JPS60193351A - Semiconductor device - Google Patents

Abstract

PURPOSE:To contrive to reduce cost of a semiconductor device, and to generate no deterioration of bonding strength by a method wherein the inside electrode of the device is made to have the three layer construction of Al - a diffusion preventing metal - Al, and a silver ball is thermocompression bonded to the part thereof. CONSTITUTION:The inside electrode of a semiconductor device is made to have the three layer construction of Al 2-a diffusion checking metal 6-Al 2, and a silver ball 1 is thermocompression bonded to the part thereof. Accordingly, a condition to make silver 6 and Si dioxide 3 to come in contact directly can be checked. As the metal 6, any metal to make no solid solution with silver at least at the temperature of 400 deg.C or less, and moreover having favorable adhesion with Al is favorable. By constructing the semiconductor device in such a way, the Al 2 of the uppermost layer diffuses in the silver ball 1, while diffusion of silver into the Al of the lowest stage and into the copper of the middle layer are hardly generated. Therefore, the value of bonding strength is not changed from the value directly after bonding, and bonding of high reliability can be realized.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a semiconductor device.

(Prior art) Conventionally, semiconductor elements (chips) such as transistors and ICs
The connection between the upper internal electrode (aluminum pad) and the external lead was performed using gold wire or aluminum wire. Normally, the former is connected by nail head bonding, and the latter by ultrasonic bonding, but because of its versatility and high speed, nail head bonding using gold wire has become the mainstream for connecting consumer semiconductor devices. There is. Nail head bonding involves forming a ball (pole up) at the tip of a gold wire using hydrogen flame (hydrogen torch) or electric discharge (electric torch), and then connecting internal electrodes on the semiconductor element and external leads using thermocompression bonding. It is something to do.

However, due to the recent rise in the price of gold, the proportion of gold wire in the manufacturing cost of semiconductor devices has increased, putting pressure on the cost. Efforts have been made to suppress this problem by making the gold wire thinner, but the thinning has already reached its limit, and the development of an alternative wire is required.

Silver, like gold, is a highly malleable metal and can be easily drawn to a wire diameter of about 30 microns.

Its electrical conductivity is the highest among metals, approximately 1.5 times that of gold. In addition, although the tensile strength of the wire has the same advantage that it can be used as a bonding wire, when bonding silver wire under the same conditions as gold wire, reliability tests showed that the bond between the silver pole and the aluminum pad was It was pointed out that failures in the On the other hand, the patent application 1983-0 based on the invention of the present inventors
According to No. 95165, silver wire can now be used to connect internal electrodes and external leads on a semiconductor element. That is, in a method in which a discharge is generated between a silver wire and a discharge electrode, a ball is formed at the tip of the silver wire, and then bonding is performed using the silver wire, the silver wire and the discharge electrode are connected to each other using the silver wire. The silver wire is placed in an air stream of a protective atmosphere gas, specifically, nitrogen or an inert gas having an oxygen concentration of 10011- or less, flowing in the direction connecting the silver wire and the discharge electrode, and from the discharge electrode to the silver wire. This is a bonding method characterized in that after generating an electric discharge and forming the tip of the silver wire into a ball shape, wire bonding is performed using the silver wire. Wire connections can be made at high speed.

However, in order to examine the reliability of the joint between the silver ball and the aluminum pad, an accelerated test was performed in which the joint was stored under high temperature after bonding, and a phenomenon in which the joint strength deteriorated was observed. In order to investigate the cause of this deterioration in bond strength, the present inventors investigated the diffusion reaction at the bond between the silver ball and the aluminum pad, and conducted a high-temperature accelerated test. It was found that as a result of direct contact between the silicon (8io, ) passivation film and silver, the bonding strength deteriorated.

(Object of the Invention) An object of the present invention is to provide a low-cost, highly reliable semiconductor device that does not cause the above-mentioned deterioration in bonding strength.

(Structure of the Invention) In the present invention, an internal electrode on a semiconductor element has a three-layer structure of aluminum, a metal for preventing expansion, and aluminum, and the internal electrode and external lead are connected by nail head bonding using a silver wire. This is a semiconductor device characterized by:

FIG. 1 is a schematic cross-sectional view of a joint between a silver ball and an aluminum pad when nail head bonding is performed using a silver wire on an IC having a conventional internal electrode structure (single layer of aluminum). Aluminum (AA') along the line designated AA' in FIG.

In order to examine the distribution of silver (Ag) and silicon (Si), line analysis was performed using an X-ray microanalyzer (XMA), and the results shown in Figure 2 were obtained. Here, the thickness of the aluminum pad is 1.2 μm, and the amount of diffusion immediately after bonding is very small, but the bonding strength in Table 1 was measured by attaching silver ball 1 to a strain gauge as shown in Figure 3. I used the method of pressing with rod 5 and reading the value when the silver ball came off. Note that the measured value is the average of 100 measured values.

