JP2023124778A - Silicon nitride substrate and silicon nitride circuit board - Google Patents

Abstract

To provide a silicon nitride substrate hardly generating color shading, an evaluation method, an evaluation device and an evaluation system of a silicon nitride substrate.SOLUTION: A silicon nitride substrate includes a first face and a second face on an opposite side of the first face. A value of an average half-value width Cave measured by a measurement method below at a measurement surface being one of the first face and the second face is larger than 0 cm-1 and smaller than 5.32 cm-1. The measurement method of an average half-value width Cave: Set one central part on the measurement surface and four marginal parts as measurement points. Measure a Raman spectrum at each of the measurement points. At each of the Raman spectrum thus measured, calculate a half-value width C of a spectral peak having a maximum strength within a range of 850 cm-1 to 875 cm-1. Set an average value of the calculated half-value widths C as an average half-value width Cave.SELECTED DRAWING: Figure 7

Description

The present disclosure relates to a silicon nitride substrate, a silicon nitride substrate evaluation method, an evaluation apparatus, and an evaluation system.

In Japanese Patent Application Laid-Open No. 2003-267786 (Patent Document 1), the color of the sintered body is blackened compared to conventional materials, and the color unevenness is reduced, and a silicon nitride ceramic sintered body having sufficient strength Techniques are described for providing the

Japanese Patent Application Laid-Open No. 2005-214659 (Patent Document 2) describes a technology related to a foreign matter inspection apparatus capable of distinguishing even foreign matter with a color having a low contrast with respect to the color of the wiring board.
JP 2016-204206 (Patent Document 3), JP 2016-204207 (Patent Document 4), JP 2016-204209 (Patent Document 5) and JP 2016-204210 (Patent Document 6 ) describes a technique for providing a silicon nitride-based ceramic member that is lightweight, has high hardness, is excellent in resistance to processing such as polishing, and is excellent in appearance quality.

Japanese Patent Application Laid-Open No. 9-227240 (Patent Document 7) discloses that the thickness of the surface tone layer portion in the silicon nitride ceramic sintered body is reduced, and the breaking strength characteristics of the surface layer and the inner layer are made uniform. It describes a technique that can

JP-A-2003-267786 JP 2005-214659 A JP 2016-204206 A JP 2016-204207 A JP 2016-204209 A JP 2016-204210 A JP-A-9-227240

Foreign matter and dirt adhering to the surface of the silicon nitride substrate cause poor contact between the silicon nitride substrate and the brazing material and poor insulation of the silicon nitride substrate itself. Appearance inspection is performed in order to detect foreign matter and dirt adhering to the surface of the silicon nitride substrate. As a method of visual inspection, after imaging the surface of the silicon nitride substrate with an imaging device such as a CCD camera, the data of the captured image is compared with pre-registered reference data to detect foreign matter and dirt. There is

Color unevenness may occur on the surface of the silicon nitride substrate. Color shading is a phenomenon in which, for example, the central portion and the edge portion of the silicon nitride substrate have different colors. If there is unevenness in color on the surface of the silicon nitride substrate, the unevenness in color may be erroneously detected as a foreign substance or dirt during an appearance inspection.

In addition, when the warpage of the silicon nitride substrate becomes large, the adhesion between the metal circuit board and the metal heat sink that are joined to the silicon nitride substrate with brazing material decreases, and during the temperature drop process in the joining process and the heat cycle during operation of the power module, There is a problem that the generated thermal stress makes it easier for the metal circuit board and the metal heat sink to separate from the silicon nitride substrate.

In one aspect of the present disclosure, it is preferable to provide a silicon nitride substrate, a silicon nitride substrate evaluation method, an evaluation device, and an evaluation system in which color unevenness is less likely to occur.

Further, in one aspect of the present disclosure, it is preferable to provide a silicon nitride substrate in which warpage is suppressed and color unevenness is less likely to occur, a method for evaluating the silicon nitride substrate, an evaluation device, and an evaluation system.

(1) One aspect of the present disclosure is a silicon nitride substrate having a first surface and a second surface opposite to the first surface, wherein the first surface and the second surface is a silicon nitride substrate having an average half width C _ave value of more than 0 cm ⁻¹ and less than 5.32 cm ⁻¹ measured by the following measurement method on the measurement surface which is one surface of the substrate.

Method of measuring the average half-value width C _ave : Measurement points are one point at the center and four points at the edges of the measurement surface. A Raman spectrum is measured at each of the measurement points. In each of the measured Raman spectra, the half width C of the spectral peak having the maximum intensity within the range of 850 cm ⁻¹ to 875 cm ⁻¹ is calculated. An average value of the calculated half-value width C is defined as an average half-value width C _ave .

A silicon nitride substrate, which is one aspect of the present disclosure, is less prone to color unevenness. In addition, warpage is suppressed and color unevenness is less likely to occur.
(2) Another aspect of the present disclosure is a silicon nitride substrate evaluation method for evaluating color unevenness of a silicon nitride substrate, wherein a Raman spectrum is measured at a measurement point on the silicon nitride substrate, and A method for evaluating a silicon nitride substrate, comprising measuring a half-value width of a spectral peak attributed to lattice vibration of silicon nitride, and evaluating color unevenness of the silicon nitride substrate based on the half-value width.

A method for evaluating a silicon nitride substrate, which is another aspect of the present disclosure, can evaluate color unevenness even if the area of the measurement point is small. In addition, color unevenness can be evaluated along with warpage.
(3) Another aspect of the present disclosure is an evaluation device for evaluating color unevenness of a silicon nitride substrate, which is a data acquisition unit configured to acquire a Raman spectrum measured at a measurement point on the silicon nitride substrate. and a half-value width measuring unit configured to measure the half-value width of a spectral peak attributed to lattice vibration of silicon nitride included in the Raman spectrum acquired by the data acquiring unit. .

An evaluation device that is another aspect of the present disclosure can evaluate color unevenness even if the area of the measurement points is small. In addition, color unevenness can be evaluated along with warpage.
(4) Another aspect of the present disclosure is an evaluation system for evaluating color unevenness of a silicon nitride substrate, comprising: a Raman measuring device for measuring a Raman spectrum at a measurement point on the silicon nitride substrate; A system for evaluating a silicon nitride substrate, comprising the evaluation device described above.

