JP2009215142A - Silicon nitride substrate, method for producing the same, silicon nitride circuit board using the same, and semiconductor module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a silicon nitride substrate having high strength, and in which warpage is properly regulated, to provide a method for producing the same, to provide a silicon nitride circuit board using the same, and to provide a semiconductor module. <P>SOLUTION: Silicon nitride raw material powder is blended with magnesium oxide of 3 to 4 wt.% and the oxide of at least one kind of rare earth element of 2 to 5 wt.% in such a manner that the total is controlled to 5 to 8 wt.%, so as to be a sheet molded body, and sintering is performed thereto. Thereafter, in a superimposed state, a plurality of the sintered compacts are heated at 1,550 to 1,700°C while applying a load of 0.5 to 6.0 kPa thereto, so as to produce a silicon nitride substrate comprising β type silicon nitride, yttrium (Y) and magnesium (Mg), and in which a variation coefficient showing the distribution of the Mg content in the surface is ≤0.20 and warpage is ≤2.0 μm/mm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a silicon nitride substrate and a method for manufacturing the same. The present invention also relates to a silicon nitride circuit board and a semiconductor module using the silicon nitride substrate.

  In recent years, power semiconductor modules (IGBT, power MOSFET, etc.) capable of high voltage and large current operation have been used in the field of inverters for electric vehicles. As a substrate used for the power semiconductor module, a ceramic circuit substrate in which a metal circuit board is bonded to one surface of an insulating ceramic substrate and a metal heat sink is bonded to the other surface can be used. A semiconductor element or the like is mounted on the upper surface of the metal circuit board. For joining the insulating ceramic substrate to the metal circuit board and the metal heat sink, for example, an active metal method using a brazing material or a so-called copper direct joining method in which a copper plate is directly joined is employed.

  In such a power semiconductor module, since a large amount of heat is generated by flowing a large current, a thermal stress based on a difference in thermal expansion coefficient between the insulating ceramic substrate, the metal circuit board, and the metal heat sink is generated. appear. As a result, the insulating ceramic substrate may be cracked and broken, or the metal circuit board or the metal heat radiating plate may be peeled off from the insulating ceramic substrate. Examples of the material for the insulating ceramic substrate include aluminum nitride and silicon nitride. However, since the insulating ceramic substrate using aluminum nitride has low mechanical strength, such a crack is likely to occur, and the power semiconductor module is used. It is difficult to use.

Therefore, an example of a silicon nitride sintered body is disclosed. In Patent Document 1 below, a fine powder of magnesium carbonate (MgCO ₃ ) or magnesium hydroxide (Mg (OH) ₂ ) that is thermally decomposed into magnesium oxide (MgO) is used as a sintering aid for forming the grain boundary phase. By doing so, the strength is improved as a sintered body in which the grain boundary phase is uniformly dispersed, and the variation in strength is reduced. Moreover, in the following Patent Document 2, a plurality of sintering aid components are mixed in advance and uniformly dispersed, and then silicon nitride powder as a main material is mixed to suppress aggregation and segregation of the sintering aid components. A high-strength sintered body is obtained.

JP-A-61-10069 JP 2004-161605 A

  However, when the conventional technique is applied to a silicon nitride substrate, there is a problem in that the warpage of the silicon nitride substrate cannot be adjusted appropriately. Generally, when the warpage of a silicon nitride substrate increases, the adhesion between the metal circuit board and the metal heat sink decreases, and the cooling process from the bonding temperature (about 800 ° C.) between the silicon nitride substrate, the metal circuit board, and the metal heat sink. Alternatively, the metal circuit board and the metal heat sink are easily separated from the silicon nitride substrate due to thermal stress generated in the heating / cooling cycle when the power semiconductor module is operated. For this reason, it is necessary to adjust the warp appropriately, but the conventional technique described above does not disclose the point of adjusting the warp of the silicon nitride substrate. Therefore, as described above, there is a problem that the warp value of the silicon nitride substrate cannot be adjusted appropriately.

  The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a silicon nitride substrate having a high strength and a suitable warp, a manufacturing method thereof, and a silicon nitride circuit substrate and a semiconductor module using the silicon nitride substrate. It is to provide.

