Manufacturing method of semiconductor module and silicon nitride substrate

Abstract

To provide a manufacturing method of a semiconductor module and a silicon nitride substrate capable of suppressing occurrence of cracking or damage to the substrate at the time of screwing.SOLUTION: A manufacturing method of a semiconductor module includes first to fifth steps. In the first step, a ceramic substrate having a front surface and a back surface and provided with one or more notch portions for screwing including opening parts is prepared. In the second step, the conductor portion is bonded to the ceramic substrate through a bonding layer containing one or two kinds of copper and silver and an active metal. In the third step, a circuit shape is provided to the conductor portion. In the fourth step, a semiconductor element is mounted on the conductor portion provided with the circuit shape to manufacture a semiconductor device. In the fifth step, the semiconductor device is fixed by screwing through the notch. In the ceramic substrate, at least one of angles (θ3) of the end portions of the opening part is larger than 90 degrees when viewed from the surface.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The embodiments described below generally relate to a method for manufacturing a semiconductor module and a silicon nitride substrate. [Background technology]

[0002] Insulating circuit boards, in which an insulating substrate and a circuit section are joined, are used as substrates for mounting semiconductor elements. Insulating circuit boards are fixed using screws. Screw fixing methods include providing screw fixing sections on the substrate and using a fixing jig. In recent years, attempts have been made to provide screw fixing sections on the substrate in order to stabilize the screw fixing position and save space. The screw fixing sections provided on the substrate are called cutout sections.

[0003] If the opening edge of the cutout portion of the ceramic substrate is a right angle as described in Patent Document 1 or 2, the screw may collide with the opening edge when fastening with a screw. It has been found that in this case, chips and cracks are likely to occur around the opening edge. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-56933 [Patent Document 2] International Publication No. 2011 / 004798 Summary of the Invention [Problem to be solved by the invention]

[0005] In conventional ceramic substrates, the edges of openings are at right angles. This has led to the problem that the substrate is prone to cracking or chipping when screwed. The present invention addresses this problem and aims to provide a ceramic substrate having a front surface (first surface) and a back surface (second surface) with at least one notch, characterized in that at least one of the angles (θ3) at the edge of the opening, where the substrate exists when viewed from the front surface, exceeds 90 degrees. [Means for solving the problem]

[0006] A method for manufacturing a semiconductor module according to an embodiment includes first to fifth steps. In the first step, a ceramic substrate is prepared, having a front surface and a back surface, and having one or more notches for screwing, including an opening. In the second step, a conductor is bonded to the ceramic substrate via a bonding layer containing one or both of copper and silver and an active metal. In the third step, a circuit shape is imparted to the conductor. In the fourth step, a semiconductor element is mounted on the conductor with the circuit shape imparted thereto, thereby producing a semiconductor device including the ceramic and the semiconductor element. In the fifth step, the semiconductor device is fixed by screws passing through the notches. In the prepared ceramic substrate, at least one of the angles (θ3) of the edge of the opening at the location where the ceramic substrate exists when viewed from the front surface is greater than 90 degrees. [Brief explanation of the drawings]

[0007] [Figure 1] 3A and 3B are schematic views showing an example of a structure of a ceramic substrate according to an embodiment, in which a cutout shape and a through hole are provided. [Figure 2] FIG. 4 is a schematic view showing an example of a cutout shape provided in the ceramic substrate according to the embodiment. [Figure 3] FIG. 4 is a schematic view showing an example of a cutout shape provided in the ceramic substrate according to the embodiment. [Figure 4] FIG. 4 is a schematic view showing an example of a cutout shape provided in the ceramic substrate according to the embodiment. [Figure 5] FIG. 4 is a schematic view showing an example of a cutout shape provided in the ceramic substrate according to the embodiment. [Figure 6] FIG. 4 is a schematic view showing an example of a cutout shape provided in the ceramic substrate according to the embodiment. [Figure 7] FIG. 4 is a schematic view showing an example of a cutout shape provided in a ceramic substrate according to an embodiment (comparative example). [Figure 8] FIG. 4 is a schematic view showing an example of a cutout shape provided in the ceramic substrate according to the embodiment. [Figure 9] FIG. 4 is a schematic view showing an example of a cutout shape provided in the ceramic substrate according to the embodiment. [Figure 10] 1 is a schematic diagram showing an example of a semiconductor device according to an embodiment; [Figure 11] FIG. 10 is a schematic view showing another example of a semiconductor device according to the embodiment. [Figure 12] 3A and 3B are schematic views showing an example of a side shape of a cutout portion of a ceramic substrate according to an embodiment. [Figure 13] FIG. 2 is a schematic view illustrating the vicinity of a cutout portion of the ceramic substrate according to the embodiment. [Figure 14] FIG. 10 is a schematic side view illustrating a state in which the semiconductor device according to the embodiment is fastened with screws. [Figure 15] FIG. 1 is a schematic plan view illustrating a state in which the semiconductor device according to the embodiment is fastened with screws. [Figure 16] 1 is a flowchart illustrating a manufacturing method according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] A method for manufacturing a semiconductor module according to an embodiment of the present invention includes first to fifth steps. In the first step, a ceramic substrate having a front and back surface and one or more notches for screwing, including an opening, is prepared. In the second step, a conductor is bonded to the ceramic substrate via a bonding layer containing one or both of copper and silver and an active metal. In the third step, a circuit shape is imparted to the conductor. In the fourth step, a semiconductor element is mounted on the conductor with the circuit shape imparted thereto to fabricate a semiconductor device including the ceramic and the semiconductor element. In the fifth step, the semiconductor device is fixed by screws passing through the notches. In the prepared ceramic substrate, at least one of the angles (θ3) at the edge of the opening at the location where the ceramic substrate exists when viewed from the front surface is greater than 90 degrees. The angle θ3 is shown in FIG. 1.

[0009] The ceramic substrate according to this embodiment may have, for example, one notch and one or more through holes. Alternatively, the ceramic substrate may have two or more notches. When multiple notches are provided, the shapes of all the notches may be the same or different from each other. Furthermore, the notches may be provided at corners of the ceramic substrate. When the ceramic substrate is rectangular, the notches may be provided on either the short side or the long side. On the other hand, the number of notches per substrate is preferably 15 or less. If the number of notches exceeds 15, the strength of the ceramic substrate may be insufficient. The shape of the ceramic substrate may be approximately circular, approximately elliptical, or approximately semicircular.

[0010] The cutout portion includes an opening that opens toward the edge of the ceramic substrate. The edge of the opening (opening edge) has a corner of the ceramic substrate. An R or C portion may be formed at the opening edge. The term "an R or C portion may be formed at the opening edge" includes forming a minute C or R portion only near the opening edge. In embodiments of the present invention, when a perpendicular line is drawn from the midpoint between the opening edges, there may be a portion where the shape of the cutout portion is asymmetrical with respect to this perpendicular line. Furthermore, a cutout portion formed in this manner may be combined with a through hole, a cutout portion whose opening is narrower than other portions, or a cutout portion whose opening is at a right angle. Whether θ3 exceeds 90 degrees is determined based on the inflection point closest to the opening, for example, in the case of a curved opening.