FIG. 3 is a side view showing configurations of a power module and a silicon nitride circuit board; It is explanatory drawing showing the manufacturing method of a silicon nitride substrate. FIG. 4 is an explanatory view showing a state in which molded bodies are arranged in layers; 10 is a photograph showing the surface of a silicon nitride substrate in the same lot as the silicon nitride substrate 3Y immediately after the nitridation process, in which color unevenness has occurred. It is explanatory drawing showing the manufacturing method of a silicon nitride circuit board. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram showing the configuration of a silicon nitride substrate evaluation system; FIG. 4 is an explanatory diagram showing the arrangement of measurement points on a measurement plane; FIG. 4 is an explanatory diagram showing half-value widths of spectral peaks after fitting; 4 is a table showing wave numbers, heights, half widths and areas of spectral peaks of silicon nitride substrates 3X and 3Y. Table showing lightness L ^* , chromaticity a* from green to red, chromaticity ^{b *} from yellow to blue, chroma C ^* , and half width at each measurement point in the first evaluation process of silicon nitride substrates 3X and 3Y is. Table showing lightness L ^* , chromaticity a* from green to red, chromaticity ^{b *} from yellow to blue, chroma C ^* , and half width at each measurement point in the second evaluation process of silicon nitride substrates 3X and 3Y is. 4 is a graph showing the average half width and lightness L ^* in the first and second evaluation processes of silicon nitride substrates 3X and 3Y. 4 is a graph showing the average half width and chroma C ^* in the first and second evaluation processes of silicon nitride substrates 3X and 3Y. 4 is a graph showing the measured temperature of the molded body, the measured temperature of the furnace, and the temperature difference between the molded body and the furnace in a predetermined temperature range of the example. 5 is a graph showing the measured temperature of the compact, the measured temperature of the furnace, and the temperature difference between the compact and the furnace in a predetermined temperature range of the comparative example. 4 is a table showing wave numbers, heights, half widths and areas of spectral peaks of silicon nitride substrates 3A and 3B. 4 is a table showing lightness L*, chromaticity a* ranging from green to red, chromaticity b* ranging from yellow to blue, chroma C*, and half width at each measurement point in evaluation processing of silicon nitride substrates 3A and 3B.

Exemplary embodiments of the present disclosure are described with reference to the drawings.
1. Configurations of Power Module 1 and Silicon Nitride Circuit Board 2 Configurations of the power module 1 and the silicon nitride circuit board 2 will be described with reference to FIG. The silicon nitride circuit board 2 includes a silicon nitride board 3 , a metal circuit 5 , a metal heat sink 7 , and brazing material layers 9 and 11 . The power module 1 includes a silicon nitride circuit board 2 , a semiconductor chip 13 and a heat sink 15 .

The silicon nitride substrate 3 has, for example, a first surface and a second surface. The first surface is the upper surface during the compact manufacturing step S2 and the sintering step S3, which will be described later. The second surface is the surface opposite to the first surface. The planar shape of the silicon nitride substrate 3 is, for example, a rectangular shape. The planar shape is the shape when viewed from the thickness direction of the silicon nitride substrate 3 . For example, the length of each side of the silicon nitride substrate 3 is 100 mm or longer.

The metal circuit 5 consists of a copper plate. A metal circuit 5 is attached to the first surface of the silicon nitride substrate 3 by a brazing material layer 9 . The metal heat sink 7 is made of a copper plate. Metal heat sink 7 is attached to the second surface of silicon nitride substrate 3 with brazing material layer 11 . A semiconductor chip 13 is attached to the metal circuit 5 . A heat sink 15 is attached to the metal heat sink 7 .

2. Manufacturing Method of Silicon Nitride Substrate 3 For example, the silicon nitride substrate 3 can be manufactured by the method shown in FIG. The manufacturing method includes a slurry preparation step S1, a compact preparation step S2, a sintering step S3, and a nitriding step S4.

(2-1) Slurry preparation step S1
For example, raw material powder is obtained by adding a sintering aid to silicon powder. Examples of sintering aids include rare earth element oxides and magnesium compounds. A slurry is prepared using the raw material powder.

Silicon powders include, for example, industrially available grade silicon powders. The median diameter D50 of the silicon powder before pulverization is preferably 6 μm or more, more preferably 7 μm or more.

The BET specific surface area of the silicon powder before pulverization is preferably 3 m ² /g or less, more preferably 2.5 m ² /g or less. The oxygen content of the silicon powder before pulverization is preferably 1.0% by mass or less, more preferably 0.5% by mass or less. The amount of impurity carbon contained in the silicon powder before pulverization is preferably 0.15% by mass or less, more preferably 0.10% by mass or less.

The purity of the silicon powder is preferably 99% or higher, more preferably 99.5% or higher. Impurity oxygen contained in the silicon powder is one of the factors that hinder the heat conduction of the silicon nitride substrate obtained by reaction sintering. The higher the purity of the silicon powder, the better the thermal conductivity of the silicon nitride substrate.

By limiting the amount of oxygen from the magnesium compound, the total amount of impurity oxygen contained in the silicon powder and the amount of oxygen from the magnesium compound is 0.1 mass with respect to the amount of silicon converted to silicon nitride. % or more and 1.1 mass % or less.

The impurity carbon contained in the silicon powder inhibits the growth of silicon nitride grains in the silicon nitride substrate obtained by reaction sintering. When the growth of silicon nitride particles is inhibited, it is difficult to densify the silicon nitride substrate. If it is difficult to densify the silicon nitride substrate, the thermal conductivity and insulating properties of the silicon nitride substrate are lowered. Therefore, it is preferable that the amount of impurity carbon contained in the silicon powder is as small as possible.

In the present specification, the BET specific surface area (m ² /g) is defined as the BET one-point method (JIS R 1626: 1996 "Measurement of specific surface area by gas adsorption BET method for fine ceramic powder using a BET specific surface area meter. method”). The median diameter D50 (μm) is the particle diameter when the cumulative frequency is 50% in the particle size distribution determined by the laser diffraction/scattering method.

