Step height standard sample, preparation method and white light interferometer calibration method

Abstract

The present invention provides a step height standard sample block, a preparation method and a white light interferometer calibration method. The step height standard sample block includes: a bottom layer and a step layer located on the bottom layer; the upper surface of the step layer has a groove, the groove is used to receive and reflect the light of the target white light interferometer, and the material of the step layer is an opaque material. Since the step height standard sample block provided by the present invention forms a step structure by a step layer with a groove, rather than forming a step structure by two layers of material, and the material of the step layer is an opaque material, the step structure in the step height standard sample block has the same refractive index and extinction coefficient on the upper and lower surfaces, so that the step height standard sample block provided by the present invention will not affect the intensity of the light irradiated on the step structure, and then the step height standard sample block provided by the present invention is used to calibrate the white light interferometer, which is conducive to reducing the calibration error of the white light interferometer and realizing fast and accurate calibration of the white light interferometer.

Description

Technical Field

[0001] The invention relates to the technical field of microelectronics metrology and testing, and in particular to a step height standard sample block, a preparation method and a white light interferometer calibration method. Background Art

[0002] Integrated circuits, large-scale integrated circuits and micro-electromechanical systems (MEMS) devices contain a large number of step structures, which have a direct impact on the overall performance of the device. Therefore, accurate measurement and monitoring of step structures is an important means to ensure device quality. At present, step height measurement instruments mainly include atomic force microscopes, scanning tunneling microscopes, nanometer measuring machines, white light interferometers, step measuring instruments, laser film thickness testers, etc. Among them, white light interferometers are used more frequently on semiconductor production lines and are non-contact measurements.

[0003] Before using a white light interferometer for measurement, it is usually necessary to calibrate the white light interferometer using a step height standard block. However, when calibrating the white light interferometer using an existing step height standard block, there is a problem that the calibration result is not accurate enough. Summary of the invention

[0004] The embodiment of the present invention provides a step height standard block, a preparation method and a white light interferometer calibration method to solve the problem that the calibration result of the existing step height standard block for calibrating the white light interferometer is not accurate enough.

[0005] In a first aspect, an embodiment of the present invention provides a step height standard sample block, comprising: a bottom layer and a step layer located on the bottom layer;

[0006] The upper surface of the step layer is provided with a groove, the groove is used to receive and reflect the light of the target white light interferometer, and the material of the step layer is an opaque material.

[0007] In a possible implementation manner, the material of the step layer is GaAlAs, and the material of the bottom layer is GaAs.

[0008] In a possible implementation, the material of the step layer is GaAs, and the material of the bottom layer is InGaP.

[0009] In a possible implementation, the groove does not pass through the edge of the step layer, and the aspect ratio of the groove is 5:2.

[0010] In a second aspect, an embodiment of the present invention provides a method for preparing a step height standard sample block, comprising:

[0011] preparing a base layer;

[0012] growing an initial step layer on the bottom layer;

[0013] A groove is etched on the upper surface of the initial step layer to prepare a step height standard sample block.

[0014] In a possible implementation, etching a groove on the upper surface of the initial step layer to prepare a step height standard sample block includes:

[0015] Spin-coating a photoresist on the upper surface of the initial step layer;

[0016] Using a mask having a preset photoresist pattern to expose and develop the photoresist to obtain a first sample;

[0017] Etching a groove on the upper surface of the initial step layer not covered with photoresist in the first sample to obtain a second sample;

[0018] The photoresist on the second sample is removed to prepare a step height standard sample block.

[0019] In a possible implementation, the groove does not pass through the edge of the step layer, and the aspect ratio of the groove is 5:2.

[0020] In a possible implementation, the material of the initial step layer is GaAlAs, and the material of the bottom layer is GaAs.

[0021] In a possible implementation, the material of the initial step layer is GaAs, and the material of the bottom layer is InGaP.

[0022] In a third aspect, an embodiment of the present invention provides a white light interferometer calibration method, which uses the step height standard block described in the first aspect or any possible implementation of the first aspect to calibrate the white light interferometer.

