JPS63236338A - Bonding wire for semiconductor integrated circuit element wiring and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain the Cu bonding wire having flexibility, high strength and a high elongation percentage by a method wherein a specific purity Cu is formed by coating on the surface of Cu wire material of specific purity. CONSTITUTION:The Cu wire having the purity of 99.99-99.999 wt. %, desirably an oxygen-free copper wire, is prepared as a core material, and the Cu of 99.999 wt. % or more in purity is formed on the surface of said core material desirably using an electrodeposition method. Pertaining to the electrodeposition of Cu, using an oxygen-free Cu wire of 99.994 wt. % for core material, for example, a refined Cu layer of purity 99.999 wt. % or above is deposited on the surface of the core material by performing electrolysis using a copper-sulfate solution which is grown in high purity. Besides, the amount of deposition of Cu is selected in such a manner that the percentage of covering of the coating layer 3 after wire drawing becomes 30-70 vol. %. Then, a wire-drawing work is conducted on the obtained material to have the desired diameter of 20-50 mumphi, for example. As a result, the desired bonding wire can be obtained.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a bonding wire used for wiring between each electrode of a semiconductor integrated circuit element such as an IC, LSI, or VLSI and each lead of a lead frame, and a method for manufacturing the same. Regarding.

Conventional technology When mounting semiconductor integrated circuit devices (IC, LSI, VLSI devices, etc.; hereinafter referred to as IC devices), the IC devices are held mechanically by an external device. A lead frame is usually used to facilitate electrical connection with a conductor or external wiring, or to improve heat dissipation.The IC element is fixed to a mounting base in the center of the lead frame, and the IC element is A large number of electrodes (terminals) formed on a semiconductor pellet are electrically connected to corresponding leads (usually called inner leads) of a lead frame by wire bonding.

Conventionally, this wire bonding has been given the A rating due to the wire's excellent corrosion resistance, high elongation rate, and high reliability.
U-ray is used.

However, since the material cost of Au wire is extremely high, attempts have been made to develop metal bonding wires that have performance equivalent to or better than that of Au wire.
, AI, Cu wire, etc. have been proposed and put into practical use. Among them, Cu is considered to be promising in the future because it is superior in terms of economy and performance.

By the way, Cu for bonding wire! jA is required to have the following performance.

1) To connect the Cu wire to each electrode on the IC element,
Usually, a ball bonding method is used, in which one end of a Cu wire is melted to form a ball, and this ball is crimped to an electrode on an IC element. It is preferable that the hardness of the molten and solidified ball is as soft as possible to avoid damage.

2) When each electrode on the IC element and each corresponding lead on the lead frame are connected with a Cu wire, the loop height must be high, and for this purpose, the strength and elongation of the C and U wires are high. It is preferable.

For the requirements of 1) above, the purity is 99.99 wt%.
By using the high-purity Cu wire of less than 99.999 wt%, the hardness during melting and solidification is made as small as possible to obtain a soft ball.

In addition, in order to meet the above requirement 2), various processing conditions and heat treatment conditions are adjusted during wire drawing so that the Cu wire rod after wire drawing can obtain as high strength and elongation as possible.

However, if the purity is 99.99 wt% or more, 99.9
Cu wire with less than 99 wt% generally forms a soft ball after melting and solidifying, but in the wire state it is similar to ordinary pure copper wire (
Purity 99.9~! ? 9.95 wt%), the strength and elongation tend to be lower than that of wire wire (9.95 wt%), so in order to compensate for these shortcomings, we made subtle adjustments to the processing conditions during wire drawing and heat embedding conditions to obtain the maximum strength and elongation. I'm trying to be able to do that. However, it is technically very difficult to adjust these conditions to optimal values, and slight variations in these conditions can easily change the internal structure of the Cu wire, which can cause the strength and elongation of the Cu wire to change. There is a drawback that it is difficult to stably obtain a Cu wire with uniform properties because of the change in properties.

As described above, the above requirements 1) and 2) are in a contradictory relationship with each other, and it is extremely difficult to manufacture a wire rod that satisfies both requirements at the same time using a single material. Therefore, the current situation is that we are seeking a harmonious point between the two properties, sacrificing some of the properties of either 1) or 2) above.

<Problems to be Solved by the Invention> An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and provide a bonding wire made of Cu wire that has flexibility, high strength, and high elongation, and a method for manufacturing the same. There is a particular thing.