  In order to achieve the above object, a silicon nitride substrate according to claim 1 is a silicon nitride substrate containing β-type silicon nitride, yttrium (Y), and magnesium (Mg). The variation coefficient indicating the distribution of the Mg amount in the film is 0.20 or less, and the warpage is 2.0 μm / mm or less.

The invention according to claim 2 is the silicon nitride substrate according to claim 1, wherein Mg (magnesium) is converted into magnesium oxide (MgO), and Y (yttrium), which is also contained, is converted into yttrium oxide (Y ₂ O ₃ ). The MgO content is 3.0 to 4.2 wt%, and the Y ₂ O ₃ content is 2.0 to 5.0 wt%. In the present invention, the total content of MgO and Y ₂ O ₃ is preferably 5.0 to 8.3 wt%, and (MgO) / (Y ₂ O ₃ ) is 0.62 to 2.2.

  The invention of the silicon nitride circuit board according to claim 3 is characterized in that a metal circuit plate is joined to one surface of the silicon nitride substrate according to claim 1 or claim 2 and a metal heat radiating plate is joined to the other surface. And

  According to a fourth aspect of the present invention, there is provided a semiconductor module comprising: the silicon nitride circuit board according to the third aspect; and a semiconductor element mounted on the silicon nitride circuit board.

  The invention of the method for producing a silicon nitride substrate according to claim 5 is characterized in that the silicon nitride raw material powder is mixed with magnesium oxide at 3 to 4% by weight and at least one rare earth element oxide at 2 to 5% by weight. The sheet molded body is sintered and then heat-treated at 1550 to 1700 ° C. while applying a load of 0.5 to 6.0 kPa in a state where a plurality of sheets are stacked. In this invention, it is preferable to mix | blend magnesium oxide and the rare earth element oxide so that it may become 5-8 wt% in total.

  According to the first and second aspects of the invention, it is possible to realize a silicon nitride substrate with high strength and appropriate warpage.

  According to the invention of claim 3, it is possible to realize a silicon nitride circuit board in which generation of cracks or peeling of the metal circuit board and the metal heat sink is suppressed.

  According to the invention of claim 4, it is possible to realize a semiconductor module in which generation of cracks or peeling of the metal circuit board and the metal heat sink is suppressed.

  According to the invention of claim 5, it is possible to provide a method for manufacturing a silicon nitride substrate having high strength and appropriately adjusted warpage.

  Hereinafter, the best mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described.

  One embodiment of the present invention is a silicon nitride substrate as an insulating ceramic substrate used in the above-described power semiconductor module and the like, and includes β-type silicon nitride, yttrium (Y), and magnesium (Mg). In the silicon nitride substrate, the variation coefficient indicating the distribution of the amount of Mg on the surface of the silicon nitride substrate is 0.20 or less. Further, the warp of the silicon nitride substrate is 2.0 μm / mm or less.

  Here, the surface of the substrate is the outermost surface of the silicon nitride substrate, that is, the surface before grinding when the silicon nitride substrate is manufactured, or polished from the outermost surface to a depth of 10% or less of the substrate thickness or 15 μm or less. This is the surface obtained.

  Further, the variation coefficient indicating the distribution of the amount of Mg is determined based on the X-ray intensity value of Mg measured at intervals of 2 μm by scanning a range of 1 mm with a beam diameter of 1 μm by EPMA at an arbitrary position on the substrate surface. It is a value obtained by dividing the deviation by its average value.

  In general, a silicon nitride substrate is composed of a grain boundary phase mainly composed of silicon nitride particles and a component added as a sintering aid. The grain boundary phase generated by using the added sintering aid as a main component maintains the bonds between the silicon nitride particles and plays a role of suppressing defects between the particles. In particular, when there are coarse defects on the surface of the silicon nitride substrate, when the stress is applied to the silicon nitride substrate, the defect becomes the starting point of the breakage and easily breaks down, so that the grain boundary phase exists uniformly dispersed. And the generation of coarse defects must be suppressed.

