JP7330089B2 - Silicon nitride substrate, silicon nitride circuit substrate and semiconductor device using the same - Google Patents

Description

TECHNICAL FIELD Embodiments generally relate to a silicon nitride substrate , a silicon nitride circuit substrate using the same, and a semiconductor device.

Ceramic substrates include various substrates such as silicon nitride substrates, aluminum nitride substrates, and aluminum oxide substrates. Some silicon nitride substrates have a three-point bending strength of 550 MPa or more.
Some aluminum nitride substrates have a thermal conductivity of 170 W/m·K or higher. The aluminum oxide substrate has a three-point bending strength of 400 to 500 MPa and a thermal conductivity of about 20 to 30 W/m·K, but is inexpensive. Ceramic substrates are selected by taking advantage of their respective characteristics.
For example, Japanese Patent Laying-Open No. 9-121004 (Patent Document 1) discloses a circuit board using a silicon nitride substrate. In Patent Document 1, a method of joining copper plates using an active metal method,
A method of forming a metallization layer through an oxide layer is disclosed. International Publication No. 2017/
Japanese Patent Application Laid-Open No. 056360 (Patent Document 2) discloses a silicon nitride circuit board in which a copper plate is joined by an active metal method. The thicker the copper plate, the better the heat dissipation and the higher current carrying capacity. On the other hand, in order to improve the reliability of TCT, the size of the protruding portion of the bonding layer is controlled. An etching process is performed to adjust the size of the protruding portion. In the etching process, different chemicals are used to treat the copper plate and the protruding portion, which has been a factor in increasing costs.
In Patent Document 1, although the metallized layer is formed via the oxide layer, the bonding strength was not necessarily satisfactory. For example, Japanese Patent Application Laid-Open No. 2015-109299 (Patent Document 3) discloses a silicon nitride circuit board provided with a copper metallized layer.

JP-A-9-121004 International Publication No. 2017/056360 JP 2015-109299 A Japanese Patent No. 6293772

Patent Document 3 aims to improve TCT characteristics by forming a metallized layer in which a glass component is added to copper. In the TCT test of Patent Document 3, the state after 10 cycles in the temperature range of -20°C to 250°C was tested. There was no problem with about 10 cycles, but the number of cycles beyond that was not always satisfactory.
When the cause was investigated, it was found that the bonding strength between the silicon nitride substrate and the metallized layer was insufficient. Moreover, there is also a problem that the insulating property is lowered after the formation of the metallized layer. Embodiments are intended to address such problems, and provide a silicon nitride substrate that enables bonding strength with a metallized layer. In addition, it also suppresses deterioration in insulation after the metallization layer is formed.

The silicon nitride sintered body according to the embodiment is a silicon nitride sintered body having an oxide layer on at least a part of the surface, and when the surface of the sintered body having the oxide layer is subjected to XRD analysis, the diffraction angle is 21.7.
The strongest peak detected at ±0.3° is I _21.7 , the strongest peak based on silicon nitride crystal grains is I _SiN , and the ratio I _21.7 /I _SiN is 0.02 or more and 0.40 or less. It is characterized by being

1 is a diagram showing an example of a silicon nitride substrate according to an embodiment; FIG. BRIEF DESCRIPTION OF THE DRAWINGS The figure which shows an example of the silicon-nitride circuit board concerning embodiment. FIG. 4 is a diagram showing another example of the silicon nitride circuit board according to the embodiment; 1A and 1B are diagrams illustrating an example of a semiconductor device according to an embodiment; FIG.

