CN113203706A

CN113203706A - Line scanning beam splitting white light interferometer

Info

Publication number: CN113203706A
Application number: CN202110534115.9A
Authority: CN
Inventors: 赵效楠; 彭思龙; 汪雪林; 顾庆毅; 王一洁; 王毅
Original assignee: Suzhou Zhongke Xingzhi Intelligent Technology Co ltd; Northeastern University Qinhuangdao Branch
Current assignee: Suzhou Zhongke Xingzhi Intelligent Technology Co ltd; Northeastern University Qinhuangdao Branch
Priority date: 2021-05-17
Filing date: 2021-05-17
Publication date: 2021-08-03
Anticipated expiration: 2041-05-17
Also published as: CN113203706B

Abstract

The invention discloses a line scanning beam splitting white light interferometer, wherein a light source part comprises an SLD light source, and the light outlet end of the SLD light source is connected with a collimator; the light beam emitted by the light outlet end of the collimator enters the beam splitting prism after passing through the first cylindrical lens and enters the reference arm and the sample arm respectively in two paths; reflected light returned by the reference arm and the sample arm enters the second telecentric lens after passing through the light splitting prism and then enters the spectrometer; the reference arm is sequentially provided with a second cylindrical lens, an achromatic lens and a reflector; a first telecentric lens, a measurement sample and a one-dimensional translation stage are arranged in the sample arm; the invention has the advantages that the SLD light source has short coherence length and high power; the cylindrical mirror generates a linear array light beam, so that linear scanning detection can be completed, and the detection precision is improved; the achromatic lens and the telecentric lens can be two lenses with different focal lengths, and a reference arm and a sample arm are not needed to meet the equal optical path condition; the telecentric lens can avoid dead angles and has the advantages of high definition precision and high energy uniformity.

Description

Line scanning beam splitting white light interferometer

Technical Field

The invention relates to the technical field of optical instruments, in particular to a line scanning beam splitting white light interferometer.

Background

The interferometer is a precision instrument for accurately measuring the change of geometric height or the change of refractive index through the change of optical path difference between two beams of coherent light. Any change of the optical path difference between the two coherent light beams can sensitively cause the movement of the interference fringe, so that the small change of the geometric length or the refractive index can be measured through the movement change of the interference fringe, and other physical quantities related to the small change can be measured, and the measurement accuracy is incomparable with any other measurement methods. At the present stage, an interferometer using white light as a light source appears, the coherence length is short, the measurement of the height of the corresponding sample surface is more accurate, the overall appearance of the measured sample can be restored, the spectroscopic white light interferometer does not need to scan in the depth direction compared with the traditional white light interference technology, and the measurement speed is greatly improved. This technique can measure absolute distance, film properties, etc.

The existing light splitting white light interferometer can only measure one point at a time, the surface appearance of a sample needs to be measured by moving a high-precision platform, and the high-precision platform is expensive and has low moving speed. In addition, in the prior art, a 45-degree cylindrical reflector is adopted in a light splitting part, and the reflector is used for shielding a sample arm to a certain extent, so that the imaging contrast of an objective lens of the sample arm is easy to reduce; the reflector is not easy to mount and adjust a mechanical structure, the structure adjusting frame can shield the sample arm to a certain extent, and effective interference fringes are difficult to generate particularly under the condition that the reflection of light on the surface of a sample is weak. In addition, in the prior art, a sample objective lens and a focusing lens both adopt common achromatic objective lenses. When the reflected light of the sample is specular reflection, the sample objective lens cannot receive enough reflected light under the off-axis view, and the detection effect cannot be achieved; the focusing lens focuses the light after the grating is split into light rays to the detector, so that uneven energy is easily caused, and the detection result is misjudged.

Chinese patent CN112325765A is an area array point scanning beam splitting white light interferometer, where an SLD light source emits a broadband spectrum, the light passes through an isolator and an optical fiber coupler in sequence, the emergent light at the end of the optical fiber is collimated by a collimator, and the collimated light is incident on a beam splitting prism, a beam of light is reflected by a third lens and focused on a reflector as a reference arm, a beam of light is incident on an XY scanning galvanometer, a beam of light with a certain field angle is reflected by the scanning galvanometer and incident on a fourth lens, and the beam of light is focused on a sample by the fourth lens to realize area array scanning. The XY scanning galvanometer is placed at the position of an object space focal plane of the fourth lens, so that light focused by the fourth lens is an image space telecentric light path. According to the technical scheme, the XY scanning galvanometer is added to replace an original mobile platform, so that a planar array type scanning form is realized. However, the XY scanning galvanometer still needs two sets of mechanical rotating units to respectively control the oscillating of the galvanometer so as to realize scanning, which increases errors and affects precision.

