JP2007197240A - Method for manufacturing gallium nitride single crystal substrate and gallium nitride single crystal substrate - Google Patents

Abstract

A low defect density gallium nitride single crystal substrate can be manufactured.
SOLUTION: A gallium nitride ingot 2 obtained by crystal growth of gallium nitride on a gallium nitride single crystal substrate 1 (cut into a cylindrical gallium nitride ingot 3 by external processing if necessary) was cut out from the latter half of the growth. Using the gallium nitride single crystal substrate 4a as a seed crystal substrate, gallium nitride is grown on the gallium nitride single crystal substrate 1 which is the seed crystal substrate to produce a new gallium nitride ingot 2, and this new gallium nitride The ingot 2 is cut out to manufacture the gallium nitride single crystal substrate 4. By repeating this manufacturing process, a low-defect gallium nitride single crystal substrate can be obtained.
[Selection] Figure 1

Description

  The present invention relates to a method for manufacturing a gallium nitride single crystal substrate used as a substrate for light emitting diodes and laser diodes in the blue to ultraviolet region, and a gallium nitride single crystal substrate.

  Nitride-based semiconductor materials have a large band gap and are of direct transition type, so that they are actively applied to short wavelength light emitting devices.

  Nitride-based semiconductor devices are formed by using a vapor phase growth method such as MOVPE (metal organic vapor phase epitaxy), MBE (molecular beam vapor phase epitaxy), or HVPE (hydride vapor phase epitaxy). It is obtained by performing epitaxial growth on top.

  However, a large number of crystal defects exist in the nitride semiconductor crystal of the nitride-based semiconductor element obtained by the above growth method. These crystal defects cause the deterioration of the characteristics and the lifetime of the nitride-based semiconductor light-emitting element. For this reason, reduction of crystal defects is desired. It is considered that the reason why the number of defects in the nitride semiconductor crystal increases is that there is no different base substrate that matches the lattice constant of the nitride semiconductor. Accordingly, there is a need for a gallium nitride (GaN) free-standing substrate whose lattice constant matches that of the nitride semiconductor.

  The GaN free-standing substrate fabrication method is fast because of its high growth rate, and the HVPE method is the mainstream. After a GaN thick film is grown on the sapphire substrate by the HVPE method, the sapphire substrate is removed by mechanical polishing or laser peeling. Thus, a method for manufacturing a GaN free-standing substrate is known.

  However, the GaN free-standing substrate produced by the above method has many crystal defects, and even if a nitride-based semiconductor device is produced on a GaN free-standing substrate containing many crystal defects, the nitride-based semiconductor device has many crystals. It will contain defects. In order to reduce crystal defects in the nitride-based semiconductor device, it is necessary to reduce crystal defects in the GaN free-standing substrate. As a method for reducing crystal defects, the defect of a GaN free-standing substrate is reduced by an ELO (Epitaxial Lateral Overgrowth, hereinafter simply referred to as lateral growth) method.

For example, in Patent Document 1 and Patent Document 2, a GaN thick film is grown on a GaAs substrate by lateral growth using the HVPE method, and the GaAs substrate is etched away to obtain a GaN free-standing substrate. There is a proposal that a GaN single crystal is epitaxially grown by the HVPE method, and a plurality of self-supporting GaN substrates are obtained by cutting the epitaxially grown GaN ingot in a direction perpendicular to the axial direction. Further, Patent Document 3 has a proposal that a GaN ingot is sliced along a plane parallel to the growth direction to form a GaN substrate.
Japanese Patent Laid-Open No. 2000-12900 JP 2000-22212 A JP 2002-29897 A

Among the as-grown GaN free-standing substrates obtained by the lateral growth of the HVPE method, there is also obtained a substrate having a portion of a low defect region whose defect density is less than 1 × 10 ⁵ pieces / cm ^3. However, this low defect region portion is a very limited portion and has the following problems.

  (A) In the case of a laser element that requires a low defect, the laser element can be made only in a considerably limited portion (low defect region portion) of the GaN free-standing substrate. That is, the area yield for obtaining a laser element chip as a product on a GaN free-standing substrate is very poor.

