JP4516057B2 - Silicon nitride wiring board and method for manufacturing the same - Google Patents

Description

  The present invention relates to a silicon nitride wiring board and a method for manufacturing the same, and in particular, in addition to the original high strength characteristics of a silicon nitride sintered body, it has high thermal conductivity and excellent heat dissipation, and nitriding has high bonding strength and conductivity of a conductor layer. The present invention relates to a silicon wiring board and a method for manufacturing the same.

  The amount of heat generated with the recent high integration and high speed of semiconductor chips has increased, and as a circuit board on which these chips are mounted, ceramic wiring boards using materials with excellent heat dissipation and good thermal conductivity are required. Has been.

For example, ceramic wiring boards made of alumina (Al ₂ O ₃ ) as a constituent material have been widely used for such applications. However, the alumina substrate has a low thermal conductivity and is insufficient in terms of heat dissipation and practical strength. In order to improve heat dissipation, aluminum nitride having excellent thermal conductivity has been widely used recently.
JP-A-5-315462

  However, the above aluminum nitride has not been sufficiently satisfactory in terms of mechanical strength. Therefore, development of a ceramic wiring board having high strength and high thermal conductivity has been demanded. Therefore, silicon nitride sintered bodies manufactured by conventional methods are focused on silicon nitride, but mechanical strength such as toughness is excellent, but in terms of thermal conductivity, compared to aluminum nitride sintered bodies. Therefore, it has not been put into practical use as an electronic material such as a semiconductor substrate that requires heat dissipation, and there is a problem that the application range is narrow.

  In response to these demands, the present inventors have studied various kinds of silicon nitride raw materials, compositions, and sintering methods, and proposed a highly thermally conductive silicon nitride sintered body having greatly improved thermal conductivity and a method for manufacturing the same. .

  However, for use as a semiconductor substrate, a surface conductor layer must be formed and wired. The surface conductor layer is formed by using an active metal method in which an active metal is used for a sintered substrate and a copper plate or the like is integrally joined as a conductor layer, or a printing paste containing a high melting point conductive material such as tungsten. There is a metallization method in which a conductor pattern is formed, and the substrate and the conductor layer are integrally formed by simultaneous firing with the substrate material.

  In the case of silicon nitride substrates, the former active metal method is partly put into practical use and used for special purposes. On the other hand, the metallization method for simultaneous firing has been studied in order to expand applications, but there are problems in terms of bonding strength and electrical resistance (conductivity), and improvement is required.

  The present invention has been made in order to cope with the above-described demands for the problems. In particular, in addition to the inherent high strength characteristics of the silicon nitride sintered body, the thermal conductivity is high and the heat dissipation is excellent. It is an object of the present invention to provide a silicon nitride wiring board having high conductivity and a method for manufacturing the same.

  In order to achieve the above object, the present inventor changed various kinds of silicon nitride powder, composition, kind of paste for forming a surface conductor layer, and firing conditions when manufacturing a silicon nitride wiring board, The effects of the elements and manufacturing conditions on the characteristics of the wiring board were compared by experiments.

As a result, a raw material mixture obtained by adding a predetermined amount of a rare earth element oxide or the like as a sintering aid to a high-purity and fine silicon nitride powder is prepared to prepare a compact, and the surface of the resulting compact is obtained. A conductor wiring pattern is printed with a silicon nitride paste containing at least a sintering aid such as a rare earth oxide and zirconium oxide (ZrO ₂ ), degreased, and then co-fired under predetermined conditions to obtain zirconium nitride (ZrN) Acquired the knowledge that a conductor layer composed of the above can be integrally formed and a silicon nitride wiring board can be obtained that has excellent characteristics such as bonding strength and electrical resistance of the surface conductor layer in addition to high mechanical strength and thermal conductivity. It was. The present invention has been completed based on these findings.

That is, in the silicon nitride wiring substrate according to the present invention, a conductor layer made of zirconium nitride is integrally formed on the surface of the silicon nitride substrate by simultaneous firing , and the silicon nitride substrate has at least a rare earth element as an oxide. Convert to contain from 2 to 17.5 wt%, thermal conductivity of 70 W / m · K or more, three-point bending strength of not less than 550 MPa, the electrical resistance value before Symbol zirconium nitride conductor layer is 10 ² Ω · cm or less, 98% by mass or more of the previous SL conductor layer is composed of zirconium nitride (ZrN), a thickness before Symbol zirconium nitride conductor layer 3～25Myuemu, before Symbol silicon substrate nitride and zirconium nitride conductor layer The bonding strength is 1.5 Kg / mm or more.

Furthermore, in the silicon nitride circuit board, before Symbol thermal conductivity of silicon nitride substrate is 90W / m · K or more, and a three-point bending strength is not less than 550 MPa.

Further, the silicon nitride substrate is 0.3 to 3.0% by mass when at least one of Hf and Mg is converted to oxide, and Al, Li, Na, K, Fe, Ba, Mn as impurity cation elements. , B are preferably contained in a total amount of 0.5% by mass or less. The silicon nitride substrate preferably contains 2% by mass or less of at least one selected from the group consisting of Ti, Zr, W, Mo, Ta, Nb, V, and Cr in terms of oxide. Furthermore, the conductor layer preferably contains 2% by mass or less of alumina (Al ₂ O ₃ ).

