Active solid-state devices (e.g. – transistors – solid-state diode – Physical configuration of semiconductor – With peripheral feature due to separation of smaller...
Reexamination Certificate
2001-03-26
2002-10-08
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Physical configuration of semiconductor
With peripheral feature due to separation of smaller...
C257S620000, C438S014000, C438S106000, C438S156000, C438S763000
Reexamination Certificate
active
06462401
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a semiconductor wafer and a method for fabricating a semiconductor wafer and, more particularly, to an improvement of the semiconductor wafer for preventing ingress of particles generated by grinding the bottom surface of the wafer.
(b) Description of the Related Art
Some semiconductor wafers are formed by a process including the steps of forming polyimide overcoat film patterns for protecting the main surfaces of semiconductor chips and grinding the bottom surface of the wafer after the polyimide film patterns are formed on the main surfaces.
A conventional method of fabricating such a semiconductor wafer will be described with reference to
FIGS. 1 and 2
.
FIG. 1
is a top plan view showing a part of the main surface of the conventional semiconductor wafer having thereon a polyimide overcoat film pattern on each of the semiconductor chips.
FIG. 2
is a sectional view taken along line II—II in
FIG. 1
, showing the wafer onto which a surface protective tape
19
is stuck after formation of the polyimide film patterns
18
.
The semiconductor wafer has thereon a plurality of semiconductor chips
11
arranged in a matrix. The fabrication process of the wafer shown includes the step of forming insulating films
14
on the substrate
13
, followed by forming thereon an interconnect pattern
16
including electrode pads
15
. Scribe lines
17
are then formed between each adjacent two of the semiconductor chips
11
. The scribe lines
17
is used for cutting the wafer in a later dicing step in which the semiconductor wafer is scribed and separated into separate semiconductor chips
11
.
Polyimide film patterns
18
are formed as overcoat layers for protecting the interconnect patterns
16
against damages or contamination. The polyimide film forming step typically includes such procedures as polyimide coating, polyimide hardening, resist coating, exposure to light, selective removal of the resist layer for patterning, selective etching of the polyimide film using the resist layer as a mask, and removal of the resist layer.
For patterning the polyimide film, the polyimide film is removed from most of the areas for all the electrode pads
15
, the areas of the scribe lines
17
, and, if any electrode pads
15
and scribe lines
17
are disposed in close proximity to one another, the gaps therebetween. The purpose of the removal of the polyimide film from the areas of the scribe lines
17
is to prevent the dicing blade used in the dicing step from a premature deterioration in sharpness. The areas of the electrode pads
15
should be exposed for the sake of bonding in a bonding step, and thus are subjected to the removal of the polyimide film.
The polyimide film patterns
18
have a certain thickness so as to protect the interconnect patterns
16
from damages and contamination. The polyimide film patterns
18
are formed in a thickness greater than or equal to 6 &mgr;m, which is significantly greater as compared with those of the insulating films
14
and interconnect patterns
16
which are not greater than 2 &mgr;m. Thus, the surface of the wafer having thereon the polyimide film patterns
18
is projected where the polyimide film patterns
18
exist, and depressed where no polyimide film
18
exist. Parallel to the scribe lines
17
, these depressions extend vertically and horizontally to form a lattice. Further, if any electrode pads
15
and scribe lines
17
are disposed in close proximity to one another and thus no polyimide film
18
is formed therebetween, the depressions over those electrode pads
15
and the depressions over those scribe lines
17
are coupled together. These depressions create gaps
20
, for example, between the wafer and the surface protective tape
19
which is stuck onto the wafer during grinding the bottom surface of the wafer.
FIG. 3
is a side view showing the grinding position in a bottom surface grinder
21
for use in the step of bottom surface grinding in the fabrication process of the semiconductor wafer. The bottom surface grinder
21
has a suction table
22
and a high-speed rotation wheel
23
in its grinding position. The wafer.
12
having thereon the polyimide film patterns onto which the surface protective tape
19
are stuck is attached to the suction table
22
, with the main surface (top surface) of the wafer
12
being directed downward. The high-speed rotation wheel
23
rotates at a high speed to grind the bottom surface of the wafer
12
. The high-speed rotation wheel
23
has a plurality of grindstones
25
protruding therefrom.
Nozzles
26
for spraying water are arranged right inside the grindstones
25
. Aside from the grinding position, the bottom surface grinder
21
has a cleaning position (not shown) for cleaning particles
24
produced by the grinding. The bottom surface grinder
21
is used to grind the bottom surface of the semiconductor wafer
12
to a desired thickness in the following manner.
That is, the wafer
12
having the surface protective tape
19
stuck thereon is attached to the suction table
22
with the top surface of the wafer
12
being directed downward. The high-speed rotation wheel
23
having the grindstones
25
is lowered to the height of the bottom surface of the wafer
12
and rotated at a high speed, so as to grind the bottom surface of the wafer
12
. Formed inside the grindstones
15
are the nozzles
26
for ejecting water to wash away the ground particles
24
produced by the grinding and to cool down the frictional heat produced by the grinding. The nozzles
26
eject water to wash away the ground particles
24
. There are some other methods which includes a grinding step without the supply of water. After the bottom surface grinding, the wafers are cleaned in the cleaning position (not shown), drained, and stored in a storage box in the order of the appearance.
In the conventional method in which all the steps up to the patterning of the polyimide film are completed before the bottom surface grinding, since the polyimide film is already removed from the areas for the electrode pads
15
and the scribe lines
17
to make depressions, the gaps
20
are generated between the surface of the wafer
12
having thereon the polyimide film patterns
18
and the surface protective tape
19
.
Due to the presence of the gaps
20
, the particles
24
produced by the bottom surface grinding, mixed with the water or air and washed around from the bottom surface to the side surface of the wafer
12
, may intrude into the interior of the wafer through gaps
20
from the periphery of the wafer. Moreover, by the capillary function, the water/air containing the ground particles
24
flows onto the main surface of the wafer along the scribe lines
17
which extend vertically and horizontally to form a lattice and are in connection with one another.
On the way of flow, the ground particles
24
adhere to the electrode pads
15
having depressions which lead to the scribe lines
17
. Of the ground particles
24
, hard and pointed ones stick into the electrode pads
15
, which are formed of relatively soft material. This wafer is cleaned in the cleaning position (not shown) after the bottom surface grinding, whereas the ground particles
24
intruding into the gaps
20
and adhered thereto are eliminated insufficiently. Although there is another cleaning step (not shown) after the removal of the surface protective tape
19
, the ground particles
24
, sticking into the electrode pads
15
, are hard to remove completely.
Patent Publication JP-A-61-232625 describes another method including the steps of preparing a wafer having thereon a polyimide film covering the entire surface of the wafer including the scribe lines and electrode pads, grinding the wafer in the bottom surface grinding step, and entirely removing the polyimide film by etching. This technique eliminates the problem that the pasting wax for pasting the wafer to the table of the bottom surface grinder reacts with the electrode pads to discolor the electrode p
McGinn & Gibb PLLC
Nelms David
Tran Mai-Huong
LandOfFree
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