JP2007230791A - Ceramic circuit board and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic circuit board which improves insulation, bonding strength, reliability and thermal conductivity and realizes excellent durability and heat dissipation over a long period of time and a method for manufacturing the same.
A ceramic circuit board 1 has at least one of a RE-Si-O-based oxide and a RE-Si-O-N-based oxide on one surface in a thickness direction of a substrate 2 made of non-oxide ceramics. An intermediate layer 3 composed of a crystalline phase containing is provided, and a metal layer 4 having a predetermined pattern shape is bonded to one surface in the thickness direction of the intermediate layer 3. The semiconductor element 11 is electrically connected to the metal layer 4.
[Selection] Figure 1

Description

  The present invention relates to a ceramic circuit board for bonding a metal pattern to a ceramic substrate, and more particularly to a ceramic circuit board suitable for a power module that requires high reliability, high heat dissipation, and high bonding strength, and a method for manufacturing the same.

  Conventionally, ceramic circuit boards for power modules that house semiconductor elements such as high-output power FETs (Field Effect Transistors) are metal circuit boards with high thermal conductivity to improve the heat dissipation of the semiconductor elements that generate heat during operation. And a ceramic substrate. A metal circuit board is joined to the surface on one side in the thickness direction of the ceramic substrate, and a metal heat sink is joined to the surface on the other side in the thickness direction. The semiconductor element is mounted on a metal circuit board and is electrically connected to an external circuit such as a control circuit.

  In a semiconductor element used in such a power module, for example, a part of atoms of silicon (Si) single crystal is substituted with a group 15 element such as nitrogen (N) and phosphorus (P), gallium (Ga), and aluminum (Al So-called impurity semiconductors replaced with group 13 elements such as) are used, and are composed of a combination of n-type and p-type semiconductors distinguished by the number of two carriers of free electrons and holes. Its role is to control power by switching the power circuit current based on the base voltage signal of electronic circuits such as IC (Integrated Circuit), but it occurs during operation as the switching speed increases. The problem is how to efficiently release a large amount of heat.

  The metal circuit board on which the semiconductor element is mounted constitutes an emitter electrode in the power circuit, and conducts a large current and plays a role of transmitting and releasing heat generated in the semiconductor element to the outside. Accordingly, the metal circuit board is required to have high thermal conductivity for diffusing heat over a wide range and enhancing heat dissipation. For example, if copper with high thermal conductivity is used for the metal circuit board, the heat generated by the operation of the semiconductor element is well transferred to the outside through the copper circuit board, effectively preventing the temperature rise of the semiconductor element. It becomes possible.

  In addition, the ceramic substrate has an insulating property, and is provided to ensure electrical insulation between the metal circuit board and the metal heat radiating plate, and conducts heat to the outside in the same manner as the metal circuit board. It plays a role.

In such a ceramic circuit board, a ceramic sintered body such as alumina (Al ₂ O ₃ ), aluminum nitride (AlN), and silicon nitride (Si ₃ N ₄ ) is used as the ceramic substrate. High thermal conductivity metals such as copper and aluminum are used.

However, in addition to higher power and higher speed of power modules and switching power supply modules, the amount of heat generated from semiconductor elements tends to increase year by year as the density and integration of semiconductor elements increase. It is preferable to use a non-oxide ceramic sintered body such as aluminum nitride (AlN) and silicon nitride (Si ₃ N ₄ ) having a thermal conductivity several times to 10 times higher than (Al ₂ O ₃ ) as the ceramic substrate. .

In order to apply a non-oxide ceramic substrate to a ceramic circuit substrate, it is indispensable to join a metal circuit board to the surface like an oxide ceramic substrate such as alumina. As a method for bonding a non-oxide ceramic substrate and a metal circuit board, a copper direct bonding method (DBC method: Direct Bonding Cupper method), an aluminum direct bonding method (DBA method: Direct Bonding).
Aluminum) and the active metal method (see Patent Documents 1 to 3).

Japanese Patent Laid-Open No. 03-290378 Japanese Patent Laid-Open No. 04-12554 JP 2001-48670 A

When a metal circuit board such as copper and aluminum is bonded to a non-oxide ceramic substrate such as aluminum nitride (AlN) and silicon nitride (Si ₃ N ₄ ), a Cu—O-based eutectic compound is obtained by using the DBC method. Therefore, it is necessary to form an oxide layer having a thickness of at least 3 to 5 μm on the surface of the non-oxide ceramic substrate by a thermal oxidation method or the like.

The mechanism of oxidation of the silicon nitride (Si ₃ N ₄ ) sintered body is largely due to the oxidation of the grain boundary layer generated at a low temperature of about 900 to 1000 ° C. and the oxidation of the silicon nitride particles themselves generated at a high temperature of 1100 ° C. or higher. The oxidation is promoted at different temperature ranges. For this reason, it is difficult to form a uniform oxide layer on the surface of the silicon nitride (Si ₃ N ₄ ) substrate. As a result, the silicon nitride (Si ₃ N ₄ ) substrate and the metal circuit board can be uniformly bonded. There is a problem that you can not.

In addition, when the grain boundary layer is oxidized, a volume change inevitably occurs, and this volume change causes fine cracks between the grain boundary layer and the silicon nitride particles. The cracks grow and connect with the oxidation time to grow into large cracks, and a stable oxide layer cannot be obtained. The cracks generated in this way are caused by deterioration of insulation, reduction of bonding strength, reduction of reliability against thermal stress during operation when a silicon nitride (Si ₃ N ₄ ) substrate and a metal circuit board are bonded, The heat dissipation of the entire power module is deteriorated due to a decrease in thermal conductivity.

  An object of the present invention is to provide a ceramic circuit board that improves insulation, bonding strength, reliability, and thermal conductivity, and realizes excellent durability and heat dissipation over a long period of time, and a method for manufacturing the same.

