JPH0587017B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a copper wire for bonding a semiconductor element, which is used to connect a semiconductor chip electrode and an external lead portion. (Prior art and its problems) Conventionally, semiconductor elements and lead frames have been wire bonded by thermocompression bonding or ultrasonic thermocompression bonding using Au wire wound around an aluminum spool. Recently, the use of economically advantageous copper wire has been considered as a substitute for gold wire. However, copper wire has the drawback of being easily oxidized and becoming hard when formed into a ball, making it very difficult to store it. Furthermore, there was a drawback that the wires wound around the spool would get tangled with each other and break during use. (Technical Problem to be Solved by the Invention) A technical problem to be solved by the present invention in order to solve the above problems is to prevent oxidation of copper wires for bonding and tangle of wires. (Technical Means for Achieving the Technical Problem) In order to achieve the above technical problem, the inventors of the present application focused on coating the surface of the copper wire with a nonionic surfactant. In addition to nonionic surfactants, there are cationic and anionic surfactants.Cationic and anionic surfactants have a high content of alkali metals and halogen elements, and also have high ion content. It is unsuitable for use because it corrodes copper due to dissociation. Also, in general nonionic surfactants,
Normally, it contains about 10 to 100 ppm of alkali metals and halogen elements as impurities, and when copper wire is coated with a nonionic surfactant containing relatively large amounts of alkali metals and halogen elements, is corroded and does not perform as expected. Based on the above results, the present inventor conducted further intensive research and found that using a nonionic surfactant with an alkali metal and halogen element content of 1 ppm or less effectively suppresses the oxidation of the copper surface. While preventing corrosion, the film thickness is
It was discovered that if the temperature is less than 20 A°, the oxidation prevention effect is not effective, and if it exceeds 500 A°, the ball shape becomes extremely poor, resulting in defective bonding, and this led to the completion of the present invention. That is, the bonding copper wire of the present invention has a content of alkali metals and halogen elements on the copper surface.
It is characterized by being coated with 1 ppm or less of a nonionic surfactant by dipping or wiping to form a surface active film with an average thickness of 20 to 500 A°. (Effects of the Invention) Since the present invention is configured as described above, it is possible to effectively prevent oxidation and corrosion of the copper surface while preventing entanglement of copper wires, and furthermore, the shape of the copper wires can be extremely reduced during bonding. A good ball can be formed and a predetermined bonding strength can be obtained. Therefore, we will address the disadvantages of using cationic and anionic surfactants, which are unsuitable for use due to their high content of alkali metals and halogen elements, as well as conventionally well-known nonionic surfactants. We were able to provide a copper wire for bonding semiconductor devices that has sufficient characteristics as a substitute for gold wire and can be produced at a much lower cost than gold wire. (Example) Examples will be described below. Samples No. 1 to 5 in Table (1) contain polyhydric alcohol esters, which are nonionic surfactants.
The contents of alkali metals and halogen elements are as shown in the table, and each sample has a purity of 99.99wt.
% of the surface of a copper plate made of high purity copper was measured in accordance with JIS-K2513. The results are also listed in the same table.

[Table] The alkali metals listed in the table are the sum of Na and K,
The halogen element refers to Cl. From this result, only when the total content of alkali metals and halogen elements is 1 ppm or less,
It has now been found that corrosion prevention effects on copper surfaces can be obtained. Samples No. 1 to 12 in Table (2) are made of 99.99wt% high-purity copper that has been repeatedly subjected to wire drawing and intermediate treatment to obtain diameters of
A product of the present invention, sample No., which is finished with a Cu wire of 30μ and coated with a polyhydric alcohol ester containing 1 ppm or less of alkali metals and halogen elements, and the average thickness of the film is within the range defined by the present invention. Sample No. 13 to 15 are comparative products in which the average film thickness is outside the range of the present invention, and Sample No. 16 is a comparative product in which the Cu wire finished in the same manner as above was not coated. Using each of these samples, bonding characteristics were measured when semiconductor chip electrodes and external lead portions were connected. The results are shown in the same table.

【table】

【table】

[Table] From the results in Table (2), it is found that the surface is coated with a nonionic surfactant containing 1 ppm or less of alkali metals and halogen elements, and the surface active agent has an average film thickness of 20 to 500 A°. It was confirmed that the products of the present invention (sample Nos. 1 to 12) on which a film was formed had the above-mentioned effects.

Claims (1)

[Claims] 1. A semiconductor device characterized by coating the surface of copper with a nonionic surfactant containing 1 ppm or less of alkali metals and halogen elements to form a surfactant film with an average thickness of 20 to 500 A°. Copper wire for bonding.