JP2016154228A - Substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a substrate excellent in electric characteristics, and having high heat conductivity.SOLUTION: The substrate is formed by laminating a base body having heat conductivity at temperature 300 K of higher than or equal to 30 W/m, and an oxide film having heat conductivity at temperature 300 K of lower than 100 W/m. The heat conductivity of the base body is higher than the heat conductivity of the oxide film.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a substrate used for manufacturing a semiconductor element, for example.

Currently, power devices, which are one of the semiconductor elements, have higher performance such as reduction of power consumption for switching operation and reduction of power loss due to heat generation for further energy saving of industrial equipment and consumer equipment. Is desired. Silicon is used as the mainstream material for power devices. However, improving the performance of devices using silicon is becoming difficult due to the theoretical limitations in electrical characteristics. Therefore, other wide gap semiconductors are attracting attention.
Examples of the wide gap semiconductor include silicon carbide, gallium nitride, and gallium oxide.

  For example, gallium oxide, which is one of wide-gap semiconductors, has excellent characteristics such as higher reverse breakdown voltage and shorter reverse recovery time than silicon when used as a power device such as a Schottky barrier diode (for example, Patent Document 1). However, in applications where a high breakdown voltage is required, the current is large and the Joule heat generated accordingly is large. Therefore, improvement in thermal conductivity is demanded.

Patent Documents 1 and 2 describe a laminate in which a β-Ga ₂ O ₃ single crystal film is formed on a β-Ga ₂ O ₃ substrate. However, this laminated body has a low thermal conductivity, and heat generated when a large current flows cannot be quickly released, which easily causes characteristic deterioration (Non-patent Document 1).
On the other hand, in order to form a β-Ga ₂ O ₃ single crystal film, the base material must be β-Ga ₂ O ₃ for lattice constant matching, and it is difficult to solve the improvement in thermal conductivity. Met.

JP 2013-102081 A JP 2013-56802 A

Appl. Phys. Lett. 92, 202118 (2008)

  An object of the present invention is to provide a substrate having excellent electrical characteristics and high thermal conductivity.

According to the present invention, the following substrates and the like are provided.
1. A base material having a thermal conductivity of 30 W / mK or more at a temperature of 300 K;
An oxide film having a thermal conductivity of less than 100 W / mK at a temperature of 300 K is laminated,
The board | substrate whose heat conductivity of the said base material is higher than the heat conductivity of the said oxide film.
2. 2. The substrate according to 1, wherein the oxide film has a thickness of 1 nm to 300 μm.
3. The board | substrate of 1 or 2 whose thickness of the said base material is 1 micrometer or more and 5 mm or less.
4). The board | substrate in any one of 1-3 whose thermal conductivity in the temperature of 300K is 30 W / mK or more.
5. The board | substrate in any one of 1-4 whose electric resistivity in the temperature of 300 K of the said base material is 0.05 ohm-cm or less.
6). The substrate according to any one of 1 to 5, wherein the base material includes one or more selected from silicon, silicon carbide, gallium nitride, aluminum nitride, copper, aluminum, molybdenum, titanium, gold, and diamond.
7). The board | substrate in any one of 1-6 whose arithmetic mean roughness of the said base material surface is 50 nm or less.
8). The substrate according to any one of 1 to 7, wherein the oxide film includes at least one of a polycrystalline oxide and an amorphous oxide.
9. The substrate according to any one of 1 to 8, wherein the oxide film contains at least gallium.
10. The atomic composition percentage ([Ga] / [Ga] + ([all metal elements other than Ga]) × 100) of gallium with respect to all metal elements contained in the oxide film is 1 at% or more and 100 at% or less. 9. The substrate according to 9.
11 The oxide film containing gallium further contains one or more metal elements A selected from silicon, germanium, tin, titanium, indium, aluminum, titanium, yttrium, samarium, cerium, and zinc, and in the oxide film The substrate according to 9 or 10, wherein the atomic composition percentage of the metal element A in all the metal elements is 0.01 at% or more and 90 at% or less.
12 12. The substrate according to 11, wherein the metal element A is one or more selected from silicon, germanium, tin, titanium, and zinc.
13. The substrate according to any one of 1 to 12, wherein a carrier concentration of the oxide film at a temperature of 300 K is 1 × 10 ¹⁴ cm ⁻³ or more and 1 × 10 ¹⁷ cm ⁻³ or less.
14 The board | substrate in any one of 1-13 which is a board | substrate for semiconductor elements.
15. A device using the substrate according to any one of 1 to 14.
16. An electric circuit including the element according to 16.15.
An electric device or a vehicle including the element according to 17.15.

