Bonding structure

Abstract

Disclosed is a bonding structure that includes an intermetallic compound crystal composed of Sn and Cu, and, an Sn alloy matrix composed of Sn and Cu, being intended for bonding a metal body or an alloy body, the intermetallic compound crystal forming an endotaxial junction with the Sn alloy matrix, and the Sn alloy matrix and/or the intermetallic compound crystal forming an epitaxial junction with the metal body or the alloy body.

Claims

1. A bonding structure comprising an intermetallic compound crystal composed of Sn and Cu, and a Sn alloy matrix composed of Sn and Cu, said bonding structure configured and adapted for bonding a metal body or an alloy body, the intermetallic compound crystal having a monoclinic or hexagonal crystal structure and forming an endotaxial junction with the Sn alloy matrix, and the Sn alloy matrix and/or the intermetallic compound crystal configured to form an epitaxial junction with the metal body or the alloy body.

2. The bonding structure according to claim 1, wherein the Sn alloy matrix forms the epitaxial junction with the metal body or the alloy body.

3. The bonding structure according to claim 1, wherein the metal body or the alloy body is composed of a simple metal, alloy or intermetallic compound of at least one metal selected from the group consisting of Sn, Cu, Al, Ni, Si, Ag, Au, Pt, B, Ti, Bi, In, Sb, Ga, Zn, Cr and Co.

4. The bonding structure according to claim 1, wherein the bonding structure contains 3 to 85% by volume of the intermetallic compound crystal.

5. The bonding structure according to claim 2, wherein the metal body or the alloy body is composed of a simple metal, alloy or intermetallic compound of at least one metal selected from the group consisting of Sn, Cu, Al, Ni, Si, Ag, Au, Pt, B, Ti, Bi, In, Sb, Ga, Zn, Cr and Co.

6. The bonding structure according to claim 2, wherein the bonding structure contains 3 to 85% by volume of the intermetallic compound crystal.

7. The bonding structure according to claim 3, wherein the bonding structure contains 3 to 85% by volume of the intermetallic compound crystal.

8. The bonding structure according to claim 5, wherein the bonding structure contains 3 to 85% by volume of the intermetallic compound crystal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a SEM image, based on STEM-EDS mapping, of a cross section of a metal particle used in this invention, obtained in Example;

(2) FIGS. 2A-a to 2A-d are transmission electron diffraction patterns of a monoclinic intermetallic compound crystal in the metal particle obtained in Example;

(3) FIGS. 2B-a to 2B-c are electron microphotographs (TEM images) of a cross section of the metal particle obtained in Example, in which the intermetallic compound crystal forms the endotaxial junction with the Sn alloy matrix;

(4) FIG. 3 is a schematic drawing explaining an exemplary equipment suitable for manufacturing the metal particle used in this invention;

(5) FIGS. 4A to 4D are SEM images, based on STEM-EDS mapping, of a cross section of a prior SnAgCu-based bonding material (powdery solder material with a particle size of 5 μm);

(6) FIG. 5A shows a TEM image and so forth of an interface between a Cu electrode and a bonding structure, obtained in Example;

(7) FIG. 5B shows TEM images and so forth of an interface between a Cu electrode and a bonding structure, obtained in Example; and

(8) FIG. 6 is a schematic cross sectional view illustrating a structure of the bonding structure of this invention.

DESCRIPTION OF THE EMBODIMENTS

(9) This invention will be further detailed below.

(10) First of all, the terms used in this specification are defined as follows, even if not specifically noted.

(11) (1) The term “metal” covers not only simple metal element, but occasionally covers also alloy or intermetallic compound containing a plurality of metal elements.

(12) (2) A certain simple metal element, when referred to herein, means not only an absolutely pure substance made of such metal element, but also substances containing slight amounts of other ingredient. In other words, the meaning of course does not exclude the cases where trace impurities that are almost not influential to such metal are contained. For example, when referred to as “Sn alloy matrix”, the matrix encompasses those having Cu, Ni, Ge, Sb, Ga, Si, Ti or Al contained so as to replace a part of Sn atoms in the crystal.

