Method for substrate evaluation, substrate evaluation device, and substrate evaluation system

Abstract

To provide a method for evaluating a substrate, a substrate evaluation device, and a substrate evaluation system capable of evaluating the degree of contamination caused by carbon.SOLUTION: In the method for evaluating a substrate, Raman spectra are acquired at a plurality of locations within an evaluation region, which is at least a part of a substrate. For each of the plurality of locations, the intensity of a spectral peak derived from carbon included in the acquired Raman spectrum is calculated. Among the plurality of locations, the number NA of locations where the intensity of the spectral peak derived from carbon is equal to or greater than a threshold value is calculated.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a substrate evaluation method, a substrate evaluation device, and a substrate evaluation system. [Background technology]

[0002] Substrates such as silicon nitride substrates are used as insulating substrates for power modules. Examples of power modules include control members for motors in electric vehicles, hybrid electric vehicles, railway vehicles, industrial equipment, etc. Silicon nitride substrates are disclosed in Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6766509 Summary of the Invention [Problem to be solved by the invention]

[0004] A circuit board is manufactured using a substrate. The portions of the circuit board between circuit patterns may be contaminated with carbon. It has been difficult to evaluate the degree of carbon contamination using conventional evaluation methods. In one aspect of the present disclosure, it is preferable to provide a substrate evaluation method, a substrate evaluation device, and a substrate evaluation system that are capable of evaluating the degree of carbon contamination. [Means for solving the problem]

[0005] One aspect of the present disclosure is a method for evaluating a substrate, which includes acquiring Raman spectra at a plurality of locations in an evaluation region that is at least a portion of the substrate, calculating the intensity of a spectral peak derived from carbon contained in the acquired Raman spectrum for each of the plurality of locations, and calculating the number NA of locations among the plurality of locations where the intensity of the spectral peak derived from carbon is equal to or greater than a threshold value.

[0006] According to the substrate evaluation method that is one aspect of the present disclosure, the degree of carbon contamination on the substrate can be accurately evaluated. Another aspect of the present disclosure is a substrate evaluation device including: a data acquisition unit configured to acquire, from a Raman measurement device, Raman spectra acquired at each of a plurality of locations in an evaluation region that is at least a portion of the substrate; an intensity calculation unit configured to calculate, for each of the plurality of locations, the intensity of a spectral peak derived from carbon contained in the acquired Raman spectrum based on the Raman spectra acquired by the data acquisition unit; and a number calculation unit configured to calculate the number NA of locations among the plurality of locations where the intensity of the spectral peak derived from carbon is equal to or greater than a threshold value.

[0007] A substrate evaluation device according to another aspect of the present disclosure is capable of accurately evaluating the degree of carbon contamination on a substrate. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a side view showing the configuration of a power module and a silicon nitride circuit substrate. [Figure 2] 1A to 1C are explanatory diagrams showing a method for manufacturing a silicon nitride substrate. [Figure 3] 1A to 1C are explanatory diagrams showing a method for manufacturing a silicon nitride circuit substrate. [Figure 4] FIG. 1 is an explanatory diagram illustrating a configuration of a substrate evaluation system. [Figure 5] FIG. 2 is an explanatory diagram showing an example of a Raman spectrum acquired by the Raman measurement device. [Figure 6] 1 is an image showing the intensities of spectral peaks derived from carbon and the intensities of spectral peaks derived from components of the substrate at each of a plurality of locations. [Figure 7] 7A is a graph showing the relationship between the carbon area ratio X and the leakage current, and FIG. 7B is a table showing the relationship between the carbon area ratio X and the leakage current. [Figure 8]1 is a graph showing the relationship between the carbon area ratio X and the hypochlorous acid treatment time. DETAILED DESCRIPTION OF THE INVENTION

[0009] Exemplary embodiments of the present disclosure will be described with reference to the drawings. 1. Configuration of power module 1 and silicon nitride circuit board 2 The configurations of a power module 1 and a silicon nitride circuit board 2 will be described with reference to Figure 1. The silicon nitride circuit board 2 includes a silicon nitride substrate 3, a metal circuit 5, a metal heat sink 7, and brazing layers 9 and 11. The power module 1 includes the silicon nitride circuit board 2, a semiconductor chip 13, and a heat sink 15.

