1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly to a semiconductor device in which reaction products such as aluminum hydroxide are prevented from forming on a bonding pad, and a method of manufacturing such a device.
2. Description of Related Art
Materials with aluminum as the main constituent, for example Al, Alxe2x80x94Cu, and Alxe2x80x94Sixe2x80x94Cu, have been used for metal wiring in semiconductor devices. Bonding pads are formed by selectively exposing such metal wiring. When openings are formed for bonding pads, the metal wiring exposed by the openings reacts with moisture in the air at room temperature. The aluminum in the wiring is thereby transformed into aluminum hydroxide, since aluminum is a very active element. Aluminum hydroxide can form in about two weeks where temperature and humidity are not controlled.
As shown in FIG. 8, an inter-layer insulating film 2, a barrier metal film 3, an aluminum layer 4, an antireflection metal film 5, and a passivation film 6 are formed as a multi-layer structure on a semiconductor substrate 1. Furthermore, a photosensitive polyimide layer (or photo-resist) 7 is formed on the passivation film 6, and the passivation film (protective film) 6 is selectively removed by dry etching to form an opening 8 using the polyimide layer 7 as a mask. This opening 8 exposes the aluminum layer 4 as bonding pad 11. If this opening 8 is left as is, an aluminum hydroxide layer 12 will form as a reaction product on the surface of aluminum layer 4.
Such an aluminum hydroxide layer 12 hinders a eutectic state between aluminum serving as the bonding pad and the bonding wire (Au or Al wire) in the subsequent bonding process, and therefore decreases the bonding yield. Therefore, in the method of manufacturing a semiconductor device, to minimize the degeneration of the surface of the bonding pad, it is common to keep the device in a controlled temperature and humidity, or confined in dry air after the front-end process (the completion of the bonding pad forming step) until the assembly is completed.
After the bonding pad is formed, the semiconductor device is completed by bonding the bonding pad to an external lead, such as a lead frame, with a metal wire, and then packaging. However, packaging is performed with the bonding area exposed to air. Thus, the surface of the aluminum serving as bonding pad reacts with moisture in the air. Accordingly, the surface of the bonding pad degenerates and erodes, and the characteristics of the semiconductor device degrade.
To solve this problem, Japanese Patent Kokai No. Sho 59-150460, No. Sho 63-272042, No. Hei 1-110749, and No. Hei 5-46978 disclose that after the bonding step, the surface of the bonding pad is covered with an insulating film, such as aluminum oxide, to prevent the aluminum serving as the bonding pad from degenerating.
However, in the conventional manufacturing method of a semiconductor device, the device must be kept in a controlled temperature and humidity or confined in dry air until the assembly is completed. Consequently, handling and storage facilities are needed for keeping the device in the proper atmosphere and additional time is required for transporting the device to the storage place.
Moreover, according to the above patents, the aluminum oxide is formed after the bonding step, and therefore the device must be kept in the above described storage place from the bonding pad forming step (front-end process) until the assembly is completed.
The object of the present invention is to provide a semiconductor device and a method of manufacturing a semiconductor device that prevents the surface of the bonding pad from degenerating until the assembly is completed.
A semiconductor device according to the present invention comprises a semiconductor substrate; a wiring layer on the semiconductor substrate; a passivation film on the wiring layer, the passivation film having a hole selectively formed to expose a surface of the wiring layer serving as a bonding pad; and an oxide layer covering all of the wiring layer exposed by the hole.
A method of manufacturing a semiconductor device according to the present invention comprises the steps of: forming a wiring layer on a semiconductor substrate; forming a passivation film on the wiring layer; selectively forming a hole in the passivation film to expose a surface of the wiring layer; and forming an aluminum oxide film on the exposed surface of the wiring layer before bonding a bonding wire to the exposed surface.
These and other objects of the present invention will be apparent to those of skill in the art from the appended claims when read in light of the following specification and accompanying figures.