JP4794799B2 - Epitaxial substrate and semiconductor multilayer structure - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an epitaxial substrate and a semiconductor multilayer structure, and more specifically, an epitaxial substrate that can be suitably used as a substrate constituting a semiconductor element such as a photonic device and an electronic device, and an element such as a field emitter, and a semiconductor multilayer Concerning structure.
[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 an application material for field emitters.
[0003]
As a substrate on which such a group III nitride film is formed, there is a so-called epitaxial substrate including an underlayer formed by epitaxial growth on a predetermined base material made of sapphire single crystal or the like. In particular, the underlayer is preferably composed of a group III nitride containing Al in order to facilitate the epitaxial growth of a group III nitride film containing Al. Furthermore, since Al-containing nitride has a large band gap, inserting an underlayer made of such a material with a large band gap between the group III nitride film and the base material can improve the efficiency of a semiconductor device or the like. It can also be improved.
[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]
[Problems to be solved by the invention]
However, in the above-described epitaxial substrate, misfit dislocations occur due to a difference in lattice constant between the base material and the underlayer, and the misfit dislocations penetrate through the underlayer as threading dislocations, and the surface thereof. That is, it reaches the surface of the epitaxial substrate. For this reason, a large amount of dislocations due to the misfit dislocations are also generated on the group III nitride film formed on the underlayer, that is, on the epitaxial substrate.
[0006]
The same phenomenon was observed not only when forming an underlayer made of Al-containing group III nitride on the substrate, but also when forming an underlayer made of Ga-containing and other group III nitrides. As a result, when a semiconductor light emitting device or the like is formed from these group III nitride films, for example, the light emission efficiency does not deteriorate, and a semiconductor light emitting device having desired characteristics cannot be obtained.
[0007]
An object of the present invention is to provide a novel epitaxial substrate capable of forming a nitride film having low dislocations and excellent crystallinity, particularly an Al-containing nitride film, and a semiconductor multilayer structure using the same. .
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a base material composed of a sapphire single crystal having a thickness of 600 μm or more, a thickness of 0.1 μm or more formed on the base material, and a surface roughness Ra. and at 2Å less, the dislocation density is at 1 × ¹⁰ 11 / cm ² or less, characterized in that it comprises an X-ray rocking curve FWHM Ru der than 200 seconds, AlN layer in (002) plane, The present invention relates to an epitaxial substrate.
[0009]
Further, the present invention is a substrate composed of a sapphire single crystal having a thickness of 600 μm or more, a thickness formed on the substrate of 0.1 μm or more, and a surface roughness Ra of 2 mm or less, dislocation density is at 1 × ¹⁰ 11 / cm ² or less, (002) plane X-ray rocking curve FWHM Ru der than 200 seconds in a AlN underlayer, formed on the AlN underlayer, III group The present invention relates to a semiconductor multilayer structure comprising a nitride layer group.
[0010]
The present inventors have conducted research for many years in order to form an Al-containing group III nitride film having a low dislocation density and a high crystallinity on a substrate made of a sapphire single crystal or the like. Conventionally, the underlayer constituting the epitaxial substrate has compensated for the lattice constant difference between the base material and the group III nitride layer group such as a group III nitride film to be formed on the epitaxial substrate, and misfit dislocations. It was considered common knowledge to be composed of a low crystallinity group III nitride containing low dislocations and a large amount of dislocations that should be suppressed. As a result, although it is possible to reduce the dislocation density due to the misfit dislocation of the target group III nitride layer group, the group III nitride layer group due to the low crystal quality of the underlayer The dislocation density therein could not be reduced sufficiently, and the crystallinity was deteriorated.
[0011]
In contrast, when the underlayer is made of a group III nitride containing a relatively large amount of Al, the inventors improve the crystallinity of the underlayer, reduce the dislocation density, and reduce the crystal quality. It has been found that even when this is improved, the lattice constant difference between the base material and the group III nitride layer group is complemented, and the occurrence of misfit dislocations 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.
