JP2003128499A - Method for producing nitride crystal substrate and nitride crystal substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a nitride crystal substrate by which a large nitride gallium single crystal substrate free from cracks and warpages can be obtained, and a nitride crystal substrate. SOLUTION: The flat nitride crystal substrate 6 free from warpages can be obtained by heating the nitride crystal substrate 6 having the curvatures constructed by forming an epitaxial growing layer 9 of the nitride crystal of the group III element on a substrate 8 for heating close to a growing temperature by a heater element and cooling it down under a condition of sandwiching it between parallel surfaces of a pedestal 2 and a press plate 4 to correct the warpage. A process for removing the substrate 8 for growing becomes easy, and the large scale independent substrate of the group III nitride crystal free from cracks and warpages can be obtained, by eliminating the warpage of the nitride crystal substrate 6.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for manufacturing a nitride crystal substrate and a nitride crystal substrate.

[0002]

2. Description of the Related Art GaN-based compound semiconductors such as gallium nitride (GaN), indium gallium nitride (InGaN) and gallium aluminum nitride (GaAlN) are in the spotlight as materials for blue light emitting diodes (LEDs) and laser diodes (LDs). ing. In addition to the optical element, the GaN-based compound semiconductor has good heat resistance and environment resistance, and therefore, electronic devices taking advantage of this feature are being developed.

By the way, this GaN compound semiconductor is
Ga that is difficult to grow in bulk and practically usable
The N substrate has not yet been obtained. The GaN growth substrate that has been widely put into practical use at present is a sapphire substrate.
The method of epitaxially growing GaN by the E method) is generally used.

[0004]

However, since the sapphire substrate has a different lattice constant from GaN, it is impossible to grow a single crystal film by growing GaN directly on the sapphire substrate. Therefore, a buffer layer of AlN or GaN is once grown on the sapphire substrate at a low temperature,
A method has been proposed in which lattice distortion is relaxed by the low-temperature grown buffer layer and then GaN is grown on the buffer layer (see Japanese Patent Laid-Open No. 63-188983).

However, even in the growth of GaN using this low temperature growth buffer layer, the substrate after the epitaxial growth warps due to the difference in the linear expansion coefficient between the sapphire substrate and GaN, and in the worst case, cracks or cracks occur. There's a problem.

Further, the warp of the substrate after the growth becomes a serious problem because the exposure state of the fine pattern in the photolithography becomes non-uniform.

Therefore, a method for growing a GaN epitaxial substrate without warpage is desired, but there is still no solution.

On the other hand, G grown thick on the sapphire substrate
Attempts have also been made to obtain a free-standing GaN substrate by removing the sapphire substrate from the aN epitaxial growth substrate by a method such as etching or polishing. If a free-standing GaN substrate is obtained, various problems due to the difference in lattice constant and the difference in linear expansion coefficient with the epitaxial layer can be solved.

However, in the process of removing the sapphire substrate, the internal strain due to the difference in linear expansion coefficient between sapphire and GaN is released, and as a result, the warp of the substrate is increased and the substrate is cracked. It has not been put to practical use. For example, “Jpn.J.Appl.Phys.Vo”
l. 38 (1999) Pt. 2, No3A, pp. L2
17-219 ", HVPE method (Hydride Vapor Phase Epit on a sapphire substrate).
axy: hydride vapor phase epitaxy method) is used to grow GaN thickly, and then a laser pulse is irradiated to peel off only the GaN layer, but there is a problem that the substrate is easily cracked during the peeling process. However, there is a problem that a large GaN substrate cannot be obtained with good reproducibility.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above problems and provide a method for manufacturing a nitride crystal substrate and a nitride crystal substrate by which a large-sized gallium nitride single crystal substrate without cracks or warpage can be obtained. .

[0011]

In order to achieve the above-mentioned object, a method for manufacturing a nitride crystal substrate according to claim 1 of the present invention comprises: epitaxially growing a group III element nitride crystal on a growth substrate; The obtained nitride crystal substrate is heated to near the growth temperature of the nitride crystal, sandwiched between parallel planes in order to correct the warp, and cooled to room temperature as it is.

