U.S. patent application number 11/019768 was filed with the patent office on 2005-06-30 for semiconductor device and method for manufacturing semiconductor device.
This patent application is currently assigned to MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.. Invention is credited to Hirose, Yutaka, Murata, Tomohiro, Tanaka, Tsuyoshi, Uemoto, Yasuhiro.
Application Number | 20050139838 11/019768 |
Document ID | / |
Family ID | 34697700 |
Filed Date | 2005-06-30 |
United States Patent
Application |
20050139838 |
Kind Code |
A1 |
Murata, Tomohiro ; et
al. |
June 30, 2005 |
Semiconductor device and method for manufacturing semiconductor
device
Abstract
A semiconductor device of the present invention includes: a
III-V nitride semiconductor layer including a channel region in
which carriers travel; a concave portion provided in an upper
portion of the channel region in the III-V nitride semiconductor
layer; and a Schottky electrode consisting of a conductive material
forming a Schottky junction with the semiconductor layer, and
formed on a semiconductor layer, which spreads over the concave
portion and peripheral portions of the concave portion, on the
III-V nitride semiconductor layer. A dimension of the concave
portion in a depth direction is set so that a portion of the
Schottky electrode provided in the concave portion can adjust a
quantity of the carriers traveling in the channel region.
Inventors: |
Murata, Tomohiro; (Osaka,
JP) ; Hirose, Yutaka; (Kyoto, JP) ; Tanaka,
Tsuyoshi; (Osaka, JP) ; Uemoto, Yasuhiro;
(Shiga, JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
600 13TH STREET, N.W.
WASHINGTON
DC
20005-3096
US
|
Assignee: |
MATSUSHITA ELECTRIC INDUSTRIAL CO.,
LTD.
|
Family ID: |
34697700 |
Appl. No.: |
11/019768 |
Filed: |
December 23, 2004 |
Current U.S.
Class: |
257/73 ; 257/471;
257/E21.158; 257/E21.407; 257/E21.453; 257/E29.127; 257/E29.253;
257/E29.321; 438/570 |
Current CPC
Class: |
H01L 29/66871 20130101;
H01L 29/2003 20130101; H01L 29/66462 20130101; H01L 29/7787
20130101; H01L 29/8128 20130101; H01L 29/42316 20130101; H01L 21/28
20130101 |
Class at
Publication: |
257/073 ;
257/471; 438/570 |
International
Class: |
H01L 029/04; H01L
021/28 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 26, 2003 |
JP |
2003-432886 |
Claims
What is claimed is:
1. A semiconductor device, comprising: a III-V nitride
semiconductor layer including a channel region in which carriers
travel; a concave portion provided in an upper portion of said
channel region in said III-V nitride semiconductor layer; and a
Schottky electrode consisting of a conductive material forming a
Schottky junction with the semiconductor layer, and formed on a
semiconductor layer, which spreads over said concave portion and
peripheral portions of the concave portion, on said III-V nitride
semiconductor layer, wherein a dimension of said concave portion in
a depth direction is set so that a portion of said Schottky
electrode provided in said concave portion can adjust a quantity of
the carriers traveling in said channel region.
2. The semiconductor device of claim 1, further comprising a film
provided between said III-V nitride semiconductor layer and said
Schottky electrode so as to open an upper side of said concave
portion.
3. The semiconductor device of claim 1, wherein said concave
portion is provided so that an opening dimension is smaller from an
upper surface side of said III-V nitride semiconductor layer toward
a bottom side of said III-V nitride semiconductor layer.
4. The semiconductor device of claim 3, wherein said concave
portion is provided so that said opening dimension is linearly
changed.
5. The semiconductor device of claim 4, further comprising a film
consisting of a crystalline material and provided between said
III-V nitride semiconductor layer and said Schottky electrode so as
to open an upper side of said concave portion.
6. The semiconductor device of claim 3, wherein said concave
portion is provided so that said opening dimension is nonlinearly
changed.
7. The semiconductor device of claim 6, further comprising a film
consisting of an amorphous material and provided between said III-V
nitride semiconductor layer and said Schottky electrode so as to
open an upper side of said concave portion.
8. A method for manufacturing a semiconductor device comprising
steps of: sequentially forming a III-V nitride semiconductor layer
and a concave portion transfer film on a substrate; forming a first
concave portion in said concave portion transfer film; and etching
said concave portion transfer film by a predetermined depth using
etching capable of etching said III-V nitride semiconductor layer
and said concave portion transfer film, and thereby forming a
second concave portion that has an equivalent shape to a shape of
said first concave portion, below said first concave portion in
said III-V nitride semiconductor layer.
9. The method for manufacturing a semiconductor device of claim 8,
wherein said concave portion transfer film consists of a
crystalline material, and the step of forming said first concave
portion includes steps of: forming a first mask pattern that
includes an opening portion in a region in which said first concave
portion is formed, on said concave portion transfer film; and
removing a part of said concave portion transfer film which part is
exposed to said opening portion of said first mask pattern by a
predetermined depth by anisotropic etching.
10. The method for manufacturing a semiconductor device of claim 9,
wherein said crystalline material is one of gallium arsenide,
silicon, silicon carbide, gallium phosphide, and diamond.
11. The method for manufacturing a semiconductor device of claim 9,
wherein said concave portion transfer film contains impurities
consisting of a group IV element or a group V element.
12. The method for manufacturing a semiconductor device of claim 9,
further comprising a step, after the step of forming said second
concave portion, of conducting a heat treatment to said III-V
nitride semiconductor layer under conditions of a temperature of
300.degree. C. or more and 1500.degree. C. or less.
13. The method for manufacturing a semiconductor device of claim 9,
wherein at the step of forming said second concave portion, an
etching depth of the etching on said concave portion transfer film
is set so that said concave portion transfer film remains on an
upper surface of said III-V nitride semiconductor layer, and the
method further comprises steps of: forming a second mask pattern
that covers said second concave portion and peripheral portions of
the second concave portion, on said concave portion transfer film
after the step of forming said second concave portion; and forming
a film that covers the peripheral portions of the second concave
portion from said concave portion transfer film by etching using
said second mask pattern.
14. The method for manufacturing a semiconductor device of claim
13, further comprising a step, between the step of forming said
second concave portion and the step of forming said film, of
conducting a heat treatment to said III-V nitride semiconductor
layer at a temperature of 300.degree. C. or more and 1500.degree.
C. or less.
15. The method for manufacturing a semiconductor device of claim
13, wherein said crystalline material that constitutes said concave
portion transfer film is one of silicon, silicon carbide, gallium
phosphide, and diamond.
16. The method for manufacturing a semiconductor device of claim
13, further comprising a step, after the step of forming said
second concave portion, of oxidizing, nitriding, or oxynitriding a
surface of said concave portion transfer film.
17. The method for manufacturing a semiconductor device of claim 8,
wherein said concave portion transfer film consists of an amorphous
material, and the step of forming said first concave portion
includes steps of: forming a first mask pattern that includes an
opening portion in a region in which said first concave portion is
formed, on said concave portion transfer film; and removing a part
of said concave portion transfer film which part is exposed to the
opening portion of said first mask pattern by a predetermined depth
by isotropic etching.
18. The method for manufacturing a semiconductor device of claim
17, wherein said amorphous material is one of amorphous silicon,
silicon oxide, silicon nitride, silicon carbide, and a III-V
nitride semiconductor.
19. The method for manufacturing a semiconductor device of claim
17, wherein said concave portion transfer film contains impurities
consisting of a group IV element or a group V element.
20. The method for manufacturing a semiconductor device of claim
17, wherein at the step of forming said second concave portion, an
etching depth of the etching on said concave portion transfer film
is set so that said concave portion transfer film remains on an
upper surface of said III-V nitride semiconductor layer, and the
method further comprises steps of: forming a second mask pattern
that covers said second concave portion and peripheral portions of
the second concave portion, on said concave portion transfer film
after the step of forming said second concave portion; and forming
a film that covers the peripheral portions of the second concave
portion from said concave portion transfer film by etching using
said second mask pattern.
21. The method for manufacturing a semiconductor device of claim
20, further comprising a step, between the step of forming said
second concave portion and the step of forming said film, of
conducting a heat treatment to said III-V nitride semiconductor
layer at a temperature of 300.degree. C. or more and 1500.degree.
C. or less.
22. The method for manufacturing a semiconductor device of claim
20, further comprising a step, after the step of forming said
second concave portion, of oxidizing, nitriding, or oxynitriding a
surface of said concave portion transfer film.
23. The method for manufacturing a semiconductor device of claim 8,
wherein said concave portion transfer film consists of a
polycrystalline material, and the step of forming said first
concave portion includes steps of: forming a first mask pattern
that includes an opening portion in a region in which said first
concave portion is formed, on said concave portion transfer film;
and removing a part of said concave portion transfer film which
part is exposed to the opening portion of said first mask pattern
by a predetermined depth by isotropic etching.
24. The method for manufacturing a semiconductor device of claim
23, wherein said polycrystalline material is one of gallium
arsenide, silicon, silicon carbide, gallium phosphide, diamond, and
a III-V nitride semiconductor.
25. The method for manufacturing a semiconductor device of claim
23, wherein said concave portion transfer film contains impurities
consisting of a group IV element or a group V element.
26. The method for manufacturing a semiconductor device of claim
23, wherein at the step of forming said second concave portion, an
etching depth of the etching on said concave portion transfer film
is set so that said concave portion transfer film remains on an
upper surface of said III-V nitride semiconductor layer, and the
method further comprises steps of: forming a second mask pattern
that covers said second concave portion and peripheral portions of
the second concave portion, on said concave portion transfer film
after the step of forming said second concave portion; and forming
a film that covers the peripheral portions of the second concave
portion from said concave portion transfer film by etching using
said second mask pattern.