MgO and Y ₂ O ₃ added as sintering aids in the silicon nitride substrate react with SiO ₂ contained in Si ₃ N ₄ or Si ₃ N ₄ to form a liquid phase in the sintering process. Among these, MgO plays the role of generating the above liquid phase at a relatively low temperature, and thus contributes to the promotion of sintering. On the other hand, the liquid phase containing MgO is liable to volatilize and segregate, and is particularly high in the sintering process. It is easy to form a grain boundary phase containing Mg generated from the liquid phase non-uniformly on the substrate surface that is easily exposed. The uniformity of the grain boundary phase containing Mg can be grasped by examining the variation coefficient indicating the distribution of Mg content on the surface of the silicon nitride substrate. For this reason, when the coefficient of variation indicating the distribution of Mg content on the surface of the silicon nitride substrate is large, a large number of coarse defects are formed on the surface of the silicon nitride substrate and the bending strength is lowered, and the silicon nitride substrate, the metal circuit board, and the metal Cracks are likely to occur when stress is applied to the silicon nitride substrate due to the joining process with the heat sink, the manufacturing process of the power semiconductor module, or the heat cycle accompanying the operation of the power semiconductor module. As described above, it is necessary to adjust the coefficient of variation indicating the distribution of Mg content on the surface of the silicon nitride substrate to an appropriate value. On the other hand, the distribution of Y amount on the surface of the silicon nitride substrate is hardly affected by the manufacturing conditions.

  Therefore, in the silicon nitride substrate according to the present embodiment, as described above, the variation coefficient indicating the distribution of the Mg amount is adjusted to 0.20 or less on the substrate surface. Thereby, the bending strength of the silicon nitride substrate can be improved. A method for adjusting the coefficient of variation will be described later.

  In addition, when the warp of the silicon nitride substrate is increased, a portion having low adhesion between the silicon nitride substrate, the metal circuit board, and the metal heat sink is likely to be generated. As a result, the silicon nitride substrate, the metal circuit board, and the metal heat sink are easily peeled off. Therefore, in the silicon nitride substrate according to the present embodiment, the warpage is suppressed to 2.0 μm / mm or less as described above. A method for suppressing warpage will be described later.

Furthermore, in the silicon nitride substrate according to the present embodiment, Mg (magnesium) is 3.0 to 4.2 wt% in terms of magnesium oxide and Y (yttrium) is 2.0 to 5.0 wt% in terms of oxide (preferably Is contained in a total amount of 5.0 to 8.3 wt%). Moreover, it is preferable to contain Mg (magnesium) and Y (yttrium) in a range where (MgO) / (Y ₂ O ₃ ) is 0.62 to 2.2 in terms of oxide. Magnesium and yttrium function as sintering aids in the production of a silicon nitride substrate, and are mainly present as grain boundary phases in the produced silicon nitride substrate. Defects are easily generated and bending strength is reduced. On the other hand, when the content of magnesium and yttrium increases, a large amount of grain boundary phases having weaker strength than silicon nitride particles are formed in the silicon nitride substrate, so that breakage easily occurs via the grain boundaries and the bending strength decreases. To do. In addition, when the ratio of the content of magnesium and yttrium is not in an appropriate range, the role as a sintering aid is insufficient, and the sintering of the silicon nitride substrate is not promoted. A phase is formed and the bending strength decreases. In the present embodiment, in order to adjust these characteristics, the contents of magnesium and yttrium are within the above ranges.

  Next, a method for manufacturing the silicon nitride substrate according to the present embodiment will be described.

  FIG. 1 shows a process diagram of a method for manufacturing a silicon nitride substrate according to the present embodiment. In FIG. 1, in the raw material adjustment / mixing step (a), the silicon nitride raw material powder contains 3 to 4% by weight of magnesium oxide and 2 to 5% by weight of oxide of at least one rare earth element, for a total of 5 to 8% by weight. And mixed with a solvent, an organic binder, a plasticizer, etc. by a ball mill or the like. Here, as the oxide of at least one kind of rare earth element, it is preferable to use the above-described yttrium oxide or the like.

  Next, in the forming step (b), the mixed raw material slurry is defoamed and thickened, and then formed into a sheet having a predetermined thickness by a known doctor blade method or the like. Although the plate | board thickness of the sheet molded object at this time can be suitably determined according to a use, it can be about 0.1-1.0 mm, for example.

  Next, in the sintering step (c), the sheet compact is sintered in a sintering furnace at a temperature of 1800 to 2000 ° C. in a nitrogen pressurized atmosphere of 0.5 to 1.0 MPa, To do.