[0011] Fig. 1 is a schematic diagram showing an example of a structure in which a cutout shape and a through hole are provided in a ceramic substrate according to an embodiment. Fig. 2 is a schematic diagram showing an example of a structure in which a cutout shape is provided in a ceramic substrate according to an embodiment. In Figures 1 and 2, symbol 1 is a ceramic substrate, and symbol 2 is a cutout portion. Symbol 3 is a through hole. Symbol P1 is a first opening end. Symbol P2 is a second opening end. Symbol Li indicates an imaginary line connecting the first opening end P1 and the second opening end P2. Symbol θ1 is the angle between the line Li and the cutout portion 2 on the side that forms the cutout (surrounded by the substrate portion). Symbol OP indicates the opening of the cutout portion 2. Figure 2 shows a structure in which the cutout portion 2 is provided so that the side that is not the opening OP is approximately trapezoidal. Figure 2 also illustrates an example of a combination of the cutout portion 2 and another cutout portion 2.

[0012] 3 to 9 are schematic diagrams showing an example of a structure in which a cutout portion 2 is provided in a ceramic substrate 1 according to an embodiment. FIG. 3 shows an example of a structure in which a substantially V-shaped cutout portion 2 is provided. In FIG. 3, symbol P3 indicates an end portion of the cutout portion 2 that is not on the opening side. Symbol θ2 is the angle of the end portion P3 that is not on the opening side.

[0013] FIG. 4 illustrates a structure in which a substantially semicircular cutout portion 2 is formed. In FIG. 4, symbol P4 indicates the midpoint between the open ends. Symbol P5 indicates the farthest point among the intersections between a perpendicular line drawn from the midpoint between the open ends and the ceramic substrate 1. Symbol P6 is the intersection point between a perpendicular line drawn from the midpoint between the open ends and the cutout portion 2 having the opening. Symbol L1 indicates the distance between the midpoint P4 and the intersection point P5. Symbol L2 indicates the distance between the midpoint P4 and the intersection point P6.

[0014] FIG. 5 is a schematic diagram illustrating a cutout portion 2 having a shape that is a combination of an approximate U-shape and an approximate V-shape. In FIG. 5, the symbol θ3 indicates the angle at which the ceramic substrate 1 is located at the end of the cutout portion 2. The symbol θ4 indicates the angle between the R portion and the boundary of the opening, or the angle between the C portion and the boundary of the opening. The boundary of the opening refers to the boundary between the opening and the ceramic substrate 1.

[0015] FIG. 6 is a schematic diagram illustrating a structure in which two cutouts 2 are not identical in shape. FIG. 7 is a schematic diagram illustrating a comparative example in which a wide cutout 2 is formed at the corner of a ceramic substrate 1. FIG. 7 also shows an example in which another cutout 2 has a shape similar to a through-hole 3. In FIG. 7, the wide cutout reduces the risk of collision during screw fastening, but the open edge of the substrate becomes sharp. This undesirably increases the risk of cracking or chipping during collision compared to when θ3 is greater than 90 degrees. In the example shown in FIG. 7, the presence of a corner, such as θ5, makes the ceramic substrate 1 prone to becoming sharp. θ5 is the angle from the extension of the straight line connecting the open edges to the point where the substrate is located. FIG. 8 is a schematic diagram illustrating a structure in which the open edge of the cutout 2 has a rounded chamfer. FIG. 9 is a schematic diagram illustrating a structure in which the open end of the cutout portion 2 is provided with a C-shaped chamfered portion.

[0016] FIG. 10 is a schematic diagram illustrating a bonded body in which conductor portions are provided on ceramic substrates 1 and bonded together. In FIG. 10, reference numeral 4 denotes the conductor portion, reference numeral 5 denotes an active metal bonding layer, and reference numeral 6 denotes the bonded body. FIG. 11 is a schematic diagram illustrating a semiconductor device in which a semiconductor element is mounted on the bonded body shown in FIG. 10. In FIG. 11, reference numeral 7 denotes the semiconductor element, reference numeral 8 denotes a bonding layer (between the semiconductor element and the conductor portion), reference numeral 9 denotes a plating film, and reference numeral 10 denotes the semiconductor device. FIG. 12 is a schematic diagram illustrating an example of the side shape of a notch portion 2 of a ceramic substrate 1.

[0017] Regarding the angle of the opening end, the angle of the ceramic substrate 1 between the cutout 2 and a straight line connecting the opening ends of the same cutout 2 is defined as θ3. In this case, the ceramic substrate 1 preferably has a portion where the angle θ3 exceeds 90 degrees. It is more preferable that the angle θ3 at both ends on the opening side of one cutout 2 is each larger than 90 degrees.

[0018] A more preferred range for the angle θ3 is 100 degrees or more and 170 degrees or less, and more preferably 100 degrees or more and 160 degrees or less. Even more preferably, the angle θ3 is 120 degrees or more and 150 degrees or less. If the angle θ3 is too small, such as less than 100 degrees, the effect of making the opening angle greater than 90 degrees may not be fully achieved. On the other hand, if the angle is greater than 170 degrees, as described above, the area occupied by the edge of the shape of the cutout portion 2 becomes too large, and there is a possibility that the ceramic substrate 1 may not have a sufficient mounting surface for the semiconductor element. Furthermore, there are two angles per opening of the cutout portion 2 where the ceramic substrate 1 is present. The difference between these two angles is preferably less than 20 degrees. Furthermore, it is even more preferable that the difference is less than 10 degrees.

[0019] When the ceramic substrate 1 has multiple cutouts 2, it is sufficient that the angle θ3 at at least one of the cutouts 2 exceeds 90 degrees. More preferably, the angle θ3 at both ends of the opening in the at least one cutout 2 is 90 degrees or greater. It is even more preferable that the angles θ3 at all of the cutouts 2 exceed 90 degrees.

[0020] An R or C portion may be formed on the substrate center side of the opening edge. When an R or C portion is formed on the substrate center side of the opening edge as described above, the angle between the boundary (inflection point) between the R or C portion and other parts and the straight line connecting the opening edges on the cutout portion 2 side is defined as θ1. The size of the R or C portion is not particularly limited, and it may be provided only near the opening edge.

[0021] 13(a) and 13(b) are schematic views illustrating the vicinity of the cutout portion of the ceramic substrate according to the embodiment. If there is no inflection point, the angles θ1 and θ3 are determined as follows: As shown in Figure 13(a), if the shape from the opening end P1 or P2 to the end P3 that is not on the opening side is approximately linear, the angles θ1 and θ3 are determined using a straight line along that shape and a straight line Li.

[0022] As shown in FIG. 13(b), if the shape from opening end P1 or P2 to end P3 is curved, first, the point in cutout portion 2 that is farthest from line Li is identified. In the example shown, end P3 corresponds to the farthest point. The shape of cutout portion 2 is approximated by an ellipse E whose major axis is a line connecting the farthest point and line Li. Cutout portion 2 is approximated by ellipse E so that the outer edge of ellipse E best fits the side surface of cutout portion 2. The boundary between the portion where ellipse E and cutout portion 2 share a common part and the portion where ellipse E and cutout portion 2 do not share a common part is identified. Angles θ1 and θ3 are calculated using a line passing through that boundary and opening end P1 or a line passing through that boundary and opening end P2 as a reference.

[0023] The end of the cutout portion 2 not facing the opening is preferably generally U-shaped, generally trapezoidal, or generally V-shaped. If the end not facing the opening is generally V-shaped, the angle toward the cutout portion 2 is preferably 70 degrees or greater. If the angle is less than 70 degrees, cracks may occur at this end. As described above, if the angle toward the cutout portion 2 of the end not facing the opening is 70 degrees or greater, the end may be generally V-shaped. The angle of the end not facing the opening is designated angle θ2. The angle θ2 is the angle between the side surfaces of the cutout portion 2. The angle θ2 is shown in Figure 3. A generally U-shaped end refers to a shape having an R-shaped portion at the end not facing the opening, as shown in Figures 4 and 8, for example. A generally trapezoidal shape refers to a shape having a C-shaped portion at the end not facing the opening, as shown in Figures 1 and 2, for example. The cutout portion 2 may also be a polygonal shape, such as a generally pentagonal or hexagonal shape.

