White light interference contourgraph

Abstract

The invention discloses a white light interference contourgraph which comprises a white light interference contourgraph body, and a common reflector is replaced by a stepped reflector in the white light interference contourgraph body. And the stepped reflector is positioned behind a transmission light path of the spectroscope in the white light interference contourgraph, receives one path of transmission light of the spectroscope, and then reflects the transmission light into the CCD in the white light interference contourgraph. The invention has the advantages that: the stepped reflector is adopted to replace a common reflector, so that a plurality of light paths with reference light paths can be formed, a plurality of interference signals are superposed, and the measurement range is widened.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical detection technology, and in particular to a white light interferometer. BACKGROUND

[0002] In semiconductor process production, the surface three-dimensional microtopography has the most direct influence on the evaluation of many technical properties of the wafer surface, and the surface three-dimensional evaluation parameters can more comprehensively and more truly reflect the characteristics of the wafer surface and measure the quality of the surface, so the measurement of the surface three-dimensional microtopography is more important.

[0003] The measurement methods of the surface three-dimensional microtopography are very rich, and can be generally divided into contact type and non-contact type, of which the non-contact measurement method is mainly used.

[0004] The white light interferometry measurement of the surface three-dimensional microtopography uses a white light interferometer. The principle is to use the interference phenomenon, use a white light source to irradiate an object, and form an interference pattern after the reflected light passes through the light splitting device of the interferometer. By observing the changes of the interference pattern, the detailed information of the surface topography of the object can be obtained. The range of the white light interferometry is generally only a few microns, in order to improve the range, the vertical position of the sample or the method of moving the mirror is generally used to adjust the optical path.

[0005] Known technologies not only move the vertical position of the sample and the mirror, but also use an additional interference optical path to improve the range; patent application No. CN202311197267.X uses a numerical direction push-scan method to improve the range; patent application No. CN202311822266.X proposes a method of using a multi-wavelength Bragg fiber grating array to improve the range; patent No. CN117073731B uses a long-period fiber grating method to improve the range.

[0006] Although the method using the optical fiber avoids mechanical movement, it is difficult to achieve a large range improvement due to the preparation process of the fiber grating, and the transmission wavelength of the optical fiber is limited to near-infrared wavelength below, which cannot be used for long waves such as mid-infrared. SUMMARY

[0007] The purpose of the present application is to improve the measurement range of the white light interferometer, use a stepped mirror, design the spectral width and the step height of the stepped mirror to superimpose multiple interference signals, thereby improving the measurement range.

[0008] The present application proposes a white light interferometer, and the technical scheme adopted is as follows: A white light interferometer, comprising a white light interferometer, wherein a stepped mirror is used to replace a common mirror; the stepped mirror is located behind the transmission light path of a beam splitter in the white light interferometer, receives the transmission light of the beam splitter, and then reflects the transmission light into a CCD in the white light interferometer; The geometric parameters of the stepped mirror are step height , Among them, is the central wavelength of the light source, is the spectral width of the light source, is the coherence length.

[0009] Further preferably, the stepped mirror has MxN rectangular blocks or 1xN one-dimensional steps, and the steps have a fixed step height .

[0010] Further preferably, the base material of the stepped mirror is metal or its alloy, or glass or crystal.

[0011] Further preferably, the stepped mirror is provided with a stepped surface, and the stepped surface is coated.

[0012] Further preferably, the stepped surface is achieved by mechanical processing, surface micro-processing or etching.

[0013] Further preferably, the coating material is a metal film or a dielectric film.

[0014] Further preferably, the dielectric film is tantalum oxide or aluminum oxide.

[0015] Further preferably, the metal film is an aluminum film, a silver film or a gold film.

[0016] Further preferably, the light source is an LED light source, an ultracoincidence spectrum light source or a halogen lamp light source.

[0017] Compared with the prior art, the present application has the following beneficial effects: The white light interferometer of the present application uses a stepped mirror to replace a common mirror, can form multiple reference light paths, superimposes multiple interference signals, and improves the measurement range. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 It is a basic structure schematic diagram of the white light interferometer of the present application. Figure 2 schematic diagram of a stepped mirror; Figure 3 standard position of feedback of the white light interferometer profiler of the present embodiment interference signal diagram of a point; Figure 4 schematic diagram of a stepped mirror with 3x3 steps; Figure 2 schematic diagram of the interference signal of a stepped mirror with 3x3 steps as shown in the figure; Figure 5 gray scale diagram of a strip waveguide in the present embodiment; Figure 6 interference diagram of a strip waveguide obtained by a white light interferometer profiler using a common mirror; Figure 7 interference diagram of a strip waveguide obtained by a white light interferometer profiler using the present invention; Wherein: 1-first lens, 2-second lens, 3-third lens, 4-beamsplitter, 5-CCD camera, 6-stepped mirror, 7-light source, 8-surface of the test object. DETAILED DESCRIPTION

[0019] The technical solutions of the present invention will be described in detail below, but the protection scope of the present invention is not limited to the described embodiments.

