JP2004111865A - Semiconductor substrate and its fabricating process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor substrate capable of obtaining a sufficient lattice relaxation effect. <P>SOLUTION: An epitaxial wafer 100 comprises the substrate 1 of GaAs (111) A surface and a laminate of buffer layer 2 that has a thickness of 50nm and is composed of GaN, an eptaxial layer 3 that has thickness of 25μm and is composed of GaN, the buffer later 4 that has a thickness of 50nm and is composed of GaN, and the eptaxial layer 5 that has a thickness of 25μm and is composed of GaN. These layers are stacked in this order by means of the halogen CVD method using Ga, HCL and NH<SB>3</SB>gases. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor substrate and a method for manufacturing the same, and more particularly, to a semiconductor substrate such as an epitaxial wafer suitable for forming a light emitting element such as a semiconductor laser element and a blue laser diode, and a method for manufacturing the same.
[0002]
[Prior art]
In recent years, there has been an increasing need for blue LEDs and lasers for use in color displays and optical discs, and GaN-based materials have been spotlighted as materials that emit light in the blue or ultraviolet region. As a substrate for forming such a GaN-based epitaxial film, it is desirable to use a GaN substrate lattice-matched with the epitaxial film to be formed, but it is very difficult to manufacture such a GaN substrate. Therefore, a sapphire substrate whose lattice constant is relatively close to that of a GaN-based epitaxial film is generally used. Further, in order to alleviate this lattice shift, a buffer layer made of GaN or AlN grown at a low temperature is usually used.
[0003]
In addition, regarding the conventional GaN-based epitaxial crystal, a single (single) low-temperature buffer layer is formed to suppress dislocation due to lattice shift, and there are reports on the effect of the low-temperature GaN buffer layer (for example, Non-Patent Document 1). However, the lattice displacement mitigation method using such a low-temperature buffer layer does not sufficiently suppress the dislocation generated due to the lattice displacement, and has a problem in reliability, for example, when a blue laser device is manufactured.
[0004]
In order to solve such inconveniences, various techniques for further suppressing the generation of dislocations due to lattice mismatch have been tried. One of them is to use a metal-organic vapor phase epitaxy (MO-CVD) method to form a low-temperature buffer layer. Is reported to have a two-stage (double) configuration (for example, see Non-Patent Document 2).
[0005]
[Non-patent document 1]
J. Appl. Phys. 71 (1992) 5543
[Non-patent document 2]
Jpn. J. Appl. Phys. Vol. 37 (1998) pp. L316-L318
[0006]
[Problems to be solved by the invention]
However, when a GaN-based epitaxial film is grown on a two-stage low-temperature buffer layer made of GaN formed using such a technique, an epitaxial layer having a sufficient thickness tends to be unable to grow. For example, the thicknesses of the buffer layer and the epitaxial layer according to Non-Patent Document 2 are 20 nm and only 1 μm, respectively. In this case, there is a serious problem that a sufficient lattice relaxation effect cannot be obtained due to the extremely thin film thickness of the epitaxial layer. It is thought that the reason why the growth of the epitaxial film is not promoted is that the low-temperature buffer layer is formed by the MO-CVD method.
[0007]
Therefore, the present invention has been made in view of such circumstances, and provides a semiconductor substrate capable of obtaining a sufficient lattice relaxation effect and capable of obtaining a highly reliable light emitting element, and a method of manufacturing the same. Aim.
[0008]
[Means for Solving the Problems]
In order to solve the above problems, a semiconductor substrate according to the present invention includes a substrate made of a compound semiconductor, a first buffer layer mainly made of GaN formed on the substrate, and a GaN formed on the first buffer layer. A first epitaxial layer comprising GaN, a second buffer layer mainly comprising GaN formed on the first epitaxial layer, and a second epitaxial layer comprising GaN formed on the second buffer layer. In this case, the first buffer layer and the second buffer layer are formed by a vapor deposition method using a reaction system containing a halide.
