JP6213414B2 - Semiconductor element and semiconductor device using the same - Google Patents

Description

  The present invention relates to a semiconductor element and a semiconductor device using the same.

  Group III nitride semiconductors such as gallium nitride (GaN) have excellent semiconductor characteristics and are therefore preferably used for semiconductor devices. For example, JP 2009-126722 A (Patent Document 1) discloses a self-standing GaN substrate made of a GaN single crystal as a substrate for a semiconductor device. However, such a self-standing GaN substrate has a high manufacturing cost and is liable to be broken, so that the enlargement of the diameter tends to be difficult.

  In contrast, Japanese Patent Application Laid-Open No. 2008-010766 (Patent Document 2) discloses a GaN thin film bonded substrate in which a GaN thin film is firmly bonded to a dissimilar substrate having a chemical composition different from that of GaN as a substrate for a semiconductor device. The With a composite substrate such as a GaN thin film bonded substrate, the ease of cracking is improved, and the thickness of the GaN thin film (GaN single crystal) can be reduced, thereby reducing the manufacturing cost and increasing the diameter. Become.

JP 2009-126722 A JP 2008-010766 A

  However, when the epitaxial layer is formed on the composite substrate as described above, the in-plane uniformity of the carrier concentration in the epitaxial layer may be lowered. When the in-plane uniformity of the carrier concentration in the epitaxial layer is lowered, there is a problem that the production yield of the manufactured semiconductor device is lowered when this is used as a semiconductor element.

  In view of the above problems, an object of the present invention is to provide a semiconductor element having excellent in-plane carrier concentration uniformity and a semiconductor device using the same.

A semiconductor element according to one embodiment of the present invention includes a composite substrate including a support substrate, a group III nitride film, and a bonding film interposed between the support substrate and the group III nitride film, and the group III nitride film. And an epitaxial layer provided on the substrate. The epitaxial layer is composed of one or more semiconductor layers, and at least one of the semiconductor layers has an average value of carrier concentration in the central region where the outer peripheral region from the outer peripheral edge to the inner side corresponding to 10% of the diameter is removed. Is 4 × 10 ¹⁵ pieces / cm ³ or more and 1.5 × 10 ¹⁶ pieces / cm ³ or less, and the variation of the dopant concentration is ± 10% or less.

  A semiconductor device according to one embodiment of the present invention is a semiconductor device using the above semiconductor element, and includes a central region of the semiconductor element as a composite substrate.

  According to the above, it is possible to provide a semiconductor element having excellent carrier concentration uniformity and a semiconductor device using the same.

It is typical sectional drawing of the semiconductor element which concerns on embodiment. It is a typical top view of the semiconductor element concerning an embodiment. It is typical sectional drawing of the manufacturing apparatus of the semiconductor element which concerns on embodiment. It is typical sectional drawing of the susceptor with which the manufacturing apparatus of FIG. 3 is provided. It is typical sectional drawing illustrated about an example of the manufacturing method of the semiconductor element which concerns on embodiment. It is typical sectional drawing illustrated about an example of the manufacturing method of the semiconductor element which concerns on embodiment. It is typical sectional drawing illustrated about an example of the manufacturing method of the semiconductor element which concerns on embodiment. It is typical sectional drawing illustrated about an example of the manufacturing method of the semiconductor element which concerns on embodiment. It is typical sectional drawing illustrated about an example of the manufacturing method of the semiconductor element which concerns on embodiment. It is a typical sectional view of a semiconductor element device concerning an embodiment. It is typical sectional drawing of the conventional susceptor. FIG. 4 is a diagram showing variation in carrier concentration in the semiconductor element of Example 1.

[Description of Embodiment of the Present Invention]
First, embodiments of the present invention will be listed and described.

  When the inventors set the carrier concentration low when forming the epitaxial layer containing the dopant on the composite substrate, the in-plane uniformity of the carrier concentration was formed on another substrate, for example, a free-standing GaN substrate. It was confirmed that it tends to be lower than that in the epitaxial layer. The inventors have found that the cause is that the composite substrate warps particularly greatly compared to other substrates during the process of forming the epitaxial layer.

  When the warpage of the substrate becomes a problem, an approach of reducing the warpage of the substrate is generally taken. However, the present inventors have found that the warpage of the composite substrate is due to the low thermal conductivity of the bonding film between the support substrate and the group III nitride film. We thought that it was difficult to reduce sufficiently.

  Therefore, the present inventors changed their ideas and conducted extensive studies to find a method of forming an epitaxial layer with high carrier concentration uniformity on a greatly warped composite substrate. As a result of intensive studies, the inventors have found a method for forming an epitaxial layer suitable for a warped composite substrate, thereby completing a semiconductor device having excellent in-plane uniformity.

