Ceramic copper circuit board and semiconductor device using same

Abstract

A ceramic copper circuit board according to the present invention is a ceramic copper circuit provided with a ceramic substrate and a copper circuit part provided on the ceramic substrate, and is characterized in that: in a cross section of the copper circuit part parallel to a first direction from the ceramic substrate toward the copper circuit part, the thickness of the copper circuit part is greater than the thickness of the copper circuit part; an arbitrary line parallel to the first direction intersects a plurality of copper crystal grains, and an average of a plurality of distances in a second direction perpendicular to the first direction between an end of each of the copper crystal grains and the line is 300 [mu] m or less.

Description

[0001] This application is a divisional application of the invention patent application with Chinese national application number 202080019221.7 filed on April 2, 2020, and invention name “Ceramic copper circuit substrate and semiconductor device using the same”. Technical Field

[0002] Embodiments generally relate to a ceramic copper circuit substrate and a semiconductor device using the same. Background Art

[0003] Ceramic copper circuit substrates are used in semiconductor devices equipped with semiconductor elements such as power elements. The ceramic substrate and the copper circuit portion are bonded to each other via a bonding layer. For the bonding layer, a silver (Ag) solder containing active metals such as titanium (Ti) is used. As a result, the bonding strength and thermal cycle characteristics are improved. With the improvement of reliability, ceramic copper circuit substrates are used in automobiles (including electric vehicles), electric railway vehicles, solar power generation equipment, inverters for industrial machinery, etc.

[0004] In semiconductor devices such as power modules, semiconductor elements are mounted on copper circuits. In addition, wire bonding or metal terminals are sometimes bonded to make the semiconductor elements conductive. In the manufacture of semiconductor devices, semiconductor elements, wire bonding, metal terminals, etc. are bonded to copper circuits.

[0005] As power modules are miniaturized, lightweighted, and mounted at high densities, the copper circuit portion becomes thicker in order to reduce thermal resistance and inductance. Ceramic copper circuit substrates with thick copper circuit portions are described in International Publication No. WO2018-180965 (Patent Document 1). Patent Document 1 improves the assemblability of ceramic copper circuit substrates by optimizing the number of grain boundaries on the surface of the copper circuit board. According to the ceramic copper circuit substrate of Patent Document 1, the bonding and alignment accuracy of semiconductor elements are improved.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: International Publication No. 2018-180965 Summary of the invention

[0009] Problems to be solved by the invention

[0010] On the other hand, in addition to the above-mentioned bonding or alignment accuracy, the problem caused by the thickening of the copper circuit portion becomes obvious. For example, in order to improve the reliability of the product, it is expected to achieve fine patterning of the copper circuit portion, as a stress relaxation of the circuit substrate as a whole, etc. In patent document 1, the main focus is on controlling the particle size on the surface of the copper circuit portion, but it is known that the particle size on the surface and inside is different due to the thickening of the copper circuit. That is, if the surface of the copper circuit is controlled, the bonding and alignment accuracy of the copper plate surface can be improved, but it is determined that in order to improve other characteristics such as fine patterning, it is necessary to control the inside of the copper circuit.

[0011] In recent years, power semiconductor modules have been miniaturized, lightweighted, and mounted at high density. As a result, the metal circuit portion is required to be thicker in order to reduce the thermal resistance and inductance of the metal circuit portion. In addition, fine patterning of the metal circuit portion is required to increase the mounting density.

[0012] Furthermore, as the junction temperature (Tj) of the power semiconductor chip increases, the reliability of the ceramic circuit substrate is also required to be improved.

[0013] The embodiment is a means for solving such a problem, and relates to a ceramic copper circuit substrate capable of making the circuit more miniaturized and improving the reliability of the ceramic circuit substrate.

[0014] Means for solving problems

[0015] The ceramic copper circuit substrate of the embodiment includes a ceramic substrate and a copper circuit portion. The copper circuit portion is provided on the first surface of the ceramic substrate. In a cross section of the copper circuit portion parallel to a first direction from the ceramic substrate toward the copper circuit portion, any line parallel to the first direction intersects with a plurality of copper crystal grains. An average of a plurality of distances in the second direction between the ends of each of the copper crystal grains in a second direction perpendicular to the first direction and the line is 300 μm or less. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a diagram showing an example of a ceramic copper circuit board according to an embodiment.

[0017] Figure 2 This is a diagram showing an example of a cross section of a copper circuit portion.

[0018] Figure 3 This is a diagram showing an example of a cross section of a copper circuit portion.

[0019] Figure 4 This is a diagram showing an example of the pattern size and the size between patterns of a copper circuit.

[0020] Figure 5FIG. 1 is a diagram showing an example of a semiconductor device according to an embodiment. DETAILED DESCRIPTION

[0021] The ceramic copper circuit substrate of the embodiment includes a ceramic substrate and a copper circuit portion. The copper circuit portion is provided on the first surface of the ceramic substrate. In a cross section of the copper circuit portion parallel to a first direction from the ceramic substrate toward the copper circuit portion, any line parallel to the first direction intersects with a plurality of copper crystal grains. An average of a plurality of distances in the second direction between the ends of each of the copper crystal grains in a second direction perpendicular to the first direction and the line is 300 μm or less.

[0022] Figure 1 An example of a ceramic copper circuit substrate. Figure 1 In the figure, 1 is a ceramic copper circuit substrate. 2 is a ceramic substrate. 3 is a copper circuit portion. 4 is a bonding layer containing solder. 5 is a back copper plate. The ceramic substrate 2 has a surface 2a (first surface) and a back surface 2b. The copper circuit portion 3 is bonded to the surface 2a of the ceramic substrate 2 via a bonding layer 4 (an example of the first bonding layer). Figure 1 In the example, a plurality of copper circuit portions 3 are bonded to the surface 2a via a plurality of bonding layers 4. The embodiment is not limited to the illustrated form. Alternatively, one copper circuit portion 3 or three or more copper circuit portions 3 may be bonded to the surface 2a. Figure 1 In the example of , the back copper plate 5 is bonded to the back surface 2b. The back copper plate 5 is not a circuit, but functions as a heat sink. The back copper plate 5 is appropriately provided as needed. Instead of the back copper plate 5, a patterned copper circuit portion may be provided on the back surface 2b.

