WO2023026633A1

WO2023026633A1 - Semiconductor film and composite substrate

Info

Publication number: WO2023026633A1
Application number: PCT/JP2022/023323
Authority: WO
Inventors: 宏之柴田; 潤吉川; 守道渡邊
Original assignee: 日本碍子株式会社
Priority date: 2021-08-27
Filing date: 2022-06-09
Publication date: 2023-03-02
Also published as: JPWO2023026633A1; JP7620719B2

Abstract

Provided is an ε-Ga2O3-based semiconductor film having a low impurity concentration. The semiconductor film contains crystals each composed of ε-Ga2O3 or an ε-Ga2O3-based solid solution as a main phase, in which the half width of a peak appearing at around 250 cm-1 in a Raman spectrum of the semiconductor film as measured by laser Raman spectroscopy is 10 cm-1 or less.

Description

Semiconductor films and composite substrates

The present invention relates to an ε-Ga ₂ O ₃ -based semiconductor film and a composite substrate including the same.

In recent years, gallium oxide (Ga ₂ O ₃ ) has attracted attention as a semiconductor material. Gallium oxide is known to have five crystal forms α, β, γ, δ and ε, among which ε-Ga ₂ O ₃ has a bandgap of about 5 eV and is It has high stability up to and can control the bandgap by forming a mixed crystal. In addition, application to a high electron mobility transistor (HEMT) requires the generation of a two-dimensional electron gas, and since ε-Ga ₂ O ₃ has a crystal structure that exhibits spontaneous polarization, it has a high withstand voltage and low power consumption. It is attracting a great deal of attention as a next-generation power semiconductor material. ε-Ga ₂ O ₃ is a metastable phase, and a single crystal substrate has not been put to practical use, and is produced by heteroepitaxial growth on a heterogeneous substrate.

For example, Patent Document 1 (Patent No. 6436538) discloses an ε-Ga ₂ O ₃ single crystal with a low impurity concentration, which is applicable to semiconductor devices and which is produced using the HVPE method (halide vapor phase epitaxy method). ing. In Non-Patent Document 1 (Yuichi Oshima et al. "Epitaxial growth of phase-pure ε-Ga ₂ O ₃ by halide vapor phase epitaxy" J. Appl. Phys, 118, 085301 (2015)), a GaN substrate is prepared by the HVPE method. and ε-Ga ₂ O ₃ semiconductor films formed on AlN substrates. Patent Document 2 (Japanese Patent Application Laid-Open No. 2019-46984) describes a first semiconductor film containing a semiconductor crystal having a metastable crystal structure as a main component, and are different in composition and contain semiconductor crystals having a hexagonal crystal structure as the main component (the main component is ε-Ga ₂ O ₃ ), thereby manufacturing a semiconductor device having excellent semiconductor characteristics. A method of making is disclosed.

Since ε-Ga ₂ O ₃ has ferroelectric properties and a crystal structure that generates spontaneous polarization, it is expected to be applied to HEMTs like GaN. Properties such as conductivity of such semiconductors are generally controlled by doping. For example, a method of including a dopant in the film-forming raw material and a method of ion implantation are used. On the other hand, unlike such intentional doping, the film may contain contamination from the film deposition chamber or impurities derived from the raw material. Since such impurities can cause variations in various characteristics of the semiconductor film, it is desirable to reduce them as much as possible. In particular, if the semiconductor film contains transition metal elements such as Fe and Ti, alkali metals such as Na, and halogen elements such as F, the semiconductor film tends to vary in characteristics.

By the way, Raman spectroscopy is known as a technique for evaluating the crystallinity of a semiconductor film. In Raman spectroscopy, the crystallinity of a substance can be evaluated by irradiating the substance with light to cause scattering, and obtaining a Raman spectrum by analyzing the scattered light. For example, when the half width of a predetermined Raman peak in the Raman spectrum of a substance is small, the substance can be evaluated as having high crystallinity. For example, Non-Patent Document 2 (Francesco Boschi, "Growth and Investigation of Different Gallium Oxide Polymorphs," UNIVERSITA DEGLI STUDI DI PARMA, Dottorato di Ricerca in Fisica, Ciclo XXIX, 2017) describes a film formed on a c-plane sapphire substrate. Although the Raman spectrum of the ε-Ga ₂ O ₃ film has been reported, the half width of the peak near 250 cm ⁻¹ was relatively broad and the crystallinity of the film was low.

Patent No. 6436538 JP 2019-46984 A

As described above, ε-Ga ₂ O ₃ has ferroelectric properties, has a crystal structure that generates spontaneous polarization, and has the advantage of being able to control the bandgap by forming a mixed crystal. It is expected to be applied to high electron mobility transistors (HEMTs) in the near future. However, there is a problem that impurities may be contained in the film, which causes variations in various characteristics of the semiconductor film. Thus, conventionally, it has been difficult to obtain an ε-Ga ₂ O ₃ -based semiconductor film containing few impurities.

The inventors of the present invention have recently developed an ε-Ga ₂ O ₃ based semiconductor film by increasing the crystallinity of the ε-Ga ₂ O ₃ based semiconductor film by controlling the half width of the peak near 250 cm ⁻¹ in the Raman spectrum. It was found that the impurity concentration of

Accordingly, an object of the present invention is to provide an ε-Ga ₂ O ₃ -based semiconductor film with a low impurity concentration.

