JP2018103222A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a high heat resistance, junction strength, and mechanical strength to be maintained as well as a favorable electrical characteristics for a long period in a junction part of a semiconductor element with a connection member in an SiC semiconductor element noted as a power device which controls a large power because of a higher breakdown field strength and a wider band gap as compared with an Si semiconductor element.SOLUTION: The above-mentioned problem is solved by a semiconductor device having a semiconductor element and a connection member connected with the semiconductor element, in which a junction part which forms a junction of the semiconductor element with the connection member has a metal matrix containing an intermetallic compound consisting of Sn and Cu and a Sn alloy, the intermetallic compound is diffused into the metal matrix, and the metal matrix contains substantially no Cu balls.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a semiconductor device having a semiconductor element and a connection member connected to the semiconductor element.

In recent years, SiC semiconductor elements using SiC (silicon carbide) have been developed.
SiC semiconductor elements are attracting attention as power devices that control high power because they have higher breakdown field strength and wider band gaps than Si semiconductor elements. The SiC semiconductor element can operate even at a high temperature of 150 ° C. or higher, which exceeds the limit of the Si semiconductor element, and theoretically can operate even at 500 ° C. or higher (see Patent Document 1).
Such a power device is used in a harsh environment such that a high temperature operation state continues for a long time and a large temperature fluctuation occurs from a high temperature operation state to a low temperature stop state. Therefore, in a semiconductor device having a semiconductor element and a connecting member connected to the semiconductor element, high bonding strength is required for a long period of time and excellent heat resistance is required for a bonding portion that forms the bonding between the two.
However, conventionally known bonding materials are not necessarily capable of satisfying the above-described requirements.

For example, the semiconductor device disclosed in Patent Document 2 cannot satisfy the above-described requirements.
That is, in Patent Document 2, for the purpose of maintaining the connection strength at a high temperature, the electrode of the semiconductor device and the electrode of the mounting substrate are connected by a connection portion having Cu balls, and the Cu balls are connected to each other by an intermetallic compound Cu _6. An electronic device connected by Sn ₅ is disclosed.
However, in the technique disclosed in Patent Document 2, Cu grows in one direction at the connection portion to generate a long axis crystal, which becomes a whisker, which causes a crack phenomenon, impairs electrical characteristics, and durability. There were problems such as worsening.

JP 2011-80796 A JP 2002-261105 A

  Accordingly, an object of the present invention is to provide a semiconductor device having a semiconductor element and a connection member connected to the semiconductor element, in which a bonding portion that forms a bond between the semiconductor element and the connection member has high heat resistance over a long period of time. Another object of the present invention is to provide a semiconductor device capable of maintaining bonding strength and mechanical strength and maintaining good electrical characteristics.

  In order to solve the above-described problem, a semiconductor device according to the present invention includes a semiconductor element and a connection member connected to the semiconductor element, and forms a junction between the semiconductor element and the connection member. Has an intermetallic compound composed of Sn and Cu and a metal matrix containing an Sn alloy, the intermetallic compound is dispersed in the metal matrix, and the metal matrix is substantially free of Cu balls. It is characterized by.

  In addition, it is preferable that the metal matrix does not substantially contain Sn alone.

The junction in the semiconductor device according to the present invention is such that an intermetallic compound composed of Sn and Cu is dispersed in a metal matrix containing an Sn alloy and Cu balls are substantially absent in the metal matrix. As a result, Cu is not generated as a long axis crystal (whisker) in one direction due to high temperature exposure, and suppression of ion migration can be prevented, so that a crack phenomenon at the joint can be prevented. By being substantially absent, Sn does not grow due to high temperature exposure, and the cracking phenomenon based on the Sn crystal growth can be prevented.
Further, the joint portion has both high temperature heat resistance due to the intermetallic compound and flexibility due to the metal matrix.
From the above, even when used in harsh environments where high-temperature operation continues for a long time, high heat resistance, bonding strength and mechanical strength can be maintained for a long time, and good electrical characteristics can also be maintained A semiconductor device can be provided.

It is a schematic cross section for demonstrating the structure of the junction part in this invention. It is an electron micrograph of 8Cu · 92Sn metal particles. It is a figure for demonstrating an example of the manufacturing apparatus suitable for manufacture of a metal particle. It is an electron micrograph of the cross section of the junction part in this invention. It is an electron micrograph of the cross section of the junction part of the prior art formed using SAC solder.

