JP5487888B2 - Method for producing n-type SiC single crystal - Google Patents

Description

  The present invention relates to a method for producing an n-type SiC single crystal, an n-type SiC single crystal obtained thereby, and its use, and more specifically, nitrogen (N) as a donor element for forming an n-type semiconductor during crystal growth Further, the present invention relates to a method for producing an n-type SiC single crystal to which a specific element is added, an n-type SiC single crystal obtained thereby, and use thereof.

  SiC single crystal is very stable thermally and chemically, excellent in mechanical strength, resistant to radiation, and excellent in breakdown voltage and high thermal conductivity compared to Si (silicon) single crystal. It has physical properties and can easily control p- and n-conductivity type electrons by adding impurities, and has a wide forbidden band width (about 3.3 eV for 4H type single crystal SiC and about 3.3 eV for 6H type single crystal SiC). 0 eV). For this reason, it is possible to realize high temperature, high frequency, withstand voltage and environmental resistance that cannot be realized with existing semiconductor materials such as Si single crystal and GaAs (gallium arsenide) single crystal. It is growing.

In order to obtain a p- and n-conductivity type SiC single crystal for a semiconductor material, a method of incorporating an impurity during crystal growth has been proposed. A p-type, n-type SiC single crystal containing an impurity and a method for manufacturing the same Is being considered.
Further, in a semiconductor element for switching, which is considered to be one of the main uses of SiC single crystal, it is an important issue to reduce resistance during energization that causes power loss. For this reason, various studies have been made.

For example, Patent Document 1 describes a method for producing a 6H n-type SiC single crystal by a sublimation recrystallization method in which 20 to 100 ppm of Al is added to SiC powder and sublimated in a nitrogen gas atmosphere. As a specific example, an example of obtaining a 6H n-type SiC single crystal having a resistivity of 0.1 Ωcm is described.
Patent Document 2 describes a method for producing a SiC single crystal in which an n-type dopant atom or a compound thereof and arsenic (As) or an As compound are added to a SiC source gas on a SiC single crystal substrate.
Further, Patent Document 3 discloses a method for producing an n-type silicon single crystal in which P (phosphorus) is doped by the Czochralski method and the silicon single crystal is grown at an Al (aluminum) concentration of 2 × 10 ¹² atoms / cc or more. And P-doped n-type silicon single crystal wafers are described.

Japanese Patent Laid-Open No. 6-21989 JP 2002-234800 A Japanese Patent Laid-Open No. 2004-224577

However, in these well-known documents, the formation of compressive stress due to the difference in N concentration in an element using an n-type SiC single crystal, that is, in n-type conduction, a large amount of N serving as a donor is doped to reduce the specific resistance value. Although it is necessary, the lattice constant decreases when the donor concentration is increased, and the formation of compressive stress is recognized that the compressive stress due to the N concentration difference increases with respect to the low-concentration epitaxial layer in the device and can generate dislocation defects. However, it is difficult to obtain an n-type SiC single crystal with reduced stress by these known techniques, and an n-type SiC single crystal with reduced stress is required.
Accordingly, an object of the present invention is to provide a method for producing an n-type SiC single crystal with reduced stress, an n-type SiC single crystal with reduced stress obtained by the method, and an application thereof.

As a result of intensive studies to achieve the above object, the present inventor has completed the present invention.
The present invention is characterized in that an n-type SiC single crystal is grown by a solution method by adding nitrogen (N) and aluminum (Al), which are donor elements for making an n-type semiconductor, to SiC. The present invention relates to a method for manufacturing type SiC single crystal.

The concentration of the nitrogen (N) element and the aluminum (Al) element in the SiC single crystal in the present invention is the content of each component in the SiC single crystal determined by the measurement method described in detail in the column of Examples described later. Indicates.
Moreover, the stress in this specification shows the stress value of the n-type SiC single crystal calculated | required by the measuring method explained in full detail in the column of the below-mentioned Example.
In addition, the addition amount of nitrogen (N) and aluminum (Al) in the present specification is the total of the elements originally contained as impurities in the graphite in the reactor and the added nitrogen (N) element respectively. And the total amount of aluminum (Al) element.

