U.S. patent application number 09/753412 was filed with the patent office on 2001-08-23 for sic device and method for manufacturing the same.
This patent application is currently assigned to Matsushita Electric Industrial Co., Ltd.. Invention is credited to Kitabatake, Makoto.
Application Number | 20010015170 09/753412 |
Document ID | / |
Family ID | 27525795 |
Filed Date | 2001-08-23 |
United States Patent
Application |
20010015170 |
Kind Code |
A1 |
Kitabatake, Makoto |
August 23, 2001 |
SiC device and method for manufacturing the same
Abstract
A method for manufacturing a device of silicon carbide (SiC) and
a single crystal thin film, which are wide band gap semiconductor
materials and can be applied to semiconductor devices such as high
power devices, high temperature devices, and environmentally
resistant devices, is provided by heating a silicon carbide crystal
in an oxygen atmosphere to form a silicon (di)oxide thin film on a
silicon carbide crystal surface, and etching the silicon (di)oxide
thin film formed on the silicon carbide crystal surface to prepare
a clean SiC surface. The above SiC device comprises a clean surface
having patterned steps and terraces, has a surface defect density
of 10.sup.8 cm.sup.-2 or less, or has at least a layered structure
in which an n-type silicon carbide crystal is formed on an n-type
Si substrate surface.
Inventors: |
Kitabatake, Makoto; (Nara,
JP) |
Correspondence
Address: |
MERCHANT & GOULD
P O BOX 2903
MINNEAPOLIS
MN
55402-0903
US
|
Assignee: |
Matsushita Electric Industrial Co.,
Ltd.
1006-Banchi Oaza-Kadoma, Kadoma-shi
Osaka
JP
571-8501
|
Family ID: |
27525795 |
Appl. No.: |
09/753412 |
Filed: |
January 2, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09753412 |
Jan 2, 2001 |
|
|
|
08993817 |
Dec 18, 1997 |
|
|
|
6214107 |
|
|
|
|
08993817 |
Dec 18, 1997 |
|
|
|
PCT/JP97/00855 |
Mar 17, 1997 |
|
|
|
Current U.S.
Class: |
117/95 ;
257/E21.054; 257/E21.06; 257/E21.062; 257/E21.064; 257/E29.081;
257/E29.104; 257/E29.143; 257/E29.148; 257/E29.338 |
Current CPC
Class: |
C30B 29/36 20130101;
H01L 21/0475 20130101; H01L 29/872 20130101; H01L 29/45 20130101;
H01L 21/0495 20130101; C30B 33/00 20130101; H01L 29/1608 20130101;
H01L 29/267 20130101; C30B 33/00 20130101; C30B 29/36 20130101;
H01L 29/47 20130101; H01L 21/0485 20130101; H01L 21/0445
20130101 |
Class at
Publication: |
117/95 |
International
Class: |
C30B 023/00; C30B
025/00; C30B 028/12; C30B 028/14 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 18, 1996 |
JP |
8-96496 |
Apr 19, 1996 |
JP |
8-98218 |
Apr 19, 1996 |
JP |
8-98219 |
Nov 15, 1996 |
JP |
8-304383 |
Claims
1. A method for manufacturing a SiC device comprising a step for
heating a silicon carbide crystal in an oxygen atmosphere to form a
silicon (di)oxide thin film on a silicon carbide crystal surface,
and a step for removing the silicon (di)oxide thin film formed on
the silicon carbide crystal surface by etching to expose a clean
surface of the SiC.
2. The method according to claim 1, comprising a first step for
implanting ions to at least a part of a surface of a SiC silicon
carbide crystal to introduce crystal defects near the SiC crystal
surface to form an amorphous layer, a second step for heating the
SiC crystal, to which the ions are implanted and the defects are
introduced and which contains the amorphous layer, in an oxygen
atmosphere to form a silicon (di)oxide thin film on the SiC crystal
surface, and a third step for etching the silicon (di)oxide thin
film formed on the SiC crystal surface.
3. The method according to claim 2, wherein the ion implanted to
the SiC surface in the first step is at least one gas selected from
the group consisting of oxygen, silicon, carbon, an inert gas,
nitrogen, and hydrogen.
4. The method according to claim 2, wherein a dose of the ions
implanted to the SiC surface in the first step is 10.sup.14
ions/cm.sup.2 or more.
5. The method according to claim 2, wherein an energy of the ions
implanted to the SiC surface in the first step is 1 keV to 10
MeV.
6. The method according to claim 2, wherein two or more types of
energies of the ions implanted to the SiC surface in the first step
are selected for multiple implantation.
7. The method according to claim 2, wherein a temperature of the
SiC is maintained at 500.degree. C. or lower when implanting ions
to the SiC surface in the first step.
8. The method according to claim 2, wherein a part of the SiC
surface is masked and a portion where ions are implanted is
patterned when ions are implanted to the SiC surface in the first
step.
9. The method according to claim 2, wherein at least one factor
selected from the group consisting of an energy of the implanted
ions, ion species, and ion density is different depending on a
place on the SiC surface and patterning is performed when ions are
implanted to the SiC surface in the first step.
10. The method according to claim 1, wherein a silicon carbide
surface on which patterned steps and terraces are formed by an
etching treatment is heated in an oxygen atmosphere to form a
silicon (di)oxide thin film on the silicon carbide crystal surface,
and the defects introduced by the etching treatment are removed by
further etching the silicon (di)oxide thin film formed on the
silicon carbide crystal surface.
11. The method according to claim 10, wherein the etching treatment
is performed by at least one method selected from the group
consisting of reactive ion etching, ion milling, plasma etching,
laser etching, mechanical cutting, and mechanical grinding.
12. The method according to claim 1, comprising a first step for
supplying carbon to a Si substrate surface maintained at low
temperature to form a thin film containing carbon on the Si
substrate surface, a second step for heating the Si substrate
surface to cause a solid phase reaction between the Si substrate
and the thin film containing carbon to carbonize the Si substrate
surface to form silicon carbide, and a third step for supplying
carbon and silicon after carbonization to grow silicon carbide so
as to obtain a silicon carbide crystal film on the Si
substrate.
13. The method according to claim 12, wherein the Si substrate
surface is maintained in a temperature range of a liquid nitrogen
temperature, -195.degree. C., to 600.degree. C. when the thin film
containing carbon is deposited on the Si substrate surface in the
first step.
14. The method according to claim 12, wherein the thin film formed
on the Si substrate surface by the first step contains carbon
corresponding to a thickness of a 1-atomic layer to 20-atomic
layers.
15. The method according to claim 12, wherein the thin film formed
on the Si substrate surface by the first step is an amorphous thin
film containing carbon.
16. The method according to claim 12, wherein a substance
containing carbon supplied to the Si substrate surface in the first
step contains at least molecular carbon.
17. The method according to claim 12, wherein the Si substrate
surface is heated to a temperature range of 800.degree. C. to
1414.degree. C., the melting point of Si, in the second step.
18. The method according to claim 12, wherein a temperature
increase rate between 600.degree. C. and 1000.degree. C. is
2.degree. C./min. to 500.degree. C./min. when heating the Si
substrate surface in the second step.
19. The method according to claim 12, wherein at least the first
and the second steps are carried out under a vacuum of not more
than 10.sup.-7 Torr.
20. The method according to claim 12, wherein at least the first
and second steps are carried out by a molecular beam epitaxy (MBE)
process under vacuum, and the third step or a part of the third
step is carried out by a chemical vapor deposition (CVD) process
providing a fast growth rate.
21. The method according to claim 12, comprising a step for
removing an oxide film from the Si substrate surface to clean the
surface before supplying carbon.
22. The method according to claim 21, wherein the cleaned Si
surface has a Si(001)2.times.1 surface reconstruction
structure.
23. The method according to claim 21, wherein the step for cleaning
the Si substrate surface comprises a step of heating to 800.degree.
C. or higher under a vacuum of not more than 10.sup.-6 Torr or in a
hydrogen atmosphere.
24. The method according to claim 21, wherein the step for cleaning
the Si substrate surface comprises a step of irradiating the
substrate surface with ultraviolet rays.
25. The method according to claim 21, wherein the step for cleaning
the Si substrate surface comprises a step of exposing the Si
substrate surface to at least one reactive etching gas selected
from the group consisting of ozone and chlorine, chloride and
fluorine, and fluoride gases.
26. The method according to claim 12, wherein an abundance ratio of
carbon to silicon on the silicon carbide surface is controlled so
that silicon atoms are always in excess of carbon atoms on the
surface for growing silicon carbide when silicon and carbon are
supplied to the surface of the SiC to grow 3C-SiC having a (001)
face in the third step.
27. The method according to claim 26, wherein the abundance ratio
of carbon to silicon on the silicon carbide surface is controlled
so that the (001) growth surface of the 3C-SiC has at least one
surface reconstruction selected from the group consisting of
3.times.2 and 5.times.2.
28. The method according to claim 26, wherein the abundance ratio
of carbon to silicon on the silicon carbide surface is controlled
so that the abundance ratio of silicon atoms to carbon atoms on the
(001) growth surface of the 3C-SiC is greater than 1 and equal to
or less than 2, in an excess silicon state.
29. The method according to claim 26, wherein a measuring means
that can evaluate the surface structure of silicon carbide during
growth is provided in a SiC formation apparatus to monitor the
3.times.2 or 5.times.2 structure of the 3C-SiC(001) surface, and an
apparatus having a mechanism for controlling the abundance ratio of
carbon to silicon on the SiC surface is used so that a 3.times.2
period or a 5.times.2 period is constantly observed when silicon
and carbon are supplied to the surface of the SiC to form a 3C-SiC
thin film having a (001) face.
30. The method according to claim 12, wherein an abundance ratio of
carbon to silicon on the silicon carbide surface is controlled so
that carbon atoms are in excess of silicon atoms on the SiC growth
surface when silicon and carbon are supplied to the surface of the
SiC to form 3C-SiC having a (111) face or an .alpha.-SiC thin film
having a (0001) face in the third step.
31. The method according to claim 30, wherein the abundance ratio
of carbon to silicon on the SiC surface is controlled so that the
ratio of silicon atoms to carbon atoms on the (111) growth surface
of the 3C-SiC or the (0001) growth surface of the .alpha.-SiC is
0.5 to 1, in an excess carbon state.
32. The method according to claim 30, wherein a measuring means
that can evaluate the surface structure of silicon carbide during
growth is provided in a SiC formation apparatus to observe the
state of the 3C-SiC(111) surface in-situ, and an apparatus having a
mechanism for controlling the abundance ratio of carbon to silicon
on the SiC surface and inhibiting the growth of a crystal other
than SiC is used when silicon and carbon are supplied to the
surface of the SiC to form a 3C-SiC thin film having a (111) face
or an a-SiC thin film having a (0001) face.
33. The method according to claim 12, wherein a Si substrate
surface used for growing a silicon carbide thin film on the Si
substrate surface is a miscut face of Si(001), an angle formed by a
direction of step edges caused by miscut and a Si<110>
crystal axis direction is 0 to 30 degrees, and the Si substrate
surface has anisotropy and comprises terraces and steps.
34. The method according to claim 33, wherein a width of the
terrace of the Si substrate surface is 0.5 nm to 100 nm.
35. The method according to claim 33, wherein pattern is formed by
an etching treatment on the Si substrate surface to introduce
terraces and steps having anisotropy.
36. The method according to claim 33, wherein an abundance ratio of
carbon to silicon on the silicon carbide surface is controlled so
that silicon atoms are always in excess of carbon atoms on the
surface for growing silicon carbide when silicon and carbon are
supplied to the SiC surface to grow 3C-SiC having a (001) face.
37. The method according to claim 36, wherein the abundance ratio
of carbon to silicon on the silicon carbide surface is controlled
so that the 3C-SiC(001) growth surface has at least one surface
rearrangement selected from the group consisting of 3.times.2 and
5.times.2.
38. The method according to claim 36, wherein the abundance ratio
of carbon to silicon on the silicon carbide surface is controlled
so that the abundance ratio of silicon atoms to carbon atoms on the
3C-SiC(001) growth surface is greater than 1 and equal to or less
than 2, in an excess silicon state.
39. The method according to claim 37, wherein a measuring means
that can evaluate the surface structure of silicon carbide during
growth is provided in a SiC formation apparatus to monitor the
3.times.2 or 5.times.2 structure of the 3C-SiC(001) surface, and an
apparatus having a mechanism for controlling the abundance ratio of
carbon to silicon on the SiC surface is used so that a 3.times.2
period or a 5.times.2 period is constantly observed when silicon
and carbon are supplied to the surface of the SiC to form a 3C-SiC
thin film having a (001) face.