[0023] The ceramic substrate 2 is preferably any one of an alumina substrate, an aluminum nitride substrate, and a silicon nitride substrate. In addition, an alusil substrate can be used. Alusil is a sintered body containing 20 to 80% alumina and the remainder zirconium oxide.

[0024] The three-point bending strength of aluminum nitride substrates or aluminum oxide substrates is about 300 to 450 MPa. The strength of Alusil high-silicon heat-resistant aluminum alloy substrates is also about 550 MPa.

[0025] The three-point bending strength of the silicon nitride substrate can be increased to more than 600MPa, and further more than 700MPa. In addition, the thermal conductivity of the silicon nitride substrate can be increased to more than 50W / (m·K), and further more than 80W / (m·K). In recent years, in particular, there are silicon nitride substrates that have both high strength and high thermal conductivity. The thickness of the silicon nitride substrate is preferably less than 0.635mm, and more preferably less than 0.3mm. Since the silicon nitride substrate has high strength, it can be thinned, which can further improve the heat dissipation. The lower limit of the thickness is not specifically set, but it is preferably more than 0.1mm. This is to ensure the electrical insulation of the silicon nitride substrate. Here, the thickness refers to the dimension in the direction connecting the ceramic substrate 2 and the copper circuit portion 3.

[0026] The ceramic copper circuit substrate of the embodiment may include one ceramic substrate or two or more ceramic substrates. For example, a plurality of ceramic substrates and a plurality of copper circuit portions may be alternately stacked in the first direction.

[0027] Figure 2 This is a diagram showing an example of a cross section of a copper circuit portion. Figure 2 yes Figure 1 An enlarged cross-sectional view of part A. Figure 2 In FIG. 8 , 7 denotes an arbitrary imaginary line. The line is parallel to a first direction from the ceramic substrate 2 toward the copper circuit portion 3 . Figure 2 , D1 represents the first direction. In addition, the line is perpendicular to the surface 2a and the back surface 2b. 8 represents the side etching amount. The side etching amount is the distance in a direction perpendicular to the first direction between the outer periphery of the surface 3a of the copper circuit portion and the outer periphery of the back surface 3b of the copper circuit portion.

[0028] The copper circuit portion is made of polycrystalline copper. The method of drawing line 7 is as follows. First, cut the ceramic copper circuit substrate parallel to the first direction D1. Take an enlarged photograph of the cross section. At this time, the enlarged photograph is taken to an extent that the ceramic substrate can be photographed and the grain boundary can be confirmed. Then, in the enlarged photograph, by drawing an arbitrary straight line perpendicular to the surface 2a, line 7 is obtained. In addition, in the case where the state of the surface 2a of the ceramic substrate surface is ambiguous and the back side 3b of the copper circuit portion 3 is regarded as a surface parallel to the surface 2a, an arbitrary straight line perpendicular to the back side 3b can also be treated as line 7.

[0029] Figure 3 An example of a cross-sectional view showing the interior of a copper circuit portion. Figure 3 Yes Figure 2 The cross section of the B part of FIG. 10 is a copper grain, and 11 is a grain boundary of the copper grain. In the cross section of the copper circuit part, an arbitrary line 7 is drawn in the vertical direction (the thickness direction of the substrate) relative to the ceramic substrate surface. Figure 312 represents the distance LH in the second direction D2 from the outer edge (grain boundary 11) of the copper crystal grain 10 farthest from any line 7 among the copper crystal grains 10 intersected by the line 7. 13 represents the length LV between the first end 10a and the second end 10b, which are the intersections of the line 7 and the outer edge of the copper crystal grain 10. The second direction is perpendicular to the first direction and parallel to the cross section.

[0030] In the ceramic copper circuit board of the embodiment, the average of the distance LH is 300 μm or less. The average of the length LV is preferably 300 μm or less.

[0031] In ceramic substrates and ceramic copper circuit substrates with copper circuit parts bonded to ceramic substrates, after bonding a copper plate to the entire surface or a portion of the ceramic substrate, circuits are mostly formed by etching the copper plate portion. In the dissolution of the copper plate by etching, the copper plate is dissolved along the crystal grain boundaries of the copper plate. Therefore, the shape of the copper grains has a greater influence on etching. That is, when the grain size is large, it becomes easy to dissolve not only in the thickness direction where the etching solution gradually digs in, but also in the surface direction. The surface direction is a direction perpendicular to the first direction. The second direction is a direction parallel to the surface direction.

[0032] Regarding the plurality of copper crystal grains intersecting the line parallel to the first direction, the average of these distances LH being 300 μm or less indicates that the copper crystal grains with relatively small sizes in the second direction are arranged in the thickness direction. Thus, the progress of etching in the surface direction can be suppressed, and the amount of side etching caused by etching can be reduced. As a result, it becomes easy to form a fine pattern circuit.

[0033] The term "fine pattern circuit" as used herein refers to a circuit board in which the dimension between patterns is about 60 to 80% of that of a normal circuit. A circuit in which at least a portion of the circuit meets the dimension between patterns within this range is a fine pattern circuit. Figure 4 The pattern size 14 and the inter-pattern size 15 of the ceramic copper circuit substrate 1 are shown in FIG. The pattern size 14 indicates the width of the electrically conductive portion including the bonding layer 4. The inter-pattern size 15 indicates the size distance between the bonding layers 4 formed on the ceramic surface. Figure 4 In the example of , a plurality of copper plates 3 are bonded to the surface 2a of the ceramic substrate 2. The plurality of copper plates 3 are arranged side by side in the second direction D2 and are bonded to the ceramic substrate 2 via a plurality of bonding layers 4. The distance in the second direction D2 between the bonding layers 4 adjacent to each other in the second direction D2 corresponds to the pattern-to-pattern dimension 15.