[0023] The embodiment of the present invention provides a step height standard block, a preparation method and a white light interferometer calibration method. The step height standard block provided by the embodiment of the present invention includes a bottom layer and a step layer located on the bottom layer; wherein the upper surface of the step layer has a groove, the groove is used to receive and reflect the light of the target white light interferometer, and the material of the step layer is an opaque material. Since the step height standard block provided by the embodiment of the present invention forms a step structure by a step layer with a groove, rather than forming a step structure by two layers of material, and the material of the step layer is an opaque material, the step structure in the step height standard block has the same refractive index and extinction coefficient on the upper and lower surfaces, so that the step height standard block provided by the embodiment of the present invention will not affect the intensity of the light irradiated on the step structure, and then the step height standard block provided by the embodiment of the present invention is used to calibrate the white light interferometer, which is conducive to reducing the calibration error of the white light interferometer and realizing fast and accurate calibration of the white light interferometer. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0025] Figure 1 is a schematic diagram of light incidence provided by an embodiment of the present invention;

[0026] Figure 2 is a schematic diagram of the cross-sectional structure of a step height standard sample block provided by an embodiment of the present invention;

[0027] Figure 3 is a flow chart of a method for preparing a step height standard sample block provided by an embodiment of the present invention;

[0028] Figure 4 is a schematic diagram of a step height standard sample preparation process provided by an embodiment of the present invention;

[0029] Figure 5 is a schematic diagram of step height standard blocks with different preset standard heights provided by an embodiment of the present invention;

[0030] Figure 6 is a flow chart of the implementation of the white light interferometer calibration method provided by an embodiment of the present invention;

[0031] Figure 7 It is a schematic diagram of the step structure in the step height standard sample block scanned and measured by white light interferometer provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0032] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present invention. However, it should be clear to those skilled in the art that the present invention may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present invention.

[0033] In order to make the purpose, technical solutions and advantages of the present invention more clear, specific embodiments will be described below in conjunction with the accompanying drawings.

[0034] First, the measurement principle of white light interferometer is explained:

[0035] The light emitted by the white light interferometer is white light, which is monochromatic light with different wavelengths and frequencies. When the coherence conditions are met, interference will be superimposed, and the width of the interference fringes will be different and the brightness will gradually weaken. Among them, the functional relationship between the optical path difference and the light intensity satisfies the following:

[0036]

[0037] Among them, I1 and I2 are the light intensities of the two beams, I0 is the background light intensity, satisfying I0=I1+I2; Δ is the optical path difference between the two beams, λ represents the wavelength of a monochromatic light; m represents the visibility of the stripes, satisfying π is the relevant envelope term; M is the coherent modulation degree, M=mv; the CCD camera converts the microscopic contour fluctuations of the measured surface into magnified plane interference fringes, extracts the height data corresponding to each pixel through the phase unwrapping algorithm, and then indirectly completes the measurement of the step structure by measuring the relative deformation of the interference fringes.

[0038] The inventor discovered in the process of implementing the present invention that according to Fresnel reflection theory, when light is incident from one medium to another, reflection and refraction occur. The electric field in the incident light can be divided into two components: S component and P component, where the S component is perpendicular to the incident surface and the P component is parallel to the incident surface. Figure 1 As shown. The reflection coefficient represents the ratio of the reflected light intensity to the incident light intensity. The reflectivity represents the ratio of the reflected light intensity to the incident light intensity, that is, the square of the reflection coefficient. The above two parameters can represent the reflection of light intensity. Under the S component and P component, the reflection coefficient and reflectivity are respectively:

[0039]

[0040]

[0041] The absorption of light by the medium surface cannot be ignored. The absorption of light by the medium can be described by the extinction coefficient k. Then the reflection coefficient and reflectivity can be expressed as:

[0042]

[0043] Where n1 and n2 represent the refractive index of the two media. S =R P =|r P | 2 , after simplified calculation:

[0044]

[0045] That is, according to the above formula, the reflectivity of the incident light is related to the refractive index n and the extinction coefficient k of the medium.

[0046] Considering that the existing step height standard blocks usually have SiO2 on the top of the step structure and Si on the bottom, it may be due to the different materials of the top and bottom of the step structure of the existing step height standard blocks, and their refractive index and extinction coefficient are also different, which in turn affects the intensity of light. The white light interferometer completes the step height measurement of the step structure based on the functional relationship between the optical path difference and the light intensity. Therefore, there is a certain calibration error in calibrating the white light interferometer based on the existing step height standard blocks.

