JP4545389B2 - Dislocation reduction method for epitaxial substrate and group III nitride layer group - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an epitaxial substrate and a method for reducing dislocations in a group III nitride layer group, and in particular, can be suitably used as a substrate constituting semiconductor elements such as photonic devices and electronic devices, and elements such as field emitters. The present invention relates to an epitaxial substrate that can be formed, and a method for reducing dislocations in a group III nitride layer group in manufacturing the device.
[0002]
[Prior art]
Group III nitride films are used as semiconductor films constituting semiconductor elements such as photonic devices and electronic devices. In recent years, group III nitride films are also attracting attention as semiconductor films constituting high-speed IC chips used for mobile phones and the like. Have been bathed. In particular, a group III nitride film containing Al is attracting attention as a material applied to a light emitting / receiving element or a field emitter in the ultraviolet region.
[0003]
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.
[0004]
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. These group III nitride films are required to have a low dislocation density in order to obtain characteristics as designed when semiconductor elements are formed.
[0005]
By the way, since the melting point of the group III nitride material is relatively high, it is difficult to produce a bulk single crystal substrate from the group III nitride material. Therefore, the group III nitride film must be produced by heteroepitaxial growth on a bulk single crystal substrate of a different material system such as a sapphire single crystal substrate. In this case, due to the lattice constant difference between the bulk single crystal substrate and the group III nitride film, a relatively large amount of misfit dislocations are generated at these interfaces, and the group III due to the misfit dislocations. A large amount of dislocations was introduced into the nitride film, and the crystal quality was significantly deteriorated.
[0006]
From this point of view, an ELO technique has been developed in which a buffer layer formed at a low temperature is inserted between the substrate and the group III nitride film, or a striped SiO ₂ mask is used.
[0007]
[Problems to be solved by the invention]
However, in the case of using the buffer layer described above, dislocations based on the low crystallinity of the buffer layer itself are generated in the group III nitride film, and the dislocation density in the group III nitride film is increased. It could not be reduced sufficiently. In addition, the conventional ELO technique has high material selectivity, and it has been particularly difficult to epitaxially grow a group III nitride film containing a large amount of Al.
[0008]
The present invention relates to a group III nitride layer group having low dislocations and excellent crystallinity, in particular, a novel epitaxial substrate capable of forming a group of nitride layers containing Al, and a group III nitride layer to be formed. It is an object of the present invention to provide a group dislocation reduction method.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a predetermined base material, a dislocation density of 1 × 10 ¹¹ / cm ² or less formed on the base material by MOCVD , and an X-ray on the (002) plane. A group III nitride underlayer made of AlN having a rocking curve half-width of 200 seconds or less, and a transition metal having a melting point of 1300 ° C. or higher, formed on the group III nitride underlayer by MOCVD , or the transition metal an intermediate layer composed of at least one only of compounds containing, formed by the MOCVD method on the intermediate layer containing the melting point 1300 ° C. or more transition metals includes at least Al, the dislocation density of 1 × 10 ¹⁰ / cm ² or less The present invention relates to an epitaxial substrate comprising a group III nitride layer group.
[0010]
Further, the present invention has, on a given substrate, the dislocation density is at 1 × 10 ¹¹ / cm ² or less, X-rays rocking curve in the (002) plane is less than 200 seconds, III group consisting of AlN A nitride underlayer, an intermediate layer composed of at least one of a transition metal having a melting point of 1300 ° C. or higher or a compound containing the transition metal is sequentially formed by MOCVD , and a group III nitride containing at least Al on the intermediate layer The present invention relates to a method for reducing dislocations in a group III nitride layer, characterized in that the dislocation density in the group III nitride layer is reduced by forming the layer group by MOCVD .
[0011]
The present inventors have conducted research for many years in order to form a group III nitride film containing Al having a low dislocation density and high crystallinity on a substrate made of sapphire single crystal or the like. Conventionally, an underlayer such as a buffer layer constituting an epitaxial substrate compensates for a difference in lattice constant between a base material and a group III nitride layer group such as a group III nitride film to be formed on the epitaxial substrate. In order to suppress the occurrence of misfit dislocations, it was considered common knowledge to be composed of a low crystal quality group III nitride formed at a relatively low temperature.