40. The method according to claim 1, comprising after cleaning of
SiC surface, and the formation and etching of silicon (di)oxide
thin film on SiC, a first step for implanting ions to a surface of
a SiC silicon carbide crystal to introduce crystal defects in the
silicon carbide crystal and a second step for heating the silicon
carbide crystal substrate, to which the ions are implanted and the
defects are introduced, in an oxygen atmosphere to form a silicon
(di)oxide thin film.
41. The method according to claim 40, wherein the ion implanted to
the SiC surface in the first step is at least one ion selected from
the group consisting of oxygen, silicon, carbon, an inert gas,
nitrogen, and hydrogen.
42. The method according to claim 40, wherein a dose of the ions
implanted in the SiC surface in the first step is 10.sup.14
ions/cm.sup.2 or more.
43. The method according to claim 40, wherein an energy of the ions
implanted in the SiC surface in the first step is 1 keV to 10
MeV.
44. The method according to claim 40, wherein two or more types of
energies of the ions implanted in the SiC surface in the first step
are selected for multiple implantation.
45. The method according to claim 40, wherein the SiC is maintained
at 500.degree. C. or lower when implanting ions in the SiC surface
in the first step.
46. The method according to claim 40, wherein an amorphous layer is
formed near the SiC surface by implanting ions in the SiC surface
in the first step, and the SiC containing the amorphous layer is
oxidized in the second step.
47. A SiC device, wherein a 3C-SiC [110] (Si(lower portion)C(upper
portion)) direction of a SiC silicon carbide film formed on a Si
substrate is parallel to a short Si [110] direction parted by step
edges among anisotropic Si [110] directions of the substrate.
48. The SiC device according to claim 47, comprising a surface
having patterned steps and terraces and having a surface defect
density of 10.sup.8 cm.sup.-2 or less.
49. The SiC device according to claim 47, comprising at least a
layered structure in which an n-type silicon carbide crystal is
formed on an n-type Si substrate surface.
50. The SiC device according to claim 49, wherein a resistivity of
the n-type Si substrate is 10.sup.2 .OMEGA..multidot.cm or
less.
51. The SiC device according to claim 49, comprising at least a
Schottky diode comprising a layered structure in which an n-type
silicon carbide crystal is formed on an n-type Si substrate
surface.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for manufacturing
a single crystal thin film of silicon carbide (SiC) that is a wide
band gap semiconductor material and can be applied to semiconductor
devices such as high power devices, high temperature devices, and
environmentally resistant devices. More particularly, the present
invention relates to a method for forming a single-phase 3C-SiC
single crystal thin film having a few crystal defects by
heteroepitaxial growth on the Si wafer substrate surface.
[0002] The method for treating the surface of SiC according to the
present invention relates to a method for forming an insulating
film and a method for forming a clean surface in forming an
electronic device such as a semiconductor device or a sensor using
silicon carbide (SiC), a method for forming a surface structure
having a trench structure or the like, and a SiC device having the
formed low defect surface.
[0003] The SiC device of the present invention can be used for a
semiconductor electronic device such as a power device or a sensor
using SiC formed on a Si substrate or 6H(4H)-SiC wafers.
BACKGROUND
[0004] In order to form a silicon carbide semiconductor device with
good reproducibility, it is required that a SiC clean surface is
formed first and then an insulating film, an electrode, or the like
is formed on the clean surface. Therefore, the structure of the SiC
clean surface and a method for forming the SiC clean surface must
be established. However, this method has not been reported. It is
known that when SiC is heated to a very high temperature of
1300.degree. C. or higher under high vacuum, Si desorbs from the
surface and the surface is covered with excessive carbon. The
carbon has been turned into graphite, and if junction interface
formation or epitaxial growth is carried out using this surface, an
impurity level is formed at the interface. Also, the temperature of
1300.degree. C. is too high and is a problem from the viewpoint of
the processing. Therefore, an improvement in the method for forming
a clean surface at low temperature has been required.
[0005] Also, in order to form a more efficient electronic device,
it is sometimes required to form structural patterns of steps and
terraces such as a trench structure on the SiC surface. However, a
method for forming the trench structure or the like into the SiC
surface, with good reproducibility, good control, and low defect,
has not been established. A surface having structural patterns,
formed by reactive ion etching with a HCl gas or an
O.sub.2+CF.sub.4 gas, ion milling with an inert gas, HF plasma
etching, laser etching using excimer lasers, or mechanical cutting
or grinding with a diamond saw, has defects of about 10.sup.9
cm.sup.-2 or more, causing a problem when forming electronic
devices.
[0006] Conventionally, 6H-type and 4H-type SiC single crystal
substrates (wafers) have been commercially available. On the other
hand, 3C-SiC, which has the highest drift speed, can only be formed
as a heteroepitaxially grown crystal on the Si substrate. When
growing silicon carbide (3C-SiC) on the Si substrate surface,
carbon and/or hydrogen gases are first supplied to the Si surface
to be carbonized by heating, and then carbon and silicon are
supplied to heteroepitaxially grow silicon carbide. In the silicon
carbide thin film formed by this conventional technique, the
formation of high density lattice defects, twins, pits, or the like
occurs at the SiC/Si interface, causing a problem when the silicon
carbide is applied to forming an electronic device. Furthermore,
single crystal grains with two types of phases grow on the Si
substrate, and an anti phase boundary (APB) is formed at the
interface of the two types of the crystal grains having a different
phase from each other, so that a number of defects are
introduced.
[0007] Conventionally, an insulating film for electronic devices
comprises a silicon (di)oxide thin film formed by subjecting SiC
itself to an oxidation treatment. For example, by subjecting a
6H-SiC(0001)Si face to wet oxidation at 1100.degree. C. for 1 hour,
a thin silicon (di)oxide thin film having a thickness of about 30
nm (300 angstroms) is formed. However, the oxidation speed of 30 nm
(300 angstroms)/hour is much lower than 700 nm (7000
angstroms)/hour for a normal Si process and is not practical. Also,
the silicon (di)oxide SiO.sub.2 is formed by oxidizing silicon
carbide containing Si atoms and C atoms in a ratio of 1:1, so that
the silicon (di)oxide contains surplus carbon atoms and has a low
electrical insulating property. Furthermore, when measuring the
refractive index and the thickness using an ellipsometer, the
refractive index is about 1.2 to 1.3, smaller than 1.4 to 1.5 for
intrinsic silicon (di)oxide. This shows that the silicon (di)oxide
contains a portion different from the intrinsic SiO.sub.2 or that
the SiO.sub.2/SiC interface is not abrupt and contains other
substances, causing a problem when it is used as the insulating
film for an electronic device that requires a clean interface.
[0008] With respect to single crystal substrates such as 6H and 4H
of SiC, the silicon carbide crystals are very hard. Therefore, it
has been known conventionally that when a single crystal is cut and
polished during the processing for wafers, a number of defects are
introduced especially to the surface. In the surface treatment for
these substrates, cleaning with an agent such as RCA cleaning has
conventionally been carried out. However, the defects present near
the silicon carbide surface cannot be removed by cleaning with an
agent such as the conventional RCA cleaning. Therefore, when an
electronic device is formed, the mobility, the reproducibility, the
breakdown voltage and the like degrade.
[0009] The single-crystal silicon-carbide wafer size is about a
diameter of 30 mm, which is too small, which is a problem from a
practical viewpoint. Therefore, SiC formed on the Si substrate
surface is expected as a wafer having a large area. However, the
electric characteristics of the SiC/Si layered structure are not
clear. Therefore, a vertical type semiconductor device in which
current flows through the SiC/Si interface has not been
implemented, for example; the loss caused by the forward voltage
drop, or the like cannot be determined.
SUMMARY OF THE INVENTION
[0010] It is an object of the present invention to provide a method
for manufacturing a single crystal thin film of silicon carbide
(SiC) that is a wide band gap semiconductor material and can be
applied to semiconductor devices such as high power devices, high
temperature devices, and environmentally resistant devices. More
particularly, it is a first object of the present invention to
provide a method for forming an insulating film, a method for
forming a clean surface for application of an electronic device
such as a semiconductor device or a sensor using silicon carbide
(SiC), a method for forming a surface structure having a trench
structure or the like, and a SiC device having the formed low
defect surface.
[0011] Next, it is a second object to provide a method for forming
a single-phase 3C-SiC single crystal thin film having few crystal
defects by heteroepitaxial growth on the Si wafer substrate
surface.
[0012] Furthermore, it is a third object of the present invention
to provide a semiconductor electronic device such as a power device
or a sensor using SiC formed on a Si substrate.
[0013] In order to achieve the above first objects, a method for
manufacturing a SiC device according to the present invention
comprises a process for forming a silicon (di)oxide thin film on a
silicon carbide crystal surface by heating a silicon carbide
crystal in an oxygen atmosphere, and a process for etching the
silicon (di)oxide thin film formed on the silicon carbide crystal
surface.
[0014] In the above method, it is preferred to include a first step
for implanting ions in at least a part of a surface of a SiC
silicon carbide crystal to introduce crystal defects near the SiC
crystal surface, a second step for heating the SiC crystal, in
which the ions are implanted and the defects are introduced, in an
oxygen atmosphere to form a silicon (di)oxide thin film on the SiC
crystal surface, and a third step for etching the silicon (di)oxide
thin film formed on the SiC crystal surface.
[0015] In the above method, it is preferred that the ion implanted
in the SiC surface in the first step is at least one ion selected
from the group consisting of oxygen, silicon, carbon, an inert gas,
nitrogen, and hydrogen.
[0016] In order to achieve the above second objects, it is
preferred to include a first step for supplying carbon to a Si
substrate surface maintained at a low temperature of about
600.degree. C. or lower to form a thin film containing carbon on
the Si substrate surface, a second step for heating the Si
substrate surface to cause a solid phase reaction between the Si
substrate and the thin film containing carbon to carbonize the Si
substrate surface to form silicon carbide, and a third step for
supplying carbon and silicon after carbonization to grow silicon
carbide so as to obtain a silicon carbide crystal film on the Si
substrate.
[0017] In the above method, it is preferred to include a step for
cleaning and removing an oxide film from the Si substrate surface
to make the clean Si surface before supplying carbon.
[0018] In the above method, it is preferred that when silicon and
carbon are supplied to the surface of the SiC to grow 3C-SiC having
a (001) face, an abundance ratio of carbon to silicon on the
silicon carbide surface is controlled under the condition where
silicon atoms are always in excess of carbon atoms on the surface
for growing silicon carbide.
[0019] In the above method, it is preferred that when silicon and
carbon are supplied to the surface of the SiC to form 3C-SiC having
a (111) face or an .alpha.-SiC thin film having a (0001) face, an
abundance ratio of carbon to silicon on the silicon carbide surface
is controlled under the condition where carbon atoms are always in
excess of silicon atoms on the SiC growth surface.
[0020] In the above method using anisotropic Si substrate, it is
preferred that a Si substrate surface used for growing a silicon
carbide thin-film on the Si substrate surface has anisotropy and
comprises terraces and steps.
[0021] In order to achieve the above third objects, it is preferred
that when silicon and carbon are supplied to the SiC surface to
grow 3C-SiC having a (001) face, an abundance ratio of carbon to
silicon on the silicon carbide surface is controlled under the
condition where silicon atoms are always in excess of carbon atoms
on the surface for growing silicon carbide.
[0022] In the above method, it is preferred to include a first step
for implanting ions in a surface of a SiC silicon carbide crystal
to introduce crystal defects in the silicon carbide crystal and a
second step for heating the silicon carbide crystal substrate, in
which the ions are implanted and the defects are introduced, in an
oxygen atmosphere to form a silicon (di)oxide thin film.
[0023] Next, a first SiC device of the present invention comprises
a surface having patterned steps and terraces and having a surface
defect density of 10.sup.8 cm.sup.-2 or less.
[0024] Next, a second SiC device of the present invention comprises
at least a layered structure in which an n-type silicon carbide
crystal is formed on an n-type Si substrate surface.
BRIEF DESCRIPTION OF DRAWINGS
[0025] FIGS. 1A-C show a method for forming a clean surface
according to a method for manufacturing a SiC device in an example
of the present invention.
[0026] FIGS. 2A-E show a method for forming a patterned clean
surface according to a method for manufacturing a SiC device in
another example of the present invention.
[0027] FIGS. 3A-C show a conceptual view for the process of a
method for growing SiC on a Si(001) substrate in another example of
the present invention.