  Next, in the heat treatment step (d), heat treatment is performed at 1550 to 1700 ° C. while applying a load (pressure) of 0.5 to 6.0 kPa in a state where a plurality of sintered silicon nitride substrates are stacked. Thus, by performing heat treatment while applying a load, it is possible to suppress warpage of the silicon nitride substrate and to uniformly disperse the grain boundary phase containing Mg on the substrate surface and to improve the bending strength. . If the heat treatment temperature at this time is lower than 1550 ° C., the effect of suppressing the warpage becomes insufficient, and the warpage of the silicon nitride substrate increases. When the temperature is higher than 1700 ° C., volatilization and segregation of the grain boundary phase component containing magnesium on the silicon nitride substrate surface is promoted, and coarse defects are easily formed on the silicon nitride substrate surface, resulting in a decrease in bending strength. Therefore, the above range is preferable for the heat treatment temperature. Furthermore, when the load applied during heat treatment is lower than 0.5 kPa, the effect of suppressing warpage is insufficient, and the content of MgO decreases due to volatilization of grain boundary phase components containing Mg, resulting in bending strength. Becomes lower. In addition, when it is higher than 6.0 kPa, the adhesion between the substrates becomes too high, so that the segregation is promoted by the transfer of grain boundary phase components including Mg between the substrates, and coarse defects are formed on the surface of the silicon nitride substrate. Is easily formed and the bending strength is lowered. Therefore, the above range is suitable for the load applied during the heat treatment. The heat treatment is performed in a state where a plurality of silicon nitride substrates are stacked, and the volatilization amount of magnesium oxide, which is a sintering aid, is adjusted and controlled so that Mg contained in the silicon nitride substrate surface is uniformly dispersed. This is for adjusting the content of MgO.

  2 and 3 are explanatory views of a load application method in the heat treatment step (d). In FIG. 2, the silicon nitride substrate 10 is sandwiched between plate materials 14 made of ceramics such as boron nitride (BN), and a load is applied by a weight 16. The material for forming the plate member 14 may be a material other than BN as long as it does not affect the composition of the silicon nitride substrate in the heat treatment step. Among materials that are generally readily available, BN is preferred. The material of the weight 16 is preferably silicon nitride, and a refractory metal such as tungsten or molybdenum can also be used. In FIG. 3, a load is applied by a hot press 18 instead of the weight 16.

  The silicon nitride substrate manufactured as described above has high bending strength, high adhesion to a metal circuit board, a metal heat sink, and the like, and is used for circuit boards such as high-frequency transistors and power semiconductor modules, or multichip modules. It can be used for various components such as a substrate for an electronic component, or a member for an electronic component such as a Peltier element heat transfer plate or a heat sink for various heating elements. When the silicon nitride substrate according to the present embodiment is used as, for example, a substrate for mounting a semiconductor element, the silicon nitride substrate is bonded to the metal circuit board and the metal heat sink, the power semiconductor module is manufactured, or the power semiconductor module is operated. The generation of cracks when subjected to repeated heat cycles can be suppressed, and a substrate with improved thermal shock resistance and heat cycle resistance can be realized.

  In addition, a Cu (copper) circuit board or an Al (aluminum) circuit board, which is a metal circuit board and a metal heat sink, is attached to one or both surfaces of the silicon nitride substrate according to the present embodiment by the DBC method (Direct Bonding Cupper copper direct bonding method). The silicon nitride circuit board is manufactured by bonding using the active metal brazing material method or the like. Here, the DBC method means that a silicon nitride substrate and a Cu circuit board or an Al circuit board are heated to a temperature equal to or higher than the eutectic temperature in an inert gas or nitrogen atmosphere, and formed Cu—O and Al—O eutectic crystals. The circuit board is directly bonded to one surface or both surfaces of the silicon nitride substrate via a eutectic compound layer using a compound liquid phase as a bonding agent. On the other hand, the active metal brazing method is a mixture or alloy of an active metal such as titanium (Ti), zirconium (Zr) or hafnium (Hf) and a metal such as silver (Ag) or copper (Cu) which forms a low melting point alloy. A Cu circuit board or an Al circuit board is bonded to one surface or both surfaces of a silicon nitride substrate by hot-press bonding in an inert gas or vacuum atmosphere through a brazing material layer. After the circuit boards are joined, the Cu circuit board or Al circuit board on the silicon nitride substrate is etched to form a circuit pattern, and the Cu circuit board or Al circuit board after the circuit pattern is formed is subjected to Ni-P plating. A silicon nitride circuit board is produced.