[0024] By providing a chamfered portion at a location other than the opening side, the effect of suppressing cracks at this end can be further enhanced. By providing this chamfered portion with an R portion or a C portion, the effect of suppressing cracks at this end can be further enhanced. Therefore, it is more preferable to provide the R portion or the C portion at a location other than the opening side.

[0025] The shape of the end portion not on the opening side is preferably a substantially V-shape (with an angle of 70 degrees or more), a substantially trapezoidal shape, or a substantially U-shape. The size of the substantially V-shape (with an angle of 70 degrees or more), a substantially trapezoidal shape, or a substantially U-shape is arbitrary. For example, these shapes may be very small and provided in only a small part of the shape of the cutout portion 2. Alternatively, these shapes may be formed over the entire cutout portion 2. If the R portion or C portion is substantially U-shaped, the effect of suppressing crack generation can be further enhanced. Therefore, it is even more preferable that the R portion or C portion be substantially U-shaped.

[0026] Here, the R portion refers to a shape obtained by rounding off the corners of the tip of the cutout portion 2 to form an approximately U-shape. The tip portion refers to the end of the cutout portion 2 that is not on the opening side. The C portion refers to a shape obtained by linearly cutting off the corners of the tip of the cutout portion 2 to form an approximately trapezoidal shape. When a C portion is provided in this manner, it is more preferable that the angle on the cutout side, which is the upper base of this trapezoid, is 30 degrees or more. In this case, it is even more preferable that the ratio of the upper base to the lower base of the approximately trapezoid (upper base / lower base) is 0.1 or more. The upper base of the approximately trapezoid is the length of the side of the tip of the cutout portion 2. The lower base of the approximately trapezoid is the length of the opening of the cutout portion 2. Therefore, the lower base of the approximately trapezoid is the length of the straight line connecting the open ends. This further reduces the possibility of cracking or chipping of the ceramic substrate 1 compared to when a ceramic substrate 1 having an approximately V-shape is screwed.

[0027] The shape of the portion not on the opening side can be determined by viewing from the surface, similar to the angle θ3. Furthermore, the side shape of the portion not on the opening side is determined by the shape when viewed from the surface formed by the side surface of the cutout portion 2. The shape may also have an R portion or a C portion.

[0028] Even if the angle between the opening ends and the cutout portion 2 (e.g., the angle shown as θ1 in FIG. 1) is less than 90 degrees, when an opening is provided at a corner of a rectangular, square, or other quadrangular ceramic substrate 1, the ceramic substrate 1 may become partially narrow at the opening end. In such cases, it may be difficult to maintain sufficient strength at the corner. Therefore, it is preferable that the interior angle of the ceramic substrate 1 at both ends of the opening be 100 degrees or more.

[0029] It is preferable that the side shape is also controlled. In the side shape, it is preferable that at least one or more of the end portion on the front surface side of the ceramic substrate 1 and the end portion on the back surface side of the ceramic substrate 1 have an R portion or a C portion. When the ceramic substrate 1 is viewed from the side, it is more preferable that both ends on the front surface side have a minute R portion or C portion, as shown in FIG. 12. At both the end portion on the front surface side and the end portion on the back surface side, the width of the notch portion 2 may be widened, and the notch portion 2 may be open.

[0030] The arithmetic mean roughness Ra of the side surface is preferably 1.2 μm or less. Furthermore, the maximum height Rz of the side surface is preferably 2.0 μm or less. Ra and Rz are specified in JIS B 0601:2013. JIS B 0601:2013 corresponds to ISO 4287:1997 / AMENDMENT 1:2009 (IDT). Surface roughness associated with processing can be controlled by adjusting the processing method. Therefore, the arithmetic mean roughness Ra of the side surface is preferably 1.2 μm or less, and the maximum height Rz of the side surface is preferably 2.0 μm or less. Methods for controlling surface roughness associated with processing include, for example, performing blasting or honing after processing, or controlling the irradiation diameter or energy density during laser processing. Controlling the surface roughness of the side surface can improve the efficiency of screw fastening.

[0031] As shown in FIG. 4, for the cutout portion 2, the midpoint between the ends of the opening OP is designated P4. When a perpendicular line is drawn from the midpoint P4, the end point of the ceramic substrate 1 on this perpendicular line that is farthest from the midpoint P4 is designated P5. The length of the ceramic substrate 1 between the midpoint P4 and the intersection point P5 is designated L1. The intersection point between the perpendicular line and the cutout portion 2 having the opening is designated P6. In this case, with respect to the length (L2) of the cutout portion 2 defined as the distance between the midpoint P4 and the intersection point P6, it is preferable that L2 / L1 is 0.1 or more and 0.4 or less. For the end of the ceramic substrate 1 farthest from the midpoint P4, when the through hole 3 is on the perpendicular line drawn from the midpoint P4 in the combination of the cutout portion 2 and the through hole 3, the end of the ceramic substrate 1 ignoring the through hole 3 is designated as the intersection point P5.

[0032] When a perpendicular line drawn from the midpoint between one end (first opening end P1) and the other end (second opening end P2) of the opening does not intersect with another cutout portion 2, L1 is the length from the intersection of this perpendicular line with the ceramic substrate 1. When a perpendicular line drawn from the midpoint between the opening ends intersects with another cutout portion 2, L1 is the distance between the line connecting the opening ends of the other cutout portions 2 and the midpoint between the opening ends. Furthermore, L2 is the longest distance between the intersection of the perpendicular lines drawn from the line connecting the opening ends with the edge of the cutout portion 2. In this case, L2 / L1 is preferably 0.1 or more and 0.4 or less. More preferably, L2 / L1 is 0.1 or more and 0.35 or less. When L2 / L1 is greater than 0.4, the ceramic substrate 1 may be prone to cracking. On the other hand, when L2 / L1 is less than 0.1, the effect of providing the cutout portion 2 may not be fully achieved. That is, when the notch 2 is not at a corner but exists in only one place, the length L1 corresponds to the length of the ceramic substrate 1.

[0033] As shown in Fig. 12, the maximum width when viewed from the side of the notch portion 2 is defined as L3, and the smallest width among the opening widths of the notch portion 2 including the maximum width L3 is defined as L4. In this case, it is preferable that 0.5 ≦ L4 / L3 < 1. The direction of the width L3 is parallel to the direction of the width L4 and parallel to the direction connecting the first opening end portion P1 and the second opening end portion P2. If L4 / L3 is less than 0.5, the opening end portion may be prone to chipping. On the other hand, if L4 / L3 is 1 or more, the effect of making the angle of the opening larger than 90 degrees cannot be sufficiently obtained, and the positional accuracy of the screwing portion may deteriorate. More preferably, L4 / L3 satisfies 0.7 < L4 / L3 < 1.

[0034] Fig. 14 is a schematic side view illustrating a state where the semiconductor device according to the embodiment is screwed. Fig. 15 is a schematic plan view illustrating a state where the semiconductor device according to the embodiment is screwed. In Figs. 14 and 15, reference numeral 11 indicates a screw. As shown in Figs. 14 and 15, when fixing the semiconductor device 10, the screw is passed through the notch portion 2. The ceramic substrate 1 is pressed toward the support plate by the screw 11, and the semiconductor device 10 is fixed to the support plate.