[0009]
In a semiconductor substrate having such a structure, the growth rate of each layer can be increased by using a CVD method using a reaction system containing a halide, that is, a halogen-based CVD method, as compared with the MO-CVD method. Specifically, the film formation rate by the halogen-based CVD method is about 10 of the MO-CVD method. The present inventor has confirmed that the thickness of the first and second epitaxial layers on the first and second buffer layers thus formed can be significantly increased as compared with the related art. The detailed mechanism of whether this is only due to the formation of the first and second buffer layers at a high deposition rate, or whether the increase in the deposition rate of the first and second epitaxial layers is also related is not yet known. However, in addition to the increase in deposition rate, other factors such as the adhesion of the buffer layer and the epitaxial layer formed by the halogen-based CVD method, the influence of the film thickness, and the presence or absence of nucleation are also complicatedly related. I cannot deny the possibility of doing it.
[0010]
Specific examples of the halogen-based CVD method include a hydride CVD method using metal Ga and HCl as a group III raw material and NH ₃ as a group V raw material, and an organic metal containing Ga as a group III raw material (for example, trimethylgallium). ; _(CH3) 3 Ga or triethyl _{gallium; (C 2 H 5) 3} Ga) and halogen-CVD method using NH ₃ as HCl and V group material and the like.
[0011]
Specifically, the plane orientation of the substrate is preferably the (111) A plane. More specifically, it is preferable that the substrate is made of a group III-V compound semiconductor, and it is particularly useful that the group III-V compound semiconductor is GaAs or InP.
[0012]
More preferably, the thickness of the first buffer layer is 10 to 100 nm, and the thickness of the second buffer layer is 5 to 70 nm. If the thickness of the first buffer layer is less than 10 nm, the first buffer layer tends to be partially interrupted during the temperature rise for forming the first epitaxial layer, and when this occurs, it is formed thereon. The first epitaxial layer may peel off. On the other hand, when the thickness of the first buffer layer exceeds 100 nm, nucleation (nucleation) tends to occur during the growth of the first buffer layer where flatness is required. The layer tends to grow in a pyramid shape, which is not preferable.
[0013]
Then, from the viewpoint of exhibiting a sufficient lattice relaxation effect, the thickness of the first or second epitaxial layer is desirably 20 to 1000 μm.
[0014]
Further, the method for manufacturing a semiconductor substrate according to the present invention is a method for effectively manufacturing the semiconductor substrate according to the present invention, wherein (a) a method of manufacturing a semiconductor substrate on a substrate made of a compound semiconductor under an environment heated to a first temperature. Supplying a first gas containing a halide, a second gas containing Ga, and a third gas containing NH ₃ to form a first buffer layer mainly composed of GaN; Supplying the first to third gases in an environment heated to a second temperature higher than the temperature of (a) to form a first epitaxial layer containing GaN on the first buffer layer; (C) supplying first to third gases in an environment heated to a first temperature to form a second buffer layer mainly composed of GaN on the first epitaxial layer; In an environment heated to a temperature of 2, the first to third And forming a second epitaxial layer containing GaN on the second buffer layer.
[0015]
In this case, it is preferable that the first temperature be a temperature in the range of 300 to 700 ° C. and the second temperature be 750 ° C. or higher. If the first temperature (film formation temperature) when forming the first buffer layer is lower than 300 ° C., the first buffer layer mainly composed of GaN tends to be insufficiently grown. On the other hand, when the first temperature exceeds 700 ° C., the amount of heat input to the substrate increases, the thermal budget deteriorates, and the first buffer layer receives thermal damage. There is a possibility that the epitaxial layer is peeled off.
[0016]
Specifically, it is preferable to use HCl gas as the first gas. More specifically, a substrate having a plane orientation of (111) A is used as the substrate, and more specifically, a substrate of III-V It is preferable to use a group III-V compound semiconductor, and it is particularly useful to use a group III-V compound semiconductor of GaAs or InP.
