JP3905785B2 - Epitaxial substrate manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an epitaxial substrate and a method for manufacturing the epitaxial substrate, and more particularly, to an epitaxial substrate and a method for manufacturing the epitaxial substrate that can be suitably used as a substrate for a semiconductor device constituting a light emitting diode element or a high-speed IC chip.
[0002]
[Prior art]
The group III nitride film is used as a semiconductor film constituting a light-emitting diode element or the like, and in recent years, has attracted attention as a semiconductor film constituting a high-speed IC chip used for a cellular phone or the like. In particular, Group III nitride films containing Al are expected to be applied to various semiconductor devices such as field emitters due to their characteristics.
[0003]
As a substrate on which such a group III nitride film is formed, there is a so-called epitaxial substrate including a base film formed by epitaxial growth on a predetermined base material. The base film is preferably made of an Al-containing group III nitride so as to facilitate the epitaxial growth of the group III nitride film. Further, since the Al-containing nitride has a large band gap, the semiconductor element can be obtained by inserting a layer made of a material having such a large band gap between the group III nitride film constituting the semiconductor element and the substrate. It is also possible to improve the efficiency.
[0004]
After the epitaxial substrate is placed on a susceptor provided in the reaction tube, the epitaxial substrate is heated to a predetermined temperature by a heating mechanism inside and outside the susceptor. Next, a group III metal feedstock and a nitrogen feedstock, and a feedstock of other elements as required are introduced into the reaction tube together with a carrier gas, and are supplied onto the epitaxial substrate, and a group III nitridation is performed according to the MOCVD method. A material film is formed.
[0005]
[Problem to be Solved by the Invention]
However, the epitaxial substrate and the group III nitride film according to the MOCVD method are performed using different film forming apparatuses due to different manufacturing conditions. Therefore, the manufactured epitaxial substrate is exposed to the atmosphere when the group III nitride film is manufactured.
[0006]
Then, the surface of the group III nitride underlayer of the epitaxial substrate surface is immediately oxidized, surface defects caused by this oxide and the like are generated, adversely affecting the epitaxial growth of the group III nitride film, In some cases, it was not possible to obtain one having good crystal quality. As a result, the characteristics of the semiconductor element made of such a group III nitride film have also deteriorated.
[0007]
The above tendency becomes prominent when the group III nitride underlayer contains Al, and becomes more prominent as the Al content in the underlayer increases. Therefore, various Al-containing group III nitride films are formed on such an Al-containing group III nitride underlayer, and the characteristics inherent to the Al-containing group III nitride film are utilized to provide excellent results. Even if it was going to obtain the semiconductor element of a characteristic, such a semiconductor element was not actually obtained.
[0008]
Therefore, after forming the Al-containing group III nitride underlayer relatively thick, an attempt was made to remove the oxidized surface layer portion by etching. However, the oxide layer cannot be easily removed with hydrogen gas or ammonia gas used in the production of the group III nitride film.
[0009]
The present invention provides a method for forming a predetermined group III nitride film on an epitaxial substrate including a base material made of a single crystal material and an Al-containing group III nitride underlayer formed on the base material. An object of the present invention is to suppress deterioration of crystal quality of the group III nitride film due to oxidation of the group III nitride underlayer and surface defects.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides:
A substrate made of monocrystalline material, in the epitaxial substrate comprising a III-nitride base film including at least Al formed on the substrate and a group III nitride underlayer anti-oxidation film formed on The antioxidant film includes at least one element selected from the group consisting of Ga, In, As, Sb, Te, Se, and a halogen element, and is formed of another group III nitride film on the base film. The present invention relates to an epitaxial substrate that is removed by etching in a film forming apparatus to be formed .
[0011]
The present inventors diligently studied to prevent oxidation of the Al-containing group III nitride underlayer surface of the epitaxial substrate. As a result, it was conceived that an antioxidant film was formed on the Al-containing group III nitride underlayer.
[0012]
Therefore, after the epitaxial substrate is manufactured by a predetermined film forming apparatus, the film forming apparatus is changed to produce a predetermined group III nitride film. For example, when manufacturing the target semiconductor element, the epitaxial substrate is Even when exposed to the above, the Al-containing group III nitride underlayer is not oxidized by the anti-oxidation film, and the occurrence of surface defects is also prevented. Therefore, deterioration of the crystal quality of the group III nitride film formed on the epitaxial substrate is suppressed, and deterioration of the characteristics of the semiconductor element is also suppressed.
