JP2004153102A - Multilayer structure of semiconductor material and its producing process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayer structure of a semiconductor material including a thick film semiconductor layer having high crystallinity, especially a multilayer structure of a GaN based material, and its producing process. <P>SOLUTION: The multilayer structure of a semiconductor material comprises a substrate 1, an insulating thin film 2 deposited on the surface 1a of the substrate 1 with voids 3 being distributed up to the surface 1a of the substrate 1, a buffer layer 4 of a first semiconductor material partially filling the voids 3, and a thick film 5 of a second semiconductor material of different kind from the first semiconductor material deposited to bury the insulating thin film 2 entirely including the remaining part 3a of the cavity 3. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a laminated structure of a semiconductor material and a method of manufacturing the same, and more particularly, to a laminated structure of a semiconductor material having a high-quality, thick semiconductor film having a flat surface, particularly a nitride having a GaN-based material as a semiconductor. The present invention relates to a laminated structure of a semiconductor material that is a compound III-V compound semiconductor and a method of manufacturing the same.
[0002]
[Prior art]
For example, a field effect transistor (FET) using a GaN-based semiconductor material has attracted attention as an FET which has excellent heat resistance and operates at a high withstand voltage. When fabricating such a GaN-based FET, it is necessary to grow a predetermined GaN-based semiconductor on a substrate.
[0003]
Generally, when manufacturing an optical element or an electronic device using a semiconductor material, prior to device processing, a starting material having a predetermined laminated structure is obtained by sequentially laminating a predetermined semiconductor material on a semiconductor substrate by an epitaxial crystal growth method. It is made.
However, since the GaN-based material has a melting point exceeding 2000 ° C. and a vapor pressure at the melting point also exceeding 10 GPa, it is extremely difficult to directly produce a single crystal as a substrate for crystal growth. Therefore, when growing a GaN-based material in a crystal, a substrate of a different material must be used.
[0004]
However, there is no substrate material whose lattice constant matches that of the GaN-based material. Therefore, for example, when GaN is crystal-grown, usually, a buffer layer is crystal-grown in advance on the surface of the substrate, and the target GaN is crystal-grown on the buffer layer. The method of relaxation is adopted.
In this case, as the substrate, for example, a sapphire (Al ₂ O ₃ ) substrate, a SiC substrate, a Si substrate, a GaAs substrate, a GaP substrate, or the like is used. Of these, the sapphire substrate is most often used. . However, the lattice mismatch between the sapphire substrate and GaN is 20% or more.
[0005]
Not only the GaN-based semiconductor material but also the above-described problem occurs when the lattice constants of the substrate and the semiconductor material grown thereon are different from each other.
In order to manufacture a practical semiconductor device, the thickness of a layer of a semiconductor material grown on a substrate needs to be at least 100 nm or more. However, when the difference between the lattice constant of the material of the substrate and the lattice constant of the semiconductor material grown on the substrate is larger than 0.5%, the thickness of the layer of the semiconductor material to be grown is 100 nm. If the number exceeds the range, there is a problem that the crystal has many defects.
[0006]
Therefore, when a thick GaN layer is formed on this sapphire substrate, crystal growth has conventionally been performed by the following two methods.
The first method is to form a buffer layer made of AlN on a sapphire substrate in advance and then grow GaN thick crystal thereon.
Specifically, trimethylaluminum (TMA) and ammonia (NH ₃ ) are used on a sapphire substrate by a metal organic chemical vapor deposition (MOCVD) method, hydrogen is used as a carrier gas, and a thickness of 50 nm is formed at 800 ° C. About AlN is grown, and then the growth temperature is raised to about 1100 ° C., and GaN is crystal-grown using trimethylgallium (TMG) and ammonia (NH ₃ ) to form a GaN thick film having a flat surface. The film is formed.
[0007]
The second method is a method in which GaN is grown on a sapphire substrate in advance to serve as a buffer layer, on which GaN is grown in a thick crystal.
Specifically, GaN is grown at a low temperature of about 500 to 600 ° C. using TMG and NH ₃ and hydrogen as a carrier gas to form a buffer layer with a thickness of about 10 to 20 nm. Is heated to about 1000 ° C. to grow GaN crystals, thereby forming a thick film having a flat surface.
[0008]
When a GaN buffer layer is formed by a gas source molecular beam epitaxy method (GSMBE method) and a GaN thick film is formed thereon, metallic Ga and plasma-converted nitrogen are formed on the substrate. Using a source, a buffer layer of GaN is formed at a low temperature of 500 to 550 ° C., and the GaN crystal is grown by raising the growth temperature to about 800 ° C. to form a thick GaN film. .
