Method for fabricating semiconductor light emitting device

Details Method for fabricating semiconductor light emitting device Method for fabricating semiconductor light emitting device

2002-03-14

2003-04-22

Nelms, David (Department: 2818)

Semiconductor device manufacturing: process

Making device or circuit emissive of nonelectrical signal

C438S040000

Reexamination Certificate

active

06551848

ABSTRACT:

Priority is claimed to Patent Application number 2001-29253 filed in Rep. of Korea on May 26, 2001, herein incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for fabricating a semiconductor light emitting device, and more particularly, to a method for fabricating a semiconductor light emitting device by which an n-type electrode can be effective formed by processing the bottom of a substrate.
2. Description of the Related Art
The need for high-density information recording has increased the demand for semiconductor visible-light emitting devices. In particular, the market release of high-density optical recording media such as digital versatile discs (DVDs) has boosted the need for visible-light emitting laser diodes. There are available a variety of compound semiconductor laser diodes (LDs) capable of visible laser emission. In particular, III-V nitride compound semiconductor laser diodes, a direct transition type that ensures high-efficiency laser oscillation, have received considerable attention because of the ability to emit blue laser light. Semiconductor-based blue light emitting diodes (LEDs) also are attractive because they can be applied to lightening devices.
In general, III-V nitride compound semiconductor light emitting devices are formed on gallium nitride (GaN) substrates to improve their light emitting characteristics.
FIG. 1
is a sectional view of a conventional GaN-based LED formed on a GaN substrate. Referring to
FIG. 1
, an n-doped GaN layer
4
, an active layer
6
, and a p-doped GaN layer
8
are sequentially formed on a GaN substrate
2
. A transparent p-type electrode
10
is formed on the p-doped GaN layer
8
, and a bonding pad
12
is formed in a predetermined region of the p-type electrode
10
.
In
FIG. 1
, reference numeral
14
denotes an n-type electrode formed on the bottom of the GaN substrate
2
. The n-type electrode
14
is attached to the bottom of the GaN substrate
2
after grinding, lapping, or polishing the bottom of the GaN substrate
2
to a thickness by which a resulting light emitting device can still be supported. During this polishing step, the bottom of the GaN substrate
2
is damaged, thereby resulting in a damaged layer
16
on the bottom of the GaN substrate
2
. As a result, the n-type electrode
14
is attached to the damaged layer
16
.
Accordingly, the properties of the resulting light emitting device degrade due to poor attachment of the n-type electrode
14
to the GaN substrate
2
. For example, a relative light emitting efficiency with respect to the voltage applied to the n-type electrode
14
may be lowered. Also, the light emission during operation of the light emitting device becomes poor, thereby shortening the lifespan.
FIG. 2
is a sectional view of a conventional GaN laser diode (LD) formed on a GaN substrate. Referring to
FIG. 2
, an n-doped GaN layer
24
, an n-doped AlGaN/GaN cladding layer
26
, an n-doped GaN waveguide layer
28
, an InGaN active layer
30
, a p-doped GaN waveguide layer
32
, a p-doped AlGaN/GaN cladding layer
34
, and a p-doped GaN layer
36
are sequentially formed on a GaN substrate
22
. The p-doped AlGaN/GaN cladding layer
34
has a ridge to be used as a current path, and the p-doped GaN layer
36
is formed on the ridge. A passivation layer
38
is formed on the p-doped AlGaN/GaN cladding layer
34
having the ridge to expose a current path region of the p-doped GaN layer
36
. A p-type electrode
40
is formed on the passivation layer
38
in contact with the exposed region of the p-doped GaN layer
36
. An n-type electrode
42
is formed on the bottom of the GaN substrate
22
by the same process as for the n-type electrode
14
of the LED shown in FIG.
1
. As a result, a damaged layer
44
is formed on the bottom of the GaN substrate
22
of the LD, and the n-type electrode
42
is formed on the damaged layer
44
, thereby causing similar problems as those occurring in the LED.
In general, when forming a III-V nitride-based compound semiconductor light devices on a GaN substrate, the bottom of the substrate is subjected to mechanical polishing to reduce the thickness of the substrate for the purpose of heat dissipation and device isolation for LEDs, and cleaved plane formation for LDs. However, during this polishing process, a damaged layer is formed on the bottom of the substrate, as described above, so that attachment of the n-type electrode to the bottom of the GaN substrate becomes unstable, thereby degrading device properties.
SUMMARY OF THE INVENTION
To solve the above-described problems, it is an object of the present invention to provide a method of fabricating a semiconductor light emitting device by which formation of a damaged layer on the bottom of a substrate on which a light emitting device is formed, in processing the bottom of the substrate is prevented so that device properties are improved.
To achieve the object of the present invention, there is provided a method for fabricating a semiconductor light emitting device, the method comprising: forming a light emitting construct including a p-type electrode on a n-type substrate; etching a bottom surface of the n-type substrate; and forming an n-type electrode on the etched bottom surface of the n-type substrate.
It is preferable that, after forming the light emitting construct and before etching the bottom surface of the n-type substrate, the bottom surface of the n-type substrate is mechanically polished. It is preferable that the light emitting construct is for a light emitting diode (LED) or a laser diode (LD).
It is preferable that the bottom surface of the n-type substrate is dry or wet etched. The dry etching may be accomplished by a method selected from the group consisting of chemical assisted ion beam etching (CAIBE), electron cyclone resonance (ECR) etching, inductively coupled plasma (ICP) etching, and reactive ion etching (RIE). Preferably, the dry etching uses Cl
2
, BCl
3
or HBr gas as a main etching gas. In this case, Ar or H
2
gas may be used as an additional gas for the drying etching. Preferably, the wet etching is accomplished using a KOH, NaOH, or H
3
PO
4
as an etchant.
In the semiconductor light emitting device fabricating method according to the present invention, the bottom surface of the n-type substrate may be polished by grinding or lapping.
It is preferable that the n-type electrode is formed by at least one material selected from the group consisting of titanium (Ti), aluminium (Al), indium (In), tantalum (Ta), palladium (Pd), cobalt (Co), nickel (Ni), silicon (Si), germanium (Ge), and silver (Ag), and is thermally treated at a temperature of 0-500° C.
The n-type substrate is preferably an n-type Group III-V compound semiconductor substrate, more preferably, an n-type GaN substrate.
According to the present invention, formation of a damaged layer in processing the bottom of the GaN substrate can be prevented so that stable attachment of the n-type on the bottom of the GaN substrate is ensured, thereby improving the properties of a light emitting device formed on the GaN substrate.


REFERENCES:
patent: 4876569 (1989-10-01), Nishitoku
patent: 5439843 (1995-08-01), Sakaguchi et al.
patent: 5744857 (1998-04-01), Yamamoto
patent: 5956362 (1999-09-01), Yokogawa et al.
patent: 6342405 (2002-01-01), Major et al.
patent: 6380551 (2002-04-01), Abe et al.

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