[0013]
The antioxidant film is appropriately removed by etching when forming the target group III nitride film.
[0014]
In a preferred embodiment of the present invention, the antioxidant film preferably contains at least one element selected from the group consisting of Al, Ga, In, As, Sb, Te, Se, and a halogen element. Specifically, the antioxidant film is composed of a simple substance, an oxide, a halide, or the like of these elements. Accordingly, the antioxidant film can be easily removed by etching with hydrogen gas, ammonia gas, or the like in a film forming apparatus in which a group III nitride film constituting the semiconductor element is to be formed in a subsequent process.
[0015]
The present invention further includes a first step of preparing a substrate made of a single crystal material,
A second step of forming a group III nitride underlayer containing at least Al on the substrate;
By immersing the group III nitride underlayer in an acid solution in which a predetermined material is dissolved, and controlling the pH and oxidation-reduction potential of the acid solution, the oxide on the surface of the group III nitride underlayer is changed. A third step of removing and forming an antioxidant film on the group III nitride underlayer;
It is related with the manufacturing method (1st manufacturing method) of the epitaxial substrate characterized by including these.
[0016]
The present invention also provides:
A first step of preparing a substrate made of a single crystal material;
A second step of forming a group III nitride underlayer containing at least Al on the substrate;
The group III nitride underlayer is immersed in a first acid solution, and the pH of the acid solution and the oxidation-reduction potential are controlled to remove oxide on the surface of the group III nitride underlayer. Process,
The group III nitride underlayer is immersed in a second acid solution in which a predetermined material is dissolved, and the pH and oxidation-reduction potential of the acid solution are controlled, whereby the group III nitride underlayer is formed. A fourth step of forming an antioxidant film on the substrate;
It is related with the manufacturing method (2nd manufacturing method) of an epitaxial substrate characterized by including these.
[0017]
According to the manufacturing method of the present invention described above, an antioxidant film can be formed on the base film while preventing oxidation of the Al-containing group III nitride base film of the epitaxial substrate. Thus, oxygen can be prevented from being mixed into the antioxidant film, and the function as the antioxidant film can be effectively achieved.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on embodiments of the invention.
[0019]
FIG. 1 is a configuration diagram showing an outline of an epitaxial substrate of the present invention. An epitaxial substrate 10 shown in FIG. 1 includes a base material 1 made of a predetermined single crystal material, a group III nitride base film 2 formed on the base material 1, and a base film 2 according to the present invention. The formed antioxidant film 3 is provided.
[0020]
The type and composition of the material of the antioxidant film 3 are not particularly limited as long as it can prevent oxidation of the group III nitride base film 2. However, as described above, Al, Ga, In, As, Sb, Te, Se, and halogen are used in order to enable easy etching removal using a group III nitride film forming apparatus to be formed later. It is preferable to include at least one element selected from the group consisting of elements. Specifically, as described above, the anti-oxidation film is composed of a simple substance of these elements, an oxide such as As ₂ O ₃ , Sb ₂ O ₃ and TeO ₂ , or GaCl ₃ , AlCl ₃ and InCl ₃ . Consists of halides and the like.
[0021]
Note that the thickness of the antioxidant film 3 is preferably 0.1 nm to 100 nm, and more preferably 0.1 nm to 1 nm. As a result, the oxidation of the group III nitride underlayer 2 can be sufficiently prevented, and the etching time for removing by etching can be sufficiently shortened.
[0022]
The group III nitride underlayer 2 needs to contain at least Al, and preferably contains 50 atomic% or more with respect to all group III elements. Further, all the group III elements are made of Al, and III Group nitride underlayer 2 is preferably made of AlN. As described above, as the Al content in the group III nitride underlayer 2 increases, the degree of oxidation and surface defect generation becomes more prominent. Oxidation and generation of surface defects are suppressed. That is, as the Al content in the group III nitride underlayer 2 increases, the effects of the present invention are remarkably exhibited.