[0017]
Furthermore, the thickness of the first buffer layer is 10 to 100 nm, the thickness of the second buffer layer is 5 to 70 nm, and the thickness of the first or second epitaxial layer is 10 to 100 nm. It is desirable to adjust the process conditions in each step so as to be 20 to 1000 μm.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail. The positional relationship such as up, down, left, and right is based on the positional relationship shown in the drawings unless otherwise specified. The dimensional ratios in the drawings are not limited to the illustrated ratios.
[0019]
FIG. 1 is a schematic sectional view showing a preferred embodiment of a semiconductor substrate according to the present invention. The epitaxial wafer 100 (semiconductor substrate) has a buffer layer 2 (first buffer layer) made of GaN having a thickness of 50 nm and an epitaxial layer 3 (first buffer layer) made of GaN having a thickness of 25 μm on a GaAs (111) A plane substrate 1. 1), a buffer layer 4 made of GaN having a thickness of 50 nm (second buffer layer), and an epitaxial layer 5 made of GaN having a thickness of 25 μm (second epitaxial layer) are stacked in this order in a two-stage structure. It is.
[0020]
The epitaxial wafer 100 configured as described above can be manufactured by, for example, a method described below. Here, the CVD apparatus 20 shown in FIG. 2 was used as a film forming apparatus. FIG. 2 is a schematic diagram showing the configuration of the CVD apparatus 20. The CVD apparatus 20 heats the entire reaction chamber 24 from outside the reaction chamber 24 made of quartz provided with a first gas introduction port 21, a second gas introduction port 22, and an exhaust port 23. And a resistance heater 25. At a position corresponding to the first gas inlet 21 in the reaction chamber 24, a source boat 27 on which a gallium metal 26 is installed is mounted.
[0021]
First, the substrate 1 is placed at a predetermined position in the reaction chamber 24 using such a CVD apparatus 20. Next, the entire inside of the reaction chamber 24 is externally heated by the resistance heater 25, and HCl is supplied from the first gas inlet 21 while the substrate 1 is kept at 500 ° C. As a result, the HCl causes a chemical reaction with Ga placed in the source boat 27 heated to about 800 ° C. to generate a group III gas, and the group III gas is supplied onto the substrate 1.
[0022]
On the other hand, NH ₃ gas as a group V material is introduced from the second gas inlet 22. At this time, the group V / group III ratio of the source gas is, for example, 200. As a result, a GaN crystal is epitaxially grown on the substrate 1 and formed into a film for a predetermined time to form the buffer layer 2.
[0023]
Next, after heating the entire inside of the reaction chamber 24 by the resistance heater 25 so that the temperature of the substrate 1 on which the buffer layer 2 is formed is 800 ° C., HCl and NH ₃ are introduced onto the buffer layer 2. . At this time, the group V / group III ratio of the source gas is set to, for example, 200. Thus, a GaN crystal is epitaxially grown on the buffer layer 2 and is formed for a predetermined time to form the epitaxial layer 3. At this time, when the epitaxial layer 3 was observed and evaluated, it was confirmed that the epitaxial layer 3 was extremely excellent in flatness and the lattice shift was reduced.
[0024]
Then, as the temperature of the substrate 1, buffer layer 2 is formed is again 500 ° C., after lowering the temperature throughout the reaction chamber within 24 performs temperature adjustment of the resistance heater 25, HCl and NH ₃ buffer layer 2 Then, a buffer layer 4 is formed on the epitaxial layer 3 in the same manner as when the buffer layer 2 is formed. After that, the temperature of the resistance heater 25 is adjusted to raise the temperature inside the reaction chamber 24 again, so that the temperature of the substrate 1 on which the buffer layer 4 is formed becomes 800 ° C., and the above-described epitaxial layer 3 is formed. The epitaxial layer 5 is formed on the buffer layer 4 in the same manner as described above.
[0025]
As another method, an organic metal halide CVD method in which TEG or TMG and HCl are introduced from the first gas inlet 21 and a chemical reaction thereof is performed without installing the source boat 27 in the reaction chamber 24 is used. You may.
[0026]
FIG. 3 is a schematic diagram showing the configuration of the CVD apparatus 30 used in this case. The CVD apparatus 30 heats the entire reaction chamber 34 from outside the reaction chamber 34 made of quartz provided with a first gas inlet 31, a second gas inlet 32, and an exhaust port 33. , And has the same configuration as the CVD apparatus 20 except that the source boat 27 is not provided.