(13) (3) The term “endotaxial junction structure” means a structure in which a substance that forms metal or alloy has other substance (intermetallic compound) precipitated therein to form a crystal grain, while creating a lattice-matched junction between these substances (for example, between alloys, between metals, and between intermetallic compounds).

(14) (4) The term “epitaxial junction” means a junction formed as a result crystal growth on an underlying metal or alloy body (electrode, for example), while creating an interface where a crystal plane of the underlying body and the crystal plane of the Sn alloy matrix and/or the intermetallic compound crystal are bonded in a lattice-matched manner.

(15) The metal particle used in this invention uniquely has a crystal structure in which the intermetallic compound crystal forms the endotaxial junction with the Sn alloy matrix.

(16) The metal particle used in this invention is manufacturable typically from a starting material combining 8% by mass of Cu and 92% by mass of Sn (referred to as 8Cu.92Sn, hereinafter). The metal particle used in this invention is obtainable by properly controlling environmental conditions so that the precipitated intermetallic compound will have monoclinic, hexagonal or other crystal structure, and will solidify to form the endotaxial junction together with the Sn alloy matrix, for example by melting 8Cu.92Sn, then by feeding the molten metal on the dish-like disk spinning at a high speed in a nitrogen gas atmosphere, so as to scatter the molten metal by the centrifugal force to produce fine droplets, followed by cooling to solidify the droplets under reduced pressure.

(17) An exemplary manufacturing apparatus suitable for manufacturing the metal particle is explained referring to FIG. 3. A granulation chamber 1 has a cylindrical top part and a conical bottom part, and has a lid 2 on the top. A nozzle 3 is perpendicularly inserted at the center of the lid 2, and a dish-type rotating disk 4 is arranged directly below the nozzle 3. Reference sign 5 denotes a mechanism that moves up and down the dish-type rotating disk 4. At the lower end of the conical bottom part of the granulation chamber 1, there is connected a delivery pipe 6 through which produced fine particles are output. The top end of the nozzle 3 is connected to an electric furnace (high frequency induction furnace) 7 that melts a metal to be granulated. An atmospheric gas controlled to contain predetermined ingredients in a mixed gas tank 8 is fed through a pipe 9 and a pipe 10 respectively into the granulation chamber 1 and to an upper part of the electric furnace 7. Pressure in the granulation chamber 1 is controlled by a valve 11 and an exhaust apparatus 12, meanwhile pressure in the electric furnace 7 is controlled by a valve 13 and an exhaust apparatus 14. Molten metal fed through the nozzle 3 on the dish-type rotating disk 4 is scattered by centrifugal force of the dish-type rotating disk 4 to produce fine droplets, and then cooled under reduced pressure to produce solid particles. The thus produced solid particles are fed through the delivery pipe 6 to an automatic filter 15 and classified. Reference sign 16 denotes a particle collection apparatus.

(18) A process of solidifying the molten metal under cooling is important for forming the crystal structure of the metal particle used in this invention.

(19) Typical conditions are as follows:

(20) dish-type rotating disk 4: with a dish-type disk having an inner diameter of 60 mm, and a depth of 3 mm, rotated at 80,000 to 100,000 rpm; and

(21) granulation chamber 1: evacuated using a vacuum chamber with an evacuation performance up to 9×10.sup.−2 Pa or around, feeding nitrogen gas at 15 to 50° C. while being concurrently evacuated, to keep the pressure inside the granulation chamber 1 to 1×10.sup.−1 Pa or below.

(22) The metal particle manufactured under such conditions is 20 μm or smaller in diameter for example, which typically ranges from 2 μm to 15 μm.

(23) The thus manufactured metal particle may be processed into sheet or paste, which may be brought into contact with an object to be bonded, allowed to melt only incompletely and then to solidify, to achieve successful bonding.

(24) A sheet composed of the metal particle 1 used in this invention is obtainable typically by subjecting the metal particle to pressure welding under rollers as described below. That is, the metal particle used in this invention is fed between a pair of pressure contact rollers that rotate in opposite directions, and the powder is pressurized by the pressure contact rollers while being heated therethrough up to 100° C. to 150° C. The sheet made from the metal particle used in this invention is thus obtained.

