JP4671580B2 - Epitaxial substrate and semiconductor device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an epitaxial substrate , and more particularly to an epitaxial substrate that can be suitably used as a substrate constituting semiconductor elements such as photonic devices and electronic devices, and elements such as field emitters.
[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 a base film formed by epitaxial growth on a predetermined base material. A sapphire single crystal is used as the base material because it is inexpensive and easily available.
[0004]
After the epitaxial substrate is placed on a susceptor provided in a predetermined reaction tube, it is heated to a predetermined temperature by a heating mechanism inside and outside the susceptor, and a Group III metal feedstock and a nitrogen feedstock, and other materials as required. An element feedstock is introduced into the reaction tube together with a carrier gas and supplied onto the epitaxial substrate, thereby forming a target group III nitride film according to the CVD method.
[0005]
[Problems to be solved by the invention]
As the sapphire single crystal substrate described above, a so-called C-plane sapphire single crystal substrate that has been conventionally oriented in the C axis (<0001> direction) has been used. However, the C-plane sapphire single crystal base material has a principal plane oriented in another crystal axis direction, for example, because the C-plane sapphire is difficult to cut out and the substrate growth rate is low. It is expensive compared with a crystal base material etc., and it is difficult to obtain a large-diameter one.
[0006]
From this point of view, an attempt has been made to use a sapphire single crystal base material having a principal surface oriented in the direction of the other crystal axis in place of the C-plane sapphire single crystal base material. However, when a base film made of a group III nitride containing Al in particular is formed on such a sapphire single crystal substrate, a large number of surface defects are generated on the base film, and the surface flatness is remarkably deteriorated. There was a problem that. Furthermore, the deterioration of crystallinity is remarkable, and when a target semiconductor device is manufactured by forming a group III nitride film on such an epitaxial substrate, the characteristics are remarkably deteriorated.
[0007]
Therefore, at present, an epitaxial substrate comprising a sapphire single crystal base material oriented in the direction of the crystal axis other than the C axis and an Al-containing base film formed on the single crystal base material can be used practically. The current situation is that it is not possible.
[0008]
The present invention includes a sapphire single crystal base material having a principal surface oriented in the direction of the crystal axis other than the C axis, and a group III nitride underlayer containing at least Al, and provides an epitaxial substrate that is sufficient for practical use. It aims at providing the said sapphire single-crystal base material which comprises an epitaxial substrate.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a sapphire single crystal substrate having a principal surface inclined at a predetermined angle from the <11-20> direction toward the <1-100> direction, and the sapphire single crystal substrate. A group III nitride underlayer containing at least Al formed on the main surface, the inclination angle is 0.05 degrees to 0.2 degrees, and the surface roughness of the group III nitride underlayer Is not more than 5 mm, the group III nitride underlayer is made of AlN, and includes a surface nitride layer in a surface layer portion of the sapphire single crystal substrate facing the group III nitride underlayer , the surface nitride layer The nitrogen content is 10 atomic% or less at a depth of 1 nm from the main surface of the sapphire single crystal substrate, and the half width of the X-ray rocking curve at the (0002) plane of the group III nitride underlayer is 350 seconds. Less than There, wherein the X-ray rocking curve is not more than 2000 seconds in (10-12) plane, those of the epitaxial substrate.
[0010]
The present invention also relates to a semiconductor device including the epitaxial substrate described above or below .
[0011]
The inventors of the present invention have intensively studied to achieve the above object. And since it is cheap compared with the above-mentioned C-plane sapphire single crystal base material and large diameter processing is easy, the main surface oriented in the a-axis (<11-20> direction) is used. The so-called A-plane sapphire single crystal substrate was noted. And the earnest examination was implemented in order to use this A surface sapphire single crystal base material for practical use.
[0012]
As a result, the main surface of the sapphire single crystal base material is cut out from the bulk sapphire single crystal member so as to be inclined at a predetermined angle from the a axis toward the m axis (<1-100> direction). By forming an Al-containing group III nitride underlayer on the inclined main surface of the obtained sapphire single crystal substrate, surface defects and surface roughness in the underlayer can be prevented and put to practical use. It has been found that an epitaxial substrate can be provided.