Means for Solving the Problems In order to obtain a bonding wire that has flexibility, high strength, and high elongation, the present inventors have developed a bonding wire that is made of a single material, and the properties of that material. We realized that even if we optimized the process and processing conditions, there were limits, and as a result of intensive research, we constructed the bonding wire from two types of materials with different properties, and created a bonding wire that combines the characteristics of both materials. The inventors have discovered that the above object can be achieved by the following methods, and have arrived at the present invention.

That is, in the present invention, the purity is 99.99 wt% or more.
Consisting of a Cu core material of less than 999 wt% and a Cu coating layer covering the core material with a purity of 99.999 wt% or more, and the coverage of the coating layer is 30 to 70 vol% of the whole.
The present invention provides a bonding wire for semiconductor integrated circuit element wiring characterized by the following characteristics.

Further, the present invention has a purity of 99.99 wt% or more.
The purity is 99.9 on the wire surface of less than 999wt% Cu.
The present invention provides a method for manufacturing a bonding wire for semiconductor integrated circuit element wiring, which is characterized by forming a coating with 99 wt% or more of Cu and drawing this material to a desired diameter.

The formation of the Cu coating is preferably performed by an electrodeposition method.

Hereinafter, the structure of the bonding wire for semiconductor integrated circuit element wiring and the method of manufacturing the same according to the present invention will be explained in detail.

FIG. 1 is an enlarged sectional view of a bonding wire 1 for wiring semiconductor integrated circuit elements according to the present invention. As shown in the figure, the bonding wire 1 of the present invention has a core material 2 made of a Cu wire, and the periphery of the core material 2 is covered with a coating layer 3 of higher purity Cu.

Heartwood 2 has a purity of 99.99 wt% or more, 99.999
It is composed of less than wt% of Cu, and is responsible for the high strength and high elongation rate of the bonding wire 1.

The reason why the purity of Cu constituting the core material 2 is limited to the above is as follows.
If the purity of Cu is less than 99.99 wt%, the hardness of the ball after melting and solidification will be too hard, and there is a risk of damaging the electrodes and Si chips on the IC element during ball bonding. ? This is because if the Cu content is t% or more, sufficient strength and elongation cannot be ensured.

In addition, what is necessary is just to use the oxygen-free copper wire of the said purity for the core material 2. This oxygen-free copper wire has the advantage of being inexpensive and easily available.

The coating layer 3 is made of Cu with a purity of 99.999 wt% or more, and is responsible for the softness of the bonding wire 1.

The reason why the purity of Cu constituting the coating layer 3 is limited to the above is that if the purity of Cu is less than 99.999 wt%, the core material 2 and the coating layer 3 will melt and integrate during pole bonding.
This is because the hardness of the solidified ball cannot be sufficiently softened, and there is a risk of damaging the electrodes and Si chips on the IC element.

The coverage rate of such a coating layer 3 is the same as that of the bonding wire 1.
The volume occupied by the coating layer 3 is 30 to 7
It is set to 0 vol%. The reason is as follows.

If the coverage is less than 30 vol %, the volume percentage occupied by the core material 2 will be large, and if the core material and the coating layer have the purity within the above range, it will not be possible to soften the hardness of the ball after melting and solidification.

Moreover, when the coverage exceeds 70 vol%, the volume percentage occupied by the core material 2 becomes small, and sufficient strength and elongation cannot be ensured when the core material and the coating layer have the above purity range.

Note that bonding wires generally used have a diameter of about 20 to 50 wires.

In the bonding wire of the present invention, the diameter of the wire is not particularly limited, but is appropriately determined based on the area of the electrode on the I'C element to be bonded, etc., and a diameter of about 20 to 50 -φ is usually used.

Next, a preferred example of the bonding wire manufacturing method of the present invention will be described.

Purity as heartwood is 99.99 wt% or more 99.999
Prepare a Cu wire of less than wt%, preferably an oxygen-free copper wire,
The surface of this core material contains Cu with a purity of 99.999wt% or more.
The coating is preferably formed by an electrodeposition method.

The electrodeposition of Cu is performed, for example, as follows.

A 99.994 wt % oxygen-free Cu wire is used as the core material, and electrolysis is performed on the surface using a highly purified copper sulfate solution to electrodeposit a purified Cu layer with a purity of 99.999 wt % or more.

In addition to the above electrodeposition method, the coating layer 2 may be formed by electroless plating, vapor deposition, sputtering, ion blasting, or the like.

The amount of Cu to be deposited may be selected so that the coverage of the coating layer 3 after wire drawing is 30 to 70 vol% of the entire wire.

