III-V nitride based semiconductor light emitting device

Details III-V nitride based semiconductor light emitting device III-V nitride based semiconductor light emitting device

1999-12-28

2003-06-10

Thomas, Tom (Department: 2811)

Active solid-state devices (e.g., transistors, solid-state diode

Combined with electrical contact or lead

Of specified material other than unalloyed aluminum

C257S094000, C257S099000, C438S022000, C438S024000, C438S604000

Reexamination Certificate

active

06577006

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device composed BN (boron nitride), GaN (gallium nitride), AlN (aluminum nitride), InN (indium nitride) or TlN (thallium nitride) or an III-V group nitride based semiconductor (hereinafter referred to as a nitride based semiconductor) which is their mixed crystal and a method of fabricating the same.
2. Description of the Background Art
In recent years, GaN based light emitting semiconductor devices have been put to practical use as light emitting semiconductor devices such as light emitting diodes or semiconductor laser devices which emit light in blue or violet. Transistors using GaN based semiconductors have been also proposed. In such GaN based semiconductor devices, electrodes in ohmic contact with the GaN based semiconductor are required.
FIGS. 6 and 7
are schematic cross-sectional views showing the steps of an example of a method of fabricating a conventional GaN based light emitting diode.
As shown in FIG.
6
(
a
), a GaN buffer layer
22
, an n-type GaN layer
23
, and a p-type GaN layer
24
are first successively formed on a sapphire substrate
21
. Thereafter, a partial region from the p-type GaN layer
24
to the n-type GaN layer
23
is etched by an RIE (Reactive Ion Etching) method or the like, to expose the n-type GaN layer
23
.
As shown in FIG.
6
(
b
), a photoresist pattern
31
is then formed on the p-type GaN layer
24
and on the exposed upper surface of the n-type GaN layer
23
. The photoresist pattern
31
has an opening
32
on the p-type GaN layer
24
. In this state, a Pt film
25
a
having a thickness of 2000 Å is formed by an electron beam evaporation method on the p-type GaN layer
24
inside the opening
32
and on the photoresist pattern
31
.
As shown in FIG.
6
(
c
), the Pt film
25
a
on the photoresist pattern
31
, together with the photoresist pattern
31
, is then removed by a lift-off method.
As shown in FIG.
7
(
d
), a photoresist pattern
33
is then formed on the p-type GaN layer
24
, on a p electrode
25
, and on the exposed upper surface of the n-type GaN layer
23
. The photoresist pattern
33
has an opening
34
on the exposed upper surface of the n-type GaN layer
23
. In this state, a Ti film
26
a
having a thickness of 200 Å and an Al film
27
a
having a thickness of 5000 Å are successively formed by an electron beam evaporation method on the upper surface of the n-type GaN layer
23
inside the opening
34
and on the photoresist pattern
33
.
Further, as shown in FIG.
7
(
e
), the Ti film
26
a
and the Al film
27
a
on the photoresist pattern
33
, together with the photoresist pattern
33
, are removed by a lift-off method. Thereafter, heat treatment for five minutes is carried out at a temperature of 600° C. in an N
2
gas atmosphere.
In the above-mentioned manner, p-side and n-side ohmic electrodes are formed.
The p electrode
25
composed of a Pt film in the above-mentioned conventional GaN based light emitting diode has a weak adhesive force. Accordingly, the p electrode
25
is easily stripped in the subsequent processes such as wire bonding. Further, the p electrode
25
is stripped relatively simply when a measuring needle is brought into contact therewith in examination of ohmic characteristics, for example.
On the other hand, alloying by heat treatment is required in order to obtain ohmic contact. Further, the p electrode
25
and an n electrode
30
must be formed in different processes. Consequently, the processes of forming the p electrode
25
and the n electrode
30
become complicated, so that it takes long.
An ohmic electrode having a laminated structure of a Ti film and an Au film has been also proposed. The ohmic electrode can be formed without being alloyed by heat treatment. However, the resistance of the ohmic electrode is easily increased at the time of heat-treating the other layers.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a semiconductor device comprising a stable ohmic electrode which is not easily stripped and can be formed in a simple process on a nitride based semiconductor.
Another object of the present invention is to provide a method of fabricating a semiconductor device in which an ohmic electrode which is not easily stripped and is stable can be formed in a simple process on a nitride based semiconductor.
A semiconductor device according to one aspect of the present invention comprises a p-type nitride based semiconductor; and an ohmic electrode formed on the p-type nitride based semiconductor. The ohmic electrode comprises a first metal film having a thickness of not less than 3 Å nor more than 150 Å which is formed in contact with the p-type nitride based semiconductor and is composed of titanium, and a second metal film which is formed in contact with the first metal film and is composed of platinum or palladium.
In the ohmic electrode in the semiconductor device, the first metal film composed of titanium has the function of cleaning the surface of the p-type nitride based semiconductor, to make ohmic contact between the second metal film composed of platinum or palladium and the p-type nitride based semiconductor easy. Consequently, the ohmic electrode is formed in a simple process without being alloyed by heat treatment.
Since the first metal film composed of titanium has a strong adhesive force to the p-type nitride based semiconductor, an adhesive force of the ohmic electrode to the p-type nitride based semiconductor is improved. Consequently, the ohmic electrode is not easily stripped.
Particularly, the thickness of the first metal film is preferably not less than 3 Å nor more than 130 Å, more preferably not less than 3 Å nor more than 130 Å, still more preferably not less than 3 Å nor more than 50 Å, and most preferably not less than 3 Å nor more than 10 Å. Consequently, sufficient ohmic characteristics can be obtained while preventing the ohmic electrode from being stripped.
The semiconductor device may further comprise a third metal film which is formed in contact with the second metal film and is composed of gold.
Thus, wire bonding can be easily performed. In this case, since the ohmic electrode composed of the first metal film and the second metal film can be formed without being alloyed by heat treatment, the first metal film, the second metal film and the third metal film can be formed in the same process.
The p-type nitride based semiconductor may contain at least one of boron, gallium, aluminum, indium and thallium.
A semiconductor device according to another aspect of the present invention comprises an n-type nitride based semiconductor; and an ohmic electrode formed on the n-type nitride based semiconductor. The ohmic electrode comprises a first metal film having a thickness of not less than 3 Å nor more than 100 Å which is formed in contact with the n-type nitride based semiconductor and is composed of titanium, and a second metal film which is formed in contact with the first metal film and is composed of platinum or palladium.
In the ohmic electrode in the semiconductor device, the first metal film composed of titanium has the function of cleaning the surface of the n-type nitride based semiconductor, to make ohmic contact between the second metal film composed of platinum or palladium and the n-type nitride based semiconductor easy. Consequently, the ohmic electrode is formed in a simple process without being alloyed by heat treatment.
Since the first metal film composed of titanium has a strong adhesive force to the n-type nitride based semiconductor, an adhesive force of the ohmic electrode to the n-type nitride based semiconductor is improved. Consequently, the ohmic electrode is not easily stripped.
Particularly, the thickness of the first metal film is preferably not less than 3 Å nor more than 50 Å, more preferably not less than 3 Å nor more than 30 Å, and still more preferably not less than 3 Å no

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