[0013]
Therefore, when a target semiconductor element in which a group III nitride film is formed on the epitaxial substrate is fabricated, deterioration of various characteristics can be suppressed, and an epitaxial substrate including a C-axis sapphire single crystal substrate is used. Thus, it becomes possible to obtain the same characteristics as those of the semiconductor element manufactured.
[0014]
In the present invention, a surface nitride layer is formed on the surface layer portion of the sapphire single crystal substrate facing the group III nitride underlayer. In this case, the group III nitride underlayer is formed on the main surface of the sapphire single crystal substrate via the surface nitride layer, and the crystallinity of the group III nitride underlayer is further increased. Can be improved. Therefore, various characteristics of a semiconductor device manufactured using the epitaxial substrate thus obtained can be further improved.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on embodiments of the invention.
[0016]
FIG. 1 is a diagram showing the crystal structure of a sapphire single crystal. As is clear from FIG. 1, the sapphire single crystal has a hexagonal crystal structure, and the C, a, and m axes are perpendicular to each other. To do.
[0017]
In the present invention, the orientation direction X of the main surface in the sapphire single crystal base material constituting the epitaxial substrate needs to be inclined at a predetermined angle from the a-axis to the m-axis. Specifically, the crystal structure shown in FIG. 1 needs to be inclined by an angle θ so as to rotate around the C axis in a plane including the a axis and the m axis. If the object of the present invention can be achieved, the value of the angle θ is not particularly limited, but is set to 0.05 degrees to 0.2 degrees.
[0018]
In this case, the surface defects of the Al-containing group III nitride underlayer formed on the sapphire single crystal substrate can be more effectively suppressed, and the surface flatness can be improved. Specifically, the surface roughness Ra of the base film can be reduced to 5 mm or less, and further to 3 mm or less.
[0019]
FIG. 2 is a configuration diagram showing an example of the epitaxial substrate of the present invention. An epitaxial substrate 10 shown in FIG. 2 includes a sapphire single crystal substrate 1 and a group III nitride base film 3 containing at least Al formed on the main surface 1A of the sapphire single crystal substrate 1. A surface nitride layer 2 is formed on the surface layer portion of the sapphire single crystal substrate 1.
[0020]
In the epitaxial substrate 10 shown in FIG. 2, the main surface 1A of the sapphire single crystal substrate 1 needs to be oriented in the X direction shown in FIG. Then, by setting the inclination angle of the main surface 1A within the preferable range described above, the surface roughness Ra of the main surface 3A of the base film 3 can be set to 5 mm or less. Therefore, when a predetermined group III nitride film is formed on the epitaxial substrate 10, the deterioration of the crystal quality can be suppressed, and a semiconductor element exhibiting good characteristics can be obtained.
[0021]
Moreover, in the epitaxial substrate 10 shown in FIG. 2, the surface nitride layer 2 is formed in the surface layer part of the sapphire single-crystal base material 1, By this, the crystallinity of the base film 3 can be improved. Surface nitrided layer 2 is formed such that the nitrogen content at a depth of 1 nm from main surface 1A of sapphire single crystal substrate 1 is preferably 10 atomic% or less. In this case, the X-ray rocking curve half-value width in the (0002) plane of the base film 3 is 350 seconds or less, the X-ray rocking curve half-value width in the (10-12) plane is 2000 seconds or less, and further 1500 seconds or less. Good crystallinity is exhibited.
[0022]
The nitrogen content and thickness of the surface nitrided layer 2 are the compositions in the thickness direction obtained by performing composition analysis by ESCA at the same time as etching the sapphire single crystal substrate 1 in the thickness direction using Ar ions. It is obtained from analysis.