[0035] According to the embodiment, when the screw 11 is provided in the notch portion 2 of the ceramic substrate 1, it is difficult for the screw 11 to collide with the ceramic substrate 1. Further, since the angle θ3 is larger than 90 degrees, even when the screw 11 collides with the ceramic substrate 1, it is possible to avoid a large force being locally applied to the ceramic substrate 1. Thereby, the occurrence of chipping or cracking of the ceramic substrate 1 can be suppressed.

[0036] The ceramic substrate 1 preferably contains, as a main component, one or two selected from silicon nitride, aluminum nitride, sialon, alumina, and zirconia. The main component refers to a component contained in an amount of 50% by mass or more. Further, it is more preferable that the ceramic substrate is any one of a silicon nitride substrate, an aluminum nitride substrate, and an aldyl substrate. Aldyl is a material containing a total of 50% by mass or more of two kinds of alumina and zirconia.

[0037] The thickness of the ceramic substrate 1 is preferably 0.1 mm or more and 3 mm or less, and more preferably 0.1 mm or more and 1 mm or less. If the thickness of the ceramic substrate 1 is less than 0.1 mm, the strength of the ceramic substrate 1 may be reduced. If the thickness of the ceramic substrate 1 is greater than 3 mm, the ceramic substrate 1 itself may become a thermal resistor, which may reduce the heat dissipation performance of the ceramic circuit board.

[0038] The three-point bending strength of the silicon nitride substrate is preferably 600 MPa or more. The thermal conductivity of the silicon nitride substrate is preferably 80 W / m·K or more. By increasing the strength of the silicon nitride substrate, the substrate thickness can be made thinner. Therefore, the three-point bending strength of the silicon nitride substrate is preferably 600 MPa or more, and even 700 MPa or more. The thickness of the silicon nitride substrate can be made thinner, 0.40 mm or less, and even 0.30 mm or less. The three-point bending strength of the aluminum nitride substrate is approximately 300 to 450 MPa. On the other hand, the thermal conductivity of the aluminum nitride substrate is 160 W / m·K or more. Because the strength of the aluminum nitride substrate is low, the substrate thickness is preferably 0.60 mm or more.

[0039] The three-point bending strength of an aluminum oxide substrate is approximately 300 to 450 MPa, but aluminum oxide substrates are inexpensive among ceramic substrates. The three-point bending strength of an aridil substrate is high at approximately 550 MPa, but its thermal conductivity is approximately 30 to 50 W / m·K. An aridil substrate is a substrate made of a sintered mixture of aluminum oxide and zirconium oxide. The ceramic substrate is preferably a nitrogen-containing ceramic substrate. Furthermore, among nitrogen-containing ceramic substrates, nitride-based ceramics are more preferable, and either a silicon nitride substrate or an aluminum nitride substrate is even more preferable.

[0040] The thickness of the ceramic substrate is preferably 0.1 mm or more and 1 mm or less. If the substrate thickness is less than 0.1 mm, the strength may be insufficient. If the substrate thickness is greater than 1 mm, the ceramic substrate 1 itself may become a thermal resistor, which may reduce the heat dissipation performance of the circuit board.

[0041] The notch 2 of the ceramic substrate 1 according to the embodiment of the present invention can be suitably used for screw fastening.

[0042] For silicon nitride substrates, the three-point bending strength is preferably 600 MPa or more. The thermal conductivity is preferably 80 W / m·K or more. By increasing the strength of the silicon nitride substrate, the substrate thickness can be reduced. For this reason, the three-point bending strength of the silicon nitride substrate is preferably 600 MPa or more, and more preferably 700 MPa or more. The thickness of the silicon nitride substrate can be reduced to 0.40 mm or less, and even 0.30 mm or less.

[0043] The three-point bending strength of an aluminum nitride substrate is approximately 300 to 450 MPa. On the other hand, the thermal conductivity of an aluminum nitride substrate is 160 W / m·K or more. Because the strength of an aluminum nitride substrate is low, a substrate thickness of 0.60 mm or more is preferable. The three-point bending strength of an aluminum oxide substrate is approximately 300 to 450 MPa, but aluminum oxide substrates are inexpensive. The three-point bending strength of an alu-zirconium substrate is high, approximately 550 MPa, but the thermal conductivity is approximately 30 to 50 W / m·K. An alu-zirconium substrate is a substrate made from a sintered mixture of aluminum oxide and zirconium oxide.

[0044] A conductor portion 4 may be bonded to a ceramic substrate 1 having the above-described cutout portion 2. A cutout portion 2 of the above shape may be formed in a bonded body 6 obtained by bonding a ceramic substrate 1 and a conductor portion 4. The conductor portion 4 may be provided on only one side of the ceramic substrate 1. The conductor portion 4 may be provided on each of both sides of the ceramic substrate 1. Here, the conductor portion 4 provided on the front surface of the ceramic substrate 1 is referred to as the front conductor portion. The conductor portion 4 provided on the back surface of the ceramic substrate 1 is referred to as the back conductor portion. The composition of the front conductor portion and the composition of the back conductor portion may be different from each other. If the composition of the front conductor portion and the composition of the back conductor portion are the same, a bonded body that is easy to use can be provided. For this reason, it is more preferable that the composition of the front conductor portion and the composition of the back conductor portion are the same.

[0045] The conductor portion 4 is preferably a copper member or an aluminum member. The copper member is made of copper or a copper alloy. The copper member is a copper plate, a copper alloy plate, a member in which a circuit shape is imparted to a copper plate, or a member in which a circuit shape is imparted to a copper alloy plate. The aluminum member is made of aluminum or an aluminum alloy. The aluminum member is an aluminum plate, an aluminum alloy plate, a member in which a circuit shape is imparted to an aluminum plate, or a member in which a circuit shape is imparted to an aluminum alloy plate. A member made by imparting a circuit shape to a copper plate is called a copper circuit. A member made by imparting a circuit shape to an aluminum plate is called an aluminum circuit.

[0046] An advantage of using aluminum for the conductor 4 is that it is less expensive than copper. When the conductor 4 is made of aluminum, an Al-based brazing filler metal such as an Al-Mg alloy brazing filler metal can be used. On the other hand, copper members have higher thermal conductivity than aluminum members. For this reason, it is preferable to use a copper member for the conductor 4. The conductor 4 may be a metallized layer or a conductive thin film other than a copper member or an aluminum member. The metallized layer is formed by firing a metal paste. The thickness of the conductor 4 may be 0.3 mm or more, or even 0.6 mm or more. Increasing the thickness of the conductor 4 can improve the heat dissipation performance of the bonded body 6. The thickness of the front conductor may be the same as or different from the thickness of the back conductor. A copper member is particularly preferable for the conductor 4. The copper member is preferably made of oxygen-free copper. As specified in JIS-H-3100, oxygen-free copper has a copper purity of 99.96 mass% or more.

[0047] The ceramic substrate 1 and the copper member may be directly bonded. A punched copper plate may be bonded to the ceramic substrate 1. A copper plate may be bonded to the ceramic substrate 1, and then the copper plate may be etched. When a brazing filler metal is used for bonding, it is preferable that the ceramic substrate 1 and the copper member are bonded via a bonding layer containing titanium. In the active metal bonding method, an active metal brazing filler metal containing Ti is used. The active metal brazing filler metal contains, for example, silver or copper as a main component (50 mass% or more) and also contains Ti. It is also preferable that the ceramic substrate and the copper member are bonded via a bonding layer containing carbon. By adding carbon to the active metal brazing filler metal, a bonding layer containing carbon can be formed. By adding carbon to the active metal brazing filler metal, the fluidity of the brazing filler metal can be improved, thereby improving the bonding strength.

