JP2007126315A - Semiconductor crystal manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor crystal manufacturing method for manufacturing a high quality group III nitride-based compound semiconductor crystal at a low cost by a flux method. <P>SOLUTION: After an n-type GaN single crystal 20 is grown to have a sufficient thickness, e.g., about 500 μm or more by the flux method, the temperature of a crucible is successively maintained at 850-880°C until a protective film and a silicon substrate 11 are dissolved completely in a flux. Thereafter, the temperature of a reaction chamber is lowered to a temperature of ≤100°C in a nitrogen gas atmosphere. However, at least one part of the protective film or the silicon substrate 11 may be dissolved in the growth process of the GaN single crystal 20. The manner of parallel simultaneous progress of these processes can be adequately controlled, for example, by the film-forming mode of the protective film. In the case that the silicon substrate 11 dissolved in the flux is added in a growing GaN single crystal 20 as an n-type additive (si), an n-type semiconductor crystal is obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a flux method in which a semiconductor crystal made of a group III nitride compound semiconductor is crystal-grown using a flux.
This method is effective for reducing the generation density of dislocations and cracks in the semiconductor crystal and reducing the production cost of the semiconductor crystal.

As conventional techniques for crystal growth of a semiconductor crystal made of a group III nitride compound semiconductor by a flux method, for example, those disclosed in Patent Documents 1 to 5 below are known.
In these conventional manufacturing methods, a template in which a semiconductor layer such as a buffer layer is stacked on a sapphire substrate, a GaN single crystal free-standing substrate, or the like is usually used as a base substrate (seed crystal).
Japanese Patent Laid-Open No. 11-060394 JP 2001-058900 A JP 2001-064097 A JP 2004-292286 A Japanese Patent Laid-Open No. 2004-300024

  However, when a template such as that described above is used, there is a large difference in thermal expansion coefficient between the desired semiconductor crystal made of a group III nitride compound semiconductor and the sapphire substrate. When a semiconductor crystal is taken out from the reaction chamber, many cracks are generated in the crystal. For this reason, when the above template is used as the base substrate, it is difficult to obtain a high-quality semiconductor crystal having a film thickness of, for example, 400 μm or more.

  In addition, when a GaN single crystal free-standing substrate is used as a base substrate, since there is no difference in thermal expansion coefficient as described above, it is possible to suppress the occurrence of cracks in a desired semiconductor crystal, but the GaN single crystal free-standing substrate is Since it is expensive, it is difficult to suppress the production cost.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to produce a high-quality semiconductor crystal at a low cost in the flux method.

In order to solve the above problems, the following means are effective.
That is, the first means of the present invention is a flux method in which a semiconductor crystal made of a group III nitride compound semiconductor is crystal-grown using a flux. The soluble material is dissolved in the above flux, and the soluble material is dissolved in the above-mentioned flux in the vicinity of the growth temperature of the semiconductor crystal during the crystal growth process of the semiconductor crystal or after the crystal growth process of the semiconductor crystal. .

However, from the viewpoint of production cost, it is desirable to use a material that is cheaper than a GaN single crystal free-standing substrate, and a material that is relatively easily dissolved in hot alkali. Such a material can be arbitrarily selected from known seed crystal materials. More specifically, for example, silicon (Si) or GaAs can be used as the above-mentioned soluble material, but other known soluble materials may be used.
Moreover, although it is disadvantageous in terms of production cost, it is of course possible to use a GaN substrate. In that case, it is preferable to use a self-standing GaN substrate having a dislocation density of 1 × 10 ⁶ [cm ⁻² ] or more and 1 × 10 ¹⁰ [cm ⁻² ] or less. If this dislocation density is too low, the free-standing GaN substrate will be difficult to dissolve in the above-mentioned flux, and if this dislocation density is too high, the crystal quality of the semiconductor that grows on the free-standing GaN substrate will be poor.