The silicon nitride sintered body according to the embodiment is a silicon nitride sintered body having an oxide layer on at least a part of the surface, and when the surface of the sintered body having the oxide layer is subjected to XRD analysis, the diffraction angle is 21.7.
The strongest peak detected at ±0.3° is I _21.7 , the strongest peak based on silicon nitride crystal grains is I _SiN , and the ratio I _21.7 /I _SiN is 0.02 or more and 0.40 or less. It is characterized by being
An example in which a silicon nitride sintered body is applied to a silicon nitride substrate will be described below. FIG. 1 shows an example of a silicon nitride substrate according to the embodiment. 2 and 3 show an example of the silicon nitride circuit board according to the embodiment. In the figure, 1 is a silicon nitride substrate, 2 is a substrate surface, 3 is an oxide layer, 4 is a central portion, 5 is a metal portion, and 10 is a silicon nitride circuit substrate.
A substrate surface 2 of a silicon nitride substrate 1 is provided with an oxide layer 3 . A substrate surface 2 indicates a location where a metal portion 5 is provided. A substrate surface 2 is provided with an oxide layer 3 . The oxide layer 3 exists where the metal portion 5 is to be provided. In FIG. 2, the oxide layer 3 and the metal portion 5 have the same size when viewed from above. 3, the oxide layer 3 is provided wider than the metal portion 5 when viewed from above. The silicon nitride circuit board 10 according to the embodiment is
It has a structure in which a metal portion 5 is provided with an oxide layer 3 interposed therebetween. Therefore, in the silicon nitride substrate 1 according to the embodiment, it suffices if the oxide layer 3 is present at the location where the metal portion 5 is desired to be provided. Therefore, oxide layer 3 may be provided on the rear surface and side surfaces of silicon nitride substrate 1 .

When the surface of the sintered body having an oxide layer is subjected to XRD analysis, the strongest peak detected at a diffraction angle of 21.7 ± 0.3 ° is I _21.7 , and the strongest peak based on silicon nitride crystal grains is I _SiN ,
The ratio I _21.7 /I _SiN is 0.02 or more and 0.40 or less.
First, the silicon nitride substrate 1 having the oxide layer 3 is subjected to XRD (X-ray diffraction) analysis. XRD analysis shall use a Bruker D8-ADVANCE. In addition, the measurement conditions are C
u target (Cu-Kα), scan type θ-2θ, scan mode Continue
ousPSDfastscan, tube voltage 40 kV, tube current 40 mA, counting time 0.5°/
min, the scanning range (2θ) is 10° to 50°, and the step width is 0.02°. It is also assumed that the measurement is performed from the direction perpendicular to the oxide layer 3 . In addition, D8- made by Bruker
An XRD analyzer with performance equivalent to ADVANCE may be used.

First, let _I21.7 be the strongest peak detected at a diffraction angle of 21.7±0.3°. Furthermore, the strongest peak intensities detected at 27.1±0.3° and 36.1±0.3° corresponding to silicon nitride crystal grains are defined as _I27.1 and _I36.1 . The total peak height of I _27.1 and I _36.1 is defined as the peak I _SiN based on silicon nitride crystal grains (I _SiN =I _27.1 +
_I36.1 ).
Moreover, the fact that it is detected at a diffraction angle of 21.7±0.3° indicates that the oxide layer 3 contains silicon oxide. In particular, silicon oxide is cristobalite (crist
obalite). Silicon oxide is called silica. silica includes quartz, tridymite,
It has various crystal phases such as cristobalite and coesite. Generally, silicon oxide is white. The silicon nitride sintered body is gray. By providing the oxide layer 3 containing silicon oxide, the location where the oxide layer 3 is provided can be visually determined. Therefore, it is preferable to provide an oxide layer containing silicon oxide.

