Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Groove formation
Reexamination Certificate
2002-10-30
2004-10-19
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Groove formation
C438S034000, C438S041000, C438S046000
Reexamination Certificate
active
06806115
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for producing a semiconductor light emitting device, and specifically a method for producing a semiconductor light emitting device including a nitride semiconductor layer as a light emitting layer on a silicon substrate; and a semiconductor light emitting device produced by such a method.
2. Description of the Related Art
A light emitting device using a nitride semiconductor material, such as GaN, InN, AlN, or a mixed crystal thereof, usually includes a nitride semiconductor layer formed of, for example, In
x
Ga
1-x
N crystals, as a light emitting layer on a sapphire substrate.
Recently, silicon (Si) substrates which are less expensive and have a larger area than a sapphire substrate have been produced. A nitride semiconductor light emitting device can be produced at lower cost by using such an Si substrate instead of a sapphire substrate.
A nitride semiconductor light emitting device produced using an Si substrate has the following problem. A nitride semiconductor layer has a larger thermal expansion coefficient than that of an Si substrate. When the temperature is once raised for epitaxial growth and then is lowered to room temperature, the nitride semiconductor layer shrinks more significantly than the Si substrate, due to the difference in the thermal expansion coefficient between the Si substrate and the nitride semiconductor layer.
FIG. 12
is a schematic perspective view of a nitride semiconductor light emitting device
500
using an Si substrate
91
. As shown in
FIG. 12
, when the temperature is raised to form a nitride semiconductor layer
92
on the Si substrate
91
by epitaxial growth and then lowered to room temperature, the nitride semiconductor layer
92
significantly shrinks. As a result, tensile stress is applied to an interface between the Si substrate
91
and the nitride semiconductor layer
92
, thus possibly causing cracks
93
.
In the case of a nitride semiconductor light emitting device having a double-hetero structure, when the cracks
93
are generated, an invalid leak current which does not contribute to light emission is increased in magnitude. This prevents output of high luminance emission. In order to produce a nitride semiconductor device having a long life and high luminance emission, it is indispensable to prevent the generation of such cracks
93
.
FIG. 13
is a schematic cross-sectional view illustrating a production step of another conventional semiconductor light emitting device
600
.
The semiconductor light emitting device
600
is produced as follows. A mask layer
41
B having openings (windows)
42
B is formed on an Si substrate
91
A using an oxide layer or the like, and then a nitride semiconductor layer
92
A is formed in each of the openings
42
B of the mask layer
41
B by epitaxial growth. Owing to such a step, a tensile stress applied to an interface between the Si substrate
91
A and the nitride semiconductor layer
92
A is alleviated, thus preventing the generation of cracks.
This method has the following problem. Depending on the size of the mask layer
41
B, the width and material of the mask layer
41
B, and the growth temperature and rate, the material used for the epitaxial growth remains on the mask layer
41
B. This raises the concentration of the material in a peripheral portion of the nitride semiconductor layer
92
A in the opening
42
B, which is in the vicinity of the mask layer
41
B, is excessively high. As a result, as shown in
FIG. 13
, the peripheral portion of the nitride semiconductor layer
92
A in the opening
42
B is about three times as thick as a central portion thereof, due to growth referred to as “edge growth”. Such a thick peripheral portion is subjected to significant local distortion, and as such is susceptible to being cracked.
As described above, the method of forming the nitride semiconductor layer
92
A by epitaxial growth in the opening
42
B prevents the central portion thereof from being cracked, but has a risk of causing cracks in the peripheral portion of the nitride semiconductor layer
92
A due to the local distortion applied to the thick portion.
When a substrate formed of a material having a smaller thermal expansion coefficient than a nitride semiconductor material, such as Si, it is difficult to produce a nitride semiconductor light emitting device having a long life and high luminance emission, with prevention of crack generation. It is not sufficient to form a nitride semiconductor layer in an opening by epitaxial growth.
SUMMARY OF THE INVENTION
According to one aspect of the invention, a method for producing a semiconductor light emitting device includes the steps of forming a mask layer having a plurality of openings on a surface of a silicon substrate; and forming a column-like multi-layer structure including a light emitting layer in each of the plurality of openings with nitride semiconductor materials. A width between two adjacent openings of the plurality of openings of the mask layer is 10 &mgr;m or less.
According to another aspect of the invention, a method for producing a semiconductor light emitting device includes the steps of forming a mask layer having a plurality of openings on a surface of a silicon substrate; and forming a column-like multi-layer structure including a light emitting layer in each of the plurality of openings with nitride semiconductor materials. A width between two adjacent openings of the plurality of openings of the mask layer is in the range of twice a thickness of the column-like multi-layer structure to 40 &mgr;m, the thickness being in a direction vertical to the planar direction of the silicon substrate.
In one embodiment of the invention, the method for producing a semiconductor light emitting device further includes the steps of removing the mask layer and providing an insulating layer for electrically insulating the column-like multi-layer structures from each other on an area of the surface of the silicon substrate from which the mask layer has been removed, and forming a transparent electrode for electrically connecting the column-like multi-layer structures to each other.
In one embodiment of the invention, the method for producing a semiconductor light emitting device further includes the steps of forming a transparent electrode on each column-like multi-layer structure; and dividing an assembly of the silicon substrate and the column-like multi-layer structures into a plurality of chips, such that each chip includes one column-like multi-layer structure.
In one embodiment of the invention, the plurality of openings are each square or rectangular. The plurality of openings each have a side in the range of 50 &mgr;m to 150 &mgr;m.
In one embodiment of the invention, the plurality of openings are each square or rectangular. The plurality of openings each have a side in the range of 200 &mgr;m to 300 &mgr;m.
In one embodiment of the invention, each column-like multi-layer structure includes a hexagonal-system gallium nitride-based compound semiconductor material. The plurality of openings are polygonal. At least one side of each polygonal opening is parallel to a <11-20> axis of the gallium nitride-based compound semiconductor material.
In one embodiment of the invention, the silicon substrate has an Si (111) plane. A <1-10> axis of the silicon substrate is parallel to the <11-20> axis of the gallium nitride-based compound semiconductor material.
In one embodiment of the invention, the mask layer is formed of a material selected from the group consisting of silicon oxide, silicon nitride, and aluminum oxide.
According to still another aspect of the invention, a semiconductor light emitting device produced by the above-described.
Thus, the invention described herein makes possible the advantages of providing a method for producing a semiconductor light emitting device using an Si substrate and still preventing cracks from being generated at an interface between the Si substrate and a nitride semiconductor layer; and a
Dohkita Tsuyoshi
Honda Yoshio
Koide Norikatsu
Kuroiwa Yousuke
Sawaki Nobuhiko
Malsawma Lex H.
Morrison & Foerster / LLP
Sharp Kabushiki Kaisha
Smith Matthew
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