[0009]
A third method is a method of forming a SiO ₂ mask having an opening on a substrate such as sapphire and then growing GaN thereon by MOCVD or the like (for example, see Patent Document 1).
[0010]
[Patent Document 1]
JP 2000-21789 A
[Problems to be solved by the invention]
However, for example, when a GaN thick film is formed using a Si substrate, even if the buffer layer is made of AlN or GaN, if the growth temperature is as low as about 500 to 600 ° C., Is about 10 to 20 nm, the buffer layer grows not in layers but in islands, and the Si substrate is exposed between the islands. It is practically impossible to grow high-quality GaN on the substrate in such a state.
[0012]
When the thickness of the buffer layer is increased, the island-like crystals disappear and the entire buffer layer can be formed. However, since the surface of the buffer layer at that time is not flat, the surface of the GaN thick film to be crystal-grown thereon is no longer flat.
In addition, when GaN is grown to a thickness of 1 μm or more, there is a problem that cracks occur in the thick film.
[0013]
Further, there is a problem that the GaN crystal in the formed thick film is not of high quality. This is because, during the formation of the buffer layer, threading dislocations (defects) that extend substantially perpendicular to the film thickness direction are generated in the buffer layer due to lattice mismatch with the substrate, and the threading dislocations remain on the buffer layer as it is. This is because it propagates to the formed GaN crystal.
When such defects occur at a high dislocation density in a formed GaN thick film, when this stacked structure is processed to produce, for example, a GaN-based FET, the withstand voltage characteristics of the FET are deteriorated, and an extremely low electric field is generated. It may cause dielectric breakdown at high strength.
[0014]
However, when a mask having a predetermined opening is formed on a substrate and a GaN-based semiconductor material is grown thereon, as described in Patent Document 1 described above, the growth layer must maintain high quality. However, the above-described problem is less likely to occur.
However, this method requires a lithography operation to form an opening in the mask, and the semiconductor material layer grown on the mask has few dislocations, but the semiconductor material grown directly on the mask opening. In this layer, a large number of dislocations are generated, and the size of the opening cannot be reduced to a predetermined area or less. Therefore, the area that can be effectively used as a device is limited.
[0015]
The present invention solves the above-described problems as described using a GaN-based material as an example. Even in the case of a semiconductor crystal having a large lattice mismatch with a substrate, the crystallinity is a single crystal and high quality. It is another object of the present invention to provide a laminated structure of a semiconductor material in which cracks are unlikely to occur even when the film thickness is increased and the surface of the thick film is flat and mirror-finished, and a method of manufacturing the same.
[0016]
In particular, it is an object of the present invention to provide a laminated structure of a semiconductor material, which is preferably a nitride III-V compound semiconductor, especially a GaN-based material, and a method of manufacturing the same.
[0017]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention,
A substrate, an insulating thin film formed on the surface of the substrate and having holes distributed to the surface of the substrate, and a layer made of a semiconductor material that covers the substrate and the insulating thin film. A laminated structure of a semiconductor material is provided.
[0018]
In the present invention,
Forming on the substrate an insulating thin film in which holes reaching the surface of the substrate are distributed, and
A method of manufacturing a laminated structure of a semiconductor material, comprising a step of epitaxially growing a semiconductor material in a hole and a surface of the insulating thin film by a selective lateral growth method using the insulating thin film as a mask. Is done.
[0019]
In addition, the above-mentioned pores have a size of an atomic order of about 5 to 10 nm in diameter.
Preferably, a step (hereinafter referred to as a first step) of forming, on the substrate, an insulating thin film in which holes reaching the surface of the substrate are distributed;
A step of epitaxially growing a first semiconductor material in the hole and partially filling the hole with the first semiconductor material (hereinafter, referred to as a second step);
A step of epitaxially growing a second semiconductor material different from the first semiconductor material by a selective lateral growth method using the insulating thin film as a mask (hereinafter, referred to as a third step). A method for manufacturing a laminated structure of a semiconductor material is provided.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows an example of the laminated structure of the present invention.
In this laminated structure, first, an insulating thin film 2 is formed on a substrate 1. The insulating thin film 2 has fine holes 3 extending from the surface 2 a of the insulating thin film 2 to the surface 1 a of the substrate 1. The diameter of the holes 3 is on the order of 5 to 10 nm in atomic order.
[0021]
The holes 3 are filled with a semiconductor material epitaxially grown on the surface 1 a of the substrate exposed in the holes 3. In this case, it is preferable that the first semiconductor material is partially filled in the holes 3 by growing a first semiconductor material, which will be described later, in this hole 3 by an epitaxial growth method. Yes, and the rest of the description will be in terms of this method.