[0047] Based on the above inventors' discovery, Figure 2 As shown, the step height standard block provided by the embodiment of the present invention includes: a bottom layer 10 and a step layer 20 located on the bottom layer.

[0048] The upper surface of the step layer 20 has a groove 21 , and the groove 21 is used to receive and reflect the light of the target white light interferometer, and the material of the step layer 20 is an opaque material.

[0049] The step height standard block provided in the embodiment of the present invention is composed of a bottom layer and a step layer located on the bottom layer, and the upper surface of the step layer has a groove, and the material of the step layer is an opaque material. Since the step structure is no longer composed of two layers of material, the step structure in the step height standard block has the same refractive index and extinction coefficient on the upper and lower surfaces, so that the step height standard block provided in the embodiment of the present invention does not affect the intensity of light irradiated on the step structure, and then the step height standard block provided in the embodiment of the present invention is used to calibrate the white light interferometer, which is conducive to reducing the calibration error of the white light interferometer and realizing fast and accurate calibration of the white light interferometer.

[0050] Optionally, the material of the step layer may be GaAlAs, and the material of the bottom layer may be GaAs, or the material of the step layer may be GaAs, and the material of the bottom layer may be InGaP, so that the step structure in the step height standard sample block provided in this embodiment has the same refractive index and extinction coefficient on the upper and lower surfaces, and has a higher refractive index.

[0051] Optionally, in the step height standard sample block provided in the above embodiment, the groove 21 does not penetrate the edge of the step layer 20 , that is, the groove 21 does not penetrate the front and rear end surfaces of the step layer 20 , nor the left and right end surfaces.

[0052] In order to facilitate the inspection of the uniformity of the step heights at different positions in the step height standard sample block, the groove 21 may be a rectangular groove. Exemplarily, the aspect ratio of the groove 21 may be 5:2.

[0053] The depth of the groove 21 is the preset standard height of the step height standard sample block.

[0054] In this embodiment, based on the calibration requirements of the white light interferometer, step height standard blocks with different preset standard heights can be obtained for calibration of the white light interferometer.

[0055] See also Figure 3 , which shows a flowchart of the implementation of the step height standard sample block preparation method provided by an embodiment of the present invention, and is described in detail as follows:

[0056] In step 301, a base layer is prepared.

[0057] In step 302, an initial step layer is grown on a base layer.

[0058] In step 303, a groove is etched on the upper surface of the initial step layer to prepare a step height standard sample block.

[0059] Among them, an initial step layer of preset thickness can be grown on the bottom layer, and a groove can be etched on the upper surface of the initial step layer based on a preset etching depth, wherein the preset etching depth is less than the preset thickness, and the preset thickness is the preset standard height of the step height standard sample block.

[0060] In this embodiment, the preset etching depth is limited to be less than the preset thickness, so that the step layer obtained after etching can be a step structure composed of one material, and the step structure in the step height standard block has the same refractive index and extinction coefficient on the upper and lower surfaces, so that the step height standard block prepared by the step height standard block preparation method provided in the embodiment of the present invention will not affect the intensity of light irradiated on the step structure, and the step height standard block prepared by the step height standard block preparation method provided in the embodiment of the present invention can be used to calibrate the white light interferometer, which is beneficial to reduce the calibration error of the white light interferometer and realize fast and accurate calibration of the white light interferometer.

[0061] Optionally, etching a groove on the upper surface of the initial step layer to prepare a step height standard sample block may include:

[0062] A photoresist is spin-coated on the upper surface of the initial step layer.

[0063] The photoresist is exposed and developed using a mask having a preset photoresist pattern to obtain a first sample.

[0064] A groove is etched on the upper surface of the initial step layer not covered with photoresist in the first sample to obtain a second sample.

[0065] The photoresist on the second sample is removed to prepare a step height standard sample block.

[0066] like Figure 4As shown, in this embodiment, the step height standard sample is prepared by material preparation, thermal oxidation, coating, exposure, development, etching, degumming and other process steps, wherein the step etching process can ensure the height of the step structure in the step height standard sample by accurately controlling the etching rate. After the degumming process is completed, the upper and lower surfaces of the step structure have the same refractive index and extinction coefficient.