  Moreover, a desired semiconductor module can be manufactured by mounting an appropriate semiconductor element on the silicon nitride circuit board.

  Examples of the present invention will be described below. However, the present invention is not limited to the examples described below.

A silicon nitride substrate was manufactured based on the manufacturing method shown in FIG. 1, and its physical properties were measured. Among the manufacturing conditions, magnesium oxide (MgO) addition amount, yttrium oxide (Y ₂ O ₃ ) addition amount, total addition amount of MgO and Y ₂ O ₃ , heat treatment temperature and load in the heat treatment process, and presence / absence of silicon nitride substrate overlap For each item of the thickness of the silicon nitride substrate, those shown in Table 1 as manufacturing conditions were employed (Examples 1 to 10). In addition, the presence or absence of the overlap of the silicon nitride substrate is indicated by a circle. In the case where there is no overlap, a heat treatment process is performed by sandwiching one silicon nitride substrate between two BN plate members 14.

As the measured physical properties, in addition to the Mg coefficient of variation of the surface of the silicon nitride substrate, magnesium oxide (MgO) content, yttrium oxide (Y ₂ O ₃ ) content, MgO / Y ₂ O ₃ content ratio, MgO And Y ₂ O ₃ total content, warpage, bending strength, Weibull modulus, fracture toughness, thermal conductivity and thermal shock test results. Among these items, it was determined whether or not the warpage, bending strength and fracture toughness were within the preset ranges (warpage: 2 μm / mm or less, bending strength: 820 MPa or more, fracture toughness: 6 MPam ^1/2 or more). .

  Further, as a comparative example, the physical properties of a silicon nitride substrate manufactured by changing the above manufacturing conditions were similarly measured and judged. The results are shown in Table 2 (Comparative Examples 1 to 13).

  Of the above physical properties, the Mg coefficient of variation was determined by the method described above by EPMA analysis of the substrate surface. As described above, the substrate surface is a surface obtained by polishing the outermost surface of the silicon nitride substrate or from the outermost surface to a depth of 10% or less of the substrate thickness.

Magnesium oxide (MgO) content and yttrium oxide (Y ₂ O ₃ ) content were measured by ICP emission analysis after measuring silicon nitride substrate by microwave decomposition treatment and acid dissolution treatment. It was determined by converting to magnesium oxide (MgO) and yttrium oxide (Y ₂ O ₃ ). Further, the content ratio of MgO / Y ₂ O ₃ and the total content of MgO and Y ₂ O ₃ were calculated from the obtained magnesium oxide (MgO) content and yttrium oxide (Y ₂ O ₃ ) content.

  Further, the warpage was measured with a three-dimensional laser measuring instrument (LT-8100 manufactured by Keyence). FIGS. 4A and 4B are explanatory diagrams of a method for measuring warpage. In FIG. 4A, a distance from a suitably set surface to the substrate surface S is measured with a three-dimensional laser measuring instrument, and a surface connecting two points at which the distance is minimum is set as a reference surface. Next, the height D of the highest point at which the height (distance) from the reference surface is the highest was taken as the warpage magnitude. As shown in FIG. 4B, the measurement of the distance from the certain surface to the substrate surface S was performed on the diagonal line of the silicon nitride substrate. The value obtained by dividing the magnitude of the warpage by the scanning distance, that is, the diagonal distance shown in FIG.

  The bending strength was measured by a three-point bending test based on JIS-R1601. A silicon nitride substrate is processed into a test piece with a width of 4 mm, set on a three-point bending jig with a distance between support rolls of 7 mm, and a load is applied at a crosshead speed of 0.5 mm / min. Calculated from

For the Weibull coefficient, a Weibull plot in which lnln (1-F) ⁻¹ was plotted against lnσ was created from the bending strength test result in accordance with JIS-R1625, and the Weibull coefficient of the slope was obtained. Here, σ is the bending strength, and F is the cumulative failure probability.

  Fracture toughness was measured by an IF method in which a Vickers indenter was pushed into a side surface of a silicon nitride substrate with a predetermined load (2 kgf (19.6 N) in this example) in accordance with JIS-R1607. At this time, the Vickers indenter was pushed so that one diagonal line of the Vickers indentation was perpendicular to the thickness direction of the silicon nitride substrate.

