Stone working – Splitting – shearing – and punching
Reexamination Certificate
2000-10-25
2002-12-03
Hail, III, Joseph J. (Department: 3723)
Stone working
Splitting, shearing, and punching
C125S023020
Reexamination Certificate
active
06488021
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for producing a semiconductor element and a cleavage apparatus for use in the method.
2. Description of the Related Art
A conventional method for producing a semiconductor element (e.g., a semiconductor laser element) will be described with reference to
FIGS. 5A through 5C
. Initially, a semiconductor multi-layer structure
11
is provided as a semiconductor wafer
1
by successively laminating a plurality of semiconductor layers including an active layer. A plurality of grooves
15
to be used for cleavage (hereinafter referred to as cleavage grooves) are provided on the front surface of the semiconductor multi-layer structure
11
along a longitudinal direction of the cavity of a semiconductor laser element (direction X in FIG.
5
A). The grooves
15
are evenly spaced and parallel to each other. The active layer is provided about 4 &mgr;m below the front surface of the semiconductor multi-layer structure
11
.
Thereafter, a stripe-patterned electrode
13
is provided on the entire front surface of the semiconductor multi-layer structure
11
excluding the cleavage grooves
15
. A back electrode
12
is provided on the entire back surface of the semiconductor multi-layer structure
11
. The wafer
1
is cut into rectangles. A plurality of short scratches are provided at an edge of the rectangular semiconductor multi-layer structure
11
along the longitudinal direction of the cavity of a semiconductor laser element (direction X). The scratches are evenly spaced as shown in FIG.
5
A.
Thereafter, the integral of the semiconductor multi-layer structure
11
, the patterned electrode
13
, and the back electrode
12
is cleaved (first cleavage) in a direction perpendicular to the cleavage grooves
15
provided between the stripes of the patterned electrode
13
, using the scratches
14
as starting points of cleavage. Thereby, a plurality of multi-element bars
16
are obtained. The multi-element bar
16
has the back electrode
12
a
on the entire back surface of he bar-shaped semiconductor multi-layer structure
11
and plurality of patterned electrodes
13
separated by the cleavage grooves
15
on the front surface of the bar-shaped semiconductor multi-layer structure
11
as shown in FIG.
5
B.
Thereafter, referring to
FIG. 5C
, each multi-element bar
16
is cleaved (second cleavage) along the cleavage grooves
15
, resulting in a plurality of semiconductor laser elements
17
. Each semiconductor laser element
17
has the patterned electrode
13
on the front surface of the semiconductor multi-layer structure
11
and the back electrode
12
a
on the back surface of the semiconductor multi-layer structure
11
. When a voltage is applied between the patterned electrode
13
and the back electrode
12
a
, laser light is emitted from a facet produced by the first cleavage.
The cleavage grooves
15
are, for example, scratches (grooves) formed mechanically by a diamond needle of a scriber or the like. In this case, there is a micro crack extending from the cleavage groove
15
inward the semiconductor multi-layer structure
11
. The micro crack reduces the strength of crystal. Therefore, when a load is applied from the back electrode
12
a
side to the cleavage groove
15
provided on the multi-element bar
16
, the multi-element bar
16
is easily cleaved along the micro crack having a lesser crystal strength. In order to conduct the second cleavage to the multi-element bar
16
on which the cleavage grooves
15
(scratches) are provided, a relatively small load is applied to the back electrode
12
a
in a longitudinal direction of the multi-element bar
16
. For example, a load is applied to the back electrode
12
a
by a roller being rotated and moved on the back electrode
12
a.
Japanese Laid-Open Publication No. 6-338662 discloses a method for forming scratches (grooves) as the cleavage grooves
15
on a semiconductor wafer in which semiconductor laser elements are provided. When the cleavage grooves
15
are formed mechanically used a scriber or the like, a plurality of cleavage grooves
15
need to be reliably provided from one edge to the other edge of the patterned electrode
13
. Such a process reduces working efficiency.
Further, the semiconductor wafer
1
is easily broken along the scratches which is being formed on the semiconductor wafer
1
. Breaks also easily occur along the scratches during the first cleavage in a direction perpendicular to the scratches. As a result, a yield of the semiconductor laser elements is lowered.
To address the above-described problems, the cleavage grooves
15
may be provided by etching. In this case, the front surface of the semiconductor wafer is first coated with a resist film, excluding portions thereof in which the cleavage grooves
15
will be provided. Such portions which has not been covered with the resist film are etched, resulting in the cleavage grooves
15
having a V-shaped cross-section as shown in FIG.
7
. In such a process, all the cleavage grooves
15
are formed at once. Therefore, the working efficiency of production of the cleavage grooves
15
is improved as compared with when the cleavage grooves
15
are formed mechanically using a scriber or the like as described above.
Japanese Laid-Open Publication No. 62-137894 discloses a cleavage apparatus
2
shown in FIG.
6
. In the cleavage apparatus
2
, etched grooves are provided as the cleavage grooves
15
on the multi-element bar
16
. The multi-element bar
16
is placed on a film
31
, and a sheet
34
is provided on the multi-element bar
16
. Further, the sheet
34
is covered with a film
32
. Thereafter, a load is applied via the film
31
to the multi-element bar
16
using a roller
33
so that the multi-element bar
16
is cleaved.
As described above, when the cleavage grooves
15
(etched grooves) are formed by etching, substantially no micro crack is generated inside the semiconductor multi-layer structure
11
unlike the scratches mechanically provided using a diamond needle or the like. Therefore, portions having low strength are not clearly provided inside the semiconductor multi-layer structure
11
. Therefore, when the multi-element bar
16
is subjected to the second cleavage, a greater load is required as compared with when the multi-element bar
16
has the cleavage grooves
15
mechanically formed. In this case, the multi-element bar
16
cannot be reliably cleaved (second cleavage) when a load applied by the roller
33
is relatively low.
In particular, in the apparatus
2
, the multi-element bar
16
is sandwiched by a pair of the films
31
and
32
, and is further held by a ring, thereby providing tension for the film
31
. A load is applied to the multi-element bar
16
using the roller
33
. Therefore, when the tension of the film
31
is changed, the load applied to the multi-element bar
16
is likely to be changed. Moreover, the film
31
or the multi-element bar
16
may be displaced due to the pressure caused by the roller
33
. The above-described reasons makes it difficult to apply a constant load to the multi-element bar
16
. It is also difficult to rotate the roller
33
smoothly while applying a constant load to the multi-element bar
16
sandwiched by a pair of the films
31
and
32
.
As described above, it is difficult to cleave the multi-element bar
16
sandwiched by a pair of the films
31
and
32
by applying a constant load to the multi-element bar
16
.
Japanese Laid-Open Publication No. 54-93356 discloses a cleavage method in which the cleavage grooves
15
having a V-shaped cross-section is formed by etching, and the insides of the cleavage grooves
15
are subjected to rough surface treatment, thereby providing micro cracks inside the semiconductor multi-layer structure
11
; and thereafter, by rotating a roller, a load is applied to a surface (back surface) of the multi-element bar
16
opposite the surface on which the cleavage groove
15
are provided so that the multi-element bar
16
is cleaved (second c
Adachi Hideto
Takamori Akira
Yamane Keiji
Hail III Joseph J.
Matsushita Electronics Corporation
RatnerPrestia
Thomas David B.
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