In the method for manufacturing a silicon nitride wiring board according to the present invention, oxygen is 1.5% by mass or less, and Al, Li, Na, K, Fe, Ba, Mn, and B as impurity cation elements are combined in a total of 0.001. Addition of 2 to 17.5% by mass of rare earth element in terms of oxide to silicon nitride powder containing 5% by mass or less and α-phase type silicon nitride of 90% by mass or more and having an average particle size of 1.0 μm or less A silicon nitride paste for forming a conductor layer containing a sintering aid containing at least a rare earth oxide and zirconium oxide on the surface of the obtained molded body is prepared by molding the raw material mixture. After the conductor wiring pattern is printed and degreased with the silicon nitride paste for forming a conductor layer in which the addition amount of zirconium oxide (ZrO ₂ ) is 1 to 12% by mass with respect to the solid component amount of the silicon nitride paste for forming a conductor layer, In a pressurized nitrogen gas atmosphere Sintering is performed at a temperature of 1750 ° C. to 1900 ° C., and the cooling rate of the sintered body from the sintering temperature to the temperature at which the liquid phase formed during sintering by the rare earth element solidifies is gradually reduced to 100 ° C. or less per hour. It is characterized by cooling.

  Furthermore, in the method for manufacturing a silicon nitride wiring board, it is preferable to add 0.3 to 3.0% by weight of at least one of Hf and Mg in terms of oxide in the silicon nitride powder. Further, at least one element selected from the group consisting of Ti, Zr, W, Mo, Ta, Nb, V, and Cr is added to the silicon nitride powder in an amount of 2% by mass or less in terms of oxide. Is also preferable. Furthermore, it is preferable that the atmosphere gas at the time of the sintering is a nitrogen gas atmosphere pressurized to 0.3 MPa or more.

  The silicon nitride powder that is used in the method of the present invention and is the main component of the silicon nitride sintered body constituting the silicon nitride wiring board has an oxygen content in consideration of sinterability, strength, and thermal conductivity. 1.5% by mass or less, preferably 0.5 to 1.2% by mass, and the content of impurity cation elements such as Al, Li, Na, K, Fe, Ba, Mn, and B is 0.5% by mass in total In the following, the α-phase type silicon nitride suppressed to preferably 0.3% by mass or less is contained in an amount of 75 to 97% by mass, preferably 80 to 95% by mass, and the average particle size is 1.0 μm or less. It is preferable to use fine silicon nitride powder of about 4 to 0.8 μm.

  As the silicon nitride raw material powder, α-phase type and β-phase type powders are known, but the α-phase type silicon nitride raw material powder tends to have insufficient strength when formed into a sintered body. On the other hand, the β-phase type silicon nitride raw material powder requires high-temperature firing, but a high-strength sintered body having a high aspect ratio and complicated fibrous silicon nitride can be obtained. Therefore, in the present invention, it is preferable that the α phase type raw material powder is fired at a high temperature to form a β phase type sintered body as the silicon nitride sintered body.

  In the present invention, the reason why the blending amount of the α-phase type silicon nitride powder is limited to the range of 75 to 97% by mass is that the bending strength, thermal conductivity and insulation of the sintered body are markedly within the range of 75% by mass or more. This is because the excellent characteristics of silicon nitride become remarkable. On the other hand, considering the sinterability, the range is up to 97% by mass. Preferably it is set as the range of 80-95 mass%.

  The silicon nitride starting material powder has an oxygen content of 1.5% by mass or less, preferably 0.5 to 1.2% by mass in consideration of sinterability, bending strength, thermal conductivity, and insulation. It is preferable to use fine silicon nitride powder containing 90% by mass or more of α-phase type silicon nitride and having an average particle size of 1.0 μm or less, preferably about 0.4 to 0.8 μm.

  By using fine raw material powder with an average particle size of 1.0 μm or less, it is possible to form a dense sintered body with a porosity of 2.5% or less even with a small amount of sintering aid. In addition, the possibility that the sintering aid may impair the heat conduction characteristics is reduced.

  Moreover, since the impurity cation element of Al, Li, Na, K, Fe, Ba, Mn, and B becomes a substance that inhibits thermal conductivity, in order to ensure a thermal conductivity of 70 W / m · K or more, The content of the impurity cation element can be achieved by making the total content 0.5% by mass or less. In particular, for the same reason, it is more preferable that the content of the impurity cation elements is 0.3% by mass or less in total. Here, since the silicon nitride powder used to obtain a normal silicon nitride sintered body contains a relatively large amount of Fe and Al in particular, the total amount of Fe and Al is the above-mentioned impurity cation element. It becomes a standard of the total content of.

  Furthermore, a high-density sintered body can be produced by using a silicon nitride raw material powder containing 90% by mass or more of an α-phase type silicon nitride excellent in sinterability compared with a β-phase type. it can.

  The rare earth elements added as sintering aids to the silicon nitride raw material powder include oxides such as Y, Ho, Er, Yb, La, Sc, Pr, Ce, Nd, Dy, Sm, and Gd, or sintering operations. Thus, these oxide substances may be used alone or in combination of two or more oxides. These sintering aids react with the silicon nitride raw material powder to form a liquid phase and function as a sintering accelerator.

