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  • C04B37/021—Joining burned ceramic articles with other burned ceramic articles or other articles by heating with metallic articles in a direct manner, e.g. direct copper bonding [DCB]
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  • C04B2237/706—Forming laminates or joined articles comprising layers of a specific, unusual thickness of one or more of the metallic layers or articles

Definitions

• the present invention relates to a substrate for a semiconductor device and a method for manufacturing the same.
• DBOC Direct Bonding of Copper Substrate
• the heat generated by the application of high voltage and high current to the semiconductor can cause thermal expansion of the components, which can lead to separation between the ceramic substrate and the electrodes. Therefore, to improve the reliability of the device, high bonding strength is required at the bonding interface between the ceramic substrate and the electrodes.
• the present invention was made to solve the above problems, and aims to provide a substrate for a semiconductor device and a manufacturing method thereof that can improve the bonding strength between a copper plate and a ceramic substrate.
• Item 1 A ceramic substrate; a copper plate bonded to at least one surface of the ceramic substrate; Equipped with The ceramic substrate has a Cu-existing region, the Cu-existing depth from the bonding interface with the copper plate being 11.0 to 20.0 ⁇ m when the integrated Cu mass concentration is 90%.
• the ceramic substrate is Alumina and Zirconia or partially stabilized zirconia; Contains 2.
• Item 3 The substrate for semiconductor device according to item 1 or 2, in which the load per unit width for peeling the copper plate from the ceramic substrate is 5.5 kg/cm or more.
• Item 4 A step of oxidizing a copper plate by a wet oxidation method; a step of bonding at least one surface of a ceramic substrate and the copper plate by a direct bonding method; Including, A method for manufacturing a substrate for a semiconductor device, wherein the oxidized copper plate contains CuO and Cu 2 O before being bonded to the ceramic substrate, and the CuO-rich copper oxide layer is formed on the surface.
• Item 5 The method for manufacturing a substrate for a semiconductor device according to item 3 or 4, wherein the Cu presence depth when the cumulative Cu mass concentration is 90% from the bonding interface with the copper plate on each surface of the ceramic substrate is 11.0 to 20.0 ⁇ m.
• the present invention makes it possible to improve the bonding strength between the ceramic substrate and the copper plate.
• FIG. 1 is a cross-sectional view showing one embodiment of a semiconductor device including a substrate for a semiconductor device according to the present invention.
• 1 shows the results of XRD measurement of the surface of a copper plate in an embodiment of the present invention.
• 1 is a cross-sectional SEM image of a copper plate according to Example 1 of the present invention.
• 4 is an EPMA mapping image of Zr and Cu in a cross section of a substrate for a semiconductor device according to Example 1 of the present invention.
• FIG. 5( a ) is a backscattered electron image near the bonding interface between a copper plate and a ceramic substrate, and FIG.
• FIG. 5 ( b ) is a schematic diagram illustrating a subdivision and averaging method for profiling an EPMA mapping image in a cross section of a substrate for a semiconductor device according to Example 1 of the present invention.
• FIG. 13 is a diagram showing the correlation of mass concentrations of Cu and Al with respect to the depth from the bonding interface in the ceramic substrate direction in the ceramic substrate according to the present invention.
• FIG. 13 is a diagram showing the integral of the Cu mass concentration with respect to the depth from the bonded interface in the ceramic substrate direction in the ceramic substrate according to the present invention.
• Figure 1 is a cross-sectional view of a semiconductor device having a substrate for a semiconductor device according to this embodiment.
• the semiconductor device is used as a power module in various electronic devices such as smartphones, personal computers, large white goods, 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).
• various electronic devices such as smartphones, personal computers, large white goods, 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).
• the semiconductor device 1 includes a semiconductor device substrate 2, a first bonding material 5, a second bonding material 5', a semiconductor chip 6, a bonding wire 7, and a heat sink 8.
• the semiconductor device substrate 2 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.
• DBOC Direct Bonding of Copper Substrate
• the first copper plate 4 has a transmission circuit formed thereon.
• the second copper plate 4' is formed in a flat plate shape.
• a semiconductor chip 6 is bonded to the upper surface of the semiconductor device substrate 2, i.e., to a portion 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.
• a heat sink 8 is bonded to the underside of the semiconductor device substrate 2, i.e., the underside 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.