27. The method for manufacturing a semiconductor device of claim
26, further comprising a step, between the step of forming said
second concave portion and the step of forming said film, of
conducting a heat treatment to said III-V nitride semiconductor
layer at a temperature of 300.degree. C. or more and 1500.degree.
C. or less.
28. The method for manufacturing a semiconductor device of claim
26, further comprising a step, after the step of forming said
second concave portion, of oxidizing, nitriding, or oxynitriding a
surface of said concave portion transfer film.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] All the matters disclosed in the claims, the specification,
and the drawings of Japanese Patent Application No. 2003-432886
filed on Dec. 26, 2003 are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a semiconductor device
using a III-V nitride semiconductor and a method for manufacturing
the semiconductor device. More specifically, the present invention
relates to a semiconductor device having a Schottky electrode
formed on a semiconductor layer consisting of a III-V nitride
semiconductor, and a method for manufacturing the semiconductor
device.
[0003] Conventionally, a III-V nitride semiconductor such as
gallium nitride (GaN) has been widely used as a material for an
active layer of an optical device since it has a direct transition
energy band structure and a wide band gap. Recently, since the
III-V nitride semiconductor is characteristically high in breakdown
field intensity and high in electron saturation velocity, use of
this III-V nitride semiconductor to a high frequency and high power
electron device has been considered.
[0004] Among electron devices using the nitride semiconductor,
development of a heterojunction field effect transistor
(hereinafter, "HFET"), in particular has been considered.
[0005] Examples of the HFET device using the III-V nitride
semiconductor include an HFET device constituted so that a GaN
layer and an aluminum gallium nitride (AlGaN) layer are formed on a
semi-insulating substrate by epitaxial growth, and so that a gate
electrode that is a Schottky electrode and a source electrode and a
drain electrode that are ohmic electrodes are provided on the AlGaN
layer. In this HFET device, a two-dimensional electron gas layer
(hereinafter, "2DEG layer") is formed near an interface of the GaN
layer with the AlGaN layer and the 2DEG layer is employed as a high
electron mobility channel region.
[0006] Nevertheless, because of presence of a high density trap
level on a surface of the III-V nitride semiconductor, carries are
captured and emitted in traps on the surface of the AlGaN layer,
with the result that a phenomenon of deterioration in high
frequency characteristics or so-called frequency dispersion
occurs.
[0007] To suppress this frequency dispersion, there are known a
method for reducing a trap density on the surface of the AlGaN
layer by covering a region between the gate electrode and the
source electrode and a region between the gate electrode and the
drain electrode on the surface of the AlGaN layer with a surface
protection film consisting of silicon nitride (SiN), and a method
for providing a surface protection film consisting of a low
concentration n type GaN on the AlGaN layer, and forming the gate
electrode interposing the surface protection film (see, for
example, Japanese Patent Application Laid-Open No.
2002-359256).
[0008] If the surface protection film consisting of SiN is used,
the trap density on the surface of the AlGaN layer can be reduced
in lateral portions of the gate electrode. However, in a fringe
region that is a lower side end of the gate electrode, surface
charge influences the channel region, with the result that the
frequency dispersion cannot be sufficiently suppressed. If the
surface protection film consisting of low concentration n type GaN
is used, a distance between the gate electrode and the channel
region is increased by a thickness of the surface protection film,
with the result that a mutual conductance (gm) of the HFET device
is reduced.
[0009] Meanwhile, as the HFET device using a gallium arsenide
(GaAs) based material, there is known an HFET device having a
so-called spike-gate structure in which a convex portion having a
V-shaped cross section is provided in a lower portion of the gate
electrode so as to decrease the influence of the surface traps
(see, for example, Japanese Patent Application Laid-Open No.
2001-102354, and H. Furukawa and six others, "High power-added
efficiency and low distortion GaAs power NET employing spike-gate
structure", Solid-State Electronics, Elsevier Ltd., 1997, Volume
41, Issue 10, pp. 1599-1604).
[0010] FIG. 10 is a cross-sectional block diagram that depicts a
conventional GaAs based HFET device including the spike-gate. As
shown in FIG. 10, an n type GaAs layer 102 and high concentration n
type GaAs layer 103 are formed on a substrate 101 in this order. A
concave portion 102a having a V-shaped cross section is provided in
an upper portion of the n type GaAs layer 102, and the high
concentration n type GaAs layer 103 is formed into a recess so as
to open the concave portion 102a and surroundings of the concave
portion 102a. In the region formed in the recess of the high
concentration n type GaAs layer 103 on the n type GaAs layer 102, a
gate electrode 104 is provided to be filled into the concave
portion 102a. In addition, a source electrode 105 and a drain
electrode 106 are provided on the high concentration n type GaAs
layer 103.
[0011] In the HFET device shown in FIG. 10, since the gate
electrode 104 is provided to be filled into the concave portion
102a, a convex portion having a V-shaped cross section is provided
on a bottom side of the gate electrode 104 (that is, on a bottom of
the concave portion 102a). A depth of the concave portion 102a is
set so that the convex portion provided on the bottom side of the
gate electrode 104 substantially functions as a gate.
[0012] By doing so, as compared with an ordinary recess structure,
a gap between an upper surface of the n type GaAs layer 102 and the
channel region can be set wide. It is, therefore, possible to
decrease the influence of the traps on the upper surface of the n
type GaAs layer 102 on the channel region, and suppress the
frequency dispersion resulting from the traps on the surface of the
n type GaAs layer 102.
[0013] In order to form the gate electrode 104 having such a
structure, the concave portion 102a is formed using an anisotropic
etchant having different etch rates according to plane
orientations. Specifically, the concave portion 102a inclined at
about 54.7 degrees with respect to the upper surface of the n type
GaAs layer 102 is formed by wet etching using an etchant having an
etch rate on a (100) plane of GaAs higher than an etch rate on a
(111) plane. The concave portion 102a is formed into a recess in a
[100] direction of the crystal plane, having a (111) plane of GaAs
as an inclined surface, and having a V-shaped cross section.
[0014] However, if the spike-gate structure of the conventional
GaAs based HFET device is applied to the HFET device using the
III-V nitride semiconductor, it is difficult to form a minute
concave portion in the upper portion of the III-V nitride
semiconductor layer. This is because crystals of the III-V nitride
semiconductor are chemically stable and no orientation dependent
anisotropic wet etching appropriate for this HFET device is
present.
[0015] As can be seen, the HFET device using the III-V nitride
semiconductor has the following disadvantages. Since it is
difficult to form the gate electrode having the concave portion on
the bottom side of the spike-gate or the like, the influence of the
traps on the upper surface of the III-V nitride semiconductor layer
on the channel region cannot be sufficiently decreased. Hence, the
frequency dispersion inhibits obtaining good high frequency
characteristics.
SUMMARY OF THE INVENTION
[0016] In view of the above-mentioned conventional disadvantages,
the present invention has been devised for the purpose of realizing
a semiconductor device using a III-V nitride semiconductor capable
of ensuring suppressing frequency dispersion resulting from surface
traps on a surface of a III-V nitride semiconductor layer.
[0017] To attain the object, the present invention provides a
constitution in which a concave portion is formed in a region, in
which a gate electrode is formed, in a III-V nitride semiconductor
layer by dry etching.
[0018] Specifically, according to a first aspect of the present
invention, there is provided a semiconductor device, comprising: a
III-V nitride semiconductor layer including a channel region in
which carriers travel; a concave portion provided in an upper
portion of the channel region in the III-V nitride semiconductor
layer; and a Schottky electrode consisting of a conductive material
forming a Schottky junction with the semiconductor layer, and
formed on a semiconductor layer, which spreads over the concave
portion and peripheral portions of the concave portion, on the
III-V nitride semiconductor layer, wherein a dimension of the
concave portion in a depth direction is set so that a portion of
the Schottky electrode provided in the concave portion can adjust a
quantity of the carriers traveling in the channel region.
[0019] In the semiconductor device of the present invention, the
portion of the Schottky electrode formed in the concave portion can
be used as a substantial gate electrode of a transistor. Due to
this, the Schottky electrode can be formed so that the upper
surface of the III-V nitride semiconductor layer is away from the
channel region by the depth of the concave portion. In addition, it
is possible to decrease the influence of traps present on the upper
surface of the III-V nitride semiconductor layer, on the channel
region. It is, therefore, possible to ensure suppressing frequency
dispersion. Besides, since the portion of the Schottky electrode
provided in the concave portion is used as the substantial gate
electrode, a substantial gate length is substantially equal to a
width of a bottom of the concave portion. Therefore, the gate
length is reduced and the semiconductor device can operate at high
rate.
[0020] It is preferable that the semiconductor device of the
present invention further comprises a film provided between the
III-V nitride semiconductor layer and the Schottky electrode so as
to open an upper side of the concave portion.
[0021] By so constituting, since the Schottky electrode is provided
on the III-V nitride semiconductor layer interposing the film, a
trap density on the upper surface of the III-V nitride
semiconductor layer can be reduced. It is, therefore, possible to
obtain the semiconductor device that can further suppress the
frequency dispersion and that has good high frequency
characteristics.
[0022] In the semiconductor device of the present invention, it is
preferable that the concave portion is provided so that an opening
dimension is smaller from an upper surface side of the III-V
nitride semiconductor layer toward a bottom side of the III-V
nitride semiconductor layer.
[0023] By so constituting, the bottom of the concave portion can be
further made small, and the substantial gate length can be,
therefore, further reduced.
[0024] In the semiconductor device of the present invention, it is
preferable that the concave portion is provided so that the opening
dimension is linearly changed.