[0067] Similarly, the groove etched in this embodiment does not penetrate through the front and rear end surfaces of the initial step layer, nor does it penetrate through the left and right end surfaces of the initial step layer, that is, the groove does not penetrate through the edge of the initial step layer.

[0068] The etched groove may be a rectangular groove. For example, the aspect ratio of the etched groove may be 5:2.

[0069] Similarly, the material of the step layer may be GaAlAs, and the material of the bottom layer may be GaAs, or the material of the step layer may be GaAs, and the material of the bottom layer may be InGaP.

[0070] For example, the step height standard blocks with different preset standard heights prepared by the step height standard block preparation method provided in the embodiment of the present invention are as follows: Figure 5 shown.

[0071] Figure 6 The following is a flowchart of the implementation of the white light interferometer calibration method provided by the embodiment of the present invention, which is described in detail as follows:

[0072] In step 601, at least one step height standard sample block of a preset standard height is obtained.

[0073] In step 602, a white light interferometer is used to measure the step height standard sample block to obtain the measured height of the step height standard sample block.

[0074] In step 603, the white light interferometer is calibrated using the measured height and the preset standard height.

[0075] The step height standard block of the preset standard height is a step height standard block having the same structure as the above embodiment, or a step height standard block prepared by the step height standard block preparation method provided in the above embodiment. Based on the step height standard block preparation method provided in the above embodiment, a set of universal step height standard blocks can be provided for the calibration of a white light interferometer.

[0076] The embodiment of the present invention uses the step height standard block in the above embodiment to calibrate the white light interferometer, compares the measurement result of the white light interferometer (i.e., the measured height) with the standard value of the step height standard block (i.e., the preset standard height), and then determines whether the measurement value of the white light interferometer is accurate and reliable. Figure 7A schematic diagram of the step structure in a step height standard sample block measured by scanning with a white light interferometer is shown. The embodiment of the present invention uses the step height standard sample block in the above embodiment to calibrate the white light interferometer, which is beneficial to reducing the calibration error of the white light interferometer and realizing fast and accurate calibration of the white light interferometer. It has certain practical value and promotion in the field of semiconductor process parameter measurement.

[0077] It should be understood that the order of execution of the steps in the above embodiment does not necessarily mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present invention.

[0078] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0079] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A step height standard block, characterized in that: include: A bottom layer and a stepped layer located on the bottom layer; The upper surface of the step layer has a groove, the groove is used to receive and reflect the light of the target white light interferometer, the depth of the groove is the preset standard height of the step height standard sample block, and the material of the step layer is an opaque material; The groove does not penetrate the edge of the step layer, and the aspect ratio of the groove is 5:

2.

2. The step height standard block according to claim 1, characterized in that: The material of the step layer is GaAlAs, and the material of the bottom layer is GaAs.

3. The step height standard block according to claim 1, characterized in that: The material of the step layer is GaAs, and the material of the bottom layer is InGaP.

4. A method for preparing a step height standard sample block, characterized in that: include: preparing a bottom layer; Growing an initial step layer on the bottom layer, wherein the material of the initial step layer is an opaque material; A groove is etched on the upper surface of the initial step layer to prepare a step height standard block, the depth of the groove is the preset standard height of the step height standard block; the groove does not pass through the edge of the step layer, and the aspect ratio of the groove is 5:

2.

5. The method for preparing a step height standard block according to claim 4, characterized in that: The step of etching a groove on the upper surface of the initial step layer to prepare a step height standard sample block comprises: Spin-coating a photoresist on the upper surface of the initial step layer; Using a mask having a preset photoresist pattern to expose and develop the photoresist to obtain a first sample; Etching a groove on the upper surface of the initial step layer not covered with photoresist in the first sample to obtain a second sample; The photoresist on the second sample is removed to prepare a step height standard sample block.

6. The method for preparing a step height standard block according to claim 4 or 5, characterized in that: The material of the initial step layer is GaAlAs, and the material of the bottom layer is GaAs.

7. The method for preparing a step height standard block according to claim 4 or 5, characterized in that: The material of the initial step layer is GaAs, and the material of the bottom layer is InGaP.

8. A white light interferometer calibration method, characterized in that: A white light interferometer is calibrated using the step height standard block as described in any one of claims 1 to 3.

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