[0023]
Detailed ESCA measurement conditions are as shown below. As an X-ray source, an X-ray with an energy of 1253.6 eV using an Mg target was used. The analysis was performed with a measurement area of 1.1 mmφ, a detection angle of 45 degrees, and a path energy of 35.75 eV, and an N1s spectrum was used to identify nitrogen atoms. The degree of vacuum at the time of measurement was 3 × 10 ⁻⁹ Torr. The etching uses Ar ⁺ ions with an acceleration voltage of 3.0 kV, and the raster area is 3 mm × 3 mm.
[0024]
The etching rate under these conditions was 40 Å / min for SiO ₂ , and the sputtering rate for Al ₂ O ₃ was confirmed to be 1/3 that for SiO ₂ . Therefore, for convenience, the sputtering rate of the nitrided surface is calculated from the Al ₂ O ₃ conversion etching rate, the time for 1 nm etching is calculated backward, and the nitrogen concentration at the time of etching is set as the nitrogen content.
[0025]
The surface nitride layer 2 is performed by placing the sapphire single crystal substrate 1 in a nitrogen-containing atmosphere such as ammonia and heating it for a predetermined time. And it forms by controlling nitrogen concentration, nitriding temperature, and nitriding time suitably.
[0026]
The surface nitrided layer 2 is not necessarily required, and even when the base film 3 is formed directly on the main surface 1A of the sapphire single crystal substrate 1 that does not have the surface nitrided layer 2, The objective can be fully achieved.
[0027]
The effect of the present invention becomes more prominent as the Al content in the underlying film 3 increases. Therefore, the Al content in the base film 3 is preferably 50 atomic% or more with respect to all group III elements, and particularly 100 atomic% or more, that is, the base film 3 is made of AlN .
[0028]
The base film 3 can contain a group III element such as Ga and In in addition to Al, and can also contain an element such as Mg, Si, or B as required. Furthermore, it is possible to include not only elements added intentionally but also impurities inevitably included depending on film forming conditions and the like, as well as trace impurities contained in raw materials and reaction tube materials.
[0029]
The underlayer 3 can be produced using a known film formation method such as a CVD method.
[0030]
【Example】
Hereinafter, the present invention will be described specifically by way of examples.
Example 1
After using a sapphire single crystal having a main surface inclined at an angle of 0.12 degrees from the a-axis direction to the m-axis direction as a sapphire single crystal substrate, and placing this on a susceptor installed in a quartz reaction tube, The sample was suction fixed and heated to 1200 ° C.
[0031]
Then, ammonia gas (NH ₃ ) was allowed to flow along with the hydrogen carrier gas for 5 minutes to nitride the main surface of the substrate. As a result of analysis by ESCA, it was found that a nitride layer was formed on the main surface by this surface nitriding treatment, and the nitrogen content at a depth of 1 nm from the main surface was 5 atomic%.
[0032]
Next, trimethylaluminum (TMA) is used as the Al feedstock, ammonia gas (NH ₃ ) is used as the nitrogen feedstock, and the reaction gas is mixed with hydrogen carrier gas at a flow rate of NH ₃ / TMA molar ratio = 500. While being introduced into the tube, it was supplied onto the base material to form an AlN base film with a thickness of 3 μm, thereby producing an epitaxial substrate. The flow rates of NH ₃ and TMA are appropriately selected according to the film formation rate so as to satisfy the molar ratio.
[0033]
When the crystallinity of the AlN base film thus obtained was examined by X-ray diffraction, the X-ray rocking curve half-width of the (0002) plane was about 250 seconds, and the X-ray rocking curve of the (10-12) plane was The full width at half maximum was about 1100 seconds, and the surface roughness Ra was 2.5 mm. Therefore, it has been found that the AlN underlayer shows good crystallinity and good surface flatness.