Figure 4 shows that after bonding, the XMA
Line analysis was performed using the following method. In this case, the diffusion reaction between aluminum and silver progresses, and an alloy layer of aluminum and silver called a zeta (ζ) phase grows. However, as shown in Table 1, the bonding strength is almost the same as that immediately after bonding.

Figure 5 shows that after a high temperature storage test at 300°C for 320 minutes after bonding, the
Line analysis was performed using the following method. In this case, the aluminum is completely diffused into the chain and the silver and silicon dioxide are in direct contact.

The bonding strength at this time is smaller than that immediately after bonding as shown in Table 1.

FIG. 6 is a schematic diagram of a joint according to the present invention; in other words, in order to prevent silver and silicon dioxide from coming into direct contact, the internal electrode has a three-layer structure of aluminum 2, metal 6 to prevent diffusion, and aluminum 2; A silver ball is heat-pressed here. The diffusion-preventing metal 6 sandwiched between aluminum may be any metal that does not dissolve silver at a temperature below 400° C. and has good adhesion to aluminum.

The present invention will be specifically described below using Examples.

(Example 1) Titanium (Ti) is used as gold 4 for diffusion prevention.

The thickness of the internal electrode is 0.5 μm of aluminum.

The thickness of titanium was 0.4 μm. After bonding with silver wire, we conducted a high temperature storage test at 300°C for 320 minutes.
XMA analysis of the joint cross section and joint strength were measured. Figure 7 shows aluminum (#) along BII' in Figure 6;
These are the results of XMA ray analysis of silver (Ag) and titanium (T).Although the top layer aluminum has diffused into the silver balls, silver has diffused into the F-most aluminum and the middle layer steel. There is almost no diffusion.As shown in Table 2, the bonding strength changes from the value immediately after bonding to A'<, and a highly reliable bond can be achieved.

(Example 2) Nickel (Ni) 'i is used as the 9 maple for diffusion prevention. The thickness of the internal electrode is aluminum 0.5 μm.
, 0.3 μm of nickel. After bonding with silver wire, a thermal lightning insulation test was conducted at 300° C. for 320 minutes in the same manner as in Example 1.

The line analysis by XMA is as shown in Figure 8, and the actual If
As in Example A 1, the aluminum in the top layer has diffused into the silver pole, but there is almost no diffusion of silver into the aluminum in the bottom layer and the nickel in the middle one. As shown in Table 2, the bonding strength is the same as the value immediately after bonding (4 & highly reliable bonding can be achieved).

(Example 3) Copper (Cu) is used as a metal for preventing diffusion. Inside'4
The thickness of the pole is aluminum 0.5μmtmQ, 4
7112L. After pounding with silver wire 3
A storage test for 7 m at 00° C. for 320 minutes was conducted in the same manner as in Example 1. The line analysis by XMA is as shown in Fig. 9, and as in Example 1, the aluminum in the top layer diffuses into the silver pole and becomes C, but the aluminum in the bottom layer and the steel in the middle jφ are diffused. There is almost no diffusion. Diffusion progresses between the aluminum in the bottom layer and the copper in the middle layer, but 1. As shown in Table j7L2, the bonding strength is the same as immediately after bonding, and highly reliable bonding can be achieved.

It is possible to provide a semiconductor device shown in Table 2 and at a low price.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a conventional internal electrode and ball joint. FIG. 2 is an XMA line analysis diagram of AA' in FIG. 1, and FIG. 3 is a schematic diagram showing a method for measuring bonding strength. FIGS. 4 and 5 are XMA line analysis diagrams of the conventional song storage test. FIG. 6 is a schematic diagram of a cross section of a joint according to the present invention. Figures 7 to 9 show XMA line segments 1... silver ball, 2... aluminum, 3
... Passivation of silicon dioxide, 4... Silicon, 5... Rod for measuring bonding strength, 6... Metal for preventing diffusion. 71 Figure 2 Δ' 30 4□ 74 Figure 75 Figure to2 76 Figure B' 2?7 Figure 78 Figure AQ O90 AρA to Cu alloy procedural amendment (voluntary) 60.6. −． 5 Month, Day 1, Showa 1980, Incident Indication 1982 Patent Application No. 049832
'5 SH2, Title of the invention Semiconductor device 36 Person making the amendment Relationship in the case Applicant 5-33-1 Shiba, Minato-ku, Tokyo (423) NEC Corporation Representative Tadahiro Sekimoto 4, Agent 5 Amendment Column 6 for a brief explanation of the drawings in the subject specification Contents of the amendment (1) On page 10, line 15 of the specification, the phrase "XMAK of the test stone" is amended to read "according to the XMA of the test product." . (2) On page 10, line 17 of the specification, [X of high temperature storage test]
Based on MA] has been corrected to read ``Based on XMA for high temperature storage test items.'' /,′

Claims (2)

[Claims] (1) The internal electrode of the semiconductor element has a three-layer structure of aluminum-diffusion prevention metal-aluminum, and the internal electrode and external lead are connected by nail head bonding with a silver wire. Semiconductor equipment. (2) The semiconductor device according to claim 1, wherein the diffusion preventing metal is a metal selected from titanium, nickel, and copper.