[0048] The active metal brazing filler metal may be a brazing filler metal combining Ag and Ti or a brazing filler metal combining copper and Ti. For example, the active metal brazing filler metal preferably contains 0% to 98% by mass of Ag (silver), 1% to 85% by mass of Cu (copper), and 1% to 15% by mass of Ti (titanium) or TiH2 (titanium hydride). Furthermore, Nb or Zr may be used instead of Ti in the active metal brazing filler metal, or Nb and Zr may be added in addition to Ti. However, the active metal brazing filler metal preferably contains 1% to 15% by mass of Ti (titanium) or TiH2 (titanium hydride). When both Ti and TiH2 are used, their total content is preferably within the range of 1% to 15% by mass. When both Ag and Cu are used, the Ag content is preferably 20% to 70% by mass and the Cu content is preferably 15% to 65% by mass. The brazing filler metal may contain 1 to 50 mass% of one or more elements selected from Sn (tin), In (indium), and Mn (manganese), if necessary. The content of Ti or TiH2 is preferably 1 to 15 mass%. Furthermore, the brazing filler metal may contain 0.1 to 2 mass% of C (carbon), if necessary.

[0049] The composition ratio of the active metal brazing material is calculated with the total of the mixed solid raw materials being 100% by mass. The solid raw materials are preferably in powder form. For example, if the active metal brazing material is made up of three elements, Ag, Cu, and Ti, then Ag + Cu + Ti = 100% by mass. If the active metal brazing material is made up of four elements, Ag, Cu, TiH2, and In, then Ag + Cu + TiH2 + In = 100% by mass. If the active metal brazing material is made up of five elements, Ag, Cu, Ti, Sn, and C, then Ag + Cu + Ti + Sn + C = 100% by mass. It is preferable to mix a solvent appropriate to the above-mentioned composition with the powder raw materials. By mixing a solvent, the brazing material can be made into a paste.

[0050] The prepared brazing paste is applied onto the ceramic substrate 1, and the conductor portion 4 is placed thereon. The obtained laminate is heated to bond the ceramic substrate 1 and the conductor portion 4. In this way, a bonded body 6 is obtained.

[0051] The bonded body 6 thus obtained may be provided with the aforementioned cutout portion 2. The ceramic substrate 1 provided with the aforementioned cutout portion 2 may be provided with a conductor portion 4. The conductor portion 4 to which a circuit shape has been previously imparted may be bonded to the ceramic substrate 1. After the conductor portion 4 is bonded to the ceramic substrate 1, the conductor portion 4 may be imparted with a circuit shape. Here, the bonded body 6 in which the conductor portion 4 has been imparted with a circuit shape is also referred to as a ceramic circuit substrate.

[0052] The side surfaces of the conductors described above preferably have an inclined shape. That is, the side surfaces of the copper members preferably are inclined with respect to the in-plane direction and the thickness direction. The in-plane direction is a direction parallel to the bonding surface between the ceramic substrate 1 and the conductors. The thickness direction is a direction connecting the ceramic substrate 1 and the conductors, and is perpendicular to the in-plane direction. The conductors are preferably made of copper members.

[0053] The thickness of the bonding layer 5 is preferably in the range of 10 μm to 60 μm. The ceramic circuit board preferably has a shape in which the bonding layer 5 protrudes from the side surface of the conductor portion. The protruding part of the bonding layer 5 is called the bonding layer protrusion portion. The ratio (L / T) of the length L to the thickness T of the bonding layer protrusion portion is preferably in the range of 0.5 to 3.0. The thickness of the bonding layer protrusion portion is the thickness of the thickest part of the bonding layer protrusion portion. The length of the bonding layer protrusion portion is the length of the longest part of the bonding layer protrusion portion that protrudes from the side surface of the conductor portion. The thickness and length of the bonding layer protrusion portion are measured from any cross section of the ceramic copper circuit board. By providing a sloped shape to the conductor portion and providing a bonding layer protrusion portion, the TCT characteristics of the ceramic copper circuit board can be improved.

[0054] Examples of the bonding layer 8 used to bond the plating film 9 to the semiconductor element 7 or the conductor portion 4 to the semiconductor element 7 include a bonding layer using copper or tin, and a bonding layer using solder paste or silver paste. Although Fig. 11 shows a structure in which the plating film 9 is provided, the plating film 9 does not necessarily have to be provided.

[0055] The ceramic substrate 1 is preferably a silicon nitride substrate with a thickness of 0.4 mm or less, and the thickness of the conductor portion is preferably 0.6 mm or more. A thin silicon nitride substrate with a thickness of 0.4 mm or less is effective in reducing the thermal resistance of the ceramic substrate. A thick copper plate with a thickness of 0.6 mm or more improves heat dissipation. Furthermore, a silicon nitride substrate with a three-point bending strength of 600 MPa or more is more likely to achieve this effect. Therefore, a silicon substrate with a thickness of 0.4 mm or less may be combined with a thick copper plate with a thickness of 0.6 mm or more.

[0056] A manufacturing method according to an embodiment of the present invention will be described.

[0057] The method for forming the cutout portion 2 can be selected arbitrarily as long as it can form the above-described cutout portion 2. Examples of methods for forming the cutout portion 2 include cutting a portion of the ceramic substrate 1 with a laser, applying pressure to the ceramic substrate 1 while it is still a green sheet to create a recess, and cutting out a portion of the ceramic substrate 1 with a jigsaw. Among these, the method using a laser is more preferable. When the cutout portion 2 is formed by laser processing, a clear visual difference that can be observed with an SEM occurs in the ceramic substrate. Therefore, whether the cutout portion 2 was formed by laser processing can be determined by observing the cutout portion 2 with an SEM. The clear visual difference that can be observed with an SEM is due to the thermal effect that occurs during laser processing. The thermally affected portion may be partially removed when honing or the like is performed. Therefore, when the above-described laser processing marks are observed in a portion of the cutout portion 2 (at least a portion of the side surface of the cutout portion 2), it can be determined that the cutout portion 2 was formed by laser processing.

[0058] When forming the cutout portion 2 in the ceramic substrate 1, it is preferable to use a high laser energy density. A high laser energy density allows for a faster scanning speed. Furthermore, when forming the cutout portion 2 using a laser, the cutout portion 2 can be formed with high positional accuracy. Furthermore, by forming the cutout portion 2 by laser processing, when the shape of the cutout portion 2 is viewed from the side of the ceramic substrate 1, it is possible to form a shape in which the surface side is open toward the center of the substrate. The laser used is not particularly limited, but is preferably one or more selected from the group consisting of CO2 laser, YAG laser (fundamental, second harmonic, third harmonic, or fourth harmonic), femtosecond laser, picosecond laser, semiconductor laser, LD laser, excimer laser, YVO4 laser, and DDL laser. Among these lasers, it is more preferable to use one or more selected from the group consisting of CO2 laser and fiber laser.