[0025] In this case, it is preferable that the semiconductor device
further comprises a film consisting of a crystalline material and
provided between the III-V nitride semiconductor layer and the
Schottky electrode so as to open an upper side of the concave
portion.
[0026] In the semiconductor device of the present invention, it is
preferable that the concave portion is provided so that the opening
dimension is nonlinearly changed.
[0027] In this case, it is preferable that the semiconductor device
further comprises a film consisting of an amorphous material and
provided between the III-V nitride semiconductor layer and the
Schottky electrode so as to open an upper side of the concave
portion.
[0028] According to a second aspect of the present invention, there
is provided a method for manufacturing a semiconductor device
comprising steps of: sequentially forming a III-V nitride
semiconductor layer and a concave portion transfer film on a
substrate; forming a first concave portion in the concave portion
transfer film; and etching the concave portion transfer film by a
predetermined depth using etching capable of etching the III-V
nitride semiconductor layer and the concave portion transfer film,
and thereby forming a second concave portion that has an equivalent
shape to a shape of the first concave portion, below the first
concave portion in the III-V nitride semiconductor layer.
[0029] According to the method for manufacturing the semiconductor
device of the present invention, it is possible to ensure that the
second concave portion having a desired depth is formed in the
region in which the gate electrode is formed on the III-V nitride
semiconductor layer based on the shape of the first concave portion
formed in the concave portion transfer film. Accordingly, by
forming the Schottky electrode to be filled into the second concave
portion, the portion of the Schottky electrode filled into the
second concave portion can be used as a substantial gate electrode.
It is, therefore, possible to ensure obtaining the semiconductor
device that can decrease the influence of traps present on the
upper surface of the III-V nitride semiconductor layer, on the
channel region, and that can suppress frequency dispersion.
[0030] In the method for manufacturing the semiconductor device of
the present invention, it is preferable that the concave portion
transfer film consists of a crystalline material, and that the step
of forming the first concave portion includes steps of: forming a
first mask pattern that includes an opening portion in a region in
which the first concave portion is formed, on the concave portion
transfer film; and removing a part of the concave portion transfer
film which part is exposed to the opening portion of the first mask
pattern by a predetermined depth by anisotropic etching.
[0031] By doing so, the first concave portion can be etched into a
desired shape according to a crystal structure of the concave
portion transfer film by orientation dependent anisotropic etching.
The second concave portion can be, therefore, formed while
controlling the shape of the concave portion according to the shape
of the first concave portion.
[0032] In the method for manufacturing the semiconductor device of
the present invention, as the crystalline material, one of gallium
arsenide, silicon, silicon carbide, gallium phosphide, and diamond
can be used.
[0033] If one of these materials is used, the first concave portion
is formed to have the V-shaped cross section by the orientation
dependent anisotropic etching. The second concave portion having
the V-shaped cross section can be, therefore, formed.
[0034] In the method for manufacturing the semiconductor device of
the present invention, it is preferable that the concave portion
transfer film contains impurities consisting of a group IV element
or a group V element.
[0035] By doing so, even if atoms that constitute the III-V nitride
semiconductor layer are inadvertently diffused into the concave
portion transfer film, the group IV impurities or group V
impurities can compensate for the reduction in the resistance of
the III-V nitride semiconductor layer. Accordingly, even if the
concave portion transfer film consisting of silicon is used, the
concave portion transfer film can be formed so as not to reduce the
resistance of the III-V nitride semiconductor layer.
[0036] It is preferable that the method for manufacturing the
semiconductor device of the present invention comprises a step,
after the step of forming the second concave portion, of conducting
a heat treatment to the III-V nitride semiconductor layer under
conditions of a temperature of 300.degree. C. or more and
1500.degree. C. or less.
[0037] By doing so, the crystal defects generated on the III-V
nitride semiconductor layer by the etching for forming the second
concave portion can be eliminated by the heat treatment. The
reliability of the semiconductor device can be, therefore,
improved.
[0038] In the method for manufacturing the semiconductor device of
the present invention, it is preferable that at the step of forming
the second concave portion, an etching depth of the etching on the
concave portion transfer film is set so that the concave portion
transfer film remains on an upper surface of the III-V nitride
semiconductor layer, and that the method further comprises steps
of: forming a second mask pattern that covers the second concave
portion and peripheral portions of the second concave portion, on
the concave portion transfer film after the step of forming the
second concave portion; and forming a film that covers the
peripheral portions of the second concave portion from the concave
portion transfer film by etching using the second mask pattern.
[0039] By doing so, the film is formed on the upper surface of the
III-V nitride semiconductor layer. Due to this, by forming the
Schottky electrode on the film to be filled into the second concave
portion, the trap density in both side portions of the Schottky
electrode on the upper surface of the III-V nitride semiconductor
layer can be reduced. It is, therefore, possible to further ensure
suppressing the frequency dispersion.
[0040] It is preferable that the method for manufacturing the
semiconductor device of the present invention further comprises a
step, between the step of forming the second concave portion and
the step of forming the film, of conducting a heat treatment to the
III-V nitride semiconductor layer at a temperature of 300.degree.
C. or more and 1500.degree. C. or less.
[0041] By doing so, the heat treatment can be conducted in a state
in which the surface of the III-V nitride semiconductor layer is
covered with the concave portion transfer film. The crystal defects
of the III-V nitride semiconductor layer can be, therefore,
eliminated while suppressing the thermal oxidation of the surface
of the III-V nitride semiconductor layer.
[0042] In the method for manufacturing the semiconductor device of
the present invention, as the crystalline material that constitutes
the concave portion transfer film, one of silicon, silicon carbide,
gallium phosphide, and diamond can be used.
[0043] If one of these materials is used, since the concave portion
transfer film is constituted by a high heat resistant material, at
the heat treatment step of eliminating the crystal defects of the
III-V nitride semiconductor layer, it is possible to ensure
suppressing degeneration, transformation, or the like of the III-V
nitride semiconductor layer due to the heat on the surface
thereof.
[0044] In the method for manufacturing the semiconductor device of
the present invention, it is preferable that the concave portion
transfer film contains impurities consisting of a group IV element
or a group V element.
[0045] If the concave portion is transferred onto the III-V nitride
semiconductor layer by the dry etching, group III gallium (Ga)
mixed into the concave portion transfer film during crystal growth
on the concave portion transfer film is diffused into the concave
portion transfer film to thereby reduce the specific resistance of
the concave portion transfer film when the concave portion transfer
film is left and used as a surface film. Due to this, the portion
into which gallium is diffused acts as a leak current path from the
gate electrode. However, by thus adding the group IV element or the
group V element to the concave portion transfer film, the group III
gallium is compensated (canceled) and the resistance of the concave
portion transfer film is increased. The gate leak current can be
thereby suppressed.
[0046] It is preferable that the method for manufacturing the
semiconductor device of the present invention further comprises a
step, after the step of forming the second concave portion, of
oxidizing, nitriding, or oxynitriding a surface of the concave
portion transfer film.
[0047] By doing so, the film formed from the concave portion
transfer film is in a state in which an oxide film, a nitride film,
or an oxynitride film is formed on an upper portion of the film and
the film can be formed to have high resistance. It is, therefore,
possible to obtain the semiconductor device which can suppress the
leak current from the gate electrode.
[0048] In the method for manufacturing the semiconductor device of
the present invention, it is preferable that the concave portion
transfer film consists of an amorphous material or a
polycrystalline material, and that the step of forming the first
concave portion includes steps of: forming a first mask pattern
that includes an opening portion in a region in which the first
concave portion is formed, on the concave portion transfer film;
and removing a part of the concave portion transfer film which part
is exposed to the opening portion of the first mask pattern by a
predetermined depth by isotropic etching.
[0049] By doing so, the first concave portion can be formed so that
the opening dimension is nonlinearly smaller toward the depth
direction by the isotropic etching.
[0050] In the method for manufacturing the semiconductor device of
the present invention, as the amorphous material, one of amorphous
silicon, silicon oxide, silicon nitride, silicon carbide, and a
III-V nitride semiconductor can be used.
[0051] In the method for manufacturing the semiconductor device of
the present invention, as the polycrystalline material, one of
silicon, silicon carbide, gallium phosphide, diamond, and a III-V
nitride semiconductor can be used.
[0052] In the method for manufacturing the semiconductor device of
the present invention, it is preferable that at the step of forming
the second concave portion, an etching depth of the etching on the
concave portion transfer film is set so that the concave portion
transfer film remains on an upper surface of the III-V nitride
semiconductor layer, and that the method further comprises steps
of: forming a second mask pattern that covers the second concave
portion and peripheral portions of the second concave portion, on
the concave portion transfer film after the step of forming the
second concave portion; and forming a film that covers the
peripheral portions of the second concave portion from the concave
portion transfer film by etching using the second mask pattern.
[0053] It is preferable that the method for manufacturing the
semiconductor device of the present invention further comprises a
step, between the step of forming the second concave portion and
the step of forming the film, of conducting a heat treatment to the
III-V nitride semiconductor layer at a temperature of 300.degree.
C. or more and 1500.degree. C. or less.
[0054] In the method for manufacturing the semiconductor device of
the present invention, it is preferable that the concave portion
transfer film contains impurities consisting of a group IV element
or a group V element.
[0055] It is preferable that the method for manufacturing the
semiconductor device of the present invention further comprises a
step, after the step of forming the second concave portion, of
oxidizing, nitriding, or oxynitriding a surface of the concave
portion transfer film.