(B) When a GaN free-standing substrate is used up to a portion of a high defect density region with a defect density exceeding 1 × 10 ⁵ pieces / cm ² , low defectivity is not required, but sufficient heat dissipation is required. Applications of high power LED elements are conceivable. However, even in such applications, as in the case of laser elements, LED elements can be made only in a fairly limited part of a GaN free-standing substrate (even if LED elements are made from parts that are not low-defect regions, reliable LED device having a low characteristic) and a considerably high-cost LED device.

  Thus, the GaN free-standing substrate, which is said to be low defects at present, is very difficult to use.

  The present invention has been made to solve the above-described problems, and provides a gallium nitride single crystal substrate manufacturing method and a gallium nitride single crystal substrate capable of manufacturing a GaN substrate having a low defect density on the entire surface. There is to do.

  1st invention uses the gallium nitride single crystal substrate cut out from the growth latter half part of the gallium nitride ingot obtained by carrying out crystal growth of the gallium nitride on the gallium nitride single crystal substrate as a seed crystal substrate, The seed crystal A method of manufacturing a gallium nitride single crystal substrate characterized in that a gallium nitride crystal is grown on a substrate to produce a new gallium nitride ingot, and the new gallium nitride ingot is cut out to produce a gallium nitride single crystal substrate. is there.

  The second invention uses, as a seed crystal substrate, a gallium nitride single crystal substrate that has been cut out and flattened from the latter half of the gallium nitride ingot obtained by crystal growth of gallium nitride on the gallium nitride single crystal substrate. A gallium nitride single crystal substrate characterized in that a gallium nitride crystal is grown on the seed crystal substrate to produce a new gallium nitride ingot, and the new gallium nitride ingot is cut out to produce a gallium nitride single crystal substrate. It is a manufacturing method.

  According to a third invention, in the first or second invention, the crystal growth is repeated by using the gallium nitride single crystal substrate cut out from the latter half of the growth of the new gallium nitride ingot as the next new seed crystal substrate. Thus, the gallium nitride single crystal substrate according to claim 1 or 2, wherein the gallium nitride single crystal substrate is manufactured.

  In the first to third aspects of the invention, HVPE, MOVPE, MBE, or the like is used for crystal growth of the gallium nitride.

A fourth invention is a gallium nitride single crystal substrate manufactured according to any one of the first to third inventions, wherein the defect density is less than 1 × 10 ⁵ pieces / cm ^2. .

  According to the present invention, a gallium nitride single crystal substrate obtained by crystallizing gallium nitride on a gallium nitride single crystal substrate and cut from the latter half of the growth with few crystal defects is used as a seed crystal substrate. Since a single crystal of gallium nitride is grown on this seed crystal substrate, a gallium nitride substrate having low defects can be obtained. In particular, the gallium nitride single crystal substrate cut out from the second half of the growth of the new gallium nitride ingot is used as the next new seed crystal substrate, and the crystal growth is repeated, so that the gallium nitride single crystal substrate whose entire surface is low-defects. Can be manufactured. Therefore, the area of devices on a gallium nitride substrate in the manufacture of devices that require low defects such as nitride lasers, and high-power nitride LEDs that do not require so low defects but heat dissipation is important. The yield can be greatly improved, and a significant cost reduction can be realized.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a manufacturing process according to the first embodiment of the present invention. First, a GaN single crystal substrate 1 (also simply referred to as a GaN substrate 1) is prepared as an initial seed crystal substrate. For producing the GaN single crystal substrate 1 serving as the seed crystal substrate, for example, after a GaN thick film is grown on the sapphire substrate by the HVPE method, the sapphire substrate is removed to produce the GaN single crystal substrate 1. Alternatively, a GaN single crystal substrate is formed by forming a mask having a large number of stripe windows and circular windows on a GaAs substrate, growing a thick GaN crystal thereon by lateral growth using the HVPE method, and then removing the GaAs substrate. 1 may be produced.