[0012]
On the other hand, even when the above-described high crystal quality Al-containing group III nitride underlayer is used, depending on the type of base material used, such as a group III nitride film formed on the underlayer, that is, on the epitaxial substrate, etc. In some cases, the crystal quality of the group III nitride layer group could not be sufficiently improved. Therefore, the present inventors conducted further intensive studies, found that the thickness of the base material constituting the epitaxial substrate has an influence on the crystal quality of the group III nitride layer group, It has been found that the crystal quality of the group III nitride layer group can be improved by setting the thickness of the substrate to a predetermined value or more.
[0013]
The reason why the thickness of the base material constituting the epitaxial substrate affects the crystal quality of the group III nitride layer group is not clear, but it is presumed to be due to the stress change depending on the thickness of the base material. .
[0014]
Therefore, according to the present invention, the crystal quality of the group III nitride layer group formed on the epitaxial substrate can be improved regardless of the type of base material constituting the epitaxial substrate. And the characteristic of the semiconductor element and device containing such a group III nitride layer group can be improved.
[0015]
The “Group III nitride layer group” in the semiconductor multilayer structure of the present invention can be composed of a single Group III nitride layer or a plurality of Group III nitride layers depending on the type of semiconductor element to be manufactured. It can also be configured as a multilayer film structure in which group nitride layers are laminated. Furthermore, it can be configured as a periodic multilayer film structure in which a plurality of group III nitride layers are alternately and periodically stacked.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on embodiments of the invention.
FIG. 1 is a configuration diagram showing an example of a semiconductor light emitting device formed using the epitaxial substrate of the present invention. A semiconductor light emitting device 30 shown in FIG. 1 includes a base material 1, an underlayer 2, an n-type conductive layer 3, a light emitting layer 4, and a p-type cladding layer 5 that are sequentially formed on the base material 1. , P-type conductive layer 6. A part of the n-type conductive layer 3 is exposed, and an n-type electrode 8 made of, for example, Al / Ti is formed on the exposed n-type conductive layer 3, and on the p-type conductive layer 6. A p-type electrode 9 made of, for example, Au / Ni is formed to constitute a so-called PIN type semiconductor light emitting device. The p-type cladding layer 5 can be omitted if necessary.
[0017]
In FIG. 1, a base material 1 and an underlayer 2 constitute an epitaxial substrate 10, and an n-type conductive layer 3 to a p-type conductive layer 6 constitute a group III nitride layer group 20.
[0018]
The thickness of the substrate 1 needs to be 600 μm or more according to the present invention, more preferably 800 μm, and particularly preferably 1000 μm. Thereby, the crystal quality of the group III nitride layer group 20 can be improved without depending on the type of the base material 1 constituting the epitaxial substrate 10.
[0019]
In addition, although the upper limit of the thickness of the base material 1 is not specifically limited, It is about 3000 micrometers at present. Even when the thickness of the substrate 1 is increased beyond the above value, the effect of the present invention cannot be obtained. Further, since it becomes difficult to obtain the base material 1 having such a thickness and the cost is increased, the manufacturing cost of the epitaxial substrate 10, and thus the semiconductor light emitting element 30 as a whole, increases.
[0020]
The substrate 1 is made of an sapphire single crystal, ZnO single crystal, LiAlO ₂ single crystal, LiGaO ₂ single crystal, MgAl ₂ O ₄ single crystal, MgO single crystal or other oxide single crystal, Si single crystal, SiC single crystal, or the like IV. Known substrate materials such as III-V group single crystals such as Group IV or IV-IV single crystals, GaAs single crystals, AlN single crystals, GaN single crystals, and AlGaN single crystals, and boride single crystals such as Zr ₂ B It can consist of In particular, when the substrate 1 is composed of a sapphire single crystal, the effects of the present invention can be exhibited more effectively.