(1) A semiconductor element according to one embodiment of the present invention includes a composite substrate including a support substrate, a group III nitride film, and a bonding film interposed between the support substrate and the group III nitride film, and a group III nitride An epitaxial layer provided on the material film, wherein the epitaxial layer is composed of one or more semiconductor layers, and at least one of the semiconductor layers extends from the outer periphery to a distance corresponding to 10% of the diameter. In the central region excluding the outer peripheral region, the average value of the carrier concentration is 4 × 10 ¹⁵ pieces / cm ³ or more and 1.5 × 10 ¹⁶ pieces / cm ³ or less, and the carrier concentration variation is ± 10% or less. .

  According to the semiconductor element, although the epitaxial layer is formed on the composite substrate, the average value of the carrier concentration is relatively low in the central region of at least one of the semiconductor layers constituting the epitaxial layer. And a layer having excellent uniformity.

  (2) The semiconductor element preferably has a diameter of 75 mm or more and 155 mm or less. Thereby, the uniformity of the carrier concentration can be further improved as compared with the conventional case.

  (3) Preferably in the semiconductor element, the layer has a thickness of 1 μm or more and 20 μm or less. Thereby, the uniformity of the carrier concentration can be further improved as compared with the conventional case.

  (4) In the above semiconductor element, preferably, the bonding film contains silicon dioxide. Thereby, the composite substrate can have a high bonding strength.

  (5) A semiconductor device according to one embodiment of the present invention is a semiconductor device using the semiconductor element, and includes a central region of the semiconductor element as a composite substrate.

  According to the semiconductor device described above, a composite substrate having a central region with excellent carrier concentration uniformity can be used as a semiconductor element, so that a semiconductor device having excellent characteristics can be manufactured at low cost.

[Details of the embodiment of the present invention]
Hereinafter, this embodiment will be described in detail. In the drawings used to describe the embodiments, the same reference numerals represent the same or corresponding parts.

<Semiconductor element>
The configuration of the semiconductor element according to this embodiment will be described with reference to FIGS. Referring to FIG. 1, a semiconductor element 10 includes a composite substrate 4 including a support substrate 1, a GaN film 2 as a group III nitride film, and a bonding film 3 interposed between the support substrate 1 and the GaN film 2. And an epitaxial layer 5 provided on the GaN film 2. In the present embodiment, the epitaxial layer 5 includes an n ⁺ GaN layer 5a and an n ⁻ GaN layer 5b.

  The diameter of the semiconductor element 10 is preferably 50 mm or more, more preferably 75 mm or more, further preferably 100 mm or more, from the viewpoint of increasing the number of semiconductor devices that can be taken from the semiconductor element 10. The above is particularly preferable.

  The composite substrate 4 is a substrate in which the support substrate 1 and the GaN film 2 are bonded together by the bonding film 3, and reduces the amount of group III nitride used compared to a self-supporting group III nitride substrate. However, it can have strength as a substrate.

  In the composite substrate 4, another film may be interposed between the bonding film 3 and the support substrate 1, and another film may be interposed between the bonding film 3 and the GaN film 2. This other film is a film provided for improving the bonding property between the bonding film 3 and the support substrate 1 and the bonding property between the bonding film 3 and the GaN film 2, and examples thereof include a SiN film.

  The support substrate 1 is a heterogeneous substrate having a chemical composition different from that of the GaN film 2. Examples of the material of the support substrate 1 include sapphire, silicon carbide (SiC), mullite, and zirconia. Further, an n-type heterogeneous substrate can be suitably used as the support substrate 1.

  The thickness of the support substrate 1 is preferably 50 μm or more and 3 mm or less, and more preferably 0.1 mm or more and 1 mm or less. When the thickness of the support substrate 1 is less than 50 μm, the strength of the composite substrate 4 tends to be insufficient, and when it exceeds 3 mm, the handling property tends to decrease or the cost tends to increase.

As the GaN film 2, an n-type GaN film doped with phosphorus or the like can be suitably used. The carrier concentration of the n-type GaN film is not particularly limited, and can be, for example, 1 × 10 ¹⁸ pieces / cm ³ or more and 5 × 10 ¹⁸ pieces / cm ³ or less.

In this embodiment, a GaN film is used as the group III nitride film. However, the group III nitride film is not limited to a GaN film, and is a compound of a group III element such as Al, Ga, In, and nitrogen. Any film made of a certain group III nitride may be used. Specifically, in addition to the above GaN, AlN, Al _x Ga _1-x N (0 <x <1), InN, In _y Ga _1-y N (0 <y <1), and the like can be given.

  The thickness of the GaN film 2 is preferably 50 μm or more and 300 μm or less, and more preferably 50 μm or more and 180 μm or less. When the thickness of the GaN film 2 is less than 50 μm, the thickness tends to be non-uniform due to the manufacturing method of the composite substrate 4, and when it exceeds 300 μm, the manufacturing cost tends to increase.

The bonding film 3 is a film having the performance of bonding the support substrate 1 and the GaN film 2. Examples of the material of the bonding film 3 include silicon dioxide (SiO ₂ ), titanium oxide (TiO ₂ ), and aluminum oxide (Al ₂ O ₃ ). Silicon dioxide is preferable because of its high bonding property. The thickness of the bonding film 3 is not particularly limited, but the thickness is preferably thin as long as the above performance can be exhibited.