According to the present invention, the following aspects are provided.
[Aspect 1]
A semiconductor film whose main phase is a crystal composed of ε-Ga ₂ O ₃ or an ε-Ga ₂ O ₃ -based solid solution,
A semiconductor film, wherein the half width of the peak near 250 cm ⁻¹ in the Raman spectrum of the semiconductor film measured by laser Raman spectroscopy is 10 cm ⁻¹ or less.
[Aspect 2]
The semiconductor film measured by laser Raman spectroscopy at the center point X of the largest circle inscribed in the outer periphery of the semiconductor film and each of the four outer peripheral points A, B, C and D on the surface of the semiconductor film. The half width of the peak near 250 cm ^-1 in the Raman spectrum of is 10 cm ^-1 or less,
i) a straight line connecting the outer peripheral points A and C and a straight line connecting the outer peripheral points B and D intersect at right angles at the center point X; and ii) each of the shortest distances of the perimeter points A, B, C, and D from the outer edge of the semiconductor film is determined to be ⅕ of the radius of the semiconductor film. .
[Aspect 3]
Aspect ¹ , wherein in the Raman spectrum of the semiconductor film, the peak intensity ratio I ₂₅₀ /I _{260 of the peak intensity I 250} near 250 cm ⁻¹ to the peak intensity I ₂₆₀ near 260 cm −1 _is 2.0 or more. 3. or the semiconductor film according to 2.
[Aspect 4]
The semiconductor film according to any one of Modes 1 to 3, wherein the half width of the peak near 113 cm ⁻¹ in the Raman spectrum of the semiconductor film is 10 cm ⁻¹ or less.
[Aspect 5]
The semiconductor film according to any one of Modes 1 to 4, wherein the surface Ti concentration of the semiconductor film is 1.0×10 ¹⁵ atoms/cm ³ or less.
[Aspect 6]
The semiconductor film according to any one of Modes 1 to 5, wherein the surface Fe concentration of the semiconductor film is 1.0×10 ¹⁵ atoms/cm ³ or less.
[Aspect 7]
The semiconductor film according to any one of Modes 1 to 6, wherein the surface Na concentration of the semiconductor film is 2.0×10 ¹³ atoms/cm ³ or less.
[Aspect 8]
The semiconductor film according to any one of Modes 1 to 7, wherein the semiconductor film has a surface F concentration of 2.0×10 ¹⁵ atoms/cm ³ or less.
[Aspect 9]
The semiconductor film according to any one of Modes 1 to 8, wherein the surface Si concentration of the semiconductor film is 1.0×10 ¹⁶ atoms/cm ³ or less.
[Aspect 10]
A composite substrate comprising a GaN single crystal substrate and the semiconductor film according to any one of aspects 1 to 9 formed on the GaN single crystal substrate.

FIG. 2 is a diagram for explaining the positions of a central point X and four peripheral points A, B, C and D on the surface of the semiconductor film of the present invention; It is a schematic cross-sectional view showing the configuration of an HVPE (halide vapor phase epitaxy) apparatus. It is a schematic cross section which shows the structure of a mist CVD (chemical vapor deposition) apparatus. 2 is a Raman spectrum measured in the semiconductor film produced in Example 1. FIG.

Semiconductor Film The semiconductor film according to the present invention has a main phase of crystals composed of ε-Ga ₂ O ₃ or ε-Ga ₂ O ₃ solid solution. Therefore, the semiconductor film according to the present invention can be called an ε-Ga ₂ O ₃ -based semiconductor film. In addition, this semiconductor film has a Raman spectrum of the semiconductor film having a half width of 10 cm ⁻¹ or less at around 250 cm ⁻¹ . Thus, by controlling the half-value width of the peak near 250 cm ⁻¹ in the Raman spectrum to increase the crystallinity of the ε-Ga ₂ O ₃ -based semiconductor film, the impurity concentration of the ε-Ga ₂ O ₃ -based semiconductor film can be reduced. can be reduced. Here, “near” a wavenumber (Raman shift) in the Raman spectrum typically means a range of ±5.0 cm ⁻¹ from that wavenumber. For example, a “peak around 250 cm ⁻¹ ” typically means a “peak between 245 and 255 cm ⁻¹ ”.

As described above, ε-Ga ₂ O ₃ has ferroelectric properties, has a crystal structure that generates spontaneous polarization, and has the advantage of being able to control the bandgap by forming a mixed crystal. It is expected to be applied to high electron mobility transistors (HEMTs) in the near future. However, there is a problem that impurities may be contained in the film, which causes variations in various characteristics of the semiconductor film. Thus, conventionally, it has been difficult to obtain an ε-Ga ₂ O ₃ -based semiconductor film containing few impurities. In this respect, according to the semiconductor film of the present invention, the impurity concentration of the ε-Ga ₂ O ₃ based semiconductor film can be reduced by increasing the crystallinity of the film, so the above-described problems can be conveniently solved.

This semiconductor film is measured at the central point X of the maximum circle (hereinafter referred to as the maximum inscribed circle) inscribed in the outer periphery of the semiconductor film on the film surface and at each of the four outer peripheral points A, B, C and D. The half width of the peak near 250 cm ⁻¹ in the Raman spectrum of the semiconductor film measured by spectroscopy is preferably 10 cm ⁻¹ or less. At this time, perimeter points A, B, C and D are such that: i) a straight line connecting perimeter points A and C and a straight line connecting perimeter points B and D intersect at right angles at center point X, and ii) Each shortest distance from the outer edge of the semiconductor film to the perimeter points A, B, C and D is determined to be 1/5 of the radius of the semiconductor film. Also, the semiconductor film is preferably circular, in which case the maximum inscribed circle of the semiconductor film 10 can coincide with the outer periphery, as shown in FIG. The ε-Ga ₂ O ₃ -based semiconductor film, in which the half width of the peak near 250 cm ⁻¹ in the Raman spectrum is 10 cm ⁻¹ or less at five points sufficiently separated from each other, extends from the center to the outer periphery of the film. It can be said that the half-value width is small over a wide range of up to, and such a semiconductor film has high crystallinity and low impurity concentration.

In the semiconductor film of the present invention, the half width of the peak near 250 cm ⁻¹ in Raman spectrum is 10 cm ⁻¹ or less, preferably 8.0 cm ⁻¹ or less, more preferably 7.0 cm ⁻¹ or less. From the viewpoint of reducing the impurity concentration, the smaller the half-width of the peak near 250 cm ^-1 in the Raman spectrum, the better. Therefore, the lower limit of the half-width of the peak near 250 cm ^-1 in the Raman spectrum is not particularly limited. It is typically 0.1 cm ⁻¹ or more, more typically 1.0 cm ⁻¹ or more.