  According to the present invention, a substrate having excellent electrical characteristics and high thermal conductivity can be provided. The substrate of the present invention can improve thermal conductivity while maintaining high pressure resistance.

It is a schematic sectional drawing which shows one Embodiment of the board | substrate of this invention. It is a schematic sectional drawing which shows other embodiment of the board | substrate of this invention.

  The substrate of the present invention includes a base material having a thermal conductivity of 30 W / mK or higher at a temperature of 300K and an oxide film having a thermal conductivity of less than 100 W / mK at a temperature of 300K. And the heat conductivity of a base material is higher than the heat conductivity of an oxide film, It is characterized by the above-mentioned. The oxide film may be immediately above the base material, and an intervening layer such as a conductive film may be provided between the base material and the oxide film. The substrate is a laminate of a base material and an oxide film.

One embodiment of the substrate of the present invention is shown in FIG.
The substrate 1 has an oxide film 20 on a base material 10.
The base material used in the present invention has a thermal conductivity of 30 W / mK or more, more preferably 50 W / mK or more, more preferably 100 W / mK or more, and particularly preferably 120 W / mK or more. When a semiconductor element is manufactured using the substrate of the present invention, the semiconductor element generates Joule heat due to a current flowing through the element. In order to quickly dissipate the generated heat, the base material preferably has a thermal conductivity of 30 W / mK or more.

  In this application, the thermal conductivity is the amount of heat that flows per unit time in a unit area of a plate when there is a difference in unit temperature at both ends of the unit thickness plate at 300K. The thermal conductivity is measured by a stationary method such as a protective hot plate method or a concentric cylinder absolute method, or the thermal diffusivity or thermal permeability is obtained by an unsteady method such as a pulse heating method, a periodic heating method or a hot wire method. It can obtain | require by calculating using a specific heat and a density from the value of. Here, the protection hot plate method is a measurement method such as a plate comparison method or a plate comparison method heat flow meter method. The concentric cylinder absolute method is a measuring method such as a concentric cylinder comparison method or a concentric sphere comparison method. The pulse heating method refers to a laser flash method or the like, the periodic heating method refers to a thermoreflectance method, a 2ω method, a 3ω method, a calorimeter method, or the like, and the hot wire method refers to a probe method or the like.

When the thermal permeability is measured, the thermal conductivity λ [W / mK] is the thermal permeability b [J / sec ^0.5 m ² K], the density ρ [kg / m ³ ], the specific heat capacity c [J / kgK] is calculated by the following formula (1).
λ = b ² / ρc (1)
Here, the density means the mass per unit volume of the sample, and can be determined by a specific gravity bottle method, a submerged weighing method, a geometric measurement (a direct measurement of the volume and mass of the sample solid), and the like. The specific heat capacity is the amount of heat required to raise the unit mass of a substance by unit temperature, and can be obtained by a measuring method such as flash method or differential scanning heat (DSC method).

When the thermal diffusivity α is measured, the thermal conductivity λ [W / mK] uses the thermal diffusivity α [m ² / sec], the density ρ [kg / m ³ ], and the specific heat capacity c [J / kgK]. And can be calculated from the following equation (2).
λ = αρc (2)

  In the present application, the thermal conductivity of the oxide film refers to a value obtained by measuring the intersection of each diagonal line on the film surface by a periodic heating thermoreflectance method at room temperature (300 K). In the thermoreflectance method, a thermoreflectance signal of a calibration reference sample is measured at a constant heating modulation frequency, and a calibration equation is created using the thermal permeability and the phase delay of the thermoreflectance signal. Next, the thermal permeability is obtained by substituting the phase lag of the thermoreflectance signal obtained by the measurement of the unknown sample into the calibration equation. The thermal conductivity is obtained from the above equation (1) from the thermal permeability, the density of the sample, and the specific heat capacity.

  Moreover, the heat conductivity of a base material and a board | substrate points out the value measured by the period heating temperature measurement method at room temperature. In the periodic heating temperature measurement method, the sample surface is heated by a periodic heating source, the radiant energy from the back surface is measured, and the thermal diffusivity is obtained. From this thermal diffusivity, the density of the sample, and the specific heat capacity, the thermal conductivity is obtained from the above formula (2).