Epitaxial layer 5 is a group III nitride semiconductor layer formed on GaN film 2 of composite substrate 4 by a CVD method. In the present embodiment, the epitaxial layer 5 includes the n ⁺ GaN layer 5a and the n ⁻ GaN layer 5b, but the configuration of the epitaxial layer 5 is not limited to this. However, from the viewpoint of crystal uniformity, the semiconductor constituting the epitaxial layer 5 is preferably made of the same element as the group III nitride film of the composite substrate 4.

  Although the thickness of the epitaxial layer 5 is not particularly limited, it is preferably 1 μm or more and 100 μm or less, more preferably 5 μm or more and 25 μm or less from the viewpoint of use as a power device having a high breakdown voltage (high withstand voltage) and low on-resistance as a semiconductor device. .

The dopant concentration of the n ⁺ GaN layer 5a is not particularly limited, and can be, for example, 1 × 10 ¹⁸ / cm ³ or more and 5 × 10 ¹⁸ / cm ³ or less. Further, the thickness of the n ⁺ GaN layer 5a is not particularly limited, and can be, for example, not less than 0.5 μm and not more than 10 μm. Thereby, when using the semiconductor element 10 as a Schottky barrier diode (SBD), the n ^<+> GaN layer 5a can be suitably functioned as a buffer layer. Each carrier concentration of n ⁺ GaN layer 5a and n ⁻ GaN layer 5b can be evaluated by secondary ion mass spectrometry (SIMS).

The carrier concentration of n ⁻ GaN layer 5b is not particularly limited, and can be, for example, 2 × 10 ¹⁵ pieces / cm ³ or more and 5 × 10 ¹⁶ pieces / cm ³ or less. Further, the thickness of the n ⁻ GaN layer 5b is not particularly limited, and can be, for example, 1 μm or more and 20 μm or less. Thereby, when using the semiconductor element 10 as SBD, the n < ^- > GaN layer 5b can be functioned suitably as a drift layer. The thickness of the n ⁻ GaN layer 5b is more preferably 5 μm or more and 25 μm or less.

Furthermore, in the present embodiment, the n ⁻ GaN layer 5b has the following characteristics. That is, the center region 5bb (the region between the solid circle and the dotted circle in FIG. 2) from the outer periphery of the n ⁻ GaN layer 5b to the inside of the distance R ₂ corresponding to 10% of the diameter R ₁ is removed. In the region surrounded by a dotted circle in FIG. 2, the average value of the carrier concentration of the n ⁻ GaN layer 5b is 4 × 10 ¹⁵ pieces / cm ³ or more and 1.5 × 10 ¹⁶ pieces / cm ³ or less, and the carrier The concentration variation is ± 10% or less.

The average value is an average value of carrier concentrations (pieces / cm ³ ) at arbitrary seven points or more in the central region 5bb. Each of the arbitrary points is in the same plane of the n ⁻ GaN layer 5b and has a different position. The above variation is a value obtained by dividing the value obtained by subtracting the minimum value from the maximum value by the value obtained by adding the maximum value and the minimum value ((maximum value−minimum value) / (maximum value + minimum value)). is there. Further, “variation is ± 10% or less” means that the obtained value does not exceed the value of “average value + 10% of average value” and “average value−value of 10% of average value”. It means not to fall below.

In FIG. 2, the central axis of the semiconductor element 10 coincides with the center point A of the solid circle that is the outer edge of the semiconductor element 10 and coincides with the center point A of the dotted circle that is a virtual circle. The length of R _{3 in} FIG. 2 is a length obtained by subtracting twice the length R ₂ corresponding to 10% of the diameter R ₁ from the diameter R ₁ of the epitaxial layer 5.

<Semiconductor element manufacturing equipment>
An example of the manufacturing apparatus of the above-described semiconductor element 10 will be described with reference to FIGS. This manufacturing apparatus is an MOCVD apparatus, and is characterized by the shape of a susceptor for placing a composite substrate.

  With reference to FIG. 3, the MOCVD apparatus 20 mainly includes a reaction vessel 14, a susceptor 15, a heater 12, a source gas supply unit 11, and a rotating shaft 13. The source gas supply unit 11 extends in the horizontal direction in FIG. 3, and the mounting surface of the susceptor 15 faces inside the source gas supply unit 11.

  The susceptor 15 is disposed inside the reaction vessel 14 (the shape of the susceptor 15 will be described later). The susceptor 15 is disposed on the heater 12 having a disk shape. A rotating shaft 13 serving as a rotating mechanism is attached to the lower part of the susceptor 15, so that the susceptor 15 can rotate with the mounting surface facing the inside of the source gas supply unit 11. That is, with this configuration, the composite substrate 4 placed on the rotating susceptor 15 is heated by the heater 12 via the susceptor 15.

