JP2002255692A - Silicon carbide epitaxial substrate and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a SiC epitaxial substrate which has a mirror surface, is few in the ruggedness of surface and is excellent in quality and a manufacturing method thereof. SOLUTION: A SiC wafer having face (11-20) which is free of micro pipe defect on the surface is entered into a growth furnace and the growth furnace is evacuated and, thereafter, is made atmospheric pressure. While flowing hydrogen gas, a receptor is heated up to 1580 deg.C by means of induction heating, hydrogen chloride gas is flown for 10 min. at the same temperature, thereafter, the hydrogen chloride gas is stopped, while flowing hydrogen gas as it is, the temperature is lowered up to 800 deg.C, the hydrogen chloride gas in the growth furnace is purged, thereafter, the temperature is elevated to 1500 deg.C again and the epitaxial growth is started. The surface of SiC epitaxial substrate which is subjected to such a pretreating method is made free of the outstanding ruggedness and the Ra value (average value of surface ruggedness) is 40 nm based on the measurement of surface roughness meter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a silicon carbide (SiC)
The present invention relates to a silicon carbide epitaxial substrate grown on a single crystal and used for an optical device or an electronic device, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Silicon carbide (SiC) has attracted attention as an environment-resistant semiconductor material because of its excellent heat resistance and mechanical strength and physical and chemical stability. In recent years, demand for SiC single crystal wafers as substrate wafers for high-frequency high-voltage electronic devices and the like has been increasing.

Power devices using SiC single crystal wafers,
When fabricating a high-frequency device, it is usually necessary to epitaxially grow a SiC thin film on a wafer.
It is common to deposit on a SiC wafer using a method called VD method (thermal chemical vapor deposition method). At this time, to obtain a high quality epitaxial thin film, the Si
The crystallinity of the C wafer is an important parameter. SiC
Normally, the (0001) plane or (000-
1) Although planes are used, threading dislocations called micropipes are present on these planes at about 50 to 100 / cm ² , and are inherited as they are during epitaxial growth. Devices fabricated on micropipes are known to have poor performance (eg, T. Kimoto et al., IEEE
Tran. Electron. Devices 46 (3) pp.471-477, 199
9) There is an urgent need to reduce micropipes. On the other hand, Takahashi et al. Have shown that micropipes do not exist in SiC single crystals grown in <1-100> or <11-20> directions (J. Takahashi et al., J. Cryst. Gr.
owth 135, 1994), and Yano et al. prototyped a MOS device using an epitaxial thin film grown on a wafer having a (11-20) plane, and in the case of 4H-SiC, a conventional (0001) plane was used. Shows that the electron mobility is about 20 times higher (H. Yan
o et. al, Mater. Sci. Forum 338-342, 2000)
Attention has been paid to epitaxial thin films grown on wafers having a (11-20) plane.

However, the result of Yano et al.
This is a result obtained by using a wafer of (11-20) plane obtained by so-called vertical cutting of a SiC single crystal grown in the axial direction in parallel with the c-axis.
In this case, in consideration of increasing the diameter of the wafer, it is necessary to grow SiC in the c-axis direction at least as long as the diameter and increase the thickness, which is technically difficult. Therefore, it is more realistic to grow a single crystal by growing the diameter in the <11-20> direction as a seed crystal using a wafer having a (11-20) plane as a seed crystal, and to create a wafer from this, It is also necessary that epitaxial growth be performed on such a wafer. But,
When epitaxial growth is performed on this surface, the conventional (0001)
Since the plane orientation is different from the plane or (000-1) plane, it is difficult to obtain the mirror surface over the entire wafer because the optimal growth conditions already obtained cannot be applied and the growth performance itself is small. There were many irregularities on the surface. For this reason, there is no micropipe and an epitaxially grown film on the (11-20) plane where good MOS characteristics can be obtained, but the morphology of the surface is inferior.

[0005]

As described above, (11-
It has been difficult to obtain a high quality substrate with a mirror surface and few irregularities on the epitaxial substrate on which an epitaxial thin film is grown on a SiC single crystal wafer having a 20) plane.

Therefore, the present invention has solved the above problems.
An object is to provide a SiC epitaxial substrate and a method for manufacturing the same.

[0007]

The present invention has been completed by finding that the above-mentioned problems can be solved by changing the pretreatment conditions of the SiC wafer before epitaxial growth.