Examples of the constituent material of the substrate having a thermal conductivity of 30 W / mK or more include silicon, silicon carbide, gallium nitride, aluminum nitride, copper, aluminum, molybdenum, titanium, gold, and diamond. The substrate may be formed of only one of the above materials, or may be formed by combining two or more.
Among the above constituent materials, diamond, silicon, silicon carbide, gallium nitride, aluminum nitride, copper, aluminum, molybdenum, and titanium are preferable because they have a thermal conductivity of 120 W / mK or more.

  In the case of manufacturing a semiconductor element using a substrate, silicon is preferable as the material of the base material from the viewpoint of productivity and cutting workability in the dicing process. In the case of manufacturing a semiconductor element from a substrate, a plurality of semiconductor elements (chips) are manufactured on one substrate and cut into individual chips by a dicing process. At this time, there is an advantage that the manufacturing cost per chip decreases as the number of chips that can be obtained from one substrate increases. Therefore, it is preferable that the substrate has a large diameter. In the dicing process, it is also important to improve productivity that the substrate can be easily cut. Silicon has a large diameter and is easy to cut.

In the case of a silicon substrate, the carrier conductivity type of the substrate is not limited, and either N-type silicon or P-type silicon can be used.
The diameter of the silicon substrate is not particularly limited, but from the viewpoint of productivity, a large-diameter substrate, for example, a substrate having a diameter of 50.8 mm (2 inches) or more is preferable, 100 mm or more is more preferable, and 300 mm or more is particularly preferable. preferable.
The crystallinity of the silicon substrate is not particularly limited, and any of single crystal silicon and polycrystalline silicon can be used.
As the silicon substrate, for example, a known silicon wafer can be used. The silicon wafer may be doped.
The carrier concentration of the substrate is preferably 10 ¹⁶ cm ⁻³ or more, more preferably 10 ¹⁸ cm, in order to obtain an electrically good bond with the conductive film or oxide film in order to produce a low resistance vertical element. ^-3 or more, more preferably 10 ¹⁹ cm ^-3 or more.

Moreover, when producing a semiconductor element (vertical semiconductor element) in which a current flows in the thickness direction of the base material, the base material is preferably a metal. In the case of manufacturing a vertical semiconductor element, it is necessary to form an electrode on the surface of the oxide film and the substrate after forming the oxide film on the substrate. Since a metal has a very low electrical resistivity, the base material can also serve as an electrode by using a metal base material. Therefore, since the electrode on the substrate surface side can be omitted, the electrode manufacturing process can be simplified. In addition, since metal has a high thermal conductivity, Joule heat generated when a current flows can be quickly dissipated and deterioration of the semiconductor element can be prevented.
Specifically, copper, aluminum, molybdenum or titanium is preferable as the metal. The base material may be an alloy containing a plurality of metals for chemical stability. Further, these metals may be laminated and used.

The thickness of the base material is not particularly limited, but it is preferable that the base material is thin from the viewpoints of suppressing material costs, stacking chips, and reducing the thickness of the semiconductor element package. However, when the thickness of the substrate is too thin, the substrate is bent or cracked depending on the weight of the substrate itself. Accordingly, the thickness of the substrate is preferably 1 μm or more and 5 mm or less, more preferably 30 μm or more and 3 mm or less, further preferably 50 μm or more and 1 mm or less, and further preferably 100 μm or more and 700 μm or less.
The thickness of the substrate is measured with a scanning electron microscope (SEM). As a measurement location, observe the field of view of a total of 5 points, the intersection of diagonal lines on the surface of the substrate, and the midpoint between the intersection and each vertex, and measure at a location that divides the field of view equally into 10 parts, for a total of 55 points. The average value is defined as the thickness of the substrate. In addition, when the thickness of a base material is thick, it measures with an optical microscope, a micrometer, etc.

The arithmetic average roughness of the substrate surface is preferably 50 nm or less. For example, when a semiconductor element is manufactured, a plurality of elements are manufactured from a single substrate. However, if the base material surface is rough, the surface of the obtained substrate also becomes rough, and there is a possibility that the characteristics of each element may easily vary. is there. In addition, the unevenness of the substrate tends to cause electric field concentration, which may cause element destruction. If the arithmetic average roughness of the substrate surface is 50 nm or less, the variation in characteristics of each element and the electric field concentration due to the unevenness can be reduced. The arithmetic average roughness of the substrate is more preferably 10 nm or less.
The arithmetic average roughness is a value measured by the measuring method of JIS B0601 '2013.