  The source gas supply unit 11 supplies the reaction vessel 14 with the first and second source gases G1 and G2 and the gas G3 as the carrier gas from the direction along the surface of the composite substrate 4. That is, the source gas supply unit 11 is a passage for flowing a reaction gas composed of the first and second source gases G1, G2 and the gas G3 to the surface 4a of the composite substrate 4. The source gas supply unit 11 of the present embodiment extends in parallel to the upper surface of the susceptor 15 and has a rectangular cross section when it can be perpendicular to the source gas flow direction (directions indicated by arrows G1 to G3 in the figure). It has a shape. The source gas supply unit 11 is a horizontal three-layer flow system, and the first gas supply unit 11a, the second gas supply unit 11b, and the third gas supply unit 11c are arranged upstream (left side in FIG. 2). have.

  The first gas supply unit 11 a is located on the side close to the surface in the direction D perpendicular to the surface 4 a of the composite substrate 4. The second gas supply unit 11b is located on the side farther from the surface than the first gas supply unit 11a in the direction D perpendicular to the surface 4a of the composite substrate 4. The third gas supply unit 11c is located farther from the surface 4a than the second gas supply unit 11b in the direction D perpendicular to the surface 4a of the composite substrate 4. That is, in the direction D perpendicular to the mounting surface of the susceptor 15, the first gas supply unit 11a, the second gas supply unit 11b, and the third gas supply unit 11c are closer to the mounting surface of the susceptor 15 in this order.

  The positions of the outlets of the first and second source gases G1, G2 and gas G3 of the first to third gas supply units 11a to 11c are the directions along the surface 4a of the composite substrate 4, that is, the first and second As shown in FIG. 3, the two raw material gases G1, G2 and G3 may be different or the same in the flow direction.

  In the MOCVD apparatus 20, the third gas supply unit 11c may be omitted. In this case, a purge mechanism or the like for suppressing the deposition of crystals by supplying the source gases G1 and G2 to the surface (upper wall in FIG. 2) facing the surface 4a of the composite substrate 4 in the reaction vessel 14. These means are preferably provided.

  Further, in the MOCVD apparatus 20 of the present embodiment, the susceptor 15 is a face-up type arranged below the reaction vessel, but is not particularly limited thereto. The MOCVD apparatus 20 may be a face-down type in which the susceptor 15 is disposed above the reaction vessel.

  The susceptor 15 is a member for arranging the composite substrate. The susceptor 15 is made of, for example, carbon, and the outer surface thereof may be coated with silicon carbide (SiC) or tantalum carbide (TaC).

  Here, the shape of the susceptor 15 is greatly different from that of the conventional susceptor. Specifically, referring to FIG. 4, the susceptor 15 supports the composite substrate 4, a curved surface 15 b that faces the composite substrate 4 supported by the support surface 15 a, and the outer periphery of the curved surface 15 b. It has a counterbore side surface 15c that connects the surface 15a.

The curved surface 15 b has a bowl shape that is recessed in the thickness direction of the susceptor 15. The most depressed central portion P of the curved surface 15b coincides with the central axis of the composite substrate 4 when viewed from the central axis direction of the composite substrate 4 to be placed. The distance D ₁ between the central portion P of the curved surface 15b and the first surface 4a of the composite substrate 4 placed on the support surface 15a is preferably 50 μm or more and 1000 μm or less, and preferably 300 μm or more and 700 μm or less. More preferred. This distance is set for the first time by measuring the warp width of the composite substrate 4 during the formation of the epitaxial layer 5 (the width warped so as to be greatly depressed toward the susceptor 15). The distance D ₁ is the shortest distance connecting the center portion P and the first face 4a a straight line.

The distance _{D 2} is the length of the counterbore side 15c may be, for example, with 50μm or 400μm or less. Thereby, during the formation of the epitaxial layer 5, it is possible to suppress the contact between the curved surface 15 b and the composite substrate 4 warped so that the central portion is greatly depressed toward the susceptor 15, and the heating of the composite substrate 4 by the susceptor 15 is more uniform. Can be The heating of the composite substrate 4 by the radiant heat of the susceptor 15 is more uniform with a certain tolerance for the amount of warpage of the composite substrate 4 than the heating of the composite substrate 4 by direct contact between the susceptor 15 and the composite substrate 4. It can be considered that one of the factors is that it can be heated to a uniform temperature and can be easily made uniform.

<Method for Manufacturing Semiconductor Device>
An example of a method for manufacturing the semiconductor element 10 using the above-described MOCVD apparatus 20 will be described with reference to FIGS.

(Preparation process)
First, referring to FIG. 5, a support substrate 1 having a bonding film 3a formed on the main surface and a GaN substrate 2a having a bonding film 3b formed on the main surface are prepared. Here, the bonding film 3 a and the bonding film 3 b are bonded together to form the bonding film 3, and are made of the same material as the bonding film 3. The GaN substrate 2a is a bulk crystal of GaN and can be obtained by a known manufacturing method.

  The method for forming the bonding film 3a on the main surface of the support substrate 1 and the method for forming the bonding film 3b on the main surface of the GaN substrate 2a are not particularly limited. Sputtering method, CVD method, pulse laser volume method, molecular beam growth Or electron beam evaporation. From the viewpoint of forming a uniform film while maintaining the formation speed of the bonding film 3a and the bonding film 3b high, the CVD method is preferable.