[0028] FIG. 4 shows a conceptual view of the growth of SiC on a Si
surface having anisotropy in another example of the present
invention.
[0029] FIG. 5 shows a method for forming a silicon (di)oxide
insulating film according to a method for manufacturing a SiC
device in another example of the present invention.
[0030] FIG. 6 shows a method for forming a silicon (di)oxide
insulating film according to a method for manufacturing a SiC
device in another example of the present invention.
[0031] FIG. 7 shows a basic structure of a silicon carbide
semiconductor device in another example of the present
invention.
[0032] FIG. 8 is a band view of a silicon carbide semiconductor
device in another example of the present invention.
[0033] FIG. 9 is a traced drawing of a scanning electron microscope
(SEM) photograph of a 3C-SiC(001) surface formed by a method for
growing SiC in Example 6 of the present invention.
[0034] FIG. 10A shows an electron spin resonance (ESR) spectrum for
a single-phase 3C-SiC single crystal thin film formed by the method
for growing SiC in Example 6 of the present invention.
[0035] FIG. 10B shows an ESR spectrum for a silicon carbide thin
film formed by a comparative example (carbonization reaction caused
by the reaction between a gas and a Si substrate surface).
[0036] FIG. 11 shows a method for forming a silicon (di)oxide
insulating film according to a method for manufacturing a SiC
device in Example 8 of the present invention.
[0037] FIG. 12 shows an ohmic characteristic evaluation device of a
silicon carbide semiconductor device in Example 10 of the present
invention.
[0038] FIG. 13 shows the I-V characteristics of an n-type
SiC/n-type Si layered structure in Example 10 of the present
invention.
[0039] FIG. 14 shows the basic structure of a Schottky diode in
Example 11 of the present invention.
[0040] FIG. 15 shows the current (I)-voltage (V) characteristics of
the Schottky diode in Example 11 of the present invention.
DETAILED DESCRIPTION
[0041] The disclosure of PCT/JP97/00855, filed Mar. 17, 1997, is
incorporated herein by reference.
[0042] In the method for manufacturing a silicon carbide SiC device
according to the present invention, a portion 13 having a high
defect density near the surface 12 of a SiC crystal 11 shown in
FIG. 1A is turned into a silicon (di)oxide thin film 14 by a
thermal oxidation treatment as shown in FIG. 1B, and this silicon
(di)oxide thin film is removed by etching the silicon (di)oxide
thin film as shown in FIG. 1C to remove the portion having a high
defect density near the silicon carbide surface and then a clean
surface 15 of SiC is formed. In a conventional etching treatment
with a HF group acidic solution used in a Si process, etching the
surface of SiC, even it is defective, is difficult. However, in the
present invention the portion 13 having a high defect density is
changed into the oxide film first and then the oxide film to remove
the portion having a high defect density near the surface to allow
the surface of the silicon carbide to be cleaned. Therefore, a SiC
clean surface can be formed using the oxidation and etching
treatment in the Si process.
[0043] In the above method, as shown in FIG. 2A, implanting ions 23
are introduced to a portion 24 having a high defect density near
the SiC crystal surface 22 at a desired position and at a desired
depth in a first step. The introduced defective portion 24 is
deeper than the defect layer 25, which exists from the first, near
the SiC surface. In a second step of thermal oxidation process, the
oxygen is supplied into the crystal from the surface through the
crystal defects introduced by the ion implantation; the area 24,
into which the crystal defects are introduced by the ion
implantation, is easily oxidized; carbon turns into a gas in the
form of carbon oxide to be removed, and silicon (di)oxide is
formed. This silicon (di)oxide thin film is removed by etching in a
third step, so that a defect layer 25, which exists from the first,
near the silicon carbide surface can be removed easily.
[0044] In the above method, it is preferred that the ion implanted
in the SiC surface in the first step is selected from any of
oxygen, silicon, carbon, an inert gas, nitrogen, and hydrogen, or a
mixture thereof, so that the implanted ions form silicon (di)oxide
or turn into a gas to be removed after oxidation.
[0045] In the above method, it is preferred that the dose of the
implanted ions is more than 10.sup.14 ion/cm.sup.2, so that
sufficient crystal defects for oxide diffusion into SiC to remove
carbon and to form silicon (di)oxide, a silicon (di)oxide
insulating film is formed at high speed, an excess substance or
structure is not formed at the SiO.sub.2/SiC interface, an abrupt
interface is formed, and a cleaner silicon carbide surface is
formed after oxide film etching. At a dose less than this value,
the oxidation does not fully proceed, defects remain, the interface
of silicon (di)oxide/silicon carbide is not abrupt, and a clean
surface cannot be formed after etching. In order to implant ions at
a dose more than 10.sup.19 ion/cm.sup.2, a very long time is
required using the normal ion current density of a conventional ion
implanting apparatus, and therefore the dose is preferably less
than this value from a practical viewpoint. In this case, it is
confirmed that the most effective and sufficient defect density for
oxidation to proceed is obtained at a dose of about 10.sup.16
ion/cm.sup.2.
[0046] In the above method, it is preferred that the energy for the
ion implantation is 1 keV to 10 MeV, so that an oxide insulating
film is effectively formed and a cleaner silicon carbide surface is
formed after oxide film etching. At 1 keV or less, the penetration
depth of the implanted ions in the silicon carbide crystal is too
small, and therefore the effect of ion implantation is small. At 10
MeV or more, the depth of penetration is too large, and the ions
are implanted in a wide range, so that a very high density dose is
required to achieve the sufficient defect density in the silicon
carbide crystal. Also, the defect density of the surface is
maintained low, so that oxidation from the surface proceeds with
difficulty, and therefore such an ion implantation energy is not
practical.
[0047] In the above method, it is preferred that multiple ion
implantation is performed at different energies to form a deep and
uniform implantation layer in the silicon carbide crystal, so that
oxidation is performed to a deep portion, a thick silicon (di)oxide
insulating film is formed, and the portion near the surface is
uniformly removed after etching of the silicon (di)oxide film.
[0048] In the above method, it is preferred that the silicon
carbide is maintained at 500.degree. C. or lower during ion
implantation, so that crystal defects introduced by ion
implantation are quenched, stabilized, and inhibited from being
annealed during ion implantation and from being changed into a
structure having a certain stability; the crystal defects are
introduced more efficiently; the diffusion of oxygen through the
crystal defects is efficient; CO.sub.2, a compound of carbon and
oxygen, is efficiently discharged from the crystal to decrease the
amount of residual carbon after oxidation to form a high
performance SiO.sub.2/SiC interface and a cleaner silicon carbide
surface is formed after oxide film etching. It is also confirmed
that in view of the problems of the apparatus and deterioration in
the silicon carbide surface, the temperature of the silicon carbide
is preferably the liquid nitrogen temperature, -195.degree. C., or
higher during ion implantation.
[0049] In the above method, it is preferred that ions are implanted
in the SiC surface in the first step to form an amorphous layer
near the SiC surface, and that the SiC containing the amorphous
layer is oxidized in the second step. The amorphous layer is easily
oxidized in the second step.
[0050] A method for forming a clean surface according to the method
for manufacturing a SiC device according to the present invention
comprises forming a defect layer by ion implantation, oxidizing it
to form a silicon (di)oxide thin film on the silicon carbide
surface, and removing this silicon (di)oxide thin film by etching.
By forming a silicon (di)oxide thin film having a certain thickness
and removing the portion, the impurities and defects present near
the silicon carbide surface can be removed to form a clean surface.
The crystal near the surface can be removed to any desired
thickness, compared with the conventional surface treatment, and
therefore a portion having a high defect density can be removed for
cleaning. If the portion having a high defect density in the
surface is thin, the defects near the surface also can be removed
by forming a silicon (di)oxide thin film on the silicon carbide
surface by a normal oxidation treatment, without using the method
for forming a thick silicon (di)oxide thin film utilizing the above
ion implantation, and etching the silicon (di)oxide thin film. By
repeating the silicon (di)oxide thin film formation and etching
several times, a cleaner silicon carbide surface can be formed.
[0051] In the above method, it is preferred that a part of the SiC
surface is masked and a portion where ions are implanted is
patterned during ion implantation to the SiC surface in the first
step. This pattern determines the structure of the surface after
the third step, so that a trench structure or the like required for
a SiC device can be formed.
[0052] In the above method, it is preferred that when ions are
implanted to the SiC surface in the first step, at least one of the
energy of implanted ions, ion species, and ion density is different
depending on the place on the SiC surface so that patterning is
performed. By changing the ion energy or the ion species, the depth
of the damage layer from the surface can be changed, so that
terraces, steps and a trench structure having any depth can be
formed with good reproducibility. In other words, the above method
for manufacturing a SiC device can be applied for forming a surface
structure having the shape of a trench structure or the like on the
silicon carbide surface. In the formation of a silicon (di)oxide
film in the first and second steps in the surface treatment method
of the present invention, the depths and amounts of the implanted
ions and the crystal defects can be patterned freely by changing
masking or the energy or dose for ion implantation. By subjecting
this patterned defect portion to the oxidation treatment, the
patterned oxide film can be formed at high speed. As shown in FIG.
2B, by forming or providing a mask 26 on the surface 22 of the
silicon carbide substrate 21, the area for ion implantation can be
patterned. Depending on the place, a defect is introduced deep in a
portion 28H where a high energy ion 27H is implanted, and a shallow
defect is introduced in a portion 28L where a low energy ion 27L is
implanted. These defects are subjected to the oxidation treatment,
so that a patterned silicon (di)oxide film 29 having any desired
thickness in any desired area can be formed as shown in FIG. 2C.
This patterned silicon (di)oxide itself can be utilized for an
electronic device. Furthermore, this patterned silicon (di)oxide
thin film is further removed by etching in the third step, so that
a silicon carbide surface 22P having the patterned clean surface is
formed as shown in FIG. 2D. This patterned silicon carbide clean
surface is subjected to the oxidation treatment again, so that a
thin silicon (di)oxide thin film 29T having a clean interface can
be formed on the surface (side) of the trench structure as shown in
FIG. 2E. By repeating the above oxidation treatment and etching
several times, a surface structure having any desired shape such as
a trench structure having a cleaner surface (side) can be
formed.
[0053] The above cleaning is effective not only for a flat surface
of SiC but also for a silicon carbide surface on which patterned
steps and terraces are formed by normal reactive ion etching, ion
milling, plasma etching, laser etching, or etching by mechanical
cutting or grinding. In other words, the defect portion introduced
near the surface during the etching process used for forming the
above pattern is easily changed into a silicon (di)oxide thin film
by an oxidation treatment, so that the defect layer can be removed
by etching the oxide film.
[0054] In the above method, it is preferred that the silicon
carbide surface on which patterned steps and terraces are formed by
the etching treatment is heated in an oxygen atmosphere to form a
silicon (di)oxide thin film and that the defects introduced by the
etching treatment are removed by further etching of the silicon
(di)oxide thin film. The defects introduced by various etching
treatments can be removed to form an applicable electronic SiC
device.
[0055] In the above method, it is preferred that the etching
treatment is performed by at least one type of method among
reactive ion etching, ion milling, plasma etching, laser etching,
mechanical cutting and grinding. All the defects introduced by the
above etching treatment can be removed as a silicon (di)oxide film
by the above oxidation or the oxidation treatment after ion
implantation.
[0056] FIGS. 3A-3C show a conceptual view for the process of a
method for growing SiC according to the method for manufacturing a
SiC device of the present invention. For a first step, substances
33 containing carbon are supplied to the surface 32 of a Si
substrate 31 in FIG. 3A for a first step to form a thin film 34
containing carbon as shown in FIG. 3B. In the first step, the Si
substrate surface is maintained at a low temperature so that the
reaction between the supplied substances 33 containing carbon and
the Si substrate surface 32 does not occur, silicon carbide is not
formed, and the thin film 34 containing carbon is formed on the Si
substrate surface. Then, the Si substrate surface is heated in a
second step to proceed a solid phase reaction between the thin film
34 containing carbon and the Si substrate surface 32. The heating
in the second step results in the carbonization of the Si substrate
surface 32 and formation of the SiC thin film 35 on the Si
substrate surface 32 as shown in FIG. 3C. The normal conventional
carbonization treatment, such as a reaction between a gas
containing carbon, for example hydrocarbon, and a Si substrate
surface starts at the highly reactive sites of the Si substrate
surface, such as the surface defects or the atomic steps of the
surface, and therefore the uniformity of the reaction is bad. This
local difference in reactivity is reflected in the inequality of
the formed SiC/Si interface to cause the formation of lattice
defects, twins, pits or the like. In the present invention,
different from the normal conventional carbonization treatment, the
Si substrate surface is maintained at low temperature to suppress
the local reaction between carbon and the Si substrate surface in
the first step and form a uniform thin film containing carbon on
the Si substrate surface. The carbonization is carried out by the
solid phase reaction between the thin film 34 containing carbon and
the Si substrate surface 32 in the second step, so that a uniform
carbonization reaction occurs on the Si substrate surface. By the
first and second steps, a silicon carbide/Si interface having
excellent uniformity is formed, so that the formation of defects
such as lattice defects, twins, or pits is inhibited. By growing
the SiC thin film in a third step in which carbon and silicon are
supplied on this SiC/Si interface having excellent uniformity, a
SiC film having few defects and having good quality can be formed
on the Si substrate surface.
