JP5499839B2 - Method for manufacturing gallium nitride based semiconductor substrate - Google Patents

Description

  The present invention relates to a method for manufacturing a gallium nitride based semiconductor substrate, and more particularly to a method for filling pits in a gallium nitride based semiconductor substrate.

  2. Description of the Related Art In recent years, light emitting diode (LED) elements using nitride semiconductors have attracted attention as light sources for illumination such as general illumination, automobile headlights, and backlights for liquid crystal televisions. Further, a semiconductor laser (LD: LASER Diode) element using a nitride semiconductor is used as a light source for writing / reading in a high-density recording optical disk device such as a Blu-ray disc, and further elements of these nitride semiconductor elements. There is a need for improved characteristics and lower prices.

  In a nitride semiconductor LED element, an element structure is mainly formed on a different substrate made of a material different from a nitride semiconductor, such as sapphire, via a base layer such as a buffer layer. On the other hand, in LD elements and high-efficiency LED elements that require high current and high output drive, crystal defects, particularly dislocation density such as threading dislocations, are a major factor in determining element characteristics. An element structure is formed on a free-standing substrate. Such a nitride semiconductor free-standing substrate is formed by growing a nitride semiconductor having a good crystallinity on a heterogeneous substrate by using a lateral growth method (ELO: Epitaxial Lateral Overgrowth) or the like. It is manufactured by removing.

  In the process of manufacturing such a nitride semiconductor free-standing substrate, for example, as described in Patent Document 1, through pits that penetrate from the front surface to the back surface of the substrate may occur. Such a free-standing substrate having penetrating pits cannot be held by vacuum suction in the process of forming an element structure, and cannot be used as it is for manufacturing a semiconductor element. Therefore, in the method for manufacturing a nitride semiconductor substrate described in Patent Document 1, after a group III element metal is attached to the through pits of the nitride semiconductor free-standing substrate by an injection device or manually, the metal is removed from the heat treatment furnace. The through pits are filled by nitriding inside.

JP 2008-162855 A

  However, the nitride semiconductor substrate manufacturing method described in Patent Document 1 requires a dedicated device for filling the through pits in addition to the crystal growth device, and recognizes the through pits existing in the substrate. Thus, there is a problem in that metal must be injected into each pit, which is complicated, increases the number of steps, and increases the manufacturing cost.

  Therefore, the present invention has been made in view of such circumstances, and an object of the present invention is to provide a method for manufacturing a gallium nitride semiconductor substrate that can obtain a gallium nitride semiconductor substrate having no through pits at low cost.

The present invention can solve the above problems by the following means (1) to (5).
(1) A first step of preparing a substrate having a gallium nitride based semiconductor layer with pits formed on the surface thereof in a vapor phase growth apparatus, and in the vapor phase growth apparatus, on the gallium nitride based semiconductor layer, Forming a pit buried layer of amorphous or polycrystalline group III nitride to fill the pit; and removing the pit buried layer by polishing to form a surface of the gallium nitride based semiconductor layer. And a third step of exposing the gallium nitride based semiconductor substrate.
(2) The vapor phase growth apparatus is a hydride vapor phase growth apparatus, and in the first step, the substrate is prepared by growing the gallium nitride based semiconductor layer on a growth substrate. A method for producing a gallium nitride based semiconductor substrate according to 1).
(3) In the second step, the pit buried layer is formed by supplying hydrogen gas onto the gallium nitride semiconductor layer to decompose the surface layer of the gallium nitride semiconductor layer to form a metal gallium film. The method for producing a gallium nitride based semiconductor substrate according to the above (2), which is formed by nitriding the coating film by supplying a nitrogen source gas.
(4) In the second step, the pit buried layer includes the pits by supplying a hydrogen gas and a hydrogen chloride gas onto the gallium nitride based semiconductor layer to decompose a surface layer of the gallium nitride based semiconductor layer. The method for producing a gallium nitride based semiconductor substrate according to the above (2), which is formed by growing a group III nitride on the surface after roughening the surface.
(5) In the second step, the pit buried layer is formed by growing a group III nitride on the gallium nitride based semiconductor layer at a temperature of 700 ° C. or higher and 950 ° C. or lower. A method for producing a gallium nitride based semiconductor substrate according to 1) or (2).