  Each main surface exposed to the outside of the bonding films 3a and 3b is preferably a mirror surface, and the bonding films 3a and 3b are preferably annealed. When each main surface is made into a mirror surface by polishing or the like, the bonding strength between the bonding films is increased, so that the bonding strength between the support substrate 1 and the GaN substrate 2a can be increased. In addition, since the bonding films 3a and 3b can be degassed by annealing the bonding films 3a and 3b, the bonding films 3a and 3b are densified, and thus the strength of the bonding film 3 can be increased. .

(Lamination process)
Next, referring to FIG. 6, the bonding films 3 are formed by bonding the exposed main surfaces of the bonding films 3 a and 3 b to each other. Thereby, a laminated body in which the support substrate 1 and the GaN substrate 2a are bonded together via the bonding film 3 is formed.

The bonding method for bonding the main surfaces to each other is not particularly limited. For example, a direct bonding method in which the main surfaces are brought into contact with each other and then heated to about 600 ° C. to 1200 ° C. to bond them. There is a surface activated bonding method in which bonding is performed in a low temperature atmosphere of about 25 ° C. to 400 ° C. after activation treatment with plasma, ions, or the like. Further, as another method, there is a high pressure bonding method for bonding in a high pressure environment of about 0.1 MPa to 10 MPa, and a high vacuum bonding method for bonding in a high vacuum atmosphere of about 10 ⁻⁶ Pa to 10 ⁻³ Pa. .

  In any of the bonding methods described above, the bonding strength between the main surfaces can be further increased by cleaning the main surfaces with a chemical solution and pure water before the bonding to clean the main surfaces. Further, the bonding strength can be further increased by raising the temperature of the laminated body after bonding to about 600 ° C. to 1200 ° C.

(Cutting process)
Next, referring to FIG. 7, the GaN substrate 2a is cut at a surface located at a desired distance from the interface with the bonding film 3 so that the GaN film 2 having a desired thickness remains. Thereby, the composite substrate 4 in which the support substrate 1 and the GaN film 2 are bonded together via the bonding film 3 is formed.

  The method for cutting the GaN substrate 2a is not particularly limited, and examples thereof include a mechanical cutting method using a wire saw, a blade saw, laser processing, electric discharge processing, water jet, and the like. The main surface exposed to the outside of the cut GaN film 2 is preferably polished. Thereby, the damaged layer on the main surface of the GaN film 2 caused by cutting can be removed, and the crystal quality of the epitaxial layer 5 formed on this main surface can be improved.

  As another cutting method, there is a cutting method in which ions such as hydrogen ions, helium ions, or nitrogen ions are implanted into a surface located at a desired distance from the interface with the bonding film 3 in the GaN substrate 2a and heat-treated. It is done. Since the surface into which ions are implanted (implanted surface) becomes brittle, it is possible to cut the implanted surface by performing a heat treatment after the ions have been implanted.

  The above-described ion implantation can be performed by using, for example, a known ion implantation apparatus. Moreover, it is preferable that the above-mentioned heat processing shall be about 300 to 600 degreeC from a viewpoint of preventing the spreading | diffusion of ion.

(Epitaxial layer formation process)
Next, an epitaxial layer 5 is formed on the GaN film 2 of the composite substrate 4. Specifically, first, as shown in FIG. 3, the composite substrate 4 is disposed on the susceptor 15 of the MOCVD apparatus 20. At this time, the GaN film 2 is disposed so as to face the gas flow path. Next, the GaN film 2 is heat-treated in an atmosphere supplied with a gas containing hydrogen (H ₂ ) and ammonia (NH ₃ ) while controlling the pressure in the reaction vessel 14 to around 27 kPa. By this heat treatment, pretreatment (thermal cleaning) for epitaxial growth is performed on the GaN film 2. The pretreatment temperature is 1000 ° C., for example.

Next, the reaction gas is supplied from the source gas supply unit 11 into the reaction vessel 14. The reaction gas includes at least a source gas, a carrier gas, and a dopant gas. The source gas can use, for example, trimethylgallium gas and NH ₃ gas, the carrier gas can use, for example, hydrogen (H ₂ ) gas, nitrogen (N ₂ ) gas, and a mixed gas thereof, and the dopant gas is For example, silane gas can be used.

For example, a source gas (eg, NH ₃ gas) containing a group V element is supplied from the first gas supply unit 11a, and a source gas (eg, trimethylgallium gas) containing a group III element is supplied from the second gas supply unit 11b. The carrier gas (for example, hydrogen gas) is supplied from the third gas supply unit 11c. The dopant gas can also be supplied from any gas supply unit, but may be supplied from both the first gas supply unit 11a and the second gas supply unit 11b, for example.