The electrical resistivity of the substrate at a temperature of 300 K is preferably 0.05 Ωcm or less.
When producing a semiconductor element, the base material becomes an electrically conductive layer. If the electrical resistivity of the substrate is 0.05 Ωcm or less, the electrical resistance value of the substrate is sufficiently low, so that the resistance value of the entire semiconductor element can also be lowered. The electric resistivity of the substrate is more preferably 0.02 Ωcm or less, further preferably 0.01 Ωcm or less, particularly preferably 0.002 Ωcm or less, and preferably 0.001 Ωcm or less. Most preferred.

The electrical resistivity is a value measured by a four-point probe method.
When measurement by the four-probe method is difficult, it can be evaluated by the following method.
A metal film capable of obtaining good contact is formed on both the front and back surfaces of the substrate, and a voltage V is applied. The current I flowing at that time is measured. Assuming that the electrode area is S and the length between the electrode front and back surfaces is L, the electrical resistivity can be obtained by the following equation.
Electric resistivity = (V · S) / (I · L)

  The oxide film used in the present invention has a thermal conductivity of less than 100 W / mK. By using an oxide film having a thermal conductivity of less than 100 W / mK, high pressure resistance can be achieved when a power device such as a diode is manufactured. The thermal conductivity of the oxide film is preferably less than 70 W / mK, more preferably less than 50 W / mK, and particularly preferably less than 30 W / mK.

  The oxide forming the oxide film is not particularly limited as long as the thermal conductivity satisfies the above requirements, and a known metal oxide can be used. For example, an oxide of In, Sn, Si, Ge, Mg, Ti, Zn, Y, Sm, Ce, Nd, Ga, or Al, and a mixed oxide containing two or more of these oxides can be given. Further, the oxide film may have a single layer structure or a stacked structure.

The metal oxide may be amorphous or crystalline, and the crystal may be polycrystalline or single crystal. In the present invention, the oxide film preferably contains one or both of a polycrystalline oxide and an amorphous oxide.
In the case where a single crystal oxide layer is formed over a base material, there is a possibility that a film including crystals having a plurality of orientations different depending on the crystal orientation of the base material may be formed. Further, the end face of the base material is often chamfered. As a result, since various orientation planes are continuously present on the film formation surface, abnormal crystal growth is likely to occur during the formation of the oxide film. Furthermore, since single crystal film formation generally requires a high temperature, impurities may diffuse from the base material to the oxide film. Polycrystalline oxides and amorphous oxides are preferred in that there is no abnormal growth and film formation at a low temperature is possible.

In addition, for example, when a semiconductor element is manufactured from the substrate of the present invention, the substrate is exposed to plasma and various reaction gases in the process, and therefore, it is preferable because the process margin is widened due to its high stability. In this respect, the oxide film preferably includes a polycrystalline oxide or both a polycrystalline oxide and an amorphous oxide.
In the semiconductor element manufacturing process, the oxide film is finely processed by etching with an acid or a reactive gas. As this processing becomes finer, higher etching accuracy is desired. In the case where the oxide film has anisotropy, the etching may proceed in an undesirable direction. Therefore, the oxide film is preferably an amorphous oxide having high isotropic properties.

  On the other hand, an amorphous film and an amorphous film containing microcrystals have a problem of low electric mobility. In the case of a semiconductor element such as a switching element, low electric mobility may increase power loss. Therefore, in this case, it is preferable that the oxide film mainly includes a polycrystalline oxide with high mobility.

In the present invention, the term “polycrystalline oxide” means an aggregate of crystalline oxides whose crystal axis directions are not necessarily aligned. An amorphous oxide means an oxide in which a diffraction peak due to a crystal is not observed in a diffraction chart obtained by X-ray analysis.
“Microcrystal” refers to a crystal grain having a size of submicron or less and no clear grain boundary.
“Polycrystalline” refers to a crystal grain size exceeding micron size and having clear grain boundaries.

In the present invention, the oxide film preferably contains a gallium element (gallium oxide). Since gallium oxide has a wide band gap, it has excellent current-voltage characteristics. For this reason, a semiconductor element manufactured using this substrate has a high breakdown electric field.
Further, gallium has a strong oxygen holding power and can prevent reduction of the film due to desorption of oxygen in the oxide film.