[0012]
When such a low crystal quality underlayer is used, the dislocation density in the group III nitride layer group can be reduced at a certain rate due to the reduction of misfit dislocations. However, the dislocation density in the group III nitride layer group could not be sufficiently reduced due to the low crystal quality of the underlayer itself.
[0013]
On the other hand, when the underlayer is made of a group III nitride containing a relatively large amount of Al, the dislocation density of the underlayer is reduced to improve the crystal quality. It was also found that the lattice constant difference between the base material and the group III nitride layer group is complemented, and the occurrence of misfit dislocations in the group III nitride is suppressed. And, due to the high crystal quality of the underlayer, the crystal quality of the group III nitride layer group can be improved, the dislocation density can be further reduced, and the crystallinity can be improved. Is found.
[0014]
However, the above-described effect of reducing the dislocation density is more remarkable as the Al content of the group III nitride layer group is smaller than the Al content of the underlayer, and the difference in Al content is larger. When the group III nitride layer group containing Al is grown on the base layer, the difference in Al content decreases as the Al content of the group III nitride layer group increases. Only by providing a quality Al-containing group III nitride underlayer, the dislocation density in the target group III nitride layer group cannot be sufficiently reduced, and the crystal quality cannot be sufficiently improved. It was out. In view of this situation, the present inventors applied ELO technology to the above-described epitaxial substrate including an Al-containing high crystal quality underlayer, and further increased the dislocation density in the group III nitride layer group to be formed. Reduced.
[0015]
However, when forming a group III nitride layer group by forming a mask made of SiO ₂ or the like on the above-described epitaxial substrate, a photolithographic process for mask formation is required, and the process becomes complicated. There was a problem. In addition, the density of dislocation density remarkably appears in accordance with the mask pattern, which is a cause of a decrease in yield in device formation. Further, particularly when a group III nitride layer containing Al is grown, the group III nitride layer is deposited on the mask, and dislocation reduction by ELO growth cannot be effectively performed.
[0016]
As an alternative technology, Jpn. J. et al. Appl. Phys. Vol. 42 (2003) p. In L1 to L3, Oshima et al. Reported that the dislocation density can be reduced by inserting a network-like and polycrystalline TiN film as an intermediate layer and using this film as a mask. However, when this technology is applied to the formation of a group III nitride layer containing Al, even when TiN is used, the effect as a mask is not obtained, and a film with severe surface irregularities is formed, which is of good quality. A group III nitride layer group containing Al could not be formed.
[Non-patent literature]
Oshima et al. Jpn. J. et al. Appl. Phys. Vol. 42 (2003) p. L1-L3
[0017]
In view of such a situation, the present inventors conducted further studies, and a uniform single crystal containing a transition metal having a melting point of 1300 ° C. or higher on the above-described epitaxial substrate having an Al-containing high crystal quality underlayer. It was investigated to insert the membrane as an intermediate layer. In this case, the intermediate layer containing a transition metal having a melting point of 1300 ° C. or higher has no effect as a mask, meaning that a group III nitride layer group containing Al is directly formed on the intermediate layer.
[0018]
Such an intermediate layer can be easily formed by a general thin film formation method or growth in an MOCVD apparatus. The dislocation propagated from the underlayer is caused by the stress generated in the intermediate layer made of a single crystal film containing a transition metal having a melting point of 1300 ° C. or higher, and the lattice mismatch at the interface between the intermediate layer and the group III nitride film. This causes a change in the propagation direction of the dislocations and causes the disappearance of dislocations due to dislocation coupling.