[0021]
The dislocation density in the underlayer 2 needs to be 1 × 10 ¹¹ / cm ² or less, more preferably 5 × 10 ¹¹ / 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 required to be 200 seconds or less, more preferably 150 seconds or less, and particularly preferably 100 seconds or less. As described above, when the underlayer 2 has high crystal quality, the crystal quality from the n-type conductive layer 3 to the p-type conductive layer 6 formed on the underlayer 2, that is, on the epitaxial substrate 10, can be improved. it can. For example, device characteristics such as the light emission efficiency of the semiconductor light emitting element 30 can be improved. Further, as a secondary effect, the warpage of the substrate can be reduced, and an improvement in device yield can be expected.
[0022]
Further, as described above, the underlayer 2 needs to be composed of Al-containing group III nitride. The Al content in the nitride is preferably 50 atomic% or more with respect to all group III elements, and the underlayer 2 is made of AlN (100 atomic% with respect to all group III elements). It is preferable. Thereby, the crystal quality of the foundation layer 2 can be improved while complementing the lattice constant difference of the base material 1, and as a result, the group III nitride layer group from the n-type conductive layer 3 to the p-type power transmission layer 6. The crystal quality of 20 can be improved.
[0023]
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.
[0024]
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 13 is not particularly limited, and is appropriately selected and set in consideration of the occurrence of cracks and usage.
[0025]
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. The film forming temperature in this patent means a set temperature of the substrate 1. In addition, from the viewpoint of suppressing surface roughness of the underlayer 2, the film forming temperature is preferably 1250 ° C. or lower.
[0026]
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.
[0027]
The n-type conductive layer 3 to the p-type conductive layer 6 can also be made of a nitride containing a group III element such as Al, Ga and In. The composition of each layer can be designed as appropriate according to the function and characteristics of each layer, the characteristics of the semiconductor light emitting element 30 to be manufactured, and the like. Further, as described above, not only the additive elements such as B, Si, Ge, Zn, Be and Mg, and the elements added intentionally, but also trace elements, raw materials, which are inevitably incorporated depending on the film forming conditions, etc. Trace impurities contained in the reaction tube material can also be included.
[0028]
【Example】
Hereinafter, the present invention will be described specifically by way of examples.
Example 1
In this example, a semiconductor light emitting device as shown in FIG. 1 was produced. A 4-inch diameter 1000 μm thick sapphire substrate was pretreated with H ₂ SO ₄ + H ₂ O ₂ and then placed in an MOCVD apparatus. As the carrier gas, while flowing of H ₂ at a flow rate of 1 m / sec, after raising the substrate to 1200 ° C., by flowing trimethyl aluminum (TMA) and NH ₃ at an average flow rate of 1 m / sec, the underlying layer on the sapphire substrate The AlN layer was grown to a thickness of 1 μm to produce an epitaxial substrate. The half width 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%.
[0029]
Next, the substrate temperature was set to 1080 ° C., and an n-GaN layer doped with Si as an n-type conductive layer was grown to a thickness of 1 μm. Next, an i-Ga _0.9 In _0.1 N layer as a light emitting layer was grown on the n-GaN layer to a thickness of 200 mm. _{Then, i-Ga} 0.9 _{In 0.1} the light emitting layer consisting of N layers, Mg-doped _p-Al 0.1 _{Ga 0.9} N layer and Mg-doped as p-type conductive layer serving as a p-type cladding layer A p-GaN layer was grown to a thickness of 100 mm and 0.3 μm, respectively.
[0030]
After the growth was completed, the n-GaN layer constituting the n-type conductive layer was removed until it was exposed, and an n-electrode made of Al / Ti was formed on the surface of the exposed portion. A p-electrode made of Au / Ni was formed on the p-GaN layer as the p-type conductive layer.