[0034]
(Example 2)
An epitaxial substrate was produced in the same manner as in Example 1 except that a sapphire single crystal having a main surface inclined at an angle of 0.18 degrees from the a-axis direction to the m-axis direction was used as the sapphire single crystal substrate. When the crystallinity of the AlN underlayer was examined by X-ray diffraction, the X-ray rocking curve half-width of the (0002) plane was about 300 seconds, and the X-ray rocking curve half-width of the (10-12) plane was about 900 seconds. And the surface roughness Ra was 3.0 mm. Therefore, it has been found that the AlN underlayer shows good crystallinity and good surface flatness.
[0035]
(Example 3)
An epitaxial substrate was produced in the same manner as in Example 1 except that a sapphire single crystal having a main surface inclined at an angle of 0.08 degrees from the a-axis direction to the m-axis direction was used as the sapphire single crystal base material. When the crystallinity of the AlN underlayer was examined by X-ray diffraction, the X-ray rocking curve half-width of the (0002) plane was about 250 seconds, and the X-ray rocking curve half-width of the (10-12) plane was about 1400 seconds. And the surface roughness Ra was 2.0 mm. Therefore, it has been found that the AlN underlayer shows good crystallinity and good surface flatness.
[0036]
(Reference Example 4)
A sapphire single crystal having a main surface inclined at an angle of 0.12 degrees in the m-axis direction from the a-axis direction is used as the sapphire single crystal base material, and the main surface of the base material is subjected to nitriding treatment. An epitaxial substrate was produced in the same manner as in Example 1 except that there was no. When the crystallinity of the AlN underlayer was examined by X-ray diffraction, the X-ray rocking curve half-width of the (0002) plane was about 320 seconds and the X-ray rocking curve half-width of the (10-12) plane was about 1900 seconds. The surface roughness Ra was 3.5 mm. Therefore, it was found that the AlN underlayer has substantially good crystallinity and surface flatness.
[0037]
(Comparative example)
An epitaxial substrate was produced in the same manner as in the example except that an A-plane sapphire single crystal was used as the sapphire single crystal substrate. The half width of the X-ray rocking curve on the (0002) plane of the AlN underlayer is 500 seconds, the half width of the X-ray rocking curve on the (10-12) plane is about 2500 seconds, and the surface roughness Ra is 6 mm. Thus, it has been found that both crystallinity and surface flatness are not sufficient.
[0038]
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 epitaxial substrate 10 shown in FIG. 2, a multilayer laminated film such as a buffer layer or a strained superlattice is inserted between the sapphire single crystal substrate 1 and the base film 3 to further improve the crystallinity of the base film 3. It can also be made.
[0039]
【The invention's effect】
As described above, according to the present invention, the sapphire single crystal substrate having a main surface oriented in the crystal axis direction other than the C axis and the group III nitride underlayer containing at least Al is sufficient for practical use. While providing an epitaxial substrate, the sapphire single-crystal base material which comprises this epitaxial substrate can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram showing a crystal structure of a sapphire single crystal.
FIG. 2 is a configuration diagram showing an example of an epitaxial substrate of the present invention.
[Explanation of symbols]
1 Sapphire single crystal substrate, 2 surface nitrided layer, 3 Al-containing group III nitride underlayer, 10 epitaxial substrate

Claims (2)

  A sapphire single crystal base material having a main surface inclined at a predetermined angle from the <11-20> direction toward the <1-100> direction, and at least Al formed on the main surface of the sapphire single crystal substrate. A group III nitride undercoat film containing, wherein the tilt angle is 0.05 degree to 0.2 degree, and the surface roughness of the group III nitride base film is 5 mm or less, the group III nitride The underlayer is made of AlN, and has a surface nitride layer in a surface layer portion of the sapphire single crystal substrate facing the group III nitride underlayer, and the nitrogen content of the surface nitride layer is the sapphire single crystal substrate 10 nm or less at a depth of 1 nm from the main surface, and the half width of the X-ray rocking curve in the (0002) plane of the group III nitride underlayer is 350 seconds or less, in the (10-12) plane Wherein the linear rocking curve half width is less than 2000 seconds, the epitaxial substrate. A semiconductor device comprising the epitaxial substrate according to claim 1 .

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