[0020] To make the content of the present invention more obvious and easy to understand, the following will be combined with the Figure 1 -attached Figure 7 and the detailed description to make further description.

[0021] In order to make the purpose, technical solutions and advantages of the present invention more clear and obvious, the present invention will be further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, and are not used to limit the present invention.

[0022] As Figure 1 shown, the present embodiment is a white light interferometer profiler, which comprises a first lens 1, a second lens 2, a third lens 3, a beamsplitter 4, a CCD camera 5, a stepped mirror 6 and a light source 7.

[0023] The light emitted by the light source 7 enters the first lens 1 and then enters the beamsplitter 4, which is divided into two paths, one of which is a reflection path (measurement light path), which is reflected to the surface 8 of the test object, and then reflected back to the beamsplitter 4 after reflection on the surface 8 of the test object, and then passes through the second lens 2 and the third lens 3 and is collected by the CCD camera; the other path is a transmission path (reference light path), which transmits light into the stepped mirror 6, and then reflects back to the beamsplitter 4, and then passes through the second lens 2 and the third lens 3 and is collected by the CCD camera 5.

[0024] As known to those skilled in the art, the basic feature of a stepped reflector is that it has a plurality of reflective planes at different heights, which are distributed in a stepped manner. The stepped reflector can be freely designed with different stepped shapes. In this embodiment, the preferred embodiment is as follows: Figure 2 The plane is divided into multiple rectangles as shown. The rectangular plane is divided into M×N parts according to the length and width, as shown in Figure 2 The figure shows 3×3=9 steps. The height distribution of each step is different in order. , and take a step at the middle height as the zero point .

[0025] like Figure 2 As shown, the basic structure of the white light interferometer profiler of this embodiment is similar to that of the ordinary white light interferometer profiler, but the ordinary reflector is replaced by a stepped reflector. Therefore, the stepped reflector has M×N steps, and has M×N distances. Therefore, without moving the sample and the stepped mirror, it is equivalent to moving the stepped mirror by M×N distances, thereby increasing the measurement range.

[0026] In this embodiment, the stepped shape of the stepped reflector can be as follows: Figure 2 The M×N rectangular blocks shown can also be 1×N one-dimensional steps, or any other arbitrary shape, but the steps have a fixed height. .like Figure 2 As shown, the stepped shape of the stepped reflector in this embodiment is 3×3 rectangular blocks.

[0027] like Figure 2 As shown, in this embodiment, the base material of the stepped reflector includes metals and their alloys, such as aluminum, stainless steel, iron, and titanium; various glasses or crystals, such as quartz glass, fluoride glass, silicon, and germanium; polymers, resins, and other materials. These materials are processed into a stepped surface through machining, surface micromachining, corrosion etching, and other methods. The reflectivity of the stepped reflector is enhanced by coating the stepped surface. The coating material can be a metal film, such as an aluminum film, a silver film, a gold film, or a dielectric film. The coating process is known to those skilled in the art.

[0028] The stepped surface mentioned in this embodiment is achieved by machining, surface micromachining, or etching, three different process methods, to achieve the purpose of forming a stepped shape on the surface of the material. The three different process methods are all known to those skilled in the art.

[0029] Machining is a traditional processing method that uses precision lathes and tools to turn, mill, plan, and grind the material to form a stepped shape.

[0030] Surface micro-machining, using magnetic rheological polishing, laser precision machining, ion beam impact and other processing methods, to form a ladder shape on the material surface.

[0031] Etching, using photolithography, wet etching or dry etching and other methods, to form a ladder shape on the material surface.

[0032] In this embodiment, the light source is an LED light source, an ultracoincidence spectrum light source or a halogen lamp light source.

