Ceramic substrate and semiconductor device substrate comprising same

Abstract

This ceramic substrate contains alumina, zirconia, yttria, and a glassy substance. The glassy substance includes Si, an alkali metal, and O as first components and one or more of Ca, Sr, and Ba as second components. The zirconia content is 5–14 wt%. When A is the value obtained by dividing the concentration in terms of oxides of the alkali metal that is a first component of the glassy substance by the total interfacial distance (grain boundary length) at which Al2O3, ZrO2, and SiO2 are adjacent to each other, B is the concentration in terms of oxides of the Si that is a first component of the glassy substance, and C is the total mass concentration in terms of oxides of the Ca, Sr, and Ba that are second components of the glassy substance, A / (B×C) is no more than 7.1×10-4.

Description

Ceramic substrate and substrate for semiconductor device including same

[0001] The present invention relates to a ceramic substrate and a substrate for a semiconductor device including the ceramic substrate.

[0002] BACKGROUND ART As a substrate for a semiconductor device used in a power transistor module or the like, a DBOC (Direct Bonding of Copper Substrate) substrate having a copper plate on the surface of a ceramic substrate is known (for example, Patent Documents 1 to 3).

[0003] JP 2022-515808 A, International Publication No. 2012 / 060341 A, International Publication No. 2020 / 115868 A

[0004] In the substrate for semiconductor device described above, a copper plate is bonded to the surface of the ceramic substrate. However, the present inventors have found that when the oxygen ion conductivity of the ceramic substrate increases, the bonding strength between the ceramic substrate and the copper plate decreases when a DC voltage is applied, and there is a risk that the copper plate may peel off.

[0005] The present invention has been made to solve the above problems, and aims to provide a ceramic substrate and a substrate for a semiconductor device that, when a copper plate is joined, can suppress peeling when a DC voltage is applied.

[0006] Item 1. A glass material comprising alumina, zirconia, yttria, and a glassy substance, wherein the glassy substance contains, as a first component, elements such as Si, an alkali metal, and O, and as a second component, elements such as at least one selected from Ca, Sr, and Ba, and the zirconia content is 5 to 14 mass %, and when the concentration of the alkali metal, which is the first component of the glassy substance, in terms of oxide, divided by the total distance (grain boundary length) of interfaces between adjacent Al2O3, ZrO2, and SiO2 is A, the concentration of Si, which is the first component of the glassy substance, in terms of oxide is B, and the total mass concentration of Ca, Sr, and Ba, which are the second components of the glassy substance, in terms of oxide, is C, the value of A / (B×C) is 7.1×10 -4 Below is a ceramic substrate.

[0007] Item 2. The ceramic substrate according to Item 1, wherein the mass ratio of the content of the alkali metal, calculated as an oxide, to the content of the vitreous second component, calculated as an oxide, is 1.0 or less.

[0008] Item 3. The ceramic substrate according to Item 1 or 2, wherein the zirconia content is 11 mass % or more.

[0009] Item 4. The ceramic substrate according to any one of Items 1 to 3, wherein the molar fraction of the yttria relative to the zirconia is 0.015 to 0.035.

[0010] Item 5. The ceramic substrate according to any one of Items 1 to 4, wherein a mass ratio of the total content of the zirconia and the yttria to the content of the alumina is 0.10 or more.

[0011] Item 6. The ceramic substrate according to any one of Items 1 to 5, wherein a mass ratio of the total content of the silica, magnesia, and the vitreous second component to the content of the alkali metal converted into oxide is 25.0 or more.

[0012] Item 7. The ceramic substrate according to any one of Items 1 to 6, having a bending strength of 550 MPa or more.

[0013] Item 8. The ceramic substrate according to any one of Items 1 to 6, having a bending strength of 700 MPa or more.

[0014] Item 9. A substrate for a semiconductor device for mounting electronic components, comprising: the ceramic substrate according to any one of Items 1 to 8; and a copper plate bonded to the ceramic substrate.