Although not essential in the manufacturing method of the present invention, the raw material powder may contain silicon nitride powder. However, since silicon nitride is more expensive than silicon, the amount of silicon nitride used should be as small as possible. The amount of silicon nitride used is preferably 50 mol % or less, more preferably 10 mol % or less, and even more preferably 5 mol % or less of silicon (in terms of silicon nitride). The silicon nitride substrate in this case is a silicon nitride substrate obtained by nitriding a sheet-like formed body containing silicon so that silicon nitride is 50 mol % or less of silicon in terms of silicon nitride.

Examples of rare earth element oxides include oxides of yttrium (Y), ytterbium (Yb), gadolinium (Gd), erbium (Er), and lutetium (Lu). These rare earth element oxides are readily available and stable as oxides. Specific examples of rare earth element oxides include yttrium oxide (Y ₂ O ₃ ), ytterbium oxide (Yb ₂ O ₃ ), gadolinium oxide (Gd ₂ O ₃ ), erbium oxide (Er ₂ O ₃ ), lutetium oxide ( Lu ₂ O ₃ ) and the like.

In the silicon nitride substrate, M1 is the number of moles of the rare earth element oxide converted to trivalent oxide (RE ₂ O ₃ : RE is a rare earth element). In the silicon nitride substrate, M2 is the number of moles of silicon converted to silicon nitride (Si ₃ N ₄ ). M2 is the number of moles of silicon nitride obtained when all silicon is nitrided. In the silicon nitride substrate, M3 is the number of moles of the magnesium compound converted to MgO.

The molar ratio of M1 to the total number of moles of M1, M2, and M3 (hereinafter referred to as the molar ratio of rare earth oxides) is, for example, 0.5 mol % or more and less than 2 mol %. When the molar ratio of the rare earth oxide is 0.5 mol % or more, the effect of the sintering aid is enhanced, and the density of the silicon nitride substrate is sufficiently increased. When the molar ratio of the rare earth oxide is less than 2.0 mol%, it is difficult to increase the grain boundary phase with low thermal conductivity, the thermal conductivity of the sintered body increases, and the amount of expensive rare earth element oxide used decreases. do. In particular, the molar ratio of rare earth oxides is preferably 0.6 mol % or more and less than 2 mol %, and more preferably 1 mol % or more and 1.8 mol % or less.

As the magnesium compound, one or more magnesium compounds containing "Si", "N" or "O" can be used. As magnesium compounds, magnesium oxide (MgO), magnesium silicon nitride (MgSiN ₂ ), magnesium silicide (Mg ₂ Si), magnesium nitride (Mg ₃ N ₂ ), and the like are preferable.

It is preferable that the ratio of the mass of magnesium silicon nitride to the total mass of the magnesium compounds (hereinafter referred to as magnesium silicon nitride mass ratio) is 87% by mass or more. When the magnesium silicon nitride mass ratio is 87 mass % or more, the oxygen concentration in the resulting silicon nitride substrate can be reduced. When the magnesium silicon nitride mass ratio is less than 87% by mass, the amount of oxygen in the silicon nitride particles after sintering increases, so the thermal conductivity of the silicon nitride substrate after sintering decreases. Therefore, in order to improve the thermal conductivity of the silicon nitride substrate, it is preferable that the magnesium silicon nitride mass ratio is high. More preferably, the mass ratio of magnesium silicon nitride is 90% by mass or more.

The molar ratio of M3 to the total number of moles of M1, M2, and M3 (hereinafter referred to as the molar ratio of the magnesium compound) is, for example, 8 mol % or more and less than 15 mol %. When the molar ratio of the magnesium compound is 8 mol % or more, the effect of the sintering aid is enhanced, and the density of the silicon nitride substrate is sufficiently increased. When the molar ratio of the magnesium compound is less than 15 mol %, the grain boundary phase with low thermal conductivity hardly increases, and the thermal conductivity of the sintered body increases. In particular, the molar ratio of the magnesium compound is preferably 8 mol % or more and less than 14 mol %, and more preferably 9 mol % or more and 11 mol % or less.

As a method for producing slurry, for example, there are the following methods. A rare earth element oxide and a magnesium compound are added to silicon powder so as to have a predetermined ratio. Next, a dispersion medium is added. The dispersion medium is, for example, an organic solvent. A dispersant is also added, if desired.

Next, a slurry, which is a dispersion of the raw material powder, is prepared by pulverizing with a ball mill. The dispersion medium is, for example, an organic solvent. Dispersion media include, for example, ethanol, n-butanol, and toluene. Examples of dispersants include sorbitan ester-type dispersants and polyoxyalkylene-type dispersants.

The amount of the dispersion medium added is preferably, for example, 40% by mass or more and 70% by mass or less with respect to the total amount of the raw material powder. The amount of the dispersant added is preferably, for example, 0.3% by mass or more and 2% by mass or less with respect to the total amount of the raw material powder. After dispersion, the dispersion medium may be removed or replaced with another dispersion medium, if necessary.
(2-2) Molded body preparation step S2
For example, a dispersion medium, an organic binder, a dispersant, etc. are added to the slurry obtained as described above. Next, vacuum defoaming is performed as necessary. Next, the viscosity of the slurry is adjusted within a predetermined range. As a result, a coating slurry is obtained.

Next, the obtained slurry for coating is formed into a sheet by a sheet forming machine. It is then cut to size and dried. As a result, a sheet-like compact is obtained.
The organic binder used to prepare the coating slurry is not particularly limited. Examples of the organic binder used for preparing the coating slurry include PVB-based resins, ethylcellulose-based resins, acrylic-based resins, and the like. Examples of PVB-based resins include polyvinyl butyral resins. The amount of the dispersion medium, organic binder, dispersant, etc. added can be appropriately adjusted according to the coating conditions.

The method for forming the coating slurry into a sheet is not particularly limited. Methods for forming the coating slurry into a sheet include, for example, a doctor blade method, an extrusion method, and the like.
The thickness of the sheet-like molded body produced in the molded body producing step S2 is, for example, 0.15 mm or more and 0.8 mm or less. The produced sheet-like molded body is cut into a predetermined size using, for example, a punching machine or the like, if necessary.