According to the present invention, an n-type SiC single crystal with reduced stress can be easily obtained.
In addition, according to the present invention, an n-type SiC single crystal with reduced stress can be obtained as compared with a conventional n-type SiC single crystal.
Furthermore, according to the present invention, an element using an n-type SiC single crystal with reduced stress can be obtained.

FIG. 1 is a graph showing changes in the stress value of an n-type SiC single crystal when the content of nitrogen (N) as a donor element is kept constant and the Al content is changed. FIG. 2 is a schematic view of an apparatus applied to a method for producing an n-type SiC single crystal by a solution growth method according to an embodiment of the present invention. FIG. 3 is a schematic view of an apparatus applied to a method for producing an n-type SiC single crystal by a sublimation method, which is one embodiment of the present invention. FIG. 4 is a schematic cross-sectional view of a wafer with an SiC epitaxial layer to which the n-type SiC single crystal obtained by the embodiment of the present invention is applied. FIG. 5 is a schematic cross-sectional view of a MOSFET using a wafer with an SiC epitaxial layer. FIG. 6 is a schematic view of Hall measurement by the Van der Pauw method for measuring the physical properties of the n-type SiC single crystal obtained by the embodiment of the present invention.

  In the present invention, it is necessary to grow a n-type SiC single crystal by adding nitrogen (N) and aluminum (Al), which are donor elements for making an n-type semiconductor, to SiC. It is possible to obtain an n-type SiC single crystal having a low specific resistance, for example, a specific resistance of 0.02 Ωcm or less and a reduced stress.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
As shown in FIG. 1, in the SiC single crystal obtained in Example 1, the N concentration [N] is 2 × 10 ¹⁹ (also expressed as 2E19) cm ⁻³ , and the Al concentration [Al] is 4 × 10 ¹⁷ (both 4E17). The n-type SiC single crystal having cm ⁻³ and [N] / [Al] = 50 has an N concentration of 2 × 10 ¹⁹ (also expressed as 2E19) in the SiC single crystal obtained in Example 2. Compared to an n-type SiC single crystal with cm ⁻³ and an Al concentration of 2 × 10 ¹⁷ (also expressed as 4E17) cm ⁻³ and [N] / [Al] = 100, the stress value is increased from 18 MPa to 5 MPa. It is confirmed that it is significantly reduced. From this, regarding the contents of N and Al in the SiC single crystal, [N] / [Al] ≦ 75, especially [N] / [Al] ≦ 50 reduces the stress of the n-type SiC single crystal. In order to reduce the specific resistance of the n-type SiC single crystal, it is necessary that 1 ≦ [N] / [Al].

In the present invention, when growing an SiC single crystal, Al is contained together with nitrogen (N) as a donor element, and an arbitrary growth method for growing an n-type SiC single crystal, for example, a solution method or a vapor phase. It is necessary to produce an n-type SiC single crystal by a method such as a sublimation method.
As the seed crystal in the SiC single crystal growth method, it is preferable to use an SiC bulk single crystal having the same crystal structure as the crystal to be grown, for example, 4H—SiC, 6H—SiC, 3C—SiC, or 15R. -SiC, especially 4H-SiC, 6H-SiC, and among them, 4H-SiC single crystals are mentioned in the solution method.

  In the solution method, for example, as shown in FIG. 2, a crucible 2 for containing a Si-containing melt 1 provided in a growth furnace (not shown) via a heat insulating material (not shown), the growth furnace A solution method in which a high-frequency coil 3 and a support bar 4 that can be raised and lowered are provided to heat and maintain the melt 1 at a constant temperature, and a seed crystal 5 is installed at the tip of the support bar 4. Using a SiC single crystal growth apparatus, if the contents of N and Al in the crystal are [N] and [Al], respectively, 1 ≦ [N] / [Al] ≦ 75, especially 1 ≦ [N] / [Al For example, the amount of N and Al in the crucible is set to 0.02 to 0.75 atm% for N and 0.01 to 0.2 atm% for Al, respectively. Crystals can be grown.