In addition to the invention described in claim 1, gallium nitride may be used as the nitride crystal.

In addition to the invention described in claim 1, a material other than the group III element nitride crystal may be used as the material for the growth substrate, and the group III element nitride crystal may be heteroepitaxially grown.

In addition to the first aspect of the invention, a sapphire single crystal may be used as a material for the growth substrate, and a group III element nitride crystal may be heteroepitaxially grown.

In addition to the invention described in claim 1, a nitride crystal of a group III element having a hexagonal crystal structure may be heteroepitaxially grown using a C plane or A plane of a sapphire single crystal as a growth substrate.

In addition to the invention described in claim 1, gallium nitride is used as a nitride crystal, and the heating temperature is 900 ° C. or higher.
The temperature may be 400 ° C. or lower.

In addition to the invention described in claim 1, heating or cooling of the nitride crystal substrate may be performed in an inert gas atmosphere or an ammonia gas atmosphere.

In addition to the invention described in claim 1, it is preferable that the nitride crystal substrate is sandwiched between parallel planes and pressed at a pressure of 4.9 × 10 ⁴ Pa or more and 4.9 × 10 ⁶ Pa or less.

In addition to the invention described in claim 1, it is preferable to correct the warp of the nitride crystal substrate until the curvature radius becomes 10 m or more.

In addition to the invention described in claim 1, the nitride crystal substrate may be selectively grown on the mask material patterned on the growth substrate.

In addition to the invention described in claim 1, a nitride crystal free-standing substrate may be obtained by removing the growth substrate from the nitride crystal substrate.

In addition to the invention described in claim 1, it is preferable that the thickness of the nitride crystal is 100 μm or more.

In addition to the invention described in claim 1, the growth substrate may be removed by mechanical processing such as polishing and grinding.

In addition to the invention described in claim 1, the growth substrate may be removed by etching.

In the nitride crystal substrate according to claim 15, after the nitride crystal of the group III element is epitaxially grown on the growth substrate, it is heated to near the growth temperature of the nitride crystal and sandwiched between parallel planes. It was cooled to room temperature as it was and the warpage was corrected.

In addition to the fifteenth aspect of the present invention, it is preferable that the nitride crystal has a thickness of 100 μm or more.

Here, the warpage of the nitride crystal substrate on which the Group III nitride crystal is epitaxially grown mainly occurs due to the difference between the linear expansion coefficient of the growth substrate and the linear expansion coefficient of the epitaxial growth layer. At the nitride crystal epitaxial growth temperature, the nitride crystal substrate is flat, and warpage occurs in the process of cooling the nitride crystal substrate to room temperature. Therefore, by heating the nitride crystal substrate with such warpage to near the epitaxial growth temperature, sandwiching between parallel planes, fixing (or pressing) with the warpage of the substrate corrected, and cooling to room temperature, A flat nitride crystal substrate without warpage can be obtained.

Here, in the generally performed straightening of metal or the like, the material is softened by heating and processed, whereas the straightening of the group III element nitride crystal substrate according to the present invention is performed by the nitride. By utilizing the fact that the crystal substrate is heated to return to a state without warpage during epitaxial growth, the point that the nitride crystal substrate itself has not softened,
This is a new point that differs from the technology used for metals and the like.

According to the present invention, a warped nitride crystal substrate obtained by epitaxially (heteroepitaxially) growing a group III nitride crystal on a growth substrate is heated to a temperature close to the growth temperature and then the space between parallel planes is increased. It is sandwiched between and is cooled in a state in which the warpage is corrected, whereby a flat nitride crystal substrate without warpage can be obtained. Furthermore, by eliminating the warpage of the epitaxially grown nitride crystal substrate,
The growth substrate can be easily removed, and a large freestanding III-nitride crystal substrate without cracks or warpage can be obtained.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a conceptual diagram showing an embodiment of a substrate straightening apparatus to which the method for producing a nitride crystal substrate of the present invention is applied.

