CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national phase application filed under 35 U.S.C. § 371 of International Application No. PCT/JP2018/001442, filed Jan. 18, 2018, designating the United States, which claims priority from Japanese Patent Application No. 2017-050091, filed Mar. 15, 2017, which are hereby incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a metal paste for joints, an assembly, a production method for an assembly, a semiconductor device, and a production method for a semiconductor device.

BACKGROUND ART

When a semiconductor device is produced, various joining materials are used in order to join a semiconductor element and a lead frame and the like (a support member) together. In the semiconductor device, a high-melting point lead solder has been used as the joining material for joining a power semiconductor, an LSI, or the like that is operated at a high temperature of higher than or equal to 150° C. Recently, an operation temperature increases to be close to a melting point of the high-melting point lead solder, in accordance with higher capacity and space saving of the semiconductor element, and thus, it is difficult to ensure connection reliability. On the other hand, a joining material not containing lead is required in accordance with tightening of RoHS regulation.

Until now, the joints of a semiconductor element using materials other than the lead solder have been considered. For example, in Patent Literature 1 described below, a technology is proposed in which silver nanoparticles are subjected to low-temperature sintering, and thus, a sintered silver layer is formed. It is known that such sintered silver has high connection reliability with respect to a power cycle (refer to Non Patent Literature 1).

A technology is also proposed in which copper particles are sintered as another material, and thus, a sintered copper layer is formed. For example, in Patent Literature 2 described below, a paste for joints containing cupric oxide particles and a reducing agent is disclosed as a joining material for joining a semiconductor element and an electrode together. In addition, in Patent Literature 3 described below, a joining material containing copper nanoparticles, any one or both of copper micro particles and copper sub-micro particles is disclosed.

Incidentally, in a case where a residual thermal stress between the semiconductor element and the support member is large, a characteristic change due to thermal strain with respect to the semiconductor element, and a damage such as a crack with respect to the semiconductor element, the joining material, and the support member occur. For this reason, the residual thermal stress between the semiconductor element and the support member causes a decrease in a yield ratio and a decrease in long-term reliability. On the other hand, in general, it is possible to reduce the residual thermal stress between the semiconductor element and the support member as a temperature at the time of joining the semiconductor element and the support member together (a joining temperature) decreases. In addition, in a case where the joining temperature is low, it is possible to reduce the energy for production. For this reason, it is preferable that the joining temperature between the semiconductor element and the support member is low. In particular, in a case where the joining temperature is lower than or equal to 250° C., it is possible to apply an organic substrate such as a glass epoxy substrate as the support member, and it is possible to apply the organic substrate to a logic, a sensor, a passive component, and the like.

A method using an alloy having a low melting point in a solder (refer to Patent Literature 4), a method of increasing a melting point by diffusing a dissimilar metal in a solder to be an alloy after the solder is melted (refer to Patent Literature 5), and the like have been reported as a method of reducing the joining temperature.

CITATION LIST

Patent Literature

Patent Literature 1: Japanese Patent No. 4928639

Patent Literature 2: Japanese Patent No. 5006081

Patent Literature 3: Japanese Unexamined Patent Publication No. 2014-167145

Patent Literature 4: Japanese Patent No. 6060199

Patent Literature 5: Japanese Patent No. 3736797

Non Patent Literature

Non Patent Literature 1: R. Khazaka, L. Mendizabal, D. Henry: J. ElecTron. Mater, 43(7), 2014, 2459-2466

SUMMARY OF INVENTION

Technical Problem

However, in the method of Patent Literature 4, in a case where the melting point of the solder is close to a use temperature of the device, the solder is softened at the use temperature, and thus, the connection reliability decreases. In addition, in a case where a heating step in which heating is performed at a temperature higher than or equal to the melting point of the solder is provided after a joining step, the solder is melted again due to the heating, and thus, causes a defect. In addition, in the method of Patent Literature 5, an intermetallic compound that is generated during the joints is brittle, and thus, a sufficient joining strength is not obtained, cycle reliability is degraded, and a thermal conductivity is low.