[0015] According to the present invention, when a copper plate is bonded to a ceramic substrate, peeling can be suppressed when a DC voltage is applied.

[0016] Fig. 1 is a cross-sectional view showing one embodiment of a semiconductor device having a substrate for a semiconductor device according to the present invention; Fig. 2 is a diagram showing boundary maps of Al2O3, ZrO2, and SiO2 and grain boundary lengths in a cross section of a ceramic substrate according to Example 1 of the present invention; Fig. 3 is a cross-sectional SEM image of a ceramic substrate according to Example 1 of the present invention; Fig. 4 is a cross-sectional SEM image of a ceramic substrate according to Comparative Example 3 of the present invention; Fig. 5 is a diagram showing the relationship between impedance and frequency in the ceramic substrates according to Example 1 of the present invention and Comparative Example 3.

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A ceramic substrate and a substrate for a semiconductor device using the same according to an embodiment of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a cross-sectional view of a semiconductor device having a substrate for a semiconductor device according to this embodiment.

[0018] <1. Overview of Semiconductor Device> The semiconductor device according to this embodiment is used as a power module in various electronic devices such as personal computers, large home appliances, railways, electric vehicles, power generation (wind power generation, solar power generation, fuel cells, etc.), air conditioners, industrial robots, commercial elevators, home microwave ovens, induction electric rice cookers, and UPS (uninterruptible power supplies).

[0019] As shown in FIG. 1, the semiconductor device 1 according to this embodiment includes a substrate 2 for a semiconductor device, a first bonding material 5, a second bonding material 5', a semiconductor chip 6, bonding wires 7, and a heat sink 8.

[0020] The substrate 2 for a semiconductor device is a so-called DBOC (Direct Bonding of Copper Substrate) substrate, and includes a plate-shaped ceramic substrate 3, which is an insulator, a first copper plate 4 bonded to one surface (top surface) of the ceramic substrate 3, and a second copper plate 4' bonded to the other surface (bottom surface). Details of the ceramic substrate 3 will be described later.

[0021] A transmission circuit is formed on the first copper plate 4. On the other hand, the second copper plate 4' is formed in a flat plate shape.

[0022] A semiconductor chip 6 is bonded to the upper surface of the semiconductor device substrate 2, i.e., to a part of the upper surface of the first copper plate 4, via a first bonding material 5. The semiconductor chip 6 and the first copper plate 4 are also connected by bonding wires 7.

[0023] On the other hand, a heat sink 8 is bonded to the lower surface of the semiconductor device substrate 2, i.e., the lower surface of the second copper plate 4′, via a second bonding material 5′. The heat sink 8 is a known material and can be made of a metal such as copper.

[0024] 2. Structure of the Ceramic Substrate Next, the ceramic substrate 3 will be described in detail. The ceramic substrate 3 includes alumina (Al2O3), zirconia (ZrO2), yttria (YO3), a vitreous material, and the remainder. The vitreous material includes a first component and a second component. The first component includes, as elements, Si, an alkali metal, and O, and the second component includes, as elements, at least one selected from Ca, Sr, and Ba. However, the vitreous material may also include other components. The contents of the constituent elements of the ceramic substrate 3 will be described below.

[0025] The alumina content is, for example, preferably 75% by mass or more and 90% by mass or less, and more preferably 85% by mass or more and 90% by mass or less.

[0026] The zirconia content is preferably, for example, 5% by mass or more and 14% by mass or less, and more preferably 11% by mass or more and 14% by mass or less. A zirconia content of 5% by mass or more can improve the strength of the ceramic substrate 3. It is also believed that this can prevent the linear thermal expansion coefficient of the ceramic substrate 3 from becoming too small, thereby reducing the difference in the linear thermal expansion coefficient between the ceramic substrate 3 and the first and second copper plates 4, 4'. As a result, it is believed that this can reduce the thermal stress generated at the bonding interface with the copper plate 4, contributing to the prevention of cracks in the ceramic substrate 3 at the bonding interface. Furthermore, a zirconia content of 11% by mass or more can increase the flexural strength of the ceramic substrate 3 (for example, a flexural strength of 700 MPa or more can be achieved, as shown in Examples 3 and 6 described below).