  The amount of the sintering aid added is in the range of 2.0 to 17.5 mass% with respect to the raw material powder in terms of oxide. When this addition amount is less than 2.0% by mass, densification or high thermal conductivity of the sintered body is insufficient, particularly when the rare earth element is an element having a large atomic weight such as a lanthanoid element. Thus, a sintered body having a relatively low strength and a relatively low thermal conductivity is formed. On the other hand, when the added amount exceeds 17.5% by mass, an excessive amount of grain boundary phase is generated, and the thermal conductivity decreases and the strength begins to decrease. In particular, it is desirable to set it as 3-15 mass% for the same reason.

In addition, magnesium (Mg) oxide (MgO) used as a selective additive component in the present invention promotes the function of the rare earth element sintering accelerator, enables densification at low temperature, and has a crystal structure. This serves to control the grain growth in and improves the mechanical strength of the Si ₃ N ₄ sintered body. When the amount of MgO added is less than 0.3% by mass in terms of oxide, the effect of addition is insufficient, whereas when the amount exceeds 3.0% by mass, the thermal conductivity decreases. The addition amount is in the range of 0.3 to 3.0% by mass. In particular, the content is desirably 0.5 to 2% by mass.

  In addition, there is an Hf compound as a component that exhibits the same effect as the above MgO. Hf compounds are added as oxides, carbides, nitrides, silicides, and borides. When combined with MgO, sintering is further promoted and the glass phase can be more effectively reduced. About addition amount, it is 0.3-3 mass%, Preferably it is 1.0-2.5 mass%. Since MgO and Hf compounds show similar effects, it is also possible to obtain a synergistic effect by adding both MgO and Hf compounds. When both are added, the total addition amount is also in the range of 0.3 to 3% by mass.

In the present invention, Ti, Zr, W, Mo, Ta, V, Nb, and Cr may be added as oxides, carbides, nitrides, silicides, and borides as other optional additive components. These compounds promote the function of the rare earth element as a sintering accelerator, and also serve to enhance the mechanical strength of the Si ₃ N ₄ sintered body by performing a dispersion strengthening function in the crystal structure. A compound of Ti and Mo is preferred. When the amount of these compounds added is less than 0.1% by mass in terms of oxide, the effect of addition is insufficient, whereas when the amount exceeds 2% by mass, the thermal conductivity, mechanical strength, Since the dielectric breakdown strength is lowered, the addition amount is in the range of 0.1 to 2% by mass. In particular, the content is desirably 0.2 to 1.0% by mass.

  The compounds such as Ti and Mo also function as a light-shielding agent that colors the silicon nitride ceramic substrate black and imparts opacity. Therefore, when manufacturing a silicon nitride wiring board used for an integrated circuit or the like that is likely to cause malfunction due to light from the sintered body, a silicon nitride having an excellent light shielding property by appropriately adding a compound such as Ti. It is desirable to use a substrate.

  Moreover, since the porosity of a sintered compact has a large influence on the thermal conductivity and strength, it is manufactured so as to be 2.5 vol% or less. If the porosity exceeds 2.5%, the leakage current as a wiring board increases rapidly, which hinders heat conduction, lowers the insulation and thermal conductivity of the sintered body, and further reduces the strength of the sintered body. .

  In addition, silicon nitride ceramic substrates are systematically composed of silicon nitride crystals and grain boundary phases, but the proportion of the crystalline compound phase in the grain boundary phase greatly affects the thermal conductivity of the sintered body. In the silicon nitride sintered body constituting the wiring board according to the invention, it is preferable that the grain boundary phase is 20% or more, more preferably 50% or more is occupied by the crystal phase. This is because if the crystal phase is less than 20%, it is difficult to obtain a sintered body having excellent heat radiation characteristics such that the thermal conductivity is 70 W / m · K or more and excellent in mechanical strength.

The silicon nitride wiring board according to the present invention is characterized in that a conductor layer made of zirconium nitride (ZrN) is integrally formed on the surface of the silicon nitride substrate. This silicon nitride wiring board is made of silicon nitride. After degreasing by printing a conductor wiring pattern with a conductor layer forming paste containing a sintering aid such as silicon nitride and rare earth oxides and zirconium oxide (ZrO ₂ ) on the surface of the substrate molded body (green sheet), It is manufactured by co-firing a patterned molded body in a pressurized nitrogen gas atmosphere.

The conductor layer forming paste is sufficiently kneaded after adding a predetermined amount of zirconium oxide (ZrO ₂ ) to the composition approximate to the composition of the silicon nitride substrate, and further adding an acrylic binder and a terpineol solvent. Prepared.

The amount of zirconium oxide (ZrO ₂ ) added to the sintering aid such as silicon nitride or rare earth oxide, which is the solid component amount in the conductor layer forming paste, is in the range of 1 to 12% by mass. When the amount of zirconium oxide (ZrO ₂ ) added is less than 1% by mass, the thickness of the conductor layer becomes insufficient, and it is difficult to form a conductor layer having a low electrical resistance value. On the other hand, when the addition amount exceeds 12% by mass, the bonding strength between the silicon nitride substrate and the conductor layer tends to decrease.