The reaction gas reaches the heated composite substrate 4 and reacts with each other, whereby the epitaxial layer 5 is formed on the GaN film 2 facing the gas flow path (source gas supply unit 11). The epitaxial layer 5 of the semiconductor element 10 according to the present embodiment includes the n ⁺ GaN layer 5a and the n ⁻ GaN layer 5b, which can be formed by appropriately adjusting the amount of each gas introduced.

For example, as growth conditions for the n ⁺ GaN layer 5a, the growth temperature is 1000 ° C. and the pressure is 100 kPa. At this time, the flow rate of the dopant gas is adjusted so that the carrier concentration in the n ⁺ GaN layer 5a is 1 × 10 ¹⁸ atoms / cm ³ or more and 5 × 10 ¹⁸ atoms / cm ³ or less. As growth conditions for the n ⁻ GaN layer 5b, for example, the growth temperature is set to 1100 ° C. lower than that of the n ⁺ GaN layer 5a, and the pressure is set to 100 kPa or more. At this time, the flow rate of the dopant gas is adjusted so that the carrier concentration in the n ⁻ GaN layer 5b is 2 × 10 ¹⁵ / cm ³ or more and 5 × 10 ¹⁶ / cm ³ or less (that is, the n ⁺ GaN layer 5a is formed). That flow is less than when growing).

  Here, in this step, the GaN film 2 facing the gas flow path is heated mainly by the radiant heat of the gas flow path, and the support substrate 1 facing the susceptor 15 is heated mainly by the radiant heat of the susceptor 15. The Since the composite substrate 4 has the bonding film 3 having low thermal conductivity between the support substrate 1 and the GaN film 2, it is difficult for the temperature uniformity between the support substrate 1 and the GaN film 2 to occur. Ideally, the radiant heat of the gas flow path and the radiant heat of the susceptor 15 coincide with each other. However, since the reaction gas passes through the gas flow path at a high speed, the GaN film actually exceeds the temperature of the support substrate 1. The temperature of 2 tends to be low.

  Due to the temperature environment as described above, the thermal expansion of the support substrate 1 becomes larger than the thermal expansion of the GaN film 2 in the composite substrate 4 when the epitaxial layer 5 is formed. As a result, the composite substrate 4 warps so as to be greatly recessed toward the susceptor 15 as shown in FIG.

  Since the conventional susceptor (see FIG. 11) does not have a curved shape like the susceptor 15, only the central portion of the composite substrate 4 comes into contact with the susceptor 15 and the outer peripheral portion from the susceptor 15 due to the large warp of the composite substrate 4. It will be in a state far away. In this case, only the central portion of the support substrate 1 is heated by heat conduction from the susceptor 15, and the outer peripheral portion of the support substrate 1 is heated by radiant heat from the susceptor 15. Is significantly reduced. For this reason, the in-plane uniformity of the temperature of the GaN film 2 is significantly reduced, and the in-plane uniformity of the dopant concentration of the epitaxial layer 5 formed thereon is also significantly reduced. This is presumably because the concentration of carriers introduced into the GaN film tends to greatly depend on the temperature of the growing GaN film.

On the other hand, the susceptor 15 provided in the MOCVD apparatus 20 has a curved surface 15 b that follows the warp of the composite substrate 4. In particular, when the susceptor 15 satisfies the distance D ₁ and the distance D ₂ set based on the warp of the composite substrate 4, the arrangement state of the susceptor 15 and the composite substrate 4 in this process is as shown in FIG. in, it can be the distance D ₃ between the susceptor 15 located immediately below the central portion of the composite substrate 4, the distance D ₄ between the susceptor 15 located immediately below the outer peripheral portion of the composite substrate 4 and the substantially coincide . That is, the distance between the composite substrate 4 and the curved surface 15b can be kept constant in the plane. Thereby, the in-plane uniformity of the temperature of the GaN film 2 is improved as compared with the conventional case, and the in-plane uniformity of the carrier concentration of the epitaxial layer 5 formed thereon is also improved.

  Then, as shown in FIG. 9, after the desired epitaxial layer 5 is formed, this process is terminated by stopping the heating and introduction of the reaction gas. Note that the warpage of the composite substrate 4 is eliminated by the temperature of the composite substrate 4 decreasing after the end of this step. Through the above steps, the semiconductor element 10 shown in FIGS. 1 and 2 is manufactured.

<Semiconductor devices>
An example of a semiconductor device including the central region of the semiconductor element 10 will be described with reference to FIG. Here, a semiconductor device as an SBD will be described.

Referring to FIG. 10, a semiconductor device 100 includes a composite substrate 104 in which a support substrate 101 and a GaN film 102 are bonded together through a bonding film 103, and n ⁺ GaN layers 105a and n ⁻ formed on the composite substrate 104. An epitaxial layer 105 composed of the GaN layer 105b, a first electrode 106 formed on the surface of the epitaxial layer 105, and a second electrode 107 formed on the surface of the support substrate 101 are provided.