The semiconductor film of the present invention has a peak intensity I ₂₅₀ near 250 cm ⁻¹ in the Raman spectrum (preferably at the center point X of the largest inscribed circle and at each of the outer peripheral points A, B, C and D) at 260 cm ^{−1 .} The peak intensity ratio I ₂₅₀ /I ₂₆₀ to the peak intensity I ₂₆₀ near ¹ is preferably 2.0 or more, more preferably 5.0 or more, and still more preferably 8.0 or more. The upper limit of I ₂₅₀ /I ₂₆₀ is preferably 50 or less, although the upper limit is not particularly limited because the higher the better. Here, “ ^around 260 cm ⁻¹ ” typically means a wavenumber obtained by adding 10 cm ⁻¹ to the peak wavenumber around 250 cm −1 . For example, when the peak top of the peak around 250 cm ⁻¹ is 245 cm ⁻¹ , the peak “around 260 cm ⁻¹ ” means the peak at 255 cm ⁻¹ .

In the semiconductor film of the present invention, the half width of the peak near 113 cm ^-1 in the Raman spectrum (preferably at the center point X of the maximum inscribed circle and each of the outer peripheral points A, B, C and D) is 10 cm ^-1 or less. is preferably 8.0 cm ^-1 or less, and even more preferably 6.0 cm ^-1 or less. From the viewpoint of reducing the impurity concentration, the smaller the half width of the peak near 113 cm ^-1 in the Raman spectrum, the better. Therefore, the lower limit of the half width of the peak near 113 cm ^-1 in the Raman spectrum is not particularly limited, It is typically 0.1 cm ⁻¹ or more, more typically 1.0 cm ⁻¹ or more.

As described above, especially when the semiconductor film contains transition metal elements such as Fe and Ti, alkali metals such as Na, and halogen elements such as F, variations in various characteristics of the semiconductor film tend to occur. In this respect, since the semiconductor film of the present invention has high crystallinity, impurities that can be contained can be reduced. That is, the Ti concentration on the surface of the semiconductor film is preferably 1.0×10 ¹⁵ atoms/cm ³ or less, more preferably 1.0×10 ¹⁴ atoms/cm ³ or less, further preferably 1.0×10 14 atoms/cm 3 or less. ¹³ atoms/cm ³ or less. The Fe concentration on the surface of the semiconductor film is preferably 1.0×10 ¹⁵ atoms/cm ³ or less, more preferably 1.0×10 ¹⁴ atoms/cm ³ or less, and still more preferably 1.0×10 ¹³ atoms/cm 3 . / cm ³ or less. The Na concentration on the surface of the semiconductor film is preferably 2.0×10 ¹³ atoms/cm ³ or less, more preferably 1.0×10 ¹² atoms/cm ³ or less, still more preferably 1.0×10 ¹¹ atoms/cm 3 . / cm ³ or less. The F concentration on the surface of the semiconductor film is preferably 2.0×10 ¹⁵ atoms/cm ³ or less, more preferably 1.0×10 ¹⁴ atoms/cm ³ or less, and still more preferably 1.0×10 ¹³ atoms/cm 3 . / cm ³ or less. Similarly, the Si concentration on the surface of the semiconductor film is preferably 1.0×10 ¹⁶ atoms/cm ³ or less, more preferably 1.0×10 ¹⁵ atoms/cm ³ or less, and still more preferably 1.0×10 15 atoms/cm 3 or less. It is 10 ¹⁴ atoms/cm ³ or less. Since the lower the concentration of each element of Ti, Fe, Na, F, and Si in the surface of the semiconductor film, the better, the lower limit is not particularly limited.

However, Si may also be used as a dopant for a semiconductor film, and in that case, the Si concentration on the surface of the semiconductor film may exceed the upper limit of the preferred range, for example, 1.0×10 ¹⁵ to 1.0×10 15 . It can be 10 ²¹ atoms/cm ³ .

As described above, the semiconductor film of the present invention has a main phase of crystals composed of ε-Ga ₂ O ₃ or ε-Ga ₂ O ₃ solid solution. In the present specification, "having a crystal composed of an ε-Ga ₂ O ₃ or ε-Ga ₂ O ₃ system solid solution as a main phase" means ε-Ga ₂ O ₃ or ε-Ga ₂ O ₃ system Crystals composed of a solid solution account for 80% by weight or more, preferably 90% by weight or more, more preferably 95% by weight or more, still more preferably 97% by weight or more, particularly preferably 99% by weight or more, and most preferably 100% by weight of the semiconductor film. % by weight. The ε-Ga ₂ O ₃ solid solution is a solid solution of ε-Ga ₂ O ₃ with other components. For example, the semiconductor film of the present invention contains ε-Ga ₂ O ₃ , Cr ₂ O ₃ , Fe ₂ O ₃ , Ti ₂ O ₃ , V ₂ O ₃ , Ir ₂ O ₃ , Rh ₂ O ₃ , In ₂ O ₃ _and Al ₂ O ₃ _. In addition, it is possible to control the bandgap, electrical properties, and/or lattice constant of the semiconductor film by dissolving these components. The solid solution amount of these components can be appropriately changed according to the desired properties. In addition, the ε-Ga ₂ O ₃ -based solid solution may contain, as other components, elements such as Si, Sn, Ge, N and Mg as dopants.

_By the way, the crystal structure of ε-Ga ₂ O ₃ has not been sufficiently elucidated at the current state of _the art _. ₃ , or what is identified as ε-Ga ₂ O ₃ may also be identified as κ-Ga ₂ O ₃ . For example, Non-Patent Document 3 (Ildiko Cora et al., "The real structure of ε-Ga ₂ O ₃ and its relation to κ-phase," CrystEngComm, 2017, 19, 1509-1516) describes the resolution of probe technology Some have suggested that the crystal structure of ε-Ga ₂ O ₃ (hexagonal) and the crystal structure of κ-Ga ₂ O ₃ (rectangular) may be confused. Therefore, the term “ε-Ga ₂ O ₃ ” herein refers not only to ε-Ga ₂ O ₃ but also to κ-Ga ₂ O ₃ . That is, in the present specification, even those identified as having the crystal structure of κ-Ga ₂ O ₃ are regarded as “ε-Ga ₂ O ₃ ”, and are referred to as “ε-Ga ₂ O ₃ ”. shall be included in the term.