A pedestal 2 is arranged at the center of the bottom of the furnace body 1,
A press plate 4 fixed to the lower end of the rod 3 is arranged above the pedestal 2. The rod 3 can be moved up and down in the directions of arrows 5a and 5b by an elevator mechanism (not shown). Therefore, when the press plate 4 descends, the nitride crystal substrate 6 placed on the pedestal 2 can be pressed. A heater 7 for heating the nitride crystal substrate 6 arranged on the pedestal 2 is arranged around the pedestal 2. That is, this substrate straightening apparatus is composed of the pressing means including the rod 3, the press plate 4, and the elevating mechanism, and the heating means including the heating heater 7.

The nitride crystal substrate 6 is placed on the pedestal 2 of this substrate straightening apparatus, and is heated to a temperature near the epitaxial growth temperature of the nitride crystal substrate 6 by the heater 7 for heating, and the press plate 4 is lowered to a predetermined pressure. In addition, by stopping the energization of the heating heater 7 and cooling it in that state,
The warpage of the nitride crystal substrate 6 is corrected. Incidentally, 8 is a growth substrate, and 9 is an epitaxial (heteroepitaxial) growth layer.

Next, specific numerical values will be described, but the present invention is not limited thereto.

[0035]

[Example] (Example 1) Diameter about 51 mm (about 2 inches)
Single crystal sapphire C-plane substrate (hereinafter "sapphire substrate"
Say. ) To MOCVD (Metal Organi)
c Chemical Vapor Deposit
ion: vapor-phase growth by metalorganic pyrolysis) Put in a furnace (not shown), at 1200 ° C. for 20 minutes in a hydrogen atmosphere,
After cleaning the sapphire substrate surface, TMG
Using (trimethylgallium) and ammonia as raw materials,
A gallium nitride film was grown to a thickness of 50 nm at 600 ° C., the sapphire substrate temperature was raised to 1050 ° C., and a gallium nitride film was grown to a thickness of 2 μm to form an epitaxial growth substrate 6.

When the warp of the gallium nitride epitaxial growth substrate 6 taken out from the MOCVD furnace was measured,
The radius of curvature of the warp of the epitaxial growth substrate was about 33 m.

This epitaxial growth substrate 6 is placed in the substrate straightening apparatus shown in FIG. 1, the atmosphere in the substrate straightening apparatus is replaced with nitrogen, and then heated to 1000 ° C. by the heater 7 for heating, and the epitaxial growth substrate is pressed to the press plate 4 and the pedestal. It was sandwiched between two parallel planes facing each other, and cooled to room temperature while applying a load of 9.8 × 10 ⁴ Pa. When the warpage of the gallium nitride epitaxial growth substrate thus obtained was measured, it was confirmed that the curvature radius of the warpage of the epitaxial growth substrate was about 60 m, and the flatness was significantly improved.

Example 2 An SiO ₂ film having a thickness of 0.6 μm was deposited by a thermal CVD method on a gallium nitride epitaxial growth substrate manufactured by the same method as in Example 1,
<1-1 on the SiO ₂ film by the photolithography process
00> and a striped window was opened in parallel to expose gallium nitride. The window width is 2 μm and the mask width is 8
μm. This epitaxial growth substrate was placed in an HVPE furnace (not shown), and a gallium nitride layer was formed on the surface of the substrate.
It was deposited to a thickness of 0 μm. The raw materials used for the growth are ammonia and gallium chloride. The growth conditions are atmospheric pressure, the substrate temperature is 1050 ° C., and the growth rate is about 90 μm / h. When the warp of the gallium nitride epitaxial substrate taken out from the HVPE furnace was measured, the radius of curvature of the warp of the epitaxial growth substrate was about 0.6 m.

This epitaxial growth substrate was placed in the apparatus shown in FIG. 1, the atmosphere in the apparatus was set to a stream of ammonia gas, and heated to 1000 ° C. by the heater 7 for heating, and then the epitaxial growth substrate was sandwiched by the press plates 4. With cooling under a load of 14.7 × 10 ⁴ Pa, the temperature was cooled to room temperature. When the warp of the gallium nitride epitaxial growth substrate thus obtained was measured, the curvature radius of the warp of the epitaxial growth substrate was about 39 m, and it was confirmed that the flatness was significantly improved.