Next, a GaN single crystal is epitaxially grown on the GaN single crystal substrate 1 by using the HVPE method (FIG. 1A), and a GaN ingot 2 having a thickness of several millimeters is produced. In the HVPE method, a Ga melt storage container is installed in a hot wall reactor, and hydrogen chloride (HCl) gas and carrier gas hydrogen gas are blown into the Ga melt to synthesize gallium chloride (GaCl). Then, the synthesized GaCl is allowed to flow in the vicinity of the GaN substrate 1 together with hydrogen gas and reacted with ammonia (NH ₃ ) to grow a GaN crystal on the heated GaN substrate 1. The MOVPE method or the MBE method can also be used for epitaxial growth of the GaN crystal.

  Next, the outer shape of the GaN ingot 2 is adjusted by outer shape processing using an outer shape grinder (FIG. 1B) to obtain a cylindrical GaN ingot 3.

  Next, the cylindrical GaN ingot 3 is cut by a slicer or the like in a direction perpendicular to the axial direction thereof (or by cleavage) to cut out the GaN substrate 4 (wafer) (FIG. 1C). Among the cut out GaN substrates 4, one of the GaN substrates 4 cut out from the upper half of the columnar GaN ingot 3, that is, the portion grown in the latter half of the GaN ingot 3 (the latter half of the growth) (for example, In the illustrated example, the uppermost GaN substrate 4a) of the two substrates in the latter half of the growth is selected as the seed crystal substrate (FIG. 1 (d)).

  Next, using the selected GaN substrate 4a as a seed crystal substrate, a GaN single crystal is epitaxially grown on the GaN single crystal substrate 1 which is the seed crystal substrate by using the HVPE method (FIG. 1A). A new GaN ingot 2 is produced. Further, the external shape of the new GaN ingot 2 is adjusted (FIG. 1B) to form a cylindrical GaN ingot 3, and the cylindrical GaN ingot 3 is cut to cut out the GaN substrate 4 (FIG. 1C). ). One of the GaN substrates 4 in the latter half of the growth of the cut out GaN ingot 3 is selected as a new seed crystal substrate (FIG. 1D).

  The above steps (FIGS. 1A, 1B, 1C, and 1D are set as one cycle) are repeated. Since the GaN substrate 4 cut out from the latter half of the growth of the GaN ingot with few crystal defects is used as the seed crystal substrate, the defect density of the obtained GaN substrate 4 decreases as repeated growth is performed.

FIG. 3 shows how the defect density of the GaN substrate 4 (and GaN substrate 5) manufactured according to the first embodiment (and the second embodiment described later) changes with the number of growths. It is the graph which plotted the result. As can be seen from FIG. 3, although depending on the growth conditions, the defect density decreases as repeated growth is performed. Although it is not known at what level the defect density finally saturates or converges, the GaN substrate 4 (or GaN substrate 5) cut out from the latter half of the growth (upper half) of the GaN ingot 3 with few defects is used as a seed crystal. By using it, it becomes possible to manufacture a GaN substrate 1 having a low defect of less than 1 × 10 ⁵ pieces / cm ² stably.

After the repeated growth described above, the defect density of the cut GaN substrate 4 is lower than a predetermined value, for example, less than 1 × 10 ⁵ pieces / cm ^2. Polishing such as polishing (chamfering if necessary) is performed to planarize (FIG. 1 (e)), and the planarized GaN substrate 5 is completed (product) (FIG. 1 (f)). The finished GaN substrate 5 is a transparent substrate having a low defect density on the entire surface.

  FIG. 2 shows a manufacturing process according to the second embodiment of the present invention. Basically the same as in the first embodiment, but the GaN substrate 4 cut out from the latter half of the growth of the cylindrically shaped GaN ingot 3 is further polished by lapping and polishing (if necessary) The difference is that the GaN substrate 5 (in the illustrated example, the uppermost GaN substrate 5a) planarized by chamfering is selected as a new seed crystal substrate (FIG. 2G).