[0027] On the other hand, by setting the zirconia content to 14% by mass or less, it is believed that excessive reaction at the bonding interface during copper plate bonding can be suppressed, and the generation of voids at the bonding interface can be suppressed. This is due to the difference in wettability between alumina and zirconia with the Cu-O eutectic liquid phase during copper plate bonding. Furthermore, by setting the zirconia content to 14% by mass or less, the impedance of the ceramic substrate 3 can be improved without increasing the silica content, as will be described later.

[0028] The yttria content is preferably 0.3 mass% or more and 2.0 mass% or less, and more preferably 0.5 mass% or more and 1.2 mass% or less. By setting the content to 0.3 mass% or more, it is thought that the proportion of the monoclinic phase in the zirconia crystal phase can be prevented from becoming excessive, while the proportion of the tetragonal phase can be increased. As a result, it is thought that the mechanical strength of the ceramic substrate 3 can be improved, and that this contributes to preventing cracks from occurring in the ceramic substrate 3 at the bonding interface.

[0029] On the other hand, by setting the yttria content to 2.0 mass % or less, it is thought that the proportion of cubic crystals in the zirconia crystal phase can be prevented from becoming excessive, while the proportion of tetragonal crystals can be increased, which is thought to improve the mechanical strength of the ceramic substrate 3 and contribute to preventing cracks from occurring in the ceramic substrate 3 at the bonding interface.

[0030] By setting the molar fraction of yttria to zirconia within the range of 0.015 to 0.035, yttria-partially stabilized zirconia (YSZ) is formed at the tip of a microcrack, which exhibits volumetric growth associated with martensitic transformation. In YSZ, yttria is dissolved in zirconia. As a result, resistance to crack propagation is increased, and fracture toughness and mechanical strength can be effectively improved.

[0031] Therefore, in the ceramic substrate 3 of this embodiment, zirconia and yttria exist as yttria-partially stabilized zirconia, but they may also exist alone. However, in the present invention, these two aspects will be described as equivalent. Therefore, even when zirconia and yttria are described individually, they may also exist in the ceramic substrate 3 as yttria-partially stabilized zirconia.

[0032] Furthermore, the mass ratio of the total content of zirconia and yttria to the content of alumina is preferably 0.10 or more. This is because a mass ratio of 0.10 or more can improve the bending strength. On the other hand, this mass ratio is preferably 0.30 or less. This is because the thermal conductivity of zirconia is lower than that of alumina, and if this mass ratio exceeds 0.30, there is a possibility that the insulating heat dissipation circuit board will not maintain sufficient thermal conductivity.

[0033] The presence of the above-mentioned alumina, zirconia, and yttria as oxides themselves in the ceramic substrate 3 can be verified by XRD or the like.

[0034] Next, the glassy substance will be described. As described above, the glassy substance contains a first component including elements such as Si, an alkali metal, and O, and a second component including at least one element selected from Ca, Sr, and Ba. However, these elements exist primarily as oxides such as silica (SiO), alkali metal oxides, calcium oxide (CaO), strontium oxide (SrO), and barium oxide (BaO), and examples thereof will be described below. The first component may also contain Mg, which exists in the glassy substance as an oxide such as magnesia (MgO).

[0035] First, the first component will be described. The silica content is preferably 0.1 mass % or more and 2.5 mass % or less. If the silica content is 0.1 mass % or more, the oxygen ion conductivity of the ceramic substrate 3 is suppressed, and the impedance can be improved, as described below. On the other hand, if the silica content is too high, there is a risk of a decrease in the strength of the ceramic substrate 3. To prevent this, the silica content is preferably 2.5 mass % or less.