[0057] In the above method, it is preferred that the Si substrate
surface is maintained in a temperature range of the liquid nitrogen
temperature, -195.degree. C., to 600.degree. C. in the first step.
At a temperature above 600.degree. C., carbon reacts with the Si
substrate surface before a thin film containing carbon is formed,
so that non-uniform SiC is formed. A temperature less than
-195.degree. C. (the liquid nitrogen temperature) can not easily be
obtained.
[0058] In the above method, it is preferred that the thin film
formed on the Si substrate surface by the first step contains
carbon corresponding to a thickness of a 1-atomic layer to a
20-atomic layer. With a 1-atomic layer or less, uniform
carbonization is not carried out on the Si surface. With a
20-atomic layer or more, the carbon thin film is stable, so that
the reaction with the Si substrate does not easily occur.
[0059] In the above method, it is preferred that the thin film
formed on the Si substrate surface in the first step is an
amorphous thin film containing carbon. The amorphous thin film is
highly reactive with the Si substrate, and carbonization occurs
more easily than with crystal thin films.
[0060] In the above method, it is preferred that the substance
containing carbon supplied to the Si substrate surface in the first
step contains at least molecular carbon other than a gas such as
hydrocarbon. Reaction with hydrocarbon or the like includes a
reaction such as cracking hydrogen-carbon bonds. Such a reaction is
complicated and can not be easily controlled. However, if molecular
carbon is contained, the reaction with Si easily occurs and can be
easily controlled.
[0061] In the above method, it is preferred that the Si substrate
surface is heated to a temperature range of 800.degree. C. to
1414.degree. C., the melting point of Si, in the second step. The
carbonization reaction on the Si substrate surface occurs at
800.degree. C. or higher. At a temperature equal to or higher than
the melting point of Si, the substrate melts and cannot be
used.
[0062] In the above method, it is preferred that the temperature
increase rate between 600.degree. C. and 1000.degree. C. for the Si
substrate surface heating is 20.degree. C./min. to 500.degree.
C./min. in the second step. With a temperature-increase rate of
500.degree. C./min. or more, uniform carbonization cannot be
carried out. With 20.degree. C./min. or less, the heating takes too
long and is not suitable from the industrial viewpoint.
[0063] In the above method, it is preferred that at least the first
and second steps are carried out under a high vacuum of not more
than 10.sup.-7 Torr. If the Si substrate is heated under a lower
vacuum than this, the surface is oxidized or the like. Therefore
uniform carbonization cannot be carried out.
[0064] In the above method, it is preferred that at least the first
and second steps are carried out by a MBE process under high
vacuum, and the third step or a part of the third step is carried
out by a CVD process providing a fast growth rate. In the MBE, the
above high vacuum is easily achieved. In the CVD, high speed film
formation that is preferable from the industrial viewpoint is
achieved.
[0065] In the above method, it is preferred to include a step for
removing an oxide film from the Si substrate surface to clean the
surface before supplying carbon. The presence of the oxide film on
the Si substrate surface degrades the uniformity and
reproducibility of carbonization, and therefore it is preferred to
form a Si clean surface beforehand. In other words, it is confirmed
that if the step for removing the oxide film or the like from the
surface of the Si substrate for cleaning is carried out before the
supply of carbon, the carbonization process becomes efficient. When
carbon is supplied to the Si clean surface for carbonization, C and
Si directly react with each other efficiently, so that the rows of
the Si dangling bonds in the Si [110] direction exposed on the
Si(001) surface are bonded to C atoms (adatom) to form a SiC atomic
configuration whose SiC [110] rows are formed by the shrinkage of
the Si [110] rows with C atoms. As a result, a SiC/Si uniform and
abrupt heteroepitaxial interface is formed. If impurities such as
the oxide film on the Si surface are present on the surface, the
shrinkage of the above Si [110] atomic rows occurs inequally, so
that a flat SiC/Si heteroepitaxial interface having few defects is
not easily formed, and a SiC thin film obtained by the growth on
this SiC/Si interface also has many defects. A uniform SiC/Si
heteroepitaxial interface having few defects can be formed by
carbonization with the process for forming a clean Si surface.
[0066] In the above method, it is preferred that the cleaned Si
surface has a Si(001)2.times.1 surface reconstruction structure.
The 2.times.1 structure can be used as the indicator of the Si(001)
clean surface. On a hydrogenated 1.times.1 surface, desorption of
hydrogen from the surface during the carbonization reaction,
degrades the uniformity of the carbonized interface.
[0067] In the above method, it is preferred that the step for
cleaning the Si substrate surface comprises a step of heating the
substrate to a temperature of 800.degree. C. or higher under a high
vacuum of not more than 10.sup.-6 Torr or in a hydrogen atmosphere.
By this step, a clean surface of the above mentioned Si substrate
can be formed. Heating under low vacuum causes oxidation of the Si
substrate surface, degradation of the uniformity and
reproducibility of SiC formation after the carbonization.
[0068] In the above method, it is preferred that the step for
cleaning the Si substrate surface comprises a step of irradiating
the substrate surface with ultraviolet light such as excimer
lasers. By irradiation with the ultraviolet light, the above Si
substrate clean surface can be formed even at lower
temperature.
[0069] In the above method, it is preferred that the step for
cleaning the Si substrate surface comprises a step of exposing the
Si substrate surface to a reactive etching gas such as ozone and
chlorine or chloride and fluorine or a fluoride gas. By etching the
Si substrate surface with these gases, a cleaner surface can be
obtained.
[0070] In the above method, it has been discovered that by exactly
controlling the abundance ratio of carbon to silicon on the surface
for growing silicon carbide enables a high performance epitaxial
thin film, in which a smooth surface is obtained with good
reproducibility without the growth of twins. Based on this
discovery, the method for manufacturing a silicon carbide thin film
has been invented. Also, it has been discovered that monitoring the
surface rearrangement structure of the above silicon carbide growth
surface enables the in-situ control of the abundance ratio of
carbon to silicon on the growth surface. Based on this discovery,
an apparatus for manufacturing a silicon carbide thin film has been
invented.
[0071] If the abundance ratio of silicon to carbon on the silicon
carbide growing surface is 1 or more (excess silicon), the (001)
face of a 3C-SiC selectively appears. Under this conditions, the
growth of twins is inhibited, so that a smooth (001) face of a
cubic crystal silicon carbide thin film can be obtained. If the
silicon/carbon abundance ratio for the uniform growth surface is 2
or more (in an excess silicon state) a single crystal of silicon
begins to grow on the silicon carbide surface, inhibiting the
growth of the silicon carbide thin film. By maintaining and keeping
the silicon/carbon abundance ratio for the growth surface greater
than 1 and equal to or less than 2, a smooth and clean cubic
crystal silicon carbide (001) face can be obtained. In this case,
the structure of the growth surface has a 3.times.2 or 5.times.2
surface rearrangement. By monitoring this surface structure, the
abundance ratio of silicon to carbon on the growing surface can be
easily controlled.
[0072] In other words, in the method for manufacturing a SiC
device, it is preferred that when supplying silicon and carbon to
the surface of the SiC to grow 3C-SiC having a (001) face, the
abundance ratio of the carbon to the silicon on the silicon carbide
surface is controlled so that silicon atoms are always in excess of
carbon atoms on the surface for growing silicon carbide.
[0073] In the above method, it is preferred that the abundance
ratio of carbon to silicon on the silicon carbide surface is
controlled so that the (001) growing surface of the 3C-SiC is kept
to have a 3.times.2 or 5.times.2 surface rearrangement during the
growth.
[0074] In the above method, it is preferred that the abundance
ratio of carbon to silicon on the silicon carbide surface is
controlled so that the abundance ratio of the silicon atoms to the
carbon atoms on the (001) growth surface of the 3C-SiC is kept at
greater than 1 and equal to or less than 2, in an excess silicon
state during the growth.
[0075] In the above method, it is preferred that when supplying
silicon and carbon to the surface of the SiC to form a 3C-SiC thin
film having a (001) face, an instrument that can evaluate the
surface structure of silicon carbide in-situ during growth, such as
a reflective high energy electron diffraction instrument, is
included in a SiC formation apparatus to monitor the 3.times.2 or
5.times.2 structure of the 3C-SiC(001) surface, and an apparatus
having a mechanism for controlling the abundance ratio of carbon to
silicon on the SiC surface is used so that the surface
reconstructions of 3.times.2 and 5.times.2 are constantly
observed.
[0076] On the other hand, under the conditions of excess carbon,
that is, a silicon/carbon abundance ratio of less than 1, a cubic
crystal silicon carbide (111) face or a hexagonal crystal silicon
carbide (0001) face selectively appears. Under this conditions, the
above cubic crystal silicon carbide (111) face or the hexagonal
crystal silicon carbide (0001) face grows smoothly with good
reproducibility. However, under the conditions of excess carbon,
that is, a silicon/carbon abundance ratio of 0.5 or less, the grown
silicon carbide thin film turns into a polycrystal so that
crystallites grow in random directions. By maintaining the
silicon/carbon abundance ratio for the growing surface more than
0.5 and less than 1, a smooth and clean cubic crystal silicon
carbide (111) face or a hexagonal crystal silicon carbide (0001)
face can be obtained. In other words, in the method for
manufacturing a SiC device, it is preferred that when silicon and
carbon are supplied to the surface of the SiC to form a 3C-SiC
having a (111) face or an .alpha.-SiC thin film having a (0001)
face, the abundance ratio of the carbon to the silicon on the
silicon carbide surface is controlled under the condition where the
carbon atoms are always in excess of the silicon atoms on the SiC
growth surface.
[0077] In the above method, it is preferred that the abundance
ratio of carbon to silicon on the SiC surface is controlled so that
the ratio of the silicon atoms to the carbon atoms on the
3C-SiC(111) or .alpha.-SiC(0001) growth surface is 0.5 to 1, in an
excess carbon state.
[0078] In the above method, it is preferred that when silicon and
carbon are supplied to the surface of the SiC to form a 3C-SiC thin
film having a (111) face or an .alpha.-SiC thin film having a
(0001) face, an instrument that can evaluate the surface structure
of silicon carbide during growth, such as a reflection high energy
electron diffraction instrument, is included in a SiC formation
apparatus to constantly observe the state of the 3C-SiC(111)
surface in-situ, and an apparatus having a mechanism for
controlling the abundance ratio of carbon to silicon on the SiC
surface and inhibiting the growth of a crystal other than SiC is
used.
[0079] With respect to the heteroepitaxial growth on a silicon
wafer, the following has been found. After a silicon wafer surface
is cleaned by heating under a vacuum of not more than 10.sup.-8
Torr before the carbonization treatment, silicon is supplied to the
wafer surface to cause the epitaxial growth of the silicon, and
this low-defect epitaxial Si surface is subjected to the
carbonization treatment, so that a heteroepitaxial silicon carbide
thin film having few twins and good crystallinity can be
formed.
[0080] With respect to heteroepitaxial growth on a silicon wafer,
first, a silicon wafer (001) surface is heated under a vacuum of
10.sup.-8 Torr to form a clean surface having a Si(001) 2.times.1
surface rearrangement. It has been found that silicon is then
supplied to the wafer surface to grow the homoepitaxial silicon to
further form a clean surface, and this surface is subjected to the
carbonization treatment, so that a heteroepitaxial silicon carbide
thin film having few twins and good crystallinity can be formed.
The silicon wafer surface cleaned by heating under vacuum often
contains many defects depending on the previous cleaning condition,
the vacuum, and the impurities in vacuum and therefore is not
easily controlled. However, the surface is clean and has few
defects after the homoepitaxial growth of the silicon, so that the
heteroepitaxial silicon carbide thin film formed by the subsequent
carbonization treatment has an improved crystallinity and a good
reproducibility.
