Semiconductor device manufacturing: process – Formation of electrically isolated lateral semiconductive... – Having substrate registration feature
Reexamination Certificate
2000-04-25
2001-10-30
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Formation of electrically isolated lateral semiconductive...
Having substrate registration feature
C438S113000, C438S400000
Reexamination Certificate
active
06309943
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to electronic packaging. More particularly, the present invention relates to a method of marking and singulating a structure.
BACKGROUND OF THE INVENTION
As is well known to those of skill in the art, integrated circuits, i.e., electronic components, are fabricated in an array on a wafer. The wafer is then cut, sometimes called diced, to singulate the integrated circuits from one another.
FIG. 1
is a cross-sectional view of a section of a wafer
10
being cut from a front-side surface
10
F of wafer
10
in accordance with the prior art. Formed in wafer
10
were integrated circuits
12
. Integrated circuits
12
were delineated by scribe lines
14
, which included a first scribe line
14
A and a second scribe line
14
B, on front-side surface
10
F of wafer
10
. For example, scribe lines
14
were formed by selective etching of a silicon oxide layer
18
on front-side surface
10
F.
To illustrate, first scribe line
14
A delineated a first integrated circuit
12
A from a second integrated circuit
12
B. Each scribe line
14
had a width WF.
A back-side surface
10
B of wafer
10
was attached to a tape
20
. Wafer
10
was then sawed with a saw blade
22
. Saw blade
22
was aligned with scribe lines
14
using an optical alignment system in a well-known manner. Saw blade
22
cut through wafer
10
along scribe lines
14
. In this manner, integrated circuits
12
were singulated. Tape
20
supported wafer
10
during sawing and supported the singulated integrated circuits
12
after sawing was complete.
Generally, width WF of scribe lines
14
was sufficient to accommodate the width of the saw cut plus tolerance in the positioning of saw blade
22
. Stated another way, width WF of scribe lines
14
was sufficiently large such that the saw cut made by saw blade
22
was always within a scribe line
14
. For example, saw blade
22
is within scribe line
14
B in FIG.
1
.
Since the optical alignment system used scribe lines
14
directly to align saw blade
22
, saw blade
22
was aligned to scribe lines
14
to within tight tolerance. Accordingly, scribe lines
14
were relatively narrow and, more particularly, were only slightly wider than saw blade
22
. To illustrate, width WF was within the range of 0.002 inches (0.051 mm) to 0.008 inches (0.203 mm).
In certain instances, it was important to protect the front-side surface of the wafer during sawing, e.g., from shards and particulates generated during sawing. To protect the front-side surface, the wafer was sawed from the back-side surface of the wafer as discussed below in reference to FIG.
2
.
FIG. 2
is a cross-sectional view of a section of a wafer
30
being cut from a back-side surface
30
B of wafer
30
in accordance with the prior art. To protect a front-side surface
30
F of wafer
30
, front-side surface
30
F was attached to a tape
32
. Tape
32
supported wafer
30
during sawing.
Saw blade
22
was aligned with scribe lines
14
-
1
on front-side surface
30
F of wafer
30
using a two-step process. First, tape
32
was aligned with scribe lines
14
-
1
. Front-side surface
30
F was attached to tape
32
. Tape
32
had area greater than the area of front-side surface
30
F such that tape
32
had an exposed region, which extended beyond wafer
30
. Tape
32
had alignment marks in the exposed region of tape
32
. As an example, see alignment holes
30
a
and
30
b
of Roberts, Jr. et al., U.S. Pat. No. 5,362,681, which is herein incorporated by reference in its entirety. In the above manner, scribe lines
14
-
1
were aligned with the alignment marks of tape
32
.
Second, saw blade
22
was aligned with the alignment marks of tape
32
. Wafer
30
was then sawed with saw blade
22
from back-side surface
30
B. However, since saw blade
22
was aligned indirectly to scribe lines
14
-
1
using alignment marks of tape
32
, a large tolerance was associated with the alignment of saw blade
22
to scribe lines
14
-
1
.
To accommodate this large tolerance, each of scribe lines
14
-
1
had a relatively large width WB. More particularly, referring now to
FIGS. 1 and 2
together, width WB of scribe lines
14
-
1
of wafer
30
, which was designed to be cut from back-side surface
30
B, was significantly larger than width WF of scribe lines
14
of wafer
10
, which was designed to be cut from front-side surface
10
F. To illustrate, width WB was approximately 0.012 inches (0.305 mm) or more.
Disadvantageously, forming scribe lines
14
-
1
with a relatively large width WB resulted in less integrated circuits
12
for any given size wafer
30
than the corresponding number of integrated circuits
12
formed in the same size wafer
10
, i.e., there was a loss of yield of integrated circuits
12
from wafer
30
. As a result, the cost of each integrated circuit
12
from wafer
30
was greater than the cost of each integrated circuit
12
from wafer
10
. However, it is desirable to minimize the cost of each integrated circuit
12
.
SUMMARY OF THE INVENTION
In accordance with the present invention, a method includes identifying and determining a position of a scribe grid on a front-side surface of a wafer with a camera. Based on this information, a computer aims a laser at a first location on a back-side surface of the wafer. The laser is fired to form a first alignment mark on the back-side surface of the wafer. Advantageously, the alignment mark is positioned with respect to the scribe grid to within tight tolerance, e.g., to within 0.001 inches (0.025 millimeters) or less.
The front-side surface of the wafer is attached to a tape to protect the front-side surface of the wafer during sawing. A saw blade is aligned with a scribe line of the scribe grid using the alignment mark on the back-side surface of the wafer. The wafer is cut from the back-side surface along the scribe line with the saw blade.
Advantageously, the wafer is cut from the back-side surface thus protecting the front-side surface of the wafer and, more particularly, the integrated circuits. Of further importance, the saw blade is precisely aligned to the scribe line using the alignment mark such that the scribe line is not fabricated with the extra large width of scribe lines of conventional wafers designed to be cut from the back-side surface.
Recall that in the prior art, in certain instances, it was important to cut the wafer from the back-side surface. However, to accommodate the large tolerance associated with back-side wafer cutting, the wafer designed to be cut from the back-side surface was formed with relatively wide scribe lines. Disadvantageously, forming the scribe lines with a relatively large width resulted in less integrated circuits for any given size wafer, i.e., a loss of yield. This resulted in a substantial increase in the cost of the integrated circuits.
In stark contrast, the wafer is cut from the back-side surface in accordance with the present invention without the associated loss of yield of the prior art. As a result, the integrated circuits of the wafer are protected during singulation yet are fabricated without the associated substantial increase in cost of the prior art.
In accordance with another embodiment of the present invention, an array of packages is marked. In accordance with this embodiment, a back-side surface of the array is scanned by a camera to identify and determine the position of fiducials on the back-side surface. Based on this information, a computer aims a laser at a first location on a front-side surface of the array. The laser is fired to form an alignment mark on the front-side surface of the array. Advantageously, the alignment mark is positioned with respect to the fiducials to within tight tolerance, e.g., to within 0.001 inches (0.025 millimeters) or less.
The back-side surface of the array is attached to a tape. A saw blade is aligned with the array using the alignment mark as a reference. The array is cut with the saw blade thus singulating the packages.
A pick and place machine removes the packages from the tape. Advantage
Glenn Thomas P.
Swiss Gary L.
Webster Steven
Amkor Technology Inc.
Gunnison McKay & Hodgson, L.L.P.
Hodgson Serge J.
Luk Olivia
Niebling John F.
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