  According to the present invention, in a vapor phase growth apparatus, an amorphous or polycrystalline group III nitride pit buried layer is formed on a gallium nitride based semiconductor layer to fill the pit, and an extra pit buried layer In the polishing process, it is not necessary to separately provide a dedicated device for filling the pits, and a gallium nitride based semiconductor substrate having no through pits can be obtained at a low cost.

It is a schematic sectional drawing (a)-(d) which shows the state of the board | substrate which has a gallium nitride type semiconductor layer in each process of the manufacturing method of the gallium nitride type semiconductor substrate which concerns on one embodiment of this invention. It is a schematic sectional drawing (a)-(d) which shows the state of the board | substrate which has a gallium nitride type semiconductor layer in each process of the manufacturing method of the gallium nitride type semiconductor substrate which concerns on one embodiment of this invention. It is the schematic top view (a) of the board | substrate which has a gallium nitride type-semiconductor layer based on one embodiment of this invention, and the schematic diagram (b) of the observation image by the fluorescence microscope around the buried pit.

  Hereinafter, embodiments of the invention will be described with reference to the drawings as appropriate. However, the manufacturing method of the gallium nitride based semiconductor substrate described below is for embodying the technical idea of the present invention, and the present invention is not limited to the following. Note that the size, positional relationship, and the like of the components shown in the drawings may be exaggerated for clarity. In addition, the embodiment described below can be applied by appropriately combining the components and the like unless otherwise specified. Further, in this specification, “single crystal” and “polycrystal” are used in a substantial sense, and actually include crystal defects and disorder of crystal axes.

<Embodiment 1>
FIGS. 1A to 1D are schematic sectional views showing states of a substrate having a gallium nitride semiconductor layer in each step of the method for manufacturing a gallium nitride semiconductor substrate according to the first embodiment. As shown in FIG. 1, the method for manufacturing a gallium nitride based semiconductor substrate of the present invention is a first method of preparing a substrate having a gallium nitride based semiconductor layer 20 having pits 25 formed on the surface thereof in a vapor phase growth apparatus. Step (a) and a second step of filling the pits by forming an amorphous or polycrystalline III-nitride pit buried layer 30 on the gallium nitride based semiconductor layer 20 in the same apparatus ( b) to (c), and a third step (d) in which the pit buried layer 30 is removed by polishing to expose the surface of the gallium nitride based semiconductor layer 20.

In the first embodiment, in the first step (a ₁ ), the substrate having the gallium nitride semiconductor layer 20 having the pits 25 formed on the surface thereof is formed on the growth substrate 10 in the vapor phase growth apparatus. It is prepared by growing the semiconductor layer 20. Thereby, a series of steps in the same vapor phase growth apparatus from the step of growing the gallium nitride based semiconductor layer 20 on the growth substrate 10 to the step of filling the pits 25 generated on the surface with the pit buried layer 30 at that time. It is convenient and preferable.

  The growth method of the gallium nitride based semiconductor layer 20 is not particularly limited. However, in the growth process of the gallium nitride based semiconductor, the gallium nitride based semiconductor layer 20 is formed as a through pit from the beginning, or finally becomes a through pit through a polishing process. Relatively large pits are likely to occur in a hydride vapor phase growth method having a relatively high growth rate. Therefore, it is particularly effective that the method for manufacturing a gallium nitride based semiconductor substrate of the present invention is applied to a hydride vapor phase growth apparatus.

  In the process of growing the single-crystal gallium nitride based semiconductor layer 20, a relatively stable facet plane (crystal plane) inclined with respect to the main crystal growth axis (particularly the c-axis) appears on the inner surface of the pit 25. In the pits 25 having the facet surface on the inner surface, the crystal growth on the inner surface is suppressed due to the crystal orientation dependency of the crystal growth of the gallium nitride based semiconductor layer 20, and the facet surface on the inner surface remains or expands. It is hard to be buried because there is a tendency to go. Therefore, in the present invention, the surface orientation dependency of crystal growth is weakened by roughening the surface of the gallium nitride based semiconductor layer 20 or growing a group III nitride having low crystallinity on the surface. Promotes group III nitride growth on the inner surface of the pit. The group III nitride grown on such a growth surface has a reduced crystallinity and is often amorphous or polycrystalline. This makes it possible to fill the pits 25 quickly.