Next, the material obtained by the above method is drawn to a desired diameter, for example, about 20 to 5 degrees φ as described above. In this way, the bonding wire of the present invention is obtained.

The wire drawing method may be, for example, continuous wire drawing using a die, but is not limited thereto.

According to such a method of manufacturing a bonding wire, particularly a method of depositing Cu by an electrodeposition method, there is an advantage that the high-purity Cu coverage can be easily adjusted within a desired range.

<Example> Examples of the present invention will be described below.

(Example) Heart material purity 99.994wt%, diameter Q, 10
Using a mmφ oxygen-free Cu wire and using a highly purified copper sulfate solution on its surface, the purity was 99.9993 wt.
% of Cu at various volume ratios and then deposited with a diameter of 30-
The wire was drawn to φ, and then annealed at 300°C for 1 minute in an atmosphere of inert gas such as nitrogen or argon to obtain bonding wire No. 1 with the coverage ratio (coating layer/core material volume ratio) shown in Table 1.
I got ~7.

Note that bonding wire No. 4 was obtained by performing the wire drawing and annealing described above without forming a coating layer on the core material.

The performance (ball hardness, breaking load, elongation rate) of the bonding wires Nos. 1 to 7 thus obtained was measured, and a bonding test was conducted using each of the wires Nos. 1 to 7. The results are shown in Table 1.

Note that the bonding test was conducted for each wire No. 1 to No. 7, as shown in FIG.
Three devices each were connected with each other, and the quality of the loop shape of the bonding wire and the occurrence of cracks in the Si chip 5 of the IC element were examined. These evaluation methods are as follows.

<Evaluation of loop shape> As shown in Figure 2, the state of the bonding wire 1 indicated by the solid line is good (O mark), and the state shown by the dotted line is bad (X mark).
And so.

<Status of Si chip cracking> O: No cracking x: Cracking Table 1 Note Medium 1 Coverage 2 Volume percentage *2 Displays the average value of 3 test pieces + 3 Displays each result of 3 test pieces Table above As is clear from the results of No. 1, bonding wires Nos. 1 to 3 of the present invention have appropriately soft ball hardness (
The breaking load was large, that is, the strength was large, the elongation rate was also moderately large, and furthermore, the Si chip etc. were not damaged by bonding, and a good loop shape was obtained.

Effects of the invention> According to the bonding wire for semiconductor integrated circuit device wiring of the present invention, by combining a core material of Cu and a coating layer of Cu with higher purity, it has flexibility, high strength, and high elongation. It is possible to provide a bonding wire that has both high efficiency and high efficiency. As a result, the hardness of the balls melted and solidified during wire bonding is soft, and the hardness of the balls that are melted and solidified during wire bonding is soft, making it possible to bond the electrodes on IC elements and the S
The i-chip is not damaged and the loop shape is improved.

Further, according to the method of manufacturing a bonding wire for semiconductor integrated circuit element wiring of the present invention, particularly the method of depositing Cu by an electrodeposition method, it is easy to adjust the volume ratio of the high-purity Cu coating layer, and moreover, it is possible to maintain a constant amount of Cu. This will enable a stable supply of.

[Brief explanation of drawings]

FIG. 1 is an enlarged sectional view of a bonding wire for semiconductor integrated circuit element wiring according to the present invention. FIG. 2 is an explanatory diagram showing the loop shape of the wire when each electrode on the IC element and the corresponding inner lead are wire-bonded. Explanation of symbols 1... Bonding wire, 2... Core material, 3... Covering layer, 4... IC element, 5... Si chip, 6-... Electrode (l Pad), 7--Inner lead FIG, IFIG, 2

Claims (3)

[Claims] (1) Purity is 99.99wt% or more 99.999wt%
The purity of the core material covering the core material is less than 99.9.
1. A bonding wire for semiconductor integrated circuit device wiring, characterized in that the bonding wire comprises a Cu coating layer of 99 wt% or more, and the coating layer has a coverage rate of 30 to 70 vol% of the whole. (2) Purity is 99.99wt% or more 99.999wt%
1. A method for manufacturing a bonding wire for semiconductor integrated circuit device wiring, which comprises coating the surface of a wire with a purity of 99.999 wt% or more with Cu and drawing this material to a desired diameter. (3) The method for manufacturing a bonding wire for semiconductor integrated circuit element wiring according to claim 2, wherein the Cu coating is formed by an electrodeposition method.