Active solid-state devices (e.g. – transistors – solid-state diode – Encapsulated
Reexamination Certificate
1999-05-03
2001-11-20
Everhart, C. (Department: 2825)
Active solid-state devices (e.g., transistors, solid-state diode
Encapsulated
C438S612000, C438S464000
Reexamination Certificate
active
06320269
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the manufacture of semiconductor wafers and more specifically to an improved process for forming holes in a passivation layer that an adhesive tape is applied to for protecting the wafer during a grinding operation.
INTRODUCTION
As the related application explains, after most of the operations on the device side of a wafer have been completed, a grinding operation is performed on the back side of the wafer to give the wafer a selected thickness. A tape is applied to the device surface of the wafer to protect it during this grinding operation. This surface is formed by the upper surface of the passivation layer and the bonding pads that are exposed through holes formed in the passivation layer. The tape has a plastic backing and an adhesive. When the tape is removed, particles of adhesive sometimes remain on the device side of the wafer and on or near the bonding pads. These particles can interfere with later operations such as welding wires to the bonding pads of a chip.
SUMMARY OF THE INVENTION
This invention is directed to the problem that the adhesive can stick to the bonding pads. I modify the normally sharp edges of the holes in the passivation layer to give them a sloping profile. The bonding tape does not pass over sharp corners that liable to cut into the adhesive and thereby cause particles of adhesive to be left on the bonding pads.
In one embodiment, a photoresist is conventionally formed over the passivation layer and holes for the bonding pads are conventionally formed in the photoresist. These holes in the photoresist layer have approximately vertical side walls and sharp edges where the side walls meet the upper surface of the resist. These sharp edges are then removed, preferably by an oxygen plasma treatment. The passivation layer is then etched in the usual way and the resulting holes in the passivation layer are given a sloped profile that permits the tape to be removed without leaving behind particles of adhesive.
In a second embodiment of my invention, the photoresist is left with the usual sharp edges but the holes in the passivation layer are etched with an isotropic etch. (Conventionally this etch is anisotropic.) The isotropic etch operates both vertically and horizontally and as is well known in other etch steps, the hole is given a greater diameter at the top than at the bottom. The resulting hole in the passivation layer has a sloping profile which helps to avoid cutting the adhesive and thereby causing adhesive particles to remain on the wafer.
Other objects and features of the invention will appear in the description of these embodiments of the invention.
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Chang Kuei-Jen
Chen Sen-Fu
Ackerman Stephen B.
Everhart C.
Robertson William S.
Saile George O.
Taiwan Semiconductor Manufacturing Company
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