KR20170036055A - Substrates for group nitride crystals and their fabrication method - Google Patents

Abstract

In one example, the present invention provides a substrate for growing a thick layer of a Group III nitride. The substrate has a first surface provided for epitaxial growth of a Group III nitride and a second surface opposite the first surface and having a plurality of grooves. The present invention also provides a method of producing a thick layer or bulk crystal of a Group III nitride using a grooved substrate. The grooved substrate in one configuration grows a thick layer or bulk crystal of Group III nitride capable of reducing bowing and / or spontaneous separation from the substrate.

Description

TECHNICAL FIELD The present invention relates to a substrate for growing Group-III nitride crystals and a method for manufacturing the same. BACKGROUND ART [0002] Substrates for group III nitride crystal growth,

Cross reference of related application

This application claims priority from U.S. Patent Application No. 62 / 049,036, filed on September 11, 2014, entitled " Substrate for Growth of Group-III Nitride Crystals and Method of Manufacturing the Same "by the inventor Tadao Hashimoto, It is included as a reference in its entirety, as fully expressed here.

The present application also relates to the following U.S. patent applications:

Filed on July 8, 2005, inventors Kenji Fujito, Tadao Hashimoto and Shuzi Nakamura entitled " Method for Growth of Group III-Nitride Crystals in Supercritical Ammonia Using Autoclaves ", PCT Patent Application No. US2005 / 024,239, No. 30794.0129-WO-01 (2005-339-1);

U.S. Patent Application Serial No. 11 / 784,339, filed on April 6, 2007, inventors Tadao Hashimoto, Makoto Saito and Shuji Nakamura entitled "Method for growing large surface area gallium nitride crystals in supercritical ammonia and large surface area gallium nitride crystals" , U.S. Provisional Patent Application No. 30794.179-US-U1 (2006-204), filed on April 7, 2006 by Tadao Hashimoto, Makoto Saito and Shuji Nakamura, entitled "Growth of Large Surface Area Gallium Nitride Crystals Methods and large surface area gallium nitride crystals ", Attorney Docket No. 30794.179-US-P1 (2006-204), under 35 USC Section 119 (e) for US provisional patent application No. 60 / 790,310;

U.S. Patent Application Serial No. 60 / 973,602, filed on September 19, 2007, inventors Tadao Hashimoto and Shuji Nakamura entitled "Gallium Nitride Bulk Crystals and Their Growth Methods", Attorney Docket No. 30794.244-US-P1 (2007-809- One);

U.S. Patent Application No. 11 / 977,661, filed on October 25, 2007, inventor Tadao Hashimoto, entitled " Method for Growing Group III-Nitride Crystals in a Mixture of Supercritical Ammonia and Nitrogen and the Group III- , Attorney Docket No. 30794.253-US-U1 (2007-774-2);

U.S. Patent Application No. 61 / 067,117, filed on February 25, 2008, inventor Tadao Hashimoto, Edward Litz and Masanori Ikari, "Method of Manufacturing Group III-Nitride Wafer and Group III-Nitride Wafer," Attorney Docket No. 62158- 30002.00 or SIXPOI-003;

U.S. Patent Application No. 61 / 058,900, filed June 4, 2008, Inventor Edward W., Tadao Hashimoto and Ikari Masanori, "Group III-nitride with improved crystallinity from the initial Group III nitride Method for producing crystals ", Attorney Docket No. 62158-30004.00 or SIXPOI-002;

U.S. Patent Application No. 61 / 058,910, filed June 4, 2008, inventors Tadao Hashimoto, Edward Litz, and Masanori Ikari, "Group-III nitride crystallization using a high pressure vessel for growth of Group- ≪ / RTI > Growth Method and Group Ill-nitride Crystals ", Attorney Docket No. 62158-30005.00 or SIXPOI-005;

U.S. Patent Application No. 61 / 131,917 filed on June 12, 2008, inventors Tadao Hashimoto, Masanori Ikari and Edward Litz, "III-nitride wafers with test method and test data for III-nitride wafers", Attorney Docket No. 62158-30006.00 or SIXPOI-001;