BRIEF DESCRIPTION OF THE DRAWINGS
[0056] FIG. 1A is a cross-sectional block diagram of a III-V
nitride semiconductor device in the first embodiment of the present
invention, FIG. 1B is a cross-sectional block diagram of a III-V
nitride semiconductor device in the first modification of the first
embodiment of the present invention, and FIG. 1C is a
cross-sectional block diagram of a III-V nitride semiconductor
device in the second modification of the first embodiment of the
present invention;
[0057] FIG. 2A is a cross-sectional block diagram of a III-V
nitride semiconductor device in the second embodiment of the
present invention, and FIG. 2B is a cross-sectional block diagram
of a III-V nitride semiconductor device in one modification of the
second embodiment of the present invention;
[0058] FIGS. 3A to 3D are cross-sectional block diagrams that
depict a method for manufacturing the III-V nitride semiconductor
device in the second embodiment of the present invention in order
of steps;
[0059] FIG. 4 is a cross-sectional block diagram of a III-V nitride
semiconductor device in the third embodiment of the present
invention;
[0060] FIGS. 5A to 5D are cross-sectional block diagrams that
depict a method for manufacturing the III-V nitride semiconductor
device in the third embodiment of the present invention in order of
steps;
[0061] FIG. 6 is cross-sectional block diagram of a III-V nitride
semiconductor device in the fourth embodiment of the present
invention;
[0062] FIGS. 7A to 7D are cross-sectional block diagrams that
depict a method for manufacturing the III-V nitride semiconductor
device in the fourth embodiment of the present invention in order
of steps;
[0063] FIG. 8 is cross-sectional block diagram of a III-V nitride
semiconductor device in the fifth embodiment of the present
invention;
[0064] FIGS. 9A to 9D are cross-sectional block diagrams that
depict a method for manufacturing the III-V nitride semiconductor
device in the fifth embodiment of the present invention in order of
steps;
[0065] FIG. 10 is cross-sectional block diagram of a conventional
GaAs-based HFET device.
[0066] FIG. 11A to 11C are cross-sectional block diagrams of a
III-V nitride semiconductor device in another modification of the
first embodiment of the present invention.
[0067] FIG. 12A to FIG. 12B are cross-sectional block diagrams of a
III-V nitride semiconductor device in another modification of the
second embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1
[0068] A III-V nitride semiconductor device in the first embodiment
of the present invention will be described with reference to the
drawings. In the present specification, the III-V nitride
semiconductor is a hybrid semiconductor including one of or two or
more of boron nitride (BN), aluminum nitride (AlN), gallium nitride
(GaN), and indium nitride (InN), and represented by a general
formula of B.sub.xAl.sub.yGa.sub.zIn.sub.1-x- -yN (where
0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1, and
.ltoreq.0z.ltoreq.z.ltoreq.1).
[0069] FIG. 1A is a cross-sectional block diagram of the III-V
nitride semiconductor device in the first embodiment of the present
invention. As shown in FIG. 1A, the III-V nitride semiconductor
device is constituted so that, for example, a buffer layer 12
having a thickness of about 10 nm to 200 nm and consisting of
aluminum nitride (AlN), a channel layer 13 having a thickness of
about 2 .mu.m to 3 .mu.m and consisting of undoped gallium nitride
(GaN), and a carrier supply layer 14 having a thickness of about 20
nm to 30 nm and consisting of n type aluminum gallium nitride
(AlGaN) are formed on a substrate 11 consisting of silicon carbide
(SiC) in this order. The thicknesses of the buffer layer 12, the
channel layer 13, and the carrier supply layer 14 are given as one
example. The thickness of the channel layer 13 may be set so that
channel layer 13 has good crystallinity and may be, for example, at
least about 1 .mu.m.
[0070] A concave portion 14a is provided in an upper portion of the
carrier supply layer 14, and a gate electrode 15 which consists of
a metallic material and in which a Schottky junction with the
carrier supply layer 14 is formed is provided on the carrier supply
layer 14 to be filled into the concave portion 14a. A depth of the
concave portion 14a is preferably 20 nm or less, more preferably
about 10 nm to 15 nm if the thickness of the carrier supply layer
14 is, for example, 25 nm. In this case, the HFET device according
to this embodiment can operate at a frequency of 2 GHz.
[0071] A source electrode 16 and a drain electrode 17 each
consisting of a metallic material and forming an ohmic contact with
the carrier supply layer 14 are provided laterally of the gate
electrode 15, respectively, on the carrier supply layer 14 at a
predetermined distance between the source electrode 16 and the
drain electrode 17. As the gate electrode 15, a multilayer film
consisting of nickel (Ni) and gold (Au) or a monolayer film
consisting of palladium (Pd) or palladium silicon (PdSi) can be
used. As the source electrode 16 or the drain electrode 17, a
multilayer film consisting of titanium (Ti) and aluminum (Al) can
be used.
[0072] The III-V nitride semiconductor device in the first
embodiment functions as an HFET having a 2DEG layer formed near an
interface of the channel layer 13 with the carrier supply layer 14
by a heterojunction between the channel layer 13 and the carrier
supply layer 14. By applying a predetermined operating voltage Vds
to the source electrode 16 and the drain electrode 17, electrons in
quantities corresponding to a potential of the gate electrode 15
travel on the 2DEG layer.
[0073] In the III-V nitride semiconductor device in the first
embodiment, by appropriately adjusting the depth of the concave
portion 14a, a convex portion provided on a bottom side of the gate
electrode 15, i.e., a portion of the gate electrode 15 filled into
the concave portion 14a substantially functions as a gate
electrode.
[0074] A first threshold voltage Vth1 is proportional to a distance
from a lower end of the concave portion 14a to an upper surface of
the channel layer 13, and a second threshold voltage Vth2 is
proportional to a thickness of the carrier supply layer 14. By
adjusting the depth of the concave portion 14a according to the
thickness of the carrier supply layer 14, therefore, the threshold
voltages Vth1 and Vth2 can be set at appropriate values.
[0075] By thus constituting the III-V nitride semiconductor device,
even if a distance from the upper surface of the carrier supply
layer 14 to the channel region (2DEG layer) is set large, the
quantity of carriers traveling in the channel region can be
adjusted using the portion of the gate electrode 15 formed in the
concave portion 14a. Accordingly, as long as the distance from the
bottom of the concave portion 14a to the channel region is equal to
the distance from the upper surface of the flat carrier supply
layer to the channel region, it is possible to decrease the
influence of traps between the upper surface of the carrier supply
layer 14 and the bottom of the gate electrode 15 on the channel
region by as much as the depth of the concave portion 14a, as
compared with the conventional configuration in which the gate
electrode is provided on the upper surface of the flat carrier
supply layer. Therefore, frequency dispersion can be suppressed and
high frequency characteristics can be improved.
[0076] In the III-V nitride semiconductor device in the first
embodiment, the concave portion 14a can be formed by performing dry
etching on the carrier supply layer 14, the surface of which is
formed flat by epitaxial growth, using a mask pattern provided to
open a region in which the concave portion 14a is formed by an
etching gas consisting of chlorine (Cl.sub.2) and sulfur
hexafluoride (SF.sub.6). By using this etching gas, the carrier
supply layer 14 consisting of AlGaN can be etched at an etch rate
of about 0.1 nm to 100 nm per minute, and it is possible to ensure
forming the concave portion 14a while controlling the depth of the
concave portion 14a.
Modification 1 of Embodiment 1
[0077] FIG. 1B is a cross-sectional block diagram of a III-V
nitride semiconductor device in the first modification of the first
embodiment of the present invention. As shown in FIG. 1B, the III-V
nitride semiconductor device in the first modification is
constituted so that a protection film 18 having a thickness of
about 100 nm to 200 nm and consisting of silicon oxide or silicon
nitride is provided in a region between the concave portion 14a and
each of the source electrode 16 and the drain electrode 17 on the
upper surface of the carrier supply layer 14.
[0078] According to the first modification of the first embodiment,
since the protection film 18 is provided on the upper surface of
the carrier supply layer 14, a trap density in both side portions
of the gate electrode 15 on the upper surface of the carrier supply
layer 14 can be reduced. It is, therefore, possible to further
ensure suppressing the frequency dispersion resulting from the
traps on the upper surface of the carrier supply layer 14, as
compared with the first embodiment.
[0079] In the configuration shown in FIG. 1B, a material for the
protection film 18 is not limited to silicon oxide or silicon
nitride but may be the other insulating material, a single crystal
silicon, amorphous silicon, gallium arsenide (GaAs), or the
like.
Modification 2 of Embodiment 1
[0080] FIG. 1C is a cross-sectional block diagram of a III-V
nitride semiconductor device in the second modification of the
first embodiment of the present invention. As shown in FIG. 1C, the
III-V nitride semiconductor device in the second modification is
constituted so that a gate electrode 15A formed in the concave
portion 14a, which is provided on the upper surface of the carrier
supply layer 14, and serving as a Schottky electrode is provided
not to be filled into the concave portion 14a but to extend along a
bottom and a wall surface of the concave portion 14a and peripheral
portions of the concave portion 14a. Since the gate electrode 15A
is not filled into the concave portion 14a, an amount of a material
used for the gate electrode 15A can be reduced and a throughput of
a step of forming the gate electrode 15A can be improved.
Embodiment 2
[0081] A III-V nitride semiconductor device in the second
embodiment of the present invention will be described hereinafter
with reference to the drawings.
[0082] FIG. 2A is a cross-sectional block diagram of the III-V
nitride semiconductor device in the second embodiment of the
present invention. In FIG. 2A, same components as those shown in
FIGS. 1A to 1C are denoted by the same reference symbols,
respectively, and will not be repeatedly described herein.
[0083] As shown in FIG. 2A, the III-V nitride semiconductor device
in the second embodiment of the present invention is constituted so
that a buffer layer 12 consisting of AlN, a channel layer 13
consisting of undoped GaN, and a carrier supply layer 14 consisting
of AlGaN are formed on a substrate 11 consisting of SiC in this
order, and so that a concave portion 14b having a V-shaped cross
section is formed in an upper portion of the carrier supply layer
14.