It is preferable that the atomic composition percentage ([Ga] / [Ga] + ([all metal elements other than Ga]) × 100) of gallium with respect to all metal elements contained in the oxide film is 1 at% or more and 100 at% or less. .
In the case of exhibiting a wide band gap and a high breakdown electric field possessed by gallium oxide, the atomic composition percentage of gallium contained in the oxide film is preferably 70 at% or more, more preferably 90 at% or more, and further 95 at% or more. Preferably, it is 98 at% or more especially preferably.
On the other hand, when it is considered that a forward voltage is applied until an exponential current starts to flow through the semiconductor element, the voltage value should be small in order to reduce power consumption.
The voltage value and the band gap are in a trade-off relationship. Therefore, when maintaining electrical conductivity while maintaining a wide band gap, the atomic composition percentage of gallium is preferably 1 at% or more and 90 at% or less, more preferably 20 at% or more and 80 at% or less, and 25 at%. The amount is preferably 60 at% or less and particularly preferably 30 at% or more and 45 at% or less.

In addition to gallium, the oxide film of the present invention further contains one or more elements A selected from silicon, germanium, magnesium, tin, titanium, indium, aluminum, yttrium, samarium, cerium, and zinc. It is preferable to contain one or more elements A selected from silicon, germanium, magnesium, tin, titanium, indium, aluminum, and zinc. The atomic composition percentage of element A in all metal elements in the oxide film is preferably 0.01 at% or more and 90 at% or less, and more preferably 30 at% or more and 70 at% or less. When the atomic composition percentage of the element A is 0.01 at% or more, the possibility of becoming a scattering source for carrier conduction is reduced, and an increase in electrical resistance can be suppressed.
In particular, tin is preferably contained for improving chemical resistance, indium is preferably contained for improving electric conduction, and inexpensive zinc is preferably contained in terms of price. Further, in the case where the oxide is a compound with indium, it is preferable to include zinc for stable amorphous state. Including Al is preferable because reduction of the film due to desorption of oxygen in the oxide film is prevented.
When the oxide film contains two or more kinds of element A, the atomic composition percentage of element A means the total atomic composition percentage of added element A.
The composition of the oxide film is measured by an ICP (Inductively Coupled Plasma) emission analyzer, XRF (X-ray Fluorescence Analysis) or SIMS (Secondary Ion Mass Spectrometry).

The carrier concentration in the oxide film at a temperature of 300 K is preferably 1 × 10 ¹¹ cm ⁻³ or more and 1 × 10 ¹⁸ cm ⁻³ or less, preferably 1 × 10 ¹² cm ⁻³ or more and 1 × 10 ¹⁷ cm ^−. It is more preferably ³ or less, and more preferably 1 × 10 ¹⁴ cm ⁻³ or more and 1 × 10 ¹⁷ cm ⁻³ or less. If the carrier concentration is 1 × 10 ¹¹ cm ⁻³ or more, the electric resistance value of the oxide film is preferably sufficiently low. On the other hand, if the carrier concentration is 1 × 10 ¹⁸ cm ⁻³ or less, the resistance does not become too low and the leakage current at the time of reverse bias is difficult to increase.

The carrier concentration is measured by CV evaluation.
In the CV evaluation, N (carrier concentration) is obtained from the slope of C ⁻² vsV using the following formula.
C = {qεN / 2 (φ−V)} ^1/2
Each symbol means the following.
C: Junction capacity of metal and oxide film per unit area
q: Elementary amount of charge ε: Dielectric constant of oxide film φ: Built-in potential at junction of metal and oxide film V: Applied voltage

  There is no restriction | limiting in particular in the film thickness of an oxide film, According to a use, it can set suitably. For example, in the case where a diode which is one of semiconductor elements is manufactured using the substrate of the present invention, the oxide film is preferably thick in order to maintain a dielectric breakdown electric field. On the other hand, if the film thickness is too thick, the resistance value of the film increases, and the voltage value at which current begins to flow when a forward voltage is applied to the diode increases. Therefore, the thickness of the oxide film is preferably 50 nm or more and 300 μm or less, more preferably 500 nm or more and 100 μm or less, and particularly preferably 900 nm or more and 50 μm or less.