[0081] FIG. 4 shows a schematic view of a Si substrate 41 surface
into which terraces and steps are introduced with anisotropy, as a
substrate for heteroepitaxial SiC growth according to the method
for manufacturing a SiC device according to the present invention.
A Si(001) surface 42 is off-cut inclined in the [110] direction,
and terraces 43 and steps 44 are introduced. The width of the
terrace 43 (the direction perpendicular to a step edge 45: an N
direction 46 in FIG. 4) is much shorter than the length of the
terrace parallel to the step edge (a P direction 47 in FIG. 4).
When the off-cut angle is 4 degrees and the height of the step 44
is a 1-atomic layer, the width of the terrace 43 is about 2 nm.
This short Si [110] atomic row (the N direction 46 in FIG. 4)
easily reacts with carbon to shrink and form a SiC atomic structure
more than the long Si [110] atomic row in the P direction 47 in
FIG. 4. In other words, on the surface into which the terraces and
the steps are introduced, the Si [110] atomic rows in the width
direction of the terraces (the N direction 46 in FIG. 4)
selectively shrink to form a SiC atomic structure with supplied
carbon 48. Thus, the inventor has confirmed that two phases of the
[Si] 3C-SiC crystal grains, which are formed on a just-cut Si(001)
surface and are a problem, are limited to one phase by introducing
the terraces and the steps. This invention enables the formation of
a single-phase 3C-SiC single crystal thin film.
[0082] When supplying the carbon 48 to the Si(001) surface
comprising the terraces 43 and the steps 44 for carbonization to
form SiC crystal grains, twins are sometimes formed if the carbon
48 is supplied as a gaseous substance such as hydrocarbon. The
inventor has confirmed that the formation of twins is inhibited if
a carbon source containing molecular beams such as molecular carbon
or carbon atoms is supplied. This is probably caused by the
following reason. With respect to the reaction between the gas
phase carbon source and the Si surface, it is believed that the
reaction with carbon starts from the Si atoms in the most reactive
state on the Si surface. The Si atoms in the most reactive state on
the Si surface are the atoms in the position of the step edges 45
present on the surface. It is believed that the carbonization of
the Si surface 42 caused by the gas phase carbon 48 starts from the
step edges 45, and twins having different azimuths easily grow at
the step edges 45. On the other hand, if not only the gas phase
carbon but also the carbon source containing molecular beams such
as carbon atoms are supplied, the reaction with the Si substrate
starts from any position where the carbon is supplied, so that the
reaction is inhibited from selectively occurring from the position
of the step edges 45, and the reaction occurs on the terraces 43.
Thus, it is confirmed that the twin growth from the position of the
step edges 45 is inhibited as well, so that a SiC crystal thin film
having few twins is formed. In this case, if the carbon is supplied
at low temperature in the first step, a carbon thin film is formed
on the substrate surface 42 without the reaction (or with small
reaction) between the carbon and the substrate surface 42, and then
a solid phase reaction between the carbon thin film and the
substrate surface occurs at the elevated temperature at which
carbonization is processed in the second step. Therefore, the above
SiC crystal grains having the same direction are uniformly formed
as described in FIG. 3.
[0083] In other words, in the method for manufacturing a SiC device
according to the present invention, it is preferred that the Si
substrate surface used for growing a silicon carbide thin film on
the Si substrate surface has anisotropy and comprises terraces and
steps.
[0084] In the above method, it is preferred that the width of the
terrace of the Si substrate surface is 0.5 nm to 100 nm. If the
width is less than 0.5 nm, the reaction occurs significantly at the
steps, so that the twins are contained. If the width is more than
100 nm, the anisotropy provided by the terraces and the steps of
the substrate is long range and does not affect the carbonization
process.
[0085] In the above method, it is preferred that the Si substrate
surface having anisotropy is a miscut face of the Si(111) or (001).
Due to the miscut, the above terraces and steps appear on the
surface.
[0086] In the above method, it is preferred that the Si substrate
surface is a miscut face of the Si(001), and that the angle between
the direction of the step edges caused by the miscut and the
Si<110> crystal axis direction is 0 to 30 degrees. The
Si(001) surface obtained by this miscut direction exhibits
directional anisotropy about the two perpendicular-to-each-other
<110> direction and enables the growth of SiC having the same
phase. Outside of this range, the anisotropy is insufficient.
[0087] In the above method, it is preferred that when supplying
silicon and carbon to the SiC surface to grow 3C-SiC having a (001)
face, the abundance ratio of the carbon to the silicon on the
silicon carbide surface is controlled so that the silicon atoms are
always in excess of the carbon atoms on the surface for growing
silicon carbide. With excess Si, the SiC(001) surface is
stabilized, so that good crystal growth proceeds. Also, the crystal
growth under the conditions of excess Si provides selective growth
in the 3C-SiC[1{overscore (1)}0] direction, so that this growth
easily occurs on the terraces in the P direction 47 in FIG. 4 to
promote the growth of single-phase SiC.
[0088] In the above method, it is preferred that the abundance
ratio of carbon to silicon on the silicon carbide surface is
controlled so that the 3C-SiC(001) growth surface has a 3.times.2
or 5.times.2 surface rearrangement. These structures serve as the
indicator of the excess Si surface.
[0089] In the above method, it is preferred that the abundance
ratio of carbon to silicon on the silicon carbide surface is
controlled so that the abundance ratio of the silicon atoms to the
carbon atoms on the 3C-SiC (001) growth surface is greater than 1
and equal to or less than 2, in an excess silicon state. The excess
Si surface having an abundance ratio greater than this range causes
growth of the Si crystal grains to inhibit a good SiC crystal
growth.
[0090] In the above method, it is preferred that when supplying
silicon and carbon to the surface of the SiC to form a 3C-SiC thin
film having a (001) face, an instrument that can evaluate the
surface structure of silicon carbide during growth, such as a
reflective high energy electron diffraction instrument, is included
in a SiC formation apparatus to monitor the 3.times.2 or 5.times.2
structure of the 3C-SiC(001) surface, and an apparatus having a
mechanism for controlling the abundance ratio of carbon to silicon
on the SiC surface is used so that a 3.times.2 period or a
5.times.2 period is constantly observed. By introducing this
apparatus, the SiC crystal growth in the excess Si state can be
precisely controlled easily.
[0091] A method for forming an insulating film on the SiC surface
after cleaning; formation and etching of silicon (di)oxide thin
film on SiC, according to the method for manufacturing a SiC device
of the present invention comprises implanting ions 53 (in FIG. 5)
in the SiC crystal surface before conventional thermal oxidation.
By implanting the ions 53 from the surface 52 of a SiC crystal 51
as shown in FIG. 5, a crystal defect 54 is introduced near the SiC
crystal surface in the first step. The oxygen, supplied by
diffusion into the crystal from the surface in the conventional
thermal oxidation in the second step, is supplied through the
crystal defect 54 introduced by the ion implantation, so that the
SiC is oxidized efficiently and rapidly in the range 54 in which
the crystal defects are introduced by the ion implantation, and the
carbon turns into a gas in the form of carbon oxide to be removed,
and therefore silicon (di)oxide is formed. In the formation of a
silicon (di)oxide film according to the present invention, the
depth and the amount of the implanted ions and the crystal defects
can be freely changed depending on the controllable energy and dose
for ion implantation. Therefore, an oxide film can be formed at any
desired depth at high speed to solve the problem of a very slow
oxidation speed of the conventional thermal oxidation. In this
case, if the dose of the implanted ions is 10.sup.14 ions/cm.sup.2
or more, the crystal defects introduced by the ion implantation in
the first step has a sufficient density for discharging carbon and
forming silicon (di)oxide in the oxidation in the second step, so
that a high performance silicon (di)oxide insulating film is
formed. If the dose is 10.sup.14 ions/cm.sup.2 or less, the density
of the introduced defects is low, so that the thickness of the
formed oxide film is not different from that without ion
implantation. In view of the problem of the apparatus, the dose is
preferably 10.sup.19 ions/cm.sup.2 or less. With a dose of this
value or more, a special ion gun or long ion-implantation time is
required, and therefore such a dose is not practical. Also, if the
silicon carbide is maintained at 500.degree. C. or lower for ion
implantation, the crystal defects introduced by ion implantation
are inhibited from being annealed and being changed into a
stabilized structure during the ion implantation, crystal defects
are more efficiently introduced, the diffusion of oxygen through
the crystal defects is efficient, and CO.sub.2, a compound of
carbon and oxygen, is efficiently discharged from the crystal to
decrease the amount of the residual carbon after oxidation to form
a high performance silicon (di)oxide insulating film. In view of
the problem of the apparatus and the problem of deterioration in
the silicon carbide surface, it is confirmed that the temperature
of the silicon carbide during ion implantation is preferably
between the liquid nitrogen temperature and 500.degree. C. If the
energy for ion implantation is 1 keV to 10 MeV, an oxide insulating
film can be effectively formed. If the energy is 1 keV or less, the
depth of the penetration of the implanted ions in the silicon
carbide crystal is too small, and therefore the effect of the ion
implantation is small. If the energy is 10 MeV or more, in addition
to requiring a special apparatus for implanting such high energy
ions, the depth of penetration is too large, and ions are implanted
in a wide range, so that a very high density dose is required to
achieve the sufficient defect density in the silicon carbide
crystal. Therefore, such an ion implantation energy is not
practical. Also, crystal defects are formed in a region very deep
from the surface, and a few or no defects are present near the
surface. Therefore, oxygen is not sufficiently supplied from the
surface in the oxidation of the second step, so that oxidation does
not proceed. When forming a thick silicon (di)oxide insulating
film, it is effective to form a deep and uniform implantation layer
69 in the silicon carbide crystal by carrying out multiple ion
implantations 66, 67 and 68 with different energies from a SiC
surface 62 as shown in FIG. 6. Furthermore, it is confirmed that if
ions are implanted in the SiC surface to form an amorphous layer
near the SiC surface in the first step, and the SiC comprising the
amorphous layer is oxidized in the second step, a good silicon
(di)oxide thin film is formed.
[0092] In other words, it is preferred that the method for
manufacturing a SiC device comprises a first step for implanting
ions in the surface of a SiC silicon carbide crystal after cleaning
to introduce crystal defects in the silicon carbide crystal and a
second step for heating the silicon carbide crystal substrate in
which the ions are implanted and the defects are introduced in an
oxygen atmosphere to form a silicon (di)oxide thin film.
[0093] In the above method, it is preferred that the ions implanted
in the SiC surface in the first step are selected from any of
oxygen, silicon, carbon, an inert gas, nitrogen, and hydrogen, or a
mixture thereof. These gases effectively introduce defects in the
SiC crystal, and, after oxidation, form silicon (di)oxide or turn
into gases to be discharged, and therefore they do not remain to
provide negative effects.
[0094] In the above method, it is preferred that the dose of the
ions implanted in the SiC surface in the first step as described
above is 10.sup.14 ions/cm.sup.2 or more.
[0095] In the above method, it is preferred that the energy of the
ions implanted in the SiC surface in the first step as described
above is between 1 keV and 10 MeV.
[0096] In the above method, it is preferred that two or more types
of energies of the ions implanted in the SiC surface in the first
step as described above are selected for multiple implantation.
[0097] In the above method, it is preferred that when implanting
ions in the SiC surface in the first step as described above, the
SiC is maintained at 500.degree. C. or lower.
[0098] In the above method, it is preferred that ions are implanted
in the SiC surface to form an amorphous layer near the SiC surface
in the first step, and that the SiC containing the amorphous layer
is oxidized in the second step. The amorphous phase is less stable
than the crystal phase, so that the amorphous phase is easily
oxidized to form a silicon (di)oxide thin film.
[0099] By the surface cleaning step according to the above method
for manufacturing a SiC device, a SiC device can be formed first
which comprises a surface having patterned steps and terraces and
has a surface defect density of 10.sup.8 cm.sup.-2 or less.
[0100] FIG. 7 shows the basic structure of the SiC device of the
present invention. The structure is a layered structure comprising
a silicon carbide/Si interface 73 with an n-type silicon carbide
crystal 71 formed on the surface of an n-type Si substrate 72 as
shown in FIG. 7. In this layered structure, the conduction band 84
of the n-type silicon carbide crystal is smoothly connected to the
conduction band 85 of the n-type Si crystal substrate at a silicon
carbide/Si interface 83 as shown in the band diagram of FIG. 8.
