Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1999-06-18
2001-05-08
Picardat, Kevin M. (Department: 2823)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S106000, C438S613000
Reexamination Certificate
active
06228753
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority benefit of Taiwan application serial no. 88107214, filed May 4, 1999, the full disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a method of fabricating a bonding pad for a semiconductor. More particularly, the present invention relates to a method for improving bonding pad surface quality.
2. Description of Related Art
In the manufacturing process of the bonding pad for an integrated circuit, the passivation layer over the wafer is patterned and then the bonding pad is exposed by forming an opening within the passivation layer. Thereafter, an alloy thermal process is performed to enhance the adhesion between the aluminum copper alloy on the surface of the bonding pad and the metal underlying thereof. Since the thermal expansion coefficient of the aluminum copper alloy is large, hillocks are created on the aluminum copper alloy by thermal stress in the metallic material due to the thermal alloying process. After the etching process for forming the opening in the passivation layer, a cleaning step performed in acid tank is required in order to remove residue on the wafer. However, the aluminum copper alloy is easily corroded by the acid solution to cause damage thereon. A polyimide is then coated over the wafer. When photolithography for the polyimide is carried out, the grain boundary of the aluminum copper alloy is attacked by the developer, leading to cracks. In addition, the aluminum copper alloy is subject to Al
2
Cu phase formation, which easily reacts with the aluminum in the aluminum copper alloy to cause a galvanic reaction and accordingly, Al
3+
is generated and leads to erosion.
Therefore, the appearance of the aluminum copper alloy on the surface of the bonding pad is seriously degraded when the alloying, cleaning and development processes are complete. However, the bonding pad is the only structure exposed by the passivation layer, and thus the appearance of the bonding pad is the only quality which the clients is capable of checking. As a result, the clients will reject the product due to the bad appearance of the bonding pad, even though no problems manifest during the wafer acceptance test (WAT). As a result, the producer who makes the bonding pad has to discard the wafers and loses substantial amounts of money.
SUMMARY OF THE INVENTION
The invention provides a method for improving bonding pad surface quality. A bonding pad is disposed on a substrate. A passivation is formed on the substrate to expose a portion of the bonding pad. A photoresist layer is then formed over the substrate. Photolithography is performed on the photoresist layer to form an opening within the photoresist layer, such that the bonding pad is exposed. Thereafter, an alloy layer is formed on the bonding pad and the photoresist layer is removed.
In one embodiment of the invention, after the opening is formed to expose the bonding pad, an alloy layer is formed over the bonding pad and the photoresist layer. Since there is no baking when forming the photoresist layer, the photoresist with no curing has poor adhesion with the passivation. Therefore, the photoresist layer can be removed by supersonic vibration and therefore the alloy layer adhered on the photoresist layer can simultaneously be removed.
As embodied and broadly described herein, the invention provides a method for improving bonding pad surface quality. Since the alloy layer is formed after the manufacture of the bonding pad structure and there is no additional process before the WAT, the appearance of the bonding pad remains smooth. Therefore, the wafers appear to be high quality wafers and can be easily sold. Additionally, the fabricating cost is reduced.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.
REFERENCES:
patent: 5612254 (1997-03-01), Mu et al.
patent: 5930664 (1999-07-01), Hsu et al.
Ho Wen-Yu
Hsieh Sung-chun
Lo Yung-Tsun
Collins D. M
Huang Jiawei
Patents J C
Picardat Kevin M.
Worldwide Semiconductor Mfg Corp
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