the same curvature.

a concave mirror illuminator, and a beam splitter installed at a distance from each of the interferometer mirrors and a second spherical concave mirror. The technical advantages of the proposed device for measuring the thickness of optically transparent films are to provide the prerequisites for improving the accuracy of manufacturing the surfaces of optical parts by reducing their dimensions (light diameters) by the implementation of work in converging beams, as well as in reducing the travel time of the movable mirror due to the reduction of its mass-beam tnyh indicators.

the invention

Formula

1. A device for measuring the thickness of optically transparent films containing successively located illuminator, irradiated as a source of IR radiation and sequentially arranged along the radiation of a flat mirror, the first and second spherically concave mirrors and the second flat mirror, the object table, installed in the center of curvature of the first a concave mirror, an interferometer of two mirrors, one of which is driven and installed with the possibility of reciprocating movement along the interferometer axis, and a beam splitter installed at the intersection of the optical axes of the interferometer mirrors and the second spherically concave mirror, the focusing element, the infrared radiation receiver and the measuring unit whose input r is electrically connected to the drive of the movable mirror, i.e. - nosti and speed of measurement.

Visny, object table is set to the center of the curvature of the second spherically

the concave mirror of the illuminator, and the beam splitter is located at a distance from each of the interferometer mirrors and the second spherical concave

FI.2

Claims (2)

Claim 1. A device for measuring the thickness of optically transparent films, containing a sequentially arranged illuminator made in the form of a source of infrared radiation and sequentially installed along the radiation of a flat mirror, the first and second spherically concave mirrors and the second flat mirror, an object stage mounted in the center of curvature of the first concave mirror, an interferometer of two mirrors, one of which has a drive and is installed with the possibility of reciprocating movement along the axis of the interferometer, and light a divider mounted at the intersection of the optical axes of the mirrors of the interferometer and the second spherically concave mirror, a focusing element, an infrared detector and a measurement unit, the input of which is electrically connected to the drive of the movable mirror, characterized in that, in order to increase the accuracy and measurement performance, interferometer mirrors are made spherically concave with the same curvature, the stage is installed in the center of curvature of the second spherically concave illuminator mirror, and the beam splitter is mounted at a distance yanii from each of the mirrors of the interferometer and the second spherical concave mirror illuminator equal to the radius of curvature of respective mirrors. 2. Device pop. 1, characterized in that the spherical mirrors of the illuminator are made with the same curvature. Compiled by B. Timofeev Editor M. Tsitkina Tehred M. Khodanich Proofreader V. Girnyak Order 562/36 Circulation 680 Subscription VNIIIPI of the USSR State Committee for Inventions and Discoveries 113035, Moscow, Zh-35, Raushskaya nab., D. 4/5 Production and printing company, Uzhhorod, st. Project, 4