[0034] For electrical conduction, bonding of semiconductor elements or metal terminals, wire bonding, etc., the width (pattern size) of the pattern is required to be above a specified value. For example, the pattern size when the copper plate thickness is 0.1 mm or more and less than 0.5 mm is preferably 0.5 mm or more. The pattern size when the copper plate thickness is 0.5 mm or more and less than 0.7 mm is preferably 0.7 mm or more. The pattern size when the copper plate thickness is 0.7 mm or more and less than 0.8 mm is preferably 1.0 mm or more.

[0035] Here, when the thickness of the copper plate is greater than 0.1 mm and less than 0.5 mm, in a conventional copper circuit substrate, the dimension between patterns is greater than 0.6 mm. In contrast, in a fine pattern circuit, the dimension between patterns is greater than 0.4 mm. Similarly, when the thickness of the copper plate is greater than 0.5 mm and less than 0.7 mm, in a conventional copper circuit substrate, the dimension between patterns is greater than 1.0 mm. In contrast, in a fine pattern circuit, the dimension between patterns is greater than 0.6 mm. When the thickness of the copper plate is greater than 0.7 mm and less than 0.8 mm, in a conventional copper circuit substrate, the dimension between patterns is greater than 1.8 mm. In contrast, in a fine pattern circuit, the dimension between patterns is greater than 1.1 mm.

[0036] In addition, by setting the average length LV in the copper circuit portion to less than 300 μm, the copper plate becomes easy to plastically deform. As a result, the stress generated in the ceramic copper circuit substrate as a joint body is relieved, the joint strength, substrate bending strength and heat cycle resistance are improved, and a ceramic circuit substrate with high reliability can be obtained.

[0037] In addition, in the ceramic copper circuit substrate, the particle size of the copper plate increases by heat treatment during joining. The coarsening of the particle size can also be controlled by controlling the additives in the copper or processing and adjusting the joining conditions such as the coarsening of the particles, but the manufacturing cost may increase due to the control. For example, by setting the distance LH and the length LV to more than 50 μm, a ceramic copper circuit substrate with good cost performance can be obtained. However, even the distance LH and the length LV below it can be manufactured, and the lower limit is not specified.

[0038] The copper circuit portion 3 will join semiconductor elements, etc. In order to reduce thermal resistance and inductance, the thickness of the copper circuit portion is preferably 0.5 mm or more, more preferably 0.8 mm or more. At this time, if the average distance LH inside the copper circuit portion is small, the side etching amount can be suppressed. Thus, a fine pattern can be formed. In addition, by stress relaxation of the joint body, the joint strength, substrate bending strength and heat cycle resistance are improved.

[0039] If the average distance LH inside the copper circuit portion exceeds 300 μm, the copper crystal grains inside the copper circuit portion become larger in the lateral direction, and the amount of side etching increases, thereby reducing the dimensional accuracy of the circuit pattern.

[0040] If the average length LV inside the copper circuit portion is greater than 300 μm, the plastic deformation of the copper circuit portion becomes small, resulting in increased stress in the bonded structure and a decrease in properties such as bonding strength.

[0041] Furthermore, if the distances LH and the lengths LV are adjusted to be less than 50 μm, the manufacturing cost will be increased due to the load caused by process control.

[0042] In addition, even when the average distance LH is less than 300 μm, if there are many copper crystal grains whose distance LH is greater than 400 μm, the side etching amount will also be uneven. The distance LH is preferably less than 400 μm. Similarly, even when the average length LV is less than 300 μm, if there are many copper crystal grains whose length LV is greater than 400 μm, the bonding strength will also be uneven. The length LV is preferably less than 400 μm.

[0043] As described above, at least one of the average distance LH and the average length LV of the copper crystal grains inside the copper circuit is preferably 300 μm or less. More preferably, both the average distance LH and the average length LV are preferably 300 μm or less. Furthermore, each distance LH and each length LV are preferably 400 μm or less. In this case, each distance LH is preferably 50 μm or more. Each length LV is preferably 50 μm or more. More preferably, each distance LH is 50 μm or more, and each length LV is 50 μm or more.

[0044] In addition, each distance LH is preferably 300 μm or less. Each length LV is preferably 300 μm or less. More preferably, each distance LH is 300 μm or less, and each length LV is 300 μm or less. At this time, each distance LH is preferably 70 μm or more. Each length LV is preferably 70 μm or more. More preferably, each distance LH is 70 μm or more, and each length LV is 70 μm or more.

[0045] In the ceramic copper circuit substrate of the embodiment, when an arbitrary straight line is drawn along the first direction in the cross section of the copper circuit portion 3, the distance LH and the length LV of the plurality of copper crystal grains intersecting the straight line are within the above range. That is, in the cross section of the copper circuit portion 3, no matter where the straight line is drawn, the distance LH and the length LV are within the above range. By forming a circuit on the ceramic substrate using the copper circuit portion 3, excellent reliability can be obtained.

[0046] In the case where the copper circuit portion is formed by processing a copper plate, the distance LH and the length LV can also be adjusted by adjusting the crystal size in the rolling process for adjusting the thickness of the copper plate. In addition, the crystal size can also be adjusted by adding trace elements to the copper plate. At this time, it is also possible to add trace elements such as tin (Sn) or zirconium (Zr) to the copper plate in advance to control grain growth. It is also possible to diffuse elements that inhibit grain growth in the copper plate into the copper plate during the bonding process when manufacturing the ceramic copper circuit substrate. Furthermore, the heat treatment process in the manufacturing process of the ceramic copper circuit substrate can also be utilized. The recrystallization temperature of copper is about 220°C. As described below, the copper plate is bonded to the ceramic substrate by active metal. In the active metal bonding method, the ceramic substrate and the copper plate are heated at 700 to 900°C. In this process, the copper plate is recrystallized. If recrystallized, the copper grains grow. By controlling this phenomenon, the size of the copper grains can also be adjusted.

