JP2004193631A - Manufacturing method of silicon carbide thin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming 3C-SiC single crystal thin film of a single phase having less crystal defects on an Si wafer by making hetero epitaxial growth on the surface of an Si substrate. <P>SOLUTION: This method comprises a step for forming a silicon carbide by supplying a carbon and then heating the surface of the Si substrate to carbonize the surface, and a step for growing the silicon carbide by supplying the carbon and the silicon after carbonizing. A lot of terraces 5 and steps 6 exist on an offcut substrate surface of the Si because different surface reactivities are shown in a P direction 8 of a long stretch of atomic row parallel to a step edge 10 and in an N direction 7 of a short atomic row on the terrace which is perpendicular to the step edge 10 and segmentalized by the step edge 10. An SiC single crystal thin film of a single phase which comprises no anti-phase boundary (APB) and has less crystal defect can be formed on account of this anisotropy. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a method of manufacturing a single crystal thin film of silicon carbide (SiC), which is a wide band gap semiconductor material applicable to semiconductor devices such as high power devices, high temperature devices, and environmental resistance devices. In particular, the present invention relates to a method for forming a single-phase 3C-SiC single-crystal thin film with few crystal defects on a Si wafer by heteroepitaxial growth on a Si substrate surface.

Conventionally, 6H-type and 4H-type SiC single-crystal substrates are commercially available, but for 3C-SiC having the highest mobility, a crystal formed by heteroepitaxial growth is formed on the Si substrate. When silicon carbide is grown on the surface of a Si substrate, first, a carbon-hydrogen gas is supplied to the surface of the Si to heat and carbonize, and then carbon and silicon are supplied to heteroepitaxially grow silicon carbide (Patent Document 1). .
JP-A-7-172997

  The silicon carbide thin film formed by this conventional technique has a high density of growth of lattice defects and twins at the SiC / Si interface, which is a problem in producing a silicon carbide substrate for forming an electronic device. there were. Furthermore, single crystal grains of two types of phases grow on the Si substrate, and an anti-phase boundary (APB) is formed at the interface between the two types of crystal grains of different phases, and a large number of defects are introduced. Met.

  FIG. 1 shows a conceptual diagram of a mechanism of a process of forming SiC crystal grains by supplying carbon to a Si surface, heating and carbonizing the Si surface. On a clean Si (001) surface, Si atoms having two dangling bonds are connected in the [110] direction. When this dangling bond is compensated for by carbon atoms, a series of Si-C atoms linked to Si-C-Si .. is formed in a [110] direction. Here, when the bond between the Si atom 2 bonded to the carbon atom 1 and the Si atom 3 located further below is broken, the Si-C-Si. 2 shrinks in the Si [110] direction to form a SiC atomic structure. On the just Si (001) surface without off-cut, the direction of the following equation (1) orthogonal to the Si [110] direction cannot be distinguished, and appears on the Si (001) surface with the same probability.

  For this reason, the contraction in the Si [110] direction occurs with almost the same probability in the two directions orthogonal to each other, and the two types of SiC crystal grains having different directions have different phases. The SiC crystal grains having different phases cannot be combined with each other by growth to be integrated, resulting in a two-phase thin film containing APB at the interface, which is a problem.

  An object of the present invention is to provide a method for forming a single-phase 3C-SiC single-crystal thin film with few crystal defects on a Si wafer by heteroepitaxial growth on a Si substrate surface in order to solve the conventional problem. And

  In order to achieve the above object, a method for producing a silicon carbide thin film of the present invention is a method for producing a silicon carbide (Si-C) thin film, in which carbon is supplied and the surface of the Si substrate is heated to carbonize the surface. The method includes a step of forming silicon carbide, and a step of growing carbon carbide by supplying carbon and silicon after carbonization, wherein terraces and steps are formed on the surface of the Si substrate having anisotropy.

  In the above structure, it is preferable that the width of the terrace on the surface of the Si substrate is not less than 5 angstroms (0.5 nm) and not more than 1000 angstroms (100 nm).

  In the above structure, in the silicon carbide forming step, it is preferable to supply carbon at a stage where the temperature of the surface of the Si substrate is 600 ° C. or lower.

  In the above structure, it is preferable that the carbon source supplied when the silicon substrate is heated to carbonize to form silicon carbide includes at least a molecular beam such as a carbon atom.

  In the above structure, in the step of growing carbon carbide by supplying carbon and Si after carbonization, the silicon carbide surface holds a structure in which excess Si atoms are added to the Si terminating surface as a growth surface. Is preferred.