(2-3) Sintering step S3, nitriding step S4
The sintering step S3 includes a degreasing step of removing the organic binder contained in the molded body, a nitriding step S4 of reacting silicon and nitrogen contained in the molded body to form silicon nitride, and a nitriding step S4. and a densification sintering step that takes place.

The degreasing step, the nitriding step S4, and the densifying sintering step may be performed sequentially in separate furnaces, or may be performed continuously in the same furnace. Also, 1,600 or more compacts are heat-treated together in one furnace. Molded bodies heat-treated in the same furnace are of the same lot.
In the sintering step S3, for example, a plurality of compacts 100A are stacked on the setter 200 as shown in FIG. The setter 200 is made of boron nitride (BN). A separation material (not shown) is sandwiched between the molded bodies 100A. A weight 300 is arranged on the plurality of compacts 100A.

In this state, a plurality of molded bodies 100A are placed in an electric furnace. Next, a degreasing step is performed. Next, decarbonization treatment is performed at a temperature of 900° C. to 1300° C. in a nitriding apparatus. Next, a nitriding step S4 is performed. In the nitriding step S4, the temperature is raised to a predetermined temperature in a nitrogen atmosphere. The temperature control in the nitriding step S4 will be described later.

Next, a densification sintering step is performed in a sintering device. The densification sintering process is performed while applying a load of 10 Pa or more and 1000 Pa or less to the molded body 100A with a weight 300, for example.
As the separating material described above, for example, a boron nitride (BN) powder layer having a thickness of about 3 μm or more and 20 μm or less can be used. The boron nitride powder layer has a function of facilitating separation of the silicon nitride substrate as a sintered body after the densification sintering step. The boron nitride powder layer is formed, for example, by applying boron nitride powder in a slurry state to one side of each compact 100A. Examples of methods for applying the boron nitride powder in a slurry state include spraying, brush coating, screen printing, and the like. The boron nitride powder preferably has, for example, a purity of 95% or more and a median diameter D50 of 1 μm or more and 20 μm or less.

A silicon nitride substrate is completed by the above steps. In the above manufacturing method, a silicon nitride substrate having a thermal conductivity of 110 W/(m·K) or more can be manufactured by using silicon powder of high purity. The silicon nitride substrate in the present embodiment is a silicon nitride substrate obtained by nitriding silicon contained in a sheet-like compact. The thickness of the silicon nitride substrate is, for example, 0.15 mm or more and 0.8 mm or less.
(2-4) Relationship between color unevenness and temperature control in nitriding step S4 In the method for manufacturing a silicon nitride substrate described above, silicon powder is used instead of silicon nitride powder, so nitriding step S4 is necessary. becomes. The inventors have newly found that the surface of the manufactured silicon nitride substrate may have color unevenness depending on the heating conditions in the nitriding step S4.

In this specification, the "surface of the silicon nitride substrate" may be the first surface or the second surface of the silicon nitride substrate. The second surface is the surface opposite to the first surface.
Further, in this specification, the term “unevenness of color” means, for example, that the color tone of the central portion of the rectangular silicon nitride substrate is different from that of the edge portion. FIG. 4 is a photograph showing the surface of a silicon nitride substrate in the same lot as the silicon nitride substrate 3Y, in which color unevenness has occurred, immediately after the nitriding process. In FIG. 4, the central portion of the silicon nitride substrate is tinged with white, while the edge portion of the silicon nitride substrate is tinged with black. That is, the tint in the center and the tint at the edges are different.

The inventor has extensively studied the mechanism of color unevenness on the surface of a silicon nitride substrate. Color unevenness is presumed to be caused by the following mechanism.
In the nitriding step S4, in a nitrogen atmosphere, for example, as shown in FIG. It is a heat treatment in the state. At this time, among the laminated molded bodies 100A, the molded body 100A sandwiched between the upper and lower molded bodies 100A is defined as a specific molded body.

Heat tends to be trapped in the central portion of the specific molded body. Therefore, the temperature of the center portion of the specific molded body is high, and the temperature of the edge portion of the specific molded body is low. The nitriding reaction easily progresses in the central portion of the specific molded body, and the nitriding reaction does not easily progress in the edge portion of the specific molded body. Since the nitriding reaction is an exothermic reaction, the temperature rises sharply at the central portion where the nitriding reaction progresses, as a result of positive feedback of the amount of heat generated. If the temperature rise at the central portion is large, a phenomenon occurs in which the temperature at the central portion exceeds the melting point of silicon and silicon melts (hereinafter referred to as thermal runaway). In addition, insufficient nitridation occurs at the edges because the temperature difference between the center and the edges increases. If the sintering process is performed in a state in which nitridation is insufficient at the edges, silicon that has not been completely nitrided will eventually remain at the edges. As a result of the above, it is presumed that color unevenness occurs.

According to the above mechanism, the color unevenness occurring on the surface of the silicon nitride substrate is considered to be caused by the temperature rising step in the nitriding step S4. If it is possible to perform the heating process while realizing a temperature distribution that reduces the temperature difference between the temperature at the central portion and the temperature at the edge portion, it is thought that thermal runaway can be suppressed and color unevenness can be suppressed.

Therefore, the temperature raising step in the nitriding step S4 is preferably a step of gradually raising the temperature while reducing the temperature difference between the temperature of the central portion and the temperature of the edge portion.
In the temperature raising step in the nitriding step S4, the temperature is raised to the maximum heating temperature. The maximum heating temperature is preferably 1390°C or higher and 1500°C or lower. In the temperature raising step in the nitriding step S4, for example, the temperature is raised stepwise. In the temperature raising process, the average temperature increase per unit time (hereinafter referred to as the heating temperature gradient) is preferably 3.1° C./h or less in the range from 1270° C. to 1340° C. When the average gradient of the heating temperature is 3.1° C./h or less, color unevenness can be suppressed.