[0059] In the method of forming the cutout portion 2 by laser processing, the cutout portion 2 may be formed by a single laser irradiation or multiple laser irradiations. Dust collection or assist gas may be used as needed. The laser may be irradiated from only one side of the ceramic substrate 1 or from both sides of the ceramic substrate 1. When irradiating the ceramic substrate 1 with the laser from both sides, positional accuracy relative to the initial irradiation surface becomes important. Therefore, it is more preferable to irradiate the ceramic substrate 1 with the laser from only one side. To form the cutout portion 2, a continuous groove may be formed, or the laser may be irradiated in a dot pattern. Of the continuous groove and dot patterns, a continuous groove is preferable. A continuous groove makes it easier to separate the cutout portion 2 from the ceramic substrate 1. The laser output mode may be pulsed or CW (continuous wave), or a combination of both. Multiple irradiations may be used to penetrate the substrate.

[0060] When a groove is formed by a laser, it is preferable that the maximum depth of the groove is controlled with respect to the thickness of the substrate. Let the thickness of the substrate be t and the maximum depth of the groove be d. In this case, it is preferable that 0.5 < d / t ≦ 1. Here, the maximum depth of the groove, when the laser is irradiated from both the front and back surfaces of the ceramic substrate 1, is represented by the total value. Further, it is more preferable that 0.7 ≦ d / t ≦ 1.0. Even more preferably, d / t is 1.0. That is, even more preferably, the formed groove exists across both the front and back surfaces. It is even more preferable that the depth d of the groove is always 1.0 with respect to the thickness t of the substrate (the groove penetrates). After the groove is formed by the laser, in order to form the notch portion 2, a separation process for separating the notch portion 2 side from the ceramic substrate 1 is performed. By making the groove depth deeper than a certain level with respect to the substrate thickness and forming the groove, it is not necessary to apply excessive pressure to obtain the shape of the notch portion 2 in the separation process. For this reason, the cost can be reduced. Further, when forming the notch portion 2, by penetrating the groove by laser processing, the generation of burrs can be suppressed. It is also preferable to adjust the condensing diameter of the laser. By adjusting the condensing diameter, energy density, etc., the influence of laser irradiation can be reduced to a certain extent, and the surface roughness of the side surface portion of the notch portion 2 can be controlled.

[0061] The surface roughness of the side surface portion of the ceramic substrate 1 and the surface roughness of the side surface portion of the notch portion 2 may be different. Preferably, when the Ra of the notch portion and the side surface portion are each measured at 5 locations, the difference between the average value of the substrate side surface portion and the average value of the side surface portion of the notch portion 2 is 3.0 μm or less. Honing may be performed on the ceramic substrate 1 as necessary. Honing may be performed before forming the notch portion 2 or after forming the notch portion 2, as long as it is a sintered ceramic substrate.

[0062] The timing of forming the cutout portion 2 is not particularly limited. If the cutout portion 2 is formed in the green sheet, the positional accuracy of the cutout portion 2 may be reduced during the subsequent sintering process. Therefore, it is preferable to form the cutout portion 2 after sintering. The cutout portion 2 may be formed after or before the conductor portion 4 is joined. If the cutout portion 2 is provided at a corner, as shown in Figure 7, the substrate portion will have a sharpened shape. If a screw hits the open end during screw fastening, the ceramic substrate 1 may be chipped. For this reason, a structure in which the cutout portion 2 is provided at a corner is not preferred.

[0063] When forming the cutout portion 2 in the ceramic substrate 1 using a laser, it is preferable to form the cutout portion 2 so that the width of the opening OP side of the cutout portion 2 is wider than the width of the end portion not on the opening side. More specifically, regarding the shape of the cutout portion 2, when the distance parallel to the line connecting the opening ends is defined as the "width," the average width of the entire cutout portion 2 is defined as Wa. The width of the opening is defined as Wo. In this case, it is preferable to satisfy 1.01≦Wo / Wa≦5.0. It is more preferable to satisfy 1.2≦Wo / Wa≦4.0. Even more preferably, it is preferable to satisfy 1.5≦Wo / Wa≦3.5. Controlling the width of the cutout portion 2 as described above prevents the opening from becoming too wide and allows the degree of opening of the opening shape to be controlled. This makes it easier to achieve the effect of controlling the angle of the portion of the opening where the substrate is located. Furthermore, controlling the shape of the cutout portion 2 can increase the torque required for screw fastening.

[0064] FIG. 16 is a flowchart illustrating a manufacturing method according to the embodiment. FIG. 16 shows a preferred example of a manufacturing method according to an embodiment. First, a ceramic substrate 1 is prepared (step St1). The ceramic substrate 1 can be produced by the method described above. A cutout portion 2 is formed in the prepared ceramic substrate 1 (step St2). This results in a ceramic substrate 1 having the cutout portion 2. Next, a conductor portion 4 is bonded to the ceramic substrate 1 (step St3). The conductor portion 4 is etched to give it a circuit shape (step St4). This results in a ceramic circuit substrate. Next, a semiconductor element 7 is mounted on the conductor portion 4 (step St5). This results in a semiconductor device 10. Finally, a screw is passed through the cutout portion 2 and the semiconductor device 10 is fixed by screwing (step S6). As described above, the order of each step and the specific processing performed in each step can be changed as appropriate.

[0065] From another perspective, the ceramic substrate 1 according to the embodiment of the present invention has a front surface 1a (first main surface) and a back surface 1b (second main surface) as shown in FIG. 10. The back surface 1b is located opposite to the front surface 1a. The ceramic substrate 1 has side surfaces s1 to s4 as shown in FIG. 1. The side surfaces s1 to s4 are continuous with the front surface 1a and the back surface 1b. The side surfaces s1 to s4 are parallel to the thickness direction connecting the front surface 1a and the back surface 1b. In the illustrated example, the side surfaces s1 and s2 are parallel to each other, and the side surfaces s3 and s4 are parallel to each other. The cutout portion 2 is provided in at least one of the side surfaces s1 to s4 and penetrates the ceramic substrate 1 from the front surface 1a to the back surface 1b. In the example shown in FIG. 1, one of the multiple cutout portions 2 has a first surface 2a and a second surface 2b that are continuous with the side surface s1 of the ceramic substrate 1. The first surface 2a and the second surface 2b are at least a part of the side surfaces of the cutout portion 2. The first surface 2a and the second surface 2b are parallel to the thickness direction of the ceramic substrate 1 and are inclined with respect to the side surface s1. The first surface 2a and the second surface 2b face each other in a direction parallel to the side surface s1. The width of the cutout portion 2 narrows as it moves away from the side surface s1. The first opening end P1 is located between the side surface s1 and one end of the first surface 2a. The second opening end P2 is located between the side surface s1 and one end of the second surface 2b. The width of the cutout portion 2 corresponds to the distance between the first surface 2a and the second surface 2b in a direction parallel to the side surface s1.

[0066] As shown in FIG. 1, the cutout portion 2 may further include a third surface 2c. The third surface 2c is continuous with the first surface 2a and the second surface 2b and is located between the other end of the first surface 2a and the other end of the second surface 2b. In the example shown in FIGS. 1 and 2, the third surface 2c is parallel to the side surface s1. The angle θ1 is also the angle between the line Li and the first surface 2a. The angle θ2 is also the angle between the first surface 2a and the third surface 2c, or the angle between the second surface 2b and the third surface 2c. The angle θ3 is also the angle between the side surface s1 at the first opening end P1 and the first surface 2a, or the angle between the side surface s1 at the second opening end P2 and the second surface 2b.