U.S. Patent Application No. 61 / 106,110, filed on October 16, 2008, inventors Tadao Hashimoto, Masanori Ikari and Edward Litz, "Design of Reactor for Group III Nitride Crystal Growth and Growth of Group III-Nitride Crystals" No. SIXPOI-004;

U.S. Patent Application No. 61 / 694,119, filed on August 28, 2012, inventor Tadao Hashimoto, Edward Litz and Sierra Hoff, entitled "Group III nitride wafers and fabrication method", Attorney Docket No. SIXPOI-015;

U.S. Patent Application No. 61 / 705,540, filed on September 25, 2012, inventor Tadao Hashimoto, Edward Litz and Sierra Hoff, entitled "Method for Growing Group III Nitride Crystals", Attorney Docket No. SIXPOI-014;

These applications are hereby incorporated by reference in their entirety as if fully set forth below.

The present invention relates to a substrate used to produce a thick layer or bulk crystal of a Group III nitride semiconductor material such as GaN and AlN. The present invention also provides a method of producing a thick layer or bulk crystal of a Group III nitride semiconductor material. A thick layer or bulk crystal of Group III nitride is used to produce wafers of Group III nitride semiconductors, such as GaN wafers.

Explanation of existing technology

The present application refers to a number of publications and patents as indicated by numbers in square brackets, e.g., [x]. The following is a list of these publications and patents:

[1] R. Dwilinski, R. Doradzinski, J. Garczynski, L. Sierzputowski, Y. Kanbara, U.S. Pat. Patent No. 6,656,615.

[2] R. Dwilinski, R. Doradzinski, J. Garczynski, L. Sierzputowski, Y. Kanbara, U.S. Pat. Patent No. 7,132,730.

[3] R. Dwilinski, R. Doradzinski, J. Garczynski, L. Sierzputowski, Y. Kanbara, U.S. Pat. Patent No. 7,160,388.

[4] K. Fujito, T. Hashimoto, S. Nakamura, International Patent Application Nos. PCT / US2005 / 024239, WO07008198.

[5] T. Hashimoto, M. Saito, S. Nakamura, International Patent Application No. PCT / US2007 / 008743, WO07117689. See also US20070234946, U.S. Serial No. 11 / 784,339, filed April 6, 2007.

[6] D 'Evelyn, U.S. Patent No. 7,078,731

[7] Sakai et al., Applied Physics Letters vol. 71 (1997) p.2259.

Each of the above-listed references cited herein are incorporated by reference in their entirety, particularly as expressed herein, in connection with the description of how to make and use a Group III nitride substrate.

Gallium nitride (GaN) and related Group III nitride alloys are key materials for a variety of optoelectronic and electronic devices such as LEDs, LDs, microwave power transistors, and solar-blind photodetectors. Currently, LEDs are widely used in displays, indicators, general lighting, and LDs are used in data storage disk drives. However, most of these devices are epitaxially grown on heterogeneous substrates such as sapphire and silicon carbide because GaN substrates are extremely expensive compared to these heteroepitaxial substrates. The heteroepitaxial growth of Group-III nitrides results in highly defective or even cracked films, which leads to the realization of high-end optical and electronic devices such as high-brightness LEDs for general illumination or high power microwave transistors Interfere.

In order to solve the fundamental problem caused by heteroepitaxy, it is essential to use a crystalline Group III nitride. In most devices, a crystalline GaN wafer is preferred because it is relatively easy to control the conductivity of the wafer and the GaN wafer will provide the least lattice / thermal mismatch with the device layers. However, due to the high nitrogen vapor pressure at high melting point and elevated temperature, it has been difficult to grow GaN crystal ingots. Currently, most of the commercially available GaN wafers are produced by hydride vapor phase epitaxy (HVPE).

Ammonothermal growth, flux growth, and high temperature melting growth have been developed to obtain GaN bulk crystals in which GaN wafers can be sliced. Amorphous growth of group III nitride crystals in supercritical ammonia [1-6]. Flux processes and hot solution growth utilize the dissolution of Group III metals. However, these methods typically require GaN seed crystals. GaN wafers grown by HVPE are typically used as seed crystals because single crystal GaN is not present in nature.

