Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Compound semiconductor
Reexamination Certificate
1999-09-24
2001-10-16
Christianson, Keith (Department: 2813)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Compound semiconductor
Reexamination Certificate
active
06303405
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a semiconductor light emitting element, its manufacturing method and a semiconductor light emitting device. More particularly, the invention relates a semiconductor light emitting element made of nitride compound semiconductors with a high quality crystal obtained by easily and reliably dividing a sapphire substrate, its manufacturing method and a semiconductor light emitting device.
Recently, semiconductor light emitting elements such as light emitting diodes (LED) and semiconductor lasers have come to be used in various fields of household electric appliances, office automation appliances, communication devices, industrial measuring instruments, and so on. Particularly, short-wavelength semiconductor lasers are being under vigorous development toward the use in high-density optical disc recording which is expected to become useful in a lot of fields.
Red semiconductor lasers currently being used have been improved in recording density as compared with infrared semiconductor lasers used theretofore. Red semiconductor lasers are light emitting elements made of InGaAlP materials for the band of 600 nm and have already been brought into practical use, with properties improved to a level usable for both read and write operations of optical discs.
However, red semiconductor lasers using these materials involve a number of problems from the standpoint of their materials, such as difficulty in reducing crystal defects and high operation voltages, which should be overcome toward the use in the next-generation optical disc recording, for example. Additionally, their oscillation wavelengths are around 460 nm minimum, and it is difficult to realize oscillation in a wavelength in the order of 420 nm, which is required for the new systems, because of their physical properties.
On the other hand, blue semiconductor lasers are being developed toward higher recording densities. Heretofore, oscillating operations have been confirmed with semiconductor lasers using II-VI compound materials. However, there are many bars against their practical use, such as their reliability which cannot be ensured over 100 hours approximately. Additionally, there are many obstacles from the viewpoint of materials against their applications to the next-generation optical disc systems, etc., such as the difficulty to reduce their oscillation wavelength below 480 nm, for example.
In contrast, nitride compound semiconductor lasers containing GaN (gallium nitride) are basically available for short wavelengths below 350 nm, and actual oscillation in 400 nm has been reported. Also regarding the reliability, it has been confirmed that an LED maintained reliability beyond ten thousand hours. Laser oscillation at a room temperature has also been confirmed recently. As these facts demonstrate, nitride compound semiconductors are materials having excellent properties meeting the requirements for various ways of use thereof, such as light sources for next-generation optical disc recording, for example.
In the present application, “nitride compound semiconductors” include III-V compound semiconductors expressed by the chemical formula B
x
In
y
Al
z
Ga
1−x−y−z
N (0≦x≦1, 0≦y≦1, 0≦z≦1), and group V elements include N and mixed crystals containing phosphorus (P) or arsenic (As) as well.
However, conventional light emitting elements using nitride compound semiconductors involve various problems explained below.
Conventional light emitting elements using nitride compound semiconductors, in general, were epitaxially grown on sapphire substrates. However, because of great differences in lattice constant between sapphire substrates and nitride compound semiconductors, a great deal of crystal defects are inevitably produced in growth crystals. These crystal defects essentially constitute an obstructive factor against improvements of various properties and lifetime of elements.
Additionally, since these elements are formed on insulating sapphire substrates, both the n-side electrode and the p-side electrode must be formed on the same side as the epitaxial growth layers. Therefore, the p-type layer, active layer and n-type layer are partly removed by etching, and the n-side electrode is formed on the n-type layer. In this structure, however, since the part actually operating as the element is formed on a thick sapphire substrate, cleavage for making cavity edges necessary for a laser is difficult.
In order to improve heat dissipation of an element, it is usual to bring the element into close contact with a heat sink. In this structure, however, even when putting the sapphire side in close contact with the heat sink, sufficient radiation of heat cannot be expected because of a low heat conductivity of the sapphire. If the electrode side is put in close contact with the heat sink, heat resistance certainly decreases. However, it is difficult to do so with the element locating the electrodes on the same side with respect to the substrate, and its production yield is bad.
Moreover, since the element has the sapphire substrate on the opposite side from the heat sink, its heat dissipation is still bad.
Furthermore, as far as the element includes the sapphire substrate, a current injected from the electrode must flow horizontally (in the lateral direction) in the element, and resistance of the element increases.
Additionally, since the geometrically shortest path between the p-side electrode and the n-side electrode is along the surface of the element, leak current becomes large.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a nitride compound semiconductor light emitting element excellent in cleavability, heat dissipation, anti-leakage, etc. by easily and reliably separating a sapphire substrate with a good reproducibility, and also relates to its manufacturing method and a semiconductor light emitting device using same.
To attain the object, the invention provides a method for epitaxially growing a nitride compound semiconductor layer on a substrate of sapphire, for example, and easily and reliably separating the substrate. The nitride compound semiconductor layer obtained by separating the substrate can be used as a new substrate to epitaxially grow a high-quality nitride compound semiconductor layer thereon.
By hydride chemical vapor epitaxy (H-CVE) using HCl (hydrochloric acid) as a transport carrier, it is fairly easy to grow a thick crystal layer of a nitride semiconductor. The inventors has noticed, however, that the crystal grown thereby contains a lot of crystal defects, since it uses a sapphire substrate as the growth substrate, and they constitute an obstructive factor against improvements of properties of the light emitting element made thereon.
On the other hand, the semiconductor layer grown by a lateral growth method employing local masks of quartz shows grain boundaries, defects and voids which are produced in portions grown on the quarts mask.
For the purpose of preventing the above-indicated various phenomena, it would be a good idea to grow GaN of approximately 100 &mgr;m on a sapphire substrate, then to remove the sapphire substrate and to use the resulting GaN layer as a substitute substrate. However, the lapping technique normally used for thinning the hard sapphire substrate are not satisfactory in throughput, and are liable to occur cracking or other troubles during the lapping process.
According to the invention, there is provided a method for manufacturing a semiconductor light emitting element, comprising the steps of: forming on a single crystal substrate an abruption mechanism susceptible to a stress; growing an epitaxial base layer of a nitride compound semiconductor on said abruption mechanism; growing an epitaxial light emitting layer of a nitride compound semiconductor on said epitaxial base layer; and separating said epitaxial base layer from said substrate by applying a stress to said abruption mechanism before or after said step of growing an epitaxial light emitting layer.
In rough cl
Itaya Kazuhiko
Nishio Johji
Nunoue Shin-ya
Saito Shinji
Yoshida Hiroaki
Christianson Keith
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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