JP3886922B2 - Diamond substrate surface treatment method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for treating a surface of a diamond substrate and a semiconductor device obtained by the method, and more particularly to the field of manufacturing a wide bandgap semiconductor having a large energy gap, the field of semiconductor surface treatment technology, and the field of semiconductor devices. It deals with high-temperature and high-power power devices, as well as radiation-resistant environmental and space devices. In recent years, with the rise of bioelectrochemistry, expectations for environmental applications using the electrochemical catalyst mechanism on the surface of thin films have increased, but the present invention that can effectively use surface electrical conduction and surface electric field is also deeply related to the field. Is.
[0002]
[Prior art]
There are almost no examples where electrical conductive carriers naturally accumulate on the surface of a semiconductor. However, diamond exhibits exceptional surface electrical conduction. When the surface of diamond is terminated with hydrogen, molecular adsorption of carbonate or the like in the air acts to cause an electrochemical reaction, and holes are generated on the surface as carriers.
[0003]
Originally, although diamond is in an insulating state, the fact that electrical conduction occurs only in the vicinity of the surface was very interesting for use. For example, when applied to a high-speed transistor, the stray capacitance is drastically reduced, so that the effect is extremely high. In addition, when used in an ion sensor, it also showed features such as being advantageous for electrode insulation and element separation.
[0004]
As a technique related to a semiconductor device using such a diamond surface, there are those disclosed below.
[0005]
[Patent Document 1]
Japanese Patent No. 3313696 (page 2-3, Fig. 1)
[0006]
[Non-Patent Document 1]
Yuji Ogawa and 4 others Diamond Symposium Abstracts, 13th, 206-207, 1999
[0007]
[Non-Patent Document 2]
Kenichi Chatan and 2 other Diamond Symposium Abstracts, 12th, 82-83 1999
[0008]
[Non-Patent Document 3]
H. Kawarada, et, al. Phys. Status Solidi A185 (2001) 79
[0009]
[Non-Patent Document 4]
T.A. Sakai, et, al. Jpn, J .; Appl. Phys. 41 (2002) 2595-2597
[0010]
[Problems to be solved by the invention]
Attempts have been made so far to increase the hole surface density of the naturally occurring diamond surface to broaden the range of applications, but conventionally, an upper limit of approximately 1-2 × 10 ¹³ / cm ² has been hitherto. there were. If the upper limit of the hole area density can be increased to make the diamond surface more active electrically, it will not only expand its application as a semiconductor, but it is also expected to develop new applications for environmental devices based on electrochemistry. Is done.
[0011]
In view of the above circumstances, and an object thereof is to provide a process how a diamond substrate surface capable of expanding the range of applications to enhance the hole surface density of the diamond surface.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides
[1] In the diamond substrate surface treatment method, the surface of diamond is exposed to plasma composed of a mixed gas of hydrogen (H ₂ ) and fluorine sulfide (SF ₆ ), and the surface conduction hole (hole) surface density of diamond is 8 It is characterized by being increased to × 10 ¹³ / cm ² or more.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0014]
In the present invention, the surface of diamond is exposed to plasma composed of a mixed gas of hydrogen (H ₂ ) and fluorine sulfide (SF ₆ ), and the upper limit of the surface conductive hole (hole) surface density of diamond is 8 × 10 ¹³ / cm 3. Increase to ² or more.
[0015]
(Example)
FIG. 1 is a configuration diagram of a substrate reaction apparatus showing an embodiment of the present invention.
[0016]
In this figure, 1 is a reaction furnace, 2 is a mixed gas of hydrogen (H ₂ ) and fluorine sulfide (SF ₆ ), 3 is a heater heating unit, 4 is a substrate mounting table, and 5 is set on the substrate mounting table 4. A diamond substrate, 6 is a short-wavelength microwave (2.45 GHz) power source, 7 is a waveguide, 8 is plasma, 9 is exhausted, and 10 is water-cooled.
[0017]
(1) First, a mixed gas 2 of hydrogen (H ₂ ) and fluorine sulfide (SF ₆ ) is supplied into the reaction furnace 1. The mixing ratio of the two kinds of gases can be set freely, but here, the ratio of SF ₆ / H ₂ was set in the range of 100 ppm or more. The mixed gas 2 was introduced into the reaction furnace 1 and the pressure was set to 20 Torr. The mixed gas 2 is irradiated with microwaves from a short wavelength microwave (2.45 GHz) power source 6. Here, the microwave is 2.45 GHz, but the selection of the frequency is not particularly problematic. The mixed gas 2 in the reaction furnace 1 was changed to a plasma 8 state by adjusting the power introduced by the microwave. At this time, the introduced microwave power is 400 W.
[0018]