(Example 3) The flat gallium nitride epitaxial growth substrate obtained in Example 2 was attached to a polishing platen with wax, and the SiO ₂ mask portion was polished and removed from the sapphire substrate by using diamond abrasive grains. . Even during the polishing process, the gallium nitride epitaxial layer was not cracked or split, and only the gallium nitride epitaxial growth layer was left and the other parts could be removed. As a result, a flat free-standing substrate of gallium nitride having a thickness of 300 μm was obtained.

Next, the basis of the optimum conditions will be described.

The growth substrate for growing gallium nitride is
It is desirable that the material be sapphire or have a coefficient of linear expansion larger than that of gallium nitride. This is because the substrate after epitaxial growth is less likely to break. It is well known that when gallium nitride is subjected to tensile stress, cracks easily occur, and the Journal of Applied Physics, Vol. 65 (19).
96) P.I. 936 and the like. Further, the sapphire substrate is preferably a C-plane or A-plane substrate. This is because the growth surface of gallium nitride that grows on the sapphire substrate becomes the C surface, and the epitaxial growth surface having the hexagonal crystal structure easily becomes a flat surface with few defects.

The heating temperature is preferably 900 ° C. or higher and # ° C. or lower. This is because if the temperature is lower than 900 ° C., the probability of cracking of the substrate increases when the substrate is sandwiched between flat surfaces.

Further, when heated to 1400 ° C. or higher, gallium nitride is decomposed. However, when the atmosphere gas is a high-pressure atmosphere containing nitrogen, the heatable temperature can be further increased.

The atmosphere for heating and straightening is preferably inert gas or ammonia gas. This is to suppress the surface deterioration of the epitaxially grown crystal.

The pressure is 4.9 × 10 ⁴ Pa or more and 4.9 × 1.
It is desirable that the pressure is 0 ⁶ Pa or less. 4.9 x 10 ⁴ Pa
If it is less than the above value, the stress that the epitaxial substrate tends to warp during cooling cannot be fully resisted, and the warp of the epitaxial substrate cannot be corrected.

For correcting the warp of the epitaxial substrate, it is desirable that the radius of curvature be 10 m or more. This is because if the radius of curvature is less than 10 m, it becomes difficult to mount the epitaxial substrate on the stepper.

The thickness of the group III nitride crystal layer is preferably 100 μm or more. This is because if the thickness of the crystal layer is less than 100 μm, the probability of cracking due to handling or the like increases when the substrate is used as a free-standing substrate.

Here, the group III nitride crystal to be epitaxially grown may have a single layer or a multilayer structure. In particular, the warpage may be corrected after growing the multi-layer structure required to make the device structure. Further, the warp of the epitaxial substrate subjected to the device process may be corrected. Further, the correction of the warp of the epitaxial substrate may be divided into several times or may be repeated. Furthermore, a large number of epitaxial substrates may be corrected simultaneously. Further, the nitride crystal substrate may be selectively grown on the mask material patterned on the growth substrate.

Further, the nitride crystal substrate after the substrate is peeled off or the nitride crystal substrate whose front and back surfaces have been polished may be corrected.

The group III nitride crystal epitaxial substrate and the group III nitride crystal free-standing substrate obtained by the present invention are
It can be widely used as a substrate for gallium nitride-based devices.

As described above, by using the present invention, it is possible to obtain a group III nitride crystal epitaxial growth substrate having no warpage. As a result, (1) cracks and breaks are less likely to occur during the handling of the process and the processing of the substrate. (2) The exposure state of the fine pattern in the photolithography process during the process can be made uniform within the wafer surface, and the device manufacturing yield is improved. (3) Since the growth substrate can be easily removed from the epitaxial substrate, the yield is improved, and a flat freestanding III-nitride crystal substrate free from cracks and cracks can be obtained. (4) When a freestanding substrate of group III nitride crystal is obtained, homoepitaxial growth of gallium nitride-based devices can be performed. As a result, an epitaxial layer with good crystallinity is obtained, and device performance is improved.