[0047] In addition, the thickness of the copper circuit portion in the first direction is preferably 0.5 mm or more, more preferably 0.8 mm or more. By setting the thickness of the copper circuit portion to the above value, the effect of fine patterning during etching can be obtained more greatly. That is, the effect of the present invention can also be obtained when the thickness of the copper circuit portion is thinner than the above value. However, since the difference with the product manufactured by the previous method is not great, it is difficult to obtain the effect brought about by the present invention.

[0048] The thickness of the ceramic substrate is not particularly limited. By thinning the ceramic circuit substrate and thickening the copper circuit portion, heat dissipation is improved. The upper limit of the thickness of the copper circuit portion is not particularly limited, but is preferably less than 5 mm. If the thickness of the copper circuit portion exceeds 5 mm, the warping becomes larger when joining by the active metal joining method. As a result, it may become difficult to thin the ceramic substrate.

[0049] In addition, the ceramic substrate 2 and the copper circuit portion 3 are preferably joined via a bonding layer 4. In addition, when a back copper plate 5 is provided, the back copper plate 5 is preferably joined to the ceramic substrate 2 via a bonding layer. In addition, a bonding layer containing Ag (silver) and Ti (titanium) is preferably provided between the ceramic substrate and the copper circuit portion. The bonding layer containing Ag and Ti is formed using an active metal brazing filler metal. Ti is an active metal. As an active metal, in addition to Ti, Zr (zirconium) can also be listed. As an active metal brazing filler metal, a mixture of Ti, Ag and Cu (copper) can be listed. For example, the content of Ti is 0.1 to 10% by weight, the content of Cu is 10 to 60% by weight, and the remainder is Ag. In addition, in the case of controlling the particle size in the copper circuit portion by diffusion of the brazing filler metal during bonding, 1 to 15% by weight of one or more selected from the group consisting of In (indium), Sn (tin), Al (aluminum), Si (silicon), C (carbon) and Mg (magnesium) can also be added as needed. The active metal bonding method using active metal brazing filler metal is to apply active metal brazing filler metal paste on the surface of the ceramic substrate, and place a copper plate on it. It is heated at 700-900°C to bond. According to the active metal bonding method, the bonding strength between the ceramic substrate and the copper circuit part can be made to be 16kN / m or more.

[0050] In addition, a metal film having one selected from the group consisting of Ni (nickel), Ag (silver) and Au (gold) as a main component may be provided on the surface of the copper circuit. Examples of these metal films include plated films, sputtered films, etc. By providing the metal film, corrosion resistance, solder wettability, etc. can be improved.

[0051] Such a ceramic copper circuit substrate is suitable for a semiconductor device in which a semiconductor element is mounted on a copper circuit portion via a bonding layer.

[0052] Figure 5 An example of a semiconductor device is shown. Figure 5 In the figure, 1 is a ceramic copper circuit substrate, 16 is a semiconductor device, 17 is a semiconductor element, 18 is a bonding layer (an example of a second bonding layer), 19 is a wire bonding, and 20 is a metal terminal. Figure 5 In the embodiment, a semiconductor element 17 is bonded to the copper circuit portion of the ceramic copper circuit substrate 1 via a bonding layer 18. Similarly, a metal terminal 20 is bonded via the bonding layer 18. The semiconductor element of the adjacent copper circuit portion is connected to the copper circuit portion by wire bonding 19. The semiconductor device of the embodiment is not limited to such a structure. For example, either the wire bonding 19 or the metal terminal 20 may be provided. In addition, a plurality of semiconductor elements 17, wire bonding 19 and metal terminals 20 may be provided in the copper circuit portion 3, respectively. In addition, semiconductor elements, wire bonding or metal terminals 20 may be bonded to the back copper plate 5 as needed. In addition, various shapes such as a lead frame shape and a convex shape may be applied to the metal terminal 20.

[0053] In addition, for the bonding layer 18 bonding the semiconductor element 17 or the metal terminal 20, a solder, a brazing material, etc. are used. The solder is preferably a lead-free solder. In addition, the solder refers to a material with a melting point of 450°C or less. The brazing material refers to a material with a melting point exceeding 450°C. In addition, a material with a melting point of 500°C or more is called a high-temperature brazing material. Examples of the high-temperature brazing material include materials having Ag as a main component.

[0054] The ceramic copper circuit substrate of the embodiment has excellent etching characteristics during circuit formation because the average distance LH is set to be less than 300 μm. In particular, the thickness of the copper circuit substrate becomes more than 0.8 mm and the thicker the copper plate becomes, the more the effect of fine pattern formation brought about by suppressing the side etching characteristics can be obtained. In the case where the copper plate becomes thicker and fine pattern formation is difficult, sometimes a poor pattern is generated due to etching residue. In addition, in order to prevent side etching, it is necessary to slow down the etching speed and other measures. From this point of view, according to this embodiment, the reliability of the ceramic copper circuit substrate can be improved and the cost performance can be improved.

[0055] The ceramic copper circuit substrate of the embodiment can relax stress because the average length LV is set to less than 300μm. In the ceramic copper circuit substrate, residual stress is generated by the bonding of the copper plate and the ceramic. Furthermore, usually, by mounting semiconductor elements on the copper circuit, stress is generated due to the thermal expansion difference between the ceramic substrate and the copper circuit due to the heat generated by the semiconductor elements. As the particle size in the copper circuit portion decreases in the direction perpendicular to the bonding surface with the ceramic substrate, the stress generated in the copper circuit portion decreases. If the stress is reduced, even if the thickness of the copper circuit portion is more than 0.5mm, cracks caused by the stress difference between the ceramic substrate and the copper circuit portion can be suppressed.

[0056] From this point of view, according to the present embodiment, the reliability of the ceramic copper circuit board can be improved.