[0010] The metal circuit 5 is made of a copper plate. The metal circuit 5 is attached to one side of the silicon nitride substrate 3 by a brazing material layer 9. The metal heat sink 7 is made of a copper plate. The metal heat sink 7 is attached to the other side of the silicon nitride substrate 3 by a brazing material layer 11. The semiconductor chip 13 is attached to the metal circuit 5. The heat sink 15 is attached to the metal heat sink 7.

[0011] 2. Method for manufacturing silicon nitride substrate 3 A method for manufacturing a silicon nitride substrate 3 will be described with reference to FIG. 2. In step (a), raw materials for the silicon nitride substrate 3 are prepared and mixed. The raw materials include silicon nitride powder, a sintering aid, and an organic binder. The sintering aid includes Mg compound powder and Y2O3 powder. The compounding ratio of the silicon nitride powder in the raw materials is, for example, 80 to 98 mass %. The compounding ratio of the Y2O3 powder in the raw materials is, for example, 0.2 to 2.0 mass %. The raw materials are in the form of a slurry. The solid concentration of the slurry is, for example, 30 to 70 mass %. Y2O3 corresponds to a rare earth oxide.

[0012] Next, in step (b), the raw material is formed into sheets, for example, by a doctor blade method, and cut. As a result, sheets 101 are obtained. Next, in step (c), a release agent is printed on the sheets 101. Next, in step (d), multiple sheets 101 are stacked and degreased in the atmosphere. The temperature during degreasing is, for example, 900°C or less, preferably 400 to 800°C. Next, in step (e), the stacked multiple sheets 101 are separated into individual sheets. The sheets 101 separated in step (e) will be referred to as pre-sintered silicon nitride substrates 102 hereinafter.

[0013] Next, in step (f), a plurality of pre-sintered silicon nitride substrates 102 are stacked. Furthermore, the stacked pre-sintered silicon nitride substrates 102 are sintered. By sintering, the pre-sintered silicon nitride substrates 102 become silicon nitride substrates 3. The sintering temperature is, for example, 1600 to 2000°C. Next, in step (g), the stacked plurality of silicon nitride substrates 3 are separated into individual substrates.

[0014] 3. Manufacturing method of power module 1 and silicon nitride circuit board 2 A method for manufacturing the power module 1 and the silicon nitride circuit board 2 will be described with reference to Figure 3. In step (h), a metal plate 105 and a metal heat sink 107 are attached to the silicon nitride substrate 3 by brazing. Next, in step (i), a portion of the metal plate 105 is removed to form a metal circuit 5. Next, in step (j), a plurality of silicon nitride circuit boards 2 are obtained by dividing. Furthermore, a semiconductor chip 13 and a heat sink 15 are attached to the silicon nitride circuit board 2. The silicon nitride circuit board 2 corresponds to the substrate 103. A substrate evaluation method can be performed on the silicon nitride circuit board 2.

[0015] 4. Configuration of Evaluation System 201 The configuration of the evaluation system 201 will be described with reference to Fig. 4. The evaluation system 201 is used to evaluate the substrate 103. The substrate 103 is, for example, a sintered body substrate, a polycrystalline substrate, or a single crystal substrate. Examples of the sintered body substrate include a silicon nitride circuit substrate 2 and a silicon nitride substrate 3.

[0016] The evaluation system 201 includes a Raman measurement device 203 and an evaluation device 205. The Raman measurement device 203 irradiates a measurement object with laser light 206 and detects Raman scattered light 208 generated by the measurement object. Thus, the Raman measurement device 203 can measure the Raman spectrum of the measurement object. The irradiation diameter of the laser light 206 is approximately 1 μm. The irradiation diameter is a diameter. Thus, the Raman measurement device 203 can measure the Raman spectrum of a narrow region.