In the conductor layer forming paste, an alumina (Al ₂ O ₃ ) powder may be further added as a selective additive component in a range of 2% by mass or less with respect to the solid component amount. Alumina is effective for densifying the conductor layer and increasing the bonding strength of the conductor layer. However, when the addition amount exceeds 2% by mass, the electrical resistance value of the conductor layer tends to increase.

  Even if a paste containing only zirconium oxide for forming the conductor layer is used, a conductor layer having high bonding strength cannot be obtained. Therefore, it is important to have a composition obtained by adding a zirconium oxide powder and, if necessary, an alumina powder to a prepared powder approximate to the composition of a silicon nitride substrate molded body.

  Then, the conductor layer forming paste prepared as described above is printed on the surface of the silicon nitride substrate molded body (green sheet) by a screen printing method or the like to form a conductor wiring pattern having a predetermined shape. Next, the obtained green sheet is degreased in an air stream at 400 ° C. to 500 ° C. for 3 to 5 hours and then subjected to pressure sintering in a pressurized nitrogen gas atmosphere at a temperature of 1750 to 1900 ° C. for 2 to 10 hours.

  By this sintering treatment, the silicon nitride substrate compact becomes a dense silicon nitride substrate, and the zirconium oxide powder in the conductor layer forming paste is nitrided in a nitrogen gas atmosphere to form a conductor layer made of zirconium nitride (ZrN). Are integrally formed so as to be deposited on the surface of the silicon nitride substrate. The conductor layer made of zirconium nitride (ZrN) has a gold color and is easily visible as a circuit conductor.

In the above sintering treatment, it is desirable that the atmosphere gas is a nitrogen gas atmosphere pressurized to 0.3 MPa or more. When the pressure of the atmospheric nitrogen gas is less than 0.3 MPa, the proportion of zirconium oxide (ZrO ₂ ) powder that is nitrided by nitrogen gas to become zirconium nitride (ZrN) decreases, which is not efficient. Therefore, it is more preferable that the atmosphere gas is a nitrogen gas atmosphere pressurized to a range of 0.5 to 1.2 MPa, more preferably 0.7 to 1.0 MPa.

  Nitrogen gas having a purity of 99% or more is the most preferable as nitrogen gas, but as an alternative atmosphere, nitrogen-inert gas consisting of an inert gas such as oxygen at 5 vol% or less, nitrogen at 50 vol% or more, and the balance Ar. A mixed gas atmosphere may be used. That is, it is important to use an atmosphere containing nitrogen as a main component and to reduce the oxygen content to 5 vol% or less as much as possible.

  The conductor layer forming paste has a composition close to that of a silicon nitride substrate molded body, so that the substrate component in the paste is well-familiar with the silicon nitride substrate, and is integrated with the silicon nitride substrate and sintered. At the same time, it has a function of bonding the deposited conductor layer to the silicon nitride substrate with high bonding strength.

  As a result, a strong conductor layer made of zirconium nitride (ZrN) is integrally formed on the surface of the silicon nitride substrate, and in addition to the high mechanical strength and thermal conductivity of the silicon nitride substrate, the bonding strength of the surface conductor layer and A silicon nitride wiring board having excellent characteristics with respect to electrical resistance and the like can be obtained.

  The thickness of the surface conductor layer formed on the surface of the silicon nitride substrate is preferably in the range of 3 to 25 μm. When the thickness of the conductor layer is less than 3 μm, it is difficult to form a conductor layer having a uniform film pressure, resulting in large variations in electric resistance values. On the other hand, when the thickness of the conductor layer exceeds 25 μm, the thermal resistance tends to increase, and the bonding strength with the silicon nitride substrate decreases.

A thin intermediate layer made of zirconium nitride (ZrN) and silicon nitride (Si ₃ N ₄ ) may be formed at the bonding interface between the surface conductor layer and the silicon nitride substrate. The part (98 to 100% by mass) consists of zirconium nitride (ZrN). The thickness of the conductor layer can be measured by elemental analysis of the cross-sectional structure of the silicon nitride wiring board using an X-ray microanalyzer (EPMA).

The electric resistance value of the surface conductor layer varies depending on the thickness of the conductor layer, but is preferably in the range of 10 ² Ω · cm or less. In the case where the electrical resistance value of the conductor layer is excessive so as to exceed 10 ² Ω · cm, it is difficult to obtain excellent conductivity as compared with the conductor layer made of conventional tungsten and propagates through the circuit conductor. The transmission speed of electrical signals cannot be improved. Therefore, it is more preferable that the electric resistance value of the conductor layer is in a range of 50 Ω · cm or less. The electrical resistance value of the conductor layer can be easily measured using, for example, an insulation resistance meter.

  Further, the bonding strength between the silicon nitride substrate and the zirconium nitride conductor layer is preferably 1.5 kg / mm or more. When the bonding strength of the conductor layer is less than 1.5 kg / mm, the silicon nitride wiring substrate is easily peeled off when subjected to a thermal cycle, and silicon nitride excellent in operational reliability and durability. A wiring board cannot be obtained. The bonding strength of the conductor layer is measured according to a normal peel strength measurement method.