[0057] In addition, the miniaturization of semiconductor elements is progressing, and on the other hand, the heat generated from the chip is increasing. Therefore, in the ceramic copper circuit substrate equipped with semiconductor elements, it is important to improve the heat dissipation. In addition, in order to improve the performance of the semiconductor device (semiconductor module), multiple semiconductor elements can be mounted on the ceramic copper circuit substrate. Even if only one of the semiconductor elements exceeds the true temperature of the element, the resistance will change to a negative temperature coefficient on the negative side. Along with this, thermal runaway occurs in which the power flows in a concentrated manner, and the semiconductor device is destroyed instantaneously. Therefore, it is very effective to improve the reliability of the connection between the semiconductor element and the copper circuit part. In addition, the semiconductor device of the embodiment can be used for PCU, IGBT, and IPM modules used in inverters of automobiles (including electric vehicles), electric railway vehicles, industrial machinery, air conditioners, etc. With regard to automobiles, the popularization of electric vehicles has made progress. The higher the reliability of the semiconductor device, the more it can improve the safety of the automobile. The same is true for electric railway vehicles, industrial equipment, etc.

[0058] Next, a method for manufacturing a ceramic copper circuit board according to an embodiment will be described. The method for manufacturing the ceramic copper circuit board is not particularly limited as long as the ceramic copper circuit board has the above-mentioned structure. Here, an example of a method for obtaining a ceramic copper circuit board with a good yield is given.

[0059] First, a ceramic substrate and a copper plate are prepared. The thickness of the copper plate is 0.5 mm or more.

[0060] In addition, the ceramic substrate is preferably one selected from an alumina substrate, an aluminum nitride substrate, and a silicon nitride substrate. In particular, considering the heat dissipation of the entire circuit substrate, the ceramic substrate is preferably a silicon nitride substrate having a thermal conductivity of 50 W / (m·K) or more and a three-point bending strength of 600 MPa or more.

[0061] In addition, when the copper circuit portion provided on the surface of the ceramic substrate is connected to the back copper plate provided on the back through the through hole, a ceramic substrate having a through hole is prepared. In the case where the through hole is provided in the ceramic substrate, the through hole can also be provided in advance at the stage of the formed body. In addition, the through hole can also be provided in the ceramic substrate (ceramic sintered body). The through hole is provided by laser processing, cutting processing, etc. As cutting processing, hole opening processing using drilling, etc. can be listed.

[0062] Regarding the copper plate, when heated under the bonding conditions with the ceramic, it is preferable to prepare a copper plate in which the average distance LH of the copper crystal grains inside is 300 μm or less. Furthermore, it is preferable to prepare a copper plate in which each distance LH is 400 μm or less. Each distance LH is preferably 50 μm or more, and more preferably 70 μm or more.

[0063] In addition, when the copper plate is heated under the bonding conditions with the ceramic, it is preferable to prepare a copper plate in which the average length LV of the copper crystal grains inside is 300 μm or less. Furthermore, it is preferable to prepare a copper plate in which each length LV is 400 μm or less. Each length LV is preferably 50 μm or more, and more preferably 70 μm or more.

[0064] When the ceramic substrate and the copper plate are bonded by an active metal bonding method, the bonding temperature is about 700 to 900° C. When the copper plate is exposed to this temperature, copper recrystallizes, so the grains become larger. It is preferred to use a copper plate containing copper grains having a shorter distance LH and a shorter length LV than the above range in such a manner that the distance LH and the length LV of the copper grains are within the above range.

[0065] In addition, the ceramic substrate and the copper plate are preferably joined by an active metal bonding method. In the active metal bonding method, an active metal brazing filler metal obtained by mixing an active metal such as Ti with Ag is used. As an active metal brazing filler metal, a mixture of Ti, Ag and Cu can be listed. In the active metal brazing filler metal, the content of Ti is 0.1 to 10% by weight, the content of Cu is 10 to 60% by weight, and the remainder is Ag. In addition, as needed, one or more selected from the group consisting of In, Sn, Al, Si, C and Mg can also be added in the range of 1 to 15% by weight.

[0066] The active metal brazing filler metal paste is made into a paste. The paste contains a brazing filler metal component and an organic substance. In the paste, the brazing filler metal component is preferably uniformly mixed. This is because if the brazing filler metal component is unevenly distributed, the brazing will be unstable, which will cause poor bonding.

[0067] There are various methods for uniformly dispersing the brazing material, and a general method of mixing powders such as mixing by dry or wet milling or blending with a stirrer, or forming an alloy in advance and pulverizing the alloy can be used.

[0068] During brazing, the copper grains become larger due to the diffusion of the brazing material into the copper plate. Therefore, when manufacturing the brazing material, it is preferred to adjust the brazing material in a manner that does not diffuse into the copper plate. Among the above-mentioned brazing material components, a combination of Ag and at least one selected from the group consisting of In and Sn is a component that inhibits diffusion. Therefore, the elements contained in the combination are mixed in a manner that becomes uniform in the paste. It is possible to mix in a sufficient time in a manner that the brazing material components become uniform, or it is possible to add a process for mixing the above-mentioned combination in advance.

[0069] The active metal brazing paste produced in this way is applied to a ceramic substrate. A copper plate is placed on the paste. Next, the ceramic substrate with the copper plate is heated at 700 to 900°C for bonding. The heating step is performed in a vacuum or a non-oxidizing atmosphere as required. In the case of performing the heating step in a vacuum, preferably 1×10 -2 Pa or less. Examples of the non-oxidizing atmosphere include a nitrogen atmosphere and an argon atmosphere.

[0070] By setting the bonding layer in a vacuum or non-oxidizing atmosphere, oxidation of the bonding layer can be suppressed. Thus, the bonding strength can be improved. In addition, the bonding temperature and time can be adjusted to adjust the diffusion of the brazing material into the copper plate.

[0071] In order to control the diffusion state of the solder components into the copper plate, it is preferred to perform a degreasing process of the active metal solder paste during the heating and joining process. In the heating and joining process, the joining temperature is maintained in the range of 700 to 900°C. Before the temperature reaches this range, the amount of solder components diffusing into the copper plate can be controlled by degreasing the organic matter in the paste. This is because: if the organic matter in the solder paste is degreased before joining, the solder in contact with the copper plate can be homogenized.

