JP4170269B2 - Method for producing group III nitride film - Google Patents

Description

  The present invention relates to a method for producing a group III nitride film, and more particularly, a group III nitride film that can be suitably used as a base film constituting a semiconductor light emitting element such as a light emitting diode element or a semiconductor element such as a high-speed IC chip. It relates to the manufacturing method.

  The group III nitride film is used as a semiconductor film constituting a semiconductor light emitting element such as a light emitting diode element. In recent years, a group III nitride film is also used as a semiconductor film constituting a semiconductor element such as a high-speed IC chip used for a mobile phone or the like. Has attracted attention.

  The group III nitride film as described above is usually formed by MOCVD. Specifically, the substrate on which the group III nitride film is to be formed is placed on a susceptor provided in a predetermined reaction tube, and a heater embedded in a heating mechanism installed in or outside the susceptor To 1000 ° C. or higher. Then, a predetermined source gas is introduced into the reaction tube together with a carrier gas and supplied onto the substrate.

  Then, a thermochemical reaction occurs on the substrate, the source gases are decomposed into constituent elements, and the constituent elements react with each other, and a target group III nitride film is deposited on the substrate. Are manufactured.

  However, when the composition of the group III nitride film changes, its lattice constant changes relatively greatly. For this reason, the difference with the lattice constant of the material which comprises a board | substrate may become large, and a misfit dislocation | rearrangement may be formed comparatively abundantly in the interface with a board | substrate.

When the group III nitride film is epitaxially grown in such a state, a large amount of dislocations may be generated in the film at a density on the order of about 10 ¹⁰ / cm ² due to propagation of the misfit dislocations. . As a result, there has been a problem that the crystallinity of the group III nitride film is deteriorated and the electrical and optical characteristics are also deteriorated.

In order to avoid such a problem, it has been attempted to form a strip-shaped mask made of SiO ₂ or the like on a substrate and laterally epitaxially grow a group III nitride film on the mask. According to this method, misfit dislocations generated at the interface with the substrate are propagated only in the lateral direction parallel to the substrate on the mask surface, and are not propagated in the longitudinal direction perpendicular to the substrate. A low dislocation group III nitride film can be formed between strip-shaped portions.

However, since this method requires a photolithography process including etching when producing the SiO ₂ mask, there is a problem that the number of processes during the production of the group III nitride film is increased and complicated.

  An object of the present invention is to provide a method for easily producing a low dislocation group III nitride film.

In order to achieve the above object, the present invention provides:
A method for producing a group III nitride film by CVD, wherein a plurality of island-like crystal parts made of a second nitride are isolated from each other on a base made of a first Al-containing nitride. In manufacturing a nitride film from a third nitride different from the second nitride by epitaxially growing the island-shaped crystal part as a nucleus , the second nitride is made of Al and Ga. The present invention relates to a method for manufacturing a nitride film, which has a selected composition .

  In the present invention, the term “base material” includes a predetermined base film made of the first Al-containing nitride in addition to the substrate made of the first Al-containing nitride.

The present inventors diligently studied to form a low dislocation group III nitride film by a simple process without using the SiO ₂ mask as described above.

  1 to 3 are conceptual diagrams for explaining the production method of the present invention.

  First, on the base material 1 made of the first Al-containing nitride on which the target group III nitride film is to be formed, a plurality of island crystal parts 2-1 to 2- 4 is formed. Then, as shown in FIG. 2, a group III nitride made of a third nitride different from the second nitride by using the island-shaped crystal portions 2-1 to 2-4 as nuclei for epitaxial growth. The object film 3A is epitaxially grown to obtain the target group III nitride film 3 as shown in FIG.

  That is, the island-shaped crystal parts 2-1 to 2-4 formed on the base material 1 are fine in size, and in the initial growth stage, grow three-dimensionally around the initial nucleus. It has the role of bending the direction of one threading dislocation laterally. Therefore, even when a relatively large amount of threading dislocations are present in the base material 1, threading dislocations propagating in the direction perpendicular to the substrate surface are significantly reduced in the island-like crystal parts 2-1 to 2-4.