• the ceramic substrate 3 contains alumina ( Al2O3 ), zirconia ( ZrO2 ), yttria ( Y2O3 ), a glass component, and the balance other than these.
• the glass component contains silica ( SiO2 ). The contents of the constituent elements of the ceramic substrate 3 will be described below.
• the matrix component of this ceramic substrate 3 is made of alumina.
• the alumina content is preferably, for example, 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.
• the zirconia content is preferably 10% by mass or more and 25% by mass or less, and more preferably 10% by mass or more and 15% by mass or less.
• the strength of the ceramic substrate 3 can be improved.
• the linear thermal expansion coefficient of the ceramic substrate 3 can be prevented from becoming too small, and the difference in the linear thermal expansion coefficient between the ceramic substrate 3 and the first and second copper plates 4, 4' can be reduced.
• the thermal stress generated at the bonding interface can be reduced, which contributes to preventing cracks from occurring in the ceramic substrate 3 at the bonding interface.
• Cu diffuses from the copper plates 4, 4' bonded to the ceramic substrate 3 preferentially through the zirconia crystal grains rather than the alumina crystal grains that make up the matrix component, diffusing into the ceramic substrate 3 and forming a Cu-containing region. Therefore, when the zirconia content is set as described above, the diffusion of Cu is promoted, and as described later, the bonding strength of the copper plates 4, 4' is increased, which is preferable.
• zirconia content it is believed that excessive reactions at the bonding interface when joining copper plates can be suppressed, and the occurrence of voids at the bonding interface can be suppressed. This is because alumina and zirconia have different wettabilities with the Cu-O eutectic liquid phase when joining copper plates.
• zirconia content it is possible to improve the impedance of the ceramic substrate 3 without increasing the silica content, as described below.
• the yttria content is preferably 0.8% by mass or more and 1.9% by mass or less. By making the content 0.8% by mass or more, it is believed 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 believed that the mechanical strength of the ceramic substrate 3 can be improved, and that this contributes to preventing the occurrence of cracks in the ceramic substrate 3 at the bonding interface.
• the ratio of the yttria content to the zirconia content is preferably 4.5% by mass or more and 7.9% by mass or less. This is believed to maintain the stability of the tetragonal phase of zirconia at an appropriate level, and contribute to preventing a decrease in the mechanical strength of the ceramic substrate 3.
• the yttria content to 1.9 mass% or less, it is believed 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. As a result, it is believed that the mechanical strength of the ceramic substrate 3 can be improved, and that this contributes to preventing the occurrence of cracks in the ceramic substrate 3 at the bonding interface.
• the silica content is preferably 0.1% by mass or more and 2.5% by mass or less. If the silica content is 0.1% by 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 high, there is a risk that the strength of the ceramic substrate 3 will decrease, but in order to suppress this, it is preferable that the silica content be 2.5% by mass or less.
• the silica content when the zirconia content is 10 mass% or more and 15 mass% or less, the silica content is preferably 0.7 mass% or more and 1.5 mass% or less. Also, when the zirconia content is more than 15 mass% and 25 mass% or less, the silica content is preferably 1.5 mass% or more and 2.0 mass% or less. In this way, by changing the silica content depending on the zirconia content, the impedance of the ceramic substrate 3 can be effectively improved.
• the glass component may contain at least one of magnesia (MgO) and calcia (CaO).
• MgO magnesia
• CaO calcia
• the content of magnesia is preferably 0.1% by mass or more and 0.8% by mass or less, and more preferably 0.15% by mass or more and 0.3% by mass or less.
• spinel crystals MgAl 2 O 4 crystals
• magnesia content 0.8 mass% or less, it is possible to suppress the excessive formation of spinel crystals, which have low mechanical strength, and it is believed that this can 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.
• the calcia content is preferably 0.03% by mass or more and 0.35% by mass or less. This allows the ceramic substrate 3 to be sintered without an excessively high firing temperature, and is believed to be able to suppress coarsening of the alumina particles and zirconia particles. As a result, it is believed that the mechanical strength of the ceramic substrate 3 can be improved, and this contributes to suppressing the occurrence of cracks in the ceramic substrate 3 at the bonding interface.