  The thermal conductivity was measured in accordance with JIS-R1611 by cutting a 5 mm square measurement sample from a silicon nitride substrate.

In the thermal shock test, a silicon nitride circuit substrate having a Cu circuit board formed on the surface of the silicon nitride substrate and a Cu heat sink formed on the back surface was held at 350 ° C. for 10 minutes, and then rapidly cooled to room temperature, and cracks in the silicon nitride substrate were observed. The occurrence was examined. This operation was repeated 10 times to determine whether or not a crack occurred. When the warp was larger than 2.0 μm / mm, it could not be used as a silicon nitride circuit board, so the thermal shock test was not performed.

As shown in Table 1 above, the added amount of MgO is 3 to 4% by weight (wt), the added amount of Y ₂ O ₃ is 2 to 5% by weight, the heat treatment temperature in the heat treatment step is 1550 to 1700 ° C., and the load is 0. In the case of a silicon nitride substrate having a thickness of 5 to 6.0 kPa and a thickness of 0.1 to 1.0 mm manufactured with overlapping, the above-described Mg variation coefficient (setting range of 0.20 or less) on the substrate surface and MgO content (setting) Range 3.0 to 4.2 wt%), Y ₂ O ₃ content (setting range 2.0 to 5.0 wt%), MgO / Y ₂ O ₃ content ratio (setting range 0.62 to ₂ ) .2), the total content of MgO and Y ₂ O ₃ (setting range 5.0 to 8.3 wt%), warpage (setting range 2 μm / mm or less), bending strength (setting range 820 MPa or more) and fracture toughness (setting) The range of 6 MPa · m ^1/2 or more is all within the set range. The Weibull coefficient also satisfies the setting range of 15 or more, and it can be seen that the variation in bending strength is small. As a result, even in the thermal shock test, the silicon nitride substrate was not broken, and all were judged to be acceptable.

Of the silicon nitride substrates stacked in the heat treatment step, the uppermost silicon nitride substrate and the lowermost silicon nitride substrate each have one surface in contact with the plate material 14, so that the sintering aid (MgO, Y ₂ O) is in contact with the plate material 14. ₃ ) Volatilization is promoted, but since the other surface is in contact with another silicon nitride substrate, volatilization is suppressed and the characteristics are not significantly impaired. The reason why volatilization of the sintering aid is promoted on the contact surface with the plate member 14 will be described later.

On the other hand, as shown in Table 2, as Comparative Example 1, a 0.32 mm thick nitridation manufactured under the conditions that the MgO addition amount was 3 wt% and the Y ₂ O ₃ addition amount was 2 wt% and the heat treatment step was not performed. In the silicon substrate, the warpage is as large as 2.9 μm / mm. This is because the warp of the silicon nitride substrate could not be suppressed because there was no heat treatment step. Further, the coefficient of variation of Mg is high (0.45), and the bending strength is low (812 MPa). This is because the Mg component on the substrate surface was not uniformly dispersed because no heat treatment was performed.

Further, as Comparative Example 2, a 0.32 mm-thick nitridation manufactured under the conditions that the MgO addition amount is 3 wt%, the Y ₂ O ₃ addition amount is 2 wt%, the heat treatment temperature is 1450 ° C., the load is 2.2 kPa, and there is an overlap. Unlike the comparative example 1, in the silicon substrate, although the heat treatment process was performed, the heat treatment temperature was low, and thus the warpage was as large as 2.5 μm / mm.

Further, as Comparative Example 3, a 0.32 mm thick nitridation manufactured under the conditions that the MgO addition amount is 3 wt%, the Y ₂ O ₃ addition amount is 2 wt%, the heat treatment temperature is 1800 ° C., the load is 2.4 kPa, and there is an overlap. In the silicon substrate, the coefficient of variation of Mg is high (0.32), and the bending strength is low (795 MPa). This is because volatilization and segregation of grain boundary phase components on the surface of the silicon nitride substrate are promoted by heat treatment at a high temperature. As a result, cracks occurred in the silicon nitride substrate in the thermal shock test. In addition, as a difference from Comparative Example 3, the amount of Y ₂ O ₃ added was 3 wt%, Comparative Example 4 in which the load was 2.6 kPa, and the amount of MgO added was 4 wt%, and the load was 1.9 kPa. In Comparative Example 5, the heat treatment temperature was as high as 1800 ° C., and the Mg coefficient of variation on the substrate surface was high (Comparative Example 4 was 0.42 and Comparative Example 5 was 0.27), and the bending strength was low (Comparative Example). 4 is 812 MPa, and Comparative Example 5 is 808 MPa). As a result, in the thermal shock test, cracks occurred in the silicon nitride substrate.