Further, I _21.7 /I _SiN is characterized by being 0.02 or more and 0.40 or less. That I _21.7 /I _SiN is 0.02 or more and 0.40 or less indicates that oxide layer 3 contains a predetermined amount of silicon oxide. In particular, it indicates that a predetermined amount of cristobalite is contained. Various metals such as copper (Cu), silver (Ag), nickel (Ni), gold (Au), molybdenum (Mo), and tungsten (W) are used for the metal portion 5 . Cristobalite is a component that hardly reacts with such metals. In particular, it is a component that hardly reacts with copper or silver. Since the reaction with the metal can be suppressed, it is possible to suppress the metal component forming the metal portion from entering into the silicon nitride substrate 1 . Therefore, deterioration of insulation can be prevented.
If I _21.7 /I _SiN is less than 0.02, the amount of cristobalite in the oxide layer 3 is insufficient. Moreover, if I _21.7 /I _SiN exceeds 0.40, the performance of the silicon nitride substrate 1 may be degraded. Since the silicon nitride substrate 1 is required to have heat dissipation properties, it has a thermal conductivity of 50 W/m.
・K or higher, or even 80 W/m·K or higher is used. If the amount of oxide layer 3 increases, there is a possibility that the heat dissipation property of the silicon nitride substrate is lowered. Therefore, I _21.7 /I _SiN is 0
. 02 or more and 0.40 or less, more preferably 0.04 or more and 0.10 or less.
The presence or absence of cristobalite in the oxide layer 3 can be determined by detecting a peak at 31.3±0.3° or 36.9±0.3° in addition to the peak at I _21.7 . can.
In addition, when the aforementioned peak overlaps with peaks of other components and is difficult to distinguish, TEM (transmission electron microscope) or Raman spectroscopy may be used. A method of analyzing the lattice spacing by TEM and the like can be mentioned.

Moreover, when the central portion of the silicon nitride sintered body is subjected to XRD analysis, I _21.7 /I _SiN is preferably 0 or more and 0.01 or less. The central portion 4 of the silicon nitride substrate 1 is a portion where the center line in the thickness direction and the center line in the long side direction of the silicon nitride substrate 1 intersect. It is assumed that the vicinity of the central portion 4 of the silicon nitride substrate 1 is subjected to XRD analysis. It is assumed that the silicon nitride substrate 1 is processed from above and the processing is performed to excavate to the central portion 4 . The measurement conditions for the XRD analysis are the same as described above. In addition, when the silicon nitride sintered body is large, the cross section may be used as the measurement surface. For example, for a silicon nitride substrate, X
The beam spot diameter of RD analysis may cover the cross section of the substrate. When this happens,
It is better to measure after cutting or ion milling.
The fact that the I _21.7 /I 2 _SiN of the center portion 4 is 0 or more and 0.01 or less indicates that the amount of cristobalite present in the center portion 4 of the silicon nitride substrate 1 is small. Further, the I _21.7 /I _SiN of the central portion 4 being zero also includes the I _21.7 of the central portion 4 being below the detection limit.
In addition, I _21.7 when the surface of the sintered body having an oxide layer was analyzed by XRD was expressed as I _21.7S
, I _21.7 at the center of the silicon nitride sintered body is defined as I _21.7C , and (I _21.7S /I _SiN
)/(I _21.7C /I _SiN ) is preferably 5 or more. The S in _I21.7S means surface. Also, C in I _21.7C means the central part.
The fact that (I _21.7S /I _SiN )/(I _21.7C /I _SiN ) is 5 or more indicates that the abundance of cristobalite is large on the surface and small inside. As described above, cristobalite can prevent the components of the metal portion 5 from entering the interior of the silicon nitride substrate 1 too much. On the other hand, if cristobalite exists inside the silicon nitride substrate 1, the thermal conductivity and strength may be lowered. Therefore, it is preferable to provide an oxide layer 3 containing cristobalite on the substrate surface 2 of the silicon nitride substrate 1 instead of using cristobalite as a sintering aid.

As described above, it is effective to provide the oxide layer 3 containing cristobalite. In other words, I _21.7 is preferably a peak based on the cristobalite crystal structure.
Also, the thickness of the oxide layer is preferably 5 μm or less. The oxide layer 3 exists at the interface with the metal portion 5 . Also, the metal portion 5 of the silicon nitride circuit board 10 is used as a portion for mounting a semiconductor element or the like. If the thickness of the oxide layer 3 is more than 5 μm, the oxide layer 3 itself becomes a thermal resistance, which may cause a decrease in heat dissipation. Therefore, the thickness of the oxide layer 3 is preferably 5 μm or less, more preferably 1 μm or less. Although the lower limit of the thickness of the oxide layer 3 is not particularly limited, it is preferably 0.1 μm or more. If the oxide layer is as thin as less than 0.1 μm, there is a possibility that the metal part and the silicon nitride substrate will react excessively and the insulating properties will deteriorate.
Moreover, it is preferable to measure the thickness of the oxide layer 3 after ion milling. It is assumed that silicon nitride substrate 1 having oxide layer 3 is milled from the direction perpendicular to oxide layer 3 . Also, it is assumed that a sample obtained by performing the XRD analysis of the aforementioned central portion may be used. In a milled sample, the thickness of the oxide layer above the silicon nitride crystal grains on the topmost surface of the silicon nitride substrate shall be determined.