In order to suppress the warping of the silicon nitride substrate, it is preferable to control the cooling conditions for each of the nitriding process and the densification sintering process as follows. In the nitriding step, it is preferable that the cooling rate in the cooling range from the maximum heating temperature to 1100° C. is 262.2° C./h or less. In the densification sintering step, it is preferable that the cooling rate in the temperature drop range from the maximum heating temperature to 800° C. is 280.7° C./h or less. Thereby, the amount of warpage of the silicon nitride substrate can be suppressed within the range of 0.1 mm to 1 mm. The amount of warpage is a numerical value obtained by measuring the amount of warpage according to the SORI standard. Specifically, the least squares plane of the upper surface of the sample is calculated (prescribed), the absolute value of the distance from the calculated least squares plane to the highest point on the upper surface of the sample, and the distance to the lowest point on the upper surface of the sample The sum with the absolute value is calculated as the amount of warpage.

3. Method for Manufacturing 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 FIG. In step S11, metal plate 105 and metal heat sink 107 are attached to silicon nitride substrate 3 by brazing. Next, in step S12, a portion of the metal plate 105 is removed to form the metal circuit 5. Next, as shown in FIG. Next, in step S13, a plurality of silicon nitride circuit boards 2 are obtained by dividing. Furthermore, the semiconductor chip 13 and the heat sink 15 are attached to the silicon nitride circuit board 2 . The silicon nitride substrate 3 included in the silicon nitride circuit board 2 is manufactured by the above-mentioned "2. Manufacturing method of the silicon nitride substrate 3", so that color unevenness is less likely to occur and the thermal conductivity is high.

4. Configuration of Evaluation System 201 The configuration of the evaluation system 201 will be described with reference to FIG. Evaluation system 201 is used to evaluate silicon nitride substrate 3 . Evaluation system 201 includes Raman measurement device 203 and evaluation device 205 .

The Raman measurement device 203 irradiates a measurement point P, which is a part of the measurement surface 301, with a laser beam 206, and detects Raman scattered light 208 generated at the measurement point P. FIG. Therefore, the Raman measurement device 203 can measure the Raman spectrum of the measurement point P. The irradiation diameter of the laser light 206 is approximately 1 μm. The irradiation diameter is the diameter. Therefore, the Raman measurement device 203 can measure Raman spectra in a narrow region.

The Raman measurement device 203 can independently move the irradiation position of the laser beam 206 in the x-direction and the y-direction. The x-direction and the y-direction are directions parallel to the measurement surface 301 respectively. The x-direction is orthogonal to the y-direction. Therefore, the Raman measurement device 203 can measure Raman spectra at each of the plurality of measurement points P on the measurement plane 301 .

The evaluation device 205 comprises a microcomputer having a CPU and semiconductor memory such as RAM or ROM, for example. Each function of the evaluation device 205 is implemented by the CPU executing a program stored in a non-transitional substantive recording medium. Also, by executing this program, a method corresponding to the program is executed.

The evaluation device 205 includes a data acquisition section 207 and a data processing section 209 . A data acquisition unit 207 acquires a Raman spectrum from the Raman measurement device 203 . The data processing unit 209 performs processing for evaluating color unevenness of the silicon nitride substrate 3 based on the Raman spectrum acquired by the data acquisition unit 207 . This processing will be described later. A data processing unit 209 corresponds to a half width measurement unit.

5. Evaluation Method of Silicon Nitride Substrate Color unevenness of the silicon nitride substrate 3 can be evaluated by the following method. For example, the evaluation system 201 can be used to evaluate color unevenness.

First, a silicon nitride substrate 3 to be evaluated is prepared. The silicon nitride substrate 3 has, for example, a first surface and a second surface. The second surface is the surface opposite to the first surface. The planar shape of the silicon nitride substrate 3 is, for example, a rectangular shape. For example, the length of each side of the silicon nitride substrate 3 is 100 mm or longer.

Next, let one of the first surface and the second surface be the measurement surface 301 . Next, a measurement point P is set on the measurement plane 301 .
The number of measurement points P to be set may be singular or plural. For example, as shown in FIG. 7, five measurement points P1 to P5 can be set. The measurement point P1 is located at the center of the measurement surface 301. FIG. Measurement points P2 to P5 are located at the edges of measurement surface 301, respectively. Each of the measurement points P2-P5 is at one of the four corners of the measurement surface 301. FIG. The distance from the measurement point P2 to the long side 401 is 10 mm. The distance from the measurement point P2 to the short side 402 is 15 mm. The distance from the measurement point P3 to the long side 401 is 10 mm. The distance from the measurement point P3 to the short side 403 is 15 mm. The distance from the measurement point P4 to the long side 404 is 10 mm. The distance from the measurement point P4 to the short side 402 is 15 mm. The distance from the measurement point P5 to the long side 404 is 10 mm. The distance from the measurement point P5 to the short side 403 is 15 mm.

Next, the Raman spectrum is measured at the measurement point P using the Raman measurement device 203 . When a plurality of measurement points P are set, the Raman spectrum is measured at each of the plurality of measurement points P.
Next, the data acquisition section 207 acquires the Raman spectrum measured at the measurement point P from the Raman measurement device 203 . When the Raman measurement device 203 measures Raman spectra at each of the plurality of measurement points P, the data acquisition unit 207 acquires Raman spectra at each measurement point P. FIG.

Next, the data processing unit 209 measures the half width of the spectral peak attributed to the lattice vibration of silicon nitride included in the Raman spectrum acquired by the data acquisition unit 207 . When the Raman measurement device 203 measures the Raman spectrum at each of the plurality of measurement points P, the data processing unit 209 measures the half width of the spectrum peak in each of the plurality of Raman spectra measured at the plurality of measurement points P. do.

For example, when the Raman spectrum is measured at each of the measurement points P1 to P5, the data processing unit 209 determines the half width C1 of the spectrum peak included in the Raman spectrum measured at the measurement point P1 and the Half-value width C2 of the spectrum peak included in the Raman spectrum, Half-value width C3 of the spectrum peak included in the Raman spectrum measured at the measurement point P3, and Half-value width of the spectrum peak included in the Raman spectrum measured at the measurement point P4 C4 and the half width C5 of the spectral peak included in the Raman spectrum measured at the measurement point P5 are measured.