  The film thickness is measured with a transmission electron microscope (TEM). As the measurement points, observe the field of view of the total of 5 points of intersection of the diagonal of the film and the intermediate point between the intersection and each vertex, and measure at the point where the field of view is equally divided into 10 equally. The value is the film thickness. When the film thickness is large, the measurement is performed in the same manner as described above using a scanning electron microscope (SEM), an optical microscope, or the like.

In the board | substrate of this invention, the heat conductivity of a base material is higher than the heat conductivity of an oxide film. That is, the relationship of the following formula is satisfied.
(Thermal conductivity of the substrate)> (Thermal conductivity of the oxide film)
Thereby, a substrate having high thermal conductivity and high pressure resistance can be obtained.

The thermal conductivity of the substrate of the present invention at a temperature of 300 K is preferably 30 W / mK or more, more preferably 50 W / mK or more, more preferably 100 W / mK or more, and particularly preferably 120 W / mK or more.
The substrate of the present invention can be produced by forming an oxide film on the base material described above.
For the formation of the oxide film, sputtering method, vacuum vapor deposition method, vacuum vapor phase method such as CVD method, atmospheric pressure CVD, spray pyrolysis method, atmospheric pressure vapor phase method such as mist CVD method, spin coating method, ink jet method, Known methods such as a liquid phase method such as a casting method, a micelle electrolysis method, and an electrodeposition method can be applied.

An annealing treatment may be performed after the oxide film is formed. By the annealing treatment, the above-described electrical bonding between the base material and the oxide film is improved.
The conditions for the annealing treatment may be appropriately adjusted according to the type of the oxide film and the like, but are usually heated at 50 to 1400 ° C. for 30 seconds to 5 hours. 60-600 degreeC is more preferable, and 80-300 degreeC is further more preferable. It is more preferable to heat for 10 minutes to 2 hours, and it is more preferable to heat for 30 minutes to 1 hour and 30 minutes.

In the substrate of the present invention, a conductive film having a thickness of 1 nm to 1 μm may be formed between the base material and the oxide film.
Another embodiment of the substrate of the present invention is shown in FIG.
The substrate 2 has a structure in which the base material 10, the conductive film 30, and the oxide film 20 are stacked in this order.
The conductive film is preferably a metal film having high electrical conductivity. In the case of a metal film, if it is too thick, the substrate may be warped by the stress of the metal layer. Therefore, the thickness of the metal film is preferably 1 μm or less, more preferably 500 nm or less, and particularly preferably 200 nm or less. As the metal, palladium, molybdenum, chromium, titanium, tantalum, zirconium or hafnium, gold, platinum, iridium, and ruthenium are preferable.

  A protective film may be stacked over the conductive film. As the protective film, a metal different from the conductive film can be used, and a metal that is difficult to oxidize, such as gold or platinum, is preferable. Alternatively, the oxide film can be formed into two layers and the oxide film in contact with the conductive film can have a role of a protective film. In this case, palladium oxide, iridium oxide, and ruthenium oxide are preferable.

Moreover, in the board | substrate of this invention, in order to assist conduction | electrical_connection on the back surface of a base material, ie, the surface on the opposite side to the surface which produces an oxide film, you may form the electrically conductive film excellent in adhesiveness. As the conductive film, chromium, titanium, tantalum, molybdenum, zirconium, or hafnium that forms a good ohmic junction with silicon is preferable.
The thickness of the conductive film is preferably 1 nm or more and 200 nm or less. If it is this range, when the heat | fever is added to a board | substrate, the curvature of the board | substrate which arises by the difference in the thermal expansion coefficient of a board | substrate and a electrically conductive film can be reduced.

The board | substrate of this invention can be used for the structural member (semiconductor film etc.) of a semiconductor element, an electrical insulation element, etc., for example. Especially, it is suitable for the substrate for semiconductor elements.
Examples of the element using the substrate of the present invention include a diode and a vertical MOSFET. A diode using the substrate of the present invention can realize high breakdown voltage and high-speed switching.

  Examples of the electric circuit using the element of the present invention include a step-up / step-down chopper circuit, an inverter / converter circuit, a power supply circuit, a switching regulator, and the like. Examples of the electric device include a mobile phone, a personal computer, an air conditioner, a refrigerator, a receiver, A lighting fixture, an electromagnetic cooker, etc. are mentioned, As a vehicle, a bicycle, a car, a railcar, an airplane, etc. are mentioned.