Disclosure of Invention

In view of the above, the present invention provides a line scanning beam splitting white light interferometer, which can solve the above problems.

For this purpose, the present invention is implemented by the following technical means.

A line-scanning beam-splitting white light interferometer, comprising: the device comprises a light source part, a collimator, a beam splitter prism, a reference arm, a sample arm and a spectrometer;

the light source part comprises an SLD light source, and the light outlet end of the SLD light source is connected with the collimator; the light beam emitted by the light outlet end of the collimator enters the beam splitter prism after passing through the first cylindrical lens and enters the reference arm and the sample arm respectively in two paths; reflected light returned by the reference arm and the sample arm passes through the light splitting prism, enters a second telecentric lens and then enters the spectrometer;

a second cylindrical lens, an achromatic lens and a reflector are sequentially arranged in the reference arm along the light path;

a first telecentric lens and a measurement sample are sequentially arranged in the sample arm along the light path; the measurement sample is placed on a one-dimensional translation stage.

Furthermore, a slit, a third telecentric lens, a grating, a fourth telecentric lens and a camera are sequentially arranged in the spectrometer along a light path; and the signal output end of the camera is electrically connected with an upper computer.

Furthermore, the third telecentric lens and the fourth telecentric lens have the same structure and comprise a P1 lens, a P2 lens, a P3 lens, a P4 lens and a P5 lens which are arranged in sequence; wherein the P1 lens is a lens with positive focal power and is used for eliminating spherical aberration; the P2 lens is a lens with negative focal power and is used for eliminating spherical aberration, coma and chromatic aberration; the P3 lens is a lens with positive focal power and is used for eliminating chromatic aberration of magnification; the P4 lens is a lens with positive optical power, the P5 lens is a lens with positive optical power, and the P4 lens and the P5 lens are used for eliminating distortion and curvature of field.

Further, the collimator is a diffraction polar achromatic mirror.

Furthermore, the first cylindrical lens is an achromatic cylindrical lens, and the light beam is focused by the first cylindrical lens to form a linear light spot.

Further, the first telecentric lens and the second telecentric lens have the same structure and comprise an O1 lens, an O2 lens, an O3 lens and an O4 lens which are arranged in sequence; wherein the O1 lens is a lens with positive focal power for eliminating spherical aberration, coma, astigmatism and distortion; the O2 lens is a lens with negative focal power and is used for eliminating spherical aberration, coma, chromatic aberration and distortion; the O3 is a lens with positive focal power and is used for eliminating astigmatism and distortion; the O4 is a lens with positive optical power for eliminating astigmatism and curvature of field.

Further, the light source part is a near-infrared broadband light source with the wavelength range of 810nm-870 nm.

Further, the light source part also comprises a red light LD and a coupler; and the red light LD passes through the coupler and then sequentially passes through the collimator, the first cylindrical lens, the beam splitter prism and the first telecentric lens to be focused on the surface of the measurement sample.

Further, the motion direction of the one-dimensional translation stage is perpendicular to the length direction of the light spot focused on the surface of the measurement sample.

The invention has the following advantages:

1. the SLD light source is adopted, so that the method has the advantages of wide spectral bandwidth, stable energy, short coherence length and high power, and is more suitable for white light interference; the cylindrical mirror is used to enable the system to generate a linear array light beam, and the scanning of the surface can be completed only by realizing the movement in one direction by the one-dimensional translation table, so that the mechanical error is reduced, and the detection precision is improved;

2. the achromatic lens and the telecentric lens can be two lenses with different focal lengths, and a reference arm and a sample arm are not needed to meet the equal optical path condition; the telecentric lens can effectively receive diffuse reflection light and specular reflection light reflected by the surface of the sample, and has the advantages of avoiding dead angles, high definition precision and high energy uniformity;

further, a telecentric lens in the spectrometer can uniformly distribute and focus light energy on the surface of the camera, so that misjudgment is avoided; the spectrometer with light splitting capability is used as a collecting end, the grating splits white light into narrow-band light, and the narrow-band light is finally converged to a camera for collection.

Drawings

In order to illustrate the embodiments of the present invention more clearly, the drawings that are needed in the embodiments will be briefly described below, it is obvious that the drawings in the following description are only one or several embodiments of the present invention, and that other drawings can be obtained by those skilled in the art without inventive effort.