[0022]
The first semiconductor material 4 fills the holes 3 from the surface 1a of the substrate, but does not fill the whole holes 3 but partially fills the holes 3. Is in an unfilled state. The first semiconductor material 4 partially filled in such a state functions as a buffer layer when a target thick film 5 is formed.
[0023]
The remaining unfilled portion 3a of the hole 3 existing on the upper part of the buffer layer 4 and the surface 2a of the insulating thin film 2 are formed in the second step by crystal growth by selective lateral growth described later. 2 buried in a thick film 5 made of a semiconductor material.
In this laminated structure, as described later, the thick film 5 is formed on the buffer layer 4 by using the insulating thin film 2 as a mask and selectively laterally growing (ELO) which is one of the epitaxial crystal growth methods. ) Method, and the vacancies 3 are fine pores on the atomic order. Therefore, the defects that propagate from the buffer layer 4 in the vertical direction are also extremely fine, so that the whole is composed of a high-quality single crystal.
[0024]
This laminated structure is manufactured through the following steps. The case where the semiconductor material is a GaN-based material will be described.
First, an insulating thin film 2 is formed on a substrate 1 as shown in FIG.
Here, for example, a Si substrate can be used as the substrate 1. Further, a sapphire substrate, a GaAs substrate, a GaP substrate, a SiC substrate, or a substrate made of a material such as ZnO, AlN, ZrB ₂ , NdGaO ₃ , LiGaO ₃ , and ScAlMgO ₄ may be used. Whichever substrate is used, it is possible to form a thick film 5 of a GaN material with high crystallinity.
[0025]
The insulating thin film 2 may be anything as long as it has an insulating property. For example, an SiO ₂ thin film, a SiN thin film, a TiN thin film, a TaO _x thin film, an Al ₂ O ₃ thin film, an AlN thin film, MoOx, WOx, TiOx And a metal oxide thin film as described above. When a Si substrate is used, a SiO ₂ thin film is preferable.
The insulating thin film 2 is formed by, for example, the MOCVD method. It is preferable to control the film thickness to about 2 to 100 nm. In such a case, for example, by appropriately selecting film forming conditions such as a film forming time, a film forming gas flow rate, and a film forming temperature, the formed insulating thin film is randomly distributed in the plane, and the diameter is atomic. The holes 3 of the order are naturally formed.
[0026]
Note that, depending on the film forming conditions, the holes 3 may not be formed in the insulating thin film 2. Considering such a situation, it is preferable to intentionally form the holes 3 by performing the following processing on the formed insulating thin film 2.
For example, the insulating thin film 2 when it is SiO ₂ thin film, first, as shown in FIG. 3, for forming the SiO ₂ thin film 2 on the surface of the substrate 1.
[0027]
Then, as shown in FIG. 4, metal Ga or metal In is directly attached to the surface of the SiO ₂ thin film 2. Then, the entire substrate is heated to a temperature of about 600 to 1000 ° C. As a result, the occurrence is a redox reaction between the SiO ₂ and metal Ga (or metal an In), SiO _2, since converted More SiO ₂ of high volatility, SiO ₂ of the high volatility desorbs As a result, as shown in FIG. 5, the trace is left as a hole 3 having the size of the atomic order of metal Ga (or metal In).
[0028]
In this case, it is preferable that the adhesion amounts of the metal Ga and the metal In are each set to a thickness of 10 atomic layers or less. If the thickness is more than 10 atomic layers, metal Ga or metal In becomes a drop (liquid), which is inconvenient.
In the second step, for example, the MOCVD method is applied to the intermediate obtained in the first step, and the first semiconductor material is selectively grown using the insulating thin film (SiO ₂ thin film) 2 as a mask. To produce an intermediate.
[0029]
The first semiconductor material is selectively nucleated from the surface 1a of the substrate and sequentially deposited in the holes 3, and a buffer layer 4 made of the first semiconductor material is formed in the holes. You.
In this case, by properly controlling the growth conditions, especially the growth time, the voids 3 are not completely filled with the first semiconductor material, but the space 3a remains above the voids 3. The buffer layer 4 is formed with a thickness. It is preferable to form the buffer layer 4 so that the space portion 3a of about 5% to 50% of the depth of the whole hole is left.
[0030]
The reason is that it is possible to carry out the selective lateral growth of the second semiconductor material in the next third step.
Here, the first semiconductor material used is appropriately selected in relation to the second semiconductor material used in the third step. For example, when the second semiconductor material used in the third step is GaN, , using _{AlGaN, Al x in y GaN,} Al x in y GaNAs m, Al x GaNP n As m, Al x in y GaNP n As m (0 ≦ y, y, m, n ≦ 1) and the like alone Can be. In this case, the buffer layer 4 becomes one layer.