Hereinafter, the present invention will be described in more detail.
FIG. 1 is a schematic cross-sectional view for explaining the structure of the joint in the present invention.
In FIG. 1, a joining portion 300 joins metal / alloy bodies 101 and 501 (Cu electrodes in FIG. 1) formed on substrates 100 and 500 arranged to face each other. The joint portion 300 includes Cu ₆ Sn ₅ (another Cu ₃ Sn) as an intermetallic compound, and includes an Sn alloy (for example, an alloy composed of 4 mass% Cu and 96 mass% Sn) as an intermetallic compound. Cu ₆ Sn ₅ is dispersed in the metal matrix, and the metal matrix is substantially free of Cu balls.

  Cu balls are included in conventional joints as disclosed in Patent Document 2 and serve as spacers between electrodes. When the balls are spherical, the average particle diameter is, for example, 10 μm to 100 μm. In addition to the spherical shape, the shape of the Cu ball includes a surface having irregularities, a rod shape, a dendritic shape, and the like. When the Cu ball has a shape other than a spherical shape, the average particle diameter is a projected area equivalent circle diameter (a diameter of a circle having an area equal to the area when the area of the projected image is maximized). Cu balls contribute to the electrical properties, heat resistance, and strength of the joint, but on the other hand, according to the study of the present inventors, they are formed as long axis crystals in one direction by high temperature exposure as described above. (Whisker) contributes to the cracking phenomenon at the joint.

  Here, “substantially free of Cu balls” as used in the present specification means that, for example, Cu balls are 3% by mass or less, preferably 1% by mass or less, more preferably 0.1% by mass or less in the joint portion 300. Particularly preferably, it can be said to contain at a ratio of 0% by mass. The ratio of Cu balls is obtained by taking an electron micrograph of the cross section of the joint 300, arbitrarily sampling 50 locations, analyzing the image, examining how much Cu balls are present in the joint 300, and converting the mass. Can be obtained.

  In the present invention, it is preferable that the metal matrix substantially does not contain Cu alone. As used herein, “substantially free of Cu simple substance” means, for example, 3% by mass or less, preferably 1% by mass or less, of Cu simple substance not showing the shape as a Cu ball and Cu ball in the joint 300, More preferably, it can be said to be contained at a ratio of 0.1% by mass or less, particularly preferably 0% by mass. That is, it is desirable that almost all of Cu alone is diffused in the metal matrix as an Sn—Cu alloy or an intermetallic compound. The proportion of simple Cu can be determined by qualitative analysis using an X-ray diffraction data apparatus.

  Since the joining part 300 does not substantially contain Cu balls and Cu alone as described above, Cu is not generated as a long axis crystal in one direction (whisker) by high temperature exposure, and the crack phenomenon at the joining part is caused. Can be prevented.

  In addition, it is preferable that the metal matrix does not substantially contain Sn alone. As used herein, “substantially free of Sn alone” means, for example, that Sn is not more than 3% by mass, preferably not more than 1% by mass, more preferably not more than 0.1% by mass, particularly preferably not more than 0.1% by mass. It can be said that it is contained at a rate of 0% by mass. That is, most of Sn alone diffuses and disappears in the metal matrix as an Sn—Cu alloy. The ratio of Sn alone can be obtained from a database by qualitative analysis using an X-ray diffraction data apparatus. Thus, since Sn alone does not substantially exist in the metal matrix, Sn does not grow due to high-temperature exposure, and a crack phenomenon based on the Sn crystal growth can be prevented.

  The substrates 100 and 500 are substrates that include semiconductor elements and constitute electronic / electrical equipment such as power devices. The metal / alloy bodies 101 and 501 are electrodes, bumps, terminals, lead conductors, or the like. 500 is a connection member provided integrally with 500. In electronic / electric equipment such as power devices, the metal / alloy bodies 101, 501 are generally configured as Cu or an alloy thereof. However, the portion corresponding to the substrates 100 and 500 is not excluded from the case where the portion is made of a metal / alloy body.

Next, the method for forming the joint in the present invention will be described.
The joint can be formed of metal particles that combine Cu and Sn. Examples of the metal particles include metal particles having a composition of 8 mass% Cu and 92 mass% Sn (hereinafter referred to as 8Cu · 92Sn).
An electron micrograph of the 8Cu.92Sn metal particles is shown in FIG. A part of the surface of the metal particles in FIG. 2 is thinly polished with a laser.
A part of the surface of the metal particles in FIG. 2 is polished to approximately 0.1 μm from the surface by a laser.
As can be understood from FIG. 2, the metal particles M of 8Cu · 92Sn are in the form of a mesh 121, a dot or film 122, etc., in an intermetallic compound CuxSny in a black metal matrix. The intermetallic compound CuxSny actually forms a three-dimensional structure. The size of the intermetallic compound CuxSny includes those of nm size (1 μm or less) in light of the scale display shown in FIG.
That is, the metal particle M has a large number of nano-sized intermetallic compounds that form a nanocomposite three-dimensional structure distributed in the metal matrix. Here, the nanocomposite three-dimensional structure refers to a three-dimensional structure made of a nanoscale size crystal of 1/10 or less of the metal particles M.
As can be understood from FIG. 2, the 8Cu · 92Sn metal particles M form a network structure of the intermetallic compound Cu ₆ Sn _{5 in} the vicinity of the surface thereof.

