Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal
Reexamination Certificate
2000-03-21
2003-07-15
Chaudhuri, Olik (Department: 2823)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
C438S031000
Reexamination Certificate
active
06593159
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor substrate including wafer-like plate-shaped crystal and a compound semiconductor crystal layer formed on the plate-shaped crystal, a method of manufacturing the semiconductor substrate, a semiconductor device, such as a semiconductor laser diode used as a light source for a pickup for an optical disk and the like, a light emitting diode used as a light source for a display device and the like, and a field effect transistor, and a method of manufacturing the semiconductor device.
Recently, nitride compound semiconductors such as GaN, InN and AlN are in the limelight as a material for a short wavelength light source and an environment resistant device because such semiconductors are of direct transition type and have a large energy gap. For example, GaN has an energy gap as large as approximately 3.4 eV at room temperature, and hence is a promising material for a light emitting element for emitting light in a range between the blue region and the ultraviolet region.
In forming a film of nitride compound semiconductor crystal, metal organic vapor deposition (hereinafter referred to as the MOCVD) is generally adopted. In the formation of a film of, for example, GaN crystal, trimethylgallium and ammonia are used as the materials, and Ga obtained by decomposing trimethylgallium and N obtained by decomposing ammonia are adhered onto a substrate having been heated at a high temperature. Thus, a monocrystal film of GaN can be obtained.
At present, a sapphire substrate is generally used as a substrate for filming the nitride compound semiconductor crystal.
In a sapphire substrate, however, the lattice constants in the a-axis direction and the c-axis direction are 4.76 Å and 12.99 Å, respectively, while those of the GaN crystal are 3.19 Å and 5.19 Å, respectively. In this manner, there is large lattice mismatch between the sapphire substrate and GaN crystal, and therefore, threading dislocations in number larger than 1×10
10
cm
−2
are caused during the film formation by the MOCVD from the interface between the sapphire substrate and the GaN crystal toward the inside of the GaN crystal.
Furthermore, since the sapphire substrate and the GaN crystal have different thermal expansion coefficients, the threading dislocations can be grown or cracks derived from the threading dislocations can be caused within the GaN crystal during temperature increase/decrease between room temperature and a high temperature exceeding 1000° C. in the MOCVD.
Since the threading dislocation can work as a non-radiative recombination center or can capture a carrier, the performance improvement of a light emitting diode can be obstructed by the threading dislocation. Also, when a light emitting diode is manufactured by using GaN crystal including a large number of threading dislocations, a leakage current can flow, or emission failure or device destruction can be caused due to degradation in quantum efficiency. In particular, when the threading dislocations are caused in a light emitting portion of the semiconductor device, the device destruction can acceleratingly proceed, resulting in largely decreasing the life time of the device.
As means for decreasing the threading dislocations, a method in which a buffer layer is inserted between the sapphire substrate and the GaN crystal is widely adopted at present. In this method, since a stress caused by the lattice mismatch between the sapphire substrate and the GaN crystal can be relaxed by the buffer layer, the occurrence of the threading dislocations within the GaN crystal can be suppressed. In addition, since a stress caused due to the difference in the thermal expansion coefficient during the temperature increase/decrease can be also relaxed by the buffer layer, the growth of the threading dislocations and the occurrence of cracks within the GaN crystal can be suppressed.
Furthermore, Japanese Laid-Open Patent Publication No. 4-297023 describes that a buffer layer of a GaN layer formed between a sapphire substrate and GaN crystal can effectively suppress the threading dislocations and that a light emitting diode manufactured by using this technique can attain luminance more than ten times as large as that of a conventional light emitting diode.
The light emitting diode including the buffer layer of a GaN layer inserted between the sapphire substrate and the GaN crystal disclosed in Japanese Laid-Open Patent Publication No. 4-297023 will now be described with reference to FIG.
15
.
As is shown in
FIG. 15
, the light emitting diode includes a buffer layer
101
of undoped GaN and a device structure
102
having a doublehetero junction structure successively stacked on a sapphire substrate
100
. The device structure
102
includes an n-type GaN layer
103
working as a first cladding layer, an undoped IN
0.2
Ga
0.8
N layer
104
working as an active layer and a p-type GaN layer
105
working as a second cladding layer successively stacked. The device structure
102
is partially removed by dry etching so as to bare the inside of the n-type GaN layer
103
. On the p-type GaN layer
105
, a p-type electrode
106
is formed, and on the etched portion of the n-type GaN layer
103
an n-type electrode
107
is formed. The sapphire substrate
100
has a thickness of 150 &mgr;m and the device structure
102
has a thickness of 50 &mgr;m.
The present inventors manufactured a light emitting diode by a method described in Japanese Laid-Open Patent Publication No. 4-297023. Owing to the buffer layer
101
inserted between the sapphire substrate
100
and the device structure
102
, the occurrence of the threading dislocations and cracks was suppressed in the device structure
102
, but still there remained threading dislocations of approximately 1×10
10
cm
−2
.
Thus, although the occurrence of the threading dislocations and cracks can be suppressed by the buffer layer
101
inserted between the sapphire substrate
100
and the device structure
102
, the suppressing effect is still disadvantageously limited.
SUMMARY OF THE INVENTION
In view of the aforementioned problem, a first object of the invention is realizing a semiconductor substrate with low threading dislocation density and low crack density on which threading dislocation and cracks occurring within a device structure can be largely decreased, and a second object is realizing a semiconductor device in which threading dislocations and cracks occurring within a compound semiconductor crystal layer formed on plate-shaped crystal as well as within a device structure formed on the compound semiconductor crystal layer can be largely decreased.
The present inventors thought that the threading dislocations occurring in the device structure
102
could be decreased when part of a large number of threading dislocations proceeding from the interface between the sapphire substrate
100
and the buffer layer
101
toward the inside of the device structure
102
were made to proceed from the interface between the sapphire substrate
100
and the buffer layer
101
toward the inside of the sapphire substrate
100
.
Therefore, they made various examinations on measures for making threading dislocations proceed from the interface between the sapphire substrate
100
and the buffer layer
101
toward the inside of the sapphire substrate
100
. As a result, they found that the threading dislocations could proceed from the interface toward the inside of the sapphire substrate
100
by setting the thickness of the sapphire substrate
100
smaller than the thickness of the n-type GaN layer
103
, thereby decreasing the threading dislocations proceeding from the interface toward the inside of the n-type GaN layer
103
.
Also, they found that when the thus obtained sapphire substrate
100
and n-type GaN layer
103
are used as a substrate and a device structure is formed on this substrate, a semiconductor device including a smaller number of threading dislocations caused in the device structure can be realized.
The
Hashimoto Tadao
Imafuji Osamu
Ishida Masahiro
Yuri Masaaki
Chaudhuri Olik
Kebede Brook
McDermott & Will & Emery
LandOfFree
Semiconductor substrate, semiconductor device and method of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Semiconductor substrate, semiconductor device and method of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor substrate, semiconductor device and method of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3032085