The present invention includes a substrate composed of a non-oxide ceramic,
A metal layer having a predetermined pattern shape;
An intermediate layer bonded to the substrate and the metal layer;
The intermediate layer is composed of a crystalline phase containing at least one of a RE-Si-O-based oxide and a RE-Si-O-N-based oxide (RE represents a rare earth element). It is a circuit board.

  In the invention, it is preferable that the thickness of the intermediate layer is 10 μm or more and 50 μm or less.

Further, the present invention is characterized in that the crystalline phase is a crystalline phase selected from RE ₂ Si ₂ O ₇ , RE ₂ SiO ₅ and RE ₁₄ Si ₉ O ₃₉ .

  The present invention is also characterized in that the rare earth element contained in the crystalline phase is at least one rare earth element selected from Sm, Tb, Dy, La, Ce, Nd, Y, Er, and Yb. .

  In the present invention, the thermal expansion coefficient of the intermediate layer is 3.0 ppm / ° C. or more and 16.0 ppm / ° C. or less, which is larger than the thermal expansion coefficient of the substrate and smaller than the thermal expansion coefficient of the metal layer. It is characterized by.

  The present invention is characterized in that the rare earth element contained in the crystalline phase is the same as the rare earth element contained in the crystalline phase present in the grain boundary layer of the non-oxide ceramic particles.

  Further, the present invention is characterized in that the non-oxide ceramic is a silicon nitride sintered body.

  In the invention, it is preferable that the metal layer is made of at least one metal selected from copper, aluminum, tungsten, molybdenum, and alloys thereof.

In the present invention, a solution containing a mixed powder of RE ₂ O ₃ powder (RE is a rare earth element) and SiO ₂ powder, an organic solvent and an organic binder is applied to the surface of a substrate made of non-oxide ceramics. A step of melting by heating in a nitrogen atmosphere to form a melt;
Crystallization of the melt to form an intermediate layer mainly composed of crystals composed of at least one of a RE-Si-O-based oxide and a RE-Si-O-N-based oxide on the surface of the substrate;
A method of manufacturing a ceramic circuit board, comprising: a step of placing a metal layer having a predetermined pattern shape on the substrate through the intermediate layer, and performing a heat treatment to join the metal layer. .

  The present invention includes an intermediate layer bonded to a substrate made of non-oxide ceramics and a metal layer having a predetermined pattern shape, and the intermediate layer includes a RE-Si-O-based oxide. And a RE—Si—O—N-based oxide (RE represents a rare earth element).

  By forming such an intermediate layer, unlike the oxidation by the thermal oxidation method, the surface of the substrate made of non-oxide ceramic can be uniformly covered with an oxide film without causing damage such as cracks. .

  Further, since the intermediate layer is an oxide, a homogeneous eutectic compound such as Cu-O is formed at the interface between the intermediate layer and the metal layer, and the metal layer can be bonded uniformly and firmly. Insulation can be improved.

  In addition, since no cracks are generated on the substrate surface, it is possible to prevent deterioration of thermal conductivity and to realize a ceramic circuit board with high heat dissipation.

  From the above, it is possible to obtain a ceramic circuit board that improves insulation, bonding strength, reliability, and thermal conductivity and realizes excellent durability and heat dissipation over a long period of time.

  Moreover, according to this invention, sufficient insulation and heat conductivity are realizable because the thickness of the said intermediate | middle layer shall be 10 micrometers or more and 50 micrometers or less.

Further, according to the present invention, the crystalline phase is a crystalline phase selected from RE ₂ Si ₂ O ₇ , RE ₂ SiO ₅ and RE ₁₄ Si ₉ O ₃₉ , so that it is very stable and the metal layer It is possible to protect the substrate surface from the high temperature atmosphere when bonding the substrate. As a result, deterioration of the bending strength of the substrate can be prevented.

  Further, according to the present invention, the rare earth element contained in the crystalline phase is at least one rare earth element selected from Sm, Tb, Dy, La, Ce, Nd, Y, Er, and Yb. The substrate surface can be protected from the atmosphere.

  Further, according to the present invention, the thermal expansion coefficient of the intermediate layer is 3.0 ppm / ° C. or more and 16.0 ppm / ° C. or less, which is larger than the thermal expansion coefficient of the substrate and larger than the thermal expansion coefficient of the metal layer. Since it is made small, the thermal stress which generate | occur | produces in a joining interface can be relieve | moderated effectively. Thereby, joint strength and reliability can be improved.

  According to the present invention, the rare earth element contained in the crystalline phase is the same as the rare earth element contained in the crystalline phase present in the grain boundary layer of the non-oxide ceramic particles.

  Thereby, the wettability and continuity between the substrate and the intermediate layer can be improved, the bonding strength of the intermediate layer can be improved, and the reliability and heat dissipation can be improved.

  Further, according to the present invention, since the non-oxide ceramic is a silicon nitride sintered body, the substrate has high strength and high thermal conductivity, and can improve reliability and heat dissipation.

  According to the present invention, since the metal layer is made of at least one metal of copper, aluminum, tungsten, molybdenum and alloys thereof, it is inexpensive and dissipates heat in terms of thermal conductivity, conductivity, and raw material costs. A highly functional ceramic circuit board can be obtained.

Further, according to the present invention, a solution containing a mixed powder of RE ₂ O ₃ powder (RE is a rare earth element) and SiO ₂ powder, an organic solvent and an organic binder is provided on the surface of a substrate composed of non-oxide ceramics. Apply and melt in a nitrogen atmosphere to form a melt, and crystallize the melt to form a crystal composed of at least one of a RE-Si-O-based oxide and a RE-Si-O-N-based oxide. A main intermediate layer is formed on the surface of the substrate. Next, a metal layer having a predetermined pattern shape is placed in contact with the substrate via the intermediate layer, and heat treatment is performed to bond the metal layer, thereby insulating, bonding strength, reliability, and heat conduction. It is possible to obtain a ceramic circuit board that improves the durability and achieves excellent durability and heat dissipation over a long period of time.