[0067] In the examples shown in FIGS. 3 and 4, the cutout portion 2 does not have a third surface 2c. In the structure shown in FIG. 3, the angle θ2 is the angle between the first surface 2a and the second surface 2b. The first surface 2a and the second surface 2b may be flat as shown in FIGS. 1 to 3 or curved as shown in FIG. 4. In the structure shown in FIG. 4, the other end of the first surface 2a and the other end of the second surface 2b are connected. As shown in FIGS. 5 and 6, the cutout portion 2 may have a concave surface 2d recessed toward the center of the ceramic substrate 1. The first surface 2a and the second surface 2b are connected to the concave surface 2d. The angle θ4 is also the angle between the other end of the first surface 2a and one end of the concave surface 2d, or the angle between the other end of the second surface 2b and the other end of the concave surface 2d. Furthermore, the length L3 shown in FIG. 12 is also the distance between a portion of the first surface 2a and a portion of the second surface 2b. The portion of the first surface 2a and the portion of the second surface 2b face each other in a direction parallel to the side surface s1. The length L4 is also the distance between another portion of the first surface 2a and another portion of the second surface 2b. The other portion of the first surface 2a and the other portion of the second surface 2b face each other in a direction parallel to the side surface s1. The portion of the first surface 2a is located on the front surface 1a side of the other portion of the first surface 2a. The portion of the second surface 2b is located on the front surface 1a side of the other portion of the second surface 2b.

[0068] (Example) (Examples 1 to 6, Comparative Examples 1 and 2) Table 1 lists the types and thicknesses of the ceramic substrates used. The thermal conductivity of the silicon nitride substrate is 90 W / m·K and the three-point bending strength is 700 MPa. The thermal conductivity of the aluminum nitride substrate is 170 W / m·K and the three-point bending strength is 400 MPa. The thermal conductivity of the alumina (aluminum oxide) substrate is 25 W / m·K and the three-point bending strength is 450 MPa. The thermal conductivity of the zirconia (zirconium oxide) substrate is 25 W / m·K and the three-point bending strength is 500 MPa. The thermal conductivity of the aluminium substrate is 25 W / m·K and the three-point bending strength is 550 MPa. A fiber laser with a wavelength of 0.1 μm (rounded to one decimal place) was used to form the notch 2.

[0069] [Table 1]

[0070] Table 2 shows the shapes of the cutout portion 2 in the examples and comparative examples listed in Table 1. Table 2 lists the angle θ1 of the opening end on the cutout portion 2 side, the angle θ2 of the end of the cutout portion 2 that is not on the opening side, the angle θ3 of the opening end on the ceramic substrate 1 side, the shape of the end of the cutout portion 2 that is not on the opening side, the angle of the boundary between portion C and the opening, and L2 / L1. For angle θ2, examples listed as 90 degrees or more indicate that the end of the cutout portion 2 that is not on the opening side was rounded. Furthermore, in the case of an R-shape, the inflection point can be used as the reference point for the substrate portion, so it can be seen that angle θ2 is large, exceeding 90 degrees.

[0071] Specifically, angle θ1 is the angle on the cutout side of the opening end of ceramic substrate 1, and is the angle of the portion of cutout portion 2 where no substrate is present (the notched portion). Angle θ2 refers to the angle of the portion of end P3 of cutout portion 2 that is not on the opening side where ceramic substrate 1 is not present. Angle θ3 is the angle on the side of the opening end where ceramic substrate 1 is present.

[0072] The shape of the end of the cutout portion 2 that is not on the opening side refers to the shape of the portion including P3. A U-shape is described as an R-shape (approximately U-shape). An approximately trapezoidal shape is described as a C-shape. A V-shape is described as an approximately V-shape. In Table 2, the angle of the boundary between the C portion and the opening refers to the shape of the boundary between the C portion and the R portion or the boundary between the C portion and the approximately V-shaped portion. If the boundary was curved, it was described as "no boundary." [Table 2]

[0073] One hundred ceramic substrates 1 each having four cutouts 2 formed therein were prepared for each example. After each ceramic substrate 1 was screwed, the positional accuracy of the screwed portions was measured. The positional accuracy during screwing was measured. An example in which the positional accuracy defect rate was 2% or less was marked with "Good." An example in which the positional accuracy defect rate was greater than 2% and less than or equal to 3% was marked with "Good." An example in which the positional accuracy defect rate was greater than 2% and less than or equal to 3% was marked with "Poor." An example in which the positional accuracy defect rate exceeded 3% was marked with "Poor." The area occupied by the cutouts 2 was also measured, and the increase compared to Example 1 was measured. The increase was calculated by setting the increase between the maximum area occupied by the cutouts 2 in the examples and the area occupied by the cutouts 2 in Example 1 as 100. An example in which the increase was greater than 0 and less than 50 was marked with "Good." An example in which the increase was greater than 50 and less than 100 was marked with "Good." The results of the increase are shown in Table 3. The positional accuracy defect rate of the screw fastening portion and the occupied area of ​​the cutout portion were measured at 400 locations (100 ceramic substrates x 4 cutouts per ceramic substrate), counting each additional cutout portion as "1" compared to Example 1, and the percentage of increase was calculated. This area increase rate is a value obtained by comparing the percentage of the cutout shape for fixing screws of the same size to substrates of the same size.

[0074] Furthermore, for 100 ceramic substrates 1 according to each example, the presence or absence of cracks and breakage was examined on the laser-processed surface and fracture surface of the cutout portions 2 provided in four locations per substrate. That is, the presence or absence of cracks and breakage was examined in 400 cutout portions 2. The presence or absence of burrs exceeding the tolerance was also examined on the side surfaces of the cutout portions 2. The incidence of burrs, chips, and cracks was examined for each example.

[0075] [Table 3]

[0076] Table 3 shows that the ceramic substrate of the example reduces the occurrence of burrs, chips, or cracks when forming the cutout compared to the conventional structure with right-angled edges. Furthermore, in the example, screws can be fastened with good positioning accuracy. By limiting the increase in the area of ​​the cutout, the area of ​​the surface on which a semiconductor element can be mounted can be maintained.

[0077] Table 4 shows the results of measuring the arithmetic surface roughness Ra and maximum surface roughness Rz of the side of the cutout. The side of the cutout 2 refers to the surface of the cutout 2 that is parallel to the thickness direction of the substrate. The shape of the cutout 2 refers to the shape of the cutout 2 when viewed from above. The opening edge refers to the shape of the side of the opening where the substrate is present.

[0078] [Table 4]

[0079] As can be seen from Tables 2, 3, and 4, for ceramic substrates with an opening edge angle θ3 of greater than 90 degrees, no chipping or cracking occurred when screwed in. This shows that controlling the shape of the substrate's cutout portion laterally also contributes to increasing the yield when screwing in. [Explanation of symbols]

[0080] 1...Ceramic substrate 2...Notch 3...Through hole 4...Conductor 5…Active metal bonding layer 6…Zygote 7...Semiconductor element 8... Bonding layer (between semiconductor element and conductor) 9...Plating film 10...Semiconductor device θ1: Angle between the opening ends and the notch θ2: Angle of the end not on the opening side θ3: The inner angle of the substrate at the edge of the notch θ4: The angle at the boundary between the R section and the opening, or the angle at the boundary between the C section and the opening P1...first open end P2: Second open end P3: Edge not on the opening side P4: Midpoint between the open ends P5: The farthest intersection of the perpendicular line drawn from the midpoint between the opening ends and the board P6: Intersection of a perpendicular line drawn from the midpoint between the opening ends and the cutout portion having the opening

Claims

1. A first step of preparing a ceramic substrate having a front surface and a back surface and having one or more notched portions for screw fastening including an opening; a second step of joining a conductor portion to the ceramic substrate via a joining layer containing one or both of copper and silver and an active metal; a third step of providing a circuit shape to the conductor portion; a fourth step of mounting a semiconductor element on the conductor portion to which the circuit shape has been imparted, thereby fabricating a semiconductor device including the ceramic and the semiconductor element; a fifth step of fixing the semiconductor device by fastening screws through the notches, In the prepared ceramic substrate, the angle of the edge of the opening at the point where the ceramic substrate exists when viewed from the surface (θ ３ ) at least one of the angles is greater than 90 degrees.