In the conventional silicon nitride wiring board formed by simultaneously firing the printed pattern and the silicon nitride substrate molding after printing the circuit conductor pattern using tungsten paste as in the prior art, tungsten (W) is used during firing. Is easily changed to a silicide compound (WSi ₂ ), and the electric resistance value increases non-uniformly, making it difficult to adjust the resistance value to a uniform resistance value. Although there was a fatal defect in which the bonding strength of the conductor layer was lowered, in the present invention, since the conductor layer is formed of zirconium nitride that does not combine with the substrate component, the electrical resistance value hardly increases, and the conductor layer There is little possibility that the bonding strength of the steel will decrease.

  Further, as described above, the silicon nitride sintered body constituting the silicon nitride wiring board has a porosity of 2.5% or less, and a silicon nitride sintered body having a thermal conductivity of 70 W / m · K or more is obtained. For this purpose, a conductor wiring pattern is printed on the silicon nitride substrate molded body prepared from the raw material and then degreased, and then at a temperature of 1750 to 1900 ° C. for about 2 to 10 hours in a pressurized nitrogen gas atmosphere. It is important that the sintered body is fired and cooled slowly at a cooling rate of 100 ° C./hour immediately after the completion of the sintering operation.

  When the cooling rate of the sintered body to the temperature at which the liquid phase solidifies after sintering is reduced to 100 ° C./hour or less, the oxygen concentration in the liquid phase is reduced and the grain boundary phase of the silicon nitride sintered body is reduced. Since the crystallization of the silicon nitride substrate is further promoted, a silicon nitride substrate sintered body with improved insulation and thermal conductivity can be obtained.

  When the sintering temperature is less than 1750 ° C., the sintered body is not sufficiently densified and the porosity becomes 2.5 vol% or more, and the insulation, mechanical strength, and thermal conductivity all decrease. . On the other hand, if the sintering temperature exceeds 1900 ° C., the silicon nitride component itself tends to evaporate and decompose.

  The cooling rate of the sintered body immediately after the completion of the above sintering operation is an important control factor for crystallizing the grain boundary phase of the silicon nitride substrate, and rapid cooling is performed so that the cooling rate exceeds 100 ° C. per hour. In such a case, the grain boundary phase of the sintered body structure becomes amorphous (glass phase), and the liquid phase generated in the sintered body accounts for less than 20% of the grain boundary phase as a crystalline phase. There is no further improvement in rate.

  The temperature range where the cooling rate should be strictly adjusted is sufficient from the predetermined sintering temperature (1750 to 1900 ° C.) to the solidification of the liquid phase produced by the reaction of the sintering aid. . Incidentally, the liquid phase freezing point in the case of using the above sintering aid is about 1600 to 1500 ° C. And by controlling the cooling rate of the sintered body at least from the sintering temperature to the liquid phase solidification temperature at 100 ° C./hour, preferably 50 ° C. or less, more preferably 25 ° C. or less, the pores of the sintered body The rate is also 2.5% or less, and 20% or more, particularly preferably 50% or more, of the grain boundary phase is a crystalline phase, and a silicon nitride substrate sintered body excellent in both thermal conductivity and mechanical strength is obtained. It is done.

  In addition, although the one where the cooling rate of the said sintered compact is slow is effective in crystallization of a grain boundary phase, when too slow, since manufacturing time becomes long, the minimum of a cooling rate is 10 degreeC or more per hour from a viewpoint of manufacturability. preferable.

  The silicon nitride wiring board according to the present invention is manufactured through the following processes, for example. That is, for a fine silicon nitride powder having a predetermined fine particle size and a small impurity content, a predetermined amount of a sintering aid, a necessary additive such as an organic binder, and Ti as required A raw material mixture is prepared by adding a compound, and then the obtained raw material mixture is molded to obtain a molded body (green sheet) having a predetermined shape. As a forming method of the raw material mixture, a general-purpose mold pressing method, a sheet forming method such as a doctor blade method, and the like can be applied.

  Subsequent to the above molding operation, the conductor forming paste is screen printed on the surface of the molded body to form a conductor wiring pattern layer having a predetermined shape, and then heated at a temperature of 400 to 500 ° C. for 1 to 2 hours in an air stream. Then, the organic binder component added in advance is sufficiently removed and degreased.

  The degreased patterned molded body is then subjected to atmospheric pressure simultaneous sintering at a temperature of 1750 to 1900 ° C. for a predetermined time in a pressurized nitrogen gas atmosphere.

  The silicon nitride wiring board manufactured by the above manufacturing method has a total oxygen amount of 3.5% by mass or less, a porosity of 2.5% or less, a maximum pore size of 0.3 μm or less, and 70 W / m · K (25 ° C.). It has the above thermal conductivity and excellent mechanical properties with a three-point bending strength of 600 MPa or more at room temperature. In addition, by adjusting the raw material composition, it is possible to obtain a high thermal conductivity silicon nitride wiring board having a thermal conductivity of 90 W / m · K or more, a three-point bending strength slightly lowering and a normal temperature of 550 MPa or more.