  The present invention is a ceramic circuit board comprising a substrate composed of non-oxide ceramics, a metal layer having a predetermined pattern shape, and an intermediate layer bonded to the substrate and the metal layer. The intermediate layer is composed of a crystalline phase containing at least one of a RE-Si-O-based oxide and a RE-Si-O-N-based oxide (RE represents a rare earth element). .

  Such a ceramic circuit board is particularly suitable for a power module that requires high reliability, high heat dissipation, and high bonding strength.

  FIG. 1 is a cross-sectional view showing a configuration of a semiconductor device 10 using a ceramic circuit board 1 according to a first embodiment of the present invention.

  The semiconductor device 10 is obtained by mounting a semiconductor element 11 on a ceramic circuit board 1 and is realized by, for example, a power module.

  The ceramic circuit board 1 is a crystalline material containing at least one of a RE-Si-O-based oxide and a RE-Si-O-N-based oxide on one surface in the thickness direction of a substrate 2 made of non-oxide ceramics. An intermediate layer 3 composed of a phase is provided, and a metal layer 4 having a predetermined pattern shape is bonded to one surface in the thickness direction of the intermediate layer 3. The semiconductor element 11 is electrically connected to the metal layer 4.

The semiconductor element 11 is, for example, a heat generating element, IGBT (Insulated Gate Bipolar).
It has a function of controlling a large current, such as a transistor (FET) and a power MOS (Metal Oxide Semiconductor) FET, and a wiring (not shown) for inputting a signal for current control is connected to the semiconductor element 11. Has been.

  The substrate 2 is a substrate made of non-oxide ceramics such as aluminum nitride and silicon nitride. Non-oxide ceramic substrates such as aluminum nitride and silicon nitride have particularly high strength and high thermal conductivity as compared with substrates composed of oxide ceramics such as alumina and zirconia, so that heat dissipation and It is suitable as a circuit board for mounting a heat generating element such as a power element that requires high mounting reliability.

  The non-oxide ceramic constituting the substrate 2 is not particularly limited, but silicon nitride is well known as a high-strength, high-toughness ceramic sintered body, and in addition, relatively high heat conduction. It is particularly preferable in that it has both high strength and high thermal conductivity.

The intermediate layer 3 is composed of a crystalline phase containing at least one of a RE—Si—O-based oxide and a RE—Si—O—N-based oxide. As the RE-Si-O-N-based oxide, rare earth oxides such as RE ₂ Si ₂ O ₇ (disilicate) and RE ₂ SiO ₅ (monosilicate) are preferable, and the RE-Si-O-N-based oxide is preferable. _{the, RE 4 Si 2 O 7 N} 4 (YAM), RESiO 2 N ( wollastonite) and _RE 10 _Si 7 ON _{4 (apatite) Si 3 N 4 -RE 2 O} 3 -SiO 2 based rare earth oxides such as Is preferred.

Among these, as the crystalline phase, RE-Si-O-based oxides are preferable, and RE ₂ Si ₂ O ₇ (disilicate) and RE ₂ SiO ₅ (monosilicate) are particularly preferable. Compared with conventional oxide coatings such as SiO ₂ film, ZrO ₂ , Al ₂ O ₃ , mullite, cordierite and YAG, this is very stable even in high temperature oxidizing atmosphere. Therefore, the surface of the substrate 2 can be protected from a high temperature atmosphere when the metal layer 4 is bonded, and the bending strength of the substrate 2 itself can be prevented from being deteriorated. The intermediate layer 3 is made of Si ₃ N ₄ -RE ₂ O ₃ —SiO ₂ such as RE ₄ Si ₂ O ₇ N ₄ (YAM), RESiO ₂ N (warastite), and RE ₁₀ Si ₇ ON ₄ (apatite). In the case of being composed of a crystalline phase, the amount of oxygen contained in the intermediate layer 3 can be increased, but since it is a non-oxide, the insulation and bonding strength are RE ₂ Si ₂ O ₇ (disilicate), RE ₂ SiO ₅ ( have poor monosilicate), as the present invention, comprehensive perspective from _RE 2 _Si 2 _{O 7} (disilicate characteristics _{improvement),} RE 2 SiO ₅ (monosilicate) are preferred.

  The rare earth element (RE) contained in the crystalline phase is preferably at least one rare earth element selected from Sm, Tb, Dy, La, Ce, Nd, Y, Er, and Yb. Since these elements have a small ionic radius among rare earths, the bonding force between molecules is large, the bonding force is high even in a high temperature atmosphere when the metal layer 4 is bonded, and the erosion resistance is excellent. Can be prevented.

  Furthermore, in addition to these rare earth elements, other additives can be used. By using these rare earth elements, the thermal expansion coefficient of the intermediate layer 3 is set to 3.0 ppm / ° C. without adding a large amount of additives. It can be adjusted to the range of 16.0 ppm / ° C. or less.

  The thermal expansion coefficient of the intermediate layer 3 is larger than the thermal expansion coefficient of 3.0 ppm / ° C. of the substrate 2 made of, for example, silicon nitride, and smaller than 16.0 ppm / ° C. of the metallic layer 4 made of copper, for example. Preferably, in order to effectively relieve the thermal stress generated between the substrate 2 and the metal layer 4, it is preferably 7.0 ppm / ° C. or more and 13.0 ppm / ° C. or less. The thermal expansion coefficient is particularly preferably 10.0 ppm / ° C., and this thermal expansion coefficient can be easily realized by using at least one rare earth element selected from Sm, Tb and Dy as the rare earth element.

  The thickness of the intermediate layer 3 is preferably 10 μm or more and 50 μm or less, and more preferably 15 μm or more and 30 μm or less. If the thickness exceeds 50 μm, peeling of the intermediate layer 3 is likely to occur, or heat conduction is hindered. Further, since the insulation is not sufficiently improved at about 5 μm, the thickness of the intermediate layer 3 is preferably 10 μm or more. In addition, in the method of forming an oxide layer by oxidizing the surface of a non-oxide ceramic substrate, when the thickness of the oxide layer is 3 to 5 μm, the oxide layer is thin and the thickness is not uniform. Therefore, sufficient insulation cannot be obtained, and even if the thickness of the oxide layer is increased, cracks due to volume expansion occur when the oxide layer is formed, and thus sufficient insulation cannot be obtained.