Further, when XRD analysis was performed on the surface of the sintered body having the oxide layer, the diffraction angle was 16.5±0.3°.
I _16.5 is the strongest peak detected in , and I _SiN is the strongest peak based on silicon nitride crystal grains.
and the ratio I _16.5 /I _SiN is preferably 0.01 or more and 0.10 or less.
I _16.5 is the peak due to silica (SiO ₂ ). I _16.5 /I _SiN is 0
. 01 or more and 0.10 or less indicates that SiO ₂ is present in the oxide layer 3 . As described above, cristobalite suppresses reaction with the metal portion 5 . If the oxide layer 3 is formed only of cristobalite, the adhesion strength between the oxide layer 3 and the metal portion 5 may decrease. For this reason, the oxide layer 3 preferably contains SiO ₂ . If I _16.5 /I _SiN is less than 0.01, the effect of providing SiO ₂ is insufficient. On the other hand, if it exceeds 0.10, SiO ₂ will be too much, and the effect of cristobalite may decrease.
In addition, I _16.5 when the surface of the sintered body having an oxide layer was analyzed by XRD was expressed as I _16.5S
, I _16.5 at the center of the silicon nitride sintered body is I _16.5C , and (I _16.5S /I _SiN
)/(I _16.5C /I _SiN ) is preferably 1.5 or more. (I _16.5S /
The fact that I _SiN )/(I _16.5C /I _SiN ) is 1.5 or more indicates that the oxide layer 3 contains a large amount of SiO ₂ .
It is also effective to combine the measurement of _I21.7S and _I16.5S with EPMA (electron probe microanalyzer) analysis in order to confirm whether they are present in the oxide layer.
XRD analysis may detect SiO ₂ in the silicon nitride sintered body. For this reason, E
The presence of the target component in the oxide layer may be confirmed in combination with PMA.

When the surface of the sintered body having an oxide layer is subjected to XRD analysis, the strongest peak detected at a diffraction angle of 28.0 ± 0.3 ° is I _28.0 , and the strongest peak based on silicon nitride crystal grains is I _SiN ,
The ratio I _28.0 /I _SiN is preferably 0.02 or more and 0.20 or less.
I _28.0 is a peak based on an alkaline earth metal element-silicon-oxygen compound. The alkaline earth metal element is one selected from Be (beryllium), Mg (magnesium), Ca (calcium), Sr (strontium), Ba (barium), and Ra (radium). Alkaline earth metal elements are group 2A elements in the Japanese periodic table. Among the alkaline earth metal elements, magnesium is preferred. magnesium-silicon-oxygen (Mg-Si
—O) compounds include Mg(SiO ₃ ) and the like. Mg--Si--O compounds are compounds that readily react with metals such as copper and silver. Therefore, by including a Mg--Si--O compound in the oxide layer 3, it is possible to improve the adhesion to the metal portion.
If I _28.0 /I _SiN is less than 0.02, the effect of providing the alkaline earth metal element--Si--O compound is small. Moreover, if I _28.0 /I _SiN exceeds 0.20 and is large, the metal part 5 may react with the silicon nitride substrate 1 to lower the insulating properties. For this reason, I _28.0
/I _SiN is preferably 0.02 or more and 0.20 or less, more preferably 0.03 or more and 0.08 or less.

