JPS6142432B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor device that is useful when assembling a semiconductor device using, for example, a solder reflow method.

Generally, when assembling a semiconductor device, that is, when mounting a semiconductor chip onto a package, so-called gigantic bonding, such as the flip-chip method and the beam lead method, is often used. Compared to wire bonding, the main characteristics of this gigantic bonding are that it requires less labor and has extremely good work efficiency, and is highly reliable due to its high mechanical strength.

By the way, a solder reflow method is used to perform the gigantic bonding. In the solder reflow method, for example, solder bumps are formed on the electrode pads of a semiconductor chip, the semiconductor chip is placed in a predetermined place on a package, and the entire package is inserted into a heating furnace for heat treatment, and the solder is reused. The semiconductor chip is connected to the leads of the package by melting.

When implementing this solder reflow method, the quality of the bonding is determined by the homogeneity, adhesion, etc. of the solder bumps formed on the electrode pads of the semiconductor chip.

Conventionally, when forming solder bumps on a semiconductor chip, for example, nickel is interposed below the solder bumps. This is an attempt to take advantage of the good adhesion between solder and nickel. However, the solder and nickel react easily, and the solder absorbs the nickel. In order to avoid this, it has been considered to interpose cobalt under the solder bumps, or to interpose cobalt and aluminum in sequence. Cobalt does not easily react with solder, and
It has good adhesion to silicon and aluminum and has an extremely excellent barrier effect. However, cobalt is an extremely active metal and is oxidized considerably even in air at room temperature. In addition, cobalt itself does not have very good adhesion with solder, so when solder bumps are formed on a cobalt layer, some parts are coated with solder and others are not, resulting in uneven surfaces. Solder bumps are formed.
With such solder bumps, gigantic bonding using a reflow method cannot be performed satisfactorily.

The present invention enables uniform solder bumps without irregularities to be formed on a cobalt layer, and will be described below.

The basic principle of the present invention is to interpose a thin layer of metal that has good adhesion to both cobalt and solder between the cobalt layer and the solder bump.

For example, a cobalt layer with a thickness of 5,000 to 6,000 [Å] is formed on an electrode pad made of aluminum, and a gold layer with a thickness of 1,000 [Å] or less is formed on top of the cobalt layer.
A metal layer made of silver, copper, nickel, or the like that has good adhesion to cobalt and solder is formed, and solder bumps are formed thereon.

The surfaces of the solder bumps formed in this manner are smooth and uniform, and if the area of the electrode bumps is the same, the heights of the solder bumps are all the same. Even if the metal layer that has good adhesion to the solder is absorbed into the solder bump, the surface of the cobalt layer is initially covered with the metal layer and no oxide film is formed, so the adhesion deteriorates. Never.

As can be seen from the above explanation, according to the present invention, the electrode pad is formed of a metal such as aluminum that has good adhesion and ohmic contact with semiconductors, and on top of that, it has good adhesion with aluminum, silicon, etc. In addition, a cobalt layer is formed, which is an excellent barrier, and a metal layer with good adhesion is formed on the cobalt layer and the solder bumps, and the solder bumps are formed on top of the cobalt layer, which provides a strong bond to the semiconductor chip. It is possible to obtain an electrode pad structure that is in close contact with the solder bump, and also to make the surface of the solder bump smooth and uniform, thereby achieving good bonding when performing, for example, gigantic bonding using the solder reflow method. becomes possible.

Claims (1)

[Claims] 1 A cobalt layer is formed on an electrode pad made of a metal that has good adhesion and ohmic contact with the semiconductor, and a thin layer of metal that has good adhesion to cobalt and solder is formed on top of the electrode pad, and then solder bumps are formed. 1. A method of manufacturing a semiconductor device, the method comprising the step of forming a semiconductor device.