[0036] The magnesia content is preferably 0.05% by mass or more and 0.5% by mass or less, and more preferably 0.10% by mass or more and 0.3% by mass or less. By setting the magnesia content to 0.05% by mass or more, the ceramic substrate 3 can be sintered without excessively high firing temperatures, and coarsening of alumina and zirconia particles is thought to be suppressed. As a result, the mechanical strength of the ceramic substrate 3 can be improved, contributing to the suppression of cracks occurring in the ceramic substrate 3 at the bonding interface with the copper plate 4. Furthermore, a sufficient amount of MgAl2O4 crystals (hereinafter referred to as "spinel crystals") can be generated in the ceramic substrate 3, which is thought to improve wettability with the Cu-O eutectic liquid phase during copper plate bonding. As a result, it is thought to contribute to the suppression of voids occurring at the bonding interface.

[0037] On the other hand, it is believed that by setting the magnesia content to 0.5 mass % or less, it is possible to suppress the excessive formation of spinel crystals, which have low mechanical strength, and improve the mechanical strength of the ceramic substrate 3. As a result, it is believed that this contributes to suppressing the occurrence of cracks in the ceramic substrate 3 at the bonding interface.

[0038] Alkali metal ions break the Si-O bonds of SiO2 and form non-bridging oxygen (NBO), which then becomes a diffusion site for ions, resulting in oxygen ion conductivity. Examples of such alkali metals include sodium, potassium, and lithium, and two or more of these may be included. These are present in the ceramic substrate 3 as sodium oxide (Na2O), potassium oxide (KO2O), and lithium oxide (Li2O). The inventors have confirmed that the same results are obtained regardless of the type of alkali metal oxide used, as will be shown in the examples below.

[0039] The second components are all glassy network-modifying oxides that are incorporated into the framework of the glassy network-forming oxides, primarily silica (SiO2), and act to change the chemical and physical properties of the glassy material. In particular, it is known that when calcium oxide (CaO), strontium oxide (SrO), and barium oxide (BaO) are contained in glassy materials containing alkali metal oxides such as those described above, ionic conduction through NBOs as diffusion sites is suppressed, thereby reducing electrical conductivity. Furthermore, the effect of reducing electrical conductivity increases in the order of CaO < SrO < BaO.

[0040] The reason for this is that the larger the difference in radius between a monovalent alkali metal ion and a divalent ion, the greater the blocking effect of the divalent ion that inhibits the migration of the alkali metal ion, and the lower the polarizability of the non-bridging oxygen ion, which strengthens the bond between adjacent alkali metal ions and oxygen ions, thereby reducing the mobility of the alkali metal ions.

[0041] For this reason, the insulating properties can be further improved by adding CaO, SrO, or BaO to a glassy material containing an alkali metal oxide, which makes it possible to improve the problem to be solved by the present invention, namely, the property that oxygen ions are conducted from the negative electrode side to the positive electrode side inside the ceramic substrate by applying a DC voltage, resulting in a decrease in the bonding strength between the electrode and the ceramic substrate.

[0042] The second component of the glass may contain one or more of CaO, SrO, and BaO.

[0043] In this ceramic substrate, the mass ratio of the alkali metal oxide content to the second component content, calculated as vitreous oxide, is preferably 1.0 or less. This effectively suppresses oxygen ion conduction. As a result, a significant decrease in the bonding strength between the ceramic substrate 3 and the copper plate after application of a DC voltage can be suppressed.

[0044] Furthermore, the mass ratio of the total content of silica, magnesia, and the vitreous second component to the content of alkali metal oxide is preferably 25.0 or more, and more preferably 30.0 or more. This allows for more effective suppression of oxygen ion conduction. In particular, it has been found that when this value is less than 25.0, the smaller the value, the greater the decrease in the bonding strength between the ceramic substrate 3 and the copper plates 4, 4' after application of a DC voltage. The upper limit of this value can be, for example, 65.0 or less.

[0045] Furthermore, since sodium affects electrical conductivity, the content of sodium in the ceramic substrate 3 in terms of oxide is preferably 0 mass % or more than 0 mass % but not more than 0.05 mass %.