The orientation of the ε-Ga ₂ O ₃ -based semiconductor film of the present invention in the substantially normal direction is not particularly limited, but c-axis orientation is preferred. However, a typical ε-Ga ₂ O ₃ -based semiconductor film is composed of ε-Ga ₂ O ₃ or a mixed crystal of ε-Ga ₂ O ₃ and a different material, and has It is oriented. The ε-Ga ₂ O ₃ -based semiconductor film may be a mosaic crystal as long as it is biaxially oriented. Mosaic crystals are aggregates of crystals that do not have distinct grain boundaries but have slightly different crystal orientations in one or both of the c-axis and a-axis. A method for evaluating the biaxial orientation is not particularly limited, and known analysis techniques such as an EBSD (Electron Back Scatter Diffraction Patterns) method and an X-ray pole figure can be used. For example, when using the EBSD method, inverse pole figure mapping of the surface (film surface) of the biaxially oriented ε-Ga ₂ O ₃ film or a cross section perpendicular to the film surface is measured. In the obtained inverse pole figure mapping, (A) it is oriented in a specific direction in the approximate normal direction of the film surface, and (B) the approximate normal direction is in the approximate in-plane direction perpendicular to the normal direction. It can be defined that the film is oriented along two axes, ie, the approximate normal direction and the approximate film surface direction, when the two conditions are satisfied. In other words, when the above two conditions are satisfied, it is determined that the crystal is oriented along two axes, the c-axis and the a-axis. For example, when the substantially normal direction of the film surface is aligned with the c-axis, the substantially in-plane direction of the film may be aligned with a specific direction (for example, the a-axis) perpendicular to the c-axis.

The semiconductor film of the present invention may have a size such that the diameter of the largest circle inscribed in its outer periphery (i.e., the largest inscribed circle) is 5.08 cm (2 inches) or more, and the diameter of the largest inscribed circle may be 10.0 cm or more. Although the upper limit of the diameter of the maximum inscribed circle is not particularly limited, it is typically 30.0 cm or less, more typically 20.0 cm or less. A typical semiconductor film is circular in shape, in which case the diameter of the largest inscribed circle of semiconductor film 10 may match the diameter of semiconductor film 10, as shown in FIG. In this specification, the “circular shape” does not have to be a perfect circular shape, and may be a substantially circular shape that can be recognized as a generally circular shape as a whole. For example, it may be a shape in which a part of the circle is notched for specifying the crystal orientation or for other purposes, or a shape in which a part of the circle is provided with a slit. The size can be determined based on the diameter of the maximum circle inscribed in the outer periphery excluding the slits. By the way, the semiconductor film of the present invention is characterized in that the half width of the peak near 250 cm ⁻¹ in the Raman spectrum is as small as 10 cm ⁻¹ or less. , is merely defined for convenience as an example so that the representative peak half-value width of the entire semiconductor film can be evaluated. Therefore, in order to uniquely determine the positions of the central point X and the peripheral points A, B, C and D, the shape of the semiconductor film is preferably circular. meaning does not change. For example, even if the shape of the semiconductor film is square or rectangular (rectangular), it is included in the semiconductor film of the present invention as long as the half width of the peak near 250 cm ⁻¹ of the semiconductor film is small. In such a semiconductor film, the maximum circle (maximum inscribed circle) inscribed in the outer periphery of the square or rectangular semiconductor film when viewed from above is defined as a virtual circle, and the center point of the virtual circle is defined as The positions of the outer peripheral points A, B, C and D can be determined from X and the diameter of the virtual circle (similarly to the circular semiconductor film described above). By evaluating the half-value widths of the peaks near 250 cm ⁻¹ at the center point X and the peripheral points A, B, C, and D determined in this manner, the same evaluation as that for a circular semiconductor film can be performed. Note that even if a slit is provided in a part of a square or rectangular semiconductor film, the maximum circle (maximum inscribed circle) that inscribes the outer edge of the square or rectangular semiconductor film when viewed from above is assumed. There is no change in defining as a circle.

The semiconductor film of the present invention can contain a Group 14 element as a dopant. Here, the group 14 element is a group 14 element according to the periodic table formulated by IUPAC (International Union of Pure and Applied Chemistry), specifically carbon (C), silicon (Si), germanium (Ge ), tin (Sn), and lead (Pb). As dopants (group 14 elements) in the semiconductor film, the total content of C, Ge, Sn, and Pb is preferably 1.0×10 ¹⁵ to 1.0×10 ²¹ /cm ³ , more preferably 1.0. ×10 ¹⁷ to 1.0×10 ¹⁹ /cm ³ . It is preferable that these dopants are homogeneously distributed in the film and that the dopant concentrations on the front surface and the back surface of the semiconductor film are approximately the same.

The thickness of the semiconductor film of the present invention may be appropriately adjusted from the viewpoint of cost and required characteristics. That is, if the thickness is too large, it takes a long time to form a film, so from the viewpoint of cost, it is preferable that the thickness is not extremely thick. On the other hand, in order to improve the crystal quality, it is preferable to make the film thick to some extent. In this manner, the film thickness may be appropriately adjusted according to desired characteristics.

The semiconductor film of the present invention may be in the form of a self-supporting film. Alternatively, the semiconductor film formed over the base substrate for film formation may be separated and transferred to another supporting substrate. The material of the other support substrate is not particularly limited, but a suitable material may be selected from the viewpoint of material properties. For example, from the viewpoint of thermal conductivity, metal substrates such as Cu, ceramic substrates such as SiC and AlN, and the like are preferable. It is also preferable to use a substrate having a coefficient of thermal expansion of 6 to 13 ppm/K at 25 to 400.degree. By using a supporting substrate having such a coefficient of thermal expansion, it is possible to reduce the difference in thermal expansion from the semiconductor film, and as a result, it is possible to suppress the occurrence of cracks in the semiconductor film and film peeling due to thermal stress. An example of such a support substrate is a substrate composed of a Cu—Mo composite metal. The composite ratio of Cu and Mo can be appropriately selected in consideration of thermal expansion coefficient matching with the semiconductor film, thermal conductivity, electrical conductivity, and the like.