In the second step in the first embodiment, the surface layer of the gallium nitride based semiconductor layer 20 is decomposed to form a metal gallium film 28 (b ₁ ), and then the film 28 is nitrided (c ₁ ). The pit buried layer 30 is formed on the gallium nitride based semiconductor layer 20 by the steps (b ₁ ) and (c ₁ ), and the pits 25 are filled.

First, in the step (b ₁ ), hydrogen gas is supplied onto the gallium nitride based semiconductor layer 20. More specifically, the substrate having the gallium nitride based semiconductor layer 20 is held in a hydrogen atmosphere or a mixed atmosphere of an inert gas such as nitrogen or argon and hydrogen. The holding time is preferably 10 minutes or more, more preferably 30 minutes or more in order to sufficiently decompose the surface layer of the gallium nitride based semiconductor layer 20, and 1 hour or less in order to avoid excessive decomposition. The holding temperature (hereinafter, the temperature is defined by the substrate temperature) is preferably 800 ° C. or higher in order to promote the decomposition of the surface layer of the gallium nitride based semiconductor layer 20, and the upper limit is that of the quartz reaction tube of the vapor phase growth apparatus. It is preferable that it is 1200 degrees C or less from a viewpoint of protection. Through this step, the surface layer of the gallium nitride based semiconductor layer 20 is decomposed by the separation of nitrogen, and a metal gallium film 28 is formed on the surface of the gallium nitride based semiconductor layer 20. This decomposition of the surface layer occurs also in the pits 25, and the metal gallium film 28 is formed also in the pits 25. The metal gallium film 28 is a collection or aggregation of minute droplets called “droplets”. Further, it is not necessary to have a hydrogen atmosphere during temperature increase or decrease.

Next, in the step (c ₁ ), a nitrogen source gas is supplied onto the gallium nitride based semiconductor layer 20 to nitride the metal gallium film 28. As the nitrogen source gas, it is preferable to use ammonia, and it is preferable to use a hydrogen atmosphere, an atmosphere of an inert gas such as nitrogen or argon, an atmosphere in which ammonia is mixed in a mixed atmosphere thereof, or an atmosphere containing only ammonia. The treatment time is preferably 10 minutes or more, more preferably 30 minutes or more in order to sufficiently react the metal gallium and the nitrogen source gas, and the upper limit is not particularly limited, but is 1 hour or less. The treatment temperature is preferably 800 ° C. or higher for efficient reaction of metal gallium and nitrogen source gas, and the upper limit is preferably 1200 ° C. or lower from the viewpoint of protecting the quartz reaction tube of the vapor phase growth apparatus. If the temperature is the same as that in the step (b ₁ ), the time required for temperature rise and fall can be saved. By this step, the metal gallium film 28 is nitrided and changed to an amorphous or polycrystalline group III nitride (this is referred to as a pit buried layer 30), and the pits 25 are filled. The pit buried layer 30 may be amorphous, but is more preferably polycrystalline.

In the step (c ₁ ) of the _first embodiment, an amorphous or polycrystalline layer is further laminated on the amorphous or polycrystalline layer formed by nitriding the metal gallium film 28. The pit buried layer 30 may be formed. To stack an amorphous or polycrystalline layer, supply a group III source gas and a nitrogen source gas as source gases in a hydrogen atmosphere, an inert gas atmosphere such as nitrogen or argon, or a mixed atmosphere of both. And grow. At this time, it is preferable in terms of utilization efficiency of the raw material to adjust the gas flow rate so that the ratio of the nitrogen source gas to the group III source gas (nitrogen source / group III source) is 4 or more and 20 or less. Further, when the ratio of the nitrogen source / group III source is relatively low in this manner, the lateral growth tends to be promoted, and the pits 25 are easily filled. The growth time is not particularly limited, but is preferably 120 minutes or more and 300 minutes or less, for example. The growth temperature is lower than the growth temperature of the gallium nitride based semiconductor layer 20 and is preferably 700 ° C. or higher and 950 ° C. or lower. If the growth temperature of the pit buried layer 30 is low and the difference from the growth temperature of the gallium nitride semiconductor layer 20 becomes too large, the gallium nitride semiconductor layer 20 is likely to crack due to the stress applied from the pit buried layer 30. Therefore, this range is preferable. The group III nitride laminated as the pit buried layer 30 is preferably substantially the same as the composition of the gallium nitride based semiconductor layer 20, and GaN is particularly suitable.