[0046] The content of the glassy oxide in the ceramic substrate 3 can be, for example, 0.9% by mass to 3% by mass, because if it is less than 0.9% by mass, oxygen ion conduction cannot be sufficiently suppressed, while if it exceeds 3% by mass, sufficient bending strength cannot be obtained.

[0047] The content of the remainder is preferably 0.5% by mass or less, and more preferably 0.05% by mass or less, calculated as oxide. This is thought to prevent excessive sintering of the ceramic substrate 3 even when the firing temperature is not excessively high, and to reduce the porosity of the ceramic substrate 3. As a result, it is thought to improve the mechanical strength of the ceramic substrate 3 and contribute to preventing cracks from occurring in the ceramic substrate 3 at the bonding interface with the copper plate 4.

[0048] In this embodiment, the contents of the constituent elements of the ceramic substrate 3 are calculated in terms of oxides as described above, but the constituent elements of the ceramic substrate 3 may or may not exist in the form of oxides. For example, at least one of Y, Mg, and Ca may not exist in the form of oxides but may be solid-solved in ZrO. Some alkali metals may not exist in the form of oxides. The contents of all alkali metals not existing in the form of oxides are also calculated in terms of oxides.

[0049] The content of the constituent elements of the ceramic substrate 3 in terms of oxide is calculated as follows. First, the constituent elements of the ceramic substrate 3 are qualitatively analyzed using an X-ray fluorescence analyzer (XRF) or an energy dispersive analyzer (EDS) attached to a scanning electron microscope (SEM). Next, each element detected by this qualitative analysis is quantitatively analyzed using an ICP optical emission spectrometer. Next, the content of each element measured by this quantitative analysis is converted into its oxide.

[0050] The element contained in the balance may be an element that is intentionally added or an element that is unavoidably mixed in. The element contained in the balance is not particularly limited, but examples thereof include Fe (iron), Ti (titanium), and Mn (manganese).

[0051] Furthermore, the glassy substance described above does not exist within the matrix grains, but exists at grain boundaries, which are regions surrounded by the matrix grains. There are three types of grain boundaries, for example, Al2O3 / Al2O3, Al2O3 / YSZ, and YSZ / YSZ. From a macroscopic perspective, there are two types of grain boundaries: those inside the ceramic substrate 3 that are not exposed to the outside (the three types described above), and those in the surface layer that is exposed to the outside. Furthermore, there is a possibility that trace amounts of glassy components may form a solid solution in Al2O3 and YSZ.

[0052] The inventors also obtained the following findings regarding glassy grain boundaries. Specifically, the findings regarding glassy grain boundaries were quantified and evaluated as follows. First, the following A to C were defined. A: The alkali metal density at the grain boundaries was simulated by calculating the mass concentration ratio (mass % / μm) of the alkali metal oxide equivalent to the total interface distance (grain boundary length) between adjacent Al2O3, ZrO2, and SiO2. The method for measuring grain boundary length will be described later. B: The mass concentration (mass %) of SiO2 was defined as B. A / B: The ratio of A to B was calculated to simulate the effect of alkali metals on the electrical insulation of silica by forming NBOs. It is believed that a high value of A / B tends to increase oxygen ion conductivity. C: The total mass concentration (mass %) of Ca, Sr, and Ba, which suppress the formation of NBOs by alkali metals, was defined as C. A / B / C (= A / (B × C)): The difficulty of NBO generation was simulated by calculating the ratio of A / B to C (1 / μm·mass %). Note that A / (B × C) can also be defined as (mass concentration in terms of alkali metal oxides / total mass concentration in terms of Ca, Ba, and Sr oxides) / (SiO2 mass concentration × total interfacial distance).

[0053] The calculated value (A / (B×C)) varies depending on the compounding ratio of the components, the diameter of the raw material powder, the firing time and temperature, etc., but the inventors have estimated that it is 7.1×10 -4 The inventors have found that the DC durability is improved and the bonding strength ratio is also excellent if the calculated value is within the following range. The inventors have also found that the lower this calculated value is, the higher the bending strength is. From the viewpoint of improving bending strength, the calculated value is 2.0 × 10 -4 More preferably, it is 1.5 × 10 or less. -4 It has been found to be particularly preferred that:

[0054] 3. Method for Manufacturing Ceramic Substrate and Substrate for Semiconductor Device Next, a method for manufacturing a ceramic substrate and a substrate for semiconductor device will be described. First, the powder materials of the above-described constituent elements are pulverized and mixed using, for example, a ball mill.