2. 2. The method for manufacturing a semiconductor module according to claim 1, wherein in the prepared ceramic substrate, the shape of the end of the cutout portion not on the opening side is approximately U-shaped, approximately trapezoidal, or approximately V-shaped, and when the shape of the end not on the opening side is approximately V-shaped, the angle of the end on the cutout side is 70 degrees or more.

3. 3. The method for manufacturing a semiconductor module according to claim 1, wherein the ceramic substrate is provided with an R portion or a C portion at a location other than the opening side of the notch.

4. 3. The method for manufacturing a semiconductor module according to claim 1, wherein the ceramic substrate has an end portion opposite to the opening side of the notch portion that is substantially U-shaped.

5. 3. The method for manufacturing a semiconductor module according to claim 1, wherein in the ceramic substrate to be prepared, a portion between an end of the cutout portion not on the opening side and an end of the opening is curved or linear.

6. In the ceramic substrate, the side surface of the notch portion is a first surface that is continuous with a first side surface of the ceramic substrate, the first side surface having the opening of the notch portion; a concave surface that is continuous with the first surface and is recessed toward the center of the ceramic substrate; and The angle (θ ３ ) is the angle between the first side surface and one end of the first surface; 3. The method for manufacturing a semiconductor module according to claim 1, wherein an angle between the other end of said first surface and said concave surface on the side where the substrate is present is 90 degrees or more.

7. 3. The method for manufacturing a semiconductor module according to claim 1, wherein the ceramic substrate has an arithmetic mean roughness Ra of 1.2 [mu]m or less on the side surface of the notch.

8. 3. The method for manufacturing a semiconductor module according to claim 1, wherein the side surface of the cutout portion of the prepared ceramic substrate has an open portion on at least one surface side.

9. 3. The method for manufacturing a semiconductor module according to claim 1, wherein, in the ceramic substrate provided, a midpoint between the two opening ends of the cutout portion is defined as P4 in a straight line connecting the two opening ends of the two opening ends, a perpendicular line perpendicular to the straight line is drawn from the midpoint P4, and an intersection point P5 is defined as an intersection point of the ends of the ceramic substrate that is farthest from the midpoint P4, a distance L1 is defined as L1, an intersection point P6 is defined as P6 and a length of the cutout portion defined as the distance between the intersection point P6 and the midpoint P4 is L2, and L2 / L1 is 0.1 or more and 0.4 or less.

10. 3. The method for manufacturing a semiconductor module according to claim 1, wherein the ceramic substrate is a nitrogen-containing ceramic substrate.

11. In the prepared ceramic substrate, the angle of the edge of the opening at the point where the ceramic substrate exists when viewed from the surface (θ ３ ) at least one of the points is 100 degrees or more, The arithmetic mean roughness Ra of the side surface of the cutout portion is 0.4 μm or more and 1.2 μm or less, The maximum surface roughness Rz of the side surface of the notch is 2.0 μm or less, 3. The method for manufacturing a semiconductor module according to claim 2, wherein P4 is the midpoint between the two opening ends of the cutout portion in a straight line connecting the two opening ends, and when a perpendicular line is drawn from the midpoint P4 so as to be perpendicular to the straight line connecting the opening ends, P5 is the intersection point of the ends of the ceramic substrate that intersects with the perpendicular line and is farthest from the midpoint P4, L1 is the distance between the midpoint P4 and point P5, P6 is the intersection point of the perpendicular line and the cutout portion having the opening, and L2 is the length of the cutout portion defined by the distance between the intersection point P6 and the midpoint P4, and L2 / L1 is 0.1 or more and 0.4 or less.

12. a first step of forming one or more notches for screw fastening, including openings, in a ceramic substrate having a front surface and a back surface using a laser, the notches being formed such that the width of the opening side of the notch is wider than the width of an end of the notch that is not on the opening side; a second step of joining a conductor portion to the ceramic substrate; a third step of providing a circuit shape to the conductor portion; a fourth step of mounting a semiconductor element on the conductor portion to which the circuit shape has been imparted, thereby fabricating a semiconductor device including the ceramic and the semiconductor element; a fifth step of fixing the semiconductor device by screwing into the notch, In the ceramic substrate prepared in the first step, the angle (θ ３ ) at least one of the angles is greater than 90 degrees.

13. In the prepared ceramic substrate, the maximum width when viewed from the side of the notch portion is defined as L3, When the smallest width of the opening width of the notch portion including the maximum width L3 is L4, 3. The method for manufacturing a semiconductor module according to claim 1, wherein 0.5≦L4 / L3≦1.

14. The ceramic substrate is provided with two or more notched portions for screw fastening, The angle (θ ３ 3. The method for manufacturing a semiconductor module according to claim 1, wherein the angle θ is greater than 120 degrees.

15. the ceramic substrate is a silicon nitride substrate, 3. The method for manufacturing a semiconductor module according to claim 1, wherein the conductor portion is made of a copper material or an aluminum material.

16. 3. The method for manufacturing a semiconductor module according to claim 1, wherein in the fifth step, the ceramic substrate of the semiconductor device is screwed to a support plate through the cutout portion, thereby manufacturing a semiconductor module including the semiconductor device and the support plate.

17. A silicon nitride substrate having a front surface, a back surface, a first side surface, and a second side surface opposite to the first side surface, a notch for screw fastening is provided at one location on each of the first side surface and the second side surface; The cutout portion has an opening, The angle (θ ３ ) is 120 degrees or more and 150 degrees or less, the shape of the end of the cutout portion not on the opening side is a substantially U-shape, a substantially trapezoidal shape, or a substantially V-shape, and if the shape of the end not on the opening side is the substantially V-shape, the angle of the end on the cutout side is 70 degrees or more; The arithmetic mean roughness Ra of the side surface of the cutout portion is 0.4 μm or more and 1.2 μm or less, The maximum surface roughness Rz of the side surface of the notch is 2.0 μm or less, In a line connecting the two opening ends of the cutout portion, the midpoint between the ends is defined as P4, and when a perpendicular line is drawn from the midpoint P4 so as to be perpendicular to the line connecting the opening ends, the intersection point of the ends of the silicon nitride substrate that intersects with the perpendicular line is defined as P5, the distance between the midpoint P4 and the point P5 is defined as L1, the intersection point between the perpendicular line and the cutout portion having the opening is defined as P6, and the length of the cutout portion defined as the distance between the intersection point P6 and the midpoint P4 is defined as L2, where L2 / L1 is 0.1 or more and 0.4 or less, The side surface of the cutout portion is a first surface continuous with the first side surface or the second side surface; a concave surface that is continuous with the first surface and is recessed toward the center of the silicon nitride substrate; and The angle (θ ３ ) is the angle between the first side surface or the second side surface and one end of the first surface, A silicon nitride substrate, wherein the angle between the other end of the first surface and the concave surface on the substrate side at the boundary is 90 degrees or more.

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