[0023]
In addition, the present inventors have clarified that the Al-containing group III nitride film has the following advantages. That is, in the Al-containing group III nitride, for example, the band gap increases as the Al content increases. Therefore, when a group III nitride film containing a relatively large amount of Al, particularly an AlN film, is formed on the epitaxial substrate 10 as shown in FIG. And mobility, that is, responsiveness can be improved.
[0024]
In forming such a high Al-containing group III nitride film with good crystal quality, the group III nitride underlayer film 2 of the epitaxial substrate 10 is also required to contain Al at the same ratio. The However, conventionally, as described above, the surface of the high Al-containing group III nitride underlayer is remarkably oxidized, and a relatively large amount of surface defects due to the oxide are generated. Therefore, the crystal quality of the high Al-containing group III nitride film formed on such a base film is also deteriorated, and the advantages inherent to this high Al-containing group III nitride film cannot be fully exploited. It was out.
[0025]
According to the present invention, even when the group III nitride underlayer 2 contains a relatively large amount of Al, the oxidation and defects can be suppressed by the antioxidant layer 3. Therefore, even when a high Al-containing group III nitride film is formed on the group III nitride underlayer 2 after removing the antioxidant film 3, the crystal quality can be maintained in a good state. By utilizing the inherent characteristics of the high Al-containing group III nitride film, it becomes possible to obtain a semiconductor light emitting device with high luminous efficiency, a highly responsive electronic device, and the like.
[0026]
The group III nitride underlayer 2 can also contain additive elements such as B, Si, Ge, Zn, Be, and Mg in addition to group III elements such as Ga and In other than Al. Furthermore, it is possible to include not only elements added intentionally but also trace elements that are inevitably taken in depending on the film forming conditions and the like, as well as trace impurities contained in the raw materials and reaction tube materials.
[0027]
The thickness of the group III nitride base film 2 is preferably set to 0.5 μm to 3 μm in order to improve the crystal quality of the group III nitride film to be formed later.
[0028]
From the same viewpoint, the half width of the X-ray rocking curve on the (002) plane of the group III nitride underlayer 2 is preferably 200 seconds or less, more preferably 100 seconds or less, and particularly preferably 60 seconds or less. preferable. Such a highly crystalline base film can be easily formed by the following preferred production method of the present invention.
[0029]
Single crystal materials constituting the substrate 1 are sapphire single crystals, ZnO single crystals, LiAlO ₂ single crystals, LiGaO ₂ single crystals, MgAl ₂ O ₄ single crystals, oxide single crystals such as MgO single crystals, Si single crystals, Group IV or IV-IV single crystal such as SiC single crystal, GaAs single crystal, AlN single crystal, GaN single crystal, III-V single crystal such as AlGaN single crystal, boride single crystal such as ZrB _2, etc. A known substrate material can be used.
[0030]
It is also possible to form a nitride layer on the surface of the base material 1 made of such a single crystal material, and form the group III nitride underlayer 2 via this nitride layer.
[0031]
Next, the manufacturing method of the present invention will be described with reference to FIG. Both the first manufacturing method and the second manufacturing method of the present invention described above, after preparing the base material 1 made of the substrate material as described above, the group III is formed on the base material 1 using a known film forming method. A nitride underlayer 2 is formed.
[0032]
The MOCVD method is preferably used in order to epitaxially grow the group III nitride underlayer 2 and easily obtain a film having good crystal quality. In this case, after the base material 1 is installed in the MOCVD apparatus, an Al source gas such as trimethylaluminum (TMA) or triethylaluminum (TEA), a nitrogen source gas such as ammonia, and other group III as necessary. A source gas or the like is introduced into the MOCVD apparatus and supplied onto the substrate 1. Then, the base material 1 is preferably heated to 1100 ° C. or higher, more preferably 1100 ° C. to 1250 ° C. to form a predetermined Al-containing group III nitride underlayer 2 from the source gas.
[0033]
Next, a predetermined acid solution is prepared, and the anti-oxidation film 3 is formed by immersing the group III nitride base film 2 taken out from the MOCVD apparatus in the acid solution.