Specific examples of the present invention will be described.
In Examples and Comparative Examples, a silicon substrate or a β-Ga ₂ O ₃ substrate was used as a base material. As the oxide film, an amorphous Ga ₂ O ₃ film, an indium gallium zinc oxide (IGZO) film, or an indium tin zinc oxide (ITZO) film was used. These physical properties are shown in Table 1. The measuring method of each physical property is as follows.

-Thermal conductivity The thermal conductivity of the oxide film at room temperature (300K) was measured by a periodic heating thermoreflectance method using a thermal microscope TM3 manufactured by Bethel.
Specifically, for measurement, a 140 nm Mo thin film was formed on amorphous Ga ₂ O ₃ (oxide film), and the surface was periodically heated with a heating laser. Heat propagates from the Mo thin film onto the amorphous Ga ₂ O ₃ , and the temperature response of the sample surface, that is, the waveform phase of the temperature change of the Mo surface causes a phase lag with respect to the waveform phase of the laser that is periodically heated. By analyzing this phase lag, the thermal permeability b of the membrane was measured.
The thermal conductivity λ was calculated from the following equation from the thermal permeability b.
λ = b ² / ρc
(Wherein λ is thermal conductivity [W / mK], b is thermal permeability [J / sec ^0.5 m ² K], ρ is density [kg / m ³ ], c is specific heat capacity [J / kgK ])

The thermal conductivity of the substrate at room temperature (300K) was determined as follows. The thermal diffusivity α was measured by a periodic heating radiation temperature measurement method using a thermowave analyzer TA3 manufactured by Bethel. The thermal conductivity λ was calculated from the following formula from the thermal diffusivity α.
λ = αρc
(In the formula, λ is thermal conductivity [W / mK], α is thermal diffusivity [m ² / sec], ρ is density [kg / m ³ ], and c is specific heat capacity [J / kgK].)

-Arithmetic average roughness The roughness curve necessary for calculating the arithmetic average roughness is a 10 μm x 10 μm range centered on the intersection of each diagonal line of the sample surface with an atomic force microscope (AFM) probe. I got it. Then, arithmetic mean roughness was calculated | required by the procedure as described in JIS B0601 '2013.

-Electrical resistivity The electrical resistivity was measured by the four probe method.

実施例１
図１に示す構造を有する基板を作製した。具体的に、基材１０としてＣＺ（Ｃｚｏｃｈｒａｌｓｋｉ）法により作製した厚さ５２５μｍ、Ｎ型の結晶方位＜１００＞、算術粗さ０．２５ｎｍのシリコン基材を使用した。基材の多数キャリアの種類に制限はないが、酸化物膜２０と同じ多数キャリアの種類であることが望ましい。酸化物膜２０として、上記のＳｉ基材（基材１０）上にスパッタリング法によって厚さ９８１．７ｎｍのアモルファス（非晶質）Ｇａ_２Ｏ_３を形成した。アモルファス酸化ガリウムはアネルバ製スパッタリング装置Ｅ−２００Ｓを用いて、５０Ｗ、ＤＣ電力５０Ｗ、アルゴンガス１００％、室温（３００Ｋ）にて成膜した。 -Carrier concentration The carrier concentration was measured by CV evaluation.

Example 1
A substrate having the structure shown in FIG. 1 was produced. Specifically, a silicon substrate having a thickness of 525 μm, an N-type crystal orientation <100>, and an arithmetic roughness of 0.25 nm, which was produced by a CZ (Czochralski) method, was used as the substrate 10. Although there is no restriction | limiting in the kind of majority carrier of a base material, It is desirable that it is the same kind of majority carrier as the oxide film 20. FIG. As the oxide film 20, amorphous (amorphous) Ga ₂ O ₃ having a thickness of 981.7 nm was formed on the Si base material (base material 10) by a sputtering method. The amorphous gallium oxide was formed into a film at 50 W, DC power 50 W, argon gas 100%, and room temperature (300 K) using an Anelva sputtering apparatus E-200S.

Table 2 shows the layer configuration of the fabricated substrate, and the evaluation results of the thermal conductivity and high breakdown voltage. The measurement method is as follows.
-Thermal conductivity The thermal conductivity of the substrate at room temperature (300K) was determined by the same method as that for the base material.
30 W / mK or more was evaluated as “◯” and less than 30 W / mK was evaluated as “×”.