[0019]
As a result, by MOCVD, an Al-containing underlayer of high crystal quality, an intermediate layer composed of at least one of a transition metal or a compound containing a transition metal having a melting point of 1300 ° C. or higher, and a group III nitride layer containing at least Al When the epitaxial substrate is composed of the group, the dislocation density of the group III nitride layer group can be remarkably reduced, and the crystal quality can be improved. Furthermore, by using an Al-containing underlayer of high crystal quality, an Al-containing group III nitride layer group can be easily formed without generating cracks.
[0020]
In a preferred embodiment of the present invention, the intermediate layer includes a single layer film containing at least one of a transition metal having a melting point of 1300 ° C. or higher or a compound containing the transition metal, or such a transition metal or a compound containing the transition metal. A film formed by multilayering at least one single crystal film including at least one of the above is used.
[0021]
The “Group III nitride layer group” is a collective term for a single group III nitride layer or a multilayer film structure in which a plurality of group III nitride layers are laminated, and the like. Adopt an appropriate configuration according to the type.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on embodiments of the invention.
FIG. 1 is a diagram showing a configuration of an epitaxial substrate of the present invention. An epitaxial substrate 10 shown in FIG. 1 is formed on a base material 1, a group III nitride underlayer 2 formed on the base material 1, an intermediate layer 3 containing a transition metal having a melting point of 1300 ° C. or higher, and the intermediate layer. Group III nitride layer group 4.
[0023]
The underlayer 2 needs to contain Al, and the content thereof is preferably 50 atomic% or more, more preferably 80 atomic% or more, and further preferably, the underlayer. 2 is preferably composed of AlN (100 atomic% with respect to all group III elements). Thereby, even when the crystal quality of the underlayer 2 is improved as shown below, the difference in lattice constant from the base material 1 can be complemented, and the intermediate layer 3 and further the group III to be formed thereon The nitride layer group 4 can be epitaxially grown while maintaining its crystal quality at a high level.
[0024]
The Al in the underlayer 2 may be contained uniformly throughout the film thickness, but may be contained so as to have a composition gradient in the film thickness direction. In the latter case, for example, by reducing the Al composition from the substrate 1 side to the intermediate layer 3 side, the tensile stress generated during the growth can be relaxed by the difference in lattice constant. The generation of cracks, which is a problem when the group III nitride layer group 4 having a large thickness is formed, can be suppressed.
[0025]
In addition to Al, the underlayer 2 can also contain group III elements such as Ga and In, and additive elements such as B, Si, Ge, Zn, Be, and Mg. 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.
[0026]
The dislocation density in the underlayer 2 is preferably 1 × 10 ¹¹ / cm ² or less, more preferably 5 × 10 ¹⁰ / cm ² or less, and particularly preferably 1 × 10 ¹⁰ / cm ² or less. Further, the half width of the X-ray rocking curve on the (002) plane of the underlayer 2 is preferably 200 seconds or less, more preferably 150 seconds or less, and particularly preferably 100 seconds or less. As described above, since the base layer 2 has such a high crystal quality, the crystal quality of the group III nitride layer group 4 formed above the base layer 2 can be improved. Therefore, device characteristics such as light emission efficiency of the finally obtained semiconductor element, for example, a semiconductor light emitting element can be improved.
[0027]
Further, the surface roughness Ra of the underlayer 2 is preferably 2 mm or less. This measurement is performed in the range of 5 μm square using AFM.
[0028]
In addition, it is preferable that the film thickness of the underlayer 2 is large, and specifically, it is preferable to form the film with a thickness of 0.1 μm or more, and more preferably 0.5 μm or more. The upper limit value of the thickness of the underlayer 2 is not particularly limited, and is appropriately selected and set in consideration of the occurrence of cracks, usage, and the like.
[0029]
The underlayer 2 can be formed using a known film forming means as long as the above requirements are satisfied. However, it can be easily obtained by using the MOCVD method and setting the film forming temperature to 1100 ° C. or higher. In addition, the film-forming temperature of this patent means the preset temperature of the base material 1 itself. In addition, from the viewpoint of suppressing surface roughness of the underlayer 2, the film forming temperature is preferably 1250 ° C. or lower.