Finally, in the third step (d ₁ ), the pit buried layer 30 is removed by polishing to expose the surface of the gallium nitride based semiconductor layer 20. Thereby, the pit buried layer 30 covering the surface of the gallium nitride based semiconductor layer 20 excluding the pit portion is removed, and the pit 25 is filled with the amorphous or polycrystalline pit buried layer 30. A substrate having a layer 20 is obtained. The polishing process is naturally a process for mirror processing of the main surface of the substrate in the manufacture of the gallium nitride based semiconductor substrate. By using this process, the excess pit buried layer 30 is removed, thereby reducing the man-hours. Can be reduced. Note that in this specification, “polishing” is used in a broad sense including grinding and chemical mechanical polishing (CMP). In particular, in the third step, after removing the pit embedding layer 30 by mechanical polishing or grinding, it is preferable to finish the mirror surface by chemical mechanical polishing. In addition, the growth substrate 10 may be removed in advance by laser irradiation (laser lift-off) or polishing before and after the main polishing step to obtain the self-supporting substrate 21 of the gallium nitride based semiconductor layer 20. Further, the back side of the gallium nitride based semiconductor layer 20 may be polished. At this time, since the pits 25 generated on the surface of the gallium nitride based semiconductor layer 20 are filled with the pit embedding layer 30, even if a part (bottom part) thereof is exposed to the back side by polishing, it does not become a through pit. .

  According to the method of manufacturing a gallium nitride based semiconductor substrate according to the first embodiment, metal gallium droplets are generated up to the bottom of the pits 25, and become a nucleus of growth of amorphous or polycrystalline group III nitride. Therefore, it is possible to satisfactorily form a crystal nucleus in the pit 25 and fill the pit 25 with high accuracy. The second step in the first embodiment can be performed not only in the HVPE apparatus but also in the MOCVD apparatus under the same conditions.

<Embodiment 2>
2A to 2D are schematic cross-sectional views showing states of a substrate having a gallium nitride semiconductor layer in each step of the method for manufacturing a gallium nitride semiconductor substrate according to the second embodiment. In the example shown in FIG. 2, components substantially the same as those of the above-described first embodiment are denoted by the same reference numerals, and description thereof is omitted as appropriate.

In the first step (a ₂ ) of the _second embodiment, the substrate having the gallium nitride based semiconductor layer 20 prepared in the vapor phase growth apparatus is a self-standing substrate of the gallium nitride based semiconductor layer 20 from which the growth substrate has been removed. It is. As described above, in the first step, a substrate having the gallium nitride based semiconductor layer 20 in which the pits 25 are generated in advance on the surface may be installed in the vapor phase growth apparatus.

Next, in the second step in the second embodiment, the surface layer of the gallium nitride based semiconductor layer 20 is decomposed to roughen the surface including the pits 25 (b ₂ ), and then the roughened surface. A step (c ₂ ) of growing group III nitride on the surface, and the pit buried layer 32 is formed on the gallium nitride based semiconductor layer 20 by the steps (b ₂ ) and (c ₂ ), The pit 25 is filled.