  According to the silicon nitride wiring board and the manufacturing method thereof according to the present invention, the conductor layer made of zirconium nitride having a small electrical resistance value is integrally formed on the surface of the silicon nitride board with a high bonding strength. Even when the thermal cycle is applied over a long period of time, a silicon nitride wiring board with less peeling of the conductor layer and excellent operational reliability and durability can be obtained.

  In particular, a silicon nitride wiring board equipped with a semiconductor device with high integration and high output because it has high thermal conductivity and excellent heat dissipation in addition to the inherent high strength characteristics of silicon nitride sintered bodies It is effective as Therefore, when a power module is prepared using this silicon nitride wiring board, a power module having high durability and high operation reliability can be formed even if the output and capacity are increased.

[Example 1]
Example 1 has an oxygen content of 1.1% by mass, Al, Li, Na, K, Fe, Ba, Mn, and B as impurity cation elements in total containing 0.10% by mass, and α phase With respect to 91% by mass of Si ₃ N ₄ (silicon nitride) powder containing 97% type silicon nitride and having an average particle size of 0.55 μm, Y ₂ O ₃ (average particle size of 0.9 μm as a sintering aid) The substrate raw material mixture was prepared by adding 7% by mass of yttrium oxide) powder and 2% by mass of HfO ₂ (hafnium oxide) powder having an average particle diameter of 1.0 μm, and further adding a dispersant. Next, the obtained substrate material mixture is pulverized and mixed in an alcohol and toluene solvent using silicon nitride balls as a grinding medium, and then an acrylic binder and a plastic material are added to obtain a substrate material slurry. Was prepared. Further, the substrate raw material slurry was formed into a sheet by a doctor blade method to produce a silicon nitride substrate formed body (green sheet) having a thickness of 0.5 mm.

On the other hand, with respect to 89% by mass of the above silicon nitride powder, 7% by mass of sintering aid yttrium oxide powder and 2% by mass of aluminum oxide (Al ₂ O ₃ ) powder and a zirconium nitride surface conductor layer are formed after sintering. A paste for forming a surface conductor layer was prepared by further adding an acrylic binder and a terpineol solvent to a blended powder to which 2% by mass of zirconium oxide (ZrO ₂ ) powder was added, and kneading sufficiently. The conductor wiring pattern layer was printed on the green sheet surface by screen printing using this paste.

  The green sheet thus patterned is degreased in an air stream at a temperature of 450 ° C. for 4 hours and then sintered in a nitrogen gas atmosphere pressurized to 0.7 MPa at a temperature of 1850 ° C. for 6 hours. The silicon nitride sintered body integrated with the surface conductor layer made of zirconium nitride (ZrN) was prepared by adjusting the cooling rate from 1 to 1500 ° C. to 100 ° C./hr and gradually cooling. Then, the silicon nitride wiring board which concerns on Example 1 was produced by carrying out nickel plating to the surface conductor layer.

[Comparative Examples 1-3]
On the other hand, as Comparative Example 1, a surface conductor layer forming paste prepared by adding and kneading only zirconium oxide (ZrO ₂ ) powder to an acrylic binder and a terpineol solvent was printed on the green sheet surface to form a conductor wiring pattern layer. A silicon nitride wiring substrate according to Comparative Example 1 was fabricated by processing under the same conditions as in Example 1 except for the points formed.

  Further, as Comparative Example 2, a conductor wiring pattern layer was formed by printing a surface conductor layer forming paste prepared by adding and kneading only zirconium nitride (ZrN) powder to an acrylic binder and a terpineol solvent on the surface of a green sheet. A silicon nitride wiring board according to Comparative Example 2 was fabricated by processing under the same conditions as in Example 1 except for the points.

  Further, as Comparative Example 3, a surface conductor layer forming paste prepared by adding and kneading only Tangten (W) powder to an acrylic binder and a terpineol solvent was printed on the surface of the green sheet to form a conductor wiring pattern layer. A silicon nitride wiring substrate according to Comparative Example 3 was fabricated by processing under the same conditions as in Example 1 except for the above.

Regarding the silicon nitride wiring boards according to Example 1 and Comparative Examples 1 to 3 thus obtained, the type of constituent phase of the surface conductor layer formed on the surface of the silicon nitride substrate is identified by EPMA, and the conductor layer The thickness, electrical resistance value, bonding strength (peel strength) of the conductor layer to the silicon nitride substrate, thermal conductivity, and three-point bending strength were measured. The electrical resistance value of the conductor layer was measured at room temperature by using an insulation resistance meter between two locations on the same plane before the nickel plating was applied. The three-point bending strength was measured after nickel plating. Each measurement result is shown in Table 1 below.

  As is clear from the results shown in Table 1, the silicon nitride wiring board according to Example 1 contains silicon nitride powder, rare earth oxide, and aluminum oxide powder together with zirconium oxide powder for forming a conductor layer. A conductor layer made of ZrN having a small electric resistance value because it is formed by degreasing, sintering, and slow cooling after forming a conductor wiring pattern layer on the surface of the silicon nitride substrate using a conductive layer forming paste. Thus, the bonding strength of the conductor layer was extremely high, the three-point bending strength of the entire wiring board was high, and a high-strength silicon nitride wiring board having high thermal conductivity was obtained.