  In the above-described present invention, by introducing terraces and steps by giving anisotropy to the surface of the Si substrate that forms silicon carbide by carbonizing, crystal grains having two types of phases, which were problems in the prior art, Is limited to one phase of crystal grains, and the formation of APB is suppressed.

  Further, when the carbon source supplied when heating the Si substrate surface to form carbonized silicon carbide is not only a gaseous substance such as a hydrocarbon, but also contains at least a molecular beam such as a carbon atom, the formation of twins is reduced. Is suppressed.

  According to the present invention, there is provided a method for producing a silicon carbide (Si—C) thin film, comprising the steps of: supplying carbon and heating the surface of a Si substrate to carbonize the surface to form silicon carbide; A step of supplying silicon to grow silicon carbide, by forming terraces and steps having anisotropy on the surface of the Si substrate, heteroepitaxially growing the surface of the Si substrate, and forming a single crystal with few crystal defects on the Si wafer. Phase 3C-SiC single crystal thin film can be formed.

  Further, the method for producing a silicon carbide thin film of the present invention enables a single-phase 3C-SiC single-crystal thin film not containing APB to grow with good controllability, and a 3C-SiC single-crystal thin film applicable to electronic devices can be formed on a Si substrate. Can be formed.

  FIG. 2 is a schematic view of the surface of the Si substrate according to the present invention in which terraces and steps are introduced with anisotropy. The Si (001) surface 4 is off-cut inclined in the [110] direction, and a terrace 5 and a step 6 are introduced. The width of the terrace (vertical direction to the step edge: N direction 7 in FIG. 2) is much shorter than the length of the terrace parallel to the step edge (P direction 8 in FIG. 2), and the off-cut angle is small. In the case of 4 degrees and the height of step 6 is one atomic layer, it is about 20 angstroms. This short series of Si [110] atoms (N direction 7 in FIG. 2) reacts with carbon and shrinks compared to the long series of Si [110] atoms in P direction 8 in FIG. It is easy to form the structure. In other words, on the surface where the terraces and steps are introduced, the array of Si [110] atoms in the width direction of the terrace (N direction 7 in FIG. 2) is selectively contracted to form a SiC atomic structure together with the supplied carbon 9. In this way, the two-phase Si crystal grains formed on the just Si (001) surface and having problems were limited to one phase by the introduction of terraces and steps, and became a single-phase SiC single-crystal thin film. The inventor has confirmed.

  When carbon 9 is supplied to the Si (001) surface including the terrace 5 and the step 6 and carbonized to form SiC crystal grains, when carbon 9 is supplied as a gaseous substance such as hydrocarbon, twins are easily formed. The present inventors have also confirmed that the formation of twins is suppressed by supplying a carbon source including a molecular beam such as an atom. This is considered for the following reasons. Considering the reaction between the carbon source in the gas phase and the Si surface, it is considered that the reaction with carbon starts from the most reactive atom on the Si surface. The most reactive Si atom on the Si surface is the atom at the position of the step edge 10 existing on the surface, and carbonization of the Si surface 4 by the carbon 9 in the gas phase is considered to start from the step edge 10. Can be At the step edge 10, since there is a step in the arrangement of Si atoms on the substrate, twins having different directions tend to grow from that position. On the other hand, when a carbon source including not only carbon in the gas phase but also a molecular beam such as a carbon atom is supplied, a reaction with the Si substrate occurs from an arbitrary position where the carbon is supplied, and is selected from the position of the step edge 10. Is prevented from occurring on the terrace 5. For this reason, it was confirmed that the growth of twins from the position of the step edge 10 was also suppressed, and an SiC crystal thin film with little twins was formed.

  Hereinafter, the present invention will be described more specifically with reference to examples.

(Example 1)
First, a Si (001) 4 ° -offcut substrate was introduced into an MBE apparatus, heated to 900 ° C or higher under a high vacuum of 10 ^-9 Torr or lower, and the Si (001) (2x1) surface rearrangement was observed by RHEED observation. The observed Si clean surface was formed. After cooling this clean surface to 400 ° C. or lower, the temperature was raised at a rate of 100-250 ° C./min. When the substrate temperature reached 400 ° C., carbon atoms were evaporated from an electron beam evaporator that irradiates an electron gun to a crucible filled with graphite particles and supplied to the substrate surface. In this case, the distance from the crucible to the substrate was about 40 cm, and the power supplied to the electron beam evaporator was suitably about 8 kV and about 100 mA. The substrate temperature was increased while being supplied with carbon, and carbonization was performed during the temperature increase process. In this case, it was confirmed that when the offcut substrate was used, the crystal directions of the SiC crystal grains formed during the carbonization process were aligned. As shown in FIG. 2, there are many terraces 5 and steps 6 on the surface of the offcut substrate, the P direction 8 of a long row of atoms parallel to the step edge 10, and the step edge perpendicular to the step edge 10. This is to show different surface reactivity in the N direction 7 of the atomic row on the short terrace divided by 10.