[0055] Next, an organic binder (for example, polyvinyl butyral), a solvent (xylene, toluene, etc.), and a plasticizer (dioctyl phthalate, etc.) are added to the pulverized and mixed powder material to form a slurry material.

[0056] Subsequently, the slurry material is molded into a desired shape by a desired molding means (for example, die pressing, cold isostatic pressing, injection molding, doctor blade method, extrusion molding, etc.) to produce a ceramic molded body.

[0057] The ceramic molded body is then fired in an oxygen atmosphere or air atmosphere to complete the ceramic substrate. In this case, the maximum temperature is preferably 1450 to 1650°C, and more preferably 1555 to 1565°C. The holding time at the maximum temperature is preferably 0.7 to 1.0 hour, and more preferably 0.8 to 0.9 hour. The rate of temperature rise from 1000°C to the maximum temperature is preferably 5 to 15°C / min, more preferably 8 to 12°C / min, and particularly preferably 9 to 11°C / min. The temperature rise time from the start to the maximum temperature is preferably 3 to 20 hours, and more preferably 5 to 15 hours.

[0058] Empirically, if the heating rate is higher than the set value, the number of voids inside the ceramic substrate increases proportionally, leading to a decrease in mechanical strength. Furthermore, since the maximum temperature is above the melting point of typical glass, the longer the time held above the glass melting point, including the heating process and the maximum temperature, the more grain growth in the matrix base material is promoted, leading to a tendency for the mesh-like glass network at the grain boundaries to break down and exhibit scattered behavior. This weakens the electrical insulating effect. Therefore, it is preferable to shorten the heating time by increasing the heating rate as described above and shorten the holding time at the maximum temperature. The firing conditions described above were optimized based on this mechanism.

[0059] Next, a method for manufacturing a substrate for a semiconductor device will be described. First, a laminate is formed by placing copper plates 4, 4' with oxidized surfaces on the upper and lower surfaces of a ceramic substrate 3, and the laminate is then heated for approximately 5 to 20 minutes (e.g., approximately 10 minutes) in a nitrogen atmosphere at 1065°C to 1083°C. By heating, a Cu—O eutectic liquid phase is generated at the interface where the ceramic substrate 3 and the copper plates 4, 4' are joined. The thickness of each copper plate 4, 4' can be, for example, 0.1 to 2.0 mm.

[0060] Subsequently, the laminate is cooled to solidify the Cu-O eutectic liquid phase, and the copper plates 4, 4' are bonded to the ceramic substrate 3. This completes the semiconductor device substrate 2. The transmission circuit formed on the copper plate 4 on the surface to which the semiconductor chip 6 is bonded can be formed by, for example, a subtractive method or an additive method.

[0061] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0062] <1. Preparation of Ceramic Substrates> Ceramic substrates according to Examples 1 to 6 and Comparative Examples 1 to 3 were prepared, each consisting of the materials shown in Table 1 as the main components. Specifically, a powder material prepared by blending the compositions shown in Table 1 in predetermined proportions was pulverized and mixed in a ball mill. In the following, sodium oxide (NaO) was used as the alkali metal oxide. However, the content of each composition shown in Table 1 is a value calculated from the ceramic substrate after manufacture, i.e., the sintered body. In Table 1, the unit of content, mass %, is expressed as wt%. The values ​​shown in Tables 1 and 2 are values ​​converted to the oxide of each element.

[0063] Next, polyvinyl butyral as an organic binder, xylene as a solvent, and dioctyl phthalate as a plasticizer were added to the pulverized and mixed powder material to form a slurry material.