[0031]
In addition, the dislocation density in each layer from the n-GaN layer which is an n-type conductive layer to the p-GaN layer which is a p-type conductive layer was 1 × 10 ⁸ / cm ² or less. Further, the half width of the X-ray rocking curve on the (002) plane was 100 seconds or less.
[0032]
(Comparative Example 1)
In the above example, an epitaxial substrate was prepared in the same manner except that the underlying layer was made of GaN formed at a low temperature of 600 ° C. instead of high crystal quality AlN, and a semiconductor light emitting device was manufactured. The dislocation density in each layer from the n-GaN layer which is an n-type conductive layer to the p-GaN layer which is a p-type conductive layer is 1 × 10 ⁹ / cm ² or less, and the X-ray rocking curve half of the (002) plane The value range was 300 seconds or less.
[0033]
(Comparative Example 2)
In the above examples, an epitaxial substrate was prepared in the same manner except that the base material was composed of a sapphire single crystal having a thickness of 430 μm instead of the sapphire single crystal having a thickness of 1000 μm, and a semiconductor light emitting device was manufactured. The dislocation density in each layer from the n-GaN layer which is the n-type conductive layer to the p-GaN layer which is the p-type conductive layer is 5 × 10 ⁸ / cm ² or less, and the X-ray rocking curve half of the (002) plane The value range was 100 seconds or less.
[0034]
As apparent from the comparison between Example 1 and Comparative Examples 1 and 2, according to the present invention, the thickness of the sapphire single crystal substrate is 600 μm or more, and the underlayer is made of an AlN layer having a high dislocation density and a crystal quality. It can be seen that the configuration improves the crystal quality of the group III nitride layer group formed on the epitaxial substrate. Therefore, device characteristics such as luminous efficiency can be improved.
[0035]
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, a multilayer laminated film such as a buffer layer or a strained superlattice can be inserted between the epitaxial substrate and the group III nitride layer group to further improve the crystal quality of the group III nitride layer group. Furthermore, the surface of the base material constituting the epitaxial substrate can be nitrided for the same purpose.
[0036]
Further, by forming the base material constituting the epitaxial substrate from a concave sapphire single crystal or the like, it is possible to reduce the warpage of the semiconductor laminated structure formed by laminating group III nitride layers.
[0037]
【The invention's effect】
As described above, according to the present invention, a novel epitaxial substrate capable of forming a nitride film having low dislocations and excellent crystallinity, particularly an Al-containing nitride film, and a semiconductor multilayer structure using the same Can be provided.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an example of a semiconductor light emitting device including an epitaxial substrate of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Base material, 2 Underlayer, 3 n-type conductive layer, 4 Light emitting layer, 5 p-type clad layer, 6 p-type conductive layer, 8 n-type electrode, 9 p-type electrode, 10 Epitaxial substrate, 20 III nitride layer Group, 30 Semiconductor light emitting devices

Claims (3)

A base material composed of a sapphire single crystal having a thickness of 600 μm or more, a thickness of 0.1 μm or more formed on the base material, a surface roughness Ra of 2 mm or less, and a dislocation density of 1 × 10 ¹¹ / cm ² or less, characterized in that it comprises an X-ray rocking curve FWHM Ru der than 200 seconds, AlN layer in (002) plane, the epitaxial substrate. A base material composed of a sapphire single crystal having a thickness of 600 μm or more, a thickness of 0.1 μm or more formed on the base material, a surface roughness Ra of 2 mm or less, and a dislocation density of 1 × 10 ¹¹ / cm ² or less, (002) Ru der X-ray rocking curve half width of less than 200 seconds in surface, and the AlN underlayer, this was formed on the AlN underlayer, and a group III nitride layer group A semiconductor laminated structure characterized by comprising. The III dislocation density of the nitride layer group is at 1 × 10 9 ^/ cm ² or less, and wherein the X-ray rocking curve is not more than 200 seconds in (002) plane, according to claim 2, wherein Semiconductor stacked structure.

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