• the content of the remainder is preferably 0.05 mass% or less in terms of oxide. This is believed to prevent the ceramic substrate 3 from being excessively sintered even though the firing temperature is not excessively high, and to reduce the porosity of the ceramic substrate 3. As a result, it is believed that the mechanical strength of the ceramic substrate 3 can be improved, and this contributes to preventing the occurrence of cracks in the ceramic substrate 3 at the bonding interface.
• the element contained in the remainder may be an element that is intentionally added, or an element that is unavoidably mixed in.
• the element contained in the remainder is not particularly limited, but examples include Fe (iron), Ti (titanium), Mn (manganese), etc.
• the content of the constituent elements of the ceramic substrate 3 is calculated in terms of oxide as described above, but the constituent elements of the ceramic substrate 3 may or may not exist in the form of an oxide.
• the constituent elements of the ceramic substrate 3 may or may not exist in the form of an oxide.
• at least one of Y, Mg, and Ca may not exist in the form of an oxide and may be solid-dissolved in ZrO2 .
• yttria may be solid-dissolved in zirconia to form PSZ (partially stabilized zirconia).
• the content of the constituent elements of the ceramic substrate 3 converted into oxides 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 oxides.
• XRF X-ray fluorescence analyzer
• EDS energy dispersive analyzer
• SEM scanning electron microscope
• XRF X-ray Fluorescence Analysis
• SEM Scanning Electron Microscope
• EDS Energy Dispersive X-ray Spectroscopy
• ICP Inductively Coupled Plasma.
• an organic binder e.g., polyvinyl butyral
• a solvent xylene, toluene, etc.
• a plasticizer dioctyl phthalate, etc.
• the slurry material is molded into the desired shape by the desired molding method (e.g., die pressing, cold isostatic pressing, injection molding, doctor blade method, extrusion molding, etc.) to produce a ceramic body.
• the desired molding method e.g., die pressing, cold isostatic pressing, injection molding, doctor blade method, extrusion molding, etc.
• the ceramic compact is fired in an oxygen or air atmosphere (1555°C to 1565°C, 0.7 to 1.0 hour) to complete the ceramic sintered body 3.
• the copper plates 4, 4' are oxidized by wet treatment using a wet oxidation method.
• each copper plate 4, 4' whose surfaces have been oxidized as described above on the upper and lower surfaces of the ceramic substrate 3, and is heated for approximately 10 to 60 minutes under nitrogen atmosphere conditions 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.
• the transmission circuit formed on the copper plate 4 on the surface to which the semiconductor chip 6 is bonded can be formed, for example, by a subtractive method or an additive method.
• the bonding strength of the copper plates 4, 4' is high if the Cu-existing depth at which the cumulative Cu mass concentration in the Cu-existing region is 90% is 11.0 to 20.0 ⁇ m, more preferably 13.0 to 18.0 ⁇ m, and even more preferably 13.0 to 16.0 ⁇ m.
• the Cu presence depth, at which the cumulative Cu mass concentration is 90% is less than 11.0 ⁇ m, the copper presence area is narrow, and the bonding strength is weakened.
• the Cu presence depth, at which the cumulative Cu mass concentration is 90% exceeds 20.0 ⁇ m, the bonding strength is reduced.
• the load per unit width required to peel the copper plates 4, 4' from the ceramic substrate 3 is measured, and this load is preferably 5.5 kg/cm or more, more preferably 6.0 kg/cm or more, and particularly preferably 8.0 kg/cm or more.
• the Cu diffusion region becomes wider as described above compared to the copper plate oxidized by the dry oxidation method. Even if a copper plate that has been oxidized by a method other than the wet oxidation method is used, the bonding strength between the copper plate 4, 4' and the ceramic substrate 3 can be improved as described above as long as the substrate for a semiconductor device can achieve the Cu presence depth as described above. In other words, the Cu presence region as described above may be formed by a method other than diffusing copper from the copper plate 4, 4' into the ceramic substrate 3.
• the copper plates 4, 4' are bonded to both sides of the ceramic substrate 3, but it is also possible to bond a copper plate to only one side of the substrate to use it as a substrate for a semiconductor device.
• the copper plates 4, 4' are bonded to both sides of the ceramic substrate 3, the Cu presence depth at which the cumulative Cu mass concentration in the Cu presence region is 90% does not have to be the same on each side of the ceramic substrate 3, and as mentioned above, it is sufficient that it is within the range of 11.0 to 20.0 ⁇ m.