[0064] Subsequently, the slurry material was formed into a sheet by a doctor blade method to prepare a ceramic compact.

[0065] Subsequently, the ceramic compact was fired in an air atmosphere at a maximum temperature of 1565°C for 0.8 hours to obtain ceramic substrates according to Examples 1 to 6 and Comparative Examples 1 to 3. The heating rate from 1000°C to the maximum temperature was 85°C / min, and the heating time from the start to the maximum temperature was 70 minutes. The size of this ceramic substrate was 0.32 mm thick, 39 mm long, and 45 mm wide.

[0066]

[0067] Then, copper plates with oxidized surfaces and a thickness of 0.3 mm were placed on the top and bottom surfaces of the ceramic substrates of the examples and comparative examples, and heated for about 10 minutes in a nitrogen atmosphere at 1070°C under atmospheric pressure. In this way, substrates for semiconductor devices according to examples 1 to 6 and comparative examples 1 to 3 were obtained.

[0068] <2. Evaluation> The following evaluations were carried out.

[0069] (1) Evaluation Method for Grain Boundary Length The mass ratio of alkali metal oxide to the vitreous second component was evaluated for the semiconductor device substrates according to Examples 1 to 6 and Comparative Examples 1 to 3. Next, the bonding strength (bonding strength before DC (Direct Current) application) of the semiconductor device substrates was measured for Examples 1 to 6 and Comparative Examples 1 to 3. Next, the bonding strength (bonding strength after DC application) was measured after applying DC 800 V for 100 hours while heating each semiconductor device substrate at 150°C. Subsequently, the crystal grain orientation distribution of Al2O3, ZrO2, and SiO2 was captured using EBSD (Electron Backscatter Diffraction) to calculate the total interface distance (grain boundary length: X1) between adjacent Al2O3, ZrO2, and SiO2. A grain boundary was defined as a misorientation between crystal grains of 5° or more. The measurement site was the center of the cross section of the ceramic substrate sandwiched between copper plates, and within the area observed at a magnification of 3,000 times, a 30 × 30 μm (900 μm 2 The measurement results of Example 1 are shown in FIG.

[0070] (2) Method for Measuring Bonding Strength The bonding strength was measured as follows. First, a predetermined length of the bonded rectangular copper plates was peeled off from the edge in the long-side direction and bent at a 90° angle. Next, the edge of the bent copper plate was clamped with a clip and pulled up vertically. The maximum value obtained at this time was defined as the measured strength. That is, bonding strength (kg / cm) = maximum pulling load (kg) / length of short side of rectangle (cm). Then, the ratio of the bonding strength after DC application to the bonding strength before DC application was calculated, and this was defined as the bonding strength ratio (%).

[0071] (3) Measurement Method of Flexural Strength The flexural strength of the ceramic substrates according to Examples 1 to 6 and Comparative Examples 1 to 3 was measured by a three-point bending test in accordance with JIS R1601:2008.

[0072] (4) Discussion on Bonding Strength and Bending Strength The results are shown in Table 2. In Examples 1 to 6, the decrease in bonding strength was less than 1.0% even before and after DC application, indicating that a high level of bonding strength was maintained. On the other hand, in Comparative Examples 1 to 3, the decrease in bonding strength was approximately 20 to 50% before and after DC application. This is thought to be due to the fact that in Examples 1 to 6, the mass ratio of the alkali metal oxide content to the oxide-equivalent content of the vitreous second component was 1.0 or less, which effectively suppressed oxygen ion conduction.

[0073] Furthermore, in Examples 1 to 6, the mass ratio of the content of alkali metals converted to oxides to the total content of silica, magnesia, and the vitreous second component converted to oxides was 25.0 or more, whereas in Comparative Examples 1 to 3, it was less than 25.0. In particular, as shown in Comparative Examples 1 to 3, it was found that the smaller this value, the lower the bonding strength ratio. Therefore, it is considered that the larger this value, the more effectively oxygen ion conduction was suppressed.