FIG. 1 is a schematic view of the present invention;

FIG. 2 is a diagram showing the optical paths from the light source to the sample arm and the reference arm in example 1 of the present invention;

fig. 3 shows a focal line spot after the first telecentric lens in embodiment 1 of the present invention;

FIG. 4 shows the focal line spots after the neutral aberration eliminating lens in embodiment 1 of the present invention;

FIG. 5 is a diagram showing an optical path of light reflected from the surface of a sample and focused on a slit in example 1 of the present invention;

FIG. 6 is a diagram showing an optical path of reflected light of a mirror focused on a slit in example 1 of the present invention;

FIG. 7 is a diagram of the spectrometer optical path in example 1 of the present invention;

FIG. 8 is a graph of MTF at a wavelength of 810nm for the spectrometer in example 1 of the present invention;

FIG. 9 is a graph of MTF at 840nm for a spectrometer in example 1 of the present invention;

FIG. 10 is a graph of MTF at 870nm wavelength for the spectrometer in example 1 of the present invention.

In the figure:

1-a light source section; 2-a collimator; 3-a first cylindrical lens; 4-a beam splitting prism; 5-a reference arm; 6-sample arm; 7-a second telecentric lens; 8-a spectrometer; 501-a second cylindrical lens; 502-an achromatic lens; 503-mirror reflector; 601-a one-dimensional translation stage; 602-a first telecentric lens; 603-measuring the sample; 801-a slit; 802-a third telecentric lens; 803-grating; 804-a fourth telecentric lens; 805-camera.

Detailed Description

The conception, the specific structure and the technical effects of the present invention will be clearly and completely described in conjunction with the embodiments and the accompanying drawings to fully understand the objects, the schemes and the effects of the present invention. It should be noted that, in the case of no conflict, the features in the embodiments of the present application may be combined with each other.

It should also be noted that, in the description of the present invention, unless otherwise explicitly specified or limited, the terms "disposed," "mounted," "connected," and the like are to be construed broadly and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

The invention will be further explained with reference to the drawings.

A line scanning beam splitting white light interferometer, as shown in fig. 1, mainly comprising: the device comprises a light source part 1, a collimator 2, a beam splitter prism 4, a reference arm 5, a sample arm 6 and a spectrometer 8;

the light source part 1 comprises an SLD light source, and the light outlet end of the SLD light source is connected with the collimator 2; preferably, the light source part 1 is a near infrared broadband light source having a wavelength ranging from 810nm to 870 nm.

Preferably, the collimator 2 is a diffraction pole achromat, and a light beam emitted from a light outlet end of the collimator 2 enters the beam splitter prism 4 after passing through the first cylindrical lens 3, and enters the reference arm 5 and the sample arm 6 respectively in two paths.

Wherein, a second cylindrical lens 501, an achromatic lens 502 and a reflective mirror 503 are sequentially arranged in the reference arm 5 along the optical path; the purpose of the design is to restore the light beam incident on the reference arm to a parallel light beam through the second cylindrical lens 501, and to adjust the light beam through the achromatic lens 502 to form a circular light spot on the surface of the reflective mirror 503, so that the reflective mirror with a small area can be used, the reference range is reduced, and the final detection error caused by the enlargement of the mirror surface processing error due to the reflection in a large range or a strip area is avoided.

A first telecentric lens 602 and a measurement sample 603 are sequentially arranged in the sample arm 6 along the light path, wherein the measurement sample 603 is placed on the one-dimensional translation stage 601. Preferably, the first telecentric lens 602 and the second telecentric lens 7 have the same structure, are both small aberration telecentric lenses, and comprise an O1 lens, an O2 lens, an O3 lens and an O4 lens which are arranged in sequence; wherein, the O1 lens is a lens with positive focal power and is used for eliminating spherical aberration, coma aberration, astigmatism and distortion; the O2 lens is a lens with negative focal power and is used for eliminating spherical aberration, coma, chromatic aberration and distortion; o3 is a lens with positive power for eliminating astigmatism and distortion; o4 is a lens with positive power to eliminate astigmatism and curvature of field. After light beams are emitted from a light source, the light beams enter the sample arm 6 after passing through the first cylindrical lens 3 and the beam splitter prism 4, linear light spots are formed on the surface of the measurement sample 603, the scanning can be completed only by moving the one-dimensional translation stage 601 after further completing the plane detection, the movement perpendicular to the length direction of the light spots can be specifically selected, the scanning area in unit time is the largest, and the translation in different directions can be selected according to actual requirements.