[0084] A gate electrode 15 is provided on the carrier supply layer
14 to be filled into the concave portion 14a. A source electrode 16
and a drain electrode 17 are provided laterally of the gate
electrode 15, respectively, on the carrier supply layer 14 at a
predetermined distance between the source electrode 16 and the
drain electrode 17. Similarly to the first embodiment, a depth of
the concave portion 14b is set so that a portion of the gate
electrode 15 provided in the concave portion 14b substantially
functions as a gate electrode.
[0085] According to the III-V nitride semiconductor device in the
second embodiment, similarly to the III-V nitride semiconductor
device in the first embodiment, the portion of the gate electrode
15 provided in the concave portion 14b can be used as the
substantial gate electrode. Due to this, it is possible to decrease
the influence of traps present on the upper surface of the carrier
supply layer 14, on the channel region by as much as the depth of
the concave portion 14b. It is, therefore, possible to ensure
suppressing frequency dispersion resulting from the traps on the
upper surface of the carrier supply layer 14.
[0086] Furthermore, the concave portion 14b is formed to have the
V-shaped cross-section, that is, formed so that an opening
dimension is linearly smaller from the upper surface side of the
carrier supply layer 14 toward the depth direction. Due to this, an
effective gate length of the gate electrode 15 can be set far
smaller than that of the gate electrode 15 in the first embodiment,
while using a normally used pattern formation technique. The III-V
nitride semiconductor device in the second embodiment can,
therefore, operate at high rate.
Modification of Embodiment 2
[0087] FIG. 2B is a cross-sectional block diagram of a III-V
nitride semiconductor device in one modification of the second
embodiment of the present invention. As shown in FIG. 2B, the III-V
nitride semiconductor device in this modification is constituted so
that a gate electrode 15A formed in the concave portion 14b, which
has the V-shaped cross section and provided on the upper surface of
the carrier supply layer 14, and serving as a Schottky electrode is
provided not to be filled into the concave portion 14b but to
extend along an inclined surface of the concave portion 14a and
peripheral portions of the concave portion 14b. Since the gate
electrode 15A is not filled into the concave portion 14b, an amount
of a material used for the gate electrode 15A can be reduced and a
throughput of a step of forming the gate electrode 15A can be
improved.
[0088] A method for manufacturing the III-V nitride semiconductor
device in the second embodiment of the present invention will now
be described with reference to the drawings.
[0089] FIGS. 3A to 3D are cross-sectional block diagrams that
depict the method for manufacturing the III-V nitride semiconductor
device in the second embodiment of the present invention in order
of steps.
[0090] As shown in FIG. 3A, the buffer layer 12 consisting of AlN,
the channel layer 13 consisting of undoped GaN, the carrier supply
layer 14 consisting of n type AlGaN, a so-called low temperature
buffer layer 21 having a thickness of 15 nm to 20 nm and consisting
of gallium arsenide (GaAs), and a concave portion transfer film 22
having GaAs subjected to crystal growth so that a plane orientation
is a (100) plane are formed on the substrate 11 consisting of SiC
in this order by growth using metal organic chemical vapor
deposition (MOCVD) or molecular beam epitaxy (MBE). As a material
for the low temperature buffer layer 21, GaAs grown into an
amorphous state at a low temperature is used, whereby crystal
lattice mismatching between the carrier supply layer 14 and the
concave portion transfer film 22 can be relaxed. The material for
the low temperature buffer layer 21 is not limited to GaAs grown at
a low temperature but may be an arbitrary material which can relax
the lattice mismatching between the carrier supply layer 14 and the
concave portion transfer film 22.
[0091] A concave portion formation mask pattern 23 including an
opening portion 23a a longitudinal direction of which is a [110]
orientation of the crystal lattice of GaAs of the concave portion
transfer film 22 and having an opening width of about 100 nm is
formed on the concave portion transfer film 22 by lithography.
[0092] As shown in FIG. 3B, a transfer concave portion 22a is
formed in the concave portion transfer film 22 exposed to the
opening portion 23a of the mask pattern 23 by wet etching using a
solution mixture of sulfuric acid (H.sub.2SO.sub.4) and hydrogen
peroxide (H.sub.2O.sub.2) as an etchant. As the etchant, the
solution mixture having a volume ratio of, for example,
H.sub.2SO.sub.4:H.sub.2O.sub.2:H.sub.2O=8:1:1 can be used.
[0093] The etchant consisting of H.sub.2SO.sub.4 and H.sub.2O.sub.2
exhibits crystal anisotropy relative to gallium arsenide crystals,
and an etch rate of the etchant on the (111) plane is far lower
than an etch rate on the (100) plane. Therefore, the transfer
concave portion 22a is formed to have the (111) plane as an
inclined surface and have a recess cross section in the [100]
orientation, i.e., a V-shaped cross section.
[0094] As shown in FIG. 3C, after removing the mask pattern 23, an
entire surface of the concave transfer film 22 is etched by a
predetermined depth by dry etching using a gas mixture of chlorine
(Cl.sub.2) and sulfur hexafluoride (SF.sub.6) as an etching
gas.
[0095] Conditions for the dry etching on the concave transfer film
22 are as follows. A flow rate of Cl.sub.2 is about 10 ml/min (in a
standard condition), a flow rate of SF.sub.6 is about 5 ml/min (in
a standard condition), a reaction chamber pressure is about 4 Pa, a
plasma output is about 600 W, and a substrate voltage is about 30
W. In the gas mixture used for the dry etching, boron trichloride
(BCl.sub.3) may be used in place of Cl.sub.2.
[0096] The etching gas consisting of Cl.sub.2 and SF.sub.6 can etch
GaAs and AlGaN. Therefore, by etching the concave transfer film 22
from the upper surface side, the low temperature buffer layer 21
and the carrier supply layer 14 are sequentially etched from the
upper surface side below the transfer concave portion 22a, and the
concave portion 14b having an equivalent V-shaped cross section to
that of the transfer concave portion 22a is formed in the carrier
supply layer 14. At this time, the depth of the concave portion 14b
can be appropriately adjusted by adjusting an etching depth of the
etching on the concave transfer film 22.
[0097] The concave portion 14b having the V-shaped cross section
can be similarly formed in the carrier supply layer 14 even by an
anisotropic physical method such as ion milling using argon (Ar) in
place of the dry etching on the concave portion transfer film
22.
[0098] As shown in FIG. 3D, after sequentially removing the concave
portion transfer film 22 and the low temperature buffer layer 21 by
the wet etching, the source electrode 16 and the drain electrode 17
are formed laterally of the concave portion 14b on the carrier
supply layer 14 using a metallic material which can form an ohmic
contact with the carrier supply layer 14, with the distance kept
between the source electrode 16 and the drain electrode 17,
furthermore, the ohmic contact is formed through a heat treatment
step. Thereafter, the gate electrode 15 is formed to be filled into
the concave portion 14b using a metallic material that can form a
Schottky junction with the carrier supply layer 14.
[0099] Through these steps, the III-V nitride semiconductor device
in the second embodiment can be obtained.
[0100] According to the method for manufacturing the III-V nitride
semiconductor device in the second embodiment, by forming the
transfer concave portion 22a in the concave portion transfer film
22 consisting of GaAs and then dry-etching the concave portion
transfer film 22, the concave portion 14b having the equivalent
cross section to that of the transfer concave portion 22a can be
formed in the carrier supply layer 14:
[0101] Further, during the etching for forming the concave portion
14b, an etch selectivity of the material (AlGaN) for the carrier
supply layer 14 to the material (GaAs) for the concave portion
transfer film 22 is controlled. It is thereby possible to ensure
forming the concave portion 14b while controlling the shape of the
concave portion 14b based on the shape of the transfer concave
portion 22a. It is particularly preferable to set the etch
selectivity at 1 or more so as to improve a pointedness of the
concave portion 14b.
[0102] In the method for manufacturing the III-V nitride
semiconductor device in the second embodiment, annealing can be
performed under conditions of a temperature of 300.degree. C. or
more and 1500.degree. C. or less after the dry etching step of
forming the concave portion 14b and at least before the formation
of the gate electrode 15, the source electrode 16, and the drain
electrode 17. If so, crystal defects generated in the carrier
supply layer 14 due to a damage of the dry etching can be
eliminated. Reliability of the III-V nitride semiconductor device
can be thereby improved.
[0103] In the method for manufacturing the III-V nitride
semiconductor device in the second embodiment, the material for the
concave portion transfer film 22 is not limited to GaAs but may be
an arbitrary material with which the transfer concave portion 22a
having the V-shaped cross section can be formed based on crystal
anisotropy. For example, single-crystal silicon, SiC, gallium
phosphide (GaP), or diamond can be used as the material for the
concave portion transfer film 22. By using one of these materials,
it is possible to ensure forming the concave portion 14b to have
the V-shaped cross section by the crystal anisotropic wet
etching.
[0104] It is more preferable that the material for the concave
portion transfer film 22 is one of silicon, SiC, GaP, and diamond.
If so, the concave portion transfer film 22 is constituted by the
high heat resistant material. Due to this, the annealing performed
to eliminate the crystal defects can be executed before the step of
removing the concave portion transfer film 22. It is, therefore,
possible to anneal the carrier supply layer 14 while the carrier
supply layer 14 is hardly exposed.