[0072] In the degreasing process of the solder paste, the temperature is maintained in the range of, for example, 250 to 500° C. The holding time is in the range of 5 to 60 minutes. As another method, setting the heating rate to the bonding temperature to 10° C. / minute or less is also effective.

[0073] The copper plates to be joined may be processed into a pattern shape in advance or may be flat plates. When a flat plate is used, etching is performed after joining to process it into a pattern shape.

[0074] Through this process, a ceramic copper circuit substrate can be manufactured. Next, a process of bonding a semiconductor element and the like to the ceramic copper circuit substrate is performed. A bonding layer is provided at a location where the semiconductor element is bonded. The bonding layer preferably contains solder or brazing material. A bonding layer is provided, and a semiconductor element is provided thereon. Furthermore, as required, a metal terminal is bonded via the bonding layer. Furthermore, a wire bond is provided as required. Furthermore, the necessary number of semiconductor elements, metal terminals, and wire bonds is provided.

[0075] (Example)

[0076] (Examples 1 to 22, Comparative Examples 1 to 9)

[0077] As ceramic substrates, silicon nitride substrates, aluminum nitride substrates and alumina substrates were prepared. The thermal conductivity of the silicon nitride substrate is 90W / (m·K), and the three-point bending strength is 650MP. The thermal conductivity of the aluminum nitride substrate is 170W / (m·K), and the three-point bending strength is 300MPa. The thermal conductivity of the alumina substrate is 20W / (m·K), and the three-point bending strength is 350MPa. The size of the ceramic substrate is 50mm in length and 40mm in width. The thickness of the silicon nitride substrate is 0.32mm. The thickness of the aluminum nitride substrate and the thickness of the alumina substrate are 0.635mm.

[0078] Next, prepare the copper plates shown in Table 1. Cut the copper plates from the base material into 40 mm in length and 30 mm in width as test copper plates for measuring the horizontal distance of grain boundaries and the vertical distance of grain boundaries after heating. After heating the test plate for measurement at 600°C in a nitrogen atmosphere for 1 hour, cut it in the transverse direction in such a way that it becomes 30 mm in length. Observe the vicinity of the center of the cut test plate (at a position about 15 mm from the end) with a scanning electron microscope (SEM: Scanning Electron Microscope) at a magnification of 20 times and take a photo. For the measurement position in the thickness direction, copper plates 1 to 9 with a thickness of 0.5 mm were measured as a whole from the back to the surface. Copper plates 10 to 18 with a thickness of 0.8 mm were measured near the ends in the thickness direction (from the upper and lower surfaces to a position of about 150 μm).

[0079] The distance LH and length LV of the copper grains in the copper plate are calculated by the following steps. First, draw an arbitrary straight line parallel to the first direction in the observed area. Then, extract 5 copper grains that intersect the straight line. 5 copper grains are randomly extracted. However, the grains cut off at the end of the observed area are excluded. For each of the 5 copper grains, measure the distance LH in the second direction between an arbitrary straight line and the outer edge of the copper grain, and show its average value as the distance LH in Table 1. In addition, for each of the 5 copper grains, measure the length LV of the intersection between an arbitrary straight line and the outer edge of the copper grain in the first direction, and show its average value as the length LV in Table 1.

[0080] Table 1

[0081]

[0082] Next, the ceramic substrate and the copper plate were bonded by an active metal bonding method. The copper plate used was a copper plate of the same size as a test copper plate for measurement cut from a base material into a length of 40 mm x a width of 30 mm. The active metal brazing filler metal used in the active metal bonding method contained 2% Ti by weight, 10% Sn by weight, 30% Cu by weight, and the remainder was Ag.

[0083] Regarding the active metal paste, a brazing material obtained by mixing the materials used simultaneously (normal mixing) and a brazing material obtained by mixing Sn and Ag in advance and then mixing (premixing) other active metal brazing material components are prepared, and each is paste-formed by mixing an organic component.

[0084] The active metal paste was applied to both sides of the ceramic substrate, and copper plates were placed on each side to perform a heat bonding process. In addition, the bonding temperature was set at 790 to 850°C, the bonding time was set at 5 to 20 minutes, and the bonding was performed in a vacuum (1×10 -2 By changing the bonding temperature and bonding time, the grain growth of the copper grains inside the copper plate is controlled.

[0085] In addition, the surface copper plate (surface copper plate) is etched to form a circuit shape. The surface copper plate is processed into any one of 2 to 4 circuit shapes, and the copper plate on the back (back copper plate) is also etched into a circuit shape. In the fine pattern formation of the surface copper plate, the pattern size is set to 0.5 mm. For the surface copper plate with a thickness of 0.5 mm, the pattern size is set to 0.8 mm when the side etching amount and the overflow amount of the solder are set to zero. For the surface copper plate with a thickness of 0.8 mm, the pattern size is set to 1.1 mm when the side etching amount and the overflow amount of the solder are set to zero. The surface copper plate with a thickness of 0.5 mm and the surface copper plate with a thickness of 0.8 mm are etched under the same conditions.

[0086] Under these manufacturing conditions, the premixed paste is more uniformly dispersed than the conventionally mixed paste, and the growth of copper grains can be suppressed. However, premixing is an additional step in conventional mixing. Therefore, the cost performance of premixing is poor compared to conventional mixing.

[0087] In addition, regarding the bonding temperature of 790 to 850° C., a low bonding temperature can suppress the growth of copper crystal grains. However, by approaching the lower limit of the bonding temperature, there is a possibility that peeling may occur easily or the bonding strength may decrease.

[0088] Regarding the bonding time of 5 to 20 minutes, a short bonding time can suppress the grain growth of copper. However, as the bonding time becomes shorter, the possibility that the brazing material will not react sufficiently becomes higher, and the bonding strength is more likely to decrease.

[0089] Therefore, in Examples 1 to 22, based on the distance LH and length LV measured in Table 1, the usual manufacturing conditions (normal mixed paste, bonding temperature 830°C, bonding time 10 minutes) were used for the copper plates with small distance LH and length LV. For the copper plates with large distance LH and length LV, the manufacturing conditions (pre-mixed paste, bonding temperature 790°C, bonding time 5 minutes) that inhibited the grain growth of copper grains were used.