That is, the present invention provides (1) a silicon carbide epitaxial substrate obtained by epitaxially growing a silicon carbide thin film on a silicon carbide single crystal wafer having no micropipe defects on its surface, wherein the surface of the silicon carbide epitaxial substrate is A silicon carbide epitaxial substrate having a roughness Ra value of 50 nm or less, (2) a plane orientation of the silicon carbide single crystal wafer is a (11-20) plane or a (1-100) plane (1) (3) A method for manufacturing a silicon carbide epitaxial substrate, comprising: performing a pretreatment on a silicon carbide single crystal wafer at a temperature of 1550 ° C. or higher, and then epitaxially growing a silicon carbide thin film on the wafer. (4) The method for producing a silicon carbide epitaxial substrate according to (3), wherein the pretreatment is performed in a hydrogen gas flowing atmosphere. (5) Hydrogen chloride is used for the pretreatment. (6) The method for producing a silicon carbide epitaxial substrate according to (3), wherein the pretreatment is performed in a mixed gas flow of hydrogen and hydrogen chloride. ,.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the temperature is set to 1550 ° C. or higher in a heat treatment performed as a pretreatment when an epitaxial thin film is grown on a SiC single crystal wafer having no micropipe defects on the surface. Si as the upper temperature limit
The temperature at which C does not sublime, for example, 2000 ° C. During the heat treatment, a hydrogen gas, a hydrogen chloride gas, or a mixed gas thereof is supplied. The reason for flowing these gases is that they react with SiC to form hydrogen compounds or chlorine compounds,
By removing the C surface modified layer, a clean surface can be obtained on an atomic scale before epitaxial growth.

[0010] Si with no micropipe defects on the surface
As the C single crystal wafer, a SiC single crystal wafer having a (11-20) plane or a (1-100) plane can be suitably used.

In the epitaxial growth, after the pre-treatment as described above, for example, a silane gas (SiH ₄ ) and a propane gas (C ₃ H ₈ ) are flowed together with a hydrogen gas at a growth temperature of about 1500 ° C. to form an SiC thin film. Perform epitaxial growth. The growth film thickness is generally about 2 to 5 μm.

Conventional micropipe defects exist (000
For the growth on the 1) plane or the (000-1) plane, the pretreatment temperature is 1400 to 1500 ° C. When the (11-20) plane was subjected to pre-treatment at a conventional temperature and then subjected to epitaxial growth, the surface morphology was poor, and especially, a large number of small round projections were present. The inventors focused on the fact that the shape of the protrusions was very similar to 3C-SiC, and as a result of study, found that 3C-SiC was generated when epitaxial growth was hindered by scratches, strain, dirt, etc. on the substrate surface. (11-20), the pretreatment temperature is 1400
At ℃ 1500 ° C., the removal of the SiC surface-modified layer was insufficient and it was judged that the surface was not sufficiently clean.

When a pretreatment temperature of 1550 ° C. or more was applied as described above, a silicon carbide epitaxial substrate having a surface roughness Ra of 50 nm or less and a good surface morphology was obtained. The degree of improvement of the surface morphology was evaluated by the value of the surface roughness Ra using a stylus type roughness meter. On the other hand, in an epitaxial film having an average Ra of more than 50 nm, when a device was formed thereon, electric field concentration was likely to occur due to surface irregularities, and the withstand voltage of the element was lowered.

[0014]

EXAMPLES (Example 1) A growth procedure for performing a pretreatment with a mixed gas of hydrogen gas and hydrogen chloride gas and thereafter performing epitaxial growth will be described. First, there is no micropipe defect on the surface on the graphite susceptor (11-2
The SiC wafer having the 0) surface is placed in a growth furnace and evacuated. Thereafter, the exhaust is stopped and hydrogen gas is introduced to bring the pressure to atmospheric pressure. The susceptor is heated by induction heating with the hydrogen gas flowing, and the temperature profile and gas introduction timing are shown in FIG. In FIG. 1, the horizontal axis is time, and the vertical axis is temperature. In this embodiment, 15
After reaching 80 ° C., hydrogen chloride gas is flowed at that temperature for 10 minutes. Examples of the flow rates of the hydrogen gas and the hydrogen chloride gas are 3 L / min and 10 mL / min, respectively. After 10 minutes, turn off the hydrogen chloride gas.
After the temperature is lowered to 0 ° C. and the hydrogen chloride gas in the growth furnace is purged, the temperature is raised to 1500 ° C. again to start epitaxial growth. For epitaxial growth, for example, silane gas (S
iH ₄ ) and propane gas (C ₃ H ₈ ) are flowed together with hydrogen gas. FIG. 2 shows a photograph of the surface of an epitaxial thin film having a (11-20) plane grown on a SiC single crystal wafer by a Nomarski optical microscope by performing such a pretreatment method. It can be seen that there is no noticeable unevenness on the surface, and the surface is flat and has good surface morphology. When measured with a surface roughness meter, the Ra value (average value of the surface irregularities) was 40 nm. In this example, the epitaxial thin film on the SiC single crystal wafer having the (11-20) plane was described, but it was confirmed that the (1-100) plane had the same effect.