To produce Group-III nitride wafers by HVPE, a thick layer of Group III nitride (> 500 micrometers) is grown on the substrate, typically sapphire, silicon carbide, silicon, or gallium arsenide. The substrate is then removed by mechanical grinding, laser-assisted separation or chemical etching. These methods, however, require an additional process to remove the substrate.

There are several techniques for spontaneous separation (or auto-separation, self-separation, self-stripping) of thick GaN films when a special buffer layer or patterning is fabricated on the front side of the crystalline substrate. For example, periodic SiO2 stripe masks on the front side of sapphire substrates enable selective growth of GaN [7]. Since the GaN layer is only partially deposited on the sapphire substrate, the thick GaN layer is separated from the substrate upon cooling after growth. Similarly, creating a periodic trench on the front side of the substrate results in a so-called cantilever epitaxy, which is also peeled off upon cooling. These selective growths typically change the direction of propagation of the dislocation and cause dislocation of the dislocation. However, this causes irregularly distributed dislocations on the surface of GaN, which is not good for lapping and polishing. In particular, chemical mechanical polishing (CMP) utilizes chemical effects, which are potential sensitive. Irregular distribution potential causes height fluctuation after CMP.

In one example, the invention provides a thick layer of Group Ill-nitride having a thickness greater than 0.5 mm or a substrate for growing bulk crystals. Substrates such as sapphire, silicon carbide, quartz, glass, or gallium nitride have grooves on the backside, which may or may not have group III nitride crystals grown.

The present invention also provides a method of growing a thick layer or bulk crystal of a Group III nitride using a substrate having grooves on its back surface. A crystal growth method suitable for growing a thick film or bulk crystal of Group-III nitride on one main surface or one side of the substrate, such as HVPE, is preferably used.

Reference is now made to the drawings, wherein like reference numerals throughout the following figures represent corresponding parts:
Figure 1 is a schematic view from the substrate edge of a substrate having a set of grooves on its back side.
In the figures, each number represents:
1. A substrate having grooves on its back side,
1a. The first side (front side)
1b. The second side (back side)
2. Groove
3. Width of groove
4. The pitch of the groove
5. Depth of groove
6. Substrate thickness
2 is a bottom plan view of a schematic substrate showing how multiple grooves are formed on the second side of the substrate;
In the figures, each number represents:
1b. The second side (back side)
2. Groove
3 is a microscope image of the back side of the grooved sapphire substrate. In the figures, each number represents:
1b. The second side (back side)
2. Groove
4 is a microscope image of the groove surface formed on the back surface of the sapphire substrate. In the figures, each number represents:
1b. The second side (back side)
2. Groove
2a. Scratches along the groove direction.
5 is a schematic flow of the production method. 5 (A) is a substrate having a first surface (front surface) prepared for the growth of Group-III nitride. 5B is a substrate having a groove made on the second surface (back surface). 5 (C) is a substrate having a Group III nitride grown on the first surface to a thickness greater than the thickness of the substrate. 5 (D) is after spontaneous separation of the Group III nitride film from the substrate. In the figures, each number represents:
1. A substrate having grooves on its back side,
2. Groove
2b. Crack
7. Substrate
8. A Group III nitride layer
9. A Group III nitride layer separated from a substrate.
Figure 6 is a schematic diagram of the bow of a Group III nitride layer.
In the figures, each number represents:
10. A method of manufacturing a substrate or a substrate comprising a Group III nitride layer
11. Boing Yang

summary

In one example, the substrate of the present invention enables thick growth of Group-III nitride such as GaN, with reduced bowing and additional spontaneous separation. Group-III nitride is commonly used in optoelectronic and electronic devices, but most devices use heteroepitaxial substrates such as sapphire, silicon carbide, and silicon. This is because there is no low-cost, high-quality, free-standing Group III nitride wafer. In recent years, GaN substrates have been produced by hydride vapor phase epitaxy (HVPE), thermal annealing, and flux methods, and AlN wafers have been produced by HVPE and physical vapor transport methods. Of these methods, HVPE is the most commonly used. HVPE production of a GaN substrate is involved with growth of a thick GaN layer on the substrate and removal of the substrate.