  Further, the crystalline phase present in the grain boundary layer of the particles of the substrate 2 contains rare earth elements derived from the ceramic sintering aid, thereby obtaining a dense ceramic sintered body having high strength and high thermal conductivity. Therefore, elements such as Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu can be suitably used. These rare earth elements are preferably contained in the range of 0.5 mol% or more and 10 mol% or less of the entire substrate 2 in terms of oxide. If the rare earth element content is less than 0.5 mol%, the sinterability is lowered and the dense and high-strength substrate 2 cannot be obtained. On the other hand, if it exceeds 10 mol%, the thermal conductivity deteriorates.

When a substrate made of silicon nitride is taken as an example of the substrate 2, for example, silicon nitride is contained in an amount of 70 mol% or more and 99 mol% or less, and at least one of the rare earth elements is 0 in terms of oxide (RE ₂ O ₃ ). An example is a silicon nitride sintered body containing 5 mol% or more and 10 mol% or less and further containing SiO ₂ as the balance. Further, sialon (SIALON) in which Al or O is dissolved in such silicon nitride may be formed.

  Thus, the substrate 2 and the intermediate layer 3 each contain a rare earth element, and considering the wettability and continuity between the substrate 2 and the intermediate layer 3, these rare earth elements are preferably the same. Since the rare earth element contained in the intermediate layer 3 is the element described above, the rare earth element contained in the substrate 2 is also at least one rare earth element selected from Sm, Tb, Dy, La, Ce, Nd, Y, Er, and Yb. An element is preferable.

  The metal layer 4 has a predetermined pattern shape. As the predetermined pattern shape, a simple circuit pattern such as a rectangular or circular circuit pattern required for input / output of signals in the semiconductor element 11 and power supply to the semiconductor element 11 is used. A pattern shape corresponding to the purpose of use, such as a simple geometric pattern, is selected.

  The metal layer 4 is preferably made of at least one metal selected from copper, aluminum, tungsten, molybdenum, and alloys thereof. In particular, from the viewpoint of thermal conductivity, raw material cost, and conductivity, copper or aluminum is preferred as the main component.

  FIG. 2 is a cross-sectional view showing a configuration of a semiconductor device 20 using the ceramic circuit board 5 according to the second embodiment of the present invention. The semiconductor device 20 is obtained by mounting the semiconductor element 11 on the ceramic circuit board 5.

  The ceramic circuit board 5 is obtained by further providing an intermediate layer 6 and a metal layer 7 on the ceramic circuit board 1 according to the first embodiment, and the same components as those of the ceramic circuit board 1 are denoted by the same reference numerals. The description is omitted.

  The intermediate layer 6 is composed of a crystalline phase containing at least one of a RE—Si—O-based oxide and a RE—Si—O—N-based oxide like the intermediate layer 3, and is opposite to the intermediate layer 3, that is, It is provided on the other surface in the thickness direction of the substrate 2.

  The metal layer 7 has a predetermined pattern shape and is bonded to the opposite side of the metal layer 4, that is, the other surface in the thickness direction of the intermediate layer 6.

  If the metal layer 4 and the metal layer 7 have the same metal and the same pattern shape, or the thermal stress generated under high temperature conditions is almost the same even if the metal or pattern shape is different, the intermediate layer 3 and the intermediate layer 3 The layer 6 is preferably composed of the same crystalline phase. Conversely, if the thermal stress generated under high temperature conditions is different because the metal layer 4 and the metal layer 7 have different pattern shapes, different metals, or different thicknesses, the thermal stress In order to absorb the difference, it is preferable that the intermediate layer 3 and the intermediate layer 6 have different thermal expansion coefficients. In order to make the thermal expansion coefficients different between the intermediate layer 3 and the intermediate layer 6, there are various types of crystalline phases, different types of rare earth elements, and the like.

  By doing in this way, the curvature of a ceramic circuit board and peeling of a metal layer can be prevented.

  For example, when the thickness of the metal layer 4 is thicker than that of the metal layer 7 or when the area of the metal layer 4 is larger than that of the metal layer 7, the thermal stress generated on the side where the metal layer 4 is bonded is high under high temperature conditions. Therefore, the thermal expansion coefficient of the intermediate layer 6 to which the metal layer 7 is bonded is made larger than that of the intermediate layer 3 to which the metal layer 4 is bonded, and thermal stress is also generated on the side to which the metal layer 7 is bonded. Thus, as a whole ceramic circuit board, the balance of thermal stress on both sides in the thickness direction can be kept uniform, and warpage of the ceramic circuit board and peeling of the metal layer can be prevented.

  Furthermore, it is possible to cause a predetermined warp by intentionally breaking the balance of thermal stresses on both sides in the thickness direction of the ceramic circuit board. The thermal expansion coefficient of a semiconductor element is about 3 ppm / ° C. When this is mounted on a ceramic circuit board, or when the ceramic circuit board is bonded and fixed to a heat sink or heat sink base made of copper or aluminum, the overall thermal expansion is achieved. The balance may be lost and the substrate may be warped. In consideration of this, it becomes possible to cause a predetermined warp in a direction opposite to the warp that would occur when a ceramic circuit board is mounted on a semiconductor element or fixed to a heat sink in advance. . Further, when the portion for fixing the ceramic circuit board is a curved surface, it is possible to cause a predetermined warp along the curved surface.

  In the second embodiment, the semiconductor device 20 may further include a heat sink 21. At this time, the metal layer 7 functions as a heat sink. The heat sink 21 is fixed to the opposite side of the semiconductor element 11, that is, to the metal layer 7. The heat sink 21 is made of a metal having high thermal conductivity such as copper and aluminum because heat dissipation is regarded as the most important.

