1. Field of the Invention
The present invention relates to a method for producing a semiconductor device. More particularly, it relates to a method for producing a semiconductor device having a metal bump which is used as a terminal electrode thereof.
2. Description of the Related Art
The terminal electrodes of a semiconductor device are usually formed by, for example, an Au wire terminal electrode. However, the electrode structure wherein a large projected metal (bump) is adhered to the electrode portion of the semiconductor device, and wires are connected to the projected metal, is known.
Since the semiconductor device having the bump does not require wire bonding, the thickness of the package of the semiconductor device is reduced and the size of the bonding pad (electrode region) of a semiconductor chip is made considerably smaller. Accordingly, a semiconductor device having a bump has an advantage in that it can be assembled in an IC card in a flat shape package and the size of the semiconductor device per se is considerably reduced. Further, since a composite device is formed by providing a plurality of semiconductor chip electric circuits, it can be packaged with a high degree of density. Nevertheless, the metal bump per se must have a good adhesion to an electrode.
FIGS. 1A to 1E are cross-sectional views explaining a conventional method for providing the above-mentioned device.
As shown in FIG. 1A, an aluminum electrode 2 is provided on a semiconductor substrate 1 and a phosphosilicate glass (PSG) film 3 is formed over the substrate 1 and the aluminum electrode 2 by a chemical vapour deposition (CVD) process. A silicon dioxide (SiO.sub.2) film may be used instead of the PSG film 3.
Then, as shown in FIG. 1B, a first resist film is coated on the PSG film 3, and exposed and developed to form a first resist pattern 4 having an opening at a required position above the electrode 2. The PSG film 3 is then etched, using the resist film pattern 4 as a mask, so that an opening 5 is formed above the electrode 2.
The resist film pattern 4, is then removed, as shown in FIG. 1C, and a barrier metal film 6 about 3 .mu.m thick and consisting of three layers of titanium (Ti), copper (Cu), and nickel (Ni) respectively, is formed on the exposed PSG film 3 and electrode 2 by a sputtering process.
Then, as shown in FIG. 1D, a second resist film is coated on the barrier metal film 6, and exposed and developed so that a second resist film pattern 7 having an opening larger than the opening 5 is formed at the opening 5. Then, a solder (PbSn) bump 8 is formed at the opening 5 by a plating method using the resist film pattern 7 as a mask. During the plating, the barrier metal film 6 is used as a plating conductive layer.
Then, as shown in FIG. 1E the resist film pattern 7 and the exposed barrier metal film 6 are removed, using the solder bump electrode 8 as a mask, by a wet etching method using a mixture of nitric acid and phosphoric acid to remove the nickel and copper, and phosphoric acid to remove the titanium. The wet etching method is used because a dry etching will cause the bump electrode to be easily etched.
Subsequently, the solder bump is melted by a heat treatment to form a semi-spherical bump 8 having a diameter of about 150 .mu.m. A gold (Au) bump may be formed instead of the solder bump, by a method similar to the above-mentioned process.
In the above mentioned method for forming the bump 8, the barrier metal film 6 is interposed between the electrode 2 and the bump 8 so that the bump 8 does not react with the electrode 2. Also the barrier metal film 6 is used as a plating conductive layer, as explained above.
In the etching of the barrier metal film 6 using the solder bump 8 as a mask, a side etching is carried out in a lower portion of the bump 8 as shown in FIG. 1D, since in the lower portion of the bump, the flow of the olating liquid becomes uneven and a battery is formed by the bump 8 and the barrier metal films 6. This deteriorates the adhesive properties between the bump 8 and the aluminum electrode 2, and the bump 8 can be easily separated from the etched barrier metal film 6.