As shown in FIG. 8, the spectral peak 305 attributed to lattice vibration of silicon nitride is, for example, a peak having maximum intensity within the range of 850 cm ⁻¹ to 875 cm ⁻¹ .
The method by which the data processing unit 209 measures the half width is, for example, as follows. As shown in FIG. 8, the data processing unit 209 performs fitting using a statistical distribution function on the spectral peak 305 to obtain a spectral peak 307 after fitting. Examples of statistical distribution functions include the Lorentz function. Data processing section 209 measures half width C at spectral peak 307 . In addition, in FIG. 8, A is the wavenumber of the spectrum peak 307. FIG. B is the height of spectral peak 307; D is the area of spectral peak 307;

When the Raman measurement device 203 measures the Raman spectrum at each of the plurality of measurement points P, the data processing section 209 calculates the average half width _Cave . The average half-value width C _ave is the average value of the half-value widths C calculated for each of the plurality of Raman spectra measured at the plurality of measurement points P. For example, when the Raman spectrum is measured at each of the measurement points P1 to P5, the average half-value width C _ave is the average value of the half-value widths C1 to C5.

The data processing unit 209 evaluates the degree of color unevenness based on the half width C, for example. For example, if the half-value width C is greater than 0 cm ⁻¹ and smaller than the threshold, it is determined that color unevenness is suppressed, and if the half-value width C is equal to or greater than the threshold, it is determined that color unevenness is significant. The threshold is, for example, 5.32 cm ⁻¹ . Note that the lower limit of the half-value width C can also be set to 0.5 cm ⁻¹ from the measurement wavenumber resolution of a commercially available Raman measurement device.

The data processing unit 209 evaluates the degree of color unevenness based on, for example, the average half width _Cave . For example, if the average half-value width C _ave is greater than 0 cm ⁻¹ and smaller than the threshold, it is determined that the color unevenness is suppressed, and if the average half-value width C _ave is equal to or greater than the threshold, it is determined that the color unevenness is significant. to decide. The threshold is, for example, 5.32 cm ⁻¹ . Note that the lower limit of the average half-value width C _ave can also be set to 0.5 cm ⁻¹ from the measurement wave number resolution of a commercially available Raman measurement device.
When the amount of strain between lattices of silicon nitride is large, the value of the half-value width becomes large. It is considered that the amount of strain between lattices of silicon nitride changes due to variations in nitriding when silicon contained in the sheet-shaped compact is nitrided. That is, it is considered that if the variation in nitriding in the silicon nitride substrate 3 is large, the amount of strain between lattices of silicon nitride becomes large, and the value of the half-value width becomes large.

6. Effect of Silicon Nitride Substrate (6-1) The silicon nitride substrate of the present disclosure is less prone to color unevenness. In addition, warpage is suppressed and color unevenness is less likely to occur.
(6-2) The silicon nitride substrate of the present disclosure has high thermal conductivity.

7. Effect of Silicon Nitride Substrate Evaluation Method (7-1) The silicon nitride substrate evaluation method of the present disclosure can evaluate color unevenness even if the area of the measurement point P is small. Therefore, for example, it is possible to evaluate the color unevenness of small silicon nitride substrates used in microdevices and the like.

(7-2) In the method for evaluating a silicon nitride substrate of the present disclosure, for example, fitting using a statistical distribution function is performed on spectral peaks, and the half-value width can be calculated for the spectral peaks after fitting. . In this case, the half width can be calculated more accurately.

8. Example (8-1) Manufacture of Silicon Nitride Substrates 3X, 3Y, 3A and 3B Silicon nitride substrates 3X, 3Y, 3A and 3B were manufactured by the method described in "2. Manufacturing method of silicon nitride substrate 3". Silicon nitride substrates 3X, 3Y, 3A, and 3B had a first surface and a second surface. The planar shapes of the silicon nitride substrates 3X, 3Y, 3A, and 3B were rectangular. The silicon nitride substrates 3X, 3Y, 3A, and 3B had a long side length of 200 mm and a short side length of 140 mm. The thickness of the silicon nitride substrates 3X, 3Y, 3A and 3B was 0.32 mm.

When manufacturing the silicon nitride substrates 3X, 3Y, 3A, and 3B, the molar ratio of the rare earth oxide was 1.2 mol % and the molar ratio of the magnesium compound was 9.8 mol %. The molar ratio of the rare earth oxide is the molar ratio of M1 to the total number of moles of M1, M2, and M3, as described above. The molar ratio of the magnesium compound is the molar ratio of M3 to the total number of moles of M1, M2, and M3, as described above.
When manufacturing the silicon nitride substrates 3X, 3A, and 3B, in the nitriding step S4, the heating temperature was raised to the maximum heating temperature in such a manner that the heating temperature was raised stepwise with the lapse of the heating time. The maximum heating temperature was 1400°C. The average heating temperature gradient in the heating range from 1270°C to 1340°C was 2.99°C/h. FIG. 14 shows the measured temperature of the compact in a predetermined temperature range, the measured temperature of the furnace, and the temperature difference between the compact and the furnace in the same lot as the silicon nitride substrate 3X. The horizontal axis in FIG. 14 indicates the elapsed time from the reference time when the measured temperature of the furnace, which is the heating temperature, reaches around 1300.degree. When the measured temperature of the furnace was around 1300° C., the temperature difference between the measured temperature of the furnace and the temperature of the compact in the furnace was 20° C. or less. Even in the silicon nitride substrates 3X heat-treated in the same lot, the temperature of the molded body did not rise sharply during the nitriding treatment, and it is presumed that "thermal runaway" did not occur. Moreover, since the silicon nitride substrates 3A and 3B are heat-treated under the same temperature rising conditions as the silicon nitride substrate 3X, it is presumed that "thermal runaway" does not occur either. The silicon nitride substrates 3A and 3B are heat-treated samples in the same lot, and the silicon nitride substrate 3X and the silicon nitride substrates 3A and 3B are heat-treated samples in different lots.