Reflected light returned by the reference arm 5 and the sample arm 6 passes through the beam splitter prism 4, enters the second telecentric lens 7 and then enters the spectrometer 8; preferably, the spectrometer 8 is provided with a slit 801, a third telecentric lens 802, a grating 803, a fourth telecentric lens 804 and a camera 805 in sequence along a light path; the signal output end of the camera 805 is electrically connected with an upper computer. Further, the third telecentric lens 802 and the fourth telecentric lens 804 have the same structure, are both small aberration telecentric lenses, and include a P1 lens, a P2 lens, a P3 lens, a P4 lens, and a P5 lens, which are arranged in sequence; wherein, the P1 lens is a lens with positive focal power and is used for eliminating spherical aberration; the P2 lens is a lens with negative focal power for eliminating spherical aberration, coma and chromatic aberration; the P3 lens is a lens with positive focal power and is used for eliminating chromatic aberration of magnification; the P4 lens is a lens having a positive power, the P5 lens is a lens having a positive power, and the P4 lens and the P5 lens are used to eliminate distortion and curvature of field. The light filtered by the slit 801 is collimated by a third telecentric lens 802 with small aberration and enters a grating 803, the working F number of the third telecentric lens 802 is smaller than that of the second telecentric lens 7, and the light split by the grating 803 is focused on a photosensitive element of a camera 805 by a fourth telecentric lens 804 with small aberration.

Preferably, in order to facilitate the operator to observe the scanning area when viewing the sample, the light source part 1 further comprises a red light LD, a coupler; the red light LD passes through the coupler, then sequentially passes through the collimator 2, the first cylindrical lens 3, the beam splitter prism 4, and the first telecentric lens 602, and is focused on the surface of the measurement sample 603, and the current scanning area is determined by observing the laser stripe on the surface of the sample.

Example 1

In this embodiment, the specific setting parameters are as follows:

the SLD light source of the light source part 1 adopts a near-infrared broadband light source with the power of 25mw, the wavelength of 810 and 870nm, the numerical aperture of 0.13 and the core diameter of 5 um;

the collimator 2 adopts a diffraction pole achromat, and the focal length is 50 mm;

the clear aperture of the first cylindrical lens 3 is 13mm, and the focal length is 50 mm; the second cylindrical lens 501 is the same as the first cylindrical lens 3;

splitting ratio 50 of beam splitter prism 4: 50;

the focal length of achromatic lens 502 is 32.5 mm;

the reflector 503 is plated with a near-infrared high-reflection film, and the reflectivity is more than 99.5%;

the entrance pupil diameter of the first telecentric lens 602 with small aberration is 13mm, the focal length is 46mm, the F number is 3.5, the length of a focusing line is 12mm, and the line width is 25 um;

the second telecentric lens 7 and the first telecentric lens 602 adopt the same lens, and the line length is 12mm focused to the slit 801 in a ratio of 1: 1;

the length of the slit 801 is 12mm, and the width of the slit is 20 um;

the entrance pupil diameter of the third telecentric lens 802 with small aberration is 26mm, the focal length is 79mm, and the F number is 3;

the fourth telecentric lens 804 and the third telecentric lens 802 adopt the same lens, the slit length is 12mm and is focused on the camera 1:1, and the light is split in the perpendicular direction of the slit by 13mm (the working wavelength is 810 and 870 nm);

the grating 803 is an 1800lp transmission grating with a blaze angle of 49.2 degrees; the effective target surface size of the camera is 12 x 13mm, and the pixel size is 9 um.

The system has the advantages of 12mm scanning line width, 0.08nm spectral resolution and higher resolution.

The working process is as follows:

the light path diagram of the light emitted by the SLD reaching the reflector and the sample is shown in fig. 2, the emergent light passes through the first cylindrical lens 602 and then enters the first telecentric lens 602 to be focused on the surface of the measurement sample 603 to form a line spot as shown in fig. 3, the specific line length is 12mm, and the line width is 25 um.

The light beam entering the reference arm 5 is restored to be parallel light beam by the second cylindrical lens 501, and the light spot is focused by the achromatic lens 502 as shown in fig. 4, and the diameter of the light spot is 8 um.