Embodiment 2 A description will be given of a growth procedure when pre-processing is performed only with hydrogen gas and thereafter epitaxial growth is performed. The temperature profile is the same as in FIG.
After the temperature reaches ° C, heat treatment is performed only with hydrogen gas without flowing hydrogen chloride gas. The procedure after the heat treatment is the same as in the first embodiment. The Ra value after growth was 45 nm. In the present example, the epitaxial thin film on the SiC single crystal wafer having the (11-20) plane was described, but it was confirmed that the same effect was obtained also on the (1-100) plane.

(Embodiment 3) A description will be given of a growth procedure in which pretreatment is performed only with hydrogen chloride gas and thereafter epitaxial growth is performed. The temperature profile is the same as in FIG.
After the temperature reaches 80 ° C, the introduction of hydrogen gas is stopped, and only hydrogen chloride gas is supplied. After the heat treatment for 10 minutes, the hydrogen chloride gas is stopped, and hydrogen gas is introduced again. The subsequent procedure is the same as in the first embodiment. The Ra value after growth was 40 nm. In this example, the epitaxial thin film on the SiC single crystal wafer having the (11-20) plane was used. However, it was confirmed that the same effect was obtained for the (1-100) plane.

Comparative Example FIG. 3 shows a conventional temperature profile and gas introduction timing as a comparative example. The procedure and gas flow rate were the same as in Example 1, except that the temperature during heat treatment was 15
It is 00 ° C. FIG. 4 shows a photograph of the surface of the epitaxial thin film on the SiC single crystal substrate having the (11-20) plane, which has been subjected to this pretreatment method, by a Nomarski optical microscope. <1-100
A large number of line-shaped morphologies in the direction and irregularities in the form of dots or small round particles were observed, indicating that the surface morphology was deteriorated. The Ra value was 100 nm.

[0018]

As described above, according to the present invention, it is possible to grow an epitaxial thin film having excellent surface morphology on a SiC single crystal wafer having no micropipe defects on the surface. In particular, the (11-20) plane and
When a SiC single crystal wafer having a (1-100) plane is used, an epitaxial thin film having excellent surface morphology can be easily obtained.
By using such a high-quality silicon carbide epitaxial substrate, an electronic device or the like having excellent electric characteristics can be manufactured with a high yield.

Furthermore, the crystal grown in the <1-100> direction has a (1--100)
Since the (11-20) plane of the crystal grown in the <11-20> direction or the (100) plane is used as the substrate, the plane obtained by vertically cutting the crystal grown in the c-axis direction is used as the substrate. It is easy to increase the diameter and is advantageous in cost.

[Brief description of the drawings]

FIG. 1 is a diagram showing a temperature profile and a gas introduction timing of a pre-growth heat treatment in the present invention.

FIG. 2 is a Nomarski optical microscope surface photograph of an epitaxial thin film on a (11-20) plane SiC single crystal wafer subjected to a pretreatment method according to the present invention.

FIG. 3 is a diagram showing a temperature profile and a gas introduction timing of a pre-growth heat treatment according to a conventional method.

FIG. 4 shows a pretreatment method performed by a conventional method (11-20)
Surface photo of epitaxial thin film on SiC single crystal wafer with surface by Nomarski optical microscope

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hirokatsu Yashiro 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division (72) Inventor Tatsuo Fujimoto 20-1 Shintomi, Futtsu-shi, Chiba New Japan (72) Inventor Masakazu Katsuno 20-1 Shintomi, Futtsu City, Chiba Prefecture Nippon Steel Corporation Technology Development Division F-term (reference) AC07 AD18 AF02 BB12 HA03

Claims (6)

[Claims] 1. A silicon carbide epitaxial substrate formed by epitaxially growing a silicon carbide thin film on a silicon carbide single crystal wafer having no micropipe defects on its surface,
The silicon carbide epitaxial substrate has a surface roughness Ra value of 50 nm.
A silicon carbide epitaxial substrate characterized by the following. 2. The method according to claim 1, wherein the plane orientation of the silicon carbide single crystal wafer is (1).
The silicon carbide epitaxial substrate according to claim 1, which is a (1-20) plane or a (1-100) plane. 3. A method for manufacturing a silicon carbide epitaxial substrate, comprising: performing a pretreatment on a silicon carbide single crystal wafer at a temperature of 1550 ° C. or higher, and thereafter epitaxially growing a silicon carbide thin film on the wafer. 4. The method of manufacturing a silicon carbide epitaxial substrate according to claim 3, wherein said pretreatment is performed in a hydrogen gas flowing atmosphere. 5. The method of manufacturing a silicon carbide epitaxial substrate according to claim 3, wherein said pretreatment is performed in a hydrogen chloride gas flowing atmosphere. 6. The method of manufacturing a silicon carbide epitaxial substrate according to claim 3, wherein said pretreatment is performed in a mixed gas atmosphere of hydrogen and hydrogen chloride.