When a thick layer of GaN or other Group III nitride is grown on a heterogeneous epitaxial substrate, the layer is highly stressed due to mismatch of lattice constant and thermal expansion coefficient. This stress causes the layer and the substrate to bow. If the bow exceeds the threshold, the layer and / or the substrate will break. In addition, even bulk epitaxial growth of bulk / thick GaN on a GaN substrate sometimes causes bouncing and cracking. Therefore, it is important to reduce the stress to reduce the thickening of the thick layer and / or the substrate on which it is grown.

Another problem in the production process of Group III nitride such as GaN by HVPE is substrate removal. Several methods such as mechanical grinding, laser lift-off, and chemical etching are currently in use, but these methods require additional processing and new growth to separate the substrate. Several instances of spontaneous separation of the GaN layer from the substrate have been reported. One method uses selective growth with a mask or trench, which nevertheless causes selective accumulation of dislocations in one region, resulting in a non-uniform distribution of dislocations. The end points of these dislocations at the surface often cause pits during the CMP process, and thus a non-uniform distribution of dislocations will cause macroscopic thickness deviations across the wafer.

Technical Description of the Invention

The present invention discloses a substrate for growth of a thick layer of a Group III nitride, which substrate may address one or more of the problems discussed above. The substrate has a main surface on a first surface or a front surface prepared for epitaxial growth of a Group III nitride and the substrate has a second major surface or a back surface opposite the first surface and having a plurality of grooves. In particular, as opposed to the same substrate except that it has no grooves on the substrate, or for the same substrate except that it has grooves on the first side or front side of the substrate on which a Group III nitride is to be grown, Nitride III nitride that is caused by epitaxial growth of the nitride.

Preferably, the first side of the substrate that does not have grooves may have one or more buffer layers and / or a highly polished surface such as AlN or GaN applied to make the surface of the first side suitable for epitaxial deposition, The second side may not be polished or highly polished, and / or may not have a buffer layer applied thereto. The second side may thus not be suitable for epitaxial deposition, but in one variant of the invention the second side is also suitable for epitaxial deposition.

The substrate may be amorphous, polycrystalline, or single crystal and may be a heterophasic material such as quartz, glass, sapphire, silicon carbide, or silicon, or the substrate may be a homogeneous epitaxial material such as GaN or AlN. The substrate may have, for example, a wurtzite crystal structure. In some examples, the substrate is monocrystalline silicon, sapphire, GaN, or AlN. The substrate is typically at least 250 micrometers thick. The substrate may be at least 500 microns thick, and the thickness may be between, for example, 250 and 500 microns.

While there are several disparate epitaxial techniques that utilize trenches on the substrate, these methods typically create trenches or grooves on the front surface of the substrate where epitaxial growth will occur. On the other hand, the present invention utilizes grooves on the backside of the substrate that do not require epitaxial growth to occur.

As shown in the side view of Fig. 1, the illustrated substrate 1 has a first side or major surface 1a, which is polished with an order Ra of less than 1 nm for epitaxial growth of a Group III nitride . The second surface or main surface 1b has a plurality of grooves 2.

Figure 2 provides a schematic view of grooves across the major surface or surface of the substrate. The back surface 1b of the substrate has grooves 2 along the crystal orientation of the substrate and / or the Group-III nitride formed in this embodiment, preferably at least some of the grooves are cleavage ) Direction or along a cleavage plane. The orientation of the cleavage cleavage or grooves along the cleavage plane allows the Group III nitride to be deposited and the substrate to be more flexible when the temperature changes, than when the same grooves are located in different directions along the substrate. For example, when c-plane sapphire is used as the substrate, the grooves are preferably formed along the m-plane of the sapphire. Preferably, the grooves are symmetrically made with respect to all possible equivalent surfaces, namely (10-10), (01-10) and (1-100) planes. However, depending on the situation, grooves can be formed along only one or two crystal planes, although the stress in the grown Group-III nitride can be asymmetric in this case.