Moreover, when the central portion of the silicon nitride sintered body is subjected to XRD analysis, I _28.0 /I _SiN is preferably 0 or more and 0.02 or less. Further, I _28.0S is the I _28.0 when the surface of the sintered body having the oxide layer is analyzed by XRD, and I _28.0 is the I _28.0 at the center of the silicon nitride sintered body.
_C , and (I _28.0S /I _SiN )/(I _28.0C /I _SiN ) is preferably 1.5 or more. This is because the central portion 4 is more alkaline earth metal element-Si than the oxide layer 3.
This indicates that there are few —O compounds. Also, when I _28.0C is zero (I _28.0C
0S /I _SiN )/(I _28.0C /I _SiN ) becomes infinity. In addition, when _I28.0C is zero, it includes below the detection limit.

Further, when XRD analysis was performed on the surface of the sintered body having the oxide layer, the diffraction angle was 32.1 ± 0.3 °
or 33.0±0.3°, or peaks are preferably detected at both of them. Also, the strongest peak at the diffraction angle of 32.1±0.3° is I _32.1 and the diffraction angle is 33.0±0.
The strongest peak at 3° is taken as I _33.0 . I _32.1 /I _SiN is 0.005 or more and 0.02
The following are preferable. Also, I _33.0 /I _SiN is preferably 0.005 or more and 0.02 or less.
I _32.1 or I _33.0 is a peak based on at least one of rare earth element-Group 4 element-oxygen compound or alkaline earth metal element-rare earth element-silicon-oxygen compound.
The rare earth elements are one or more selected from Y (yttrium), lanthanide elements, and actinide elements. 1 selected from Y and lanthanoid elements as rare earth elements
A species or two or more species are preferred. Lanthanide elements include Ce (cerium), P
r (praseodymium), Gd (gadolinium), Dy (dysprosium), Er (erbium) and Yb (ytterbium) are preferred.
Also, the Group 4 element is one or more selected from Ti (titanium), Zr (zirconium), and Hf (hafnium). Group 4 elements are group 4A elements in the Japanese periodic table.
The rare earth element-group 4 element-oxygen compound is preferably a rare earth element-titanium-oxygen compound. Examples of rare earth element-titanium-oxygen compounds include Y ₂ TiO ₅ , YbTi
_O3 and the like. As the alkaline earth metal element-rare earth element-silicon-oxygen compound, a magnesium-rare earth element-silicon-oxygen compound is preferable. Examples of magnesium-rare earth element-silicon-oxygen compounds include MgY ₄ Si ₅ O ₁₃ , Mg ₂ Y ₃ (
SiO ₄ ) ₃ F and the like. Examples of the alkaline earth metal element-rare earth element-silicon-oxygen compound include CaY ₄ (SiO ₄ ) ₃ O and the like.
The rare earth element-group 4 element-oxygen compound or the alkaline earth metal element-rare earth element-silicon-oxygen compound also has the function of improving the adhesion to the metal part.
Silicon nitride substrate 1 having oxide layer 3 as described above is suitable for silicon nitride circuit substrate 10 . Moreover, it is preferable that the silicon nitride circuit board 10 has the metal portion 5 provided on the oxide layer 3 of the silicon nitride substrate 1 .

The metal part 5 is made of copper (Cu), silver (Ag), nickel (Ni), gold (Au), molybdenum (
Mo), tungsten (W), and various other metals are used. Moreover, the metal part 5 is preferably a metallized layer or a thin film layer. The metallized layer is a metal paste hardened by heat treatment. Also, the thin film layer is a film formed by a film forming method such as sputtering or plating.
A metallized layer or a thin film layer is effective for forming a metal portion having a thickness of 0.1 mm or less. A metallized layer can be formed by applying a metal paste to a portion where a metal portion is desired to be formed. Similarly, the thin film layer can be formed only in the places where the metal parts are desired by masking the places where the metal parts are not to be formed. Therefore, the number of etching steps can be reduced. Also, even if etching is performed, the load can be reduced by reducing the thickness of the metal portion.

Although silicon nitride substrates and silicon nitride circuit substrates have been described above as examples, the silicon nitride sintered bodies according to the embodiments can be used in various other fields. For example, by providing a metal portion on a silicon nitride sintered body roller provided with an oxide layer, antistatic properties and a flexible surface can be obtained.