  Since the basic mechanism of carbonization is that the carbon atom 1 reacts with the Si [110] atomic sequence 2 on the Si (001) surface and contracts, it is easier to shorten the sequence of the Si [110] atomic sequence. It is thought that it can shrink and form a uniform 3C-SiC (001) / Si (001) interface. On the surface of the offcut substrate shown in FIG. 2, the contraction of the Si [110] atom sequence easily occurs in the N direction, and the Si (bottom) and C (top) directions of the [110] of the 3C-SiC crystal coincide with the N direction. I do.

  When the substrate temperature reached 1050 ° C., silicon was also supplied from the Knudsen cell in addition to carbon, and was kept at 1050 ° C. thereafter. In this case, the temperature of the Si Knudsen cell was kept at 1357 ° C. The crystallinity of the substrate surface is always observed by RHEED in the MBE growth chamber, and in-situ analysis is performed. The amount of C / Si supplied to the 3C-SiC (001) growth surface was controlled so that the 3C-SiC (001) surface always maintained a stable (3x2) surface rearrangement structure (surface controlled growth). The 3C-SiC (001) (3x2) surface has a structure in which excess Si atoms are added to the Si-terminated surface, and has a Si-excess surface compared to the structure of SiC with C / Si = 1 . In the growth of the 3C-SiC (001) surface by this surface controlled growth, since Si atoms are always supplied from the Si excess surface, the growth in the direction of Si (top) C (bottom) occurs selectively and the crystal grain Grow longer in this direction. If the selective growth direction of the crystal grains coincides with the P direction 8 in FIG. 2 which is long on the terrace on the surface of the off-cut substrate, the growth of the crystal grains proceeds on the terrace without interruption by steps. Thus, a single-phase 3C-SiC single crystal can be easily grown. On the other hand, in the antiphase domain having a relationship of 90 degrees with the crystal direction, the selective growth direction is the N direction 7 in FIG. 2, and the growth is always inhibited by the steps. When the two types of antiphase domains grow, crystal grains whose selective growth direction coincides with the P direction 8 grow selectively, and the other antiphase domain disappears as the growth progresses. it is conceivable that. Above, the crystal direction of 3C-SiC formed by carbonization of the off-cut surface was Si (bottom) C (top) // N direction, but this crystal orientation is Si considering the selective growth on the terrace (Top) coincides with the C (bottom) // P direction. In other words, if the carbonization treatment and the surface controlled growth are performed, a 3C-SiC single crystal having a uniform orientation is selectively grown, and the growth of other air phase domains is inhibited. A phase 3C-SiC single crystal thin film is obtained.

  FIG. 3 shows an SEM photograph of a single-phase 3C-SiC (001) surface having a thickness of 1000 Å (100 nm) obtained by performing the above-mentioned surface controlled growth for 3 hours. It can be observed that crystal grains with uniform orientation are selectively grown on the terrace and coreless to form a large single crystal. For a film thickness of 1000 angstroms (100 nm), the size of each crystal grain observed was about 1000 angstroms (100 nm). When the growth of the thin film was further continued, these crystal grains became larger and coreless to form larger single crystal grains as the film thickness increased.

  FIG. 4 shows (a) the ESR spectrum of the single-phase 3C-SiC single-crystal thin film having a thickness of 1000 angstroms (100 nm), and (b) a two-phase single-layer 3C-SiC thin film including APB formed on the just-cut Si (001) surface. This is shown in comparison with the ESR spectrum of the thin film. The spectrum of the Si dangling bond corresponding to the lattice defect observed in (b) was not confirmed in (a) formed by the method of manufacturing a silicon carbide thin film of the present invention, and the lattice caused by APB in the thin film was not observed. It was confirmed that defects were dramatically reduced.

  In this embodiment, an off-cut substrate was used as the Si substrate having anisotropy. However, if the surface has anisotropy and includes terraces and steps, it is a just-cut substrate and anisotropic etching is performed. The surface may have irregularities due to, for example, the surface. The off-cut direction is not limited to the [110] direction. If the [110] direction is not equivalent to the following formula (Formula 2) and has anisotropy, It may be off-cut in any direction.