  For this reason, a group III nitride film made of a nitride different from the island-like crystal part is formed by using such island-like crystal parts 2-1 to 2-4 as nuclei for epitaxial growth and epitaxially growing from these island-like crystal parts. Thus, the low dislocation group III nitride film 3 can be formed by inheriting the low dislocation property of the island-like crystal parts 2-1 to 2-4.

  Further, in the initial growth process of the group III nitride film grown on these island-like crystal parts, the lateral growth is promoted, so that the lowering of dislocation in the initial growth process is further promoted.

  Such a tendency becomes more prominent when the half-value width of the (002) X-ray rocking curve of the base material or the base film 1 is 90 seconds or less.

  The island-like crystal part can be produced by appropriately controlling the film forming conditions in the CVD method or the like, and the following three growth principles are conceivable.

  The first principle is due to a difference in lattice constant between the first Al-containing nitride constituting the base material and the second nitride constituting the island-shaped crystal part. That is, when the lattice constant of the second nitride is larger than that of the first Al-containing nitride, the second nitride is formed on the substrate composed of the first Al-containing nitride. When an attempt is made to produce a constructed film, the film grows according to the SK mode. As a result, the second nitride does not actually grow as a uniform film, but grows three-dimensionally around a predetermined nucleus, and finally an island-like crystal part is obtained.

  The second principle is due to the oxidation of the main surface of the base material composed of the first Al-containing nitride. That is, in the case where the main surface of the base material is oxidized and an oxide film is partially formed, when the film made of the second nitride is formed on the base material, the second The nitride is selectively deposited and aggregated on the exposed portion of the nitride except the portion where the oxide film is formed on the main surface of the base material. As a result, the second nitride does not grow as a uniform film, but grows three-dimensionally with the exposed nitride portion as a nucleus, and as a result, an island-like crystal portion is obtained.

  The third principle is due to aggregation due to composition fluctuation. That is, the first Al-containing nitride constituting the base material is not uniformly distributed in the base material, but is distributed with a certain degree of bias and is in a completely uniform state. It is not. Therefore, when an attempt is made to produce a film composed of the second nitride on such a substrate, the constituent elements in the second nitride are selectively selected according to the composition distribution in the substrate. It will accumulate and become agglomerated. As a result, the second nitride does not grow as a uniform film, but is configured as an island-shaped crystal part that is partially aggregated and three-dimensionally grown.

  Further, as described above, the nitride film made of the third nitride is epitaxially grown with the island-shaped crystal portion serving as a nucleus, but as is apparent from FIG. 2, the nitride film is formed only from the island-shaped crystal portion. It grows directly on the base material at a certain rate and contributes to film formation.

  Furthermore, the nitride film composed of the third nitride includes not only a single layer but also a multilayer film structure in which a plurality of nitride layers such as a strained superlattice are stacked. Furthermore, a composition gradient film whose composition is continuously or stepwise inclined in the thickness direction is also included.

  The group III nitride film obtained by the above manufacturing method can be used particularly as a semiconductor film constituting a semiconductor element such as a high-speed IC chip or a light-emitting diode element. As a result, the light emission efficiency of the semiconductor light emitting device, the high speed response of the semiconductor device, and the like are significantly improved.

  As described above, according to the present invention, a group III nitride film having low dislocations and excellent crystallinity can be formed by a simple method using the MOCVD method or the like. Therefore, by forming a semiconductor element from the group III nitride film, the crystallinity of the entire element can be improved and good element characteristics can be imparted.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail based on embodiments of the invention.
In the present invention, it is necessary to form a plurality of island-like crystal parts made of the second nitride independent from each other on the base made of the first Al-containing nitride. The size of the island-shaped crystal part is not particularly limited as long as a nitride film made of the target third nitride can be manufactured using this as a nucleus.

However, it is preferable that the average area of the upper surface of the island-shaped crystal portion is larger, and practically about 100 μm ² . Further, the lower limit of the average area of the upper surface of the island-shaped crystal part is preferably 0.0001 μm ² , and more preferably 1 μm ² . As a result, the intended low dislocation nitride film can be efficiently produced in a relatively short time.

  The epitaxial growth conditions of the target group III nitride film include the types of the first Al-containing nitride constituting the substrate, the types of the second nitride constituting the island-shaped crystal part, and The selection is made as appropriate depending on the type of the third nitride constituting the nitride film, the size of the island-like crystal portion, and the like.