[0105] Examples of the etchant for forming the transfer concave
portion 22a having the V-shaped cross section if the material other
than GaAs is used for the concave portion transfer film 22, will be
shown according to the materials as follows. If silicon (Si) is the
material for the concave portion transfer film 22, the transfer
concave portion 22a can be formed by anisotropic wet etching using,
as the etchant, a solution mixture of potassium hydroxide (KOH) and
tetra-methyl ammonium hydroxide (TMAH) or by anisotropic dry
etching using, as the etchant, chlorine (Cl.sub.2) gas. If gallium
phosphide (GaP) is the material for the concave portion transfer
film 22, the transfer concave portion 22a can be formed by
anisotropic wet etching using, as the etchant, a solution mixture
of hydrogen bromide (HBr), hydrogen peroxide (H.sub.2O.sub.2), and
water (H.sub.2O) at a volume ratio of 1:1:3 or by anisotropic dry
etching using an etchant mainly containing chlorine (Cl.sub.2) gas.
If silicon carbide (SiC) is the material for the concave portion
transfer film 22, the transfer concave portion 22a can be formed by
dry etching using, as the etchant, a gas mixture of chlorine
(Cl.sub.2) and sulfur hexafluoride (SF.sub.6). If diamond (C) is
the material for the concave portion transfer film 22, the transfer
concave portion 22a can be formed by anisotropic dry etching using,
as the etchant, a hydrogen chloride (HCl) gas.
[0106] It is noted that, in the first and second embodiments, the
carrier supply layer 14 may have a layered structure composed of a
first carrier supply layer 140 made of
Al.sub.uGa.sub.1-uN(0.ltoreq.u.ltoreq.1) and a second carrier
supply layer 141 made of Al.sub.vGa.sub.1-vN (0.ltoreq.v.ltoreq.1,
u.noteq.v), as shown in FIG. 11A to FIG. 11C and FIG. 12A to FIG.
12B. With this structure, the first carrier supply layer 140 and
the second supply layer 141 are different from each other in
composition, resulting in difference from each other in etch rate
in dry etching. Thus, the second carrier supply layer 141 is
selectively etched out of the first carrier supply layer 140 and
the second carrier supply layer 141.
Embodiment 3
[0107] A III-V nitride semiconductor device in the third embodiment
of the present invention will be described with reference to the
drawings.
[0108] FIG. 4 is a cross-sectional block diagram of the III-V
nitride semiconductor device in the third embodiment of the present
invention. In FIG. 4, same components as those shown in FIG. 2A are
denoted by the same reference symbols, respectively, and will not
be repeatedly described herein.
[0109] As shown in FIG. 4, the III-V nitride semiconductor device
in the third embodiment is constituted so that a buffer layer 12
consisting of AlN, a channel layer 13 consisting of undoped GaN,
and a carrier supply layer 14 consisting of n type AlGaN are formed
on a substrate 11 consisting of SiC in this order, and so that a
concave portion 14b having a V-shaped cross section is formed in
the carrier supply layer 14.
[0110] In a region on an upper surface of the carrier supply layer
14 in which region a gate electrode 15 is formed, a low temperature
buffer layer 31 consisting of silicon grown under a low temperature
condition, and a protection film 32 consisting of single-crystal
silicon are formed in this order so as to open the upper part of
the concave portion 14b. The low temperature buffer layer 31 is
provided to relax crystal lattice mismatching between the carrier
supply layer 14 and the protection film 32.
[0111] The gate electrode 15 is formed on the protection film 32 so
as to be filled into opening portions of the low temperature buffer
layer 31 and the protection film 32 and the concave portion 14b. A
source electrode 16 and a drain electrode 17 are formed in regions
in which the low temperature buffer layer 31 and the protection
film 32 are not formed on the upper surface of the carrier supply
layer 14.
[0112] In the semiconductor device in the third embodiment, since
the protection film 32 is provided on the carrier supply layer 14,
a trap density can be reduced in both side portions of the gate
electrode 15 on the upper surface of the carrier supply layer 14.
It is, therefore, possible to further ensure suppressing the
frequency dispersion resulting from the traps on the upper surface
of the carrier supply layer 14, as compared with the second
embodiment.
[0113] In the III-V nitride semiconductor device in the third
embodiment, group IV impurities or group V impurities such as
nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), or
bismuth (Bi) impurities are preferably added to each of the low
temperature buffer layer 31 and the protection film 32. By doing
so, even if gallium or aluminum is inadvertently doped into the low
temperature buffer layer 31 and the protection film 32 during
crystal growth on the low temperature buffer layer 31 and the
concave portion transfer film (=protection film 32), the group IV
impurities or group V impurities contained in the low temperature
buffer layer 31 and the protection film 32 can compensate for the
inadvertently doped gallium or aluminum and the low temperature
buffer layer 31 and the protection film 32 can be kept to have high
resistance. Accordingly, even if the low temperature buffer layer
31 and the protection film 32 are formed using silicon, a gate leak
current resulting from a reduction in specific resistance of
protection film 32 does not occur.
[0114] It is also preferable that an upper portion of the
protection film 32 is oxidized, nitrided, or oxynitrided. By doing
so, the protection film 32 can be formed to have a high resistance
and can be used as a low-leakage and high-reliability protection
film.
[0115] Further, a material for the protection film 32 is not
limited to silicon but may be GaAs, SiC, GaP, or diamond. If one of
these materials is used as the material for the protection film 32,
the material which can relax the lattice mismatching between the
protection film 32 and the carrier supply layer 14 may be selected
as the material for the low temperature buffer layer 31.
[0116] A method for manufacturing the III-V nitride semiconductor
device in the third embodiment of the present invention will now be
described with reference to the drawings.
[0117] FIGS. 5A to 5D are cross-sectional block diagrams that
depict the method for manufacturing the III-V nitride semiconductor
device in the third embodiment of the present invention in order of
steps. In FIGS. 5A to 5D, same components as those shown in FIGS.
3A to 3D are denoted by the same reference symbols, respectively,
and will not be repeatedly described herein.
[0118] As shown in FIG. 5A, the buffer layer 12 consisting of AlN,
the channel layer 13 consisting of undoped GaN, the carrier supply
layer 14 consisting of n type AlGaN, the low temperature buffer
layer 41 having silicon grown under the low temperature condition,
and a concave portion transfer film 42 having silicon subjected to
crystal growth so that a plane orientation is a (100) plane are
formed on the substrate 11 in this order using MOCVD or MBE. A
concave portion formation mask pattern 23 including an opening
portion 23a a longitudinal direction of which is a [110]
orientation of the crystal lattice of silicon of the concave
portion transfer film 42 is formed on the concave portion transfer
film 42 by lithography.
[0119] At the crystal growth step shown in FIG. 5A, a reduction in
the specific resistance of the concave portion transfer film 42
sometimes disadvantageously occurs due to inadvertent doping of
gallium or aluminum into the low temperature buffer layer 41 and
the concave portion transfer film 42. To avoid this, the low
temperature buffer layer 41 and the concave portion transfer film
42 may be formed while adding thereto group IV impurities or group
V impurities. By doing so, the group IV impurities or group V
impurities can prevent the specific resistance of the concave
portion transfer film 42 from being reduced by the inadvertent
doping of gallium or aluminum.
[0120] As shown in FIG. 5B, a transfer concave portion 42a is
formed in the concave portion transfer film 42 exposed to the
opening portion 23a of the mask pattern 23 by wet etching using a
solution mixture of potassium hydroxide (KOH) and propyl alcohol as
an etchant. As the etchant, the solution mixture having a volume
ratio of, for example, KOH:propyl alcohol: H.sub.2O=23.4:13.3:63.3
can be used.
[0121] The etchant consisting of KOH and propyl alcohol exhibits
crystal anisotropy relative to silicon crystals, and an etch rate
of the etchant on the (111) plane is far lower than an etch rate on
the (100) plane. Therefore, the transfer concave portion 42a is
formed to have the (111) plane as an inclined surface and have a
V-shaped cross section.
[0122] As shown in FIG. 5C, after removing the mask pattern 23, an
entire surface of the concave transfer film 22 is etched by dry
etching using a gas mixture of chlorine (Cl.sub.2) and sulfur
hexafluoride (SF.sub.6) as an etching gas, thereby forming the
concave portion 14b in the carrier supply layer 14. A mask pattern
43 that covers a region including the concave portion 14b and
peripheral portions of the concave portion 14b is formed on the
concave portion transfer film 22.
[0123] As shown in FIG. 5D, by sequentially removing exposed parts
of the concave portion transfer film 42 and the low temperature
buffer layer 41 by the etching using the mask pattern 43, the
protection film 42a is formed out of the concave portion transfer
film 42. After removing the mask pattern 43, the source electrode
16 and the drain electrode 17 are formed laterally of the concave
portion 14b using a metallic material which can form an ohmic
contact with the carrier supply layer 14, with the distance kept
between the source electrode 16 and the drain electrode 17 and the
ohmic contact is formed through a heat treatment step. Thereafter,
the gate electrode 15 is formed to be filled into the concave
portion 14b using a metallic material that can form a Schottky
junction with the carrier supply layer 14.
[0124] Through these steps, the semiconductor device in the third
embodiment can be obtained.
[0125] According to the method for manufacturing the III-V nitride
semiconductor device in the third embodiment, since the protection
film 42A is formed out of the concave portion transfer film 42, the
upper surface of the carrier supply layer 14 is not exposed during
manufacturing of the III-V nitride semiconductor device. A crystal
interface on the upper surface side of the carrier supply layer 14
can be, therefore, kept in a favorable condition.
[0126] In the method for manufacturing the III-V nitride
semiconductor device in the third embodiment, after the steps of
forming the gate electrode 15, the source electrode 16, and the
drain electrode 17, the upper portion of the protection film 42A
may be, for example, oxidized or nitrided by plasma oxidation or
plasma nitriding or may be oxynitrided by the plasma oxidation and
the plasma nitriding. By doing so, the resistance of the protection
film 42A can be increased and the reliability of the protection
film 42A can be improved.