First, in step (b ₂ ), hydrogen gas and hydrogen chloride are supplied onto the gallium nitride based semiconductor layer 20. That is, the substrate having the gallium nitride based semiconductor layer 20 is held in a mixed atmosphere of hydrogen and hydrogen chloride. The flow rate of hydrogen chloride is preferably 5 sccm or more and 100 sccm or less. The holding time is preferably 10 minutes or more, more preferably 30 minutes or more in order to sufficiently decompose the surface layer of the gallium nitride based semiconductor layer 20, and 1 hour or less in order to avoid excessive decomposition. The holding temperature is preferably 800 ° C. or higher in order to promote the decomposition of the surface layer of the gallium nitride based semiconductor layer 20, and the upper limit is 1200 ° C. or lower from the viewpoint of protecting the quartz reaction tube of the vapor phase growth apparatus. preferable. By this process, the surface layer of the gallium nitride based semiconductor layer 20 is decomposed by the separation of nitrogen, and the generated metallic gallium droplets are removed by hydrogen chloride gas, and the surface including the pits 25 of the gallium nitride based semiconductor layer 20 Is roughened.

Next, in step (c ₂ ), a group III nitride is grown on the roughened surface of the gallium nitride based semiconductor layer 20. In order to grow a group III nitride, a group III source gas and a nitrogen source gas are supplied as source gases in a hydrogen atmosphere, an atmosphere of an inert gas such as nitrogen or argon, or a mixed atmosphere of both. At this time, it is preferable in terms of utilization efficiency of the raw material to adjust the gas flow rate so that the ratio of the nitrogen source gas to the group III source gas (nitrogen source / group III source) is 4 or more and 20 or less. Further, when the ratio of the nitrogen source / group III source is relatively low in this manner, the lateral growth tends to be promoted, and the pits 25 are easily filled. The growth time is not particularly limited, but is preferably 120 minutes or more and 300 minutes or less, for example. The growth temperature is lower than the growth temperature of the gallium nitride based semiconductor layer 20 and is preferably 700 ° C. or higher and 950 ° C. or lower. If the growth temperature of the pit buried layer 30 is low and the difference from the growth temperature of the gallium nitride semiconductor layer 20 becomes too large, the gallium nitride semiconductor layer 20 is likely to crack due to the stress applied from the pit buried layer 30. Therefore, this range is preferable. By this step, an amorphous or polycrystalline group III nitride layer (this is referred to as a pit buried layer 32) is grown on the gallium nitride based semiconductor layer 20, and the pits 25 are filled. The group III nitride grown as the pit buried layer 32 is preferably substantially the same as the composition of the gallium nitride based semiconductor layer 20, and GaN is particularly suitable.

Finally, in the same manner as in the first embodiment, in the third step (d ₂ ), the pit buried layer 32 is removed by polishing to expose the surface of the gallium nitride based semiconductor layer 20. According to the method for manufacturing a gallium nitride based semiconductor substrate according to the second embodiment, the rough surface of the surface of the gallium nitride based semiconductor layer 20 is roughened in a short time, so that the amorphous or The growth of polycrystalline group III nitride can be promoted, and the pits 25 can be easily filled in a short time.

  FIG. 3A is a schematic top view of a substrate having a gallium nitride based semiconductor layer according to the second embodiment, and FIG. 3B is a schematic view of an image observed by a fluorescence microscope around the buried pit. FIG. FIG. 2D shows the AA cross section in FIG. The pits 25 generated in the gallium nitride based semiconductor layer 20 have a substantially hexagonal shape or a substantially dodecagonal shape when viewed from above, and in many cases, have a substantially hexagonal pyramid shape constituted by facet surfaces {11-22}. It has become. After the third step, a region where the pits 25 of the gallium nitride based semiconductor layer 20 are buried has a pit buried layer 32 and is an amorphous or polycrystalline region 39. In particular, the polycrystalline region 39 is often an aggregate of crystal grains having different crystal orientations. Further, most of the substrate surface around the amorphous or polycrystalline region 39 is a single crystal region 29 where the surface of the single crystal gallium nitride based semiconductor layer 20 is exposed, and is used as a region for epitaxial growth of the element structure. The

  The pits 25 generated in the gallium nitride based semiconductor layer 20 need only be filled by the pit buried layer 32 so as not to be through pits after the third step. A concave portion may remain in the amorphous or polycrystalline region 39 of the semiconductor layer 20 or the gallium nitride based semiconductor substrate 21. Although the thickness of the pit buried layer 32 (considered by the thickness of the layer formed on the single crystal region 29) can be changed according to the thickness and warpage of the gallium nitride based semiconductor layer 20, no through pits are generated. In order to reliably fill the bottom of the pit 25, the thickness is preferably 40 μm or more, and is preferably 100 μm or less so as not to become excessively thick.