  From the viewpoint of thermal design, it is preferable to make the thickness of the intermediate layer 3 thinner than the thickness of the intermediate layer 6. This is because heat generated when the semiconductor element 11 is driven spreads in a direction parallel to the main surface of the ceramic circuit board 5 through the metal layer 4 having higher thermal conductivity than the substrate 2, the intermediate layer 3, and the intermediate layer 6. This is because it is conducted in the thickness direction of the ceramic circuit board 5 or is emitted from the metal layer 4 into the air.

  The heat absorbed by the heat sink 21 may be radiated into the air, or may be further moved through a heat medium.

  FIG. 3 is a cross-sectional view showing a configuration of a semiconductor device 30 using the ceramic circuit board 8 according to the third embodiment of the present invention. The semiconductor device 30 is obtained by mounting the semiconductor element 11 on the ceramic circuit board 8.

  The ceramic circuit board 8 is obtained by further providing an intermediate layer 9 on the ceramic circuit board 1 according to the first embodiment. The same components as those of the ceramic circuit board 1 are denoted by the same reference numerals, and description thereof is omitted. .

  The intermediate layer 9 is composed of a crystalline phase containing at least one of a RE—Si—O-based oxide and a RE—Si—O—N-based oxide, like the intermediate layer 3, and the intermediate layer 3, the metal layer 4, In other words, it is provided on one surface in the thickness direction of the intermediate layer 3.

  When two intermediate layers are provided between the substrate 2 and the metal layer 4, it is preferable to configure each intermediate layer such that the thermal expansion coefficient of the intermediate layer 9 is larger than the thermal expansion coefficient of the intermediate layer 3. In the case of only the intermediate layer 3 as in the first embodiment, the thermal expansion coefficient is preferably configured to be around the average value of the thermal expansion coefficient of the substrate 2 and the thermal expansion coefficient of the metal layer 4. When the difference between the thermal expansion coefficient of the substrate 2 and the thermal expansion coefficient of the metal layer 4 is large, the difference between the thermal expansion coefficient of the substrate 2 and the thermal expansion coefficient of the intermediate layer 3 and the thermal expansion coefficient of the metal layer 4 and the intermediate The difference from the thermal expansion coefficient of the layer 3 also becomes large, and there is a possibility that the thermal stress cannot be sufficiently relaxed.

  Therefore, as in the present embodiment, two intermediate layers are provided, and the difference between the thermal expansion coefficient of the intermediate layer 3 and the thermal expansion coefficient of the intermediate layer 9 is determined as the difference between the thermal expansion coefficient of the substrate 2 and the thermal expansion coefficient of the intermediate layer 3. And the difference between the thermal expansion coefficient of the metal layer 4 and the thermal expansion coefficient of the intermediate layer 9, that is, the difference between the thermal expansion coefficient of the substrate 2 and the thermal expansion coefficient of the metal layer 4. The difference between the thermal expansion coefficient of the substrate 2 and the intermediate layer 3 in the first embodiment, and the thermal expansion coefficient of the metal layer 4 and the middle Since the difference from the thermal expansion coefficient of the layer 3 can be made smaller, the thermal stress can be relaxed more effectively.

  Considering the operational effects of the third embodiment, it is obvious that the intermediate layer is not limited to two layers, but may be three or more layers. In the case where there are three or more intermediate layers, the thermal expansion coefficient may be sequentially increased from the intermediate layer provided on the substrate 2 to the intermediate layer joined to the metal layer 4.

Below, the manufacturing method of a ceramic circuit board is demonstrated.
A method for manufacturing a ceramic circuit board includes a solution comprising a mixed powder of RE ₂ O ₃ powder (RE is a rare earth element) and SiO ₂ powder, an organic solvent and an organic binder on the surface of a substrate made of non-oxide ceramics. A step of applying, and forming a melt by heating and melting in a nitrogen atmosphere, and crystallizing the melt and comprising at least one of a RE-Si-O-based oxide and a RE-Si-O-N-based oxide. A step of forming an intermediate layer mainly composed of crystals on the surface of the substrate; and a metal layer having a predetermined pattern shape is disposed on the substrate in contact with the intermediate layer, and heat treatment is performed to form the metal layer. Joining.

For example, when the non-oxide ceramic is silicon nitride, first, as a starting material of the substrate, silicon nitride powder, rare earth element (Group 3 element) oxide (RE ₂ O ₃ ) powder, If necessary, SiO ₂ powder for precipitating the grain boundary crystal phase is mixed.

  The silicon nitride powder can be used in either α type or β type, but the particle size is 0.4 μm or more and 1.2 μm or less, and the amount of cationic impurities is 1% by mass or less, particularly 0.5% by mass or less. There is an appropriate amount of impurity oxygen of 0.5 wt% or more and 2.0 wt% or less. The powder may be produced by any method such as a direct nitriding method or an imide decomposition method. Sialon powder can also be used.

Further, _RE 2 _{O 3} powder, instead of SiO ₂ powder, can either be used a powder of complex oxide of _RE 2 _{O 3} and SiO _2, a compound of silicon nitride and _RE 2 _{O 3} and SiO ₂ Powder can also be used.

In preparing these powders, the mixing ratio of each powder is adjusted so as to satisfy the above-described substrate composition. For example, in order for the excess oxygen amount to satisfy a predetermined SiO ₂ / RE ₂ O ₃ molar ratio, oxygen inevitably contained in silicon nitride or oxygen adsorbed in the manufacturing process is considered as SiO ₂ content. Thus, the amount of rare earth oxide and the amount of SiO ₂ powder added are adjusted.

  Each powder is weighed at a predetermined ratio and thoroughly mixed with a vibration mill, a rotary mill, a barrel mill, etc., and then the obtained mixed powder is processed by a desired molding means such as die press, casting molding, waste mud molding, and extrusion molding. A silicon nitride substrate can be obtained by molding into an arbitrary shape by injection molding, cold isostatic pressing, a doctor blade, or the like, and firing the molded body.