[0090] In contrast, in Comparative Examples 1 to 3, for the copper plates with large distance LH and length LV measured in Table 1, the usual manufacturing conditions (normal mixed paste, bonding temperature 830°C, bonding time 10 minutes) were adopted. In Comparative Examples 4 to 5, for the copper plates with further large distance LH and length LV measured in Table 1, the manufacturing conditions for suppressing the grain growth of copper crystal grains (pre-mixed paste, bonding temperature 790°C, bonding time 5 minutes) were adopted. In Comparative Examples 6 to 9, the manufacturing conditions for further promoting the grain growth of copper crystals (bonding temperature 850°C, bonding time 20 minutes) were adopted.

[0091] Table 2 shows the obtained ceramic copper circuit boards.

[0092] Table 2

[0093]

[0094] Next, for the obtained sample, the cross-sectional structure is observed by SEM, and the distance LH and the length LV are measured. Based on the measured distance LH and length LV, distances LH1 to LH4 and lengths LV1 to LV4 are obtained. Distance LH1 is the maximum value of multiple distances LH. Distance LH2 is the average value of multiple distances LH. Distance LH3 is the minimum value of multiple distances LH. Distance LH4 is the difference between the maximum value (LH1) and the minimum value (LH3). Length LV1 is the maximum value of multiple lengths LV. Length LV2 is the average value of multiple lengths LV. Length LV3 is the minimum value of multiple lengths LV. Length LV4 is the difference between the maximum value (LV1) and the minimum value (LV3).

[0095] The results are shown in Table 3.

[0096] Table 3

[0097]

[0098] As can be seen from the table, the distance LH1 and the length LV1 of the ceramic copper circuit board of the example are within the range of the preferred embodiment. On the other hand, the distance LH1 and the length LV1 of the comparative example are larger than those of the example.

[0099] Next, the amount of side etching was investigated for the ceramic copper circuit boards of Examples and Comparative Examples. The horizontal distance between the surface and the back of the copper circuit portion was measured using an optical microscope, and the longest distance was defined as the amount of side etching.

[0100] Furthermore, the inter-pattern dimension was measured using a projector. As the inter-pattern dimension, the distance between the portion of the bonding layer where the side etching amount was measured and another bonding layer adjacent to the portion was measured.

[0101] In addition, as the bonding strength between the copper circuit portion and the ceramic substrate, the peel strength was measured. The peel strength was measured by peeling the copper circuit portion formed in advance with a width of 3 mm along the first direction at 50 mm / min. In addition, the bonding strength of the ceramic circuit substrate was measured by pressing the ceramic circuit substrate from the top and bottom directions using a three-point bending fixture.

[0102] Next, the reliability of the ceramic copper circuit boards of the examples and comparative examples was evaluated. As the reliability, the bonding property of the semiconductor element was evaluated.

[0103] In this evaluation, samples cut for measuring the copper crystal grain size and samples measured for bonding strength or three-point bending strength were not used, but samples prepared under the same conditions as in the examples and comparative examples were used for reliability evaluation.

[0104] The bondability of the semiconductor element uses lead-free solder to bond the semiconductor element and the metal terminal. Wire bonding is further provided to make the semiconductor element and the metal terminal conductive. Thus, a semiconductor device is manufactured. Next, a temperature cycle test (TCT) is performed on the semiconductor device to investigate the incidence of poor conduction. In TCT, -40°C × 30 minutes → room temperature × 10 minutes → 150°C × 30 minutes → room temperature × 10 minutes is set as one cycle, and the peeling area caused by cracks after 300 cycles is calculated by ultrasonic flaw detection (SAT: Scanning Acoustic Tomograph). Then, the non-peeling area ratio η is evaluated. The non-peeling area ratio η sets the case where no cracks are generated by TCT as η = 100%, and the case where cracks are generated in the entire joint surface of the ceramic copper circuit substrate by TCT is set as η = 0%.

[0105] Table 4 shows the respective measurement results.

[0106] Table 4

[0107]

[0108] In the ceramic copper circuit substrate of the embodiment, for the ceramic copper circuit substrate that both the distance LH2 and the length LV2 satisfy the condition of less than 300μm, when the copper plate thickness is 0.5mm, the side etching amount is less than 0.10mm. When the copper plate thickness is 0.8mm, it is less than 0.20mm. As the side etching amount decreases, the size between patterns becomes larger. That is, for the ceramic copper circuit substrate of the embodiment, even under the same etching conditions as the comparative example, the size between patterns can be reduced, and a fine pattern can be formed. In addition, due to the stress relaxation effect of the copper circuit portion, the bonding strength is more than 24kN / m. For silicon nitride substrates, the three-point bending strength is 600MPa. For aluminum nitride substrates, the three-point bending strength is 250MPa. For aluminum oxide substrates, the three-point bending strength is more than 300MPa. In this way, according to the embodiment, a ceramic copper circuit substrate with high reliability is obtained.

[0109] In addition, among the ceramic copper circuit substrates of the examples, the ceramic copper circuit substrates in which only either the distance LH2 or the length LV2 is 300 μm or less can obtain ceramic copper circuit substrates with good side etching amount or ceramic copper circuit substrates with good bonding strength and three-point bending strength due to stress relaxation.

[0110] Good results were obtained with the ceramic copper circuit board satisfying the distance LH1 and the length LV1 of 300 μm or less, respectively.

[0111] Good results were obtained with the ceramic copper circuit board satisfying the distance LH3 and the length LV3 of 200 μm or less, respectively.

[0112] Good results were obtained with the ceramic copper circuit board satisfying the distance LH4 and the length LV4 of 220 μm or less, respectively.

[0113] In contrast, the side etching amount of the comparative example was large, resulting in a state where no pattern was formed (short circuit), and the bonding strength and three-point bending strength were low. From this result, it is known that the distance LH and the length LV affect the side etching amount, bonding strength, and three-point bending strength.