  Examples of the Si-containing melt include any melt in which Si and the above ratios of N and Al are added. Further, as a Si-containing melt, X is a component composed of one or more elements which are components added to promote dissolution of Si and C and C from a graphite crucible and / or from the viewpoint of the quality of the grown crystal. As an essential component, for example, a raw material solution containing Ti and / or Cr as X, for example, an element other than Si, Cr and C as X and rare earth elements, transition Examples thereof include those containing any one element selected from metal elements and alkaline earth elements. The element N may be introduced into the melt by introducing all or part of the necessary amount as nitrogen gas. When N element and / or Al element is contained in the crucible and / or support rod (for example, carbon rod) of the SiC single crystal growth apparatus, the amount of N and / or Al added from the outside is included in the apparatus. It is necessary to consider the amount. The melt needs to contain Al, but can further contain Ga, In, Ge, or Te.

  The temperature is controlled by high-frequency induction heating, for example, by observing the temperature of the melt surface with a radiation thermometer and / or a thermocouple installed inside a supporting part (for example, a carbon rod), for example, W-Re (tungsten / lenium). ) It can be performed by the temperature controller based on the measured temperature obtained by measuring the temperature using a thermocouple.

In the method for producing an n-type SiC single crystal using the above-described solution method SiC single crystal production apparatus, a known production method in the solution method, for example, the shape of the graphite crucible, the heating method, the heating time, the atmosphere, the temperature rise Crystal growth can be performed by applying a temperature rate and a cooling rate.
For example, the heating time by high-frequency induction heating (approximately the time from the preparation of raw materials to the SiC saturation concentration) is about 30 minutes to 200 hours (for example, about 3 to 10 hours), depending on the size of the crucible, The atmosphere includes a rare gas, for example, an inert gas such as He, Ne, Ar, or a part of them replaced with N ₂ . Further, a part of the inert gas may be replaced with methane gas.
The growth temperature in the crystal growth is preferably performed in a melt heated to a temperature of 1800 to 2100 ° C.

In the sublimation method, for example, the seed crystal 13 is attached to the inner surface of a graphite crucible lid filled with SiC powder and Al as a sublimation raw material 12 in a graphite crucible 11, and placed inside a quartz tube, When Ar and N ₂ gases are N and Al, respectively, the contents of N and Al in the crystal are [N] and [Al], respectively, 1 ≦ [N] / [Al] ≦ 75, especially 1 ≦ [N] / [Al] The SiC powder and the Al sublimation raw material are heated to a temperature of 2300 ° C. or higher, for example, 2300 ° C., and the SiC single crystal substrate is heated to a temperature of 2200 ° C. or higher, for example, 2200 ° C. Thus, the SiC single crystal 15 can be grown on the seed crystal 14 by reducing the pressure in the quartz tube. The amount of N and Al can grow an n-type SiC single crystal with N being 0.02 to 0.75 atm% and Al being 0.01 to 0.2 atm% with respect to SiC. The raw material needs to contain Al, but may further contain Ga, In, Ge, or Te.

According to the method of the present invention, an n-type SiC single crystal having a small specific resistance even if the amount of nitrogen (N) is reduced, preferably a specific resistance of 0.02 Ωcm or less and a carrier concentration (n) of 5 × 10 ¹⁸ cm. ^An n-type SiC single crystal having a level of ⁻³ or more, particularly 10 ¹⁹ cm ^{−3 and} an n-type conductivity can be easily obtained. The n-type SiC single crystal can be 3C-SiC, 4H-SiC, 6H-SiC or 15R-SiC, especially 6H-SiC, 4H-SiC, among them, according to the growth temperature of 1850 ° C. or higher by the solution method. A 4H—SiC single crystal can be obtained stably.