When manufacturing the silicon nitride substrate 3Y, in the nitriding step S4, the heating temperature was raised to the maximum heating temperature in such a manner that the heating temperature was raised stepwise with the lapse of the heating time. The maximum heating temperature was 1400°C. The average heating temperature gradient in the heating range from 1270°C to 1340°C was 4.67°C/h. FIG. 15 shows the measured temperature of the compact in a predetermined temperature range, the measured temperature of the furnace, and the temperature difference between the compact and the furnace in the same lot as the silicon nitride substrate 3Y. The horizontal axis in FIG. 15 indicates the elapsed time from the reference time when the measured temperature of the furnace, which is the heating temperature, reaches around 1300.degree. When the measured temperature of the furnace was around 1300°C, the temperature difference between the measured temperature of the furnace and the temperature of the compact in the furnace exceeded 20°C, reaching a maximum of 44.9°C. That is, even in the silicon nitride substrates 3Y heat-treated in the same lot, it is conjectured that a rapid temperature rise of the molded body occurs in the nitriding process, and "thermal runaway" occurs.

The thermal conductivity of the silicon nitride substrate 3X was 129 W/(m·K). The thermal conductivity of the silicon nitride substrate 3Y was 120 W/(m·K). The thermal conductivity of the silicon nitride substrates 3A, 3B was 124.4 W/(m·K).
(8-2) Evaluation of Color Unevenness The half-value width _Cave was calculated for each of the silicon nitride substrates 3X, 3Y, 3A, and 3B according to the method described in “5. Silicon Nitride Substrate Evaluation Method”. The measurement surfaces 301 were the first surfaces of the silicon nitride substrates 3X, 3A, and 3B, the first surface of the silicon nitride substrate 3Y, and the second surface of the silicon nitride substrate 3Y. In any measurement plane 301, measurement points P are measurement points P1 to P5 shown in FIG.

The Raman spectrum measurement conditions were as follows.
Raman measurement device: Nanophoton RAMANforce Standard VIS-NIR-HS
Excitation wavelength: 532.06 nm
Excitation power density: 1.76×10 ⁶ W/Cm ²
ND filter: 99.23% (240/255)
Center wavelength of spectrometer: 520.00 cm ^-1
Grating: 1200gr/mm
Slit width: 50 μm
Exposure time: 1 sec
Averaging: 20 times Objective lens: TU Plan Fluor 5x/ NA 0.15
A spectral peak 305 attributed to lattice vibration of silicon nitride was a peak having the maximum intensity within the range of 850 cm ⁻¹ to 875 cm ⁻¹ . A Lorentzian function was used as a statistical distribution function when fitting the spectrum peak 305 .

In addition, lightness L ^* , chromaticity a ^* , chromaticity b ^* , and chroma C ^* were measured at each of the measurement points P1 to P5. In addition, the silicon nitride substrates 3X, 3Y, 3A, and 3B were visually observed to determine the presence or absence of color unevenness. A color difference meter (manufactured by Konica Minolta, trade name: CR-400) was used to measure lightness L ^* , chromaticity a ^* , chromaticity b ^* , and chroma C ^* . The light source of the colorimeter was a xenon lamp. The gauge had a diameter of 8 mm. The illumination diameter was 11 mm. Lightness L ^* , chromaticity a ^* , chromaticity b ^* , and chroma C ^* were measured according to JIS Z8722. Lightness L ^* , chromaticity a ^* , chromaticity b ^* , and chroma C ^* were measured under conditions including regular reflection light.

The processing from the measurement of the Raman spectrum to the calculation of the half-width _Cave and the processing of measuring the lightness L ^* , chromaticity a ^* , chromaticity b ^* , and chroma C ^* are collectively referred to as evaluation processing. The silicon nitride substrates 3X and 3Y were evaluated twice. The silicon nitride substrates 3A and 3B were evaluated once.
The wave number A, height B, half width C, and area D of the spectral peak 307 are shown in FIGS. 9 and 16. FIG. "3X-1" means that the measurement surface 301 is the first surface of the silicon nitride substrate 3X. "3Y-1" means that the measurement surface 301 is the first surface of the silicon nitride substrate 3Y. "3Y-2" means that the measurement surface 301 is the second surface of the silicon nitride substrate 3Y. "3A-1" means that the measurement surface 301 is the first surface of the silicon nitride substrate 3A. 3B-1" means that the measurement surface 301 is the first surface of the silicon nitride substrate 3B.

FIG. 10 shows the lightness L ^* , chromaticity a ^* , chromaticity b ^* , chroma C ^* , and half width C at each measurement point in the first evaluation process of the silicon nitride substrates 3X and 3Y. FIG. 11 shows the lightness L ^* , chromaticity a ^* , chromaticity b ^* , chroma C ^* , and half width C at each measurement point in the second evaluation process for the silicon nitride substrates 3X and 3Y. FIG. 17 shows the lightness L*, chromaticity a*, chromaticity b*, chroma C*, and half width C at each measurement point in the evaluation process of the silicon nitride substrates 3A and 3B. 10, 11, and 17 also show the presence or absence of color unevenness and the average value of each measured value calculated for each measured surface.

FIG. 12 shows the average half width C _ave and the lightness L ^* in the first and second evaluation processes of the silicon nitride substrates 3X and 3Y. FIG. 13 shows the average half width C _ave and the chroma C ^* in the first and second evaluation processes of the silicon nitride substrates 3X and 3Y. 12 and 13 also show the standard deviation range of the half-value width C centered on the average half-value width _Cave .

The average half width C _ave of silicon nitride substrates 3X, 3A, and 3B with no color unevenness was smaller than 5.32 cm ⁻¹ . The average half-value width C _ave of the silicon nitride substrate 3Y with uneven color was greater than 5.32 cm ⁻¹ . Therefore, there was a correlation between the presence or absence of color unevenness and the average half width _Cave . From this evaluation result, it was confirmed that color unevenness can be evaluated based on the average half width C _ave . Further, it was confirmed that the silicon nitride substrate having a small average half-value width _Cave hardly causes color unevenness. As for the color unevenness of the silicon nitride substrate 3Y, only slight color unevenness was observed on one of the four sides of the substrate by visual observation.