  Such metal particles are centrifuged in a centrifugal field forcibly formed by supplying molten metal having a composition of 8% by mass of Cu and 92% by mass of Sn on a dish-shaped disk that rotates at high speed, for example, in a nitrogen gas atmosphere. Molten metal dispersed as droplets by force or the like can be obtained by forcibly self-organizing in a rapid cooling and solidification process under controlled environmental conditions.

  An example of a production apparatus suitable for producing metal particles will be described with reference to FIG. The granulation chamber 1 has a cylindrical shape at the top and a cone shape at the bottom, and has a lid 2 at the top. A nozzle 3 is inserted vertically in the center of the lid 2, and a dish-shaped rotating disk 4 is provided immediately below the nozzle 3. Reference numeral 5 denotes a mechanism for supporting the dish-shaped rotating disk 4 so as to be movable up and down. The generated particle discharge pipe 6 is connected to the lower end of the cone portion of the granulating chamber 1. The upper part of the nozzle 3 is connected to an electric furnace (high frequency furnace) 7 for melting the metal to be granulated. The atmospheric gas adjusted to a predetermined component in the mixed gas tank 8 is supplied to the inside of the granulating chamber 1 and the upper part of the electric furnace 7 through the pipe 9 and the pipe 10, respectively. The pressure in the granulating chamber 1 is controlled by the valve 11 and the exhaust device 12, and the pressure in the electric furnace 7 is controlled by the valve 13 and the exhaust device 14, respectively. The metal supplied from the nozzle 3 onto the dish-shaped rotating disk 4 becomes fine droplets due to the centrifugal force generated by the dish-shaped rotating disk 4 and the action in the parallel air flow environment centrifugal field created by the blowing airflow along the rotation axis. It is scattered and cooled to solid particles. The generated solid particles are supplied from the discharge pipe 6 to the automatic filter 15 and separated. Reference numeral 16 denotes a fine particle collecting apparatus.

  When the high-speed rotating body is disk-shaped or conical, if there is no centrifugal field, the centrifugal force applied to the molten metal varies greatly depending on the position of the molten metal supplied to the rotating body. Hard to get a body. However, when an inert gas is blown up from the lower part of the rotating shaft and filled into the lower part of the desk, a uniform air flow is created by centrifugal force, and a centrifugal field is created within the range of 2 m from the center of rotation to supply it on a dish-shaped disk that rotates at high speed. It receives a uniform centrifugal force at the peripheral edge of the dish and is dispersed and scattered into small droplets with uniform grains. The scattered droplets are rapidly cooled in a centrifugal field gas, fall as solidified particles, and are collected.

  The molten metal is self-assembled during rapid cooling and solidification, and individual fine particles become metal particles having the nanocomposite structure.

  The higher the number of revolutions of the dish-shaped disk, the smaller the diameter of the obtained metal particles. When a dish-shaped disk having an inner diameter of 35 mm and a depth of 5 mm is used, in order to obtain particles having an average particle diameter of 100 μm or less, it is desirable that the rotation be 100,000 rotations or more per minute. As a result, the centrifugal force increases, intermetallic compounds lighter than Sn accumulate on the surface layer, and the nanocomposite structure is easily formed.

The temperature of the atmospheric gas supplied to the granulation chamber may be room temperature, but the oxygen concentration in the granulation chamber is on the order of 0 ppm or less, and the granulation chamber has an internal pressure of 10% or more with respect to atmospheric pressure. There is a need to. In the case of continuous operation for a long time, in order to maintain the rapid cooling effect of the molten metal droplets, it is desirable to control the air flow rate so that the granulation chamber temperature is 100 ° C. or less, preferably 40 ° C. or less. This rapid cooling step facilitates formation of the mesh basket structure.
The metal particles M have a diameter of 20 μm or less, for example.

  When the 8Cu · 92Sn metal particles M are processed into a sheet or paste and melted and solidified between the two members to be joined, the intermetallic compound of the three-dimensional structure of the metal particles M is separated and recombined. As a result, a new three-dimensional structure of the intermetallic compound is formed. The metal matrix does not substantially contain Cu balls, and preferably does not substantially contain Cu alone or Sn alone.