Since the main carrier is the electrons in the n-type
semiconductor, such a factor that inhibits electron movement is not
present at the interface of this silicon carbide/Si layered
structure, allowing current to flow without resistance. In other
layered structures, p-type SiC/p-type Si, for example, a valence
electron band 86, in which holes exist as the main carrier, is not
smoothly connected as the conduction band in the above n-type
SiC/n-type Si. Therefore, a step is produced at the silicon
carbide/Si interface 83, a voltage drop occurs in the forward
direction, and resistance is generated with the carrier movement
(the current flow). In these other types of layered structures, the
electric conduction has resistance at the silicon carbide/Si
interface 83. This resistance causes a problem when a vertical-type
silicon carbide power device is formed using the silicon carbide
formed on a Si substrate surface. It is confirmed that the
resistance is minimum when the above silicon carbide/Si layered
structure in which the n-type silicon carbide contacts the n-type
Si substrate is included. The layered structure having an
n-SiC/n-Si structure according to the present invention is
effective for various types of silicon carbide semiconductor
devices in which current flows across this interface, and devices
such as low loss Schottky diodes, metal oxide semiconductor field
effect transistors (MOSFET), metal semiconductor field effect
transistors (MESFET) and insulated gate bipolar transistor (IGBT)
can be formed.
[0101] In other words, it is preferred that the above SiC device
comprises at least a layered structure in which an n-type silicon
carbide crystal is formed on an n-type Si substrate surface.
[0102] In the above SiC device, it is preferred that the
resistivity of the n-type Si substrate is 10.sup.2
.OMEGA..multidot.cm or less. When a vertical-type SiC device is
formed on a conductive Si substrate having a resistivity of the
above value or lower, current easily flows in the Si substrate, and
the heat generating power loss cause by the current is less, so
that a highly efficient SiC device can be implemented.
[0103] Also, it is preferred that the above SiC device comprises at
least a Schottky diode comprising a layered structure in which an
n-type silicon carbide crystal is formed on an n-type Si substrate
surface. According to such a structure, a vertical-type Schottky
diode can be formed in which the electric junction at the SiC/Si
interface is negligible and high breakdown voltage and low loss can
be implemented.
EXAMPLE 1
[0104] Using a commercially available product (a SiC wafer
manufactured by CREE Corporation in the United States), the
6H-SiC(0001) silicon carbide wafer Si face, in which many defects
due to surface polishing are contained near the surface, was
introduced into a normal wet oxidation apparatus for the Si process
to carry out an oxidation treatment in a wet oxidation atmosphere,
in which oxygen was bubbled with boiling water for flow supply, at
1100.degree. C. for 1 hour. The thus formed oxide film had a
thickness of about 40 nm. The refractive index of this oxide film
was measured by ellipsometry. However, a reasonable value for a
silicon (di)oxide film was not obtained. It seems that because of
the defects or impurities near the surface, a clean SiO.sub.2/SiC
interface was not formed. This oxide film was subjected to a
buffered hydrofluoric acid treatment, in which the oxide film was
dissolved in a mixed solution of hydrofluoric acid and an aqueous
solution containing 40 vol. wt % of ammonium fluoride (for example,
a ratio of the hydrofluoric acid to the aqueous solution containing
40 vol. wt % of ammonium fluoride is 1:6), for removal. The defect
layer near the surface was removed, and a clean surface was formed.
This clean surface was introduced into the above oxidation
apparatus again to carry out the above oxidation treatment again.
The refractive index of the second oxide film was measured with an
ellipsometer. The refractive index was 1.45 with a thickness of 30
nm. Also, it was confirmed that the defects near the surface were
removed and that a high performance silicon (di)oxide film having a
clean interface was formed. Here, only the 6H-SiC was described.
However, it was confirmed that other SiCs such as 4H and 3C were
also effective and that the surface was not limited to the (0001)
face.
[0105] It was confirmed by ESR (electron spin resonance)
measurement that the thus formed clean surface had a defect density
of 1.times.10.sup.8 cm.sup.-2 or less.
EXAMPLE 2
[0106] Another example of the surface treatment method for silicon
carbide according to the method for manufacturing a SiC device
according to the present invention will be illustrated. As a first
step, a 6H-SiC(0001) face: 4-degree off Si face single crystal
substrate was introduced into an ion implantation apparatus, and
oxygen ions were implanted at an energy of 30 keV in a dose of
1.times.10.sup.16. In the distribution of the oxygen implanted in
the SiC crystal in this case, the peak position was at a depth of
about 60 nm from the surface. Also the portion turned into an
amorphous portion by the defects introduced by the ion implantation
was at a depth of about 80 nm from the surface. In this case, the
temperature of the substrate during oxygen implantation was
maintained at 100.degree. C. or lower. This implanted SiC substrate
was taken out from the ion implantation apparatus and, as a second
step, introduced into a normal wet oxidation apparatus to carry out
an oxidation treatment in a wet oxygen atmosphere at 1100.degree.
C. for 1 hour in a manner similar to that of Example 1. The thus
formed oxide film had a thickness of 150 nm, which was much larger
than the 30 nm for the wet oxidation without ion implantation. The
refractive index of this oxide film was measured by an
ellipsometer. It was confirmed that the refractive index was 1.45
and that a high performance silicon (di)oxide film with a clean
interface was formed. Here, the ion energy of 30 keV was described.
However, an oxide film was effectively formed if the ion energy was
within the range of the present invention. The dose and the
temperature of SiC other than those of this example were also
effective as long as they were within the range of the present
invention. Furthermore, it was confirmed that an oxide film having
a greater thickness, a thickness of 280 nm, was obtained by
carrying out not only implantation at 30 keV but also that at 150
keV in a dose similar to that at 30 keV. Here, only the 6H-SiC was
described. However, it was confirmed that other SiCs such as 4H and
3C were also effective and that the surface was not limited to the
(0001) face. The thus formed oxide film was, as a third step,
removed by a buffered hydrofluoric acid treatment, in which the
oxide film was dissolved in a mixed solution of hydrofluoric acid
and a 40 vol. % ammonium fluoride aqueous solution (for example,
1:6), to form a silicon carbide clean surface.
[0107] It was confirmed by ESR (electron spin resonance)
measurement that the thus formed clean surface had a defect density
of 1.times.10.sup.8 cm.sup.-2 or less.
EXAMPLE 3
[0108] An example of the surface treatment method for silicon
carbide according to the method for manufacturing a SiC device
according to the present invention will be illustrated. As a first
step, a 6H-SiC(0001) face: 4-degree off Si face single crystal
substrate was introduced into an ion implantation apparatus, and
neon ions were implanted at an energy of 30 keV in a dose of
5.times.10.sup.16. The distribution of the neon implanted in the
SiC crystal in this case was substantially the same as that of the
oxygen in Example 2, and the peak position was at a depth of about
60 nm from the surface. Also, the portion turned into an amorphous
portion by the defects introduced by the ion implantation was at a
depth of about 90 nm from the surface. In this case, the
temperature of the substrate during neon implantation was
maintained at 100.degree. C. or lower. This implanted SiC substrate
was taken out from the ion implantation apparatus and, as a second
step, introduced into a normal wet oxidation apparatus to carry out
an oxidation treatment in a wet oxygen atmosphere at 1100.degree.
C. for 1 hour in a manner similar to that of Example 1. The thus
formed oxide film had a thickness of 150 nm, which was much larger
than the 30 nm for the wet oxidation without ion implantation. The
refractive index of this oxide film was measured with an
ellipsometer. It was confirmed that the refractive index was 1.45
and that a high performance silicon (di)oxide film with a clean
interface was formed. These thickness and refractive index were
substantially the same as those for the oxygen ion implantation in
Example 1. Here, the ion energy of 30 keV was described. However,
an oxide film was effectively formed if the ion energy was within
the range of the present invention. The dose and the temperature of
SiC other than those of this example were also effective as long as
they were within the range of the present invention. Furthermore,
it was confirmed that an oxide film having a greater thickness, a
thickness of 280 nm, was obtained by carrying out not only
implantation at 30 keV but also that at 150 keV. Here, only the
6H-SiC was described. However, it was confirmed that other SiCs
such as 4H and 3C were also effective and that the surface was not
limited to the (0001) face. The ions implanted in the first step
were oxygen or neon in Examples 2-3. However, a good silicon
(di)oxide thin film was also formed by using other ions, e.g. a
substance such as silicon that is turned into an insulating
material such as silicon (di)oxide by oxidation, a substance such
as carbon that is turned into a gas such as carbon dioxide by
oxidation, a substance that is a stable gas, such as nitrogen,
argon, krypton, or xenon, and a substance such as hydrogen that is
turned into water by oxidation and turned into a gas at high
temperature. The thus formed oxide film was, as a third step,
removed by a buffered hydrofluoric acid treatment similar to that
in Example 2 to form a silicon carbide clean surface.
[0109] It was confirmed by ESR (electron spin resonance)
measurement that the thus formed clean surface had a defect density
of 1.times.10.sup.8 cm.sup.-2 or less.
EXAMPLE 4
[0110] Oxygen ions were implanted as described in Example 2 in a
portion of a silicon carbide substrate (diameter: 30 mm) similar to
that used in Example 2, while part of the ion beams was blocked
using a metallic mask made of stainless steel. The portions where
implantation was carried out at an energy of 30 keV and at an
energy of 150 keV+30 keV were formed each with a size of 5 mm by 5
mm. The doses for ion implantation were 1.times.10.sup.16
ions/cm.sup.2 for the implantation at 30 keV and 1.times.10.sup.16
ions/cm.sup.2 at each energy for the multiple implantation at 150
keV+30 keV. The ion implanted silicon carbide substrate was
subjected to an oxidation treatment similar to that in Example 2. A
SiO.sub.2 film was formed which had a thickness of 30 nm in the
masked region that was not subjected to ion implantation, a
thickness of 150 nm in the 30 keV ion implanted region, and a
thickness of 280 nm in the 30 keV+150 keV ion implanted region.
When the patterned oxide film was removed by a buffered
hydrofluoric acid treatment similar to that in Example 2, silicon
carbide clean surfaces were formed in the 5-mm-by-5-mm patterns at
depths of 60 nm and 120 nm.
[0111] It was confirmed by ESR (electron spin resonance)
measurement that the thus formed clean surface had a defect density
of 1.times.10.sup.8 cm.sup.-2 or less.
[0112] It was confirmed that the defect density further decreased
if this clean silicon carbide surface was subjected to the above
oxidation treatment and the oxide film etching treatment again. The
defect density further decreased if the above oxidation treatment
and the oxide film etching treatment were repeated several
times.
EXAMPLE 5
[0113] A silicon carbide surface was subjected to reactive ion
etching in a CF.sub.4+O2 atmosphere using an Al thin film as a mask
to form a pattern. It was confirmed by ESR measurement that this
surface had a defect density of 10.sup.9 cm.sup.-2 or more. This
surface was subjected to an oxidation treatment by a method similar
to that illustrated in Example 1 to form an oxide film. This oxide
film was removed by a buffered hydrofluoric acid treatment similar
to that in Example 1. The defect density was 10.sup.8 cm.sup.-2 or
less.
[0114] In this case, it was also confirmed that with a silicon
carbide surface on which a pattern was formed by reactive ion
etching using other gases such as HF, ion milling with an inert gas
such as Ar at several keV, plasma etching with a hydrogen chloride
gas, laser etching using excimer lasers, mechanical cutting with a
diamond saw or the like, or grinding using a diamond paste, the
above silicon carbide clean surface was formed by the method for
forming and etching a silicon (di)oxide film according to the
present invention.
[0115] Furthermore, the above silicon carbide clean surface was
also formed by forming a relatively thick oxide film by ion
implantation similar to those in Example 2 or 3, to the silicon
carbide surface, on which a pattern was formed by an etching
treatment, and removing this oxide film.
[0116] The defect density further decreased if the above oxidation
treatment and the oxide film etching treatment were repeated
several times as in Example 4.
EXAMPLE 6
[0117] A Si(001) 4-degree-offcut in the [110] direction substrate
was introduced into a MBE apparatus and heated to 900.degree. C. or
higher under a high vacuum of not more than 10.sup.-9 Torr to form
a Si clean surface on which a Si(001)(2.times.1) surface
reconstruction was observed by Reflective High Energy Electron
Diffraction (RHEED).
