JP3915252B2 - Method for manufacturing silicon carbide semiconductor substrate - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a silicon carbide semiconductor substrate for forming a semiconductor element.
[0002]
[Prior art]
For the purpose of controlling high frequency and high power, power semiconductor elements (hereinafter referred to as power devices) using silicon (hereinafter referred to as Si) have been improved in performance by various devices. However, the power device may be used in the presence of high temperature or radiation, and the Si power device may not be used under such conditions.
[0003]
Also, the application of new materials is being studied in response to the demand for higher performance than Si power devices. Since silicon carbide (hereinafter referred to as SiC) taken up by the present invention has a wide forbidden band width (3.26 eV for 4H-SiC and 3.02 eV for 6H-SiC), it has controllability and resistance to electrical conductivity at high temperatures. Since it has excellent radiation properties and has a dielectric breakdown voltage that is about an order of magnitude higher than that of Si, it can be applied to high breakdown voltage devices. Furthermore, since SiC has an electron saturation drift velocity approximately twice that of Si, it is suitable for high-frequency and high-power control.
[0004]
However, in order to apply the excellent physical properties of SiC to a power device, element technology as sophisticated as Si process technology is required. That is, after finishing the surface of the SiC substrate to be a mirror surface, it is necessary to optimize process conditions such as epitaxially growing a SiC thin film, doping a donor or an acceptor, or forming a metal film or an oxide film.
[0005]
In epitaxial growth, it is important to obtain a thin film having an intended carrier density and good crystallinity. Conventionally, the epitaxial growth of SiC has been performed at about 1500 ° C. using monosilane and propane as reaction gases.
Conventionally, in the epitaxial growth of Si, it has been known to use a silane gas containing chlorine as a source gas (for example, SiCl ₄ ). On the other hand, in the epitaxial growth on SiC, a report using SiCl ₂ H ₂ or the like as a source gas for forming cubic 3C-SiC [for example, E.niemann et al. Inst. Phys. Conf. Ser. No. 142, pp. 165-168] and applications using a hydrocarbon containing chlorine (for example, CH ₃ Cl) for heteroepitaxial growth of 3C—SiC on a silicon semiconductor substrate [Japanese Patent Laid-Open No. 4-124815] However, there was no such example for the growth of hexagonal 4H or 6H—SiC thin films, and it was not known to add hydrogen chloride.
[0006]
In addition, regarding the hexagonal 4H or 6H—SiC thin film growth, there is an example in which hydrogen chloride is used for the surface treatment of the substrate before the thin film growth [for example, AABurk, Jr., LBRowland, J. Crystal Growth, vol.167. , pp.586-595, (1996)]. It is said that the morphology of the growth layer surface can be controlled by this treatment. In addition, it has been reported that unintentional doping of aluminum at the substrate / growth layer interface can be suppressed by the same substrate treatment [AABurk, Jr., LBRowland, Appl. Phys. Lett, vol.68, pp.382-384 1996. ].
[0007]
[Problems to be solved by the invention]
In order to obtain a SiC semiconductor device having excellent characteristics, it is also necessary to obtain a higher quality epitaxial layer, that is, a thin film having an intended carrier density and a low crystal defect density and good crystallinity even in the epitaxial growth of a SiC thin film. It is.
[0008]
[Means for Solving the Problems]
As a result of an experiment of adding hydrogen chloride during epitaxial growth, the inventor has found that hydrogen chloride addition is effective.
The present invention for the above problems solved, epitaxial method of manufacturing a silicon carbide semiconductor substrate to grow a silicon carbide epitaxial layer on a silicon carbide semiconductor substrate, hydrogen, monosilane, in an atmosphere with the addition of hydrogen chloride gas in propane A method of manufacturing a silicon carbide semiconductor substrate for growing a layer,
The silicon carbide semiconductor substrate is either 4H-SiC or 6H-SiC;
The amount of hydrogen chloride added is 0.1 to 1% by volume,
Furthermore, the temperature at the time of epitaxial growth shall be 1450 degreeC-1550 degreeC.
[0009]
By doing so, the substrate surface is cleaned, the etch pit density which is a crystal defect is reduced, and the film quality of the epitaxial layer such as carrier mobility is improved.
In particular, the amount of hydrogen chloride added is preferably 0.1 to 0.8%, more preferably 0.2 to 0.6% by volume.
[0010]
In the concentration range of 0.2 to 0.6%, the effect becomes more remarkable.
It is assumed that the silicon carbide semiconductor substrate is 4H—SiC or 6H—SiC.
4H—SiC or 6H—SiC is a crystal suitable for a high-temperature semiconductor device or the like having a wide forbidden band width, and improved crystallinity was observed by adding hydrogen chloride gas as shown in Examples.
[0011]
The surface of the silicon carbide semiconductor substrate is a (0001) Si plane, a (000-1) carbon plane, or a plane having an offset angle of several degrees from these planes.
Such a crystal plane is a plane suitable for epitaxial growth because a smooth plane is obtained.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, experiments and examples conducted for the present invention will be described.