(8-3) Evaluation of Warpage For each of the silicon nitride substrates 3X, 3Y, 3A, and 3B, warpage was measured from the first surface side and the second surface side. The warp was measured using a warp measuring device manufactured by Softworks Co., Ltd. This warpage measuring apparatus measures the amount of warpage of a plate-shaped object to be measured by arranging three line lasers and taking an image with a high-resolution camera. In this warpage measuring apparatus, the least squares plane of the upper surface of the object to be measured is calculated (prescribed). Then, the sum of the absolute value of the distance from the calculated least-squares plane to the highest point on the upper surface of the object to be measured and the absolute value of the absolute value of the distance to the lowest point on the upper surface of the object to be measured was calculated as the amount of warpage. The calculation method is based on the SORI (SEMI M1, ASTM F 1451) standard.
(1) Measurement Results of Warp from First Surface Side The amount of warp of the silicon nitride substrate 3X is 0.779 mm, the amount of warp of the silicon nitride substrate 3Y is 0.999 mm, and the amount of warp of the silicon nitride substrate 3A is 0.779 mm. 840 mm, and the amount of warpage of the silicon nitride substrate 3B was 0.751 mm.
(2) Measurement Results of Warp from Second Surface Side The warp amount of the silicon nitride substrate 3X is 0.653 mm, the warp amount of the silicon nitride substrate 3Y is 0.879 mm, and the warp amount of the silicon nitride substrate 3A is 0.653 mm. 679 mm, and the amount of warpage of the silicon nitride substrate 3B was 0.581 mm.
(3) Consideration The silicon nitride substrates 3X, 3Y, 3A, and 3B all meet the acceptance criteria of "1 mm or less" in terms of the amount of warpage, but the silicon nitride substrates have an average half-width _Cave of less than 5.32 cm ⁻¹ . In the substrates 3X, 3A, and 3B, it was found that the amount of warp was further suppressed to 0.840 mm or less.

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 various modifications can be made.

(1) In the method for evaluating a silicon nitride substrate of the present disclosure, for example, fitting using a statistical distribution function may not be performed on spectral peaks. In this case, it is possible to measure the half width C of the spectral peak without fitting.

(2) A power module other than the power module 1 may be manufactured using the silicon nitride substrate 3 .
(3) A plurality of functions possessed by one component in the above embodiment may be realized by a plurality of components, or a function possessed by one component may be realized by a plurality of components. . Also, a plurality of functions possessed by a plurality of components may be realized by a single component, or a function realized by a plurality of components may be realized by a single component. Also, part of the configuration of the above embodiment may be omitted. Moreover, at least part of the configuration of the above embodiment may be added or replaced with respect to the configuration of the other above embodiment.

(4) In addition to the evaluation system 201 described above, a non-transitional entity such as a higher-level system having the evaluation system 201 as a component, a program for making a computer function as the evaluation device 205, a semiconductor memory storing this program, etc. The present disclosure can also be realized in various forms such as a recording medium, a quality control method for a silicon nitride substrate, and the like.

DESCRIPTION OF SYMBOLS 1... Power module, 2... Silicon nitride circuit board, 3... Silicon nitride board, 5... Metal circuit, 7... Metal radiator plate, 9, 11... Brazing material layer, 13... Semiconductor chip, 15... Heat sink, 100A... Molded body , 105... Metal plate, 107... Metal radiator plate, 200... Setter, 201... Evaluation system, 203... Raman measuring device, 205... Evaluation device, 206... Laser beam, 207... Data acquisition unit, 208... Raman scattered light, 209 ... data processing unit 300 ... weight 301 ... measurement surface 305, 307 ... spectrum peaks 401, 404 ... long side 402, 403 ... short side

Claims (8)

A silicon nitride substrate having a first surface and a second surface opposite to the first surface,
Nitriding with an average half width C _ave value of more than 0 cm ⁻¹ and less than 5.32 cm ⁻¹ measured by the following measurement method on a measurement surface that is one of the first surface and the second surface Silicon substrate.
Method of measuring the average half-value width C _ave : Measurement points are one point at the center and four points at the edges of the measurement surface.
A Raman spectrum is measured at each of the measurement points. In each of the measured Raman spectra, the half width C of the spectral peak having the maximum intensity within the range of 850 cm ⁻¹ to 875 cm ⁻¹ is calculated. An average value of the calculated half-value width C is defined as an average half-value width C _ave . The silicon nitride substrate according to claim 1,
The planar shape of the silicon nitride substrate is a rectangular shape,
A silicon nitride substrate, wherein each side of the silicon nitride substrate has a length of 100 mm or more. The silicon nitride substrate according to claim 1 or 2,
A silicon nitride substrate having a thermal conductivity of 110 W/(m·K) or more. A silicon nitride substrate evaluation method for evaluating color unevenness of a silicon nitride substrate, comprising:
Measure a Raman spectrum at a measurement point on the silicon nitride substrate,
Measure the half width of the spectral peak attributed to the lattice vibration of silicon nitride contained in the Raman spectrum,
Evaluating color unevenness of the silicon nitride substrate based on the half-value width;
Evaluation method of silicon nitride substrate. A method for evaluating a silicon nitride substrate according to claim 4,
The spectral peak is a peak with maximum intensity within the range of 850 cm ^-1 or more and 875 cm ^-1 or less,
Evaluation method of silicon nitride substrate. A method for evaluating a silicon nitride substrate according to claim 4 or 5,
Fitting using a statistical distribution function is performed on the spectral peak,
calculating the half width at the spectral peak after performing the fitting;
Evaluation method of silicon nitride substrate. An evaluation device for evaluating color unevenness of a silicon nitride substrate,
a data acquisition unit configured to acquire a Raman spectrum measured at a measurement point on the silicon nitride substrate;
a half-value width measuring unit configured to measure a half-value width of a spectral peak attributed to lattice vibration of silicon nitride included in the Raman spectrum acquired by the data acquiring unit;
An evaluation device comprising: An evaluation system for evaluating color unevenness of a silicon nitride substrate,
A silicon nitride substrate evaluation system comprising: a Raman measuring device for measuring a Raman spectrum at a measurement point on said silicon nitride substrate; and the evaluation device according to claim 7 .

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