Next, a method for manufacturing a silicon nitride sintered body according to the embodiment will be described. As long as the silicon nitride sintered body according to the embodiment has the above structure, the method for producing the same is not particularly limited.
First, a silicon nitride sintered body is prepared. Thermal conductivity of 50W when used for silicon nitride circuit board
/m·K or more and a three-point bending strength of 600 MPa or more. The silicon nitride substrate preferably has a thickness of 0.7 mm or less, more preferably 0.1 mm or more and 0.4 mm or less. By thinning the substrate, the thermal resistance of the silicon nitride substrate can be lowered. When used for wear-resistant members such as rollers, it preferably has a thermal conductivity of 30 W/m·K or less and a three-point bending strength of 800 MPa or more. Silicon nitride sintered bodies used for circuit boards and silicon nitride sintered bodies used for wear-resistant members are preferably distinguished by thermal conductivity. Flash method shall be used for thermal conductivity measurement. In addition, the three-point bending strength is JIS-R-1601
shall be measured in accordance with For example, Japanese Patent No. 6293772 (Patent Document 4) is exemplified as a silicon nitride substrate.
Moreover, the silicon nitride sintered body preferably contains one or more of an alkaline earth metal element, a Group 4 element, and a rare earth element in the grain boundary phase. For inclusion in the grain boundary phase, it is preferable to use one or more of alkaline earth metal elements, Group 4 elements, and rare earth elements as a sintering aid.

Next, the step of forming an oxide layer shall be performed. The step of forming the oxide layer includes a step of heat-treating the silicon nitride sintered body. Moreover, the process of apply|coating and baking an oxide paste is mentioned. Moreover, the process of forming a thin film of an oxide is mentioned.
For the step of heat-treating the silicon nitride sintered body, a method of heat-treating in an oxygen-containing atmosphere is effective. Moreover, the heat treatment temperature is preferably 1100° C. or higher. Cristobalite tends to be formed in the oxide layer at a high temperature of 1100° C. or higher. In addition, the upper limit of the heat treatment temperature is preferably 1500° C. or less. If the heat treatment temperature exceeds 1500° C., cristobalite may be formed even inside the silicon nitride sintered body. For this reason, the heat treatment temperature is 1100° C. or higher15
00° C. or less is preferable.
In addition, if the silicon nitride sintered body contains one or more of an alkaline earth metal element, a Group 4 element, and a rare earth element in the grain boundary phase, alkaline earth metal element-silicon-oxygen compound, rare earth An oxide layer containing one or more of an element-group 4 element-oxygen-based compound or alkaline earth metal element-rare earth element-silicon-oxygen-based compound can be formed.

Moreover, the process of apply|coating and baking an oxide paste is mentioned. If an oxide paste is used, a paste containing cristobalite and SiO ₂ is prepared. For the oxide paste, if necessary, one of alkaline earth metal element-silicon-oxygen compound, rare earth element-Group 4 element-oxygen compound, or alkaline earth metal element-rare earth element-silicon-oxygen compound Alternatively, two or more of them shall be contained. The oxide paste is applied to the silicon nitride sintered body and fired.
Moreover, the process of forming a thin film of an oxide is mentioned. The oxide thin film is formed by a deposition method such as a sputtering method.

Further, in the case of the step of heat-treating the nitride sintered body, since the silicon nitride sintered body is heat-treated, a uniform oxide film can be obtained. Moreover, since the silicon nitride sintered body itself is oxidized, the adhesion between the oxide layer and the silicon nitride sintered body can be improved. In addition, the oxide layer in the portion where the metal portion is not provided may be left as it is, or may be removed in advance.
In addition, in the process using an oxide paste, an oxide layer can be formed at a desired location by applying the paste to a desired location. Also, in the step of forming an oxide thin film, by providing a mask, an oxide layer can be formed at a required location.
Through the steps described above, a silicon nitride sintered body having an oxide layer can be produced.