The n ⁻ GaN layer 105b corresponds to the n ⁻ GaN layer 5b located in the central region 5bb, and each of the support substrate 101, the GaN film 102, the bonding film 103, and the n ⁺ GaN layer 105a is n located in the central region 5bb. ^- the support substrate 1, GaN film 2 located GaN layer 5b and the same position, corresponding to the bonding film 3 and the n ⁺ GaN layer 5a. The n ⁺ GaN layer 105a functions as a buffer layer, and the n ⁻ GaN layer 5b functions as a drift layer.

The first electrode 106 is a Schottky electrode that is in Schottky contact with the n ⁻ GaN layer 105b. As the first electrode 106, a conventionally known Schottky electrode can be used. For example, a Ni electrode, an Au electrode, a Pd electrode, an Rd electrode, or a Pt electrode can be used.

  The second electrode 107 is an ohmic electrode that is in ohmic contact with the support substrate 1. As the second electrode 107, a conventionally known ohmic electrode can be used. For example, a Ti electrode, an Al electrode, or a Ti / Al electrode can be used.

Such a semiconductor device 100 can be manufactured as follows, for example. First, the first electrode 106 and the second electrode 107 are formed on both surfaces (the surface of the n ⁻ GaN layer 105 b and the surface of the support substrate 101) of the semiconductor element 10. The formation method in particular of the 1st electrode 106 and the 2nd electrode 107 is not restrict | limited, For example, an electron beam evaporation method can be used. Next, the semiconductor element 10 is cut into a desired size so as to include a chip so as to include each formed electrode. Thereby, the semiconductor device 100 can be manufactured.

<Effect>
Conventionally, when the carrier concentration of the epitaxial layer formed on the composite substrate is set low, the carrier concentration is removed in the central region where the outer peripheral region from the outer peripheral edge of the epitaxial layer to the inner side corresponding to 10% of the diameter of the epitaxial layer is removed. There was a tendency that it was difficult to make the variation of the average value of ± 10% or less. In other words, when manufacturing a plurality of chips from a semiconductor element having a predetermined diameter, there are many regions where the carrier concentration does not satisfy a predetermined low concentration, so a chip (semiconductor device) that satisfies the desired semiconductor characteristics is planned. It means you can't get a number.

On the other hand, in the semiconductor element 10 including the composite substrate 4 described above, the average value of the carrier concentration in the central region 5bb of the n ⁻ GaN layer 5b is 4 × 10 ¹⁵ / cm ³ or more and 1.5 × 10 ¹⁶ / Despite the low value of cm ³ or less, the carrier concentration variation is ± 10% or less. This is because the semiconductor element 10 is manufactured using the MOCVD apparatus 20 including the susceptor 15 having the above-described characteristic shape. The shape of the susceptor 15 is the same as that of the composite substrate 4 in the epitaxial layer forming step. It is designed by predicting the warpage of the film by simulation or by measuring it in advance.

As described above, the semiconductor element 10 according to the present embodiment includes the n ⁻ GaN layer 5b having excellent carrier concentration uniformity as compared with the related art even though the average value of the carrier concentration is low. Can do. Therefore, more semiconductor devices 100 can be manufactured using one semiconductor element 10. Since the semiconductor device 100 can have the n ⁻ GaN layer 5b having a low carrier concentration average value of 4 × 10 ¹⁵ / cm ³ or more and 1.5 × 10 ¹⁶ / cm ³ or less, for example, It can be suitably used for SBD.

  Conventionally, the above-described variation in carrier concentration has tended to increase as the diameter of the epitaxial layer increases. In order to obtain an epitaxial layer having a large diameter, a composite substrate having a large diameter is required. However, since the composite substrate having a large diameter has a greater degree of warpage during the epitaxial layer forming process, the carrier concentration varies. This is because of a further increase.

  On the other hand, according to the semiconductor element 10 according to the present embodiment, the above-described average value and variation value of the carrier concentration can be maintained even if the diameter is in the range of 75 mm to 155 mm. Therefore, more semiconductor devices 100 can be manufactured using one semiconductor element 10.

  Conventionally, the above-described variation in carrier concentration has tended to increase as the thickness of the epitaxial layer increases. On the other hand, according to the semiconductor element 10 according to the present embodiment, the above-described average value and variation value of the carrier concentration are maintained even when the epitaxial layer has a relatively large thickness of 1 μm to 20 μm. be able to.

  Further, although silicon dioxide is excellent in the bondability between the support substrate 1 and the GaN film 2, it has a tendency to have a particularly low thermal conductivity. For this reason, when the bonding film containing silicon dioxide is used, it is estimated that the warpage of the composite substrate becomes larger. However, according to the semiconductor element 10 according to the present embodiment, even when the bonding film 3 contains silicon dioxide, the above-described average value and variation value of the dopant concentration can be maintained. The composite substrate 4 having the bonding film 3 containing silicon dioxide is excellent in that it can have high bonding strength.