<Embodiment 3>
The method for manufacturing a gallium nitride based semiconductor substrate according to the third embodiment omits the step (b ₂ ) of the _second embodiment, and the same reference numerals are used for the configurations substantially similar to those of the second embodiment. The description and illustration will be omitted as appropriate. In the third embodiment, an amorphous or polycrystalline group III nitride layer 32 is directly grown on the gallium nitride based semiconductor layer 20 to fill the pits 25. Preferred growth conditions and modes of the pit buried layer 32 are the same as those in the second embodiment. According to the method for manufacturing a gallium nitride based semiconductor substrate according to the third embodiment, polycrystalline nuclei can be formed in a short time on substantially the entire surface of the gallium nitride based semiconductor layer 20, and the pits are buried using the crystal nuclei as a growth starting point. The buried layer 32 can be grown. In the temperature lowering process after the growth process of the gallium nitride based semiconductor layer 20, the pit buried layer 32 may be grown by supplying a source gas.

  The pit buried layers 30 and 32 as described above may be formed on the gallium nitride based semiconductor layer 20 and then heated again to newly grow a single crystal layer on the pit buried layer. . If a single crystal layer capable of epitaxial growth of the device structure can be grown on the pit buried layers 30 and 32, the step of removing the pit buried layer can be omitted.

  Hereinafter, each component in the manufacturing method of the gallium nitride based semiconductor substrate of the present invention will be described.

(Gallium nitride semiconductors, Group III nitrides)
“Group III nitride” is a nitrogen compound of a group III element. For example, GaN, AlGaN, InGaN, or the like, the general formula Al _x In _y Ga _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) , X + y ≦ 1). Further, B may be used as the group III element, and a mixed crystal in which part of N of the group V element is substituted with As and P can also be used. The “gallium nitride based semiconductor” is a group containing particularly gallium among such group III nitrides. The gallium nitride based semiconductor layer 20 is preferably formed of GaN from which good crystallinity is easily obtained. Further, the gallium nitride based semiconductor layer 20 may be a single layer, or may be composed of a plurality of layers including an underlayer, for example. Further, these group III nitrides can be appropriately doped with impurities, and it is preferable to use Si or O as the n-type impurity and Mg as the p-type impurity.

(Growth substrate)
The growth substrate 10 only needs to be capable of epitaxial growth of a gallium nitride based semiconductor. In order to prevent cracking or cracking of the gallium nitride semiconductor, the growth substrate 10 preferably has a diameter of 2 inches to 4 inches and a thickness of 0.5 mm to 2 mm. Specific materials for the growth substrate 10 of the gallium nitride semiconductor include sapphire and spinel (MgAl ₂ O ₄ ) whose main surface is any one of the C-plane, R-plane, and A-plane, as well as SiC (6H, 4H). 3C), Si, GaAs, ZnS, ZnO, diamond and the like. In such a heterogeneous substrate made of a material different from the nitride semiconductor, it is preferable to use a sapphire substrate having a C plane (0001) as a main surface. In addition, a nitride semiconductor substrate such as GaN, AlN, or AlGaN may be used. Further, the growth substrate 10 may be one in which the main surface that is the growth surface of the gallium nitride based semiconductor is off-angled (for example, 0.01 ° or more and 3.0 ° or less on the sapphire C surface).

(Vapor phase growth method and equipment)
Examples of the group III nitride crystal growth method (apparatus) include methods (apparatuses) such as metal organic chemical vapor deposition (MOCVD) and hydride vapor phase epitaxy (HVPE). ) Is available. The MOCVD method is easy to control the growth rate and film thickness. In the MOCVD apparatus, ammonia (NH ₃ ) is used as the source gas for the source gas, and trimethylgallium (TMG), trimethylaluminum (TMA), trimethylindium (TMI), or the like is used as the group III source gas. The HVPE method can grow at a higher speed than the MOCVD method. In the HVPE apparatus, NH ₃ and a group III element halide (eg, GaCl) are used as a source gas. When doping impurities as described above, a dopant gas such as silane (SiH ₄ ) or cyclopentadienyl magnesium (Cp ₂ Mg) is supplied together with these source gases.