Next, the step of forming the metal part shall be performed. The metal part shall be formed on the oxide layer. Various metals such as copper (Cu), silver (Ag), nickel (Ni), gold (Au), molybdenum (Mo), and tungsten (W) can be used for the metal portion.
Also, the metal part is preferably a metallized layer or a thin film layer. The metallized layer is a metal paste hardened by heat treatment. Also, the thin film layer is a film formed by a film forming method such as sputtering or plating. A metallized layer or a thin film layer is effective for forming a metal portion having a thickness of 0.1 mm or less. A metallized layer can be formed by applying a metal paste to a portion where a metal portion is desired to be formed. Similarly, the thin film layer can be formed only in the places where the metal parts are desired by masking the places where the metal parts are not to be formed.
Moreover, a semiconductor device can be manufactured by mounting a semiconductor element or the like on the metal portion. Also, a metal member such as a terminal may be mounted on the metal portion.

(Example)
(Examples 1 to 4, Reference Example 1, Comparative Examples 1 to 3)
A silicon nitride substrate shown in Table 1 was prepared. The silicon nitride substrates were uniformly 50 mm long, 40 mm wide, and 0.32 mm thick. A silicon nitride substrate having an oxide layer was prepared by performing heat treatment under different heat treatment conditions. The grain boundary phase component indicates the metal element detected in the grain boundary phase. Moreover, the thermal conductivity and the three-point bending strength of the silicon nitride substrate are the values before the heat treatment. In Comparative Example 3, the silicon nitride substrate of Comparative Example 1 was not subjected to heat treatment.

XRD analysis was then performed. The XRD analysis was performed from the direction of viewing the oxide layer perpendicularly. XRD analysis was also performed on the central portion of the silicon nitride substrate. Note that the central portion is a point where the longitudinal direction (vertical direction) of the substrate and the center line in the thickness direction intersect.
For XRD analysis, D8-ADVANCE manufactured by Bruker was used. The measurement conditions are Cu target (Cu-Kα), scan type θ-2θ, scan mode Cont
innousPSDfastscan, tube voltage 40 kV, tube current 40 mA, counting time 0.
Scanning was performed at 5°/min, a scanning range (2θ) of 10° to 50°, and a step width of 0.02°.
Table 2 shows the results.

I _21.7 is the strongest peak detected at a diffraction angle (2θ) of 21.7±0.3°. Also, I _16.5 is the strongest peak detected at a diffraction angle (2θ) of 16.5±0.3°.
Also, I _28.0 is the strongest peak detected at a diffraction angle (2θ) of 28.0±0.3°. Also, I _32.1 is the strongest peak detected at a diffraction angle (2θ) of 32.1±0.3°. Also, I _33.0 is the strongest peak detected at a diffraction angle (2θ) of 33.0±0.3°. Also, I _SiN is the larger of the peaks detected at either diffraction angle of 27.0±0.3° or 36.1±0.3°.
In Table 2, "0" indicates that the peak shown on the side of each molecule was below the detection limit. Incidentally, below the detection limit means that the ratio to I _{2 SiN} is less than 0.001.
As can be seen from the table, the silicon nitride substrates according to the examples have I _21.7S /I _SiN of 0.02 to 0.02.
It was in the range of 40. In contrast, in Comparative Example 1, no I _21.7S peak was detected.
Also, in Comparative Example 2 in which the heat treatment temperature is high, I _21.7S /I _SiN exceeded 0.40. Moreover, since Comparative Example 3 does not have an oxide layer, no XRD analysis was performed.