[0118] The Si(001)2.times.1 clean surface was formed by heating the
Si substrate under high vacuum here. However, it was confirmed that
the cleaning was successively performed at a vacuum of not more
than 10.sup.-6 Torr and/or in a hydrogen gas atmosphere under a
lower vacuum. Under a vacuum poorer than this vacuum, SiC was
formed in random directions on the Si surface before cleaning, so
that heteroepitaxial growth was not carried out uniformly. Also,
the cleaning was successively performed by irradiation with light
having a wavelength of the ultraviolet light range, such as excimer
lasers or deuterium lamp light, rather than heating. Also, a clean
surface was formed by exposure to a reactive etching gas such as
ozone and chlorine or chloride and fluorine or a fluoride gas,
rather than under high vacuum.
[0119] After this clean surface was cooled to 400.degree. C. or
lower, the temperature was raised again at a temperature increase
rate of 100.degree. C. per minute. From the moment when the
substrate temperature reached 400.degree. C., carbon atoms were
vaporized from an electron beam evaporater apparatus, in which a
crucible filled with graphite chunks was irradiated by an electron
gun, and molecular carbons (carbon clusters or carbon atoms) were
supplied to the substrate surface to carry out the first step. In
this case, the distance from the crucible to the substrate was
about 40 cm, and the suitable power supply to the electron beam
evaporater apparatus was about 8 kV and 100 mA. The carbon supplied
to the substrate surface formed a carbon thin film until the Si
substrate temperature reached 600.degree. C. at which point the
reaction between the Si substrate surface and carbon started. The
carbon thin film formed on the Si substrate surface by the first
step, had a thickness of about a 5-atomic layer.
[0120] In the first step of the present invention, the carbon
supply started from at 400.degree. C. while the temperature of the
substrate rose, and a thin film containing carbon was formed while
the temperature rose from 400.degree. C. to 600.degree. C. However,
it was confirmed that the carbon thin film was also formed with the
substrate temperature being constant or changed in the range of
-195.degree. C. to 600.degree. C. and that such a temperature was
effective. The temperature should be 600.degree. C. or lower, and
it is not limited to 400.degree. C. in the first step. If carbon is
supplied at a temperature of 600.degree. C. or higher in the first
step, pits are easily formed under the SiC/Si interface, so that
crystal grains having different crystal directions grow easily.
[0121] Also, it was confirmed that if the formed carbon film was in
the range of a 1- to 20-atomic layer, good crystalline silicon
carbide was formed by carbonization in the second step. With a
1-atomic layer or less, the reaction was uniformless. With
20-atomic layers or more, the carbon thin film was very stable, so
that the reaction did not easily occur in the second step. It was
confirmed that the formed carbon thin film was also effective if it
contained hydrogen, chlorine, or the like, other than carbon. In
this case, the thin film containing carbon formed by the first step
was an amorphous thin film. In the carbonization of the second
step, the amorphous thin film was more reactive than crystalline
thin films, so that SiC having few defects, that is a high
performance carbonized layer, was efficiently formed.
[0122] In this example, the carbon was supplied from the electron
beam evaporater apparatus in the form of an atom (a molecule) or a
cluster, and therefore the supply was different from that of
gaseous carbon. It was confirmed that if 1.times.10.sup.-7 Torr or
more of a gaseous carbon source such as C.sub.2H.sub.4 was supplied
during the formation of the thin film of this example, the
formation of single-phase 3C-SiC described in the example
deteriorated, so that a number of twins were formed. This is
probably because during the carbonization reaction in the second
step, the reaction between the gas and the Si substrate surface
selectively occurs at the steps of the Si substrate surface and/or
the defects, so that the formed silicon carbide contains a number
of lattice defects, twins, pits or the like. Thus, it was confirmed
that, in order to implement the method for manufacturing a silicon
carbide thin film according to the present invention, the supply of
molecular beams of carbon rather than gaseous carbon was effective
and it was effective to form a carbon thin film on a substrate
surface maintained at low temperature in the first step. In this
case, it was confirmed that a carbon thin film was also formed in
the first step, with a carbon source in which a hydrocarbon gas was
cracked using a filament and that such a carbon source was
effective.
[0123] The substrate temperature was raised while the carbon was
supplied, and the carbonization treatment of the second step was
carried out under a temperature of 800.degree. C. or more. In this
case, it was confirmed that the SiC crystal grains formed in the
carbonization process had the same crystal direction. This is
because a number of terraces and steps are present in the offcut
substrate surface, so that the surface reactivity is different
between in the P direction of the long atomic rows parallel to step
edges and in the N direction (shown in FIG. 4) of the short atomic
rows, on the terraces, perpendicular to the step edges and parted
by the step edges on the off cut Si(001) substrate surface. In
other words, it is believed that since the basic mechanism of the
carbonization is a solid phase reaction between the carbon thin
film having a several-atomic layer and the Si(001) surface causing
Si [110] and carbon to shrink, shorter Si [110] atomic rows can
shrink more easily to form a uniform 3C-SiC(001)/Si(001) interface.
In the above offcut substrate surface, the shrinkage of the Si
[110] atomic rows occurs more easily in the N direction (shown in
FIG. 4). and the Si(lower portion)C(upper portion) direction of the
[110] of the 3C-SiC crystal is equal to the N direction.
[0124] In the second step, it was confirmed that carbonization
occurred if the temperature of the Si substrate was raised in the
range of 800.degree. C. to the melting point of Si. Also, it was
confirmed that if the temperature increase rate was in the range of
20.degree. C./minute to 500.degree. C./minute between 600.degree.
C. and 1000.degree. C. at which carbonization proceeds,
heteroepitaxial silicon carbide was formed on the Si substrate
surface. At a temperature increase rate higher than this range, it
was difficult to raise the temperature of the substrate uniformly.
At a temperature increase rate lower than this range, the
uniformity of the interface degraded. If the first and second steps
described so far were carried out under a high vacuum of not more
than 10.sup.-7 Torr, twin occurrence was inhibited, and such
processes were effective.
[0125] From the moment the substrate temperature reached
1050.degree. C., silicon was supplied from a Knudsen cell in
addition to carbon to carry out the third step. In this case, the
temperature of the Si Knudsen cell was maintained at 1357.degree.
C. The crystallinity of the substrate surface was constantly
monitored by RHEED in the growth chamber of the MBE to carry out
in-situ analysis. The amount of C/Si supplied to the 3C-SiC(001)
growth surface was controlled so that the 3C-SiC(001) surface
constantly maintained a stable (3.times.2) surface reconstruction
structure (surface-structure-controlled growth). The
3C-SiC(001)(3.times.2) surface has a structure in which excess Si
atoms are added to the Si-terminated surface. In the growth of the
3C-SiC(001) surface by this surface-structure-controlled growth, Si
atoms are supplied from the surface having excessive Si constantly,
so that the growth in the Si(upper portion)C(lower portion)
direction selectively occurs and the crystal grains grow longer in
this direction. If the selective growth direction of the crystal
grains is equal to the long P direction on the terraces of the
off-cut substrate surface, the growth of the crystal grains
proceeds on the terraces without being disturbed by the steps, so
that the growth of a single-phase 3C-SiC single crystal is easily
proceeded. On the other hand, in the anti-phase domain in the
position forming an angle of 90 degrees with respect to the above
crystal direction, the selective growth direction is in the N
direction, so that the growth is constantly inhibited by the steps.
It is believed that when two types of the above anti-phase domains
grow, the crystal grains, whose selective growth direction is equal
to the P direction, selectively grow, and the anti-phase domain
disappears from the growing surface after long-time growth. The
above crystal direction of the 3C-SiC formed by carbonization of
the off-cut surface was in the Si(lower portion)C(upper portion)/N
direction. This crystal direction is equal to the Si(upper
portion)C(lower portion)//P direction considering the selective
growth on the terraces. In other words. if the above carbonization
treatment and the surface-structure-controlled growth are carried
out, the 3C-SiC single crystal having the same azimuth selectively
grows, and the growth of other anti-phase domains is inhibited. If
the 3C-SiC single crystal having a certain thickness is grown, a
single-phase 3C-SiC single crystal thin film is obtained.
[0126] FIG. 9 shows a tracing of a scanning electron microscope
(SEM) photograph of a single-phase 3C-SiC(001) surface having a
thickness of 100 nm subjected to the above surface control growth
for 3 hours. It can be observed that crystal grains having the same
azimuth selectively grow on the terraces to proceed coalescence to
form a large single crystal. The observed crystal grains had a size
of about 100 nm with respect to the thickness of 100 nm. If the
growth of this thin film further continued, these crystal grains
became further coalesce to form large single crystal grains.
[0127] FIG. 10A shows an ESR spectrum from a single-phase 3C-SiC
single crystal thin film having a thickness of 100 nm grown by the
method for forming a silicon carbide thin film according to the
present invention. FIG. 10B shows an ESR spectrum for a silicon
carbide thin film formed by another method (carbonization reaction
caused by the reaction between a hydrocarbon gas and a Si substrate
surface) for comparison. The spectrum of Si dangling bonds
corresponding to the lattice defects observed in FIG. 10B was not
observed in FIG. 10A formed by the method for manufacturing a
silicon carbide thin film according to the present invention, and
it was confirmed that the lattice defects in the thin film were
remarkably decreased.
[0128] In this example, the off-cut substrate was used as the
Si(001) substrate having anisotropy. However, a just-cut substrate
having a surface to which pattern is provided by anisotropic
etching may be used if its surface has anisotropy and comprises
terraces and steps. The direction for the off-cut is not limited to
the [110] direction. The substrate off-cut in any direction may be
used if the length (width) of the terrace in the [110] direction
and that in the [110] direction (forming an angle of 90 degrees
with respect to the [110] direction) are not equal and are
anisotropic. In order to fully ensure the anisotropy to form
single-phase SiC efficiently, the direction of the step edges of
the Si surface preferably forms an angle in the range of 0 to 30
degrees with respect to the Si<110> direction.
[0129] In this example, the angle of the off-cut was 4 degrees, and
the width of the terrace was about 2 nm. However, a good
single-phase 3C-SiC single crystal thin film was also obtained if
the angle of the off-cut was varied to change the width of the
terrace in the range of 0.5 nm to 100 nm. With a terrace width of
less than 0.5 nm, a number of twins were formed by carbonization,
so that a single-phase single crystal thin film was not formed.
Also, with a terrace width of more than 100 nm, the anisotropy did
not act effectively in the carbonization mechanism, so that a
two-phase thin film comprising an anti-phase boundary (APB) was
formed.
[0130] In this example, the 3C-SiC(001) surface had a (3.times.2)
surface reconstruction and maintained an excess Si surface in which
additional Si was present on the Si terminate (001) surface for
growth in the process for supplying carbon and silicon after
carbonization to grow SiC(001). The present invention was also
effective when the growth was carried out so that the surface
rearrangement maintained other reconstruction structures
(5.times.2), (7.times.2), . . . (2n+1.2)(n is a positive integer).
Also, the present invention was effective with the (2.times.1)
surface, that is the Si terminate 3C-SiC (001) surface. The
suitable Si/C abundance ratio of the excess Si surface is in the
range of 1 to 2. If the Si/C ratio was 2 or more, the crystal
grains of Si deposited on the SiC surface to inhibit the growth of
SiC, so that SiC having good crystallinity was not grown.
[0131] In this example, the Si(001) surface was described. However,
the inventor confirmed that the above method for growing SiC
according to the present invention was also effective for other
surfaces of the Si substrate, such as a Si(111) face. The process
for forming a thin film containing carbon in the first step, the
cleaning of the Si substrate, and the use of the Si substrate
having anisotropy were similar to those of the method for growing a
3C-SiC (001) face. For controlling the Si/C ratio during growth, an
excess C surface was suitable for the growth of the 3C-SiC(111),
contrary to the 3C-SiC(001). With excess Si, a 3C-SiC(001) facet
appeared on the 3C-SiC(111) surface, so that the roughness of the
surface was perceived, and Si crystal grains grew in some cases.
The suitable Si/C ratio was in the range of 1 to 0.5. In a Si/C
ratio of 0.5 or less, the roughness of the surface of the
3C-SiC(111) film was perceived. The inventor confirmed that the
optimal conditions for growing the 3C-SiC(111) face and an
.alpha.-SiC(0001) surface were substantially the same. In other
words, the excess C surface is suitable for growing the
.alpha.-SiC(0001) surface. Out of the optimal conditions, problems
similar to those of the 3C-SiC(111) occurred.