(25) The metal particle used in this invention may alternatively be allowed to disperse in an organic vehicle to obtain an electroconductive paste.

(26) Note that the sheet or the electroconductive paste may be mixed with other particle such as SnAgCu-based alloy particle and/or Cu particle without adversely affecting the effects of this invention, so as to obtain a mixture of the metal particle. Such other particle may be coated with a metal such as silicon.

(27) FIG. 6 is a schematic cross sectional view explaining a structure of the bonding structure of this invention.

(28) As seen in FIG. 6, a bonding structure 300 mutually bonds metal/alloy bodies 101, 501 (Cu electrodes, in FIG. 6) respectively formed on substrates 100, 500 that are arranged opposingly. The bonding structure 300 contains the intermetallic compound crystal and the Sn alloy matrix, the intermetallic compound crystal forms the endotaxial junction with the Sn alloy matrix, and the Sn alloy matrix is bonded with the metal bodies or alloy bodies 101, 501. The intermetallic compound is typically composed of Cu.sub.6Sn.sub.5 (and also Cu.sub.3Sn).

(29) The substrates 100, 500, provided with semiconductor elements, are typically those composing electrical/electronic devices such as power device, meanwhile the metal/alloy bodies 101, 501 are bonding materials typically in the form of electrodes, bumps, terminals, or lead conductors integrally provided on the substrates 100, 500. In the electrical/electronic devices such as power device, the metal/alloy bodies 101, 501 are usually composed of Cu or Cu alloy. This, however, does not preclude any components that correspond to the substrates 100, 500 from being composed of such metal/alloy bodies.

(30) The bonding structure of this invention may be formed using the aforementioned metal particle used in this invention. The present inventors has confirmed that the bonding structure of this invention, obtained by using the metal particle after heating, has a crystal structure similar to the crystal structure of the metal particle.

(31) The metal particle used in this invention has the crystal structure in which the intermetallic compound crystal forms the endotaxial junction with the Sn alloy matrix. Meanwhile, the bonding structure of this invention has a structure in which the Sn alloy matrix and/or the intermetallic compound crystal, and the metal/alloy bodies 101, 501 are kept to form the epitaxial junction.

EXAMPLE

(32) This invention will further be explained referring to Example and Comparative Example, without limiting this invention.

Example 1

(33) Using 8Cu.92Sn as a starting material and the manufacturing apparatus illustrated in FIG. 3, a metal particle with a diameter of approximately 3 to 13 μm was manufactured.

(34) Conditions employed were as follows:

(35) dish-type rotating disk 4: with a dish-type disk having an inner diameter of 60 mm, and a depth of 3 mm, rotated at 80,000 to 100,000 rpm; and

(36) granulation chamber 1: evacuated using a vacuum chamber with an evacuation performance up to 9×10.sup.−2 Pa or around, feeding nitrogen gas at 15 to 50° C. while being concurrently evacuated, to keep the pressure inside the granulation chamber 1 to 1×10.sup.−1 Pa or below.

(37) FIG. 1 is a SEM image, based on STEM-EDS mapping, of a cross section of the metal particle used in this invention, obtained in Example. It is observed from FIG. 1 that the metal particle used in this invention contains the intermetallic compound crystal and the Sn alloy matrix.

(38) FIGS. 2A-a to 2A-d are transmission electron diffraction patterns obtained from different sites in the metal particle, which includes metal particle (FIG. 2A-a), Sn alloy matrix (FIG. 2A-b), intermetallic compound crystal (FIG. 2A-d), and interface between Sn alloy matrix and intermetallic compound crystal (FIG. 2A-c). From FIG. 2A-d, the intermetallic compound crystal was confirmed to have a monoclinic crystal structure.