The present invention has been made in consideration of the circumstances described above, and an object thereof is to provide a metal paste for joints in which it is possible to perform the joints at a low-temperature of lower than or equal to 250° C., and to obtain an assembly having a sufficient joining strength, an assembly including a sintered body of the metal paste for joints and a production method for an assembly, and a semiconductor device including a sintered body of the metal paste for joints and a production method for a semiconductor device.

Solution to Problem

The present inventors have focused on and studied a sintered copper die bonding material using a sintering phenomenon of copper particles that is known in the related art. The sintered copper die bonding material of the related art is excellent in thermal conductivity and cycle fatigue resistance, and is inexpensive, but a high temperature of higher than or equal to 280° C. is necessary for joining the sintered copper die bonding material, and in a case where the sintered copper die bonding material of the related art is used, it is difficult to set a joining temperature (a sintering temperature) to be lower than or equal to 250° C. However, as a result of intensive studies of the present inventors, the present inventors have found that it is possible to perform the joints at a low temperature by combining the copper particles having a specific volume average particle diameter and a predetermined amount of specific carboxylic acid in a metal paste for joints containing copper particles, and to obtain an assembly having a sufficient joining strength, and thus, have completed the present invention.

That is, a metal paste for joints according to one aspect of the present invention contains: metal particles; and a monovalent carboxylic acid having 1 to 9 carbon atoms. In the metal paste for joints, the metal particles include sub-micro copper particles having a volume average particle diameter of 0.12 μm to 0.8 μm, and a content of the monovalent carboxylic acid having 1 to 9 carbon atoms is 0.015 part by mass to 0.2 part by mass with respect to 100 parts by mass of the metal particles. According to such a metal paste for joints, it is possible to perform joints at a low temperature of lower than or equal to 250° C., and to obtain an assembly having a sufficient joining strength. In addition, according to such a metal paste for joints, it is possible to perform the joints without a pressure (pressureless joints), and to obtain an assembly having a sufficient joining strength even in the pressureless joints.

In one mode, a content of metal paste for joints further contains a carboxylic acid having carbon atoms of greater than or equal to 10. In this mode, a content of the carboxylic acid having carbon atoms of greater than or equal to 10 is 0.07 part by mass to 2.10 parts by mass with respect to 100 parts by mass of the metal particles. In this mode, the effects of the present invention become remarkable.

In one mode, the metal particles further include flake-shaped micro copper particles having a maximum diameter of 2 μm to 50 μm and an aspect ratio of greater than or equal to 3.0. In this mode, a content of the sub-micro copper particles is 30 mass % to 90 mass % on the basis of a total mass of the metal particles, and a content of the micro copper particles is 10 mass % to 70 mass % on the basis of the total mass of the metal particles. In this mode, it is possible to sufficiently reduce volume contraction at the time of sintering the metal paste for joints, it is easy to ensure a joining strength of an assembly that is produced by sintering the metal paste for joints, and in a case where the metal paste for joints is used for joining the semiconductor element, a semiconductor device tends to exhibit a more excellent die shear strength and more excellent connection reliability.

In one mode, the metal particles further include at least one type of metal particles selected from the group consisting of zinc and silver, at a content of 0.01 mass % to 10 mass % on the basis of the total mass of the metal particles. In this mode, in a case where an adherend is gold or silver, a joining force is improved.

In one mode, the monovalent carboxylic acid having 1 to 9 carbon atoms includes at least one type selected from the group consisting of an acetic acid, a hexanoic acid, and a butyric acid. In this mode, the effects of the present invention become remarkable.

In one mode, the metal paste for joints contains a solvent component at a content of 2 mass % to 50 mass % on the basis of a total mass of the metal paste for joints. In this mode, it is possible to adjust the metal paste for joints to have a more suitable viscosity, and it is difficult to inhibit the sintering of the copper particles.