The light reflected by the sample surface is focused to the slit 801 by the first telecentric lens 602 and the second telecentric lens 7 at magnification ratio of 1:1, and it can be known that the light spot of the focusing slit is also shown in fig. 3, and the specific light path diagram is shown in fig. 5:

the reflected light of the reflective mirror 503 is focused to the slit 801 by the achromatic lens 502, the second cylindrical lens 501 and the second telecentric lens 7, and similarly, the light spot is also shown in fig. 3, and the light path diagram is shown in fig. 6:

after entering the slit 801 of the spectrometer 8, as shown in fig. 7, the specific optical path diagram sequentially passes through a third telecentric lens 802 with small aberration, a grating 803, and a fourth telecentric lens 804 with small aberration, and finally enters the surface of the light-sensitive sensor of the camera 805 to form an electrical signal, and a corresponding interference image is formed by computer processing.

MTF curves of three groups of spectrometers with different wavelengths of 810nm, 840nm and 870nm are respectively shown in FIGS. 8, 9 and 10, and the MTFs at 55lp/mm camera Nyquist frequency are all greater than 0.65 (generally, the MTFs are greater than 0.1 camera to be resolved), so that the resolution is higher.

Although the present invention has been described in detail with reference to examples, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A line-scanning beam-splitting white light interferometer, comprising: the device comprises a light source part (1), a collimator (2), a light splitting prism (4), a reference arm (5), a sample arm (6) and a spectrometer (8);

the light source part (1) comprises an SLD light source, and the light outlet end of the SLD light source is connected with the collimator (2); the light beam emitted by the light outlet end of the collimator (2) enters the beam splitter prism (4) after passing through the first cylindrical lens (3), and enters the reference arm (5) and the sample arm (6) respectively in two paths; reflected light returned by the reference arm (5) and the sample arm (6) passes through the light splitting prism (4), enters a second telecentric lens (7) and then enters the spectrometer (8);

a second cylindrical lens (501), an achromatic lens (502) and a reflective mirror (503) are sequentially arranged in the reference arm (5) along a light path;

a first telecentric lens (602) and a measurement sample (603) are sequentially arranged in the sample arm (6) along a light path; the measurement sample (603) is placed on a one-dimensional translation stage (601).

2. The line scanning split white light interferometer according to claim 1, wherein the spectrometer (8) is provided with a slit (801), a third telecentric lens (802), a grating (803), a fourth telecentric lens (804) and a camera (805) in sequence along the optical path; and the signal output end of the camera (805) is electrically connected with an upper computer.

3. The line scanning split white light interferometer of claim 2, wherein the third telecentric lens (802) and the fourth telecentric lens (804) are identical in structure and comprise a P1 lens, a P2 lens, a P3 lens, a P4 lens and a P5 lens which are arranged in sequence; wherein the P1 lens is a lens with positive focal power and is used for eliminating spherical aberration; the P2 lens is a lens with negative focal power and is used for eliminating spherical aberration, coma and chromatic aberration; the P3 lens is a lens with positive focal power and is used for eliminating chromatic aberration of magnification; the P4 lens is a lens with positive optical power, the P5 lens is a lens with positive optical power, and the P4 lens and the P5 lens are used for eliminating distortion and curvature of field.

4. The line scanning spectroscopic white light interferometer of claim 1, wherein the collimator (2) is a diffractive polar achromatic mirror.

5. The line scanning split white light interferometer according to claim 1, wherein the first cylindrical lens (3) is an achromatic cylindrical lens, and the light beam is focused by the first cylindrical lens (3) to form a linear light spot.

6. The line scanning split white light interferometer of claim 1, wherein the first telecentric lens (602) and the second telecentric lens (7) are identical in structure and comprise an O1 lens, an O2 lens, an O3 lens and an O4 lens which are arranged in sequence; wherein the O1 lens is a lens with positive focal power for eliminating spherical aberration, coma, astigmatism and distortion; the O2 lens is a lens with negative focal power and is used for eliminating spherical aberration, coma, chromatic aberration and distortion; the O3 is a lens with positive focal power and is used for eliminating astigmatism and distortion; the O4 is a lens with positive optical power for eliminating astigmatism and curvature of field.

7. The line scanning spectroscopic white light interferometer of claim 1, wherein the light source section (1) is a near infrared broadband light source having a wavelength in the range of 810nm to 870 nm.

8. The line scanning split white light interferometer of claim 1, wherein the light source section (1) further comprises a red LD, a coupler; the red light LD passes through the coupler and then sequentially passes through the collimator (2), the first cylindrical lens (3), the beam splitter prism (4) and the first telecentric lens (602) to be focused on the surface of the measurement sample (603).

9. The line scanning spectroscopic white light interferometer of claim 1, wherein the direction of motion of the one-dimensional translation stage (601) is perpendicular to the length direction of the spot focused on the surface of the measurement sample (603).