(2) The surface of the diamond substrate 5 was exposed to the microwave plasma 8 generated in the reaction furnace 1, and the surface chemical reaction was advanced with time to perform surface treatment. At this time, it was found that the (H ₂ + SF ₆ ) mixed gas 2 used in the present invention exhibits a very large effect. That is, a large amount of carrier holes are generated on the surface of the diamond substrate 5. This makes it possible to realize a surface density with a carrier hole surface density of 1 × 10 ¹⁴ / cm ² or more.
[0019]
FIG. 2 shows the treatment time dependence of the electrical resistance change that occurs when the diamond thin film surface of the embodiment of the present invention is exposed to the plasma of the (H ₂ + SF ₆ ) mixed gas.
[0020]
In this figure, the horizontal axis represents the processing time (minutes), and the vertical axis represents the sample electrical resistance (MΩ). The processing conditions at this time were a microwave power of 400 W, a gas total pressure of 30 Torr, and a substrate temperature of 600 ° C.
[0021]
As can be seen from this figure, when the gas mixture ratio (SF ₆ / H ₂ ) was 600 ppm (indicated by ●), the surface electrical resistance decreased to 1/4 of the initial value in the treatment time of 4 minutes. This is due to an increase in surface carrier hole area density and an increase in carrier mobility μ. Incidentally, □ the gas mixing ratio (SF ₆ / H ₂₎ shows the characteristic in the case of 300 ppm.
[0022]
Now, how the carrier hole surface density increases can be seen in FIG.
[0023]
In FIG. 3, the horizontal axis indicates the processing time (minutes), the vertical axis indicates the surface hole area density (10 ¹⁴ / cm ² ), and the measurement is based on the Hall effect experiment.
[0024]
As is clear from FIG. 3, the surface hole surface density is 8 × 10 ¹³ / cm ^{2 when the} processing time is about 3 minutes, and if it exceeds this value, the surface hole surface density is sufficiently high. The range can be expanded.
[0025]
That is, when the gas mixing ratio (SF ₆ / H ₂ ) is 600 ppm, the hole surface density can be reliably increased by exposing the diamond surface to microwave plasma of (H ₂ + SF ₆ ) mixed gas. Proven. In particular, it can be seen that the wall of 1 × 10 ¹⁴ / cm ² has been broken through at the time of the 4-minute treatment.
[0026]
In addition, a semiconductor device (device) can be formed on the surface of the diamond substrate obtained as described above. For example, it can be expected to be used for a wide band gap semiconductor device having a large energy gap, as well as bio-related devices such as surface catalysis and surface immunity.
[0027]
That is, an ultrahigh electric field is generated on the diamond surface, and the value thereof is set to a high value reaching 1 × 10 ⁷ / cm ² . If this electric field is partially leaked from the diamond surface, this electric field is strongly related to the electrochemical action of the surface, so that it can be expected to be applied to bio-related devices such as surface catalysis and surface immunity.
[0028]
Further, it is possible to realize a Stark effect, that is, a commercial device having a built-in effect of an electric field caused by nearby electrons or ions or an externally applied electric field on a spectral line in a gas, a liquid, and a solid.
[0029]
In the above embodiment, the surface treatment of the diamond substrate is used, but the present invention can also be applied to the case where a thin diamondoid semiconductor film is interposed on the diamond substrate.
[0030]
In addition, this invention is not limited to the said Example, A various deformation | transformation is possible based on the meaning of this invention, and they are not excluded from the scope of the present invention.
[0031]
【The invention's effect】
As described above in detail, the present invention has the following effects.
[0032]
(A) A hole surface density of 1 × 10 ¹⁴ / cm ² or more can be realized on the surface of the diamond substrate.
[0033]
(B) Surface electrical resistance can be reduced by more than two digits by surface treatment of the diamond substrate. If this effect is utilized, it is very convenient for the power application of a diamond semiconductor device, and a high power operation type semiconductor device with reduced loss can be realized.
[0034]
(C) Use in bio-related devices such as surface catalysis and surface immunity can be expected.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a reaction apparatus of a semiconductor device showing an embodiment of the present invention.
FIG. 2 is a graph showing the treatment time dependence of the electrical resistance change that occurs when the surface of the diamond thin film of the example of the present invention is exposed to plasma of a (H ₂ + SF ₆ ) mixed gas.
FIG. 3 is a diagram showing how the carrier hole area density on the diamond surface of the present invention increases.
[Explanation of symbols]
1 reactor 2 hydrogen (H ₂₎ mixed gas 3 heater heating part 4 substrate mounting table 5 diamond substrate 6 short wavelength microwave (2.45 GHz) power supply 7 waveguide 8 plasma 9 exhaust fluorine sulfide (SF ₆₎ 10 Water cooling

Claims (1)

The diamond substrate surface is characterized by exposing the surface of diamond to plasma composed of a mixed gas of hydrogen and fluorine sulfide to increase the surface conduction hole (hole) surface density of the diamond to 8 × 10 ¹³ / cm ² or more. Method.

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