Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Responsive to electromagnetic radiation
Reexamination Certificate
1999-10-08
2001-09-04
Le, Vu A. (Department: 2824)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Responsive to electromagnetic radiation
C438S048000
Reexamination Certificate
active
06284561
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of forming a metal plate on a semiconductor wafer, and more particularly, to a method of forming a metal plate of a fingerprint sensor chip on a semiconductor wafer.
2. Description of the Prior Art
The biometric sensor chip used for the prior art fingerprint detector is a semiconductor product. The biometric chip comprises approximately ninety thousand metal sensor plates arrayed in a 300×300 pixel matrix. This matrix is sandwiched between an inter-metal dielectric (IMD) and a passivation layer, and is used as the sensor array of the fingerprint detector.
When the finger of the user touches the passivation layer of the biometric sensor chip, each sensor plate in the sensor array detects the static voltage in its area relative to the finger. The changing topography of the finger causes relative changes in voltage in each sensor plate across the sensor array. This pattern of relative voltages generates an image of the fingerprint, which can be passed on to external circuitry for recognition.
Please refer to FIG.
1
and FIG.
2
.
FIG. 1
is a layout schematic diagram of a sensor plate
22
of the biometric sensor array of the prior art.
FIG. 2
is a cross-sectional view along line
2
—
2
of the biometric sensor chip shown in
FIG. 1. A
prior art biometric sensor array comprises ninety thousand metal sensor plates
22
, and each sensor plate
22
is formed on the surface of a semiconductor wafer
10
. The semiconductor wafer
10
comprises a dielectric layer
12
, a metallic line layer made of several interconnection lines
14
positioned on the dielectric layer
12
, an IMD
15
covering the interconnection lines
14
and the dielectric layer
12
, a metal plate positioned on the IMD
15
to be a sensor plate
22
, and a passiviation layer
24
covering the sensor plate
22
and the IMD
15
to protect the circuitry on the semiconductor wafer
10
. The IMD
15
is a compound structure which comprises spin on glass (SOG)
18
and a silicon oxide layer
20
.
In the formation of the prior art biometric sensor chip, a dielectric layer
12
is deposited on the surface of the semiconductor wafer
10
, then a first metallic layer is formed on the dielectric layer
12
and is processed into the interconnection lines
14
using photolithography and etching. These interconnection lines
14
electrically connect the sensor array to the image recognition circuit of the biometric sensor chip, or to other internal circuitry. An SOG
18
is formed on the interconnection lines
14
and the dielectric layer
12
to form a spacer on both sides of each interconnection line
14
which smoothes the corners between each interconnection line
14
and the dielectric layer
12
. Next, a silicon oxide layer
20
is formed on the interconnection lines
14
and the dielectric layer
12
to prevent the interconnection lines
14
from being corroded by subsequent processes, and which completes the formation of the IMD
15
compound structure.
After the IMD
15
is formed on the semiconductor wafer
10
, a second metallic layer is formed on the silicon oxide layer
20
which also undergoes photolithography and etching to form the sensor plates
22
. Finally, a passiviation layer
24
is formed on the sensor plates
22
and the IMD
15
to protect the circuitry on the semiconductor wafer
10
. When the finger of the user touches the passivation layer
24
, each sensor plate
22
senses the static voltage in its area relative to the finger, and all ninety thousand sensor plates
22
together make a relative fingerprint image.
However, the area between each interconnection line
14
is very uneven with the SOG spacers
18
and the interconnection lines themselves. Consequently, the silicon oxide
20
, which is of uniform thickness and which is formed across this uneven surface, is not a level surface. When the metal sensor plates
22
are formed on this uneven silicon oxide layer
20
, they become distorted, with raised edges and a sunken center. Such non-planar metal sensor plates adversely affect the sensitivity and accuracy of the entire sensor chip as the distance from an individual sensor plate to the user's finger is not consistent across the area of the sensor plate.
Furthermore, the uneven topography of the sensor plates
22
causes the passivation layer
24
to be uneven. This is especially true when the passivation layer
24
is deposited on the raised edges of the sensor plates
22
, which causes peaks and valleys to form in the passivation layer
24
. Consequently, when the biometric sensor chip is mounted on a printed circuit board (PCB) and it undergoes a cleaning process, the high-pressure water used in cleaning will strike the slopes of the passivation layer
24
and generate cracks. Water droplets will then be able to infiltrate down into the interconnection layer through these cracks and cause short-circuiting. The cracks also weaken the passivation layer
24
of the biometric sensor chip, making it more susceptible to damage during packaging and actual use.
SUMMARY OF THE INVENTION
It is therefore a primary objective of the present invention to provide a method of forming a metal plate of a fingerprint sensor chip on a semiconductor wafer to solve the above mentioned problems.
In a preferred embodiment, the present invention relates to a method of forming a metal plate on a semiconductor wafer, the semiconductor wafer comprising a first dielectric layer and two line-shaped conductors positioned on the first dielectric layer, each of the two line-shaped conductors comprising two vertical side walls positioned on its two opposite sides, a recess being formed between the two conductors and above the surface of the first dielectric layer, and the recess comprising two corners formed between the two vertical side walls of the two conductors in the recess and the surface of the first dielectric layer, the method comprising:
forming two spacers at the two corners of the recess by using a filling material to create two slopes above the two corners;
forming a second dielectric layer uniformly on the two conductors and the recess, the second dielectric layer positioned on the recess creating a shallow trench on its top end and its bottom end being higher than the top ends of the two conductors;
forming an approximately rectangular photoresist layer on the shallow trench;
performing a dry-etching process to vertically remove the second dielectric layer positioned on the two conductors and making the top end of the second dielectric layer positioned on each of the two conductors lower than the bottom end of the shallow trench;
removing the photoresist layer;
forming a sacrifice layer on the surface of the second dielectric layer by using a spin-coating method;
performing an etching-back process on the sacrifice layer and the second dielectric layer to form an approximately rectangular platform above the recess and two shallow trenches above the two conductors;
forming an approximately rectangular metal plate on top of the platform; and
forming a third dielectric layer uniformly on the semiconductor wafer for protecting the metal plate.
It is an advantage of the present invention that the passivation layer on the metal sensor plate has a very even surface, which can improve the sensitivity and the accuracy of the fingerprint sensor chip.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment which is illustrated in the various figures and drawings.
REFERENCES:
patent: 5476808 (1995-12-01), Kusaka et al.
patent: 6046068 (2000-04-01), Orava et al.
patent: 6061464 (2000-05-01), Leger
Hsu Winston
Le Vu A.
Smith Bradley
United Microelectronics Corp.
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