  The second nitride and the third nitride need to be different from each other. The first Al-containing nitride may be composed of a nitride having the same material and composition as the second nitride or the third nitride.

Further, in the present invention, when the second nitride contains Al, the Al composition of the second nitride constituting the island-shaped crystal portion is the same as that of the first Al-containing nitride constituting the substrate. Al smaller than the composition Ikoto are preferred. As a result, when a thin film made of the second nitride is to be formed relatively thin by CVD or the like, a compressive stress is applied to the thin film from the base material. Therefore, the thin film grows in accordance with the SK mode without forming a uniform film, and is divided by the compressive stress, and exhibits an island shape as described above.

  As a result, the target island-shaped crystal part can be easily formed only by the conventional CVD method by appropriately selecting the first Al-containing nitride and the second nitride.

Specifically, the second nitride has a composition of Al _x1 Ga _x2 In _x3 N (x1 + x2 + x3 = 1, x1, x2, x3 ≧ 0), and the first Al-containing nitride is Al _y1 Ga. In the case of having a composition of _y2 In _y3 N (y1 + y2 + y3 = 1, y1> 0, y2, y3 ≧ 0), the Al composition x1 of the second nitride and the Al composition y1 of the first Al-containing nitride Preferably satisfies the relationship x1 ≦ y1-0.1. Thereby, the dislocation density in the target group III nitride film can be reduced to 10 ¹⁰ / cm ² or less.

Furthermore, by satisfying the relationship of x1 ≦ y1-0.5, the dislocation density of the target group III nitride film can be easily reduced to 10 ⁹ / cm ² or less, and further to 10 ⁸ / cm ² or less. be able to.

  The above-mentioned composition means an average composition in the island-shaped crystal part composed of the second nitride and in the base material composed of the first Al-containing nitride. In the material, it may change continuously or stepwise in the thickness direction. Moreover, you may be comprised so that a composition may change periodically with forms, such as a strain superlattice.

  The first to third nitrides may contain additional elements such as Ge, Si, Mg, Zn, Be, P, and B as necessary. Moreover, it is not restricted to the element added consciously, It can also contain the trace impurity O or C contained in film-forming conditions, a raw material, and the reaction tube material.

  Further, the first Al-containing nitride constituting the base material preferably has a half-value width in a (002) X-ray rocking curve of 90 seconds or less, and more preferably 50 seconds or less. As a result, it is possible to further promote dislocation reduction in the nitride film made of the third nitride. From the same viewpoint, it is preferable that the surface roughness Ra of the substrate is 2 mm or less.

When the base material means a base film, the base base material for supporting the base film includes a sapphire single crystal, a ZnO single crystal, a LiAlO ₂ single crystal, a LiGaO ₂ single crystal, a MgAl ₂ O ₄ single crystal, III-V such as oxide single crystal such as MgO single crystal, group IV or group IV-IV single crystal such as Si single crystal, SiC single crystal, GaAs single crystal, AlN single crystal, GaN single crystal, and AlGaN single crystal It can be composed of a known substrate material such as a group single crystal or a boride single crystal such as ZrB ₂ .

  Further, on the base substrate made of the above-mentioned single crystal, an oxide single crystal such as a ZnO single crystal or MgO single crystal, a Si single crystal, a SiC single crystal, or a group IV or IV-IV group single crystal, a GaAs single crystal An epitaxial substrate having an epitaxially grown film made of a group III-V single crystal such as InP single crystal or a mixed crystal thereof can also be used.

  In particular, when using a sapphire single crystal, that is, when the base material is formed directly from a sapphire single crystal, or a base substrate is formed from a sapphire single crystal, and an epitaxial film is formed on the base base material for epitaxial growth. When a substrate is prepared and used as a base material, it is preferable to subject the main surface of the sapphire single crystal base material to surface nitriding treatment.

  The surface nitriding treatment is performed by placing the sapphire single crystal substrate in a nitrogen-containing atmosphere such as ammonia and heating it for a predetermined time. Then, the thickness of the nitride layer formed on the main surface is controlled by appropriately controlling the nitrogen concentration, nitriding temperature, and nitriding time.

