JP2013023408A - Diamond substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a single crystal diamond substrate with excellent flatness of surface without a defect such as a crack, capable of reducing the cost because of a high growing rate, and to provide a thick film diamond substrate obtained by the method.SOLUTION: The diamond substrate is obtained by growing diamond on a base diamond substrate of crystal structure {111} having an off angle of 2° or more by means of chemical vapor deposition (CVD) under a condition expressing lateral growth.

Description

  The present invention relates to a diamond substrate obtained by lateral growth type epitaxial growth on a diamond substrate.

In epitaxial growth of a single crystal diamond film, comparing the {100} crystal structure with the {111} crystal structure, the {100} crystal structure can be increased in area and cost by employing a mosaic or heteroepitaxial growth method and plasma CVD. However, even if a P-type semiconductor can be obtained by doping, it is difficult to obtain an N-type.
On the other hand, the {111} crystal structure can be both P-type and N-type, but so far there is only a high-temperature and high-pressure synthesis method using a diamond seed crystal, and there are limitations on the apparatus, and a large-sized substrate is obtained. There is a difficult problem.

As described in the non-patent literature, the {111} crystal structure was cracked due to epitaxial growth and could not be thickened.
Further, the flatness of the film surface, which is important in device characteristics, cannot be ensured.

Hydrogen incorporation control in high quality homoepitaxial diamond (111) growth, DIAMOND AND RELATED MATERIALS, (1999) Vol.8, p1291-1295

  An object of the present invention is to provide a method for producing a single crystal diamond substrate which is free from defects such as cracks, has excellent surface flatness, has a high growth rate and can be produced at low cost, and a thick film diamond substrate obtained thereby.

  The method for manufacturing a diamond substrate according to the present invention is performed under conditions where lateral growth is manifested on a mother diamond substrate having a crystal structure {111} having an off angle of 2 ° or more using chemical vapor deposition (CVD). It is obtained by growing diamond.

In the present invention, lateral growth is expressed in chemical vapor deposition (CVD) by forming an off angle (inclined surface) of 2 ° or more on the surface of a crystal structure {111} mother substrate such as synthetic diamond. It is a thing.
Although details will be described later, as shown in Non-Patent Document 1, if the mother diamond substrate does not have an off-angle, cracks will occur on the surface under slow conditions and if it is not a thin film of about 10 to 20 μm. In the present invention, a crystal structure {111} base diamond substrate having a high off-angle of 2 ° or more is used, so that the generation of cracks during epitaxial growth is suppressed and the surface can be flattened.
In the present invention, the off angle is preferably in the range of 2 to 10 °.

In the present invention, the supply concentration of the carbon source gas in the CVD is preferably in the range of 0.001 to 10%, particularly a relatively high concentration of 0.05% or more, and further 0.2 to 10% or 1.0 to Lateral growth is possible under conditions of a high concentration such as 10%, and a thick film can be obtained at high speed.
In the present invention, plasma CVD using microwaves can be employed as the CVD.

In the present invention, since the lateral growth is performed by CVD on a mother diamond substrate having a crystal structure {111} having a high off angle of 2 ° or more, a thick film having a thickness of 50 μm or more can be grown. A free-standing single crystal {111} -grown diamond substrate can be obtained by separating the substrate from the mother substrate.
Further, when CVD film formation is used for a device or the like, a thick film having a film thickness of 20 μm or more can be formed on a diamond substrate having a crystal structure {111} having an off angle of 2 ° or more by using CVD.
In particular, it is possible to form a thick film having a thickness of 50 μm or more with excellent surface flatness and few defects.

  Since the present invention forms an off angle of 2 ° or more on the {111} mother diamond substrate for epitaxial growth, high-speed lateral growth of a thick film excellent in flatness can be realized without generating cracks on the surface. By separating the grown thick film from the diamond substrate, a free-standing single crystal diamond substrate can be obtained, the mother diamond substrate can be used repeatedly, and the free-standing diamond substrate can be used as the mother diamond substrate, so that the cost is low.

The optical microscope of the surface property of the formed film by the difference in the off angle of a mother diamond substrate is shown. (A) shows a low-magnification photograph, and (b) shows a high-magnification photograph. An AFM image (atomic force microscope image) is shown, (a) shows an off angle of 2 °, and (b) shows an off angle of 0.5 °. The surface photograph of a formation film is shown, (a) shows the thing by the manufacturing method which concerns on this invention, (b) shows the thing by the conventional method. The photograph of the growth hill by the spiral growth on the {111} mother diamond substrate as a starting point is shown, (a) shows the case of the single screw dislocation and (b) shows the case of the double screw dislocation. The formula for estimating the off-angle that causes lateral growth from spiral growth starting from screw dislocations is shown.

For epitaxial growth using the {111} single crystal mother diamond substrate according to the present invention, CVD (chemical vapor deposition) can be used, and it is particularly preferable to use plasma CVD using microwaves.
The lateral growth conditions are preferably a pressure of 10 to 200 Torr, a substrate temperature of 600 to 1200 ° C., and a microwave output of 100 to 5,000 W.
Further, methane gas diluted with hydrogen, ethane gas, or a mixed gas of these with carbon monoxide, carbon dioxide, oxygen, argon, and nitrogen can be used as the carbon source gas.
For example, the concentration of methane gas in hydrogen gas can be set in the range of 0.001 to 10%, preferably 0.05 to 10%, particularly 0.2 to 10% Fast film growth.
The {111} single crystal diamond film (growth diamond substrate) according to the present invention can obtain both p-type and n-type semiconductor films by doping.
Boron and phosphorus are typical examples of doping atoms.

Next, film formation by epitaxial growth was comparatively investigated by changing the off-angle of the {111} mother diamond substrate.
FIGS. 1 to 3 show the results of films epitaxially grown under the conditions of hydrogen gas flow rate 200 sccm, methane gas flow rate 0.5 sccm, 7 kPa, 150 W, 1020 ° C., 20 h.
FIG. 3 (a) shows a surface optical microscope image when the off-angle of the mother diamond substrate is 9 ° and FIG. 3 (b) is a conventional off-angle of 0 °.
In the conventional method with an off angle of 0 °, many cracks were generated on the surface, whereas those with an off angle of 9 ° according to the present invention were normal with no cracks.
FIG. 1 shows an optical microscope image of the surface by changing the off-angle. Step-like spiral growth is observed on the surface when the off-angle is 1 ° and 0.5 °, whereas the off-angle is 2 ° and 4 °. The one was flat without spiral growth.
As shown in FIG. 2, when the off angle of 2 ° in (a) is RMS = 0.06 nm, the off angle of 0.5 ° in (b) is RMS = 3.38 nm. Met.
Here, RMS is a value indicating the magnitude of surface roughness, and a formula disclosed in Japanese Patent Application Laid-Open No. 2010-251599 can be used.

Next, using a 2.45 GHz microwave plasma CVD apparatus, a {111} mother diamond substrate with an off angle of 9 °, hydrogen gas 399 sccm, methane gas 1 sccm, oxygen gas 0.25 sccm, 1200 W, substrate temperature 900 ° C., growth time 100 Implemented time growth.
As a result, a growth film having a thickness of about 0.1 mm could be obtained, and a self-supporting {111} single crystal growth diamond substrate could be obtained by laser cutting.

Next, the reason why the off angle of the mother diamond substrate is set to 2 ° or more will be described.
FIG. 4 shows a photograph of a growth hill of step growth in which a mesa structure is formed on a {111} mother diamond substrate by an etching method and spiral growth of a substantially triangular shape starting from a screw dislocation is performed.
The step-step interval Ws-s was the minimum Ws-s≈9 nm for the single screw dislocation (a) and the minimum Ws−s≈6 nm for the double screw dislocation (b).
FIG. 5 shows a schematic diagram.
In order to limit the off angle so as to achieve lateral growth, Wt <6 nm, θ> 1.97 ° from the condition of Wt <Ws−s, Wt = 0.206 [nm] / tan θ, and the off angle θ is about 2 If it is more than °, lateral growth can be suppressed.

  The diamond substrate is excellent in semiconductor characteristics as compared with Si, GaAs, SiC, GaN, etc., and the growth diamond substrate according to the present invention can be grown at a high speed and has a flat surface without generation of cracks. , Optical devices, white devices, etc. are expected to expand into a wide range of fields.

Claims (5)

  It is obtained by growing diamond on a mother diamond substrate having a crystal structure {111} having an off angle of 2 ° or more using chemical vapor deposition (CVD) under conditions where lateral growth occurs. Diamond substrate manufacturing method. In the condition where the lateral growth is expressed,
The method for producing a diamond substrate according to claim 1, wherein the supply amount of the carbon source gas is 0.001 to 10%.   3. The method for manufacturing a diamond substrate according to claim 1, wherein the CVD is plasma CVD.   A single crystal diamond substrate obtained by separating a growth film by CVD obtained by the method according to claim 1 from the mother diamond substrate.   A film forming method comprising forming a thick film having a thickness of 20 μm or more on a diamond substrate having a crystal structure {111} having an off angle of 2 ° or more by using CVD.