[0030]
In addition, since there is a possibility that the film formation temperature of the group III nitride layer group 4 formed above the underlayer is 1250 ° C., the melting point of the transition metal used for the intermediate layer is 1300 in consideration of a margin. It is desirable that the temperature is not lower than ° C. This is because it is necessary to prevent the intermediate layer 3 from being melted during the formation of the group III nitride layer group 4 and having the island-like structure due to the influence of the surface tension or the like. The upper limit of the melting point is not particularly limited, and is appropriately selected in consideration of the intended use, consistency with the process, and the like.
[0031]
However, the intermediate layer 3 includes a transition metal having a melting point of 1300 ° C. or higher, and is a single crystal made of, for example, any one of Ti, TiNx, Ni, NiNx, Cr, CrNx, or at least one of these multilayer films. It is preferable to be comprised from a film | membrane. Further, when the group III nitride film layer group 4 containing Al is grown, since a hole filling effect due to lateral growth cannot be expected, a uniform film having no large voids is preferable.
[0032]
Further, in order to perform epitaxial growth of the group III nitride layer group 4 in a good state, the thickness of the intermediate layer 3 is preferably 0.5 nm or more, and more preferably 1 nm or more. The upper limit of the thickness of the intermediate layer 3 depends on the thickness of the group III nitride layer to be formed, but is about 100 nm. Even if the thickness of the intermediate layer 3 exceeds 100 nm, there is no change in the degree of epitaxial growth.
[0033]
The intermediate layer 3 can be formed using a known film forming means as long as the above requirements are satisfied. For example, the MOCVD method can be used to form the same layer as the underlayer 2 or a different batch. Or PVD methods, such as sputtering and vacuum evaporation, and various CVD methods can also be used. Various assist methods such as plasma and light can be used in combination. Further, in order to change the composition or crystal system of the intermediate layer, it is possible to add a heat treatment in an appropriate gas atmosphere. In this case, in order to promote single crystallization, it is preferable to add a heat treatment in an atmosphere containing any one of hydrogen, nitrogen, and ammonia at a substrate temperature of 1000 ° C. or higher.
[0034]
The intermediate layer 3 is substantially made of a transition metal having a melting point of 1300 ° C. or higher, or a compound of the transition metal, and includes an element contained in the underlayer 2 or the group III nitride layer group 4, such as Al, Ga, In , B or other group III elements or Si, Ge, Zn, Be, Mg, and the like can also be included. Furthermore, 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 material and the reaction tube material can be included.
[0035]
Further, the substrate 1 is composed of a single crystal of sapphire, a single crystal of ZnO, a single crystal of LiAlO _{2, a} single crystal of LiGaO _{2, a} single crystal of MgAl ₂ O _{4, a} single crystal of MgO, a single crystal of Si, a single crystal of SiC, or the like. Group IV or IV-IV single crystals, GaAs single crystals, AlN single crystals, GaN single crystals, III-V single crystals such as AlGaN single crystals, and boride single crystals such as ZrB ₂ are known substrates. It can consist of materials.
[0036]
In particular, when the base material 1 is composed of a sapphire single crystal, it is preferable to perform nitriding treatment on the main surface 1A of the base material 1 to form a surface nitrided layer on the main surface 1A. Thereby, the crystal quality of the underlayer 2, the intermediate layer 3, and the nitride layer group 4 can be further improved. The nitriding treatment can be performed by placing the substrate 1 in an atmosphere containing nitrogen such as ammonia and heating it to a predetermined temperature.
[0037]
Note that, by using the combination of the substrate 1, underlying layer 2, intermediate layer 3, on the intermediate layer 3, as a group III nitride layer group 4 containing at least ^{Al, 1 × 10 10 / cm} 2 Hereinafter, a group III nitride film having a dislocation density of 5 × 10 ⁹ / cm ² or less can be realized.
[0038]
As a preferable average composition of group III nitride layer group 4, it is desirable that the Al composition is equal to or less than the Al composition of underlying layer 2. In this case, in addition to the effect of the intermediate layer 3, the effect of in-plane compression stress due to the composition difference promotes the reduction of dislocations, and the group III nitride layer group 4 with lower dislocations can be realized.
