JPS59132145A - Forming method of electrode of semiconductor device - Google Patents

Abstract

PURPOSE:To reduce the unit price of a material, to increase bonding strength, and to enhance reliability, by using silver as a bump material. CONSTITUTION:A silicon oxide film 13 is formed on a silicon wafer 11 as an insulating film. A contact hole is provided in the film 13. A titanium and tungsten alloy metal layer 14 as a barrier metal and then a metal layer 15 are sequentially deposited. Thereafter, a photoresist 16, which is patterned only on an area where an electrode is not required, is deposited on the metal layer 15. With the photoresist 16 as mask, silver is plated. A silver bump 17 of a required amount is deposited and formed. Then, the resist 16 is removed. With the silver bump 17 as a mask, unnecessary metal layer 15 and alloy layer 14 are sequentially etched away.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for forming electrodes of a semiconductor device.

[Prior art]

BACKGROUND OF THE INVENTION In semiconductor devices, especially those assembled by glass-sealing bonding, such as small signal diodes, the electrodes on the functional areas of the chip must form bumps. That is, on the front side of the chip, a hemispherically raised metal layer formed to a thickness of several microns to several tens of microns needs to be electrically and mechanically connected to the functional area.

In order to satisfy these requirements, the electrode structure of the conventional device is based on a silicon wafer (1) on which a base region (2) as a functional region is diffused, as shown in FIG.
A silicon oxide film (3) is formed on top as an insulating film,
In addition, the contact hole is left open, and after forming an electrode with aluminum, silver is generally plated on the contact hole.Also, in highly reliable semiconductor devices, barrier After a titanium/tungsten layer (4) as a metal and then a gold layer (5) are sequentially formed by vapor deposition or sputtering, gold bumps (6) are formed by selective plating or the like.

However, with such conventional electrode forming means, in the case of the former aluminum-silver system, there was a problem that the adhesive strength of the aluminum-silver amount was not stable. This is because silver plating is applied on aluminum, which is easily oxidized, so the surface condition is unstable and the adhesive strength between aluminum and silver is weak.Since it is easy to use, the unit cost of the chip itself is high. Met.

[Summary of the invention]

In view of these shortcomings of the conventional methods, the present invention seeks to provide a method for forming electrodes using silver bumps to obtain chips with high mechanical strength and low cost.

[Embodiments of the invention]

Hereinafter, one embodiment of the electrode forming method according to the present invention will be described in detail with reference to FIGS. 2 to 6.

In this embodiment method, first, a silicon oxide film 03 as an insulating film is formed on a silicon wafer ←0 on which a base region α as a functional region has been diffused, and this oxide film α
After opening a contact hole in j, a barrier metal layer such as a titanium-tungsten alloy layer a4) and a gold layer a4 are sequentially deposited by vapor deposition or sputtering. The gold layer (the thickness of one layer may be extremely thin, at most several hundred to several thousand layers (Fig. 2)). Next, the gold layer (151) is formed using photolithography. A butter-nickeled photoresist Q6) is deposited only on areas that do not require electrodes (Fig. 3), and silver plating is applied using this photoresist αQ as a mask to cover the required amount of silver bumps αD. After that, the photoresist αe is removed (Fig. 5), and the unnecessary gold layer (151) and titanium-tungsten alloy layer α4 are sequentially etched away using the silver bump layer as a mask. In this way, the desired electrode structure is obtained (Fig. 6).

However, in forming the lever electrode, the titanium-tungsten alloy layer (14) directly bonded to the functional area, ie, the space area a, prevents interdiffusion between the upper layer metal and silicon.
It exists for the purpose of improving adhesion strength, and may have a thickness of several hundred to several thousand layers. In addition, the gold layer A is used to prevent oxidation in the storage atmosphere after the metallization process and to prevent weakening of the adhesion strength of silver. The thickness of the bump body should be the minimum thickness that can withstand the requirements, and silver for the bump body was selected based on experimental results that showed it to be reliable as a replacement for gold.

Note that although the above embodiment has been described for the case where it is applied to a small signal diode, the semiconductor device 2 using other bumps may also be used.
For example, it is of course applicable to transistors and ICs that use 7-eighth bonding, and titanium-tungsten alloy is used as an example as a barrier metal.
Other metals with similar properties2 such as tungsten,
Molybdenum or the like may also be used.

〔Effect of the invention〕

As detailed above, according to the method of the present invention, the unit cost of multiple materials can be reduced by using silver as the bump material, and an electrode structure with strong υ adhesive strength and high reliability can be easily obtained by known means. There are characteristics that can be used.

[Brief explanation of drawings]

FIG. 1 is a chip cross-sectional view showing an electrode structure formed by a conventional forming method, and FIGS. 2 through 6 are cross-sectional views showing the electrode structure formed by an embodiment of the present invention in the order of steps. αυ...Silicon oxide film, αri...Base region (functional area), (131...Silicon oxide film, ■
...Titanium-tungsten alloy layer (rear metal layer), α5---gold layer, ae...photoresist, αη...silver metal layer.

Claims (1)

[Claims] The process involves sequentially depositing a barrier metal layer such as titanium, tungsten, tungsten, or molybdenum, and then a gold layer on the functional area in which the contact hole has been opened. A process of depositing a resist and using this photoresist as a mask to deposit and form silver bumps on the gold layer, and a process of sequentially etching away the gold layer and then the barrier metal layer using the silver bumps as a mask. A method for forming an electrode of a semiconductor device, the method comprising: