JP2001247397A - Silicon carbide single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a silicon carbide single crystal excellent in device characteristics and having a slight electrical anisotropy due to stacking faults. SOLUTION: This silicon carbide single crystal 1 comprises an assembly 2 of screw dislocations, the stacking faults 3 and edge dislocations 4 and is obtained by dividing the assembly 2 of the screw dislocations into sections in the direction of the axis (extending the dislocation lines) of the screw dislocations with the stacking faults 3 or the edge dislocations 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a silicon carbide (SiC) single crystal suitable for producing a semiconductor device.

[0002]

2. Description of the Related Art As shown in FIG. 5A, a SiC crystal produced by a sublimation method using a (0001) plane as a growth plane has a large number of micropipe defects 102 and screw dislocations 103. These defects cause a reverse leakage current when a diode is manufactured on the substrate 101 made of the SiC crystal.

As shown in FIG. 5B, after forming an n ⁻ -type epitaxial layer 104 on a substrate 101 made of 4H—SiC crystal doped with an n-type impurity, a micropipe defect 102 and a screw dislocation 103 are formed. The p ⁺ -type region 105 is formed in the formed region, and the p ⁺ -type region 10 is formed.
5 and the electrode 107 connected to the substrate 101 are formed.
8 was fabricated, and the influence of micropipe defects 102 and screw dislocations 103 existing on the substrate 101 on device characteristics was investigated. As a result, it was found that the micropipe defect 102 has a fatal effect on device characteristics, and that the screw dislocation 103 softens the breakdown characteristics of the IV and lowers the breakdown voltage by 5 to 35%.
(PG Neudeck et al. (NASA Lewis)
Research Center et al.) Mat. Re
s. Soc. Symp. Proc. Vol. 512 (1
998) 107-112) On the other hand, in JP-A-5-262599, (000)
1) A plane perpendicular to the plane, for example, (1-100) plane or (11-
It has been proposed to grow a SiC single crystal free of micropipe defects and screw dislocations by using the 20) plane as a growth plane.

However, the thus grown Si
Stacking faults are widely formed in the C single crystal over the entire area.
When a current crosses the stacking fault, a large resistance is generated. Therefore, a large electric anisotropy occurs in a direction crossing the stacking fault and in a direction parallel to the stacking fault, which causes a serious problem in device fabrication.

[0005]

SUMMARY OF THE INVENTION In view of the foregoing, it is an object of the present invention to provide a silicon carbide single crystal capable of reducing reverse leakage current and reducing electrical anisotropy caused by stacking faults. .

[0006]

Means for Solving the Problems To achieve the above object, the invention according to claim 1 is characterized in that the silicon carbide single crystal contains an aggregate (2) of screw dislocations. A preferred set of screw dislocations is a bundle of a plurality of screw dislocations whose distance to the nearest dislocation line is 1 μm or less.

[0007] As described above, a micropipe defect and a screw dislocation are not present alone, but a screw dislocation acts on a silicon carbide single crystal which is an aggregate of the screw dislocation, whereby the reverse leakage current is reduced. The electrical anisotropy due to stacking faults can be reduced. The spacing at which the interaction occurs is about 1 μm.

[0008] The invention according to claim 2 includes an aggregate (2) of screw dislocations and a stacking fault (3), and the aggregate of the screw dislocations is caused by the stacking fault and extends in the dislocation line of the screw dislocation. It is characterized by being divided into

With such a silicon carbide single crystal, the same effect as the first aspect can be obtained.

According to a third aspect of the present invention, an aggregate of screw dislocations (2), a stacking fault (3) and an edge dislocation (4) are included, and the aggregate of screw dislocations is a stacking fault or an edge-like dislocation. It is characterized in that the dislocation is divided in the direction of extension of the dislocation line of the screw dislocation by dislocation.

With such a silicon carbide single crystal, the same effects as those of the first aspect can be obtained.

According to the present invention, the surface of the silicon carbide single crystal substrate containing micropipe defects and screw dislocations is coated with a coating material and then heat-treated. It is possible to produce by.

Further, according to the first to fourth aspects of the present invention, as described in the fifth aspect, it is possible to use the substrate for epitaxially growing a high-quality silicon carbide single crystal having a small reverse leakage current.

The reference numerals in the parentheses of the above means indicate the correspondence with the specific means described in the embodiments described later.

[0015]

(First Embodiment) FIG. 1 shows a cross-sectional view of a silicon carbide single crystal according to a first embodiment of the present invention.

The silicon carbide single crystal 1 shown in FIG.
It is composed of a single crystal substrate of H, 3C or 15R-SiC. This silicon carbide single crystal 1 includes an aggregate 2 of screw dislocations, a stacking fault 3, and an edge dislocation 4. It is divided in the axis (extending dislocation line) direction.

Stacking faults 3 are formed in silicon carbide single crystal 1 having such a structure, but stacking faults 3 are only formed locally, and extend over the entire region of silicon carbide single crystal 1. Since it is not formed by the method, electric anisotropy hardly occurs due to stacking faults.

The silicon carbide single crystal 1 having such a structure is manufactured by covering the surface of a single crystal substrate containing micropipe defects and screw dislocations with a coating material and then performing a heat treatment. In other words, the micropipe defect is repaired by performing a heat treatment in a state where the single crystal substrate is covered with the coating material, and the screw dislocation aggregate 2,
Since the stacking faults 3 and the edge defects 4 are present, the silicon carbide single crystal 1 has the structure shown in FIG.

Using the silicon carbide single crystal 1 having such a structure as a substrate, a PN diode 5 was manufactured as shown in FIG. First, the n-type impurity into the main surface of the doped silicon carbide single crystal 1 n ^- -type epitaxial layer 6 is grown, then, n ^- micropipe defects of the type epitaxial layer 6 is disposed on the repaired portion By performing ion implantation into the region, ap ⁺ type region 7 is formed. Subsequently, electrode 8 electrically connected to p ⁺ -type region 7 and electrode 9 electrically connected to the back surface of silicon carbide single crystal 1 are formed. Thereby, the PN diode 5 is manufactured.

When the IV characteristics of the PN diode 5 in the reverse direction were evaluated, the leakage current in the reverse direction was extremely small and good device characteristics (breakdown characteristics) were exhibited.

It is presumed that such a result was obtained for the following reason.

When a screw dislocation or a micropipe defect is present alone, the forbidden band becomes narrow due to the strain and the leak current increases, or the doped impurity abnormally diffuses due to the strain, and the PN junction failure or the like occurs. This causes an increase in leakage current. On the other hand, in a state where the screw dislocations are dense as in the aggregate 2 of the screw dislocations, the respective strains interfere with each other, and the forbidden band returns to the original state, or the doped impurity does not diffuse abnormally.

When the screw dislocation coexists with the stacking fault 3, the slip dislocation slips at a position where the screw dislocation crosses the stacking fault 3, as confirmed from the result of the TEM analysis.
Since the dislocation line of the screw dislocation is bent and discontinuous, the reverse leakage current that may flow along the dislocation core of the screw dislocation is prevented by the stacking fault 3.
In addition, it is considered that the same effect occurs when the screw dislocation and the edge dislocation 4 cross each other.

When epitaxial growth is carried out using the off plane of a crystal containing stacking faults, that is, when n ⁻ -type epitaxial layer 6 is grown using the off plane of silicon carbide single crystal 1 as a substrate, the crystal is inherited from the substrate. When the screw dislocation intersects with the stacking fault 3 during epitaxial growth, it is blocked by the stacking fault 3 and converted into an edge dislocation in the C plane, which is no longer inherited.

As described above, although the reason is not clear, by using the silicon carbide single crystal 1 having the above structure, the reverse leak current could be reduced.

As described above, the micropipe defect is repaired, and the silicon carbide single crystal 1 having the screw dislocation aggregate 2, the stacking fault 3, and the edge dislocation 4 is formed, so that the reverse leakage current is reduced. In addition, a single crystal with little electrical anisotropy due to stacking faults can be obtained.

In this embodiment, the silicon carbide single crystal 1 in which the aggregate 2, the stacking faults 3, and the edge dislocations 4 of the screw dislocations are formed has been described. In the case of the blockage, the silicon carbide single crystal 11 containing the screw dislocation aggregate 2 as shown in FIG. 3 or the screw dislocation aggregate 2 and the stacking fault 3 as shown in FIG. Carbide single crystal 21 in which aggregate 2 is axially divided by stacking faults 3
May be formed. Also in these cases, the PN diode 5 is formed and the IV
When the characteristics were evaluated, the same effects as described above could be obtained.

From this, at least in the silicon carbide single crystal in which the micropipe defect has been repaired and the screw dislocation aggregate 2 has been formed, the reverse leakage current can be reduced.
It can be said that electrical anisotropy due to stacking faults can be reduced.

In the above-described embodiment, the case where the aggregate 2 of screw dislocations, the stacking fault 3, and the edge dislocations 4 are formed by repairing the micropipe defect has been described. If the aggregate 2 of screw dislocations, the stacking fault 3, and the edge dislocations 4 are formed by a method other than that described above, the silicon carbide single crystal 1 having a small reverse leakage current and excellent device characteristics can be obtained. Can be.

[0030]

EXAMPLES (Example 1) As a sample of a silicon carbide single crystal 1 having a micropipe defect, a 6H-SiC single crystal substrate doped with an n-type impurity was prepared. This 6H-
The SiC single crystal substrate had a thickness of about 1 mm and a micropipe defect density of about 100 / cm ² .

The (000) of this 6H—SiC single crystal substrate
A 3C-SiC film having a thickness of about 20 μm was formed on the surfaces 1) and (000-1) by the CVD method. At this time, the film forming conditions were as follows: the substrate temperature was 1500 ° C., and the SiH ₄ flow rate was 2 to 8 SC.
CM, C ₃ H ₈ flow rate 1~5sccm, the H ₂ flow rate 11S
LM, and the deposition time was 5 hours.

However, SCCM is “Specific
Cubic cm / min ”, and the SLM is“ Spic
effective liter / min ".

Thereafter, the sample was accommodated in a graphite crucible (not shown) embedded in silicon carbide powder and subjected to a heat treatment. The heat treatment conditions at this time are as follows:
° C and a pressure of 79.8 kPa (600 T) in an Ar atmosphere.
orr), and the heating time was 24 hours.

After the heat treatment, the sample was taken out of the graphite crucible, polished from the surface of the sample to a thickness of about 50 μm, and the surface of the sample was observed. As a result, before heat treatment, 6H-Si
The micropipe defect that had been opened on the surface of the C single crystal substrate was closed, and it was revealed that the micropipe defect was repaired by the above process.

Further, a sample was cut out in parallel with the c-axis, and a portion where a micropipe defect was present was analyzed in detail by TEM.

As a result, in the region where the micropipe defect was present (or in the vicinity thereof), an aggregate 2 of a plurality of screw dislocations (about 7 in a slice of about 1 μm in width × about 0.05 μm in thickness) was formed. Existed.

Further, there were a large number of stacking faults 3 generated in the C plane so as to cut the screw dislocation aggregate 2 in the axial direction at intervals of about 0.01 to 1 μm. However, this stacking fault is generated by spreading only at the repaired portion and its periphery, and has a radius of about 10 around the screw dislocation aggregate 2.
It spread in the range of μm or less.

The screw dislocation aggregate 2 and the stacking fault 3
It was confirmed that at some of the intersections, the aggregate 2 of screw dislocations slipped due to the stacking fault 3 and became discontinuous.

Further, edge dislocations 4 parallel to the C plane were also observed.
It was confirmed that the aggregate 2 of the screw dislocations was discontinuous at the intersection of the edge dislocations 4 with the edge dislocations 4.

Subsequently, a 3.5 ° off-axis substrate was prepared from the sample in which the micropipe defects were closed as described above, and a PN diode 5 as shown in FIG. 2 was prepared.