[0039]
Of course, even when the Al composition of the underlayer 2 and the nitride layer group 4 are equal, a sufficient dislocation reduction effect can be expected. Since the Al composition with respect to all group III elements of the underlayer 2 is 50% or more, preferably 80% or more, more preferably 100% (that is, the underlayer is AlN), it has been difficult to achieve low dislocation conventionally. Even in a region where the Al composition with respect to all group III elements in the nitride layer group 4 is 50% or more, and even when the underlayer is AlN, a low dislocation can be realized.
[0040]
【Example】
Hereinafter, the present invention will be described specifically by way of examples.
Example 1
A sapphire substrate having a diameter of 2 inches and a thickness of 430 μm was pretreated with H ₂ SO ₄ + H ₂ O ₂ and then placed in an MOCVD apparatus. As the carrier gas, H ₂ was flowed at a flow rate of 1 m / sec, the substrate was heated to 1200 ° C., and trimethylalmenium (TMA) and NH ₃ were flowed at an average flow rate of 1 m / sec. An AlN layer as a base layer was grown to a thickness of 1 μm. The full width at half maximum of the X-ray diffraction rocking curve on the (002) plane of the AlN layer was 90 seconds, the dislocation density was 2 × 10 ¹⁰ / cm ² , and it was found that the crystal quality was excellent. Further, the surface roughness Ra was 2%.
[0041]
Next, Ti was vacuum-deposited to a thickness of 20 nm on the AlN layer, and placed in the MOCVD apparatus again. The substrate temperature was set to 1200 ° C., NH ₃ was allowed to flow for 1 minute at an average flow rate of 1 m / sec, and heat treatment was applied to form a Ti film as a single crystal TiN _x film.
[0042]
Next, the substrate temperature is set to 1200 ° C., TMA and NH ₃ are allowed to flow at an average flow rate of 1 m / sec, and an AlN layer as a group III nitride layer group is interposed on the AlN layer via the intermediate layer made of the single crystal TiNx. A film was formed to a thickness of 3 μm. When the dislocation density in the AlN film was measured by TEM observation, it was found to be 1 × 10 ⁹ / cm ² . Further, a flat film having a surface roughness Ra of 2.5 mm could be formed.
[0043]
The cross-sectional TEM observation results are shown in FIGS. In FIG. 2, it can be confirmed that the dislocation density is remarkably reduced in the AlN layer as the group III nitride layer group, which is the upper layer of the intermediate layer containing Ti. FIG. 3 shows an enlarged view of the intermediate layer containing Ti, and it can be confirmed that the film containing Ti is uniformly formed with a thickness of about 20 nm. Further, FIG. 4 shows a lattice image of a film containing Ti, and it can be confirmed that a single crystal film is formed.
(Example 2)
[0044]
An AlN layer as a base layer was grown on the sapphire substrate to a thickness of 1 μm, as in Example 1.
[0045]
Next, Ni was vacuum-deposited on the AlN layer to a thickness of 5 nm and placed in the MOCVD apparatus again. The substrate temperature was 1200 ° C., NH ₃ was flowed at an average flow rate of 1 m / sec for 15 seconds, and heat treatment was applied to form a NiN _x film.
[0046]
Next, the substrate temperature is set to 1200 ° C., TMA and NH ₃ are allowed to flow at an average flow rate of 1 m / sec, and AlN as a group III nitride layer group is passed over the AlN layer through the intermediate layer made of the single crystal NiNx. A film was formed to a thickness of 3 μm. It dislocation density of the AlN film is 5 × 10 ⁸ / cm ² as measured by TEM observation was found. Further, a flat film having a surface roughness Ra of 2.0 mm could be formed.
[0047]
(Comparative Example 1)
In the above embodiment, a GaN film as a low-temperature buffer layer was used as the underlayer, and an AlN film as a group III nitride layer group was tried on it. It could not be realized. The half width of the (002) rocking curve of the present GaN underlayer was 300 seconds.