  Examples according to the present invention will be described in detail below. Needless to say, the present invention is not limited to the following examples.

<Example 1>
First, a C-plane sapphire substrate 10 (A-plane orientation flat) having a diameter of 3 inches and a thickness of 0.5 mm was placed in a reactor of the MOCVD apparatus, and H ₂ was used as a carrier gas at 500 ° C. (the same applies to the following). Then, NH ₃ gas is supplied at a flow rate of 8.0 slm and TMG gas is supplied at a flow rate of 40 sccm for 60 minutes to form a GaN buffer layer having a thickness of about 1.2 μm. Subsequently, the temperature is raised to 1080 ° C., NH ₃ gas is supplied at a flow rate of 4.6 slm, TMG gas is supplied at a flow rate of 130 sccm for 420 minutes, and a GaN underlayer having a thickness of about 70 μm is grown. 10 is removed from the MOCVD apparatus. Next, the substrate 10 on which the underlayer is grown is placed in the reactor of the HVPE apparatus, about 500 g of metallic gallium is placed on a Ga boat, NH ₃ gas is supplied at a flow rate of 1.3 slm, HCl gas (at 1020 ° C.). The HCl gas reacts with the metallic gallium in the Ga boat and is supplied as GaCl gas, and hence “GaCl gas” is supplied for 150 minutes at a flow rate of 160 sccm. The thick film 20 is grown. At this time, a plurality of pits 25 having a size (diameter on the surface) of about 300 μm are generated on the surface of the GaN thick film 20.

Subsequently, in the same HVPE apparatus, the reaction furnace is kept in an H ₂ atmosphere for 10 minutes while maintaining the temperature at 1020 ° C. As a result, the surface of the GaN thick film 20 is exposed to the H ₂ atmosphere and etched, and metallic gallium droplets 28 are generated on the surface. Thereafter, NH ₃ gas is supplied onto the substrate 10 at a flow rate of 1.0 slm for 10 minutes to react the droplets 28 and NH ₃ , so that the GaN thick polycrystal 30 (pit buried layer) is formed on the surface of the GaN thick film 20. ) Grow. Then, the temperature is lowered to 800 ° C., NH ₃ gas is supplied onto the substrate 10 at a flow rate of 1.0 slm, and GaCl gas is supplied at a flow rate of 100 sccm for 100 minutes to further grow the GaN polycrystal 30 on the GaN thick film 20. Thereafter, the temperature is lowered to around room temperature and the substrate 10 is taken out from the HVPE apparatus. When the substrate taken out is observed, the surface of the GaN thick film 20 is covered with the polycrystalline layer 30 having a thickness of about 15 μm, and the pits 25 generated in the GaN thick film 20 are formed in the polycrystalline layer 30 from the bottom. It has been buried, and it can be confirmed that the diameter has been reduced to about 200 μm.

<Example 2>
First, the substrate 10 on which the underlayer and the GaN thick film 20 are grown as in Example 1 is placed in the reactor of the HVPE apparatus. Subsequently, in the same apparatus, the temperature in the reactor was increased to 1020 ° C. in an N ₂ atmosphere, the interior of the reactor was switched to an H ₂ atmosphere, and HCl gas was further supplied onto the substrate 10 at a flow rate of 10 sccm. Hold for a minute. As a result, the surface of the GaN thick film 20 is exposed to a mixed atmosphere of H ₂ and HCl to be etched and roughened. Then, the temperature is lowered to 800 ° C., NH ₃ gas is supplied onto the substrate 10 at a flow rate of 1.3 slm and GaCl gas is supplied at a flow rate of 120 sccm for 180 minutes, and a GaN polycrystal 32 (pit buried layer) is formed on the GaN thick film 20. ) Grow. Thereafter, the temperature is lowered to around room temperature and the substrate 10 is taken out from the HVPE apparatus. When the substrate taken out is observed, it can be confirmed that the surface of the GaN thick film 20 is covered with the polycrystalline layer 32 having a thickness of about 100 μm. Further, the substrate 10 is polished from the polycrystalline layer 32 side to expose the surface of the GaN thick film 20. When the portion where the pits 25 are formed on the surface of the GaN thick film 20 is observed with a differential interference image of a scanning electron microscope, it can be confirmed that the pits 25 disappear while leaving a substantially circular trace. Further, when the same portion is observed with a fluorescence microscope, the substantially hexagonal polycrystalline region 39 which is the surface of the pit embedding layer 32 and the surface of the GaN thick film 20 around it are different from each other in emission color. A crystal region 29 is seen, and it can be confirmed that the pit 25 is almost completely filled.