・ Evaluation of withstand voltage (dielectric breakdown voltage) A metal film is formed on the surface of a silicon substrate, an oxide film is further laminated on the metal film, and a metal electrode (surface electrode) is formed on the oxide film. Form. A metal film is formed on the back surface of the silicon substrate to form a back electrode. A reverse voltage was applied between the front electrode and the back electrode, and a voltage at which a current began to flow exponentially was defined as a withstand voltage (withstand voltage).
A dielectric breakdown electric field was calculated using this withstand voltage. In addition, since the oxide film of an Example and a comparative example has a carrier concentration of 10 ¹⁶ cm ⁻³ or more, and the thickness of the depletion layer changes in direct proportion to the electric field, the “withstand voltage (dielectric breakdown voltage)” The dielectric breakdown electric field was defined as “x2 / oxide film thickness”. Note that in the case where the carrier concentration is as low as less than 10 ¹⁶ cm ⁻³ and the metal oxide can be regarded as an insulator, “breakdown voltage (dielectric breakdown voltage) / film thickness of oxide” is defined as a dielectric breakdown electric field.
The case where the dielectric breakdown electric field was 0.3 MV / cm or more was evaluated as “◯”, and the case where the dielectric breakdown electric field was less than 0.3 MV / cm was evaluated as “x”.

・ Whether it can be used for power devices Based on the above evaluation results, the case where it can be used for a power device was evaluated as “◯”, and the case where it could not be used was evaluated as “×”.

Examples 2-4
Substrates having the layer structure shown in Table 2 were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2. The oxide film of Example 4 was made of amorphous Ga ₂ O ₃ and IGZO.

Comparative Examples 1-4
Substrates having the layer structure shown in Table 3 were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 3.

The board | substrate of this invention can be used for a semiconductor element, for example.
The element using the substrate of the present invention can be used in an electric circuit, an electric device or a vehicle.

1, 2 substrate 10 base material 20 oxide film 30 conductive film

Claims (17)

A base material having a thermal conductivity of 30 W / mK or more at a temperature of 300 K;
An oxide film having a thermal conductivity of less than 100 W / mK at a temperature of 300 K is laminated,
The board | substrate whose heat conductivity of the said base material is higher than the heat conductivity of the said oxide film.   The substrate according to claim 1, wherein the oxide film has a thickness of 1 nm to 300 μm.   The board | substrate of Claim 1 or 2 whose thickness of the said base material is 1 micrometer or more and 5 mm or less.   The board | substrate in any one of Claims 1-3 whose heat conductivity in the temperature of 300K is 30 W / mK or more.   The board | substrate in any one of Claims 1-4 whose electrical resistivity in the temperature of 300K of the said base material is 0.05 ohm-cm or less.   The substrate according to claim 1, wherein the base material includes one or more selected from silicon, silicon carbide, gallium nitride, aluminum nitride, copper, aluminum, molybdenum, titanium, gold, and diamond.   The arithmetic mean roughness of the base material surface is 50 nm or less, The board | substrate in any one of Claims 1-6.   The substrate according to claim 1, wherein the oxide film includes at least one of a polycrystalline oxide and an amorphous oxide.   The substrate according to claim 1, wherein the oxide film contains at least gallium.   The atomic composition percentage ([Ga] / [Ga] + ([all metal elements other than Ga]) × 100) of gallium with respect to all metal elements contained in the oxide film is 1 at% or more and 100 at% or less. The substrate according to claim 9.   The oxide film containing gallium further contains one or more metal elements A selected from silicon, germanium, tin, titanium, indium, aluminum, titanium, yttrium, samarium, cerium, and zinc, and in the oxide film The substrate according to claim 9 or 10, wherein an atomic composition percentage of the metal element A in all metal elements is 0.01 at% or more and 90 at% or less.   The substrate according to claim 11, wherein the metal element A is one or more selected from silicon, germanium, tin, titanium, and zinc. The substrate according to claim 1, wherein a carrier concentration of the oxide film at a temperature of 300 K is 1 × 10 ¹⁴ cm ⁻³ or more and 1 × 10 ¹⁷ cm ⁻³ or less.   The substrate according to claim 1, which is a substrate for a semiconductor element.   The element using the board | substrate in any one of Claims 1-14.   An electric circuit comprising the element according to claim 15.   An electric device or a vehicle including the element according to claim 15.

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