Manufacturing Method of Semiconductor Film The semiconductor film of the present invention can be preferably manufactured by using a GaN single crystal substrate as a base substrate and forming a film of an ε-Ga ₂ O ₃ based material thereon. A method for forming the semiconductor layer can be a known method, and preferred examples include the mist CVD method (mist chemical vapor deposition method), the HVPE method (halide vapor phase epitaxy method), and the MBE method (molecular beam epitaxy method). , MOCVD (metal organic chemical vapor deposition), and hydrothermal synthesis, and mist CVD or HVPE is particularly preferred. In vapor phase growth methods such as mist CVD and HVPE, the thickness of the underlying substrate is desirably thick from the viewpoint of suppressing warpage, preferably 0.5 mm or more, more preferably 0.8 mm or more, and even more preferably. is 1.4 mm or more. On the other hand, the thickness is desirably thinner from the viewpoint of cost, preferably 1.0 mm or less, more preferably 0.5 mm or less. In this manner, the film thickness of the base substrate may be appropriately adjusted according to the desired characteristics. Although the upper limit of the thickness of the underlying substrate is not particularly limited, it is typically 5.0 mm or less, more typically 4.0 mm or less. In addition, the ε-Ga ₂ O ₃ -based semiconductor film, in which the half width of the peak near 250 cm ⁻¹ is as small as 10 cm ⁻¹ or less over a wide range from the center to the outer periphery of the film, is formed while rotating the underlying substrate. can be preferably realized by performing

The HVPE method and the mist CVD method, which are particularly preferable film forming methods, will be described below.

The HVPE method (halide vapor phase epitaxy) is a kind of CVD, and is a method applicable to film formation of compound semiconductors such as Ga ₂ O ₃ and GaN. In this method, a Ga raw material and a halide are reacted to generate a gallium halide gas, which is supplied onto a base substrate for film formation. At the same time, O ₂ gas is supplied onto the underlying substrate for film formation, and the gallium halide gas reacts with the O ₂ gas to grow Ga ₂ O ₃ on the underlying substrate for film formation. It is a method that enables high-speed and thick film growth and has a proven track record in industry. Examples of film formation of not only ε-Ga ₂ O ₃ but also α-Ga ₂ O ₃ and β-Ga ₂ O ₃ have been reported. It is

FIG. 2 shows an example of a vapor phase growth apparatus (HVPE apparatus) using the HVPE method. The HVPE apparatus 20 includes a reactor 22, a susceptor 26 on which a base substrate 24 for film formation is placed, an oxygen raw material supply source 30, a carrier gas supply source 28, a GeCl ₄ supply source 32, and a Ga raw material supply source 34. , a heater 36 and a gas discharge section 38 . Any reactor that does not react with the raw material is applied to the reactor 22, and is, for example, a quartz tube. Any heater capable of heating up to at least 700° C. (preferably 900° C. or higher) is applied as the heater 36, and is, for example, a resistance heating type heater.

Metal Ga is placed inside the Ga raw material supply source 34, and halogen gas or hydrogen halide gas such as HCl is supplied. The halogen gas or halogenated gas is preferably _Cl2 or HCl. The supplied halogen gas or halogenated gas reacts with metal Ga to generate gallium halide gas, which is supplied to the base substrate 24 for film formation. The gallium halide gas preferably contains GaCl and/or _GaCl3 . Oxygen source supply 30 can supply an oxygen source selected from the group consisting of _O2 , _H2O and _N2O , with _O2 being preferred. These oxygen source gases are supplied to the base substrate at the same time as the gallium halide gas. A GeCl ₄ source 32 supplies GeCl ₄ vapor generated by bubbling the GeCl ₄ liquid into the reactor 22 . Note that the Ga source gas and the oxygen source gas may be supplied together with a carrier gas such as _N2 or a rare gas.

The gas discharge section 38 may be connected to a vacuum pump such as a diffusion pump or a rotary pump, for example, not only for discharging unreacted gas in the reactor 22 but also for controlling the pressure in the reactor 22. good. This can improve the suppression of gas phase reactions and the growth rate distribution.

ε-Ga ₂ O ₃ is formed on the film formation base substrate 24 by heating the film formation base substrate 24 to a predetermined temperature using the heater 36 and simultaneously supplying the gallium halide gas and the oxygen source gas. be done. The film formation temperature is not particularly limited as long as ε-Ga ₂ O ₃ is formed and impurities in the film are reduced, but is typically 250° C. to 900° C., for example. The partial pressures of the Ga raw material gas and the oxygen raw material gas are also not particularly limited. For example, the partial pressure of the Ga source gas (gallium halide gas) may be in the range of 0.05 kPa to 10 kPa, and the partial pressure of the oxygen source gas may be in the range of 0.25 kPa to 50 kPa.

When depositing an ε-Ga ₂ O ₃ -based semiconductor film containing a group 14 element as a dopant, or when depositing a mixed crystal film with ε-Ga ₂ O ₃ containing oxides of In or Al, etc. Alternatively, a separate supply source (for example, the GeCl ₄ supply source 32 in FIG. 2) may be provided to supply the halides or the like, or the halides may be mixed and supplied from the Ga source supply source 34 . Alternatively, a material containing a Group 14 element, In, Al, or the like may be placed in the same location as the metal Ga, reacted with a halogen gas or a hydrogen halide gas, and supplied as a halide. These halide gases supplied to the base substrate 24 for film formation react with the oxygen source gas, like gallium halide, to form oxides, which are incorporated into the ε-Ga ₂ O ₃ based semiconductor film.