  The firing is usually performed in a nitrogen gas atmosphere, and the firing temperature is suitably in the range of 1700 ° C. to 2000 ° C. By sintering under such conditions, a sintered body densified so that the relative density exceeds 98% can be obtained. If the firing temperature exceeds 2000 ° C., the silicon nitride crystal grows and there is a risk that the bending strength will deteriorate. Conversely, if it is lower than 1700 ° C., densification becomes difficult.

  Further, after the firing, it can be further densified by a hot isostatic firing (HIP) method. Furthermore, by performing slow cooling in the cooling process after firing, or by heat treating the sintered body again at a temperature of 1000 ° C. or higher and 1700 ° C. or lower, crystallization of grain boundaries is achieved, and bending strength and heat conduction are improved. It is possible to further improve the characteristics.

  When high dimensional accuracy is required for the silicon nitride substrate, a part of the silicon nitride powder is replaced with Si powder to produce a molded body, which is heat-treated at 800 ° C. to 1500 ° C. in a nitrogen-containing atmosphere. The shrinkage during firing can be reduced by reacting and generating silicon nitride to increase the density of the molded body and firing under the above-described firing conditions.

Next, an intermediate layer is formed on the surface of the silicon nitride substrate thus obtained. The intermediate layer is formed by vapor deposition, CVD (Chemical Vapor Deposition), EB (Electron Beam) -PVD (Physical Vapor Deposition), and sputtering, etc., thin film formation, spraying, slurry coating, and printing. However, in terms of being able to strictly control the amount of excess SiO ₂ contained in the intermediate layer, a thermal spraying method, a slurry coating method, or a printing method is preferable, and a slurry coating method or a printing method is preferable in that it can be easily formed. Is preferred.

For example, a mixed powder of the composite mixed powder of SiO ₂ powder and _RE 2 _{O 3} powder and the oxide powder, or a SiO ₂ powder and _RE 2 _{O 3} powder and the oxide powder, the excess SiO ₂ in these powders The amount is adjusted to a predetermined range, and the slurry of the powder is adjusted.

  This slurry is prepared by mixing an organic solvent, an organic binder, and a mixed powder at a predetermined ratio and adjusting to a predetermined viscosity.

  Next, the prepared slurry is applied to the surface of the silicon nitride substrate by spraying, or uniformly applied by a dipping method, or printed on the entire surface of the substrate or only at a predetermined position by a printing method. Prepare. Next, by heat-treating the base material, the slurry is heated and melted in a nitrogen atmosphere to form a melt, and the melt is crystallized to form an intermediate layer composed of a target crystalline phase. Can do.

The heat treatment temperature is preferably 1400 ° C. or higher and 1700 ° C. or lower, although it depends on the type of RE ₂ O ₃ used. When the heat treatment temperature is lower than 1400 ° C., it becomes difficult to precipitate a desired crystalline phase, or the resulting intermediate layer becomes insufficiently densified, resulting in a porous layer in which many pores remain. On the other hand, when the heat treatment temperature is higher than 1700 ° C., SiO ₂ is volatilized and a desired crystalline phase cannot be deposited.

Note that it is preferable that the SiO ₂ powder and RE ₂ O ₃ powder used as raw materials have a purity of 95% or more.

  Further, the above-mentioned slurry is uniformly applied or printed on the surface of the formed shape of the silicon nitride substrate before firing by the same method as described above, and this is fired, whereby the silicon nitride substrate and the intermediate layer are simultaneously formed. It is also possible to form.

Next, a metal layer is joined to the intermediate layer obtained as described above.
The metal layer is joined in accordance with a normal DBC method, for example, with copper, and a metal layer having a predetermined circuit pattern shape is joined to the intermediate layer to obtain a ceramic circuit board.

  Specifically, first, a copper plate processed into a predetermined pattern shape is placed in contact with the intermediate layer. Next, heat treatment is performed in an inert atmosphere such as a nitrogen atmosphere or in a vacuum at a temperature not higher than the melting point of copper (1083 ° C.) and lower than the melting point of the Cu—O eutectic compound (1065 ° C.). The intermediate layer and the metal layer are joined by wetting the surface of the intermediate layer with the compound liquid phase and cooling and solidifying the liquid phase.

  By manufacturing in such a process, a ceramic circuit board having high thermal conductivity, high electrical insulation, high strength and high reliability can be manufactured.

  The following silicon nitride powder, rare earth element oxide powder, and silicon oxide powder were used as the raw material powder for the silicon nitride substrate.

Silicon nitride powder produced by a direct nitriding method with an average particle size of 1.2 μm, oxygen content of 1% by mass and α rate of 90%, and various rare earths with a purity of 99.9% and an average particle size of 1.2 μm An oxide powder and a SiO ₂ powder having a purity of 99.9% and an average particle diameter of 1.6 μm were prepared.

Next, a mixed powder composed of the above silicon nitride powder 89.5 mol%, RE ₂ O ₃ powder 3 mol%, and SiO ₂ powder 7.5 mol% is prepared, an acrylic resin binder and a solvent toluene are added, and silicon nitride is added. Using the balls made, the mixture was pulverized by a rotary mill for 48 hours to prepare a slurry.

  The obtained slurry was molded using a doctor blade method to produce a green sheet molded body having a thickness of 0.3 mm. The green sheet molded body thus obtained was appropriately laminated and cut to obtain a sheet-like sintered body having a size of 60 mm × width 60 mm × thickness 2 mm after firing as a sample for insulating evaluation. Moreover, the green sheet molded body was appropriately laminated and cut to obtain a sheet-shaped molded body having a size of 20 mm × 40 m × width 2 mm after firing as a metal circuit peel strength measurement sample. Furthermore, as a sample for thermal cycle test evaluation, a sheet-like molded body having a size of 60 mm × 60 × width × 2 mm after firing was obtained in the same manner as the sample for insulating evaluation. In addition, as a sample for measuring the bending strength of the silicon nitride substrate after forming the intermediate layer in a high-temperature atmosphere, a sheet-like molded body having a size of 10 mm × 40 × width × 2 mm after firing was obtained.