  On the other hand, in Comparative Example 1 using only a zirconium oxide powder as a solid component and using a paste for forming a conductor layer that does not contain silicon nitride powder or a sintering aid as a co-material of the substrate, a conductor layer made of ZrN However, it has been found that the bonding strength of the conductor layer is extremely low, and the durability and reliability of the entire wiring board is greatly reduced.

  Further, even in the case of using a conductor layer forming paste that contains only zirconium nitride powder as a solid component and does not contain silicon nitride powder or a sintering aid, as in Comparative Example 2, ZrN However, it was found that the bonding strength of the conductor layer is extremely small, and the durability and reliability of the entire wiring board are greatly reduced.

Further, in Comparative Example 3 in which the conventional W paste was used as the conductor layer forming paste, the W component changed to a silicide compound (WSi ₂ ) during the sintering, so the electrical resistance value of the conductor layer relatively increased. At the same time, it has been found that the bonding strength of the conductor layer is lowered, and the durability and reliability of the entire wiring board are greatly lowered.

[Examples 2 to 26]
Silicon nitride (Si ₃ N ₄ ) raw material powder used in Example 1 as Examples 2 to 26, Y ₂ O ₃ powder, MgO powder, HfO ₂ powder, and average particle diameter as shown in Table 2 In addition to various rare earth oxide powders of 0.9 to 1.0 μm, various compound (Al ₂ O ₃ ) powders having an average particle size of 0.4 to 0.5 μm were prepared so as to have a composition ratio shown in Table 2. The raw material mixtures were prepared respectively. Next, each raw material mixture obtained was molded under the same conditions as in Example 1 to prepare a silicon nitride substrate molded body (green sheet) for each Example.

On the other hand, it was prepared as shown in Table 2 as a conductor layer forming paste for each example. That is, the silicon nitride (Si ₃ N ₄ ) powder, rare earth oxide, zirconium oxide (ZrO ₂ ) powder, and aluminum oxide (Al ₂ O ₃ ) powder used in Example 1 were mixed with an acrylic binder and a terpineol series. By adding to a solvent and kneading sufficiently, a paste for forming a surface conductor layer for each example was prepared.

  Next, each of the above-mentioned surface conductor layer forming pastes was screen-printed to print a conductor wiring pattern layer on the green sheet surface. The printing amount of the paste was adjusted so that the final conductor layer thickness was a value shown in Table 2.

  And each molded object (green sheet) which formed the conductor wiring pattern layer was baked on the sintering conditions shown in Table 2, and the silicon nitride wiring board which concerns on Examples 2-26 was manufactured, respectively.

[Comparative Examples 4 to 11]
On the other hand, as shown in Table 3 as Comparative Examples 4 to 11, those using a paste for forming a surface conductor layer in which ZrO ₂ was added in an amount smaller than the preferable range defined in the present invention (Comparative Example 4), ZrO ₂ Using a paste for forming a surface conductor layer added in an excessive amount beyond the preferred range specified in the present invention (Comparative Example 5), adding Y ₂ O ₃ as a sintering aid component of the substrate in an excessive amount (Comparative Example 6), Yb ₂ O ₃ as a sintering aid component of the substrate added excessively (Comparative Example 7), and the cooling rate of the sintered body immediately after sintering was excessively 400 ° C / hr (Comparative Example 8), HfO ₂ as a substrate material composition added excessively (Comparative Example 9), MgO as a substrate material composition added excessively (Comparative Example 10), substrate material composition TiO ₂ as an excess was added After molding, pattern formation, and degreasing treatment under the same conditions as in Example 2 except for the one (Comparative Example 11), the firing treatment is carried out under the sintering conditions shown in Table 3, respectively. A silicon nitride wiring board was manufactured.

  Regarding the silicon nitride wiring boards according to Examples 2 to 26 and Comparative Examples 4 to 11 thus obtained, the types of constituent phases of the surface conductor layer formed on the surface of the silicon nitride board are identified by EPMA, and the conductor The layer thickness, electrical resistance value, bonding strength (peel strength) of the conductor layer to the silicon nitride substrate, thermal conductivity and three-point bending strength were measured. The measurement results are shown in Tables 2 to 3 below.

  As is apparent from the results shown in Tables 2 and 3 above, the surface conductor layer is formed on the surface of a silicon nitride molded body having a predetermined substrate material composition containing a component approximate to the substrate material composition and zirconium oxide. In the silicon nitride wiring board according to each of the embodiments manufactured by printing in a paste, sintering in a pressurized nitrogen gas atmosphere, and slowly cooling after sintering, a conductor made of ZrN having a small electrical resistance value As a result, a high strength silicon nitride wiring board having a high thermal conductivity and a high three-point bending strength of the entire wiring board was obtained.

  On the other hand, as shown in Comparative Examples 4 to 11, in the silicon nitride wiring board in which the substrate material composition, the paste composition for forming the conductor layer, and the cooling rate condition after sintering are outside the range defined as preferable in the present invention, It can be confirmed that any of the characteristics such as the electric resistance value, the bonding strength, the thermal conductivity, the three-point bending strength, etc. of the surface conductor layer is insufficient.