<Example 3>
First, in the same manner as in Example 1, the GaN thick film 20 is grown on the base layer grown on the substrate 10 in the reactor of the HVPE apparatus. Subsequently, in the same HVPE apparatus, the temperature is lowered to 800 ° C., NH ₃ gas is supplied onto the substrate 10 at a flow rate of 0.9 slm, and GaCl gas is supplied at a flow rate of 50 sccm for 120 minutes. Polycrystal 32 (pit buried layer) is grown. Thereafter, the temperature is lowered to around room temperature and the substrate 10 is taken out from the HVPE apparatus. When the substrate taken out is observed, the surface of the GaN thick film 20 is covered with the polycrystalline layer 32 having a thickness of about 40 μm, and the pits 25 generated in the GaN thick film 20 are formed on the polycrystalline layer 32 from the bottom. It can be confirmed that it has been buried.

  The method for producing a gallium nitride based semiconductor substrate of the present invention can be applied to the production of a crystal growth substrate for semiconductor elements such as light emitting devices such as LEDs and LDs, and electronic devices using nitride semiconductors.

DESCRIPTION OF SYMBOLS 10 ... Growth substrate, 20 ... Gallium nitride semiconductor layer, 21 ... Gallium nitride semiconductor substrate, 25 ... Pit, 28 ... Metal gallium coating, 29 ... Single crystal region, 30, 32 ... Pit buried layer, 39 ... Non Crystalline or polycrystalline regions

Claims (4)

A first step in which a gallium nitride based semiconductor layer is grown on a growth substrate in a hydride vapor phase growth apparatus, and a substrate having a gallium nitride based semiconductor layer with pits formed on the surface is prepared;
In the hydride vapor phase growth apparatus, hydrogen gas is supplied onto the gallium nitride based semiconductor layer to decompose the surface layer of the gallium nitride based semiconductor layer to form a metal gallium film, and then a nitrogen source gas is supplied. Forming an amorphous or polycrystalline group III nitride by nitriding the coating to form a pit buried layer of amorphous or polycrystalline group III nitride to fill the pits; Process,
And a third step of exposing the surface of the gallium nitride semiconductor layer by removing the pit buried layer by polishing, and a method of manufacturing a gallium nitride semiconductor substrate. In the second step, the pit buried layer forms an amorphous or polycrystalline group III nitride by nitriding the metal gallium film, and further amorphous or polycrystalline group III nitride. The method for producing a gallium nitride based semiconductor substrate according to claim 1, wherein the gallium nitride based semiconductor substrate is formed by laminating these layers. A first step in which a gallium nitride based semiconductor layer is grown on a growth substrate in a hydride vapor phase growth apparatus, and a substrate having a gallium nitride based semiconductor layer with pits formed on the surface is prepared;
In the hydride vapor phase growth apparatus, after supplying a hydrogen gas and a hydrogen chloride gas onto the gallium nitride based semiconductor layer to decompose the surface layer of the gallium nitride based semiconductor layer to roughen the surface including the pits, A second step of filling the pits by growing a group III nitride on the surface to form an amorphous or polycrystalline group III nitride pit buried layer;
And a third step of exposing the surface of the gallium nitride semiconductor layer by removing the pit buried layer by polishing, and a method of manufacturing a gallium nitride semiconductor substrate. In the second step, the pit buried layer, the gallium nitride-based semiconductor layer at a temperature of 700 ° C. or higher 950 ° C. or less, according to claim 1 to 3 is formed by growing a Group III nitride The manufacturing method of the gallium nitride semiconductor substrate as described in any one of these .

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