[0127] It is noted that execution of the step of oxidizing the
upper portion of the protection film 42A is not limited to a timing
after the formation of the gate electrode 15, the source electrode
16, and the drain electrode 17 but may be after the formation of
the concave portion 14b and before the step of forming the
protection film 42A out of the concave portion transfer film 42. In
addition, at the step of oxidizing the upper portion of the
protection film 42A, a silicon nitride film may be selectively
formed to cover the concave portion 14b, an entire surface of the
concave portion transfer film 42 may be thermally oxidized, and the
protection film 42A may be formed out of the thermally oxidized
concave portion transfer film 42.
[0128] Furthermore, in the method for manufacturing the III-V
nitride semiconductor device in the third embodiment, annealing can
be performed under conditions of a temperature of 300.degree. C. or
more and 1500.degree. C. or less after the dry etching step of
forming the concave portion 14b and before the step of forming the
protection film 42A out of the concave portion transfer film 42. If
so, crystal defects generated in the carrier supply layer 14 can be
eliminated while the carrier supply layer 14 is covered with the
concave portion transfer film 42. Reliability of the III-V nitride
semiconductor device can be thereby improved.
[0129] In the method for manufacturing the III-V nitride
semiconductor device in the third embodiment, the material for the
concave portion transfer film 42 is not limited to single-crystal
silicon but may be an arbitrary material with which the transfer
concave portion 42a having the V-shaped cross section can be formed
based on crystal anisotropy. For example, SiC, GaP, or diamond can
be used as the material for the concave portion transfer film 42.
By using one of these materials, similarly to use of single-crystal
silicon, the concave portion 14b having the V-shaped cross section
based on the crystal anisotropy can be formed in the concave
portion transfer film 42. It is, therefore, possible to ensure
forming the concave portion 14b having the V-shaped cross section
in the carrier supply layer 14. Besides, since SiC, GaP, and
diamond have high heat resistance, the crystal defects on the
carrier supply layer 14 can be eliminated by the annealing while
covering the carrier supply layer 14 with the concave portion
transfer film 42.
Embodiment 4
[0130] A III-V nitride semiconductor device in the fourth
embodiment of the present invention will be described with
reference to the drawings.
[0131] FIG. 6 is a cross-sectional block diagram of the III-V
nitride semiconductor device in the fourth embodiment of the
present invention. In FIG. 6, same components as those shown in
FIG. 2A are denoted by the same reference symbols, respectively,
and will not be repeatedly described herein.
[0132] As shown in FIG. 6, the III-V nitride semiconductor device
in the fourth embodiment is constituted so that a buffer layer 12
consisting of AlN, a channel layer 13 consisting of undoped GaN,
and a carrier supply layer 14 consisting of n type AlGaN are formed
on a substrate 11 consisting of SiC in this order, and so that a
concave portion 14c having a semicircular cross section is provided
in the carrier supply layer 14. A gate electrode 15 is formed on
the carrier supply layer 14 so as to be filled into the concave
portion 14. A source electrode 16 and a drain electrode 17 are
formed laterally of the gate electrode 15 at a distance between the
source electrode 16 and the drain electrode 17. A depth of the
concave portion 14c is set so that a portion of the gate electrode
15 provided in the concave portion 14c substantially functions as a
gate electrode, similarly to the first embodiment.
[0133] According to the III-V nitride semiconductor device in the
fourth embodiment, similarly to the III-V nitride semiconductor
device in the first embodiment, the portion of the gate electrode
15 provided in the concave portion 14c can be used as the
substantial gate electrode. Due to this, it is possible to decrease
the influence of traps present on the upper surface of the carrier
supply layer 14, on the channel region by as much as the depth of
the concave portion 14c. It is, therefore, possible to ensure
suppressing frequency dispersion resulting from the traps on the
upper surface of the carrier supply layer 14.
[0134] Furthermore, since the concave portion 14c is formed to have
the semicircular cross-section, an effective gate length of the
gate electrode 15 can be set small. The III-V nitride semiconductor
device in the fourth embodiment can, therefore, operate at high
rate. The cross-sectional shape of the concave portion 14c is not
limited to the semicircular shape but may be an arbitrary shape as
long as the concave portion 14c is formed so that an opening
dimension is nonlinearly smaller from the upper surface side of the
carrier supply layer 14 toward the depth direction. The
cross-sectional shape of the concave portion 14c may be, for
example, a U shape or a semielliptic shape.
[0135] A method for manufacturing the III-V nitride semiconductor
device in the fourth embodiment of the present invention will now
be described with reference to the drawings.
[0136] FIGS. 7A to 7D are cross-sectional block diagrams that
depict the method for manufacturing the III-V nitride semiconductor
device in the fourth embodiment of the present invention in order
of steps. In FIGS. 7A to 7D, same components as those shown in
FIGS. 3A to 3D are denoted by the same reference symbols,
respectively, and will not be repeatedly described herein.
[0137] As shown in FIG. 7A, the buffer layer 12 consisting of AlN,
the channel layer 13 consisting of undoped GaN, the carrier supply
layer 14 consisting of n type AlGaN, and a concave portion transfer
film 51 consisting of amorphous or polycrystalline silicon are
formed on the substrate 11 in this order using MOCVD or MBE. A mask
pattern 23 including an opening portion 23a is formed on the
concave portion transfer film 51 by lithography.
[0138] At the step of forming the concave portion transfer film 51,
the concave portion transfer film 51 consisting of amorphous
silicon may be formed by, for example, vacuum deposition or
sputtering instead of the MOCVD or the MBE.
[0139] As shown in FIG. 7B, a transfer concave portion 51a is
formed in the concave portion transfer film 51 exposed to the
opening portion 23a of the mask pattern 23 by performing an
isotropic on the concave portion transfer film 51. By performing
the isotropic etching on the concave portion transfer film 51, the
transfer concave portion 51a can be formed so that the opening
dimension is nonlinearly smaller from the surface side toward the
depth direction.
[0140] As shown in FIG. 7C, after removing the mask pattern 23, an
entire surface of the concave transfer film 51 is etched by a
predetermined depth by dry etching using a gas mixture of, for
example, chlorine (Cl.sub.2) and sulfur hexafluoride (SF.sub.6) as
an etching gas. As a result, the carrier supply layer 14 is etched
from the upper surface side below the transfer concave portion 51a,
and the concave portion 14c having the semicircular cross section
is formed in carrier supply layer 14.
[0141] As shown in FIG. 7D, after performing annealing so as to
eliminate the crystal defects generated by the dry etching, the
concave portion transfer film 51 is removed by wet etching or dry
etching. After removing the mask pattern 43, the source electrode
16 and the drain electrode 17 are formed laterally of the concave
portion 14c on the carrier supply layer 14 using a metallic
material which can form an ohmic contact with the carrier supply
layer 14, with the distance kept between the source electrode 16
and the drain electrode 17, and the ohmic contact is formed through
a heat treatment step. Thereafter, the gate electrode 15 is formed
to be filled into the concave portion 14c using a metallic material
that can form a Schottky junction with the carrier supply layer
14.
[0142] Through these steps, the semiconductor device in the fourth
embodiment can be obtained.
[0143] According to the method for manufacturing the III-V nitride
semiconductor device in the fourth embodiment, the transfer concave
portion 51a is formed in the concave portion transfer film 51
consisting of GaAs and the concave portion transfer film 51 is then
subjected to the dry etching, whereby the concave portion 14c
having an equivalent shape to that of the transfer concave portion
51a can be formed in the carrier supply layer 14. Further, by using
amorphous silicon as the material for the concave portion transfer
film, the cross-sectional shape of the transfer concave portion 51a
is formed into the semicircular shape, the U shape, or the
semielliptic shape. The transfer concave portion 51a can be,
therefore, formed so that the opening dimension is nonlinearly
smaller toward the depth direction.
[0144] Further, during the etching for forming the concave portion
14c, an etch selectivity of the material (AlGaN) for the carrier
supply layer 14 to the material (Si) for the concave portion
transfer film 51 is controlled. It is thereby possible to ensure
forming the concave portion 14c while controlling the shape of the
concave portion 14c based on the shape of the transfer concave
portion 51a. It is particularly preferable to set the etch
selectivity at 1 or more.
[0145] In the method for manufacturing the III-V nitride
semiconductor device in the fourth embodiment, the annealing can be
performed under conditions of a temperature of 300.degree. C. or
more and 1500.degree. C. or less after the dry etching step of
forming the concave portion 14c and before removing the concave
portion transfer film 51. If so, crystal defects generated in the
carrier supply layer 14 due to a damage of the dry etching can be
eliminated. Reliability of the semiconductor device can be thereby
improved. Besides, since the annealing is performed before the
concave portion transfer film 51 is removed, the carrier supply
layer 14 can be annealed while the carrier supply layer 14 is
hardly exposed.
[0146] In the method for manufacturing the III-V nitride
semiconductor device in the fourth embodiment, the material for the
concave portion transfer film 51 is not limited to amorphous
silicon but may be an arbitrary material with which the concave
portion 14c can be formed by the isotropic etching so that the
opening dimension is nonlinearly smaller toward the depth
direction. For example, silicon oxide, silicon nitride, silicon
oxynitride, silicon carbide, or III-V nitride semiconductor can be
used as the material for the concave portion transfer film 51.
[0147] Moreover, the material for the concave portion transfer film
51 is not limited to amorphous silicon but may be a polycrystalline
material consisting of, for example, gallium arsenide, silicon,
silicon carbide, gallium phosphide, diamond, or III-V nitride
semiconductor.