That is, in the wiring board according to Comparative Example 4 using the surface conductor layer forming paste to which ZrO ₂ is added in an excessive amount, a sufficiently thick conductor layer is not formed, and its electric resistance value is large and the current-carrying characteristics are inferior. . In the wiring board according to Comparative Example 5 using the surface conductor layer forming paste contrast the addition of ZrO ₂ to excess, although larger electric resistance value lower thickness of the surface conductor layer, the bonding strength is very small It was found that the durability was low.

Further, in the wiring substrate according to Comparative Example 6 in which Y ₂ O ₃ as a substrate sintering aid component was added in an excessive amount, densification of the silicon nitride substrate did not proceed sufficiently, and the strength and thermal conductivity were low. It was insufficient. Furthermore, in the wiring board according to Comparative Example 7 in which an excessive amount of Yb ₂ O ₃ as a sintering aid component of the board was added, the mechanical strength represented by the three-point bending strength was insufficient.

Furthermore, in the wiring substrate according to Comparative Example 8 in which the cooling rate of the sintered body immediately after sintering was excessively 400 ° C./hr, crystallization of the grain boundary phase of the silicon nitride substrate did not proceed sufficiently, and heat dissipation Sex became insufficient. Further, a wiring board according to Comparative Example 9 in which HfO ₂ as a substrate material composition was added in excess, a wiring board according to Comparative Example 10 in which MgO as a substrate material composition was added in excess, and TiO ₂ as a board material composition in excess In the wiring substrate according to Comparative Example 11 added to the above, the thermal resistance of the silicon nitride substrate was increased, the thermal conductivity was lowered, and the heat dissipation was insufficient.

Claims (10)

A conductor layer made of zirconium nitride is integrally formed on the surface of the silicon nitride substrate by simultaneous firing ,
The silicon nitride substrate is at least a rare earth element containing from 2 to 17.5 wt% in terms of oxide, the thermal conductivity of 70 W / m · K or more, or three-point bending strength is 550MPa or more, before Symbol nitride electrical resistance of zirconium conductive layer is not more than 10 ² Ω · cm, more than 98 wt% of the pre-Symbol conductor layer is composed of zirconium nitride (ZrN), thickness before Symbol zirconium nitride conductor layer be 3~25μm , silicon nitride wiring board, wherein the bonding strength of 1.5 Kg / mm or more before and Symbol silicon nitride substrate and the zirconium nitride conductor layer. 2. The silicon nitride wiring board according to claim 1, wherein the silicon nitride substrate has a thermal conductivity of 90 W / m · K or more and a three-point bending strength of 550 MPa or more. In the silicon nitride substrate, at least one of Hf and Mg is converted into an oxide in an amount of 0.3 to 3.0% by mass, and Al, Li, Na, K, Fe, Ba, Mn, The silicon nitride wiring board according to claim 1, wherein B is contained in a total amount of 0.5% by mass or less. The silicon nitride substrate contains at least one selected from the group consisting of Ti, Zr, W, Mo, Ta, Nb, V, and Cr in an amount of 2% by mass or less in terms of oxide. Item 14. The silicon nitride wiring board according to Item 1. Silicon nitride circuit board according to any one of claims 1 to 4 wherein the conductor layer is characterized by containing alumina (Al 2 _{O 3)} 2 mass% or less. 1.5% by mass or less of oxygen, 0.5% by mass or less of Al, Li, Na, K, Fe, Ba, Mn, and B as impurity cation elements, and 90% by mass of α-phase silicon nitride A raw material mixture containing 2 to 17.5% by mass of a rare earth element in terms of an oxide is added to silicon nitride powder having an average particle size of 1.0 μm or less to prepare a molded body. A silicon nitride paste for forming a conductor layer containing a sintering aid containing at least a rare earth oxide and zirconium oxide on the surface of the molded body, and oxidizing the solid content of the silicon nitride paste for forming a conductor layer A conductor wiring pattern is printed with a silicon nitride paste for forming a conductor layer with an addition amount of zirconium (ZrO ₂ ) of 1 to 12% by mass, degreased, and then at a temperature of 1750 ° C. to 1900 ° C. in a pressurized nitrogen gas atmosphere. Sintering temperature above A method of manufacturing a silicon nitride wiring board, characterized in that the cooling rate of the sintered body that reaches the temperature at which the liquid phase formed during sintering by the rare earth element solidifies is gradually reduced to 100 ° C./hour or less. . 7. The method of manufacturing a silicon nitride wiring board according to claim 6 , wherein at least one of Hf and Mg is added to the silicon nitride powder in an amount of 0.3 to 3.0% by weight in terms of an oxide. At least one element selected from the group consisting of Ti, Zr, W, Mo, Ta, Nb, V, and Cr is added to the silicon nitride powder in an amount of 2% by mass or less in terms of oxide. A method for manufacturing a silicon nitride wiring board according to claim 6 . The method for manufacturing a silicon nitride wiring board according to claim 6, wherein the atmosphere gas during the sintering is a nitrogen gas atmosphere pressurized to 0.3 MPa or more. The method for producing a silicon nitride wiring board according to claim 6 , wherein alumina (Al ₂ O ₃ ) powder is added in an amount of 2% by mass or less to the silicon nitride paste for forming a conductor layer.