[0114] In addition, there is a difference in the non-peeled area ratio η between the example and the comparative example. This is because the side etching amount, the bonding strength, and the three-point bending strength are improved by controlling the distance LH1 and the length LV1 inside the copper circuit in the example.

[0115] In contrast, in the comparative example, the non-peeled area ratio η deteriorates. This is because the distance LH2 and the length LV2 of the copper crystal grains are large in the copper circuit portion, and the side etching amount increases. In addition, the thermal stress inside the ceramic copper circuit substrate increases due to the decrease in the bonding strength and the three-point bending strength, thereby increasing the load on the bonding portion.

[0116] Several embodiments of the present invention are illustrated above, but these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other ways, and various omissions, substitutions, changes, etc. can be made without departing from the scope of the main purpose of the invention. These embodiments and their modifications are included in the scope and main purpose of the invention, and are also included in the invention recorded in the claims and their equivalents. In addition, the above-mentioned embodiments can be implemented in combination with each other.

[0117] Explanation of symbols

[0118] 1 Ceramic copper circuit substrate

[0119] 2 Ceramic Substrate

[0120] 3 Copper circuit part (surface copper plate)

[0121] 4. Joining layer (solder)

[0122] 5 Copper circuit part (copper back plate)

[0123] 6 Copper circuit cross-section (enlarged view of part A)

[0124] 7 A line drawn arbitrarily perpendicular to the thickness direction of the substrate

[0125] 8 Side etching amount

[0126] 9 Internal cross-section of the copper plate (enlarged view of part B)

[0127] 10 Copper grains

[0128] 11 Copper grain boundaries

[0129] 12 Distance (LH)

[0130] 13 Length (LV)

[0131] 14 Pattern size

[0132] 15 Pattern size

[0133] 16 Semiconductor devices

[0134] 17 Semiconductor components

[0135] 18 Bonding layer

[0136] 19 Wire Bonding

[0137] 20 Metal Terminals

Claims

1. A ceramic copper circuit substrate, characterized in that: It has: Ceramic substrate; A copper circuit portion disposed on the ceramic substrate; and a first bonding layer provided between the ceramic substrate and the copper circuit portion and containing an active metal brazing filler metal component, In a cross section of the copper circuit portion parallel to a first direction from the ceramic substrate toward the copper circuit portion, an arbitrary line drawn along the first direction intersects a plurality of copper crystal grains. An average of a plurality of distances in the second direction between the line and ends of the copper crystal grains in a second direction perpendicular to the first direction that are farthest from the line is 50 μm or more and 300 μm or less, The outer edge of each of the plurality of copper grains includes a first end and a second end intersecting the line, A maximum value of a length between the first end and the second end of each of the plurality of copper crystal grains in the first direction is 301 μm or more.

2. The ceramic copper circuit substrate according to claim 1, characterized in that: A maximum value of the plurality of distances is 400 μm or less.

3. The ceramic copper circuit substrate according to claim 1 or claim 2, characterized in that: The minimum value of the plurality of distances is 200 μm or less.

4. The ceramic copper circuit substrate according to claim 1 or claim 2, characterized in that: A difference between a maximum value of the plurality of distances and a minimum value of the plurality of distances is 220 μm or less.

5. The ceramic copper circuit substrate according to claim 1 or claim 2, characterized in that: An average of the lengths of each of the plurality of copper crystal grains between the first end and the second end in the first direction is 300 μm or less.

6. The ceramic copper circuit substrate according to claim 5, characterized in that: The maximum value of the plurality of lengths is 512 μm or less.

7. The ceramic copper circuit substrate according to claim 5, characterized in that: The minimum value of the plurality of lengths is 200 μm or less.

8. The ceramic copper circuit substrate according to claim 5, characterized in that: A difference between a maximum value of the plurality of lengths and a minimum value of the plurality of lengths is 220 μm or less.

9. The ceramic copper circuit substrate according to claim 1 or claim 2, characterized in that: The ceramic substrate is any one of an aluminum oxide substrate, an aluminum nitride substrate and a silicon nitride substrate.

10. The ceramic copper circuit substrate according to claim 1 or claim 2, characterized in that: The thickness of the ceramic substrate in the first direction is 0.7 mm or less.

11. The ceramic copper circuit substrate according to claim 1 or claim 2, characterized in that: The first bonding layer includes at least one of Ti and Zr and at least one selected from the group consisting of Ag, Cu, Sn, In, Al, Si, C, and Mg.

12. The ceramic copper circuit substrate according to claim 1 or claim 2, characterized in that: It has: a plurality of said copper circuit portions; and The plurality of first bonding layers respectively provided between the ceramic substrate and the plurality of copper circuit portions have a minimum distance between adjacent first bonding layers less than 1.0 mm.

13. The ceramic copper circuit substrate according to claim 1 or claim 2, characterized in that: The copper circuit portion has a thickness in the first direction of 0.5 mm or more.

14. A semiconductor device, characterized in that: It has: The ceramic copper circuit substrate according to any one of claims 1 to 13; and A semiconductor element is mounted on the copper circuit portion via a second bonding layer.

15. A method for manufacturing a ceramic copper circuit substrate, characterized in that: Apply active metal brazing paste on the ceramic substrate. A copper plate is arranged on the active metal solder paste. The ceramic substrate and the copper plate are bonded by maintaining the bonding temperature in the range of 700° C. to 900° C. for 5 to 60 minutes, The copper plate is etched to form a copper circuit portion. In the manufactured ceramic copper circuit substrate, in a cross section of the copper circuit portion parallel to a first direction from the ceramic substrate toward the copper circuit portion, an arbitrary line drawn along the first direction intersects a plurality of copper crystal grains, An average of a plurality of distances in the second direction between the line and ends of each of the copper crystal grains in a second direction perpendicular to the first direction that are farthest from the line is 50 μm or more and 300 μm or less.

16. A method for manufacturing a semiconductor device, characterized in that: Implementing the method for manufacturing the ceramic copper circuit substrate according to claim 15, A semiconductor element is mounted on the copper circuit portion via a second bonding layer.

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