The substrate will eventually have a plurality of grooves on the second side and the grooves will have a greater reduction in substrate bouling than the comparative substrate when the Group III nitride is deposited and / or the temperature is changed from the epitaxial growth conditions to room temperature / RTI > and / or < / RTI > In this example, the comparison substrate may have no grooves and otherwise may be the same as the substrate of the present invention. Alternatively, the comparative substrate may have grooves on the front surface where the Group-III nitride is deposited rather than on the backside of the comparative substrate, and otherwise may be the same as the substrate of the present invention. The grooved substrate of the present invention preferably has sufficient rigidity that the surface of the front surface under epitaxial deposition conditions when the Group III nitride is initially deposited on the substrate has approximately the same bowing as its surface has at room temperature.

The spatial relationship is determined by the size and placement of the grooves on the second side of the substrate. The parameters that can be used to characterize the size and placement of the grooves are, for example, groove width, groove depth, groove pitch, groove shape, groove orientation relative to the crystal faces of the substrate (as described above), scratches on the surface of the grooves , And substrate thickness. A combination of each of these parameters may be used to provide the desired substrate flexibility.

Referring to Figure 1, in one example, the width 3 of the groove is preferably between 100 micrometers and 300 micrometers, the groove substrate 5 is preferably 50 micrometers and the thickness 6 of the substrate 1, Lt; / RTI > The grooves are spaced from each other. The bubbles can be parallel or intersect. The parallel grooves may all be spaced at the same distance from one another so that all of the parallel grooves have the same period. Alternatively, the parallel grooves may be arranged on the substrate such that the first set of grooves have a first period of spacing and the second set of grooves have a second period of spacing that is different from the spacing of the first period . Alternatively, the spacing between adjacent parallel grooves may not be periodic. The spacing between adjacent grooves may be smaller near the center of the second surface of the substrate where the stress is greater than the spacing between adjacent grooves in the peripheral region farther from the center of the second surface of the substrate. The pitch 4 of the individual grooves or sets of grooves as discussed is preferably between 0.1 mm and 5 mm. These grooves may have the pattern illustrated in FIG. 2, for example, as described above. The pattern for the set of grooves illustrated in FIG. 2 may have a three-fold symmetry. The shapes formed by intersecting the grooves may be the same so that all the grooves have, for example, a shape of a triangle, or the shapes may be a mixture of different shapes as shown in FIG. 2, For example triangular, and some other parts, for example, another shape such as a hexagon having a different length or the same length. 3 is a microscope image of an actually grooved sapphire substrate. The grooves may also have a curved shape, such as an arc-shaped bottom, as shown in FIG. 1, or the bottom of the grooves may be flat or V-shaped depending on how the grooves are formed. As shown in Figure 4, it is desirable to have scratches along the grooves. One particular substrate having these grooves is a sapphire substrate, and a Group III nitride such as gallium nitride is deposited on the first side of the substrate.

In this example, the groove width, depth, and pitch are significantly larger than the width, depth, and pitch of the grooves formed in the first surface of the comparative substrate on which the Group III nitride is grown. The requirement for flatness of the first side of the comparative substrate during epitaxial deposition of Group-III nitride limits the size and placement of the grooves within the first side of the comparative substrate. Therefore, the substrate as provided herein differs from the substrate having grooves on the side on which the Group III nitride is to be grown, because the substrate placement, shape and / or size are different so that the substrate affects Group-III nitride growth differently.

The substrate of the present invention can have a first surface of an undamaged flat substrate to ensure epitaxial growth of high quality Group III nitride. Grooves on the second side (back side) reduce the mechanical strength of the substrate. When the thickness of the Group III nitride layer approaches or exceeds the thickness of the substrate, the stress caused by mismatching of the crystal lattice and / or the thermal expansion may cause a crack that begins to compress and / or bend or start from scratches formed in the grooves So that portions of the substrate are slightly moved and can be absorbed by these grooves. This can reduce stress and / or bowing in the Group III nitride layer and can also induce spontaneous separation of the Group III nitride layer from the substrate upon cooling.