[0034]
In the first manufacturing method, a predetermined material is dissolved in advance in the acid solution as a raw material of the antioxidant film 3. By taking out from the MOCVD apparatus, the surface of the group III nitride underlayer 2 is immediately oxidized and defects due to this oxide are generated. Therefore, by appropriately controlling the pH and oxidation-reduction potential of the acid solution, the oxide is removed and at the same time, the constituent components of the material are synthesized on the group III nitride underlayer 2 to thereby prevent the antioxidant layer 3. To precipitate. That is, in the first manufacturing method, the removal of the oxide and the formation of the antioxidant film 3 are performed simultaneously.
[0035]
Specifically, the pH of the acid solution is preferably set to 4 or less, more preferably 2 or less. Moreover, it is preferable to set the oxidation-reduction potential of the acid solution to −1.8 V or more.
[0036]
The immersion time is appropriately set according to the pH and oxidation-reduction potential of the acid solution, the material component and composition of the group III nitride base film 2, the material component and thickness of the antioxidant film 3 to be formed, and the like. To do.
[0037]
Moreover, although the said material changes according to the material component and composition, etc. of the antioxidant film | membrane 3, as above-mentioned, the antioxidant film | membrane 3 is comprised from Al, Ga, In, As, Sb, Te, Se, and a halogen element. In the case of containing at least one element selected from the group, it is composed of a material containing these elements. Specifically, these elements are composed of simple elements, oxides such as As ₂ O ₃ , Sb ₂ O ₃ and TeO ₂ , or halides such as GaCl ₃ , AlCl ₃ and InCl ₃ .
[0038]
In order to achieve the above pH, it is preferable to use acids such as hydrochloric acid, hydrofluoric acid and phosphoric acid, and a mixed solution thereof. In addition, it can dilute with water as needed.
[0039]
The oxidation-reduction potential can be realized by appropriately controlling the voltage value to be applied to the electrode disposed in the acid solution. Further, the potential can be adjusted by adding a solution such as hydrogen peroxide.
[0040]
The pH and redox potential of the acid solution are not limited to the above ranges. For example, even when the pH is larger than 4, removal of the oxide and formation of the antioxidant film 3 can be performed simultaneously by adjusting the redox potential. However, the removal efficiency, the precipitation efficiency, and the like are deteriorated as compared with the case where the pH and the oxidation-reduction potential are limited to the above ranges.
[0041]
In the second manufacturing method, a first acid solution and a second acid solution in which materials are dissolved as raw materials for the antioxidant film 3 are prepared. Then, the surface of the group III nitride underlayer 2 is immersed by immersing the group III nitride underlayer 2 taken out from the MOCVD apparatus in the first acid solution and appropriately controlling its pH and oxidation-reduction potential. The oxide formed in the step is removed. Next, the group III nitride underlayer 2 is immersed in the second acid solution, and the desired antioxidant film 3 is formed from the above material without causing other impurities to precipitate on the surface of the group III nitride underlayer 2. It is formed by synthesis and precipitation. That is, in the second manufacturing method, the removal of the oxide and the formation of the antioxidant film 3 are performed separately.
[0042]
The pH of the first acid solution is preferably 4 or less, and more preferably 2 or less. The redox potential of the first acid solution is preferably −1.8 V or more.
[0043]
Further, the pH of the second acid solution is preferably 4 or less, and more preferably 2 or less. The redox potential of the second acid solution is preferably −1.8 V or higher.
[0044]
The immersion time in the first acid solution and the second acid solution depends on the pH and oxidation-reduction potential of the acid solution, the material components and composition of the group III nitride underlayer 2, and the oxidation to be formed. It is appropriately set according to the material component and thickness of the prevention film 3.
[0045]
Moreover, although the said material changes according to the material component and composition, etc. of the antioxidant film | membrane 3, as above-mentioned, the antioxidant film | membrane 3 is comprised from Al, Ga, In, As, Sb, Te, Se, and a halogen element. In the case of containing at least one element selected from the group, it is composed of a material containing these elements. Specifically, as described above, these elements are composed of simple elements, oxides such as As ₂ O ₃ , Sb ₂ O ₃ and TeO ₂ , or halides such as GaCl ₃ , AlCl ₃ and InCl ₃ .