[0048]
(Comparative Example 2)
An AlN film as a group III nitride layer group was formed in the same manner as in the example except that the underlayer was composed of AlN formed at a low temperature of 600 ° C. When the dislocation density in the AlN film was measured by TEM observation, it was found to be 3 × 10 ¹¹ / cm ² .
[0049]
As is apparent from the examples and comparative example 1, it can be seen that the epitaxial growth of the AlN film cannot be performed when the intermediate layer is not provided. In addition, as apparent from the examples and comparative example 2, when a low crystal quality AlN undercoating film formed at a low temperature is used instead of the high crystal quality AlN undercoating film, the finally obtained group III It can be seen that the dislocation density of the AlN film as the nitride layer group cannot be reduced, and the crystal quality cannot be improved.
[0050]
While the present invention has been described in detail based on the embodiments of the present invention with specific examples, the present invention is not limited to the above embodiments of the invention and does not depart from the scope of the present invention. All changes and modifications are possible. For example, in this example, the entire intermediate layer is a nitride film, but it is also possible to nitride only the surface layer to give a distribution to the composition.
[0051]
Further, a multilayer laminated film such as a buffer layer or a strained superlattice may be inserted between the intermediate layer and the group III nitride layer group to further improve the crystal quality of the group III nitride layer group.
[0052]
【The invention's effect】
As described above, according to the present invention, a group III nitride layer group having low dislocations and excellent crystallinity, particularly a nitride layer group containing Al, can be formed, and a novel epitaxial substrate is provided. can do. Furthermore, a method for reducing dislocations in the group III nitride layer group can be provided.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an example of an epitaxial substrate of the present invention.
FIG. 2 is a TEM image showing a cross-sectional state of the epitaxial substrate of the present invention.
FIG. 3 is a TEM image showing a cross-sectional state of the epitaxial substrate of the present invention.
FIG. 4 is a TEM image showing a cross-sectional state of the epitaxial substrate of the present invention.
[Explanation of symbols]
1 base material, 2 ground layer, 3 intermediate layer, 4 group III nitride layer group, 10 epitaxial substrate

Claims (6)

A predetermined substrate;
A group III nitride formed of AlN , formed by MOCVD on the substrate, having a dislocation density of 1 × 10 ¹¹ / cm ² or less and an X-ray rocking curve half-width of (002) plane of 200 seconds or less. A material underlayer,
An intermediate layer made of at least one of a transition metal having a melting point of 1300 ° C. or higher or a compound containing the transition metal, formed by MOCVD on the group III nitride underlayer;
A group III nitride layer group including at least Al and having a dislocation density of 1 × 10 ¹⁰ / cm ² or less formed by MOCVD on the intermediate layer containing a transition metal having a melting point of 1300 ° C. or higher is provided. A featured epitaxial substrate.   The epitaxial substrate according to claim 1, wherein the intermediate layer has a thickness of 0.5 nm to 100 nm.   The epitaxial substrate according to claim 1, wherein the intermediate layer is made of any one of Ti, TiNx, Ni, NiNx, Cr, and CrNx. A group III nitride underlayer made of AlN having a dislocation density of 1 × 10 ¹¹ / cm ² or less on a predetermined substrate and an X-ray rocking curve half-width of (002) plane of 200 seconds or less, melting point an intermediate layer composed of at least one only of compounds containing 1300 ° C. or more transition metals or the transition metal sequentially formed by the MOCVD method, by further MOCVD method III nitride layer group containing at least Al on the intermediate layer A dislocation reduction method for a group III nitride layer group, wherein the dislocation density in the group III nitride layer group is reduced by forming the group.   5. The method for reducing dislocations in a group III nitride layer according to claim 4, wherein the thickness of the intermediate layer is 0.5 nm to 100 nm.   6. The method for reducing dislocations in a group III nitride layer according to claim 4, wherein the intermediate layer is made of any one of Ti, TiNx, Ni, NiNx, Cr, and CrNx.

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