  The soluble material may be left undissolved at least until the semiconductor crystal grows to a thickness that can stably exist alone as a seed crystal for crystal growth. Therefore, it is most desirable in terms of production efficiency that the above-mentioned soluble material is almost disappeared by dissolution in the flux during the crystal growth period until a semiconductor crystal having a desired thickness is formed. Moreover, the state without such excess and deficiency can be produced also by setting various conditions, such as the thickness of said soluble material, suitably.

The aforementioned Group III nitride compound semiconductor, binary, ternary, or quaternary _{"Al 1-xy Ga y In x} N; 0 ≦ x ≦ 1,0 ≦ y ≦ 1,0 ≦ x + y Semiconductors having an arbitrary mixed crystal ratio represented by the general formula ≦ 1 ”are included, and semiconductors to which p-type or n-type impurities are added are also included in these“ Group III nitride compound semiconductors ”. Category.

Furthermore, the second means of the present invention is that, in the first means, an impurity for controlling a carrier concentration in the semiconductor crystal is included in at least a part of the soluble material. However, as such an impurity, an n-type impurity, a p-type impurity, or a soluble material having both types of impurities may be used. Moreover, you may form the whole said soluble material only with those impurities.
A third means of the present invention is to use silicon (Si) as the soluble material in the first or second means.

According to a fourth means of the present invention, in any one of the first to third means, a protective film is formed on the exposed surface of the soluble material, and the thickness or the thickness of the protective film is formed. The film pattern controls the time or dissolution rate at which the soluble material is dissolved in the flux.
As such a protective film material, for example, aluminum nitride (AlN), tantalum (Ta), or the like can be used. These protective films can be formed by a known method such as crystal growth, vacuum deposition, or sputtering.

The film formation pattern can be formed using a known technique such as photolithography or etching. In addition, the dissolution time can be advanced as the thickness of these protective films decreases, and the dissolution rate should be set higher as the exposed area of the soluble material with respect to the flux becomes wider. Can do.
By the above means of the present invention, the above-mentioned problem can be effectively or rationally solved.

The effects obtained by the above-described means of the present invention are as follows.
That is, according to the first means of the present invention, the soluble material is dissolved in the flux during the crystal growth step of the semiconductor crystal or near the growth temperature of the semiconductor crystal after the crystal growth step of the semiconductor crystal. The stress does not act between the base substrate and the semiconductor crystal due to the temperature lowering action when taking out the desired semiconductor crystal from the reaction chamber. Therefore, according to the first means of the present invention, the generation density of cracks in the semiconductor crystal can be greatly reduced as compared with the conventional case.
Further, as the above-mentioned soluble material, for example, a relatively inexpensive material such as silicon (Si) can be used. Therefore, according to the first means of the present invention, the GaN single crystal free-standing substrate is used as the base substrate. The production cost can be kept lower than in the conventional case used as the above.

In addition, according to the second means of the present invention, the phenomenon that the soluble material is dissolved in the flux can be used as an impurity addition process. Therefore, when the impurity needs to be added, the addition of the impurity is performed. The processing need not be performed by other methods. At the same time, the necessary impurity material can be saved.
As such a soluble material, for example, silicon (Si; third means of the present invention) can be used.

According to the fourth means of the present invention, the dissolution of the soluble material is started from the time when the exposed surface of the soluble material comes into contact with the high-temperature flux, and the dissolution rate is the exposed surface. Therefore, by appropriately setting these conditions, it is possible to arbitrarily set the dissolution start time, the required dissolution time, the dissolution rate, and the like of the above-described soluble material. In addition, the time required for dissolving the above-mentioned soluble material can be arbitrarily adjusted by the type, thickness, flux temperature, etc. of the soluble material.
In addition, when the above-mentioned soluble material is used as an impurity added to a semiconductor crystal by using the second means of the present invention, the dissolution rate and the required time for dissolution of the above-mentioned soluble material are appropriately controlled. By doing so, the impurity concentration in the desired semiconductor crystal can be arbitrarily controlled.

In addition, as an alkali metal which comprises a flux, it is especially desirable to use sodium (Na).
Further, as the gas containing nitrogen (N), nitrogen gas (N ₂ ), ammonia gas (NH ₃ ), or a mixed gas of these gases can be used.