  These molded bodies were degreased at 600 ° C. and then fired at a firing temperature of 1900 ° C. for 10 hours in a nitrogen atmosphere by gas pressure firing to obtain a silicon nitride substrate.

Similarly, Y ₂ O ₃ powder and CaO powder were prepared in an aluminum nitride powder having an average particle diameter of 1.0 μm, an acrylic resin binder and toluene as a solvent were added, mixed and pulverized to prepare a slurry. The obtained slurry was molded using a doctor blade method to obtain a sheet molded body. Further, the obtained sheet molded body was degreased and then fired at a firing temperature of 1900 ° C. for 10 hours in a nitrogen atmosphere by gas pressure firing to obtain an aluminum nitride substrate.

Next, a mixed powder of RE ₂ O ₃ powder and SiO ₂ powder shown in Table 1 was mixed with an acrylic resin binder, a solvent terpineol, and a plasticizer DBP (dibutyl phthalate) to prepare a paste. The obtained paste was applied to both sides of a silicon nitride substrate and an aluminum nitride substrate by screen printing so as to have a predetermined thickness. At this time, the paste was applied in the range of 56 mm × 56 mm, which was slightly smaller than the main surface of the substrate, for the samples for insulating evaluation and thermal cycle test evaluation. Further, the sample for measuring the metal circuit peel strength was applied in a range of 16 mm × 36 mm, so that the application range was at the center position of the substrate.

  Next, after the solvent content of the paste was dried, this substrate was treated at a heat treatment temperature shown in Table 1 in a nitrogen gas atmosphere to obtain a substrate having an intermediate layer formed on the surface.

  Further, a copper plate having a thickness of 0.3 mm was placed in contact with each other on the intermediate layer. At this time, the shape of the copper plate was set to a shape in which an electrode can be formed based on the method described in JIS-C2141 test method for ceramic material for electrical insulation for the sample for insulation evaluation. Moreover, about the sample for a metal circuit peeling strength measurement, the copper plate of 14 mm x 50 mm was arrange | positioned so that the unjoined part might be made in the edge part of a longitudinal direction. This unbonded portion is provided to grip the unbonded portion and pull the copper plate in the direction perpendicular to the silicon nitride substrate when the metal circuit peel strength is measured later. For the sample for thermal cycle test evaluation, a copper plate of 54 mm × width 54 mm, which is slightly smaller than the intermediate layer, is arranged on both sides in the thickness direction of the silicon nitride substrate, and is positioned at the center so as not to protrude from the intermediate layer. Arranged.

  Next, a heat treatment was performed at 1170 ° C. while applying a load of about 50 Pa to the substrate on which the intermediate layer was formed and the copper plate, and the copper plate was bonded to the silicon nitride substrate and the aluminum nitride substrate to obtain a ceramic circuit substrate. .

  The rare earth elements contained in the crystalline phase present in the grain boundary layer of the substrate, the rare earth elements contained in the intermediate layer, and the heat treatment temperature of the intermediate layer are as described in Table 1.

Further, as Comparative Example 1, an intermediate layer is not provided, and a silicon nitride circuit board in which a copper plate is bonded to a substrate obtained by oxidizing the surface of a silicon nitride substrate at 1200 ° C. using a thermal oxidation method. A silicon nitride circuit board obtained by bonding a copper plate to an intermediate layer containing no rare earth element formed in the same manner as the intermediate layer of the example using SiO ₂ powder, Zr ₂ O powder, and Al ₂ O ₃ powder instead of the layer is obtained. It was.

  The properties of Examples and Comparative Examples thus obtained were measured by the following methods, and the results are shown in Table 1.

  Crystal identification: The crystal of the grain boundary phase of the substrate and the crystal of the intermediate layer were identified by X-ray diffraction measurement.

  Measurement of the thickness of the intermediate layer: The substrate on which the intermediate layer was formed was cut, the cross section thereof was observed with an electron microscope, and the average of the thickness of the intermediate layer having an arbitrary cross section was 10 points.

  Measurement of bending strength in high-temperature atmosphere: Using the above-mentioned sample for measuring bending strength, the bending strength in a high-temperature atmosphere at 1000 ° C., which is equivalent to the bonding temperature of the metal layer, was measured. The bending strength is measured by a four-point bending test method in which a specimen for measuring the bending strength is placed between fulcrums of the lower span 30 mm, and the load between the two spans 10 mm is applied to the center between the lower spans. The measurement was performed while the inside of the load point covered with a heat insulating material was heated with a heater. The measurement was performed by measuring the load when the bending strength measurement sample was broken, and calculating the strength from the load and the dimensions of the bending strength measurement sample.

  Measurement of metal circuit peel strength: The above-mentioned sample for measuring metal circuit peel strength is fixed to a base, and the unbonded portion of the end of the copper plate bonded to this sample is pulled upward in the vertical direction with respect to the silicon nitride substrate. The load at the time when peeling occurred was measured. The peel strength was calculated as the peel strength by dividing this load by the bonding width (14 mm).

  Measurement of insulation: Volume resistivity was measured based on a description measurement method based on a test method for ceramic materials for electrical insulation according to JIS-C2141.