[0046]
In order to achieve the above pH, it is preferable to use acids such as hydrochloric acid, hydrofluoric acid and phosphoric acid, and a mixed solution thereof as in the first production method described above. In addition, it can dilute with water as needed. Further, the oxidation-reduction potential can also be realized by appropriately controlling the voltage value to be applied to the electrode disposed in the acid solution as described above.
[0047]
In the second production method, the pH and redox potential of the acid solution are not limited to the above ranges. For example, even when pH is higher than 4, the oxide can be removed or the antioxidant film 3 can be formed by adjusting the oxidation-reduction potential. However, the removal efficiency, the precipitation efficiency, and the like are deteriorated as compared with the case where the pH and the oxidation-reduction potential are limited to the above ranges.
[0048]
【Example】
Hereinafter, the present invention will be described specifically by way of examples. In this example, the defect density was calculated by counting the point-like abnormally grown portions of 1 μm or more present on the surface of the finally obtained GaN film, and the crystal quality was evaluated.
[0049]
Example 1
A sapphire single crystal base material was used as the base material, and this was placed on a susceptor installed in an MOCVD apparatus and then fixed by suction. Next, the substrate was heated to 1200 ° C. with a heater in the susceptor.
[0050]
Next, trimethylaluminum (TMA) is used as the Al feedstock, ammonia gas (NH ₃ ) is used as the nitrogen feedstock, and these feedstock gases together with the hydrogen carrier gas at a flow rate of NH ₃ / TMA = 400 And an AlN base film was formed to a thickness of 1 μm.
[0051]
Next, the sapphire single crystal substrate including the AlN underlayer is taken out of the MOCVD apparatus and exposed to the atmosphere for a predetermined time, and then the AlN underlayer is adjusted to pH = 1, oxidation-reduction potential = 0.4V, As oxide. The substrate was immersed in a dissolved hydrochloric acid solution for 5 minutes, and an As ₂ O ₃ film was formed as an antioxidant film on the AlN base film to produce an epitaxial substrate.
[0052]
Next, the sapphire single crystal base material including the As ₂ O ₃ film is put in the MOCVD apparatus again, the base material is heated to 1000 ° C., and hydrogen gas is allowed to flow at a flow rate of 1000 sccm, whereby the As ₂ O ₃ film Was removed.
[0053]
Next, the sapphire single crystal substrate is heated to 1050 ° C., trimethylgallium (TMG) is used as a Ga feedstock, ammonia gas (NH ₃ ) is used as a nitrogen feedstock, and these source gases are hydrogen and nitrogen carrier gas. At the same time, it was introduced into the reaction tube at a flow rate of NH ₃ / TMG = 3000 and supplied onto the AlN underlayer to form a GaN film with a thickness of 3 μm.
[0054]
When the pit density on the surface of the obtained GaN film having an inner diameter of 0.1 μm or more was examined, it was confirmed to be 0.1 pieces / mm ² .
[0055]
(Example 2)
After forming an AlN base film having a thickness of 1 μm on a sapphire single crystal substrate in the same manner as in Example 1, it was immersed in a hydrochloric acid container having a pH = 1 and a redox potential = 0.2 V for 5 minutes. Then, it is immersed in a hydrochloric acid solution in which pH = 1, redox potential = 0.4V, and As oxide is dissolved for 5 minutes, and an As ₂ O ₃ film is formed as an antioxidant film on the AlN base film. Then, an epitaxial substrate was produced.
[0056]
Next, the As ₂ O ₃ film was removed by etching in the same manner as in Example 1, and then a GaN film was formed to a thickness of 3 μm. When the pit density on the surface of the obtained GaN film having an inner diameter of 0.1 μm or more was examined, it was confirmed to be 0.1 pieces / mm ² .
[0057]
(Comparative example)
In the above embodiment, without forming the _As 2 _{O 3} film as anti-oxidation film, after removal of the sapphire single crystal substrate comprising the AlN underlayer from the MOCVD apparatus, and placed in back MOCVD apparatus, and examples Similarly, a GaN film having a thickness of 3 μm was formed. When the pit density on the surface of the obtained GaN film having an inner diameter of 0.1 μm or more was examined, it was confirmed that it had a defect density of 5 / mm ² .