  In the above-described composition formula of the group III nitride compound semiconductor constituting the desired semiconductor crystal, at least a part of the group III elements (Al, Ga, In) is boron (B) or thallium ( Tl) or the like, or at least part of nitrogen (N) can be replaced with phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), or the like.

  Moreover, as said p-type impurity (acceptor), well-known p-type impurities, such as alkaline-earth metal (For example, magnesium (Mg), calcium (Ca), etc.), for example can be added. As the n-type impurity (donor), for example, known n-type impurities such as silicon (Si), sulfur (S), selenium (Se), tellurium (Te), or germanium (Ge) are used. Can be added. Moreover, two or more elements may be added simultaneously to these impurities (acceptor or donor), or both types (p-type and n-type) may be added simultaneously. These impurities can be added to a desired semiconductor crystal, for example, by being previously melted in a flux.

Moreover, as a crystal growth apparatus to be used, any apparatus capable of performing the flux method may be used. For example, the apparatus described in Patent Documents 1 to 5 can be applied or applied. However, it is desirable that the temperature of the reaction chamber of the crystal growth apparatus when performing crystal growth according to the flux method can be arbitrarily controlled to rise and fall to about 1000 ° C. Further, it is desirable that the pressure in the reaction chamber can be arbitrarily controlled to increase or decrease to about 100 atm (about 1.0 × 10 ⁷ Pa). Moreover, it is desirable that the electric furnace, stainless steel container (reaction container), raw material gas tank, and piping of these crystal growth apparatuses are formed of, for example, a stainless steel (SUS) material, an alumina material, copper, or the like.

Hereinafter, the present invention will be described based on specific examples.
However, the embodiments of the present invention are not limited to the following examples.

1. Creation of Base Substrate Hereinafter, a procedure for creating the base substrate (template 10) used in the crystal growth process by the flux method will be described with reference to FIG.
(1) First, the protective film 15 is formed on the back surface of the silicon substrate 11 (the soluble material of the present application). The protective film 15 may be formed by laminating an AlN layer according to, for example, the MOVPE method, or an appropriate metal such as tantalum (Ta) may be formed using a sputtering apparatus or a vacuum evaporation apparatus. Anyway.

(2) Next, by crystal growth according to the MOVPE method, a buffer layer 12 made of AlGaN is laminated on a silicon substrate 11 having a thickness of about 400 μm, and a GaN layer 13 is further laminated thereon. This GaN layer 13 may be partially dissolved in the flux until the growth of the desired semiconductor crystal by the flux method is started. Therefore, the GaN layer 13 is laminated so as not to disappear at that time.
The template 10 (underlying substrate) can be manufactured by the above steps (1) and (2).

2. Configuration of Crystal Growth Device FIG. 2 is a configuration diagram of the crystal growth device according to the first embodiment. This crystal growth apparatus includes a raw material gas tank 21 for supplying nitrogen gas, a pressure regulator 22 for adjusting the pressure of the growth atmosphere, a leak valve 23, and an electric furnace 25 for performing crystal growth. The electric furnace 25, the piping connecting the raw material gas tank 21 and the electric furnace 25, etc. are made of stainless steel (SUS) or alumina material, copper, or the like.

A stainless steel container 24 (reaction chamber) is disposed inside the electric furnace 25, and a crucible 26 (reaction container) is set in the stainless steel container 24. The crucible 26 can be formed of, for example, boron nitride (BN) or alumina (Al ₂ O ₃ ).
The temperature in the electric furnace 25 can be arbitrarily controlled to rise and fall within a range of 1000 ° C. or less. The crystal atmosphere pressure in the stainless steel container 24 can be arbitrarily controlled by the pressure regulator 22 within a range of 1.0 × 10 ⁷ Pa or less.