[0017] The Raman measurement device 203 can move the irradiation position of the laser light 206 independently in the x direction and the y direction. The x direction and the y direction are both parallel to the measurement surface. The x direction is perpendicular to the y direction. Therefore, the Raman measurement device 203 can measure the Raman spectrum at each of multiple locations 303 in the measurement object.

[0018] The evaluation device 205 includes a microcomputer having a CPU and a semiconductor memory such as a RAM or a ROM. Each function of the evaluation device 205 is realized by the CPU executing a program stored in a non-transitory tangible recording medium. Furthermore, by executing this program, a method corresponding to the program is performed.

[0019] The evaluation device 205 includes a data acquisition unit 207, a calculation unit 209, and an evaluation unit 211. The data acquisition unit 207 acquires Raman spectra from the Raman measurement device 203. The calculation unit 209 calculates, for each of the multiple locations 303, the intensity of a spectral peak derived from carbon (hereinafter referred to as carbon intensity) contained in the acquired Raman spectrum, based on the Raman spectrum acquired by the data acquisition unit 207.

[0020] Furthermore, the calculation unit 209 calculates the number NA of locations 303 where the carbon intensity is equal to or greater than the threshold value, out of the plurality of locations 303. In addition, based on the Raman spectrum acquired by the data acquisition unit 207, the calculation unit 209 calculates the intensity of the spectral peak (hereinafter referred to as the intensity of the substrate component) originating from the component of the substrate 103 contained in the acquired Raman spectrum for each of the multiple locations 303.

[0021] Furthermore, the calculation unit 209 calculates the number NB of locations 303 where the intensity of the substrate component at the location 303 is equal to or greater than the threshold value TB, out of the plurality of locations 303. The calculation unit 209 corresponds to the intensity calculation unit and the number calculation unit. The evaluation unit 211 evaluates the degree of contamination of the substrate 103 based on the number NA. For example, the evaluation unit 211 evaluates the degree of contamination of the substrate 103 based on a carbon area ratio X, which will be described later.

[0022] 5.Board evaluation method A method for evaluating a substrate will be described with reference to Figures 4 to 8. The method for evaluating a substrate is carried out, for example, using an evaluation system 201. As shown in Figure 4, Raman spectra are acquired at a plurality of locations 303 in an evaluation region 301 using a Raman measurement device 203.

[0023] The evaluation area 301 is at least a part of the substrate 103. The evaluation area 301 may be a part of the substrate 103 or may be the entire substrate 103. The multiple locations 303 are arranged at intervals of, for example, 50 μm. The multiple locations 303 are arranged at equal intervals across the entire evaluation area 301, for example.

[0024] Next, the data acquisition unit 207 of the evaluation device 205 acquires a Raman spectrum from the Raman measurement device 203. An example of a Raman spectrum is shown in Fig. 5. SA in Fig. 5 is a Raman spectrum acquired at location 303A, which is one of the multiple locations 303. SB in Fig. 5 is a Raman spectrum acquired at location 303B, which is one of the multiple locations 303.

[0025] The Raman spectra acquired from the Raman measurement device 203 include those corresponding to each of the multiple locations 303. That is, for any location 303, there exists a Raman spectrum measured at that location 303.

[0026] Next, the calculation unit 209 performs the following calculation based on the Raman spectrum acquired by the data acquisition unit 207. The calculation unit 209 calculates the carbon intensity for each of the multiple locations 303. For example, the calculation unit 209 selects one location 303 from the multiple locations 303. The calculation unit 209 calculates the carbon intensity at the selected location 303 from the Raman spectrum measured at the selected location 303. The calculation unit 209 associates the calculated carbon intensity with the selected location 303. The calculation unit 209 performs the above process for all locations 303. As a result, the carbon intensity at any location 303 is associated with that location 303.