In one mode, the solvent component includes a solvent component having a boiling point of higher than or equal to 300° C. In this mode, a content of the solvent component having a boiling point of higher than or equal to 300° C. is 2 mass % to 50 mass % on the basis of the total mass of the metal paste for joints. In this mode, plasticity and adhesiveness are applied to the metal paste for joints until immediately before the start of the sintering, and it is easy to perform the joints without a pressure.

In one mode, the solvent component having a boiling point of higher than or equal to 300° C. includes at least one type selected from the group consisting of isobornyl cyclohexanol, tributyrin, butyl stearate, and octyl octanoate. In this mode, it is easier to perform the joints without a pressure.

A production method for an assembly according to one aspect of the present invention includes: a step of preparing a laminated body in which a first member, the metal paste for joints described above, and a second member are laminated in this order, and of sintering the metal paste for joints at a temperature of lower than or equal to 250° C. in a state of receiving self-weight of the first member or in a state of receiving the self-weight of the first member and a pressure of less than or equal to 0.01 MPa. According to the production method, it is possible to obtain the assembly having a sufficient joining strength by using the metal paste for joints described above. In addition, it is possible to reduce a residual thermal stress between members, and thus, it is possible to prevent a damage such as a crack from occurring on the member, and to obtain an effect of improving a yield ratio according to a reduction in thermal strain. In addition, it is possible to reduce the energy of the joining step.

A production method for a semiconductor device according to one aspect of the present invention includes: a step of preparing a laminated body in which a first member, the metal paste for joints described above, and a second member are laminated in this order, and of sintering the metal paste for joints at a temperature of lower than or equal to 250° C. in a state of receiving self-weight of the first member or in a state of receiving the self-weight of the first member and a pressure of less than or equal to 0.01 MPa. In this method, at least one of the first member and the second member is a semiconductor element. According to the production method, it is possible to obtain a semiconductor device having a sufficient joining strength by using the metal paste for joints described above. In addition, it is possible to reduce the residual thermal stress between the members, and thus, it is possible to prevent a characteristic change due to thermal strain with respect to a semiconductor, a damage such as a crack with respect to the member from occurring, and to obtain an effect of improving a yield ratio according to a reduction in the thermal strain. In addition, it is possible to reduce the energy of the joining step, and the semiconductor device produced by the production method can be excellent in the connection reliability.

An assembly according to one aspect of the present invention includes: a first member; a second member; and a sintered body of the metal paste for joints described above, the sintered body joining the first member and the second member together. In the assembly, the first member and the second member are joined together through the sintered body of the metal paste for joints having a sufficient joining force. In addition, the assembly includes the sintered body of the metal paste for joints containing copper that is excellent in the thermal conductivity, and thus, can be excellent in heat dissipating properties of the member.

In one mode, at least one of the first member and the second member contains at least one type of metal selected from the group consisting of copper, nickel, silver, gold, and palladium, on a surface in contact with the sintered body. In this mode, it is possible to further increase adhesion properties between at least one of the first member and the second member, and the sintered body.

A semiconductor device according to one aspect of the present invention, includes: a first member; a second member; and a sintered body of the metal paste for joints described above, the sintered body joining the first member and the second member together. In the semiconductor device, at least one of the first member and the second member is a semiconductor element. The semiconductor device has the sintered body of the metal paste for joints that has a sufficient joining force and contains copper having a high thermal conductivity and a high melting point, and thus, has a sufficient die shear strength, is excellent in the connection reliability, and can also be excellent in power cycle resistance.

Advantageous Effects of Invention

According to the present invention, it is possible to provide a metal paste for joints in which it is possible to perform the joints at a low temperature of lower than or equal to 250° C., and to obtain an assembly having a sufficient joining strength, an assembly including a sintered body of the metal paste for joints and a production method for an assembly, and a semiconductor device including a sintered body of the metal paste for joints and a production method for a semiconductor device.