The n-type SiC single crystal obtained by the method of the present invention has a small specific resistance over a wide temperature range, preferably a specific resistance of 0.02 Ωcm or less, and can be suitably used as a semiconductor material. It can be used for applications such as MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) that can be used for the switching elements shown.
Since the n-type SiC single crystal of the present invention has a small specific resistance and stress (compressive stress), the MOSFET can be highly reliable.

Examples of the present invention will be described below.
In each of the following examples, the growth of the n-type SiC single crystal was performed using an SiC single crystal manufacturing apparatus by a solution method shown in FIG. The temperature of the Si-containing melt at a high temperature (1850 to 2100 ° C.) can be confirmed by using a radiation thermometer installed in the observation window above the melt surface where the Si-containing melt surface can be directly observed. The temperature before and after contact was measured. In addition, a thermocouple was installed inside the support rod (carbon rod) to which the seed crystal was bonded (at a position 2 mm from the seed crystal), and the temperature immediately after contact with the melt was measured.

Confirmation that the obtained SiC single crystal was n-type and evaluation of the n-type SiC single crystal were performed as follows.
1) Specific resistance, carrier concentration, characteristics evaluation and confirmation of conductivity type of SiC single crystal SiC single crystal is cut into a square having a thickness of 900 μm and a side of 5 mm, and an ohmic electrode using Ni at four corners as shown in FIG. The carrier concentration was obtained from the following equation from the specific resistance value obtained by Hall measurement by a room temperature (26 ° C.) Van der Pauw method (Van der Pau method). Also, the conductivity type was confirmed by the polarity of the Hall voltage at the time of Hall measurement.
n = 1 / qμρ
(In the formula, n represents carrier concentration, q represents elementary charge, μ represents mobility, and ρ represents specific resistance.)

2) Measurement of N concentration and Al concentration in SiC single crystal The obtained SiC single crystal was measured using SIMS (Secondary Ion-microprobe Mass Spectrometer).
Measuring device: IMS-6F manufactured by Cameca
3) Measurement of stress value About the obtained SiC single crystal, the stress value converted from the amount of peak shift was calculated | required from the comparison with the undoped 4H-SiC peak value by Raman measurement. The measurement is performed on five points of the sample, and the average value is shown as the stress value.
The sample was irradiated with light of an argon ion (Ar ⁺ ) laser by a microscopic Raman spectroscope using a microscope lens, and Raman measurement was performed by measuring the Raman scattered light from the sample with a spectroscope. When strain is present in the crystal, the peak frequency of the Raman band cysts compared to the case of the unstrained crystal. Strain can be estimated from this shift amount, and since the strain and stress are in a linear relationship, the shift amount of the Raman peak is known to be proportional to the stress (F. Cerdeira et al. Phys. Rev. B.5- 2.580 (1972) and Applied Physics Vol. 75, No. 10 (2006) 1224). Further, it is known that the strain caused by the compressive stress shifts to the high frequency side. For this reason, the compressive stress can be obtained from the exact amount of change in the frequency.
Measuring apparatus: Tobin Yuon Ramanar U-1000

Example 1
Using the SiC single crystal manufacturing apparatus shown in FIG. 2, Si 60 atm%, Cr 40 atm% as raw materials, N (total amount supplied as nitrogen gas) 0.1 atm% and Al 0.1 atm% for SiC in a graphite crucible The 4H—SiC single crystal was immersed as a seed crystal for 1 to 200 hours in the melt that was charged and heated to a growth temperature of 2010 ° C., and was grown for about 10 hours at [N] / [Al] = 50.
About the obtained SiC single crystal, Al addition amount (ratio with respect to SiC), N and Al content, and Hall measurement were performed and evaluated. The results obtained are summarized below.