That is, the n-type impurity concentration is 5 × on the substrate.
After growing an n ⁻ -type epitaxial layer 6 made of 6H—SiC of about 10 ¹⁶ / cm ³ to a thickness of about 3 μm,
^The p-type impurity concentration in the ⁻ type epitaxial layer 6 is 1 × 10 ¹⁹
/ Cm ³ about to become so boron and carbon are continuously ion-implanted to form a p ⁺ -type region 7, further, the p ⁺ -type region 7 electrically connected to the electrodes 8 and the silicon carbide single crystal 1 The PN diode 5 having a diameter of about 130 μm was formed by forming the electrode 9 electrically connected to the back side of the PN diode 5.
Then, the IV characteristics of the PN diode 5 in the reverse direction were evaluated.

As a result, the breakdown voltage at a reverse leakage current of 1 μA was about 450 V, and the reverse breakdown current was very low and the breakdown voltage was high. Note that the withstand voltage at this time is determined by preparing a PN diode 5 at a portion where no crystal defect is formed and performing IV-direction in the reverse direction.
It was equivalent to the case where the characteristics were evaluated.

On the other hand, for comparison, as shown in FIG. 5 (a), a PN diode was fabricated in the same manner as above using a crystal in which micropipe defects and screw dislocations alone remained as a substrate, and the IV characteristics were obtained. The leakage current in the reverse direction was large, the breakdown voltage at a leakage current of 1 μA was as low as about 150 V, and the rectification characteristics were not good.

[Brief description of the drawings]

FIG. 1 is a view showing a cross section of a silicon carbide single crystal 1 according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a cross section of a PN diode manufactured using silicon carbide single crystal 1 shown in FIG.

FIG. 3 is a diagram showing a cross section of silicon carbide single crystal 1 in another example of the first embodiment.

FIG. 4 is a diagram showing a cross section of silicon carbide single crystal 1 in another example of the first embodiment.

5A is a diagram showing a substrate 101 on which micropipe defects and screw dislocations are formed, and FIG. 5B is a diagram showing a cross section of a PN diode formed using the substrate 101 of FIG. .

[Explanation of symbols]

1 ... silicon carbide single crystal, 2 ... collection of screw dislocations, 3 ... stacking faults, 4 ... edge dislocations, 5 ... PN diode, 6 ... n ^-
Type epitaxial layer, 7 ... p ⁺ type region, 8 ... electrode, 9 ...
electrode.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Atsuto Okamoto 41-cho, Yokomichi, Nagakute-machi, Aichi-gun, Aichi Prefecture Inside Toyota Central Research Institute, Inc. 41, Yokomichi, Toyota Central Research Laboratory Co., Ltd. (72) Inventor, Yoshiki Senoo, 41, Nagakute-cho, Aichi-gun, Aichi Prefecture 1-1-1 Showa-cho, Kariya-shi, Japan Inside DENSO Corporation (72) Inventor Hiroyuki Kondo 1-1-1, Showa-cho, Kariya-shi, Aichi F-term inside DENSO Corporation 4G077 AA02 AA03 AB01 BE08 FE19 HA02 TK01 TK06

Claims (5)

[Claims] 1. A silicon carbide single crystal comprising an aggregate of screw dislocations (2). 2. An assembly of screw dislocations comprising an aggregate of screw dislocations (2) and a stacking fault (3).
Are separated in the direction of extension of the dislocation line of the screw dislocation by the stacking fault (3). 3. An assembly (2) of screw dislocations, a stacking fault (3) and an edge dislocation (4) are included, and the assembly (2) of screw dislocations is either the stacking fault (3) or the stacking fault (3). A silicon carbide single crystal characterized in that it is divided by an edge dislocation (4) in a direction in which a dislocation line of the screw dislocation extends. 4. After coating the surface of a silicon carbide single crystal substrate containing micropipe defects and screw dislocations with a coating material,
The silicon carbide single crystal according to any one of claims 1 to 3, wherein the silicon carbide single crystal is manufactured by heat treatment. 5. A silicon carbide single crystal grown epitaxially using the single crystal according to claim 1 as a substrate.