  In order to obtain a preform sheet made of the metal particles M, the powder containing the metal particles M can be obtained by, for example, processing by metal-to-metal bonding using a cold welding method. Various metal-to-metal joints using the cold welding method are known. In the present invention, those known techniques can be applied. For example, the powder containing the metal particles M according to the present invention is supplied between a pair of pressure rollers that rotate in opposite directions, and pressure is applied to the powder from the pressure rollers to the metal particles M constituting the powder. Causes metal-to-metal bonding. In actual processing, it is desirable to apply heat of about 100 ° C. to the powder from the pressure roller. As a result, a preform sheet made of the metal particles M is obtained.

  When a preform sheet is obtained by performing an intermetallic joining process using a cold pressure welding method on the powder containing the metal particles M, inside the preform sheet, the metal particles M and other particles of the present invention are: Although the outer shape changes, the internal structure of the particles is almost intact. That is, the preform sheet has a nanocomposite structure including an nm-sized intermetallic compound composed of a plurality of metal components. Therefore, the molded body preserves the operational effects of the metal particles according to the present invention as they are.

Next, the preform sheet is interposed between the two members to be joined and baked (baking treatment) to form a joined portion. The baking process temperature is, for example, 250 ° C., and the baking process time is appropriately adjusted.
Alternatively, in order to efficiently form the joint using the metal particles M, for example, a conductive paste in which the metal particles M are mixed in an organic vehicle is formed.
Then, the conductive paste is applied to one surface of the two members to be joined, and baked (baking treatment) to form a joined portion. The baking process temperature is, for example, 250 ° C., and the baking process time is appropriately adjusted.

  In addition, the ratio of 3 volume% or more and 85 volume% or less is preferable with respect to the whole metal particle M, and the ratio of 10 volume% or more and 75 volume% or less is more preferable with respect to the metal particle M whole. According to such metal particles M, it is possible to obtain a highly reliable and high quality bonded portion further excellent in heat resistance.

  By the way, in the high temperature holding test (HTS) at 350 ° C. of the 40 μm-thick fired sheet, which was interposed between the two members to be joined with the preform sheet prepared as described above and fired at 250 ° C., at the start of the test From about 60 hours to about 100 hours, the shear strength increased from about 60 MPa to about 80 MPa, and in the time region exceeding 100 hours, the test result was obtained that was stabilized at about 70 MPa.

  In the thermal cycle test (TCT) of the fired sheet (−55 to 200 ° C.), the shear strength is stabilized at about 50 MPa over the entire cycle (1000 cycles) after exceeding about 200 cycles. The test results were obtained.

FIG. 4 shows a state (FIG. 4 (a)) after the bonded portion prepared under the above conditions is stored at room temperature for 1 day and a state after the bonded portion is stored at 220 ° C. for 150 hours (FIG. 4 (b)). ) Is an electron micrograph of the cross section. From FIG. 4A, it was confirmed that the metal matrix substantially does not contain Cu balls. Specifically, the Cu ball in the joint was 0% by mass. Moreover, when Cu simple substance and Sn single substance in a junction part were each measured by the method shown above, both were 0 mass%.
Further, from FIG. 4 (b), Cu is not formed as a long axis crystal in one direction (whisker) even after the joint is exposed at high temperature, and Sn crystal growth is not confirmed, It was suggested that the crack phenomenon at the joint can be prevented.

  On the other hand, FIG. 5 shows a state (FIG. 5 (a)) of a conventional joint formed using SAC (96.5Sn3Ag0.5Cu) solder after storage for 1 day at room temperature, and the joint at 220 ° C. It is an electron micrograph of the section of the state after storing for 150 hours (Drawing 5 (b)). The presence of Cu balls in the metal matrix can be confirmed from FIG. In addition, after the joint was stored at 220 ° C. for 150 hours (FIG. 5B), whisker and Sn crystal growth was confirmed, indicating that a crack phenomenon occurred in the joint.

  The present invention has been described in detail with reference to the accompanying drawings. However, the present invention is not limited to these, and various modifications can be made by those skilled in the art based on the basic technical idea and teachings. It is self-evident that you can think of it.

M metal particle 1 granulating chamber 2 lid 3 nozzle 4 rotating disk 5 rotating disk support mechanism 6 particle discharge pipe 7 electric furnace 8 mixed gas tank 9 pipe 10 pipe 11 valve 12 exhaust device 13 valve 14 exhaust device 15 automatic filter 16 particulate collection device 100,500 Substrate 101,501 Metal / alloy body 121,122 Intermetallic compound 300 Joint

Claims (2)

A semiconductor device having a semiconductor element and a connection member connected to the semiconductor element,
A joint portion that forms a joint between the semiconductor element and the connection member is:
An intermetallic compound composed of Sn and Cu and a metal matrix containing an Sn alloy;
The intermetallic compound is dispersed in the metal matrix;
The metal matrix is substantially free of Cu balls;
Semiconductor device. The metal matrix does not substantially contain Sn alone,
The semiconductor device according to claim 1.