[0027]
In this case, first, the substrate 1 is placed at a predetermined position in the reaction chamber 34. Next, while the entire inside of the reaction chamber 34 is heated from the outside by the resistance heater 35 and the substrate 1 is kept at 500 ° C., TEG or TMG and HCl are supplied from the first gas inlet 31 and the second NH ₃ gas as a group V raw material is introduced from the gas inlet 32. At this time, the group V / group III ratio of the source gas is set to, for example, 200. As a result, a GaN crystal is epitaxially grown on the substrate 1 and formed into a film for a predetermined time to form the buffer layer 2.
[0028]
Next, after heating the entire inside of the reaction chamber 34 by the resistance heater 35 so that the temperature of the substrate 1 on which the buffer layer 2 is formed becomes 800 ° C., TEG or TMG, HCl, and NH ₃ are added to the buffer layer. 2 on top. At this time, the group V / group III ratio of the source gas is, for example, 200. Thus, a GaN crystal is epitaxially grown on the buffer layer 2 and is formed for a predetermined time to form the epitaxial layer 3. At this time, when the epitaxial layer 3 was observed and evaluated, it was confirmed that the epitaxial layer 3 was extremely excellent in flatness and the lattice shift was reduced.
[0029]
Next, the temperature of the resistance heater 35 is adjusted so that the temperature of the substrate 1 on which the buffer layer 2 is formed becomes 500 ° C. again, and the entire temperature inside the reaction chamber 34 is lowered. Then, TEG or TMG, HCl, and NH ₃ is introduced on the buffer layer 2, and a buffer layer 4 is formed on the epitaxial layer 3 in the same manner as the formation of the buffer layer 2 described above. After that, the temperature of the resistance heater 35 is adjusted to raise the temperature inside the reaction chamber 34 again, so that the temperature of the substrate 1 on which the buffer layer 4 is formed becomes 800 ° C., and the above-described epitaxial layer 3 is formed. The epitaxial layer 5 is formed on the buffer layer 4 in the same manner as described above.
[0030]
Here, a photoluminescence (PL) method was performed on the epitaxial wafer 100 to evaluate the optical characteristics of the epitaxial layers 3 and 5 thus obtained. For comparison, the same measurement was performed on an epitaxial wafer having a single-stage structure having only the buffer layer 2 and the epitaxial layer 3 formed by the same method. The measurement was performed at room temperature.
[0031]
FIG. 4 is a graph showing an emission spectrum of the epitaxial wafer. The horizontal axis in the figure indicates the emission wavelength from the epitaxial wafer, and the vertical axis indicates the emission intensity. In the figure, curves L1 and L2 indicate the emission spectra of the epitaxial wafer 100 and the epitaxial wafer of the comparative example, respectively. Further, a peak existing near a wavelength of 360 nm corresponds to light emission from a band edge. The peak present at a wavelength of about 570 nm is generally referred to as a “yellow peak”, and is regarded as a peak due to a deviation in stoichiometry of the crystal. The lower the intensity, the better the crystal is formed. It suggests that
[0032]
From these results, it was confirmed that the epitaxial wafer 100 having the two-stage structure of the present invention had higher band-edge emission near the wavelength of 360 nm than the wafer of the comparative example, and had better crystal quality. . In addition, the epitaxial wafer 100 having a two-stage structure of the present invention has a lower 'yellow peak' intensity around a wavelength of 570 nm than the wafer of the comparative example. It was found that the crystal quality was significantly improved.
[0033]
Further, TEM observation of a crystal cross section of the epitaxial wafer 100 was performed to evaluate the dislocation state of the buffer layers 2 and 4 and the epitaxial layers 3 and 5. FIG. 5 shows a cross-sectional TEM photograph of the vicinity of the buffer layer 4 as the second layer in the epitaxial wafer 100. From this, it was found that the linear dislocations were reduced by the buffer layers 2 and 4.