In the mist CVD method, a raw material solution is atomized or dropletized to generate mist or droplets, the mist or droplets are transported to a film formation chamber equipped with a substrate using a carrier gas, and the mist or droplets are generated in the film formation chamber. It is a method of thermally decomposing and chemically reacting droplets to form and grow a film on a substrate. It does not require a vacuum process and can produce a large amount of samples in a short time. FIG. 3 shows an example of a mist CVD apparatus. The mist CVD apparatus 40 shown in FIG. 3 includes a mist generating chamber 42 for generating mist M from carrier gas G and raw material solution L, and mist M being sprayed onto substrate 56 to form semiconductor film 58 through thermal decomposition and chemical reaction. A film forming chamber 50 is provided. The mist generating chamber 42 includes a carrier gas inlet 44 through which carrier gas G is introduced, an ultrasonic vibrator 46 provided in the mist generating chamber 42, and a film forming chamber 50 through which the mist M generated in the mist generating chamber 42 is introduced. and a duct 48 for conveying to. A raw material solution L is accommodated in the mist generating chamber 42 . The ultrasonic vibrator 46 is configured to apply ultrasonic vibrations to the raw material solution L to generate the mist M together with the carrier gas G. As shown in FIG. The film forming chamber 50 includes a nozzle 52 for blowing the mist M introduced through the duct 48 onto the substrate 56, a stage 54 to which the substrate 56 is fixed, and the stage 54 and the substrate provided near the rear surface of the stage 54. A heater 62 for heating 56 and an exhaust port 64 for discharging the carrier gas G are provided.

The raw material solution L used in the mist CVD method is not limited as long as it is a solution from which an ε-Ga ₂ O ₃ based semiconductor film can be obtained. Examples include those obtained by dissolving an organic metal complex or a halide in a solvent. Examples of organometallic complexes include acetylacetonate complexes. Moreover, when a dopant is added to the semiconductor layer, a dopant component solution may be added to the raw material solution. Furthermore, an additive such as hydrochloric acid may be added to the raw material solution. Water, alcohol, or the like can be used as the solvent.

Next, the obtained raw material solution L is atomized or dropletized to generate a mist M or droplets. A preferred example of a method of atomizing or forming droplets is a method of vibrating the raw material solution L using an ultrasonic oscillator 46 . After that, the obtained mist M or droplets are transported to the film forming chamber 50 using the carrier gas G. FIG. The carrier gas G is not particularly limited, but one or more of oxygen, ozone, inert gas such as nitrogen, and reducing gas such as hydrogen can be used.

A substrate 56 is provided in the deposition chamber 50 . The mist M or droplets transported to the film forming chamber 50 are thermally decomposed and chemically reacted there to form a semiconductor film 58 on the substrate 56 . Although the reaction temperature varies depending on the type of raw material solution L, it is preferably 300 to 800°C, more preferably 400 to 700°C. The atmosphere in the film forming chamber 50 is not particularly limited as long as a desired semiconductor film can be obtained. is selected from either

The semiconductor film thus obtained can be used as it is or divided into semiconductor elements. Alternatively, the semiconductor film may be peeled off from the underlying substrate to form a single film. In this case, in order to facilitate peeling from the underlying substrate, a peeling layer may be provided in advance on the surface (film formation surface) of the underlying substrate. Examples of such a peeling layer include those in which a C-implanted layer or an H-implanted layer is provided on the surface of the underlying substrate. Alternatively, C or H may be injected into the film at the initial stage of film formation of the semiconductor film, and a peeling layer may be provided on the semiconductor film side. Further, a supporting substrate (mounting substrate) different from the underlying substrate is adhered and bonded to the surface of the semiconductor film formed on the underlying substrate (that is, the surface opposite to the underlying substrate), and then the semiconductor film is separated from the underlying substrate. can be peeled off. As such a support substrate (mounting substrate), a substrate having a coefficient of thermal expansion of 6 to 13 ppm/K at 25 to 400° C., for example, a substrate composed of a Cu—Mo composite metal can be used. Examples of methods for bonding and bonding the semiconductor film and the support substrate (mounting substrate) include known methods such as brazing, soldering, and solid phase bonding. Furthermore, an ohmic electrode, an electrode such as a Schottky electrode, or another layer such as an adhesive layer may be provided between the semiconductor film and the support substrate.

In the manufacture of semiconductor elements such as power devices, functional layers such as drift layers are formed on semiconductor films. For the formation of a functional layer such as a drift layer, known methods are possible, and preferred examples include mist CVD, HVPE, MBE, MOCVD, and hydrothermal synthesis. HVPE methods are particularly preferred.

Composite Substrate The semiconductor film of the present invention can be produced by preferably using a GaN single crystal substrate as a base substrate and forming a film of an ε-Ga ₂ O ₃ based material thereon. That is, according to the present invention, there is provided a composite substrate comprising a GaN single crystal substrate and the above-described semiconductor film formed on the GaN single crystal substrate.

The present invention will be explained more specifically by the following examples.

Example 1
(1) Fabrication of ε-Ga ₂ O ₃ -based semiconductor film by mist CVD method (1a) Preparation of base substrate A c-plane GaN single crystal having a thickness of about 0.4 mm and a diameter of 5.08 cm (2 inches) was used as the base substrate. Prepared the substrate.

(1b) Preparation of Raw Material Solution Metal Ga was added to hydrochloric acid and the mixture was stirred at room temperature for 3 weeks to obtain a gallium chloride solution with a gallium ion concentration of 3 mol/L. Water was added to the resulting gallium chloride solution to prepare an aqueous solution having a gallium ion concentration of 55 mmol/L. Ammonium hydroxide was added to this aqueous solution to adjust the pH to 4.0 to obtain a raw material solution.