• Ceramic substrates according to Examples 1 and 2 and Comparative Examples 1 and 2 were prepared, each consisting of the following materials as main components. In other words, the ceramic substrates according to Examples 1 and 2 and Comparative Examples 1 and 2 are the same. Specifically, first, a powder material prepared by mixing the compositions shown in Table 1 in a predetermined ratio was pulverized and mixed in a ball mill. In Table 1, mass% is expressed as wt%. The values shown in Table 1 are values calculated as the oxide of each element.
• polyvinyl butyral as an organic binder xylene as a solvent, and dioctyl phthalate as a plasticizer were added to the ground and mixed powder material to form a slurry-like substance.
• the slurry material was formed into a sheet using the doctor blade method to produce a ceramic compact.
• the ceramic molded body was then fired in an air atmosphere at 1565°C for 0.8 hours to obtain the ceramic substrates according to Examples 1 and 2 and Comparative Examples 1 and 2.
• the dimensions of the ceramic substrates were 0.32 mm thick, 39 mm long, and 45 mm wide.
• the copper plates according to Examples 1 and 2 and Comparative Examples 1 and 2 were prepared and subjected to an oxidation treatment on the surface.
• oxidation was performed by the above-mentioned wet oxidation method
• Comparative Examples 1 and 2 oxidation was performed by the dry oxidation method.
• the copper plates according to Comparative Examples 1 and 2 were heated for 5 minutes in a heat treatment furnace heated to 300° C. to form an oxide film of Cu 2 O. The thickness of each copper plate was about 0.3 mm.
• the copper plates according to the Examples and Comparative Examples, whose surfaces were oxidized were placed on the upper and lower surfaces of a ceramic substrate and heated under a nitrogen atmosphere at 1065° C. for the time shown in Table 2 below. In this way, substrates for semiconductor devices according to Examples 1 and 2 and Comparative Examples 1 and 2 were obtained.
• Example 2 Quantitative analysis of elements (area analysis method) In Example 1, a region including the Cu electrode, the bonding interface, and the ceramic substrate was subjected to surface analysis for Zr and Cu using a field emission electron probe microanalyzer (EPMA). The results are shown in FIG.
• EPMA field emission electron probe microanalyzer
• the element concentration (mass%) was averaged in 256 small areas in the horizontal direction (X direction) (this is called the X-direction average element concentration).
• the element concentration distribution was measured using a field emission electron probe microanalyzer (EPMA).
• EPMA field emission electron probe microanalyzer
• JXA-8530F, JEOL was used as the EPMA.
• Figure 6 is a graph with the Y direction in Figure 5, i.e., the depth direction of the ceramic substrate, as the vertical axis, and the average element concentration in the X direction at each depth is plotted on the vertical axis.
• the horizontal axis of this graph has the bonding interface between the copper plate and the ceramic substrate as the origin.
• the bonding interface is synonymous with the point where the Al concentration rises from 0 wt%.
• the mass concentration after the start of that section is defined as 0 wt%.
• the results in Figure 6 show that the diffusion distance of Cu tends to be longer when the copper plate is oxidized by wet processing and when the electrode bonding time is long.
• the Cu concentration in Fig. 6 was integrated in the Y-axis direction and plotted as a graph in Fig. 7.
• the Cu diffusion depth at which the integrated Cu mass concentration in the Cu diffusion region was 90% was determined.
• the bonding strength and Cu diffusion depth are shown in Table 4.
• Comparing Example 1 and Example 2 as the bonding time increases, the Cu diffusion region tends to increase in the Y direction, while the bonding strength tends to decrease. Comparing Example 1 and Comparative Example 1, the bonding times are the same, but Comparative Example 1 has a narrower Cu diffusion region and lower bonding strength. This shows that the melting point of the copper oxide layer is lowered, promoting Cu diffusion, and as a result, the bonding strength is higher. However, there is no proportional relationship between the Cu diffusion region in the Y direction and the bonding strength, and once the Cu diffusion region reaches a certain level, the bonding strength begins to decrease.
• Substrate for semiconductor device 3 Ceramic substrate 4, 4': Copper plate

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