[0053]

In summary, according to the present invention, the following excellent effects are exhibited.

It is possible to realize the method for manufacturing a nitride crystal substrate and the provision of the nitride crystal substrate in which a large-sized gallium nitride single crystal substrate without cracks or warpage can be obtained.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing an embodiment of a substrate straightening apparatus to which a method for manufacturing a nitride crystal substrate of the present invention is applied.

[Explanation of symbols]

1 furnace body Two pedestals 3 rod 4 Press board 6 Nitride crystal substrate (epitaxial growth substrate) 7 Heating heater 8 Growth substrate 9 Epitaxial (heteroepitaxial) growth layer

Continued front page    F term (reference) 4G077 AA03 BE15 DB08 ED06 FE10                       FJ03 HA02 TA04 TB05 TK01                 4K030 AA11 AA13 BA08 BA38 BB02                       CA05 DA03 DA09 FA10                 5F045 AB14 AC03 AC12 AF09 BB11                       DB02 GH08

Claims (16)

[Claims] 1. A group III element nitride crystal is epitaxially grown on a growth substrate, and the obtained nitride crystal substrate is heated to a temperature close to the growth temperature of the nitride crystal and parallel planes are formed to correct warpage. A method for manufacturing a nitride crystal substrate, which is characterized in that it is sandwiched between and then cooled to room temperature. 2. The method for producing a nitride crystal substrate according to claim 1, wherein gallium nitride is used as the nitride crystal. 3. The method for producing a nitride crystal substrate according to claim 1, wherein a material other than the group III element nitride crystal is used as the material for the growth substrate, and the group III element nitride crystal is heteroepitaxially grown. 4. The method for producing a nitride crystal substrate according to claim 1, wherein a sapphire single crystal is used as a material of the growth substrate, and a group III element nitride crystal is heteroepitaxially grown. 5. The production of a nitride crystal substrate according to claim 1, wherein a C-face or A-face of a sapphire single crystal is used as the growth substrate, and a nitride crystal of a group III element having a hexagonal crystal structure is heteroepitaxially grown. Method. 6. The method for producing a nitride crystal substrate according to claim 1, wherein gallium nitride is used as the nitride crystal, and the heating temperature is 900 ° C. or higher and 1400 ° C. or lower. 7. The method for producing a nitride crystal substrate according to claim 1, wherein heating or cooling of the nitride crystal substrate is performed in an inert gas atmosphere or an ammonia gas atmosphere. 8. The nitride crystal substrate according to claim 1, wherein the nitride crystal substrate is sandwiched between parallel planes and pressed with a pressure of 4.9 × 10 ⁴ Pa or more and 4.9 × 10 ⁶ Pa or less. Production method. 9. The method for producing a nitride crystal substrate according to claim 1, wherein the warpage of the nitride crystal substrate is corrected until the radius of curvature becomes 10 m or more. 10. The method for producing a nitride crystal substrate according to claim 1, wherein the nitride crystal substrate is selectively grown on a mask material patterned on the growth substrate. 11. The method for producing a nitride crystal substrate according to claim 1, wherein the nitride crystal free-standing substrate is obtained by removing the growth substrate from the nitride crystal substrate. 12. The method for producing a nitride crystal substrate according to claim 1, wherein the thickness of the nitride crystal is 100 μm or more. 13. The method for producing a nitride crystal substrate according to claim 1, wherein the growth substrate is removed by mechanical processing such as polishing and grinding. 14. The method for producing a nitride crystal substrate according to claim 1, wherein the growth substrate is removed by etching. 15. A group III element nitride crystal is epitaxially grown on a growth substrate and then heated to near the growth temperature of the nitride crystal and cooled to room temperature while being sandwiched between parallel planes to correct warpage. A nitride crystal substrate characterized by being formed. 16. The nitride crystal has a thickness of 100 μm.
The nitride crystal substrate according to claim 15, which is as described above.