Method for forming aluminum bumps by CVD and wet etch

Details Method for forming aluminum bumps by CVD and wet etch Method for forming aluminum bumps by CVD and wet etch

2001-03-30

2002-10-01

Smith, Matthew (Department: 2825)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

To form ohmic contact to semiconductive material

C438S612000, C438S614000, C438S615000, C438S113000, C438S026000

Reexamination Certificate

active

06458683

ABSTRACT:

FIELD OF THE INVENTION
The present invention generally relates to a method for forming aluminum bumps on a semiconductor structure and more particularly, relates to a method for forming aluminum bumps on a semiconductor structure by a chemical vapor deposition technique and a wet etch technique with significantly reduced number of processing steps.
BACKGROUND OF THE INVENTION
In the fabrication of semiconductor devices, the ever increasing device density and the decreasing device dimensions demand more stringent requirements in the packaging or interconnecting techniques for such devices. In recent years, a flip chip attachment method has been widely used in the packaging of semiconductor chips. In the flip chip attachment method, instead of attaching a semiconductor die to a lead frame in a package, an array of bumps is first formed on the surface of the die. The formation of the bumps may be carried out by a variety of methods depending on the electrically conductive material that is used to form the bumps. For instance, evaporation, electrodeposition, stencil printing, screen printing have all been used to form electrically conductive bumps on flip chips.
The more frequently utilized bump fabrication techniques are a metal deposition process and a plating process. To carry out either of the processes, a series of barrier and seed layers of metal are first deposited on the surface of the semiconductor wafer. These layers are later removed by a wet etching process everywhere except under the die pads and the layers are used to improve adhesion of subsequent layers and to form a barrier to stop metal diffusion from the bump material to the underlying die pad. In a typical bump forming process, a layer of a photoresist material is then deposited over the surface of the semiconductor wafer. A photo mask is then used to pattern the locations over each of the die pads that a bump is to be formed. An etching process, such as plasma etching is used to expose the die pads, while the openings in the photoresist layer determines the shape and height of the bump to be formed.
The electrically conductive bump, which is typically formed of gold or aluminum, can be electroplated or sputtered over the die pad and the barrier and seed layers. Once the plating or sputtering step is completed, a series of wet etching steps is used to remove the photoresist layer and the various barrier and seed layers that cover the remainder area of the wafer while the bumps protect the underlying material from being etched. While gold is the most commonly used material, other electrically conductive materials such as copper, tin-lead and aluminum as well as layered composites of these materials can also be utilized.
A conventional method for forming gold bump is illustrated in FIGS.
1
A~
1
I. As shown in
FIG. 1A
, an input/output (I/O) pad
12
formed on a semiconductor substrate
14
is first provided for a semiconductor structure
10
. On top of the I/O pad
12
, is then deposited a passivation layer
16
of an insulating material. The passivation layer
16
is formed by a photolithographic method using a mask (not shown) to provide an opening
18
for the I/O pad
12
. In the next step of the process, as shown in
FIG. 1B
, a diffusion barrier layer
20
of TiW is conformally deposited into the pad opening
18
. On top of the TiW barrier layer
20
, is then deposited a gold seed layer
22
, as shown in FIG.
1
C. Both the TiW barrier layer and the Au seed layer may be suitably deposited by using a sputtering technique or an electroplating technique. On top of the semiconductor structure
10
, is then coated, most likely by a spin coating technique, a thick photoresist layer
24
.
In the next step of the process, as shown in
FIG. 1E
, the photoresist layer
24
is patterned by a mask (not shown) and an opening
26
is formed by a dry etching method such as plasma etching. The opening
26
is then filled, by an electroplating process of Au, as shown in FIG.
1
F. The photoresist layer
24
is then stripped by a dry etching method leaving the Au bump
28
exposed on the semiconductor
10
. In the next two steps of the process, as shown in
FIGS. 1H and 1I
, the gold seed layer
22
is etched away by a wet etch method and then, the TiW barrier layer
20
is etched away by a wet etch method exposing only the gold bump
28
above the passivation layer
16
.
The conventional gold bump forming process requires numerous photolithographic steps, numerous deposition steps and various dry etching and wet etching steps. It is a time consuming and laborious process which severely impacts the yield of the semiconductor device.
FIGS.
2
A~
2
F demonstrates a conventional process for forming aluminum bumps which requires at least two photolithographic steps, a sputtering step and numerous etching steps. A conventional semiconductor structure
30
is first provided which has a metal pad layer, or an input/output layer
32
formed on a substrate
34
. The I/O metal pad layers
32
may be advantageously formed of a conductive metal such as aluminum, or aluminum that has an alloy content, for instance, aluminum with less than 3 wt. % copper. On top of the I/O pad layer
32
, is then deposited a passivation layer
36
with an insulating material such as SiO
2
, Si
3
N
4
, SiON, SOG or polyimide. The passivation layer
36
is preferably a photo-sensitive material such that it can be imaged by placing a mask
38
on top. This is shown in FIG.
2
A.
After an opening
40
is formed by a dry etch method in the passivation layer
36
, as shown in
FIG. 2B
, an aluminum layer
42
is sputter deposited into the opening
40
and on the top surface
44
of the remaining passivation layer
36
. After the aluminum sputtering process is completed, a second photoresist layer
46
is deposited and patterned on the aluminum layer
42
for forming the aluminum bump. This is shown in FIG.
2
D.
In the final steps of the conventional aluminum bump filing process, as shown in
FIGS. 2E and 2F
, a dry etch method, such as plasma etching is used to form the aluminum bump
50
by using the photoresist layer
46
to define the bump. The photoresist layer
46
is then subsequently removed in a wet etch process to complete the formation of the aluminum bump
50
. The conventional aluminum bump forming process, as shown in FIGS.
2
A~
2
F, therefore requires numerous photolithographic and other chemical processing steps which are time consuming and laborious leading to a low yield of the process.
It is therefore an object of the present invention to provide a method for forming aluminum bumps that does not have the drawbacks or shortcomings of the conventional methods.
It is another object of the present invention to provide a method for forming aluminum bumps that does not require multiple steps of photolithography.
It is a further object of the present invention to provide a method for forming aluminum bumps that only requires a single photolithographic process.
It is another further object of the present invention to provide a method for forming aluminum bumps by a chemical vapor deposition process to selectively deposit aluminum.
It is still another object of the present invention to provide a method for forming aluminum bumps by a chemical vapor deposition process and a wet etch process.
It is yet another object of the present invention to provide a method for forming aluminum bumps by using a passivation layer and a photoresist layer with an opening therein as a mold for depositing aluminum and forming the bump.
It is still another further object of the present invention to provide a method for forming aluminum bumps that require a reduced number of processing steps than the conventional formation methods.
SUMMARY OF THE INVENTION
In accordance with the present invention, a method for forming aluminum bumps by chemical vapor deposition and wet etch is provided.
In a preferred embodiment, a method for forming aluminum bumps by chemical vapor deposition and wet etch can be carried out by the operating steps of first providing a pre-processed ele

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