EXAMPLE 7
[0132] After a silicon carbide thin film having a thickness of 100
nm was formed on a Si substrate according to Example 6, the
substrate was introduced into a CVD apparatus to grow silicon
carbide at high speed. The substrate was heated to 1300.degree. C.
by induction heating. A hydrogen gas was supplied as the carrier
gas at a flow rate of 2 slm, and a silane gas and a propane gas
were supplied at 1 sccm and 0.4 sccm respectively. The growth
chamber was subjected to vacuum by a rotary pump and maintained at
about 100 Torr. By carrying out growth under the conditions for 5
hours, a low defect silicon carbide thin film having a thickness of
12 microns grew. This example comprises carrying out at least the
first and second steps with a MBE apparatus under high vacuum and
carrying out the third step or a part of the third step with a CVD
apparatus, and is suitable for growing a thick heteroepitaxial film
for electronic devices.
EXAMPLE 8
[0133] In this example, a SiC surface treatment method for making a
silicon (di)oxide film according to the method for manufacturing a
SiC device will be described. A 6H-SiC(0001) face: 4-degree off Si
face single crystal substrate was introduced into an ion
implantation apparatus, and oxygen ions were implanted at an energy
of 30 keV in a dose of 1.times.10.sup.16 cm.sup.-2. The
distribution of the oxygen implanted in a SiC crystal 111 in this
case was as shown in FIG. 11, and a peak position 115 was at a
depth of about 60 nm from a surface 112. Also, the portion 114,
turned amorphous by the defects introduced by ion 113 implantation,
was at a depth about 80 nm from the surface. In this case, the
temperature of the substrate during oxygen implantation was
maintained at 100.degree. C. or lower. This implanted SiC substrate
was removed from the ion implantation apparatus and introduced into
a normal wet oxidation apparatus to carry out an oxidation
treatment in a wet oxygen atmosphere at 1100.degree. C. for 1 hour.
The thus formed oxide film had a thickness of 150 nm, which was
much larger than 30 nm for the wet oxidation without ion
implantation. The refractive index of this oxide film was measured
by an ellipsometer. It was confirmed that the refractive index was
1.45 and that a high performance silicon (di)oxide film with a
clean interface was formed. Here, the ion energy of 30 keV was
described. However, an oxide film was effectively formed if the ion
energy was within the range of the present application. The dose
and the temperature of SiC other than those of this example were
also effective as long as they were within the range of the present
invention. Furthermore, it was confirmed that an oxide film having
a greater thickness, a thickness of 280 nm, was obtained by
carrying out not only implantation at 30 keV but also that at 150
keV. Here, only the 6H-SiC was described. However, it was confirmed
that other SiCs such as 4H and 3C were also effective and that the
surface was not limited to the (0001) face.
EXAMPLE 9
[0134] In this example, another SiC surface treatment method for
making silicon (di)oxide film according to the method for
manufacturing a SiC device will be described. A 6H-SiC(0001) face:
4-degree off Si face single crystal substrate was introduced into
an ion implantation apparatus, and neon ions were implanted at an
energy of 30 keV in a dose of 5.times.10.sup.6 cm.sup.-2. The
distribution of the neon implanted in the SiC crystal in this case
was substantially the same as that of the oxygen in Example 8, and
the peak position was at a depth of about 60 nm from the surface.
Also, the portion turned into an amorphous portion by the defects
introduced by the ion implantation was at a depth about 90 nm from
the surface. In this case, the temperature of the substrate during
oxygen implantation was maintained at 100.degree. C. or lower. This
implanted SiC substrate was taken off from the ion implantation
apparatus and introduced into a normal wet oxidation apparatus to
carry out an oxidation treatment in a wet oxygen atmosphere at
1100.degree. C. for 1 hour. The thus formed oxide film had a
thickness of 150 nm, which was much larger than 30 nm for the wet
oxidation without ion implantation. The refractive index of this
oxide film was measured with an ellipsometer. It was confirmed that
the refractive index was 1.45 and that a high performance silicon
(di)oxide film having a clean interface was formed. These thickness
and refractive index were substantially the same as those for the
oxygen ion implantation in Example 8. Here, the ion energy of 30
keV was described. However, an oxide film was effectively formed if
the ion energy was within the range of the present invention. The
dose and the temperature of SiC other than those of this example
were also effective as long as they are within the range of the
present invention. Furthermore, it was confirmed that an oxide film
having a greater thickness, a thickness of 280 nm, was obtained by
carrying out not only implantation at 30 keV but also at 150 keV.
Here, only the 6H-SiC was described. However, it was confirmed that
other SiCs such as 4H and 3C were also effective and that the
surface was not limited to the (0001) face. The ions implanted in
the first step were oxygen or neon in Examples 8 and 9. However, a
good silicon (di)oxide thin film was also formed by using other
ions, e.g. a substance such as silicon that is turned into an
insulating material such as silicon (di)oxide by oxidation, a
substance such as carbon that is turned into a gas such as carbon
dioxide by oxidation, a substance that is a stable gas, such as
nitrogen, argon, krypton, or xenon, and a substance such as
hydrogen that is turned into water by oxidation and turned into a
gas at high temperature.
EXAMPLE 10
[0135] A Si(001) 4-degree-offcut in the [110] direction substrate
of n-type Si having a resistivity of 10 .OMEGA..multidot.cm was
introduced into a MBE apparatus and heated to 900.degree. C. or
more under a high vacuum of not more than 10-8 Torr to form a Si
clean surface on which a Si(001)(2.times.1) surface reconstruction
was observed by RHEED. After this clean surface was cooled to
400.degree. C. or lower, the temperature was raised again at a
temperature increase rate of 100.degree. C. per minute. From the
moment when the substrate temperature reached 400.degree. C.,
carbon atoms were vaporized from an electron beam evaporater
apparatus in which a crucible filled with graphite chunks was
irradiated by an electron gun and supplied to the substrate
surface. In this case, the distance from the crucible to the
substrate was about 40 cm, and the suitable power supply to the
electron beam vapor deposition apparatus was about 8 kV and 100 mA.
The substrate temperature was raised while the carbon was supplied,
and the carbonization treatment was carried out in the process of a
temperature increase of 800.degree. C. or more. In this case, it
was confirmed that the SiC crystal grains formed in the
carbonization process had the same crystal direction. This is
because a number of terraces and steps are present in the offcut
substrate surface, so that the surface reactivity is different
between in the P direction of the long atomic rows parallel to the
step edges and in the N direction of the short atomic rows, on the
terraces, perpendicular to the step edges and parted by the step
edges.
[0136] It is believed that as the basic mechanism of the
carbonization is that a solid phase reaction between the carbon
thin film having a several-atomic layer and the Si(001) surface
causes Si [110] and carbon to shrink, shorter Si [110] atomic rows
can shrink more easily to form a uniform 3C-SiC(001)/Si(001)
interface. In the above offcut substrate surface, the shrinkage of
the Si [110] atomic rows occurs more easily in the N direction, and
the Si(lower portion)C(upper portion) direction of the [110] of the
3C-SiC crystal is equal to the N direction.
[0137] From the moment the substrate temperature reached
1050.degree. C., silicon was supplied from a Knudsen cell in
addition to carbon. In this case, the temperature of the Si
Knudesen cell was maintained at 1357.degree. C. The crystallinity
of the substrate surface was constantly observed by RHEED in the
growth chamber of the MBE to carry out in-situ analysis. The amount
of C/Si supplied to the 3C-SiC(001) growth surface was controlled
so that the 3C-SiC(001) surface constantly maintained a stable
(3.times.2) surface rearrangement structure (surface control
growth). The 3C-SiC(001)(3.times.2) surface has a structure in
which excess Si atoms are added to the Si-terminated surface and
has excess Si compared with the structure of SiC with C/Si=1. In
the growth of the 3C-SiC(001) surface by this surface control
growth, Si atoms are supplied from the surface having excess Si
constantly, so that the growth in the Si(upper portion)C(lower
portion) direction selectively occurs. If the direction is equal to
the P direction, the growth of the crystal grains proceeds on the
terraces without being disturbed by the steps, so that the growth
of a single-phase 3C-SiC single crystal is easily obtained. On the
other hand, in the anti-phase domain in the position forming an
angle of 90 degrees with respect to the above crystal direction,
the selective growth direction is in the N direction, so that the
growth is constantly inhibited by the steps. It is believed that
when two types of the above anti-phase domains grow, the crystal
grains whose selective growth direction is equal to the P direction
selectively grow, and the other anti-phase domain disappears after
long-time growth. The above crystal direction of the 3C-SiC formed
by carbonization of the offcut surface was in the Si(lower
portion)C(upper portion)//N direction. This crystal direction is
equal to the Si(upper portion)C(lower portion)//P direction
considering the selective growth on the terraces. In other words,
if the above carbonization treatment and the surface control growth
were carried out, the 3C-SiC single crystal having the same azimuth
selectively grows, and the growth of other anti-phase domains was
inhibited. If the 3C-SiC single crystal having a certain thickness
(20 nm or more) were grown, a single-phase 3C-SiC single crystal
thin film was obtained. In this case, an n-type Si substrate was
used. By introducing nitrogen into the growth chamber so that the
vacuum was 10.sup.-8 Torr or more for further growing the above
SiC, N was doped to make the SiC thin film of n-type as well.
[0138] This single-phase silicon carbide film was further grown by
the CVD method to form silicon carbide having a thickness of 30
microns on the Si substrate. In this case, a hydrogen gas, a silane
gas, and a propane gas were introduced into the CVD growth chamber
at 2 LM, 1 sccm, and 0.4 sccm respectively. The crystal growth was
performed at a reduced pressure of about 100 Torr, with these gases
being sucked by a rotary pump. The substrate was put on a susceptor
of graphite and heated to about 1300.degree. C. by induction
heating at a high-frequency of 20 kHz. By also introducing a
nitrogen gas at about 1 sccm during growth, the growing silicon
carbide became an n-type semiconductor.
[0139] As shown in FIG. 12, the surface on the SiC 121 side of the
n-SiC/n-Si layered structure formed as described above was
subjected to electron beam vapor deposition of Ni and heat
treatment at 900.degree. C. in an Ar atmosphere to form an
electrode 128. In this case, a Si substrate 122 had a thickness of
0.5 mm, and the SiC thin film 121 had a thickness of 30 microns.
Also, an AlSi electrode 127 was formed on the back surface on the
Si side by a sputtering deposition method to form the electrode on
the Si side. These electrodes were ohmically connected to Si and
SiC respectively. Voltage was applied to the electrodes 127 and 128
on the above Si and SiC sides to measure the I-V characteristics.
Linear characteristics that do not have polarity as shown in FIG.
13 were observed. This shows that the conductors at the SiC/Si
interface were smoothly connected without discontinuity. The
current flowing across this SiC/Si interface does not feel the
interface and feels only a simple electric resistance of the
current path. In this example, the resistivity of the Si substrate
was 10.sup.2 .OMEGA..multidot.cm. However, in the range of 10.sup.2
.OMEGA..multidot.cm or less, good I-V characteristics were
observed. For other SiC/Si interface combinations, n-SiC/p-Si,
p-SiC/n-Si, and p-SiC/p-Si, the I-V characteristics of the above
SiC/Si had polarity, and the discontinuity of the band at the
interface was confirmed.
EXAMPLE 11
[0140] An n-SiC/n-Si layered structure was formed in a manner
similar to that of Example 10. Only this layered structure had low
resistance I-V characteristics. It was confirmed that in a Schottky
diode in which a gold Schottky electrode 149 was formed on a SiC
141 surface by an electric resistance heating vapor deposition
method, when current flowed in a direction across the SiC/Si
interface, forward direction voltage drop or the like did not occur
at the interface, resulting in an ideal low resistance. The other
electrode is the same as that in Example 10. FIG. 15 shows the I-V
characteristics of the Schottky diode of Example 11 shown in FIG.
14. The resistance in the forward direction was minimal compared
with other structures such as p-SiC/p-Si.
[0141] As described above, according to the present invention, a
method for manufacturing a device and a single crystal thin film of
silicon carbide (SiC), which are wide band gap semiconductor
materials and can be applied to semiconductor devices such as high
power devices, high temperature devices, and environmentally
resistant devices, can be provided. More particularly, the present
invention can provide a method for forming an insulating film and a
method for forming a clean surface in application for an electronic
device such as a semiconductor device or a sensor using silicon
carbide (SiC), a method for forming a surface structure having a
trench structure or the like, and a SiC device having the formed
low defect surface. Furthermore the present invention can provide a
method for forming a single-phase 3C-SiC single crystal thin film
having a few crystal defects on a Si wafer by heteroepitaxial
growth on the Si substrate surface.
* * * * *