Further, as Comparative Example 6, a nitriding nitride having a thickness of 0.32 mm manufactured under the conditions that the MgO addition amount is 3 wt%, the Y ₂ O ₃ addition amount is 2 wt%, the heat treatment temperature is 1600 ° C., the load is 6.5 kPa, and there is an overlap. In the silicon substrate, the coefficient of variation of Mg on the substrate surface is high (0.46), and the bending strength is low (798 MPa). This is because segregation of grain boundary phase components on the surface of the silicon nitride substrate was promoted because the load during heat treatment was increased to 6.5 kPa. As a result, cracks occurred in the silicon nitride substrate in the thermal shock test.

Further, as Comparative Example 7, a silicon nitride substrate having a thickness of 0.32 mm manufactured under the conditions that the MgO addition amount is 3 wt%, the Y ₂ O ₃ addition amount is 2 wt%, the heat treatment temperature is 1600 ° C., no load is applied, and there is an overlap. Then, since there was no load in the heat treatment process, the effect of suppressing the warp was not sufficient, and the warp was as large as 3.0 μm / mm. Further, the content of MgO is low (2.9 wt%), and the bending strength is low (802 MPa). This is because the volatilization of the grain boundary phase component on the surface of the silicon nitride substrate was promoted by the heat treatment under the condition of no load.

Further, as Comparative Example 8, a 0.32 mm thick nitridation manufactured under the conditions of 3% by weight of MgO and 3% by weight of Y ₂ O ₃ , heat treatment temperature of 1600 ° C., load of 2.1 kPa and no overlap. In a silicon substrate, the coefficient of variation of Mg on the substrate surface is high (0.23), the content of MgO is low (2.9 wt%), the bending strength is low (780 MPa), and the fracture toughness is also low (5.9 MPam ^{1 / 2} ) This is because volatilization and segregation of grain boundary phase components were promoted because the silicon nitride substrate was not overlapped in the heat treatment step. As a result, cracks occurred in the silicon nitride substrate in the thermal shock test. In this comparative example, one silicon nitride substrate is sandwiched between two BN plates 14. Since the BN material has a density of 80% and many vacancies, the sintering aid evaporated from the silicon nitride substrate in the heat treatment process is adsorbed by the BN material or volatilizes in the atmosphere via the BN material. it is conceivable that.

Further, as Comparative Example 9, a silicon nitride substrate having a thickness of 0.32 mm manufactured under the conditions that the MgO addition amount is 3% by weight, the Y ₂ O ₃ addition amount is 3% by weight, the heat treatment temperature is 1600 ° C., no load is applied, and there is no overlap. Then, since there is no load in the heat treatment process, the warpage is as large as 3.2 μm / mm, and since the heat treatment is performed under the condition without overlapping, volatilization and segregation of grain boundary phase components are promoted, and the coefficient of variation of Mg on the substrate surface is increased. As high as 0.23, the MgO content is reduced to 2.9 wt%, and the bending strength is reduced to 788 MPa.

Further, as Comparative Example 10, a 0.32 mm-thick nitridation manufactured under the conditions that the MgO addition amount was 3 wt%, the Y ₂ O ₃ addition amount was 1 wt%, the heat treatment temperature was 1600 ° C., the load was 3.0 kPa, and there was overlap. In the silicon substrate, bending strength and fracture toughness are lowered (bending strength: 734 MPa, fracture toughness: 5.1 MPam ^1/2 ). This is because the amount of Y ₂ O ₃ as a sintering aid is as small as 1% by weight, so the content of Y ₂ O ₃ is low (1.0 wt%), and the content of MgO and Y ₂ O ₃ is low. This is because the total amount is as low as 4.1 wt% and the content ratio of MgO / Y ₂ O ₃ is as high as 3.2, and a brittle and defect-rich grain boundary phase is formed. As a result, cracks are generated in the silicon nitride substrate in the thermal shock test.