[0074] For Example 1 and Comparative Example 3, despite the same zirconia and yttria content, a significant difference occurred in the bond strength before and after DC application. Therefore, SEM images of the cross sections of the ceramic substrates were obtained and are shown in Figures 3 and 4, respectively. Comparing Figures 3 and 4, YSZ (the white areas indicated by B2 and C2 in the figures) exhibited scattered behavior, and no mechanism of grain boundary interconnection was confirmed, indicating that this was not due to differences in YSZ distribution. Therefore, despite the same amount of YSZ added, the significant difference in the degree of bond strength deterioration before and after DC application is thought to be due to the mass ratio of the alkali metal oxide equivalent to the mass of the vitreous second component in terms of oxide. That is, in Example 1, this value being 1.0 or less indicates that the bond strength was maintained. On the other hand, in Comparative Example 3, this value being higher than 1.0 indicates that the bond strength was reduced.

[0075] FIG. 5 shows the results of impedance measurements carried out for Example 1 and Comparative Example 3. In FIG. 5, for example, 1.0E+03 means 1 times 10 to the power of 3. The measurement method was an AC impedance measurement method. A DC voltage of 98.4 V was applied to the semiconductor device substrate, and then an AC voltage of 1 Vrms was applied to measure the impedance. As a result, it was confirmed that Example 1 had a higher impedance in the low frequency range of 1.0E-03 to 1.0E+01 (Hz) than Comparative Example 3, and that the insulation properties were improved. This is thought to be because Example 1 has a higher calcia content than Comparative Example 3.

[0076] The flexural strengths of Examples 1 to 6 and Comparative Examples 1 to 3 all showed values ​​of 550 MPa or higher. A flexural strength of 550 MPa or higher means that the substrate can be used as a DBOC substrate for a variety of applications. In particular, Examples 3 and 6 have higher flexural strengths than Examples 1, 2, 4, and 5 because they contain a higher zirconia content and a lower silica content.

[0077] (5) Consideration of grain boundary length The results are shown in Table 3. The above-mentioned X1, A, B, C, A / (B×C), bonding strength ratio, and bending strength were calculated. As shown in Examples 1 to 6, A / (B×C) was 7.1×10 -4 It was found that within the following range, DC durability was improved and the bonding strength ratio was also excellent. On the other hand, in Comparative Examples 1 to 3, the calculated value (A / (B×C)) was 7.1×10 -4 The bonding strength ratio was lower than that of Examples 1 to 6.

[0078] 2... Substrate for semiconductor device 3... Ceramic substrate 4, 4'... Copper plate

Claims

1. A glass material containing alumina, zirconia, yttria, and a glassy substance, the glassy substance containing, as a first component, elements Si, an alkali metal, and O, and as a second component, elements at least one selected from Ca, Sr, and Ba, the content of the zirconia being 5 to 14 mass%, the concentration of the alkali metal, which is the first component of the glassy substance, in terms of oxide, divided by the total interface distance (grain boundary length) between adjacent Al2O3, ZrO2, and SiO2, respectively, is A, the concentration of Si, which is the first component of the glassy substance, in terms of oxide, is B, and the total mass concentration of Ca, Sr, and Ba, which are the second components of the glassy substance, in terms of oxide, is C, the value of A / (B×C) is 7.1×10 -4 Below is a ceramic substrate.

2. The ceramic substrate according to claim 1, wherein the mass ratio of the content of said alkali metal, calculated as an oxide, to the content of said vitreous second component, calculated as an oxide, is 1.0 or less.

3. The ceramic substrate according to claim 1, wherein the zirconia content is 11 mass % or more.

4. The ceramic substrate according to claim 1, wherein the mole fraction of said yttria to said zirconia is 0.015 to 0.

035.

5. The ceramic substrate according to claim 1, having a flexural strength of 550 MPa or more.

6. The ceramic substrate according to claim 1, having a flexural strength of 700 MPa or more.

7. A substrate for a semiconductor device for mounting electronic components, comprising: the ceramic substrate according to claim 1; and a copper plate joined to the ceramic substrate.

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