[0027] Examples of spectral peaks derived from carbon include the G band and the D band. The calculation unit 209 calculates the intensity of the G band, the intensity of the D band, or the intensity of both the G band and the D band as the carbon intensity. The G band has a Raman shift of 1480 to 1710 cm. -1 It is preferable that the spectral peaks derived from carbon do not overlap with the spectral peaks derived from the components of the substrate 103.

[0028] The intensity of a spectral peak is, for example, the area of ​​the spectral peak. The area of ​​the spectral peak can be calculated, for example, by the Covell method. Next, the calculation unit 209 calculates the number NA of locations 303 where the carbon intensity is equal to or greater than the threshold value TA among the plurality of locations 303. The value of the threshold value TA can be set appropriately. For example, the threshold value TA can be set by Otsu's binarization method, adaptive binarization method, or a combination of both.

[0029] Furthermore, the calculation unit 209 calculates the intensity of the substrate component for each of the multiple locations 303. For example, the calculation unit 209 selects one location 303 from the multiple locations 303. The calculation unit 209 calculates the intensity of the substrate component at the selected location 303 from the Raman spectrum measured at the selected location 303. The calculation unit 209 associates the calculated intensity of the substrate component with the selected location 303. The calculation unit 209 performs the above process for all locations 303. As a result, the intensity of the substrate component at any location 303 is associated with that location 303.

[0030] The components of the substrate 103 are, for example, the main components of the substrate 103. The components of the substrate 103 are components contained in an uncontaminated substrate 103. For example, when the substrate 103 is a silicon nitride circuit substrate 2, spectral peaks derived from the components of the substrate 103 include spectral peaks derived from Ag lattice vibrations of β-S3N4.

[0031] Next, the calculation unit 209 calculates the number NB of locations 303 where the intensity of the substrate component is equal to or greater than a threshold TB among the plurality of locations 303. The value of the threshold TB can be set appropriately. For example, the threshold TB can be set by Otsu's binarization method, adaptive binarization method, or a combination of both.

[0032] Fig. 6 shows an example of the results of the calculation performed by the calculation unit 209. Three images IMG-1 to IMG-3 are shown in Fig. 6. Image IMG-1 shows the results of the calculation performed by the calculation unit 209 on an uncleaned substrate 103. Image IMG-2 shows the results of the calculation performed by the calculation unit 209 on a substrate 103 that has been cleaned with hypochlorous acid for 5 minutes. Image IMG-3 shows the results of the calculation performed by the calculation unit 209 on a substrate 103 that has been cleaned with hypochlorous acid for 180 minutes.

[0033] Each of the images IMG-1 to IMG-3 consists of a plurality of pixels. The plurality of pixels contained in one image each correspond to one location 303. If the carbon intensity at any location 303 is equal to or greater than a threshold value TA, the brightness of the pixel corresponding to that location 303 is low. Also, if the substrate component intensity at any location 303 is equal to or greater than a threshold value TB, the brightness of the pixel corresponding to that location 303 is high.

[0034] Image IMG-2 had fewer pixels with low brightness (i.e., locations 303 where the carbon intensity was equal to or greater than the threshold value TA) than image IMG-1. Furthermore, image IMG-3 had even fewer pixels with low brightness than image IMG-2. In other words, the longer the cleaning time, the fewer the locations 303 where the carbon intensity was equal to or greater than the threshold value TA. The calculation unit 209 can, for example, display images IMG-1 to IMG-3 on a display device.

[0035] Next, the calculation unit 209 calculates the carbon area ratio X expressed by the following formula (1): The carbon area ratio X is expressed in %.

[0036] Equation (1) X = (NA / (NA+NB)) × 100 In the example of image IMG-1, the carbon area ratio X was 39.6%. In the example of image IMG-2, the carbon area ratio X was 34.8%. In the example of image IMG-3, the carbon area ratio X was 0.1%.

[0037] The evaluation unit 211 evaluates the substrate 103 based on the carbon area ratio X. For example, the evaluation unit 211 evaluates the substrate 103 as being better the lower the carbon area ratio X. For example, the evaluation unit 211 evaluates the substrate 103 as being better when the carbon area ratio X is equal to or less than a threshold value, compared to when the carbon area ratio X exceeds the threshold value. "Good" means that the degree of contamination by carbon is low. "Good" means, for example, that the degree of contamination by glassy carbon is low.