(1c) Film formation preparation A mist CVD apparatus 40 having the configuration shown in FIG. 3 was prepared. The configuration of the mist CVD apparatus 40 is as described above. In the mist CVD apparatus 40, the raw material solution L obtained in (1b) above was accommodated in the mist generating chamber . A c-plane GaN substrate having a diameter of 5.08 cm (2 inches) was set on the stage 54 as the substrate 56, and the distance between the tip of the nozzle 52 and the substrate 56 was set to 120 mm. The temperature of the stage 54 was raised to 520° C. by the heater 62 and held for 30 minutes for temperature stabilization. A flow control valve (not shown) was opened to supply nitrogen gas as the carrier gas G into the film forming chamber 50 through the mist generating chamber 42, and the atmosphere in the film forming chamber 50 was sufficiently replaced with the carrier gas G. After that, the flow rate of carrier gas G was adjusted to 1.7 L/min.

(1d) Film Formation The raw material solution L was atomized by the ultrasonic vibrator 46, and the generated mist M was introduced into the film formation chamber 50 by the carrier gas G. As shown in FIG. A semiconductor film 58 was formed on the substrate 56 for 60 minutes by allowing the mist M to react in the deposition chamber 50, particularly on the surface of the substrate 56 (specifically, the GaN substrate). Table 1 shows the base substrate and film formation conditions.

(2) Evaluation of semiconductor film (2a) Surface EDX
As a result of EDX measurement of the obtained film surface, only Ga and O were detected, and it was found that the obtained film was Ga oxide.

(2b) Surface EBSD
An inverse pole figure orientation mapping of the Ga oxide film surface was performed using an SEM (SU-5000, manufactured by Hitachi High-Technologies Corporation) equipped with an electron beam backscatter diffraction device (EBSD) (Nordlys Nano, manufactured by Oxford Instruments). It was performed with a field of view of 25 μm×20 μm. Using the software (Twist) attached to the device, non-patent document 4 (F. Mezzadri, et al., "Crystal Structure and Ferroelectric Properties of ε-Ga ₂ O ₃ Films Grown on (0001)-Sapphire," Inorg Chem. 2016, 55, 12079-12084), the space group of ε-Ga ₂ O ₃ (hexagonal crystal), unit cell parameters (sides and angles), and crystal information on atomic positions are registered in a database and used. EBSD measurement was performed using

The conditions for this EBSD measurement were as follows.
<EBSD measurement conditions>
・Acceleration voltage: 15 kV
・Spot intensity: 70
・Working distance: 22.5mm
・Step size: 0.5 μm
・Sample tilt angle: 70°
・Measurement program: Aztec (version 3.3)

From the obtained inverse pole figure orientation mapping, it was found that the Ga oxide film had a biaxially oriented crystal structure in which the c-axis was oriented in the substrate normal direction and the in-plane orientation was also oriented. From these results, it was confirmed that the obtained semiconductor film was an oriented film with a crystal structure composed of ε-Ga ₂ O ₃ .

(2c) Raman spectrum The Raman spectrum at the center point X of the film surface of the semiconductor film 58 and the outer peripheral points A, B, C and D was measured using a laser Raman spectrometer LabRAM ARAMIS manufactured by Horiba, Ltd., using operation software LabSpec (Ver. 5.78). The optical system was a Zernite-Turner type spectroscopic system of a backscattering system, and a semiconductor-pumped solid-state laser (DPSS, 532 nm) was used as a light source. A Si wafer was used for calibration before the sample measurement. The measurement of the Raman spectrum for the semiconductor film 58 was carried out by adjusting the laser output to 24 mW, the hole (confocal hole diameter) to 400 μm, the center wave number of the spectrometer to 520 cm ⁻¹ , the slit to 100 μm, the grating to 1800 gr/mm, and the objective lens to Magnified by 100x and run in point analysis mode. The exposure time was 60 seconds, the number of times of accumulation was 2, and the wavenumber range was 100 to 900 cm ⁻¹ . The neutral density filter was appropriately set so that the count of the strongest peak was 3000 or more and 50000 or less. In addition, the Ne lamp was used during the measurement, and the obtained spectrum was corrected so that the wave number of the peak top of the peak caused by the Ne lamp emission line was 278.28 cm ⁻¹ . Baseline correction is performed by setting “Type” to “Lines”, “Degree” to “5”, “Attach” to “No”, “Style” to “-”, and selecting “Auto ' and went. The spectrum thus obtained is shown in FIG. For the obtained spectrum, the wavenumbers of the peak tops of the peaks near 250 cm ⁻¹ at the central point X and the peripheral points A, B, C and D are N _X , N _A , N _B , N _C and N _D , And the peak top wavenumbers of the peaks near 113 cm ⁻¹ were defined as N _X , N _A , N _B , N _C and N _D . Further, the half widths at wavenumbers _NX , _NA , _NB , _NC and _ND were defined as _WX , _WA , _WB , _WC and _WD . Furthermore, the peak intensity I 250 at the center point X and the ^peripheral points A, B, C and D with peak tops near ₂₅₀ cm ⁻¹ to the peak intensity I ₂₆₀ at 260 cm −1 The peak intensity ratio I ₂₅₀ /I ₂₆₀ was determined. In this example, for example, the wavenumber N _X at the peak top of the peak near 250 cm ⁻¹ is 251.1 cm ⁻¹ , and the half width W _X for this peak is calculated to be 8.8 cm ⁻¹ , which is crystalline. It was found to be high ε-Ga ₂ O ₃ . The results were as shown in Table 2.

(2d) Concentration of Each Element A secondary ion mass spectrometer (SIMS) was used to analyze the composition of the ε-Ga ₂ O ₃ film surface, and the concentrations of Fe, Ti, Na, F and Si were measured. The conditions for this D-SIMS analysis were as follows. The results were as shown in Table 2.