[Experiment 1]
A mirror-polished 4H—SiC single crystal is used as a silicon carbide semiconductor substrate (hereinafter referred to as a substrate) before epitaxial growth, and is tilted 8 degrees from the (0001) Si plane in the <1, 1, -2, 0> direction. A polished surface was used.
[0013]
First, the substrate is cut into 5 mm square chips by a dicer, washed with an organic solvent and an acid, and then placed on a graphite susceptor coated with SiC with the Si surface to be etched facing up. A susceptor on which a substrate is placed is inserted into a quartz reaction tube, and a vacuum of 1 Pa or less is applied.
Next, vapor phase etching is performed. In the gas phase etching, heating was performed at 1350 ° C. for 5 minutes while flowing a mixed gas in which hydrogen and hydrogen chloride were mixed at a flow rate of 1 L / min and 10 mL / min. The method of heating the susceptor is high frequency induction heating.
[0014]
Subsequently, an SiC thin film is epitaxially grown. Hydrogen (H ₂ ), monosilane (SiH ₄ ), propane (C ₃ H ₈ ), and hydrogen chloride (HCl) mixed at a flow rate of 3 L, 0.3 mL, 0.25 mL, and 3 to 30 mL per minute, respectively. It introduced into the reaction tube. In this state, it was heated at 1500 ° C. for 2 hours. Then, a 4H type SiC thin film is epitaxially grown on the substrate. The carrier density of the thin film was 5 × 10 ¹⁵ cm ⁻³ .
[0015]
In order to evaluate the dislocation density of the grown film, etching with potassium hydroxide (KOH) was performed. For this etching, a method of immersing the sample in potassium hydroxide heated to 400 ° C. in a nickel (Ni) crucible for 30 seconds was used. The defect density was counted by SEM observation.
FIG. 1 is a characteristic diagram showing the relationship between the hydrogen chloride concentration [HCl / (H ₂ + SiH ₄ + C ₃ H ₈ + HCl)] during epitaxial growth and the etch pit density in the SiC thin film. From this figure, the etch pit density decreases when the hydrogen chloride concentration is 0.1 to 0.8%, especially when the hydrogen chloride concentration is 0.2 to 0.6%. I understand that I can do it.
[0016]
Etch pits can be formed at the positions of dislocations, which are linear defects in the epitaxial layer, and reflect the quality of crystallinity, and are electrically trapped carriers.
FIG. 2 is a characteristic diagram showing the relationship between etch pit density and carrier mobility, which the inventors have experimented with. The mobility decreases rapidly as the etch pit density increases. From this, it can be seen that if the etch pit density is reduced by an order of magnitude, the mobility can be almost doubled. The van der Pauw method was used as the mobility evaluation method. That is, nickel (Ni) electrodes are formed at the four corners on the epitaxial layer of the sample by sputtering using a metal mask. The electrode has a diameter of 200 μm and a thickness of 400 nm. Thereafter, annealing was performed at 1050 ° C. for 5 minutes in an argon (Ar) atmosphere in order to obtain ohmic contact except for rectification.
[0017]
Accordingly, from FIGS. 1 and 2, the crystallinity of the growing epitaxial layer is improved when the hydrogen chloride concentration is 0.1 to 0.8%, more preferably 0.2 to 0.6%. It can be concluded that epitaxial growth should be performed under such conditions.
This is presumably because the surface is sufficiently cleaned and etched during epitaxial growth. There may also be gettering action of metal impurities found in silicon semiconductors.
[0018]
In the above example, only the results under the etching conditions of 1500 ° C. were described, but the same experiment was conducted in the range of 1450 to 1550 ° C., and the hydrogen chloride concentration was 0.5 to 1% at 1450 ° C., and the concentration was 0 at 1550 ° C. It was found to be 0.1 to 0.3%. The growth surface is not only the (0001) Si surface of 4H—SiC, but also the (000-1) C surface of 4H—SiC, the Si, C surface of 6H—SiC, or a surface inclined at a minute angle from these surfaces. It can also be applied to.
[0019]
【The invention's effect】
As described above, according to the present invention, during the epitaxial growth of the SiC semiconductor substrate, the epitaxial layer is grown by adding 0.1 to 1.0% hydrogen chloride by volume and growing at 1450 to 1550 ° C. The crystallinity of the SiC semiconductor device can be improved, and the characteristics of the SiC semiconductor device can be improved.
[Brief description of the drawings]
FIG. 1 is a characteristic diagram showing the relationship between HCl concentration and etch pit density during epitaxial growth. FIG. 2 is a characteristic diagram showing the relationship between etch pit density and mobility.

Claims (2)

The method of manufacturing a silicon carbide semiconductor substrate to grow a silicon carbide epitaxial layer on a silicon carbide semiconductor substrate,
A silicon carbide semiconductor substrate manufacturing method for growing an epitaxial layer in an atmosphere in which hydrogen chloride gas is added to hydrogen, monosilane, and propane,
The silicon carbide semiconductor substrate is either 4H-SiC or 6H-SiC;
The amount of hydrogen chloride added is 0.1 to 1% by volume,
Furthermore, the temperature during epitaxial growth is 1450 ° C. to 1550 ° C.,
A method for producing a silicon carbide semiconductor substrate, comprising: 2. The method for producing a silicon carbide semiconductor substrate according to claim 1, wherein the amount of hydrogen chloride added is 0.2 to 0.6% by volume.

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