  Measurement of thermal resistance: A heating element was mounted on a copper plate, and the heating element was energized to generate heat, and the temperature of the heating element during operation was calculated from the temperature-dependent change in the resistance value of the heating element to calculate the thermal resistance. . As the heating element, an element in which a tungsten electrode is embedded in an aluminum nitride substrate and generates heat due to the resistance of the tungsten electrode when energized is used. The heating element is mounted using a Sn-Ag-Cu Pb-free solder, which has a relatively high thermal conductivity of about 80 W / mK compared to Pb-based solder. Was used for a reflow oven set at 5 minutes. Wire bonding was applied to the heating element using an aluminum wire having a diameter of 0.3 mm, and external wiring was applied. Further, the temperature dependence of the resistance value of the heating element was obtained by holding the element at a temperature of 0 to 150 ° C. in advance before mounting and measuring the change in resistance value with respect to the temperature at that time. In this way, a copper heat sink capable of flowing cooling water at 25 ° C. is brought into contact with the opposite surface of the silicon nitride substrate on which the heating element is mounted via grease so that the temperature of the cooling water can be measured by a thermocouple. I made it. A power of 10 to 200 W is applied to such a heat generating module, the resistance value of the element when the heat generating element generates heat is measured, and the element temperature is determined from the temperature dependence of the resistance value of the heat generating element measured in advance. Calculated. Further, a value obtained by dividing the difference between the element temperature and the cooling water temperature by the calorific value was obtained as a thermal resistance value (° C./W).

  Thermal cycle test: The thermal cycle test was conducted by holding the above-described sample for thermal cycle test in a gas phase at −40 to 150 ° C. for 30 minutes each. Samples are taken every 50 cycles up to 100 cycles, and every 100 cycles exceeding 100 cycles, and a continuous test is conducted up to 1000 cycles. The ultrasonic flaw detection method is used for each cycle to check whether the copper plate is peeled off or not. Observed. As a test result, the number of cycles in which peeling was observed was shown.

In Examples 1 to 23, the insulation property is as high as 10 ¹² Ω or more, the peel strength of the metal circuit is 60 N / cm or more, and the thermal resistance is as low as 0.4 ° C./W or less. Peeling did not occur unless it was 500 times or more.

Moreover, the thickness of the intermediate layer was 10 μm or more and 50 μm or less. In Example 13, the intermediate layer thickness was as thin as 5 μm, and the insulating property was slightly lowered to 10 ¹⁰ Ω. On the contrary, in Example 16, the intermediate layer thickness is as thick as 80 μm and the insulation is as high as 10 ¹⁴ Ω, but the thermal resistance value as a ceramic circuit board is slightly increased to 0.40 ° C./W, so that heat dissipation is achieved. Tended to be relatively bad, but it did not adversely affect performance.

  In addition, Examples 8 and 18 in which the rare earth element contained in the crystalline phase of the intermediate layer and the rare earth element contained in the crystalline phase present in the grain boundary layer of the substrate are the same have high insulating properties. In addition, a ceramic circuit board having high peel strength of the metal circuit and particularly high insulation and reliability was obtained.

  Furthermore, in Example 24 and Example 25 using aluminum nitride as the substrate, in addition to high insulation and reliability, ceramic circuit boards excellent in heat dissipation due to the high thermal conductivity of aluminum nitride and low thermal resistance was gotten.

On the other hand, Comparative Example 1 and Comparative Example 2 have a low insulation property of 10 ⁹ Ω, a peel strength of the metal circuit as low as 24 N / cm or less, a thermal resistance higher than 0.4 ° C./W, and a metal obtained by a thermal cycle test. Delamination also occurred within 50 times, and the circuit board was extremely inferior in characteristics.

It is sectional drawing which shows the structure of the semiconductor device 10 using the ceramic circuit board 1 which is the 1st Embodiment of this invention. It is sectional drawing which shows the structure of the semiconductor device 20 using the ceramic circuit board 5 which is the 2nd Embodiment of this invention. It is sectional drawing which shows the structure of the semiconductor device 30 using the ceramic circuit board 8 which is the 3rd Embodiment of this invention.

Explanation of symbols

1, 5, 8 Ceramic circuit board 2 Substrate 3, 6, 9 Intermediate layer 4, 7 Metal layer 10, 20, 30 Semiconductor device 11 Semiconductor element 21 Heat sink

Claims (9)

A substrate made of non-oxide ceramics;
A metal layer having a predetermined pattern shape;
An intermediate layer bonded to the substrate and the metal layer;
The intermediate layer is composed of a crystalline phase containing at least one of a RE-Si-O-based oxide and a RE-Si-O-N-based oxide (RE represents a rare earth element). Circuit board.   The ceramic circuit board according to claim 1, wherein the intermediate layer has a thickness of 10 μm to 50 μm. The ceramic circuit board according to claim 1, wherein the crystalline phase is a crystalline phase selected from RE ₂ Si ₂ O ₇ , RE ₂ SiO _5, and RE ₁₄ Si ₉ O ₃₉ .   The rare earth element contained in the crystalline phase is at least one rare earth element selected from Sm, Tb, Dy, La, Ce, Nd, Y, Er, and Yb. Ceramic circuit board.   The thermal expansion coefficient of the intermediate layer is 3.0 ppm / ° C. or more and 16.0 ppm / ° C. or less, and is larger than the thermal expansion coefficient of the substrate and smaller than the thermal expansion coefficient of the metal layer. 2. The ceramic circuit board according to 1.   2. The ceramic circuit board according to claim 1, wherein the rare earth element contained in the crystalline phase is the same as the rare earth element contained in the crystalline phase present in the grain boundary layer of the non-oxide ceramic particles. .   The ceramic circuit board according to claim 1, wherein the non-oxide ceramic is a silicon nitride sintered body.   The ceramic circuit board according to claim 1, wherein the metal layer is made of at least one metal selected from copper, aluminum, tungsten, molybdenum, and alloys thereof. Applying a solution containing a mixed powder of RE ₂ O ₃ powder (RE is a rare earth element) and SiO ₂ powder, an organic solvent and an organic binder to the surface of the substrate made of non-oxide ceramic;
A melt is formed by heating and melting in a nitrogen atmosphere, and the melt is crystallized to mainly include crystals composed of at least one of a RE-Si-O-based oxide and a RE-Si-O-N-based oxide. Forming an intermediate layer on the surface of the substrate;
A method of manufacturing a ceramic circuit board, comprising: placing a metal layer having a predetermined pattern shape on the substrate through the intermediate layer, and performing a heat treatment to join the metal layer.

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