<D-SIMS analysis conditions (when detecting Fe, Ti and Na)>
・ Attention elements: Fe, Ti, Na
・Equipment: IMS-7f manufactured by CAMECA
・Primary ion species: O2 ²⁺
・Primary ion acceleration energy: 8 keV
・Secondary ion polarity: Positive
・Detection area: diameter 30 μm

<D-SIMS analysis conditions (when detecting F and Si)>
・ Attention elements: F, Si
・Equipment: IMS-7f manufactured by CAMECA
・Primary ion species: Cs ⁺
・Primary ion acceleration energy: 15.0 keV
・Secondary ion polarity: Negative
・Detection area: diameter 30 μm

Example 2
In the above (1c) and (1d), when forming a film by the mist CVD method, the temperature of the stage 54 is stabilized at 500° C. before film formation is started, and the temperature is raised to 520° C. over 20 minutes. A semiconductor film was prepared and various evaluations were performed in the same manner as in Example 1, except that the film was made to have the same thickness. The peak top wavenumber N _X of the peak near 250 cm ⁻¹ is 246.8 cm ⁻¹ , and the half width W _X for this peak was calculated to be 6.7 cm ⁻¹ . From this, it was found that the peak near 250 cm ^-1 was a sharp peak. Also, this semiconductor film had a low impurity concentration. The results were as shown in Tables 1 and 2.

Example 3
Various evaluations were performed in the same manner as in Example 1, except that the ε-Ga ₂ O ₃ -based semiconductor film was produced by the HVPE method described below instead of the mist CVD method (above (1)). The peak top wavenumber N _X of the peak near 250 cm ⁻¹ is 248.3 cm ⁻¹ , and the half width W _X for this peak was calculated to be 7.0 cm ⁻¹ . From this, it was found that the peak near 250 cm ^-1 was a sharp peak. Also, this semiconductor film had a low impurity concentration. The results were as shown in Tables 1 and 2.

(1′) Preparation of ε-Ga ₂ O ₃ -based semiconductor film by HVPE method (1a′) Preparation of base substrate A crystal substrate was prepared.

(1b') Film Formation An HVPE apparatus 20 having the configuration shown in FIG. 2 was prepared. The configuration of the HVPE device 20 is as described above. Metallic Ga was placed in reactor 22 and hydrogen chloride gas (HCl) was supplied. Metal Ga and hydrogen chloride were thereby reacted to produce a Ga halide, which was supplied to the base substrate 24 for film formation. At the same time, O ₂ gas as an oxygen source and N ₂ gas as a carrier gas were introduced into the reactor 22 . In this manner, film formation by the HVPE method was performed at a growth temperature of 550° C. for 15 minutes to obtain the base substrate 24 for film formation and the semiconductor film formed thereon as a composite material.

Example 4
In the above (1b') in the HVPE method, the film formation was started after the growth temperature was stabilized at 550 ° C., and the temperature was raised to 580 ° C. over 30 minutes. A semiconductor film was produced and various evaluations were performed. The peak top wave number N _X of the peak near 250 cm ⁻¹ is 254.9 cm ⁻¹ , and the half width W _X for this peak was calculated to be 5.9 cm ⁻¹ . From this, it was found that the peak near 250 cm ^-1 was a sharp peak. Also, this semiconductor film had a low impurity concentration. The results were as shown in Tables 1 and 2.

Example 5 (Comparison)
In the above (1c) and (1d) in the mist CVD method, except that the temperature of the stage 54 was stabilized at 500° C. during film formation, the semiconductor film was produced and various evaluations were performed in the same manner as in Example 1. gone. The peak top wavenumber N _X of the peak near 250 cm ⁻¹ is 251.9 cm ⁻¹ , and the half width W _X for this peak was calculated to be 16.5 cm ⁻¹ . From this, it was found that the peak near 250 cm ⁻¹ was a broad peak. In addition, this semiconductor film had a high impurity concentration. The results were as shown in Tables 1 and 2.

Example 6 (Comparison)
A semiconductor film was prepared and various evaluations were performed in the same manner as in Example 3, except that the growth temperature was stabilized at 500° C. in (1b′) above in the HVPE method. The peak top wavenumber N _X of the peak near 250 cm ⁻¹ is 251.7 cm ⁻¹ , and the half width W _X for this peak was calculated to be 14.3 cm ⁻¹ . From this, it was found that the peak near 250 cm ⁻¹ was a broad peak. In addition, this semiconductor film had a high impurity concentration. The results were as shown in Tables 1 and 2.

Claims

A semiconductor film whose main phase is a crystal composed of ε-Ga 2 O 3 or an ε-Ga 2 O 3 -based solid solution,
A semiconductor film, wherein the half width of the peak near 250 cm −1 in the Raman spectrum of the semiconductor film measured by laser Raman spectroscopy is 10 cm −1 or less.
The semiconductor film measured by laser Raman spectroscopy at the center point X of the largest circle inscribed in the outer periphery of the semiconductor film and each of the four outer peripheral points A, B, C and D on the surface of the semiconductor film. The half width of the peak near 250 cm -1 in the Raman spectrum of is 10 cm -1 or less,
i) a straight line connecting the outer peripheral points A and C and a straight line connecting the outer peripheral points B and D intersect at right angles at the center point X; and ii) each shortest distance of said perimeter points A, B, C and D from the outer edge of said semiconductor film is determined to be 1/5 of the radius of said semiconductor film. film.
The peak intensity ratio I 250 / I 260 of the peak intensity I 250 near 250 cm −1 to the peak intensity I 260 near 260 cm −1 in the Raman spectrum of the semiconductor film is 2.0 or more. 3. The semiconductor film according to 1 or 2.
3. The semiconductor film according to claim 1, wherein the half width of the peak near 113 cm −1 in the Raman spectrum of said semiconductor film is 10 cm −1 or less.
3. The semiconductor film according to claim 1, wherein the surface Ti concentration of said semiconductor film is 1.0×10 15 atoms/cm 3 or less.
3. The semiconductor film according to claim 1, wherein the surface Fe concentration of said semiconductor film is 1.0×10 15 atoms/cm 3 or less.
3. The semiconductor film according to claim 1, wherein the surface Na concentration of said semiconductor film is 2.0×10 13 atoms/cm 3 or less.
3. The semiconductor film according to claim 1, wherein the surface F concentration of said semiconductor film is 2.0×10 15 atoms/cm 3 or less.
3. The semiconductor film according to claim 1, wherein the surface Si concentration of said semiconductor film is 1.0×10 16 atoms/cm 3 or less.
A composite substrate comprising a GaN single crystal substrate and the semiconductor film according to claim 1 or 2 formed on the GaN single crystal substrate.