Manufacturing method of compound semiconductor wafer

Details Manufacturing method of compound semiconductor wafer Manufacturing method of compound semiconductor wafer

2002-01-25

2003-11-18

Fourson, George (Department: 2823)

Semiconductor device manufacturing: process

Formation of semiconductive active region on any substrate

On insulating substrate or layer

C438S489000, C438S507000, C438S503000, C438S795000, C117S090000, C117S103000, C117S104000, C117S915000, C117S952000

Reexamination Certificate

active

06649494

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a manufacturing method of a compound semiconductor wafer made of a compound semiconductor including nitrogen in its composition and used in a short wavelength laser, a high-temperature operating transistor, etc.
Conventionally, it has been known that a compound semiconductor including at least one element selected from Ga, Al, B, As, In, P and Sb and N (hereinafter, referred to as nitride semiconductor) has broad bandgap energy from the ultraviolet region to the visible region, and therefore, is a potential semiconductor material for light emitting and light receiving devices. A typical example of the nitride semiconductor is a compound semiconductor expressed by a general formula B
x
Al
y
Ga
z
In
1-x-y-z
N, where 0≦x≦1, 0≦y≦1, 0≦z≦1, and 0≦x+y+z≦1. Recently, there has been an increasing demand for a good-quality and large-area nitride semiconductor wafer, and most of all, a free-standing wafer (self-standing wafer), realized as an underlying substrate used when manufacturing a device from the nitride semiconductor.
The free-standing nitride semiconductor wafer is a wafer made of a nitride semiconductor alone excluding any material other than the nitride semiconductor. Generally, in order to obtain the free-standing nitride semiconductor wafer, a method of conducting epitaxial growth of a nitride semiconductor film on a substrate made of a material other than the nitride semiconductor and removing the substrate later is used. As is disclosed in, for example, U.S. Pat. No. 6,071,795, a technique of irradiating a beam of laser light from an excimer KrF laser or a Nd/YAG laser to the substrate from the back surface thereof (laser lift-off) has been known as one of the methods of removing the substrate.
FIGS. 13A and 13B
are cross sections showing the steps of forming a conventional free-standing nitride semiconductor film.
Initially, a sapphire substrate
101
(for example, a sapphire wafer measuring two inches across), which is transparent with respect to laser light from the excimer KrF laser or Nd/YAG laser, is prepared. Then, the sapphire substrate
101
is placed in a hydride vapor phase epitaxy (hereinafter, abbreviated to HVPE) apparatus.
Subsequently, in the step shown in
FIG. 13A
, a nitride semiconductor film
102
, for example, made of GaN and having a thickness of approximately 300 &mgr;m, is formed on the sapphire substrate
101
through HVPE. At this point, the nitride semiconductor film
102
has a plane portion
102
a
located on the top surface of the sapphire substrate
101
and a side surface portion
102
b
located on the side surface of the sapphire substrate
101
.
Then, strong laser light having, for example, a wavelength of 355 nm, is irradiated to the sapphire substrate
101
from the back surface thereof. Because the sapphire substrate
101
transmits light and the irradiated laser light has an extremely short pulse width, the laser light is absorbed in the plane portion
102
a
of the nitride semiconductor film
102
only at a region in contact with the sapphire substrate
101
, that is, the back surface portion. As a result, the back surface portion of the plane portion
102
a
of the nitride semiconductor film
102
is heated, and undergoes heat dissociation to be decomposed to gallium and nitrogen, whereupon a nitrogen gas is released. Thus, the nitride semiconductor film
102
separates from the sapphire substrate
101
as laser light scans the surface of the sapphire substrate
101
entirely. Then, by removing the sapphire substrate
101
, the nitride semiconductor film
102
that will be made into a free-standing nitride semiconductor wafer can be obtained. Thereafter, one or two or more crystalline layers of a compound semiconductor including at least one element selected from Ga, Al, B, As, In, P and Sb and N in its composition (a compound semiconductor expressed by a general formula B
x
Al
y
Ga
z
In
1-x-y-z
N, where 0≦x≦1, 0≦y≦1, 0≦z≦1, and 0≦x+y+z≦1) are grown through epitaxial growth on the nitride semiconductor film
102
, whereby various kinds of compound semiconductor devices can be obtained.
As another method of obtaining the free-standing nitride semiconductor wafer, there also has been known a method of obtaining a nitride semiconductor film that will be made into the free-standing nitride semiconductor wafer by mechanically polishing the sapphire substrate
101
.
As a still another method of obtaining the freestanding nitride semiconductor wafer, there has been attempted a method of using a GaAs substrate, an Si substrate, etc., which are materials that can be readily removed by means of etching, instead of the sapphire substrate, so that the GaAs substrate or Si substrate is removed not by means of polishing but by means of wet etching after the epitaxial growth of the nitride semiconductor film through HVPE.
However, the above conventional methods have inconveniences as follows.
That is, according to the method shown in
FIGS. 13A and 13B
, of the entire nitride semiconductor film
102
, the back surface portion of the plane portion
102
a
is decomposed by irradiation of laser light, so that it is relatively easy to separate the plane portion
102
a
of the nitride semiconductor film
102
from the sapphire substrate
101
. However, because laser light is hardly irradiated to the side surface portion
102
b
of the nitride semiconductor film
102
, it is generally difficult to decompose a region in the vicinity of the interface of the side surface portion
102
b
and the sapphire substrate
101
. Hence, for example, if the sapphire substrate
101
and the nitride semiconductor film
102
are heated in trying to separate the nitride semiconductor film
102
and the sapphire substrate
101
from each other, a difference in coefficients of thermal expansion between the side surface portion
102
b
of the nitride semiconductor film
102
and the sapphire substrate
101
produces stress, which is applied intensively to the side surface portion
102
b
of the nitride semiconductor film
102
. Accordingly, a crack occurs on the side surface portion
102
b,
which may possibly result in a braking of the plane portion
102
a
of the nitride semiconductor film
102
.
And, the crystal orientation differs in the sapphire substrate
101
between the side surface portion and the top surface portion. Moreover, crystallinity is disturbed by machining treatment or the like during the manufacturing of the substrate, and the crystallinity at the side surface portion
102
b
of the nitride semiconductor
102
is so poor that there is a portion having an almost polycrystalline structure. For this reason, the side surface portion
102
b
of the nitride semiconductor film
102
, in general, readily causes a breaking or a chipping, which becomes one of the factors of the occurrence of inconveniences.
Also, according to the method of removing the sapphire substrate
101
by means of polishing, the side surface portion
102
b
of the nitride semiconductor
102
is also polished while the sapphire substrate
101
is polished. Hence, mechanical stress readily causes a crack or a breaking that would run up to the plane portion
102
a
of the nitride semiconductor film
102
from a point where such a crack or breaking caused first on the side surface portion
102
b
. Thus, if this method is used, it is difficult to obtain an independent large-area nitride semiconductor film
102
with satisfactory reproducibility.
Also, according to the method of using the GaAs substrate or Si substrate and removing the GaAs substrate or Si substrate not by means of polishing but by means of etching, the nitride semiconductor film
102
readily breaks when handled in the form of a wafer after the substrate is removed, and a significant crack or breaking readily occurs in the nitride semiconductor film
102
from a point where it breaks first. Hence, if this method is used, it is also difficult to obtain an independent large-area nitride semiconducto

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