Further, as Comparative Example 11, a 0.32 mm-thick nitride film manufactured under the conditions that the MgO addition amount is 3 wt%, the Y ₂ O ₃ addition amount is 6 wt%, the heat treatment temperature is 1600 ° C., the load is 2.1 kPa, and there is an overlap. In a silicon substrate, since the amount of Y ₂ O ₃ as a sintering aid is as large as 6% by weight, the content of Y ₂ O ₃ is also increased to 6.0 wt%, and the contents of MgO and Y ₂ O ₃ This is because the total amount of MgO / Y ₂ O ₃ is as high as 9.1 wt%, and the MgO / Y ₂ O ₃ content ratio is as small as 0.52, and a large amount of fragile grain boundary phases are formed. As a result, cracks are generated in the silicon nitride substrate in the thermal shock test.

Further, as Comparative Example 12, a nitrided nitride having a thickness of 0.32 mm manufactured under the conditions of MgO addition amount of 2% by weight, Y ₂ O ₃ addition amount of 2% by weight, heat treatment temperature of 1600 ° C., load of 3.0 kPa, and overlap. In the silicon substrate, bending strength and fracture toughness are lowered (bending strength: 767 MPa, fracture toughness: 5.8 MPam ^1/2 ). This is because the amount of MgO, which is a sintering aid, is as low as 2 wt%, so the content of MgO is low (2.1 wt%), and the total content of MgO and Y ₂ O ₃ is also 4.1 wt%. This is because a grain boundary phase with many defects was formed. As a result, cracks are generated in the silicon nitride substrate in the thermal shock test.

Further, as Comparative Example 13, a nitrided nitride having a thickness of 0.32 mm manufactured under conditions of MgO addition amount 5 wt%, Y ₂ O ₃ addition amount 3 wt%, heat treatment temperature 1600 ° C., load 2.3 kPa, and with overlap. This is because, in the silicon substrate, the amount of MgO, which is a sintering aid, is as large as 5% by weight, so the content of MgO is as large as 5.2% by weight, and a large amount of fragile grain boundary phases are formed. As a result, cracks are generated in the silicon nitride substrate in the thermal shock test.

  As described above, the silicon nitride substrate manufactured in the setting range of the manufacturing conditions shown in Table 1 has the Mg coefficient of variation and other characteristics in the setting range shown in Table 1, and the silicon nitride substrate has cracks. Although it does not occur and does not lead to destruction, it can be seen that if any of the manufacturing conditions are out of the set range, the warpage of the silicon nitride substrate increases or the silicon nitride substrate is destroyed.

It is process drawing which shows an example of the manufacturing method of the silicon nitride board | substrate concerning this invention. It is explanatory drawing of the application method of the load in the heat processing process shown by FIG. FIG. 6 is another explanatory diagram of a load application method in the heat treatment step shown in FIG. 1. It is explanatory drawing of the measuring method of curvature.

Explanation of symbols

10 Silicon nitride substrate 14 Plate material 16 Weight 18 Hot press

Claims (5)

  In a silicon nitride substrate containing β-type silicon nitride, yttrium (Y), and magnesium (Mg), the variation coefficient indicating the distribution of the amount of Mg on the surface of the silicon nitride substrate is 0.20 or less, and the warpage is 2 A silicon nitride substrate having a thickness of 0.0 μm / mm or less. 2. The silicon nitride substrate according to claim 1, wherein when Mg (magnesium) is converted into magnesium oxide (MgO) and Y (yttrium) contained therein is converted into yttrium oxide (Y ₂ O ₃ ), the MgO content is 3 A silicon nitride substrate, characterized by 0.0 to 4.2 wt% and a Y ₂ O ₃ content of 2.0 to 5.0 wt%.   3. A silicon nitride circuit board comprising: a metal circuit board bonded to one surface of the silicon nitride substrate according to claim 1; and a metal heat dissipation plate bonded to the other surface.   A semiconductor module comprising: the silicon nitride circuit board according to claim 3; and a semiconductor element mounted on the silicon nitride circuit board. Silicon nitride raw material powder is mixed with magnesium oxide 3-4 wt% and at least one rare earth element oxide 2-5 wt%, formed into a sheet, sintered, and then stacked in layers A method for producing a silicon nitride substrate, wherein heat treatment is performed at 1550 to 1700 ° C. while applying a load of 0.5 to 6.0 kPa in a heated state.

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