3. Crystal Growth Process Hereinafter, a crystal growth process by a flux method using the crystal growth apparatus of FIG. 2 will be described with reference to FIGS.
(1) First, Na (ie, flux) alkali metal and Ga, which is an element III, are placed in a reaction vessel (crucible 26), and the reaction vessel (crucible 26) is used as a reaction chamber (stainless steel vessel) of the crystal growth apparatus. 24), the gas in the reaction chamber is exhausted. However, the above-mentioned optional additives such as alkaline earth metals may be put in advance in the crucible as necessary. In addition, when these operations are performed in the air, Na is immediately oxidized, so the operation of setting the substrate and raw materials in the reaction vessel is performed in a glove box filled with an inert gas such as Ar gas. .

(2) Next, while raising the temperature of the crucible from 850 ° C. to 880 ° C., nitrogen gas (N ₂ ) is fed into the reaction chamber of the crystal growth apparatus in parallel with this temperature raising step. The gas pressure in the reaction chamber is maintained at about 3 to 5 atmospheres (3 to 5 × 10 ⁵ Pa). At this time, the protective film 15 of the template 10 is immersed in a melt of Ga and Na generated as a result of the temperature rise, and the crystal growth surface of the template 10, that is, the exposed surface of the GaN layer 13 is Arranged near the interface between the melt and nitrogen gas.

  By setting the conditions as described above, the vicinity of the interface between the melt of Ga and Na and the nitrogen gas is continuously supersaturated with the material atoms of the group III nitride compound semiconductor, so that the desired semiconductor crystal (n Type GaN single crystal 20) can be grown smoothly from the crystal growth surface of the template 10 (FIG. 3-A). Here, the n-type semiconductor crystal (n-type GaN single crystal 20) is obtained because the silicon substrate 11 melted in the flux is added to the growing crystal as an n-type additive (Si). (FIG. 3-B).

  However, the protective film 15 may be thickly stacked so that the silicon substrate 11 does not melt into the flux during the crystal growth process. In this case, a semiconductor crystal not doped with silicon (Si) can be grown.

4). Dissolution of crystal growth substrate When the n-type GaN single crystal 20 is grown to a sufficient film thickness of, for example, about 500 μm or more by the above crystal growth process, the temperature of the crucible is continuously maintained at 850 ° C. or more and 880 ° C. or less for protection. Waiting for all of the film 15 and the silicon substrate 11 to dissolve in the flux (FIGS. 3-B to C), the gas pressure of nitrogen gas (N ₂ ) is set to 3 to 5 atm (3 to 5 × 10 ⁵ Pa). ) The temperature of the reaction chamber is lowered to 100 ° C. or lower while maintaining the degree.

  However, the step of dissolving the silicon substrate 11 in the flux and the above-described temperature lowering step may be performed in some overlap. Further, for example, as described above, at least a part of the protective film 15 and the silicon substrate 11 may be dissolved in the flux during the growth process of the GaN single crystal 20. The mode of parallel and simultaneous progress of these steps can be appropriately adjusted depending on, for example, the form of the protective film 15.

5. Flux removal Next, the n-type GaN single crystal 20 (desired semiconductor crystal) is taken out from the reaction chamber of the crystal growth apparatus, the temperature is lowered to 30 ° C. or lower, and the surroundings are also maintained at 30 ° C. or lower. Then, the flux (Na) attached around the n-type GaN single crystal 20 is removed using ethanol.
By sequentially executing the above steps, it is possible to manufacture a high-quality semiconductor single crystal (n-type GaN single crystal 20) having a thickness of 400 μm or more with fewer cracks than the conventional method at low cost by the flux method. it can.

[Other variations]
The embodiment of the present invention is not limited to the above-described embodiment, and other modifications as exemplified below may be made. Even with such modifications and applications, the effects of the present invention can be obtained based on the functions of the present invention.
(Modification 1)
For example, in Example 1 described above, the protective film 15 is formed on the back surface of the template 10 to form the base substrate (seed crystal). However, the protective film is not necessarily formed on the back surface of the base substrate. For example, a desired semiconductor crystal has a predetermined thickness based on the etching rate of a soluble material (Si substrate 11) under a predetermined crystal growth condition without forming a protective film on the back surface of the template as described above. Alternatively, the thickness of the soluble material may be set so that the soluble material dissolves in the flux and disappears during the period until crystal growth.