[0058]
As described above, as is clear from the examples and comparative examples, the GaN film formed on the AlN base film after the removal of the As ₂ O ₃ film as the antioxidant film forms the As ₂ O ₃ film. It can be seen that the surface defects are extremely large as compared with the GaN film directly formed on the AlN base film. Therefore, even when the epitaxial substrate having the As ₂ O ₃ film is exposed to the atmosphere, the surface of the AlN film as the base film is not oxidized, and the generation of surface defects due to this oxide is suppressed. I understand that.
[0059]
The present invention has been described in detail based on the embodiments of the invention with specific examples. However, the present invention is not limited to the embodiments of the invention, and does not depart from the scope of the invention. All changes and modifications are possible. For example, in the above-described embodiment, the crystal quality of the GaN film is improved by inserting a multilayer film such as a buffer layer or a strained superlattice between the GaN film and the epitaxial substrate, or by making the growth conditions multistage. It can also be made.
[0060]
【The invention's effect】
As described above, according to the present invention, in an epitaxial substrate including a base material made of a single crystal material and an Al-containing group III nitride base film formed on the base material, the base film is formed on the base film. Since the antioxidant film is provided, oxidation of the base film and generation of surface defects are suppressed, and deterioration of the crystal quality of the group III nitride film formed on the epitaxial substrate is suppressed.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an outline of an epitaxial substrate of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Base material, 2 (Al containing) group III nitride base film, 3 Antioxidation film, 10 Epitaxial substrate

Claims (10)

A first step of preparing a substrate made of a single crystal material;
A second step of forming a group III nitride underlayer containing at least Al on the substrate;
By immersing the group III nitride underlayer in an acid solution in which a predetermined material is dissolved, and controlling the pH and oxidation-reduction potential of the acid solution, the oxide on the surface of the group III nitride underlayer is changed. A third step of removing and forming an antioxidant film on the group III nitride underlayer;
A method for manufacturing an epitaxial substrate, comprising: 2. The method for manufacturing an epitaxial substrate according to claim 1 , wherein the third step is performed by setting the pH of the acid solution to 4 or less and the oxidation-reduction potential to −1.8 V or more. 3. The third step is performed by dissolving a material containing at least one element selected from the group consisting of Al, Ga, In, As, Sb, Te, Se, and a halogen element in the acid solution. the anti-oxidation layer is characterized in that it comprises at least one element, method for manufacturing an epitaxial substrate according to claim 1 or 2. A first step of preparing a substrate made of a single crystal material;
A second step of forming a group III nitride underlayer containing at least Al on the substrate;
The group III nitride underlayer is immersed in a first acid solution, and the pH of the acid solution and the oxidation-reduction potential are controlled to remove oxide on the surface of the group III nitride underlayer. Process,
The group III nitride underlayer is immersed in a second acid solution in which a predetermined material is dissolved, and the pH and oxidation-reduction potential of the acid solution are controlled, whereby the group III nitride underlayer is formed. A fourth step of forming an antioxidant film on the substrate;
A method for manufacturing an epitaxial substrate, comprising: 5. The method for producing an epitaxial substrate according to claim 4 , wherein the third step is performed by setting the pH of the first acid solution to 4 or less and the oxidation-reduction potential to −1.8 V or more. . The epitaxial substrate according to claim 4 or 5 , wherein the fourth step is performed by setting the pH of the second acid solution to 4 or less and the oxidation-reduction potential to -1.8V or more. Production method. In the fourth step, a material containing at least one element selected from the group consisting of Al, Ga, In, As, Sb, Te, Se, and a halogen element is dissolved in the second acid solution. The method for manufacturing an epitaxial substrate according to claim 4 , wherein the antioxidant film contains the at least one element. Al content of the III nitride underlayer film, characterized in that at least 50 atom% based on the total group III elements, method for manufacturing an epitaxial substrate according to any one of claims 1 to 7 . The method for manufacturing an epitaxial substrate according to claim 8 , wherein the group III nitride underlayer is made of AlN. Characterized in that said III X-ray rocking curve in the (002) plane of the nitride base film is less than 200 seconds, method for manufacturing an epitaxial substrate according to any one of claims 1 to 9.

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