Component concentration, component concentration ratio, specific resistance, carrier concentration and stress measurement results Al addition amount (atm%) 0.1
Al concentration 4 × 10 ¹⁷ cm ⁻³
N concentration 2 × 10 ¹⁹ cm ⁻³
[N] / [Al] 50
Conductivity type n
Specific resistance (Ωcm) 0.02
Carrier concentration (cm ⁻³ ) 5 × 10 ¹⁸
Stress (MPa) 5
The stress measurement results are shown together with the results of Example 2 in FIG.

Example 2
A SiC single crystal was grown for about 10 hours in the same manner as in Example 1 except that the addition amount of Al was 0.01 atm% with respect to SiC and [N] / [Al] = 100.
The results measured in the same manner as in Example 1 are shown below.

Component concentration, component concentration ratio, specific resistance, carrier concentration, and stress measurement results Al addition amount (atm%) 0.01
Al concentration 2 × 10 ¹⁷ cm ⁻³
N concentration 2 × 10 ¹⁹ cm ⁻³
[N] / [Al] 100
Conductivity type n
Specific resistance (Ωcm) 0.02
Carrier concentration (cm ⁻³ ) 5 × 10 ¹⁸
Stress (MPa) 18
The stress measurement results are shown together with the results of Example 1 in FIG.

Example 3
Crystal growth was carried out for about 10 hours in the same manner as in Example 1 except that the addition amounts of Al and N were changed to 0.2 atm% and Al 0.2 atm% with respect to SiC.
The results measured in the same manner as in Example 1 are shown below.

Component concentration, component concentration ratio, specific resistance, carrier concentration, and stress measurement results Al addition amount (atm%) 0.2
Al concentration 8 × 10 ¹⁷ cm ⁻³
N concentration 4 × 10 ¹⁹ cm ⁻³
[N] / [Al] 50
Conductivity type n
Specific resistance (Ωcm) 0.02
Carrier concentration (cm ⁻³ ) 1 × 10 ¹⁹
Stress (MPa) 6

  From the above results, it is shown that the stress value + in FIG. 1 is a compressive stress, and the stress value of the n-type SiC single crystal obtained in Example 1 and Example 3 where [N] / [Al] = 50. Indicates that the stress value of the n-type SiC single crystal obtained in Example 2 where [N] / [Al] = 100 is significantly reduced.

Example 4
FIG. 4 shows a schematic sectional view of a wafer with an epitaxial layer using the n-type SiC single crystal obtained in Example 1. FIG. Note that n ⁺ in FIG. 4 indicates n-type conduction and high concentration doping.
The epitaxial layer was formed on a wafer based on the n-type SiC single crystal formed in Example 1 using a CVD apparatus at the following composition gas and temperature.
Source gas: SiH ₄ , C ₃ H ₈
Doping gas: N ₂
Carrier gas: H ₂
Growth temperature: about 1600 ° C

Example 5
FIG. 5 shows an example in which the wafer with an epitaxial layer obtained in Example 4 is applied to a MOSFET (abbreviation of Metal Oxide Semiconductor Field Effect Transistor, which is used as a switching element).

  By the method for producing a SiC single crystal of the present invention, an n-type SiC single crystal having a small specific resistance and stress (compressive stress) that gives an epitaxial wafer and a MOSFET that can exhibit stable performance can be produced.

DESCRIPTION OF SYMBOLS 1 Si-containing melt 2 Crucible 3 High frequency coil 4 Support rod 5 Seed crystal 11 Crucible 12 Sublimation raw material 13 Seed crystal 14 Growth crystal 15 Raw material vapor

Claims (2)

  An n-type SiC single crystal characterized in that nitrogen (N) and aluminum (Al), which are donor elements for making an n-type semiconductor, are added to SiC and an n-type SiC single crystal is grown by a solution method. Manufacturing method.   2. The concentration ratio between N and Al in the SiC single crystal is expressed by [N] and [Al], and 1 ≦ [N] / [Al] ≦ 50. The manufacturing method as described in.

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