  Such a setting is advantageous in terms of productivity because it is not necessary to separately provide a time for dissolving the soluble material. In the first embodiment, the desired semiconductor crystal once generated is dissolved in the flux at the same time as the soluble material constituting the base substrate is dissolved in the flux. . However, if the setting as described above is performed, the soluble material (Si substrate 11) is etched during the execution of the crystal growth step, so that it is not necessary to provide a step for dissolving the soluble material. For this reason, if the setting as described above is performed, it is possible to minimize the occurrence of such waste.

  In addition, by appropriately adjusting the thickness of the protective film, it is possible to prevent the soluble material (Si substrate 11) from being dissolved into the flux for a while after the start of crystal growth. The semiconductor layer laminated immediately above 10 may be a non-doped semiconductor layer, and the semiconductor layer laminated thereon may be an n-type semiconductor layer doped with silicon (Si).

(Modification 2)
In the first embodiment, the protective film 15 is uniformly formed on the back surface of the template 10 to form a base substrate (seed crystal). However, these protective films are etched using an appropriate etching pattern. Thus, a part of the back surface of the soluble material may be exposed according to the etching pattern. In this case, the exposed portion of the soluble material comes into contact with the flux from the beginning and reacts with the flux to dissolve, so even with such a setting, the dissolution rate and dissolution of the above-described soluble material constituting the base substrate The time required can be optimized. At this time, it is possible to optimize the dissolution rate of the above-mentioned soluble material by adjusting the size of the window portion of the protective film that exposes a part of the back surface of the soluble material, the arrangement density of the window, etc. Become.

  In addition, if the soluble material is made of silicon (Si) and the above-mentioned window is formed, the soluble material that dissolves in the flux from an early stage can be used as an n-type impurity. A desired semiconductor crystal can be formed into an n-type semiconductor crystal having an appropriate carrier concentration from the time when crystal growth is started. Such carrier concentration can be optimized by adjusting the dissolution rate of the soluble material. Moreover, the window part of the protective film formed in the back surface of said soluble material can be formed with the general well-known etching technique which has a photolithography process, a dry etching process, etc.

  The present invention is useful for manufacturing a semiconductor device using a semiconductor crystal made of a group III nitride compound semiconductor. Examples of these semiconductor devices include other general semiconductor devices such as FETs in addition to light emitting elements and light receiving elements such as LEDs and LDs.

Sectional drawing in the creation process of the template 10 of Example 1. Configuration diagram of crystal growth apparatus of embodiment 1 Sectional drawing in the crystal growth process of the semiconductor crystal of Example 1. Sectional drawing in the crystal growth process of the semiconductor crystal of Example 1. Sectional drawing in the crystal growth process of the semiconductor crystal of Example 1.

Explanation of symbols

10: Template 11: Silicon substrate 12: AlN buffer layer 13: GaN layer (seed crystal)
15: Protective film 20: n-type GaN single crystal

Claims (4)

In a flux method in which a semiconductor crystal made of a group III nitride compound semiconductor is grown using a flux,
At least a part of the base substrate for crystal growth of the semiconductor crystal, a soluble material that dissolves in the flux,
The soluble material during the crystal growth step of the semiconductor crystal, or
Near the growth temperature of the semiconductor crystal after the crystal growth step of the semiconductor crystal,
A method for producing a semiconductor crystal, wherein the semiconductor crystal is dissolved in the flux. The soluble material is at least partly,
2. The method for producing a semiconductor crystal according to claim 1, further comprising an impurity for controlling a carrier concentration in the semiconductor crystal. 3. The method of manufacturing a semiconductor crystal according to claim 1, wherein silicon (Si) is used as the soluble material. Forming a protective film on the exposed surface of the soluble material;
The semiconductor according to any one of claims 1 to 3, wherein the time or rate at which the soluble material is dissolved in the flux is controlled by the thickness or the film formation pattern of the protective film. Crystal production method.

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