[0038] 6. Example 1 A plurality of substrates 103 were prepared. Each of the plurality of substrates 103 was a silicon nitride circuit substrate 2. The substrate evaluation method was carried out for each of the plurality of substrates 103.

[0039] When evaluating the substrate, the spectral peak derived from carbon was taken as the G band. The spectral peak derived from the components of the substrate 103 was taken as the Ag lattice vibration of β-S3N4. The spectral peak intensity was the area of ​​the spectral peak calculated by the Cobel method. The thresholds TA and TB were set by Otsu's binarization method, adaptive binarization method, or a combination of the two.

[0040] The number NA, the number NB, and the carbon area ratio X were calculated for each of the multiple substrates 103. Furthermore, the leakage current between the circuit patterns was measured for each of the multiple substrates 103. The relationship between the carbon area ratio X and the leakage current is shown in FIGS. 7A and 7B. The values ​​on the vertical axis in FIG. 7A and the values ​​listed in the column "Leakage current (relative value (%))" in FIG. 7B are relative leakage current values ​​when the leakage current for a substrate 103 with a carbon area ratio X of 0.1% is set to 100.

[0041] The higher the carbon area ratio X, the larger the leakage current. The higher the level of carbon contamination, the larger the leakage current, so the results shown in Figures 7A and 7B indicate that the carbon area ratio X is a value that reflects the level of carbon contamination. In addition, the substrate evaluation method can be used to evaluate the likelihood of dielectric strength failure.

[0042] 7. Example 2 A plurality of substrates 103 were prepared. Each of the plurality of substrates 103 was a silicon nitride circuit substrate 2. The plurality of substrates 103 were subjected to hypochlorous acid treatment for different periods of time. The substrate evaluation method was carried out for each of the plurality of substrates 103.

[0043] When evaluating the substrate, the spectral peak derived from carbon was taken as the G band. The spectral peak derived from the components of the substrate 103 was taken as the Ag lattice vibration of β-S3N4. The spectral peak intensity was the area of ​​the spectral peak calculated by the Cobel method. The thresholds TA and TB were set by Otsu's binarization method, adaptive binarization method, or a combination of the two.

[0044] The number NA, number NB, and carbon area ratio X were calculated for each of the multiple substrates 103. The relationship between the carbon area ratio X and the hypochlorous acid treatment time is shown in FIG. 8. The longer the hypochlorous acid treatment time, the smaller the carbon area ratio X. Since the longer the hypochlorous acid treatment time, the lower the level of carbon contamination, the results shown in FIG. 8 indicate that the carbon area ratio X is a value that reflects the level of carbon contamination. Furthermore, the substrate evaluation method can be used to evaluate the cleaning effect of the cleaning solution.

[0045] 8. Benefits of PCB Evaluation Methods (1) The substrate evaluation method allows accurate evaluation of the degree of carbon contamination on the substrate 103. In particular, the substrate evaluation method allows accurate evaluation of the degree of glassy carbon contamination on the substrate 103.

[0046] It is difficult to distinguish between glassy carbon and organic matter when SEM-EDS is used to evaluate the substrate 103. Furthermore, since the window material of the X-ray detection device is made of Be or the like, when the X-ray detection device is used to evaluate the substrate 103, the detection sensitivity of carbon, which is a light element, is low.

[0047] (2) In the substrate evaluation method, the carbon area ratio X is calculated. The carbon area ratio X is a value that reflects the degree of carbon contamination. Therefore, the degree of carbon contamination on the substrate 103 can be accurately evaluated.

[0048] (3) By using the substrate evaluation method, for example, the substrate 103 after being cleaned with a cleaning liquid can be evaluated. In this case, the cleaning effect by the cleaning liquid can be evaluated.

