Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
1999-03-12
2001-10-02
Utech, Benjamin L. (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
C438S710000, C438S712000, C438S719000, C438S720000
Reexamination Certificate
active
06297160
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to the fabrication of semiconductor circuits, and more specifically to a method for forming bonding pads such that bonding pad corrosion is eliminated for bonding pads whose top metal surface contain minute amounts of copper and silicon.
(2) Description of the Prior Art
For many of the advanced semiconductor devices, device signals such as ground, power and I/O signals require numerous bonding pads. With the increased density of components within a chip and with increased sophistication of the circuitry contained within the chip, further demands are placed on the number of bonding pads for each chip. For many designs, the number of bonding pads becomes the limiting factor on chip size and chip function.
Improvements in packing density cannot be realized by simply shrinking the design rules or adding more levels of metal wiring.
Aluminum grows a passivating oxide layer in air and is as a consequence protected against corrosion. Aluminum wiring used in semiconductors, however, contains copper, which does not have a passivating oxide, and the Al—Cu alloy used is more vulnerable to corrosion. The corrosion of aluminum wires is caused by several sources such as chlorine transported through the plastic packaging and the passivation materials, chlorine from the etching compounds and as etching by-products, phosphorous acid formed from excess phosphorous in the phosphosilicate glass, etc. Only a small amount of chlorine is required to cause severe local corrosion of the aluminum lines. Aluminum corrosion can, in addition, occur very quickly after metal etching.
To avoid etching introduced corrosion, chlorine compounds and elemental chlorine must be removed from the metal surface immediately after plasma etching. This is usually accomplished by a water rinse or a water vapor treatment.
Modern metal structures use multi-levels of dissimilar materials such as Ti/TiN/Al—Cu/TiN or Ti/Al—Cu/TiN which increases the possibility of electromechanical corrosion.
Copper is electro-positive with respect to hydrogen and is not vulnerable to corrosion. However, in air copper oxide grows linearly with time, indicating the lack of a protective oxide. This lack of a passivating oxide makes copper more vulnerable to chemical corrosion. To avoid or minimize this corrosion, most applications of copper metalization involve some protective layer deposited on top of the copper.
FIG. 1
shows a cross section of a typical Prior Art bond pad. Bonding pads serve the function of providing device signals such as ground, power and I/O signals to semiconductor devices. In this capacity a bonding pad provides an electrical path between the semiconductor device and the electrical circuitry and components with which the semiconductor device interfaces. The bonding pad structure provides for an opening to which one contact point of the semiconductor devices is connected, from this bonding pad opening the electrical path continues through the bonding pad to a metal plate that connects with the electrical circuitry and components with which the semiconductor device interfaces. Where this connecting electrical path consists of Al—Cu, top metal surface corrosion and pitting is a problem within the opening of the bonding pad.
Referring now specifically to
FIG. 1
, there is shown a cross section of a typical Prior Art bonding pad. The metal layer
10
connects the bonding pad with the electrical circuitry and components with which the semiconductor device interfaces, the semiconductor device is connected to the bonding pad via the opening
18
. A layer
14
of Al—Cu provides the electrical path between metal
10
and opening
18
. A layer
26
of dielectric is deposited over the metal layer
10
, a via hole
12
is etched in this dielectric layer
26
. A passivation layer
24
is deposited on top of the Al—Cu layer
14
, the opening
18
is etched into this passivation layer
24
. The passivation layer
24
is separated from the metal layer
14
by a layer
16
of anti-reflective coating (ARC). Surface pitting
20
and surface corrosion
22
occur on the surface of top metal layer
14
within the opening
18
of the bonding pad.
FIG. 2
shows the processing steps required to create a typical Prior Art bonding pad. The numbers indicated within the following description of the processing steps required to created a Prior Art bonding pad refer to the numbers that have previously been used under FIG.
1
. The bonding pad is constructed starting with the original metal
10
(
FIG. 2
, step 1). On top of this metal
10
a layer
26
of dielectric is deposited (step 2). Via
12
is created within the dielectric
26
(step 3), a layer
14
of Al—Cu is deposited across the dielectric
26
and the via
12
(step 4). A layer
16
of ARC is deposited on top of the layer
14
of Al—Cu (step 5). A passivation layer
24
is deposited over the ARC layer
16
(step 6). The bonding pad opening
18
is etched within the passivation layer
24
(step 7).
U.S. Pat. No. 5,661,081 (Hsue et al.) teaches an Al or Al alloy bonding pad. However, this reference differs from the invention.
U.S. Pat. No. 5,731,243 (Peng et al.) shows a method to reduce residue formation over an Al bond pad.
U.S. Pat. No. 5,559,056 (Weiler) shows a bond layer over a bonding pad.
U.S. Pat. No. 5,525,546 (Harada et al.) shows an Al alloy bonding pad and method.
U.S. Pat. No. 5,565,378 (Harada et al.) shows a method of passivating an Al bonding pad using an O
3
solution.
SUMMARY OF THE INVENTION
It is the primary objective of the present invention to prevent surface pitting and corrosion of the top level metal within bonding pads.
A bonding pad is a semiconductor structure that provides an interface between a semiconductor device and other electrical circuitry and components. A bonding pad is therefore in physical contact with a metal layer (the metal layer that provides electrical stimuli to the semiconductor device) and provides electrical continuity between that layer of metal and the semiconductor device. According to the present invention, a layer of pure aluminum is deposited on the top layer of metal within the bonding pad. This layer of pure aluminum stops the surface pitting and corrosion of the top metal surface within the bonding pad.
REFERENCES:
patent: 5476815 (1995-12-01), Kawasumi
patent: 5525546 (1996-06-01), Harada et al.
patent: 5559056 (1996-09-01), Weiler
patent: 5565378 (1996-10-01), Harada et al.
patent: 5595934 (1997-01-01), Kim
patent: 5661081 (1997-08-01), Hsue et al.
patent: 5707894 (1998-01-01), Hsiao
patent: 5731243 (1998-03-01), Peng et al.
patent: 5824234 (1998-10-01), Jou et al.
patent: 5854119 (1998-12-01), Wu et al.
patent: 5904556 (1999-05-01), Suzuki et al.
patent: 5911887 (1999-06-01), Smith et al.
patent: 5930664 (1999-07-01), Hsu et al.
Ackerman Stephen B.
Saile George O.
Taiwan Semiconductor Manufacturing Company
Utech Benjamin L.
Vinh Lan
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