[0033] As shown in Figure 1 , in this embodiment, the design of the ladder-shaped mirror should be matched with the center wavelength of the light source and the spectral width of the light source. The step parameters of the ladder-shaped mirror are related to the coherence length , and the coherence length is related to the center wavelength of the light source and the spectral width of the light source, and the relationship is: (1) In order to achieve the best effect, that is, the interference fringes formed between the two adjacent steps of the ladder-shaped mirror are neither interrupted nor overlapped, the step height of the ladder-shaped mirror is equal to the coherence length , that is: (2) According to formula (3), the relationship between the light intensity collected by the CCD camera 5 and the sample height z to be measured is: (3) Wherein, is the background intensity, is the zero position, is the coherence length, is the period visibility, is the center wavelength of the light source.

[0034] According to formula (3), when different step surfaces of the ladder-shaped mirror are used, the optical path of the set zero position in the reference light path can be changed, which will affect the sample height z to be measured.

[0035] The white light interference profiler provided in the technical scheme of the present application uses a ladder-shaped mirror to replace a common mirror, and the ladder-shaped mirror has MxN steps, so it has MxN reflection planes. Therefore, without moving the sample and the ladder-shaped mirror, the ladder-shaped mirror is equivalent to being moved by MxN distances, thereby improving the measurement range.

[0036] ​Specifically, as shown in Figure 3 the selected light source 7, the center wavelength of the known light source is 500 nm, the spectral width of the light source is 100 nm, and the formula (1) is obtained: =2.5μm, the width of the interference signal of one step in the stepped mirror is about 2.5μm, and the interference signal of the stepped mirror with 3x3 steps is shown in Figure 2 Figure 4 , the range is increased by 9 times compared with the ordinary mirror.

[0037] Specific application examples This example uses an LED light source with a center wavelength of 500 nm and a spectral width of 100 nm. According to formulas (1) and (2), the step height of the stepped mirror is 2.5μm. According to the 3x3 arrangement of the stepped mirror, as shown in Figure 2 , the height increases from left to right and from top to bottom, and the darker the color in the figure, the higher the height. The interference signal with the height brought by the stepped mirror is shown in Figure 2 Figure 4

[0038] As shown in Figure 5 , the test sample is a strip waveguide with a width of about 200μm and a height of about 20μm. The height is represented by gray scale in the figure, and the whiter the color, the higher the height.

[0039] In order to show the effect of the present application, a step is first tested, i.e. a white light interferometer with an ordinary mirror is used for testing, and the measurement range is 2.5μm as shown in Figure 3 . The measurement result is shown in Figure 6 , which only shows part of the inclined edge of the strip waveguide. This is because the bottom surface (-10μm) and the top surface (10μm) of the waveguide are far beyond the measurement range.

[0040] After using the stepped mirror of the present embodiment, the system range is increased to 22.5μm, and the measurement result is shown in Figure 7 , and the whole shape of the waveguide can be seen, and the range is improved.

[0041] The above examples only illustrate the technical idea of the present application, and cannot limit the protection scope of the present application. Any modification made according to the technical idea of the present application on the basis of the technical scheme falls within the protection scope of the present application.​​​​​​​​​

Claims

1. A white light interferometer profiler, comprising a white light interferometer profiler, characterized in that: The stepped reflector replaces the ordinary reflector in the white light interferometer profilometer; the stepped reflector is located behind the transmission light path of the beam splitter in the white light interferometer profilometer, and the stepped reflector receives one path of the transmitted light from the beam splitter and then reflects the transmitted light into the CCD in the white light interferometer profilometer; The geometrical parameter of the stepped reflector is the step height , in, is the central wavelength of the light source, is the spectral width of the light source, is the coherence length.

2. The white light interferometer profiler according to claim 1, characterized in that The stepped reflector has a stepped shape of M×N rectangular blocks or 1×N one-dimensional steps with a fixed step height between the steps. .

3. The white light interferometer profiler according to claim 1, wherein: The base material of the stepped reflector is metal and its alloy or glass or crystal.

4. The white light interferometer profiler according to claim 3, characterized in that: A stepped reflector is provided with a stepped surface, and a film is coated on the stepped surface.

5. The white light interferometer profiler according to claim 4, characterized in that: The stepped surface is achieved by machining, surface micromachining or corrosion etching.

6. The white light interferometer profiler according to claim 4, characterized in that: The coating material is a metal film or a dielectric film.

7. The white light interferometer profiler according to claim 6, characterized in that: The dielectric film is tantalum oxide or aluminum oxide.

8. The white light interferometer profiler according to claim 6, characterized in that: The metal film is an aluminum film, a silver film or a gold film.

9. The white light interferometer profiler according to claim 1, characterized in that: The light source is an LED light source, a supercontinuum light source or a halogen lamp light source.

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