Next, a step of providing a metal portion was performed. A copper metallized layer having a thickness of 0.1 mm was formed as the metal portion. The copper metallized layer is formed by applying a copper paste onto the oxide layer and firing to harden it. Also, the thickness of the copper metallized layer was set to 0.1 mm. Thus, silicon nitride circuit boards according to the example and the comparative example were produced.
The silicon nitride circuit board was measured for thermal conductivity, thermal resistance, bonding strength of metal portions, and insulation.
For the thermal conductivity, the thermal conductivity of the silicon nitride substrate was measured by the flash method after the heat treatment and before the metal portion was provided.
As for the thermal resistance, the thermal resistance of the silicon nitride circuit board of Comparative Example 3 is taken as 100. The thermal resistance of each silicon nitride circuit board was measured, and when the difference from Comparative Example 3 was 10 or less, it was indicated as a good product (o), and when it exceeded 10, it was indicated as a defective product (x).
Moreover, the bonding strength of the metal portion was determined by a tape test. After applying the tape on the metal part, the tape was removed. When the remaining amount of the metal part after peeling off the tape was 50% or more, it was evaluated as good (o), and when it was less than 50%, it was evaluated as defective (x).
In addition, regarding insulation, those with a dielectric strength of 17 kV/mm or more are the best (○), 14 to 1
Those with a voltage of 6 kV/mm were regarded as good (Δ), and those with a voltage of less than 14 kV/mm were regarded as defective (x). The results are shown in Table 3
It was shown to.

As can be seen from the table, the silicon nitride circuit board according to the example had high bonding strength of the metal portion. Moreover, since the oxide film was thin with a thickness of 5 μm or less, it was possible to prevent a decrease in thermal conductivity.
For this reason, even if the metal portion was provided, a decrease in thermal resistance could be prevented. Insulation was also maintained. Therefore, it can be seen that the metal portion does not penetrate into the inside of the silicon nitride substrate.
On the other hand, Comparative Example 1 lacked bonding strength. Also, it was confirmed that the dielectric strength was slightly lowered. It is considered that the metallized layer and the silicon nitride substrate reacted excessively because cristobalite was not formed. Also, in Comparative Example 2, the oxide layer was too thick, so the thermal conductivity was lowered. A decrease in thermal conductivity leads to a decrease in heat dissipation as a circuit board. Also, in Comparative Example 3, since no oxide layer was provided, the bonding strength was insufficient.

Although some embodiments of the present invention have been illustrated above, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments are
It can be embodied in various other forms, and various omissions, replacements, changes, etc. can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the scope of the invention described in the claims and equivalents thereof. Moreover, each of the above-described embodiments can be implemented in combination with each other.

Reference Signs List 1 Silicon nitride substrate 2 Substrate surface 3 Oxide layer 4 Central portion 5 Metal portion 10 Silicon nitride circuit substrate 11 Semiconductor element 20 Semiconductor device

Claims (5)

In a silicon nitride substrate used for a circuit board made of a silicon nitride sintered body having an oxide layer on at least a part of the surface, XRD analysis of the sintered body surface having the oxide layer shows a diffraction angle of 21 based on the cristobalite crystal structure. The strongest peak detected at .7±0.3° is I _21.7S , the strongest peak based on silicon nitride crystal grains is I _21.7S , and the ratio I _21.7S /I _SiN is 0.02 or more and 0.02. I _16.5S is the strongest peak detected at a peak diffraction angle of 16.5±0.3° based on silica , and the ratio I _16.5S /I _SiN is 0.01 or more and 0.01 or more. 10 or less, the strongest peak detected at a diffraction angle of 28.0 ± 0.3 °, which is a peak based on an alkaline earth metal element-silicon-oxygen compound, is defined as I 28.0S, and the ratio _{I 28 .0S} /I _SiN is 0.02 or more and 0.20 or less,
XRD analysis of the central portion of the silicon nitride sintered body shows that I _21.7C /I _SiN is 0 or more and 0.01 or less, and I _28.0C /I _SiN is 0 or more and 0.02 or less,
A silicon nitride substrate having a thickness of 0.1 mm or more and 0.7 mm or less . 2. The silicon nitride substrate according to claim 1, wherein the oxide layer has a thickness of 5 [mu]m or less. When the surface of the sintered body having the oxide layer is subjected to XRD analysis, peaks are detected at one or both of diffraction angles of 32.1 ± 0.3 ° and 33.0 ± 0.3 °. The silicon nitride substrate according to any one of claims 1 to 2 . 4. A silicon nitride circuit board according to claim 1, wherein a metal portion is provided on the oxide layer of the silicon nitride substrate. 5. A semiconductor device, wherein a semiconductor element is mounted on the metal part of the silicon nitride circuit board according to claim 4 .

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