Embodiment 5
[0148] A III-V nitride semiconductor device in the fifth embodiment
of the present invention will be described with reference to the
drawings.
[0149] FIG. 8 is a cross-sectional block diagram of the III-V
nitride semiconductor device in the fifth embodiment of the present
invention. In FIG. 8, same components as those shown in FIG. 6 are
denoted by the same reference symbols, respectively, and will not
be repeatedly described herein.
[0150] As shown in FIG. 8, the III-V nitride semiconductor device
in the fifth embodiment is constituted so that a buffer layer 12
consisting of AlN, a channel layer 13 consisting of undoped GaN,
and a carrier supply layer 14 consisting of n type AlGaN are formed
on a substrate 11 consisting of SiC in this order, and so that a
concave portion 14c having a semicircular cross section is provided
in the carrier supply layer 14.
[0151] In a region on an upper surface of the carrier supply layer
14 in which region a gate electrode 15 is formed, a protection film
61 consisting of amorphous silicon is formed to open an upper
portion of the concave portion 14c. The gate electrode 15 is formed
on the protection film 61 so as to be filled into the opening
portion of the protection film 61 and the concave portion 14c. A
source electrode 16 and a drain electrode 17 are formed in regions
in which the protection film 61 is not formed on the upper surface
of the carrier supply layer 14.
[0152] In the III-V nitride semiconductor device in the fifth
embodiment, since the protection film 61 is provided on the carrier
supply layer 14, a trap density can be reduced in both side
portions of the gate electrode 15 on the upper surface of the
carrier supply layer 14. It is, therefore, possible to further
ensure suppressing the frequency dispersion resulting from the
traps on the upper surface of the carrier supply layer 14, as
compared with the fourth embodiment.
[0153] In the III-V nitride semiconductor device in the fifth
embodiment, group IV impurities or group V impurities such as
nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), or
bismuth (Bi) impurities are preferably added to the protection film
61. By doing so, even if gallium or aluminum is inadvertently doped
into the protection film 61 during crystal growth on the protection
film 61, the group IV impurities or group V impurities contained in
the protection film 61 can compensate for the inadvertently doped
gallium or aluminum and the protection film 61 can be kept to have
high resistance. Accordingly, even if the protection film 61 is
formed using silicon, a gate leak current resulting from a
reduction in specific resistance of protection film 61 does not
occur.
[0154] It is also preferable that an upper portion of the
protection film 61 is oxidized, nitrided, or oxynitrided. By doing
so, the protection film 61 can be formed to have a high resistance
and can be used as a low-leakage and high-reliability protection
film.
[0155] Further, a material for the protection film 61 is not
limited to amorphous silicon but may be the other amorphous
material such as silicon oxide or silicon nitride.
[0156] A method for manufacturing the III-V nitride semiconductor
device in the fifth embodiment of the present invention will now be
described with reference to the drawings.
[0157] FIGS. 9A to 9D are cross-sectional block diagrams that
depict the method for manufacturing the III-V nitride semiconductor
device in the fifth embodiment of the present invention in order of
steps. In FIGS. 9A to 9D, same components as those shown in FIGS.
7A to 7D are denoted by the same reference symbols, respectively,
and will not be repeatedly described herein.
[0158] As shown in FIG. 9A, the buffer layer 12 consisting of AlN,
the channel layer 13 consisting of undoped GaN, the carrier supply
layer 14 consisting of n type AlGaN, and a concave portion transfer
film 51 consisting of amorphous or polycrystalline silicon are
formed on the substrate 11 in this order using MOCVD or MBE. A mask
pattern 23 including an opening portion 23a is formed on the
concave portion transfer film 51 by lithography.
[0159] At the step of forming the concave portion transfer film 51,
the concave portion transfer film 51 consisting of amorphous
silicon may be formed by, for example, vacuum deposition or
sputtering instead of the MOCVD or the MBE.
[0160] At the crystal growth step shown in FIG. 9A, a reduction in
the specific resistance of the concave portion transfer film 42
sometimes disadvantageously occurs due to inadvertent doping of
gallium or aluminum into the concave portion transfer film 51. To
avoid this, the concave portion transfer film 51 may be formed
while adding thereto group IV impurities or group V impurities. By
doing so, the group IV impurities or group V impurities can prevent
the specific resistance of the concave portion transfer film 51
from being reduced by the inadvertent doping of gallium or
aluminum.
[0161] As shown in FIG. 9B, a transfer concave portion 51a is
formed in the concave portion transfer film 51 exposed to the
opening portion 23a of the mask pattern 23 by performing isotropic
etching on the concave portion transfer film 51. By performing the
isotropic etching on the concave portion transfer film 51, the
transfer concave portion 51a can be formed so that the opening
dimension is nonlinearly smaller from the surface side toward the
depth direction.
[0162] As shown in FIG. 9C, after removing the mask pattern 23, an
entire surface of the concave transfer film 51 is etched by a
predetermined depth by dry etching using a gas mixture of, for
example, chlorine (Cl.sub.2) and sulfur hexafluoride (SF.sub.6) as
an etching gas, thereby forming the concave portion 14c having the
semicircular cross section in carrier supply layer 14. A mask
pattern 43 that covers a region including the concave portion 14c
and peripheral portions of the concave portion 14c is formed on the
concave portion transfer film 51.
[0163] As shown in FIG. 9D, by removing an exposed part of the
concave portion transfer film 51 by the etching using the mask
pattern 43, a protection film 51A is formed out of the concave
portion transfer film 51. After removing the mask pattern 43, the
source electrode 16 and the drain electrode 17 are formed laterally
of the concave portion 14c on the carrier supply layer 14 using a
metallic material which can form an ohmic contact with the carrier
supply layer 14, with the distance kept between the source
electrode 16 and the drain electrode 17 and the ohmic contact is
formed through a heat treatment step. Thereafter, the gate
electrode 15 is formed to be filled into the concave portion 14c
using a metallic material that can form a Schottky junction with
the carrier supply layer 14.
[0164] Through these steps, the semiconductor device in the fifth
embodiment can be obtained.
[0165] According to the method for manufacturing the III-V nitride
semiconductor device in the fifth embodiment, since the protection
film 51A is formed out of the concave portion transfer film 51, the
upper surface of the carrier supply layer 14 is not exposed during
manufacturing of the III-V nitride semiconductor device. A crystal
interface on the upper surface side of the carrier supply layer 14
can kept in a favorable condition.
[0166] In the method for manufacturing the III-V nitride
semiconductor device in the fifth embodiment, after the steps of
forming the gate electrode 15, the source electrode 16, and the
drain electrode 17, the upper portion of the protection film 51A
may be, for example, oxidized or nitrided by plasma oxidation or
plasma nitriding or may be oxynitrided by the plasma oxidation and
the plasma nitriding. By doing so, the resistance of the protection
film 51A can be increased and the reliability of the protection
film 51A can be improved.
[0167] In the method for manufacturing the III-V nitride
semiconductor device in the fifth embodiment, annealing can be
performed under conditions of a temperature of 300.degree. C. or
more and 1500.degree. C. or less after the dry etching step of
forming the concave portion 14c and before the step of forming the
protection film 51A out of the concave portion transfer film 51. If
so, crystal defects generated in the carrier supply layer 14 can be
eliminated while the carrier supply layer 14 is covered with the
concave portion transfer film 51. Reliability of the semiconductor
device can be thereby improved.
[0168] In the method for manufacturing the III-V nitride
semiconductor device in the fifth embodiment, the material for the
concave portion transfer film 51 is not limited to amorphous
silicon but may be an arbitrary material with which the concave
portion 14c can be formed by the isotropic etching so that the
opening dimension is nonlinearly smaller toward the depth
direction. For example, silicon oxide, silicon nitride, silicon
oxynitride, silicon carbide, or III-V nitride semiconductor can be
used as the material for the concave portion transfer film 51.
[0169] Moreover, the material for the concave portion transfer film
51 is not limited to amorphous silicon but may be a polycrystalline
material consisting of, for example, gallium arsenide, silicon,
silicon carbide, gallium phosphide, diamond, or III-V nitride
semiconductor.
[0170] In the III-V nitride semiconductor devices in the first
embodiment to the fifth embodiment, the material for the substrate
11 is not limited to SiC but may be, for example, sapphire or
silicon. By appropriately selecting the material for the buffer
layer 12 according to the material for the substrate 11, the
channel layer 13 and the carrier supply layer 14 can be formed to
make lattice matching relative to the substrate 11.
[0171] Furthermore, each of the III-V nitride semiconductor devices
in the first embodiment to the fifth embodiment is constituted to
function as the HFET by providing the channel layer 13 and the
carrier transfer layer 14. However, the configuration of each of
the III-V nitride semiconductor devices in the first embodiment to
the fifth embodiment is not limited to this but may be such that
the channel region is formed in one semiconductor layer consisting
of a III-V nitride semiconductor or in a multilayer structure
consisting of a plurality of III-V nitride semiconductor. For
example, each of the III-V nitride semiconductor devices in the
first embodiment to the fifth embodiment may be constituted to
function as a metal semiconductor FET ("MESFET") by forming one
channel layer consisting of n type GaN instead of the channel layer
13 and the carrier supply layer 14.
[0172] As stated so far, the semiconductor device and the method
for manufacturing the semiconductor device according to the present
invention can advantageously reduce the frequency dispersion
resulting from the traps between the III-V nitride semiconductor
and the Schottky electrode and improve the high frequency
characteristics of the device. Therefore, the semiconductor device
and the method for manufacturing the semiconductor device according
to the present invention are useful as a semiconductor device
having a Schottky electrode provided on a semiconductor layer
consisting of a III-V nitride semiconductor and a method for
manufacturing the semiconductor device.
* * * * *