  In the present embodiment, the off-cut angle was 4 degrees and the terrace width was about 20 angstroms (2 nm). However, even if the off-cut angle was changed to change the terrace width, the terrace width was 5 angstroms. In the range of (0.5 nm) -1000 angstroms (100 nm), a good single-phase 3C-SiC single crystal thin film was obtained. In the case of a terrace width of 5 angstroms (0.5 nm) or less, many twins are formed by carbonization, and a single-phase single-crystal thin film cannot be formed. At a terrace width of 1000 Å (100 nm) or more, the anisotropy did not function effectively in the carbonization mechanism, and a two-phase thin film containing APB was obtained.

  In the present embodiment, the supply of carbon was started from 400 ° C. during the heating of the substrate in the carbonization process, but the temperature can be applied as long as the temperature is 600 ° C. or less, and the temperature is not limited to 400 ° C. When carbon is supplied and carbonized from a temperature of 600 ° C. or higher, pits are easily formed at the SiC / Si interface, and crystal grains having different crystal orientations are likely to grow in the thin film.

In this embodiment, carbon is supplied from an electron beam evaporator in the form of atoms or clusters, which is different from the supply of gaseous carbon. When a gaseous carbon source such as C ₂ H _{4 is} supplied at 5 × 10 ⁻⁸ Torr or more during the formation of the thin film of this embodiment, the formation of single-phase 3C-SiC described in the embodiment is deteriorated, and a large number of twins are formed. Was confirmed. From this, it was confirmed that supply of non-gaseous molecular beam carbon was necessary to realize the method of forming a silicon carbide thin film of the present invention.

  In the present embodiment, in the process of growing carbon carbide by supplying carbon and silicon after carbonization, the 3C-SiC (001) surface has a (3x2) surface rearrangement and is added on the Si-terminated (001) surface. The surface was grown while retaining the Si-excess surface where Si was present. The present invention is also applicable to a case where the surface rearrangement is grown so as to retain Si-excessive other rearrangement structures (5x2), (7x2),... (2n + 1,2) (n is any positive integer) Was effective. In addition, it was effective also on the (2 × 1) surface which is a Si-terminated (001) surface.

  In the present embodiment, the Si (001) surface has been described, but the inventor has confirmed that the present invention is also effective on other surfaces of the Si substrate such as the Si (111) surface.

FIG. 4 is a conceptual diagram of a process for carbonizing the surface of a Si (001) substrate. FIG. 2 is a schematic view of the surface of a Si substrate used in the method for manufacturing a silicon carbide thin film according to one embodiment of the present invention. FIG. 4 is a trace diagram of an SEM photograph of a 3C-SiC (001) surface formed by the method for manufacturing a silicon carbide thin film according to one embodiment of the present invention. (a) is a trace diagram of an ESR spectrum of a single-phase 3C-SiC single-crystal thin film formed by the method of manufacturing a silicon carbide thin film of one embodiment of the present invention, (b) is a just-cut Si (001) of a comparative example The trace figure of the ESR spectrum of the thin film of two phases containing APB formed on the surface.

Explanation of reference numerals

1 Carbon atom 2 Si substrate atom bonded to carbon (Si [110] atom sequence)
3 Si substrate atoms below Si atoms bonded to carbon 4 Si substrate surface 5 Terrace 6 Step 7 N direction perpendicular to step edge 8 P direction parallel to step edge 9 Supply carbon 10 step edge

Claims (5)

  A method for producing a silicon carbide (Si-C) thin film, comprising: supplying carbon and heating the surface of a Si substrate to carbonize the surface to form silicon carbide; and supplying carbon and silicon after carbonization to carbonize. A method for producing a silicon carbide thin film, comprising a step of growing silicon, wherein anisotropic terraces and steps are formed on the surface of the Si substrate.   2. The method of manufacturing a silicon carbide thin film according to claim 1, wherein the width of the terrace on the surface of the Si substrate is not less than 5 Å (0.5 nm) and not more than 1000 Å (100 nm).   The method for producing a silicon carbide thin film according to claim 1, wherein in the silicon carbide forming step, carbon is supplied at a stage where the temperature of the surface of the Si substrate is 600 ° C. or lower.   2. The method for producing a silicon carbide thin film according to claim 1, wherein the carbon source supplied when the silicon substrate is heated to carbonize to form silicon carbide includes at least a molecular beam such as a carbon atom. 2. The carbonized carbon according to claim 1, wherein, in the step of supplying carbon and Si after carbonization to grow silicon carbide, the silicon carbide surface holds a structure in which an excess of Si atoms are added to the Si terminating surface as a growth surface. A method for manufacturing a silicon thin film.

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