  As described above, since the nitride film made of the third nitride is directly formed on the base material at a certain ratio, the sapphire single crystal having the surface nitride layer formed in this way is used as the base material. As a result, the crystallinity of the nitride can be further improved. However, even if such surface nitriding treatment is performed, the object of the present invention can be sufficiently exhibited.

  FIG. 4 is a cross-sectional view showing an example of a semiconductor light emitting device having a group III nitride film manufactured according to the manufacturing method of the present invention described above.

  A semiconductor light emitting device 10 shown in FIG. 4 includes a substrate 11, a base layer 12 made of, for example, AlN, and a first conductive layer 13 made of, for example, n-AlGaN. Further, on the first conductive layer 13, for example, a first cladding layer 14 made of, for example, n-AlGaN, and a light emitting layer 15 made of, for example, i-AlGaN, formed on the first cladding layer 14. The second cladding layer 16 made of, for example, p-AlGaN formed on the light emitting layer 15 and the second conductive layer made of, for example, p-AlGaN, formed on the second cladding layer 16. It comprises a layer 17.

  A part of the first conductive layer 13 is exposed, and an n-electrode 18 having a configuration of, for example, Al / Ti is formed on the exposed surface. On the second conductive layer 17, for example, a p-electrode 19 having a configuration of Au / Ni is formed.

  In the semiconductor light emitting device 10 shown in FIG. 4, for example, the substrate 11 is regarded as a base material in the present invention, and the island-like crystal part as described above is formed on the substrate 11. As a result, the underlayer 12 is formed. Then, according to the present invention, dislocations in the underlayer 12 are remarkably reduced, and as a result, the crystallinity of the underlayer 12 can be improved. Accordingly, the crystallinity of the first conductive layer 13 and the like formed on the base layer 12 is also improved, so that the light emission efficiency of the semiconductor light emitting element 10 can be improved.

  In this case, the substrate for epitaxial growth of the present invention is constituted by the substrate 11 and the island-like crystal portion formed on the substrate.

  Further, for example, the base layer 12 is newly regarded as the base material of the present invention, and after the island-like crystal part as described above is formed on the base layer 12, the island-like crystal part is used as a nucleus for epitaxial growth. Thus, the first conductive layer 13 is formed. According to the present invention, dislocations in the first conductive layer 13 are significantly reduced, and as a result, the crystallinity of the first conductive layer can be improved. Therefore, the crystallinity of the first cladding layer 14 and the like formed on the first conductive layer 13 is also improved. In this case, the light emission efficiency of the semiconductor light emitting element 10 can be improved.

  Note that the base layer, the conductive layer, the clad layer, and the like can be manufactured according to known deposition conditions in a known MOCVD method. However, when the underlayer 12 or the first conductive layer 13 is formed by epitaxial growth from the island crystal part, for example, as described above, the film is formed in consideration of the size of the island crystal part. Adjust conditions accordingly.

Hereinafter, the present invention will be described specifically by way of examples.
(Example 1)
A base substrate was composed of a C-plane sapphire single crystal, which was placed on a susceptor installed in a quartz reaction tube, and then fixed by suction. Next, the base substrate was heated with a heater in the susceptor until the surface temperature reached 1200 ° C. Next, ammonia gas (NH ₃ ) was introduced into the reaction tube and held for 5 minutes.

Next, trimethylaluminum (TMA) is used as the Al feedstock, NH ₃ is used as the nitrogen feedstock, and these source gases are introduced into the reaction tube together with the hydrogen carrier gas so that TMA / NH ₃ = 0.5 sccm / 350 sccm. And supplied on the base material. Then, an AlN film was formed to a thickness of 1 μm by epitaxial growth for 60 minutes, and a base material composed of the sapphire single crystal base material and the AlN epitaxial film was obtained. When the crystallinity of the AlN epitaxial film was evaluated, an X-ray rocking curve half width of 50 seconds was obtained.

Next, the surface temperature of the base material is set to 1070 ° C., trimethylgallium (TMG) is additionally introduced as a Ga feedstock, and the flow rate ratio of the feedstock gas is TMA / TMG / NH ₃ = 0.1 sccm / 0.9 sccm By supplying on the AlN epitaxial film so as to be / 3000 sccm, a plurality of island-like crystal parts made of Al _0.1 Ga _0.9 N having an upper surface average area of 1 μm ² were formed.