[0049] 9. Other Embodiments Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments and can be implemented in various modified forms.

[0050] (1) In the substrate evaluation method of the present disclosure, the carbon area ratio X is calculated. For example, the substrate 103 may be evaluated based on the number NA. For example, the smaller the number NA, the better the substrate 103 can be evaluated. Also, for example, when the number NA is equal to or less than a threshold, the substrate 103 can be evaluated as being better than when the number NA exceeds the threshold.

[0051] (2) The numbers NA and NB may be used to calculate a judgment value other than the carbon area ratio X. Then, the substrate 103 may be evaluated based on the judgment value. (3) The silicon nitride substrate 3 may be used to manufacture a power module other than the power module 1.

[0052] (4) Multiple functions of one component in the above embodiments may be realized by multiple components, or one function of one component may be realized by multiple components. Also, multiple functions of multiple components may be realized by one component, or one function realized by multiple components may be realized by one component. Also, part of the configuration of the above embodiments may be omitted. Also, at least part of the configuration of the above embodiments may be added to or substituted for the configuration of another of the above embodiments.

[0053] (5) In addition to the above-described evaluation system 201, the present disclosure can also be realized in various forms, such as a higher-level system that includes the evaluation system 201 as a component, a program for causing a computer to function as the evaluation device 205, a non-transient physical recording medium such as a semiconductor memory on which this program is recorded, a method for controlling the quality of substrates, a method for controlling the production of substrates, etc. [Explanation of symbols]

[0054] 1...power module, 2...silicon nitride circuit board, 3...silicon nitride substrate, 5...metal circuit, 7...metal heat sink, 9, 11...brazing material layer, 13...semiconductor chip, 15...heat sink, 101...sheet, 102...silicon nitride substrate before sintering, 103...substrate, 105...metal plate, 201...evaluation system, 203...Raman measurement device, 205...evaluation device, 206...laser light, 207...data acquisition unit, 208...Raman scattered light, 209...calculation unit, 211...evaluation unit, 301...evaluation area, 303...location

Claims

1. acquiring Raman spectra at a plurality of locations in an evaluation region that is at least a portion of the substrate; Calculating the intensity of a spectral peak attributable to carbon contained in the acquired Raman spectrum for each of the plurality of locations; Calculating the number NA of locations where the intensity of the spectrum peak derived from the carbon is equal to or greater than a threshold value among the plurality of locations; How to evaluate the board.

2. 2. The method for evaluating a substrate according to claim 1, calculating the intensity of a spectral peak attributed to a component of the substrate contained in the acquired Raman spectrum for each of the plurality of locations; Calculating the number N B of locations among the plurality of locations where the intensity of the spectral peak derived from the component of the substrate is equal to or greater than a threshold value; Calculate the carbon area ratio X represented by the following formula (1): How to evaluate the board. Formula (1) X=(NA / (NA+NB))×100

3. 3. The method for evaluating a substrate according to claim 1 or 2, evaluating the substrate after cleaning with the cleaning solution; How to evaluate the board.

4. 3. The method for evaluating a substrate according to claim 1 or 2, The spectral peaks derived from the carbon include at least one of a G band and a D band. How to evaluate the board.

5. 3. The method for evaluating a substrate according to claim 1 or 2, The substrate is a sintered substrate, a polycrystalline substrate, or a single crystal substrate. How to evaluate the board.

6. a data acquisition unit configured to acquire, from a Raman measurement device, Raman spectra acquired at a plurality of locations in an evaluation region that is at least a portion of the substrate; an intensity calculation unit configured to calculate, for each of the plurality of locations, an intensity of a spectral peak derived from carbon contained in the acquired Raman spectrum based on the Raman spectrum acquired by the data acquisition unit; a number calculation unit configured to calculate a number NA of locations among the plurality of locations where the intensity of the spectrum peak derived from the carbon is equal to or greater than a threshold; A substrate evaluation device comprising:

7. A substrate evaluation system comprising the Raman measurement device and the substrate evaluation device according to claim 6 .

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