[0031]
Further, the buffer layer 4 may have a multilayer structure by stacking a plurality of GaN-based materials. For _{example, AlGaN / GaN, AlINGaN / InGaN} , Al x In y GaN / Al x In y GaNAs m, Al x In y GaNAs m / Al x In y GaPAs m (0 ≦ y, y, m ≦ 1) and sequentially They may be stacked to form a buffer layer.
The crystal growth (filling) of the first semiconductor material into the holes 3 is preferably performed at a high growth temperature. Specifically, the growth temperature is preferably set to 600 ° C. or higher.
[0032]
The reason is that the quality of the grown crystal becomes high, so that the thick film formed in the third step can also be made high quality, and the migration of the first semiconductor material on the substrate surface 1a in the hole. Is promoted, so that the crystal growth of the semiconductor material can be realized uniformly without causing unevenness on the entire surface 1a of the substrate.
When the above-mentioned buffer layer is formed of AlGaN, several atomic layers of metal Al are attached to the substrate surface 1a in the holes before introducing the N source (NH ₃ ), and then TMG, TAM, and NH ₃ are added. Al _x Ga _1-x N (0 <x ≦ 1) may be introduced.
[0033]
Prior to the introduction of NH ₃ , metal Ga is attached to the surface 1 a in the pores, and then TMG, TMA, and NH ₃ are introduced to make Al _x Ga _1-x N (0 ≦ x <1). Is also good.
Even when a third step described later is performed using these buffer layers, the surface of the formed thick film made of the second semiconductor material becomes flat and mirror-finished.
[0034]
Further, it is preferable that the growth temperature during the crystal growth of Al _x Ga ₁ -xN (0 ≦ x ≦ 1) be set to 650 to 900 ° C. This is because the buffer layer can be uniformly formed on the substrate surface 1a.
In that _case, when the Al composition in Al x _{Ga 1-x} N as low as 0 ≦ x ≦ 0.2 is optimal to set the growth temperature to 650 to 750 ° C.. By increasing the growth temperature as the Al composition becomes higher (up to a maximum of 900 ° C.), the buffer layer can be formed uniformly.
[0035]
In the third step, a crystal of a second semiconductor material is grown on the intermediate of FIG. 6 obtained in the second step, for example, by applying the MOCVD method, and the laminated structure of the present invention as shown in FIG. To manufacture.
In the third step, first, the crystal growth of the second semiconductor material proceeds on the buffer layer 4, and the upper space portion 3a in the hole is buried with the second semiconductor material. After the completion of the filling of the holes, the selective lateral growth proceeds on the surface 2a of the insulating thin film 2, and the thick film 5 made of the second semiconductor material is formed.
[0036]
In the thick film 5, threading dislocations are propagated at a position located almost directly above the buffer layer 4 in the hole 3. On the other hand, the propagation of threading dislocations is suppressed at a position above the surface 2a of the insulating thin film 2, and the crystal grown there is of high quality.
Since the pores 3 are ultrafine pores having a diameter on the order of atoms, it can be said that the ratio of the entire diameter area of the pores 3 to the crystal growth surface is extremely small.
[0037]
Therefore, the dislocation density of threading dislocations in the formed thick film 5 is extremely low, and the crystallinity of the thick film 5 is of high quality as a whole.
The second semiconductor material to be used is selected in relation to an optical element or an electronic device to be manufactured via the laminated structure of the present invention. For example, GaN is used for the purpose of manufacturing a GaN-based device. Can be.
[0038]
Then, for example, the first semiconductor material as described above is selected in relation to the second semiconductor material.
Although the above description has been made with reference to GaN-based materials, the semiconductor material used in the present invention is not limited to this, and other nitride-based III-V compound semiconductors such as AlGaN, AlInGaN, and AlInGaNAsP can be used. You may.
[0039]
【Example】
First, a Si substrate whose surface was chemically etched with hydrofluoric acid was prepared. The Si substrate was set in an MOCVD apparatus, and operated at a substrate temperature of 400 ° C. under the conditions that SiH ₄ and O ₂ were supplied at a flow rate of 15 sccm and 30 sccm, respectively, to form a plasma, and a 100 nm thick SiO ₂ thin film was formed.
[0040]
In another experiment, a SiO ₂ thin film was formed under the same conditions, and its surface and cross section were observed by SEM. As a result, fine holes having a diameter of 5 to 10 nm were formed in the thin film up to the surface of the Si substrate. And the integrated value of the diameter area of these fine pores was about 10% with respect to the whole area of the SiO ₂ thin film.