Next, the surface temperature of the base material is changed to 1200 ° C., the island-like crystal portion is used as a nucleus, and the flow rate ratio of the raw material supply gas is TMA / TMG / NH ₃ = 0.95 sccm / 0.05 sccm / 350 sccm. Thus, an Al _0.95 Ga _0.05 N film was formed to a thickness of 1 μm. When the dislocation density of this Al _0.95 Ga _0.05 N film was measured by TEM observation, it was 1 × 10 ⁹ / cm ² .

(Example 2)
An island crystal part was prepared in the same manner as in Example 1 except that the base substrate temperature was heated so that the surface temperature was 900 ° C. to prepare an AlN epitaxial film, and Al _0.95 Ga _{0. A 05} N film was prepared. When the crystallinity of the Al _0.95 Ga _0.05 N film was examined by X-ray diffraction, a rocking curve half-width of about 300 seconds was obtained. The dislocation density of the Al _0.95 Ga _0.05 N film was measured by TEM observation and found to be 8 × 10 ⁹ / cm ² .

(Comparative example)
An Al _0.95 Ga _0.05 N film was produced in the same manner as in the example except that the island-like crystal part was not formed. When the dislocation density of the Al _0.95 Ga _0.05 N film was measured by TEM observation, it was 5 × 10 ¹⁰ / cm ² .

As described above, as is apparent from the examples and comparative examples, the group III nitride film produced according to the production method of the present invention has a dislocation density reduced to 10 ¹⁰ / cm ² or less and good crystallinity. I understand.

  Therefore, by constructing a semiconductor light emitting element or the like from the group III nitride film produced by the manufacturing method of the present invention, the light emission efficiency can be improved. Similarly, by configuring a semiconductor element such as a high-speed IC chip from the group III nitride film, the response characteristics can be improved.

  As described above, the present invention has been described in detail based on the embodiments of the present invention with specific examples. However, the present invention is not limited to the embodiments of the present invention, and various modifications can be made without departing from the scope of the present invention. And can be modified.

  For example, in the above embodiment, the step of forming the island-shaped crystal part on the substrate and the step of epitaxially growing the nitride film using the island-shaped crystal part as a nucleus are performed using the same apparatus. Different devices can also be used. Furthermore, in the above-mentioned examples, etc., the case where the island-shaped crystal part is grown directly on the base material is described. By appropriately controlling the film formation conditions, a multilayer film structure such as a buffer layer or a strained superlattice can be formed, and an island-like crystal part can be formed through this buffer layer or the like.

It is a conceptual diagram for demonstrating the manufacturing method of the group III nitride film of this invention. Similarly, it is a conceptual diagram for explaining the method for producing a group III nitride film of the present invention. Similarly, it is a conceptual diagram for explaining the method for producing a group III nitride film of the present invention. It is a block diagram which shows an example of the semiconductor light-emitting device which comprises the group III nitride film manufactured according to the manufacturing method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base material 2-1 to 2-4 Island-like crystal part 3A, 3 Group III nitride film

Claims (5)

A method for producing a group III nitride film by CVD, wherein a plurality of island-like crystal parts made of a second nitride are isolated from each other on a base made of a first Al-containing nitride. In manufacturing a nitride film from a third nitride different from the second nitride by epitaxially growing the island-shaped crystal part as a nucleus , the second nitride is made of Al and Ga. A method for producing a nitride film, which has a selected composition . ^{2. The} method of manufacturing a nitride film according to claim 1, wherein an average area of an upper surface of the island-shaped crystal part is 0.0001 μm ^{2 to} 100 μm ² . The second nitride contains Al, and the Al composition of the second nitride is smaller than the Al composition of the first Al-containing nitride. A method for manufacturing a nitride film. The first of the half-value width of the (002) X-ray rocking curve Al-containing nitride is equal to or less than 90 seconds, the manufacturing method of the nitride film according to any one of claims 1-3. Characterized in that it comprises a group III nitride film fabricated by the manufacturing method according to any one of claims 1-4, the semiconductor device.

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