  That is, the planarized GaN substrate 5 (5a) is used as a seed crystal substrate, and a GaN single crystal is epitaxially grown on the GaN single crystal substrate 1 as the seed crystal substrate by using the HVPE method (FIG. 2A )), A new GaN ingot 2 is manufactured, and the outer shape of the new GaN ingot 2 is further adjusted (FIG. 2 (b)) to form a cylindrical GaN ingot 3, and the cylindrical GaN ingot 3 is cut (or Then, the GaN substrate 4 is cut out (FIG. 2 (c)), and the GaN substrate 4 in the latter half of the growth (upper half) of the cut out GaN substrate 4 is subjected to surface processing such as polishing to be planarized (FIG. 2). 2 (e)), the planarized GaN substrate 5 is selected as a new seed crystal substrate (FIG. 1 (g)).

By repeating the above steps (FIGS. 2 (a), (b), (c), (e), and (g) are taken as one cycle), as shown in FIG. A small number of GaN substrates 5 can be obtained. When the defect density of the GaN substrate 5 becomes, for example, 1 × 10 ⁵ pieces / cm ² or less, the obtained GaN substrate 5 is regarded as a finished product (product) (FIG. 2 (f)). A nitride laser or the like is produced.

  In the first embodiment, the case where the GaN substrate 4a obtained from the uppermost part of the GaN ingot 3 is used as the seed crystal substrate has been described. However, the GaN substrate 4a cut out from the uppermost part (uppermost surface) of the GaN ingot 3 is used. In such a case, roughness such as growth stripes or pits may be seen on the surface. In such a case, a clean crystal cannot be grown on the GaN substrate. A GaN substrate processed and planarized by polishing or the like is preferably used as a seed crystal substrate. Also, when the roughness of the GaN substrate 4 cut out from the latter half of the growth of the GaN ingot 3 is not particularly severe, or when the GaN substrate 4 cut out from the middle of the latter half of the growth of the GaN ingot 3 is used, polishing or the like is performed. A GaN substrate whose surface is processed may be used as a seed crystal substrate.

It is process drawing which shows 1st Embodiment of the manufacturing method of the gallium nitride single crystal substrate based on this invention. It is process drawing which shows 2nd Embodiment of the manufacturing method of the gallium nitride single crystal substrate based on this invention. It is the graph which showed the relationship between the frequency | count of growth with respect to the GaN board | substrate manufactured by 1st and 2nd embodiment, and defect density.

Explanation of symbols

1 GaN single crystal substrate (GaN substrate)
2 GaN Ingot 3 Columnar GaN Ingot 4 Cut Out GaN Substrate 4a Topmost GaN Substrate 5 Flattened GaN Substrate 5a Topmost GaN Substrate

Claims (4)

  A gallium nitride single crystal substrate cut from the latter half of the gallium nitride ingot obtained by crystal growth of gallium nitride on the gallium nitride single crystal substrate is used as a seed crystal substrate, and the gallium nitride is deposited on the seed crystal substrate. A method for producing a gallium nitride single crystal substrate, characterized in that a new gallium nitride ingot is produced by crystal growth, and the new gallium nitride ingot is cut out to produce a gallium nitride single crystal substrate.   A gallium nitride single crystal substrate cut out and flattened from the latter half of the gallium nitride ingot obtained by crystal growth of gallium nitride on the gallium nitride single crystal substrate is used as a seed crystal substrate. A method of manufacturing a gallium nitride single crystal substrate, comprising: forming a new gallium nitride ingot by crystal growth of gallium nitride; and cutting out the new gallium nitride ingot to manufacture a gallium nitride single crystal substrate.   Using the gallium nitride single crystal substrate cut out from the latter half of the growth of the new gallium nitride ingot as a next new seed crystal substrate, a gallium nitride single crystal substrate is manufactured by repeating the crystal growth. The method for producing a gallium nitride single crystal substrate according to claim 1 or 2. A gallium nitride single crystal substrate manufactured by the manufacturing method according to claim 1, wherein the defect density is less than 1 × 10 ⁵ pieces / cm ² .

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