<Example 1>
A composite substrate was produced as follows. First, a mullite substrate having a diameter of 100 mm and a thickness of 0.5 mm was prepared as a supporting substrate, and a GaN substrate made of GaN single crystal having a diameter of 155 mm was prepared as a group III nitride film. Next, a bonding film made of silicon dioxide was formed on each of one main surface of the mullite substrate and one main surface of the GaN substrate by sputtering. Then, the mullite substrate and the GaN substrate were bonded together by raising the temperature to about 800 ° C. with these bonding films in contact with each other. Then, the GaN substrate was cut using a wire saw so that GaN having a thickness of 0.1 mm remained on the bonding film.

As a result, a composite substrate including a mullite substrate (support substrate), a GaN film (group III nitride film), and a SiO ₂ film interposed between the mullite substrate and the GaN film was manufactured. The thickness of the SiO ₂ film was 1 μm.

Next, the composite substrate was placed on the susceptor 15 of the CVD apparatus 20 shown in FIG. 3, and the RF coil 12 was heated to raise the temperature of the susceptor 15 to 1000 ° C. Then, trimethylgallium gas, NH ₃ gas, and silane gas were introduced as reaction gases, and an epitaxial formation step was performed by MOCVD.

Here, referring to FIG. 4, in the first embodiment, the diameter of the curved surface 15b of the susceptor 15 is 100 mm, and the protruding support surface 15a is located at a part of the outer peripheral end. Before heating, the distance D ₁ between the central portion P of the curved surface 15b and the surface of the composite substrate placed on the support surface 15a is 600 μm, and the distance D ₂ that is the length of the counterbore side surface 15c is 200 μm. Met. These distances were set by observing the degree of warpage of the composite substrate in advance when the same composite substrate was subjected to the epitaxial formation step.

In this step, an n ⁺ GaN layer as a buffer layer and an n ⁻ GaN layer as a drift layer were formed. Regarding each formation condition, the dopant concentration and thickness of the buffer layer are 1.0 × 10 ¹⁸ atoms / cm ³ and 1 μm, and the dopant concentration and thickness of the drift layer are 6.0 × 10 ¹⁵ atoms / cm 2. It was set to be cm ³ and 7μm.

  As a result, a semiconductor element having a diameter of 100 mm, in which an epitaxial layer composed of a buffer layer and a drift layer was formed on the GaN film of the composite substrate, was manufactured.

<Comparative Example 1>
A semiconductor element was manufactured by the same method as in Example 1 except that the susceptor 30 having the shape shown in FIG. 11 was used instead of the susceptor 15. The susceptor 30 having such a shape has been conventionally used, and the composite substrate disposed on the susceptor 30 is accommodated in the recess of the susceptor 30.

<Characteristic evaluation>
About the manufactured semiconductor element of Example 1, the carrier concentration of the drift layer was measured, and the average value and the variation were calculated. Specifically, one outer peripheral edge, an outer peripheral edge at a position opposite to the outer peripheral edge in the same plane of the surface of the drift layer, and an imaginary straight line connecting these two outer peripheral edges are equally spaced 7 The dopant concentration at one point was measured by SIMS. The result is shown in FIG.

  Referring to FIG. 12, it was confirmed that the drift layer included in the semiconductor element of Example 1 had high in-plane uniformity. Further, the variation in carrier concentration at nine points included in the central region of the drift layer was ± 10% or less. On the other hand, when the same measurement was performed on the drift layer included in the semiconductor element of Comparative Example 1, the carrier concentration variation at 9 points was ± 36%.

  The embodiments and examples disclosed herein are illustrative in all respects and should not be construed as being restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1,101 Support substrate 2,102 GaN film 3,103 Bonding film 4,104 Composite substrate 5,105 Epitaxial layer 5a, 105an ⁺ GaN layer 5b, 105b n ^- GaN layer 5bb Central region 10 Semiconductor element 20 MOCVD apparatus 11 Raw material Gas supply unit 11a First gas supply unit 11b Second gas supply unit 11c Third gas supply unit 12 Heater 13 Rotating shaft 14 Reaction vessel 15, 30 Susceptor 15a Support surface 15b Curved surface 15c Counterbore side 100 Semiconductor device 106 First Electrode 107 Second electrode.

Claims (5)

A composite substrate including a support substrate, a group III nitride film, and a bonding film interposed between the support substrate and the group III nitride film;
An epitaxial layer provided on the group III nitride film,
The epitaxial layer is composed of one or more semiconductor layers,
The dopant of the epitaxial layer is silicon,
At least one of the semiconductor layers has an average value of the carrier concentration of 4 × 10 ¹⁵ atoms / cm ³ or more in the central region where the outer peripheral region from the outer peripheral edge to the inner side of the distance corresponding to 10% of the diameter is removed. 5 × 10 ¹⁶ / cm ³ or less, and the variation of the carrier concentration is ± 10% or less.   The semiconductor element according to claim 1, wherein the semiconductor element has a diameter of 75 mm or more and 155 mm or less.   The semiconductor element according to claim 1, wherein the layer has a thickness of 1 μm to 20 μm.   The semiconductor element according to claim 1, wherein the bonding film includes silicon dioxide. A semiconductor device using the semiconductor element according to any one of claims 1 to 4,
A semiconductor device comprising the central region of the semiconductor element as a composite substrate.

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