The inside of the apparatus was evacuated to a degree of vacuum of 5 × 10 ⁻⁶ Pa or less by a turbo pump, then the degree of vacuum was increased to 1 Pa, and the substrate temperature was raised to 800 ° C.
[0041]
Then, while rotating the substrate at 900 rpm, the substrate surface was coated with TMG (58 nmol / min) as the Ga source, TMA (58 nmol / min) as the Al source, and NH ₃ (12 l / min) as the N source for 4 minutes. Supplied. This supply amount corresponds to the amount of crystal growth of AlGaN having a thickness of 50 nm.
Then, the substrate temperature was raised to 1300 ° C., supply of TMA was stopped, and GaN was grown for 15 minutes to form a thick film having a thickness of 500 nm.
[0042]
The substrate was taken out of the apparatus and the GaN thick film was visually observed. The surface was extremely flat and had a metallic glossy mirror surface.
When the optical characteristics of the GaN thick film were examined by photoluminescence (PL), the emission intensity at the band edge (365 nm) was remarkably strong, and emission at a deep level was hardly observed. Thus, it was confirmed that the GaN crystal in the GaN thick film was of high quality.
[0043]
【The invention's effect】
As apparent from the above description, according to the present invention, it is possible to manufacture a laminated structure having a high-quality and thick semiconductor layer. In particular, by applying the present invention to a GaN-based material, a high-quality GaN layer can be formed in a thick film, and thus, for example, it is possible to manufacture an electronic device that operates with high withstand voltage and low on-resistance. it can.
[0044]
Further, since the diameter of pores in the insulating thin film can be reduced to several tens of nm or less, in the formed thick film, the area that can be effectively used as a device is less likely to be restricted, and as described in Patent Document 1. The effect of eliminating the need for a lithography operation for a simple mask is obtained.
[Brief description of the drawings]
FIG. 1 is a sectional view showing an example of a laminated structure of the present invention.
FIG. 2 is a cross-sectional view showing a state where an insulating thin film is formed on a substrate.
FIG. 3 is a cross-sectional view showing a state where a SiO ₂ thin film is formed on a substrate.
FIG. 4 is a sectional view showing a state in which a metal is directly attached to an insulating thin film.
FIG. 5 is a cross-sectional view showing a state where holes are formed in the SiO ₂ thin film by heating the intermediate of FIG. 4;
FIG. 6 is a cross-sectional view showing a state in which holes of a SiO ₂ thin film are partially filled with a first semiconductor material.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Substrate 1a Surface 1 of substrate 1 Insulating thin film 2a Surface of insulating thin film 2 Hole 3a Portion of remaining hole 4 Buffer layer (first semiconductor material)
5 Thick film (second semiconductor material)

Claims (12)

A substrate, an insulating thin film formed on the surface of the substrate and having holes distributed to the surface of the substrate, and a layer made of a semiconductor material that covers the substrate and the insulating thin film. A laminated structure of a semiconductor material characterized by the above-mentioned. 2. The laminated structure according to claim 1, wherein said insulating thin film is made of an oxide. _3. The laminated structure according to claim ₂ , wherein the insulating thin film is made of SiO ₂ , Al ₂ O ₃ , or TaOx. The laminated structure of a semiconductor material according to claim 2, wherein the vacancy is a trace formed by reducing a part of the insulating thin film and removing the part. The laminated structure of a semiconductor material according to claim 4, wherein the substance that reduces a part of the insulating thin film is a metal atom. The laminated structure of a semiconductor material according to claim 5, wherein the metal atom is In or Ga. Forming on the substrate an insulating thin film in which holes reaching the surface of the substrate are distributed, and
A method for manufacturing a laminated structure of a semiconductor material, comprising a step of epitaxially growing a semiconductor material in holes and on a surface of the insulating thin film by a selective lateral growth method using the insulating thin film as a mask. After forming an insulating thin film on the substrate, a substance for reducing the insulating thin film is partially deposited on the surface of the insulating thin film, and then the whole is heated to insulate the portion where the substance is deposited. 8. The method according to claim 7, further comprising the step of reducing the thin film and desorbing the reaction product to form voids. 9. The method according to claim 8, wherein the substance that reduces the insulating thin film is a metal atom. 10. The method according to claim 9, wherein the metal atom is In or Ga. 11. The method according to claim 9, wherein the deposition thickness of the metal atoms is 10 atomic layers or less. 8. The method according to claim 7, wherein the formation of the insulating thin film, the formation of the holes, and the epitaxial growth of the semiconductor material are all performed using the same apparatus.

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