(39) FIGS. 2B-a to 2B-c are electron microphotographs (TEM images) of cross section of the metal particle, in which the monoclinic intermetallic compound crystal forms the endotaxial junction with the Sn alloy matrix, in the metal particle (FIG. 2B-a) obtained in Example. In FIG. 2B-b, it was observed that the monoclinic intermetallic compound crystal that contains Sn and Cu forms the endotaxial junction with the Sn alloy matrix forms. Now the endotaxial junction means a state in which the Sn alloy matrix and the intermetallic compound precipitated therein during production of the metal particle, are bonded in a lattice-matched manner. FIG. 2B-c shows a transmission electron diffraction pattern of an interface between the Sn alloy matrix and the intermetallic compound crystal.

(40) The transmission electron diffraction patterns shown in FIGS. 2A-a to 2A-d and the electron microphotographs (TEM images) in FIGS. 2B-a to 2B-c were observed at normal temperature (room temperature).

(41) Next, the thus obtained metal particle was cold welded into sheet, and the obtained sheet was subjected to a high temperature storage (HTS) test conducted at 350° C. It was observed that the shear strength increased from approximately 60 MPa up to approximately 80 MPa over a 100-hour period after the start of test, and remained constant at around 60 MPa in the time zone beyond 100 hours.

(42) It was also found from a temperature cycle test (TCT) (−40 to 200° C.), that the shear strength remained constant at around 50 MPa, approximately beyond the 200-th cycle and over the whole cycles thereafter (1000 cycles).

(43) As a Comparative Example, FIGS. 4A to 4D are SEM images, based on STEM-EDS mapping, of cross sections of a conventional SnAgCu-based bonding material (powdery solder material with a particle size of 5 μm). It was confirmed from FIGS. 4A to 4D that the conventional SnAgCu-based bonding material is free of intermetallic compound, instead having a single metal element dispersed therein. It is therefore a matter of course that there is no observable endotaxial junction between the intermetallic compound crystal and the Sn alloy matrix, unlike this invention. It was also confirmed that Sn—Cu alloy that forms the metal matrix does not have the intermetallic compound crystal structure as a stable phase in high-temperature operating region. Such conventional SnAgCu-based bonding material is almost hopeless to achieve heat resistance and strength, comparable to those of the metal particle used in this invention.

(44) Then homogeneously mixed were 70 parts by mass of the thus obtained metal particle and 30 parts by mass of Si-coated Cu powder, and the mixture was subjected to dry powder rolling to manufacture a presheet (50 μm thick).

(45) The sheet was placed between Cu electrodes that form the metal body, and then subjected to melt bonding. The bonding structure was formed by using the metal particle used in this invention, which was allowed to melt initially at the melting point of Sn (231.9° C.). Remelting temperature of the bonding structure after solidified is governed by the melting points of Cu.sub.xSn.sub.y (Cu.sub.3Sn: approx. 676° C., Cu.sub.6Sn.sub.5: approx. 435° C.), which are higher than the melting point of Sn. The bonding structure that excels in heat resistance, reliability and quality may therefore be formed. Such characteristics of the bonding structure were found to be effective for electrical interconnect and electroconductive bonding material used in power control semiconductor element that causes large heat emission.

(46) FIGS. 5A and 5B are TEM images of the interface between the Cu electrode and the bonding structure obtained above. It was confirmed from FIGS. 5A and 5B that the Sn alloy matrix forms the epitaxial junction with the Cu electrode. From TEM images on the lower left and on the right in FIG. 5B, the Sn alloy matrix (bright area) in the bonding structure was confirmed to form the epitaxial junction with the Cu electrode (dark area). The image on the upper left in FIG. 5B is a transmission electron diffraction pattern of the Sn alloy matrix.

(47) The electrode in this invention may be composed of simple metal, alloy body or intermetallic compound of at least one metal selected from the group consisting of Sn, Cu, Al, Ni, Si, Ag, Au, Pt, B, Ti, Bi, In, Sb, Ga, Zn, Cr and Co. Each of these substances can form the epitaxial junction, with the Sn alloy matrix.

(48) This invention has been detailed referring to the attached drawings. This invention is, however, not limited by the description above. It is obvious that those skilled in the art will arrive at various modifications on the basis of the basic technical spirit and teaching of this invention.