[0034]
【The invention's effect】
As described above, according to the semiconductor substrate and the method for manufacturing the same of the present invention, a two-stage structure is formed by alternately laminating a buffer layer and an epitaxial layer by a CVD method using a reaction system containing a halide. A sufficient lattice relaxation effect can be obtained by suppressing dislocations in the epitaxial layer. In addition, by using such a semiconductor substrate of the present invention, a high-quality GaN crystal layer can be formed, and as a result, a light emitting element such as a semiconductor laser element or a blue laser diode having excellent reliability can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view showing a preferred embodiment of a semiconductor substrate according to the present invention.
FIG. 2 is a schematic diagram illustrating a configuration of a CVD apparatus 20.
FIG. 3 is a schematic diagram illustrating a configuration of a CVD apparatus 30.
FIG. 4 is a graph showing an emission spectrum of the epitaxial wafer.
FIG. 5 shows a TEM photograph of a cross section near the buffer layer 4 in the epitaxial wafer 100.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... board | substrate, 2 ... buffer layer (1st buffer layer), 3 ... epitaxial layer (1st epitaxial layer), 4 ... buffer layer (2nd buffer layer), 5 ... epitaxial layer (2nd epitaxial layer), 20, Reference numeral 30: CVD apparatus, 24, 34: reaction chamber, 100: epitaxial wafer (semiconductor substrate).

Claims (13)

A substrate made of a compound semiconductor;
A first buffer layer mainly made of GaN formed on the substrate;
A first epitaxial layer comprising GaN formed on the first buffer layer;
A second buffer layer mainly composed of GaN formed on the first epitaxial layer;
A second epitaxial layer comprising GaN formed on the second buffer layer,
A semiconductor substrate, wherein the first buffer layer and the second buffer layer are formed by a vapor deposition method using a reaction system containing a halide. 2. The semiconductor substrate according to claim 1, wherein the plane orientation of the substrate is a (111) A plane. The semiconductor substrate according to claim 1, wherein the substrate is made of a group III-V compound semiconductor. 4. The semiconductor substrate according to claim 3, wherein said III-V compound semiconductor is GaAs or InP. The semiconductor substrate according to any one of claims 1 to 4, wherein the first buffer layer has a thickness of 10 to 100 nm, and the second buffer layer has a thickness of 5 to 70 nm. The semiconductor substrate according to claim 1, wherein a thickness of the first or second epitaxial layer is 20 to 1000 μm. In an environment heated to a first temperature, a first gas containing a halide, a second gas containing Ga, and a third gas containing NH ₃ are supplied onto a substrate made of a compound semiconductor, mainly Forming a first buffer layer comprising GaN;
In an environment heated to a second temperature higher than the first temperature, the first to third gases are supplied to form a first epitaxial layer containing GaN on the first buffer layer. Forming;
Supplying the first to third gases under an environment heated to the first temperature to form a second buffer layer mainly composed of GaN on the first epitaxial layer;
Supplying the first to third gases under an environment heated to the second temperature to form a second epitaxial layer containing GaN on the second buffer layer;
A method for manufacturing a semiconductor substrate comprising: The method according to claim 7, wherein the first temperature is in a range of 300 to 700 ° C., and the second temperature is 750 ° C. or higher. 9. The method according to claim 7, wherein an HCl gas is used as the first gas. The method for manufacturing a semiconductor substrate according to claim 7, wherein a substrate having a (111) A plane is used as the substrate. The method for manufacturing a semiconductor substrate according to claim 7, wherein a substrate made of a group III-V compound semiconductor is used as the substrate. The method of manufacturing a semiconductor substrate according to claim 11, wherein the III-V compound semiconductor uses GaAs or InP. The first buffer layer has a thickness of 10 to 100 nm, the second buffer layer has a thickness of 5 to 70 nm, and the first or second epitaxial layer has a thickness of 10 to 100 nm. Adjusting the process conditions in each of the steps so as to be 20 to 1000 μm;
A method for manufacturing a semiconductor substrate according to claim 7.

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