Figure 5 presents a schematic process of the present invention. The substrate 7 is prepared to have a suitable front face for epitaxial growth of the Group III nitride (Fig. 5 (A)). A plurality of grooves are formed on the back surface of the substrate to form the substrate 1 (Fig. 5 (B)). In contrast to the prior art trenches or grooves in which grooves are formed on the first side of the substrate, the groove width, depth and pitch are considerably larger in this example. In addition, it is desirable to have a number of mechanical scratches along the groove direction. Because of this nature, the grooves can be most preferably created with a multi-wire saw that creates an arc-shaped groove bottom. Another method of forming the grooves is chemical etching at room temperature or elevated temperature. For example, a sapphire substrate can be etched by high temperature (> 80 DEG C) phosphoric acid, and the silicon carbide and silicon can be etched in a mixed solution of hydrofluoric acid and nitric acid, or in molten alkali-hydroxide (sodium hydroxide, potassium hydroxide, have. Although additional time is needed, the grooves can be made using other mechanical methods such as wafer dicing or by dry etching, such as reactive ion etching. The grooves can also be laser etched into the substrate surface.

The first side may be flat. Alternatively, the first side may comprise a periodic SiO2 stripe mask on the first side as described above for reference [7] and / or a periodic SiO2 stripe mask on the first side, for example as described in reference [6] Holes, cuts, and / or grooves.

The first side (front side) of the substrate may be prepared for epitaxial deposition before and / or after the grooves are formed or during the grooving process. If the process for making the grooves contaminates the surface of the first side on which the Group-III nitride is to be deposited, preferably the substrate can be cleaned and / or polished to remove contaminants. A Group III nitride 8 such as GaN, AlN, InN or their solid solution is grown on the first side of the substrate as shown in Figure 5 (C). The growth method is preferably HVPE, but other methods such as metalorganic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), salt growth, flux growth, high temperature lysis growth, epitaxial sputtering can be used.

When the thickness of the Group III nitride layer becomes large, the substrate and the layer begin to warp. If the layer undergoes a tensile stress as in the case of a sapphire substrate, the substrate 1 and the layer 8 become concave as shown in Fig. 5 (C). Conversely, when the layer undergoes compressive stress, the substrate 1 and layer 9 become convex. In either case, the bowing can be reduced by the grooves on the back side of the substrate. To fabricate a freestanding substrate of Group III nitride, the layer thickness is preferably greater than 500 micrometers. In addition, the layer thickness preferably exceeds the substrate thickness.

After the thick layer growth of the Group III nitride, the Group III nitride layer on the substrate is cooled. Upon cooling, the Group III nitride layer is sometimes completely or partially peeled off the substrate, as shown in Figure 5 (D). While this mechanism of spontaneous separation is not known, spontaneous separation tends to occur when the Group III nitride layer thickness is greater than 500 micrometers or when the layer thickness exceeds the substrate thickness.

Comparative Example - Example 1

A thick layer of GaN was grown by HVPE on a sapphire substrate with no grooves. A single-sided polished c-plane sapphire substrate with a 2-inch diameter and less than 5 degrees of cut was mounted in the HVPE reactor. The Group III source was GaCl synthesized in the reaction chamber by flowing HCl into molten Ga. The Group V source was NH ₃ . First, a GaN buffer layer was grown at about 900 DEG C for 10 minutes at an HCl flow rate of 20 sccm and an NH3 flow rate of 3.5 slm. Thereafter, a GaN thick film layer was grown at about 1030 DEG C for 16 hours at an HCl flow rate of 60 sccm and an NH3 flow rate of 2 slm. The total thickness of GaN was approximately 2900 micrometers. After growth, the GaN layer on the substrate was cooled, but the GaN layer was not separated from the substrate. The crystal bowing was 607 micrometers in the growth direction (convex). The bowing 11 was measured as the height difference between the edge and the center of the substrate 10 (Fig. 6).

Grooved  Fabrication of Substrate - Example 2

Grooves are formed on the back side of the 2-inch c-plane sapphire substrate. Miss cuts on the main or main surface were within 5 degrees of the c-plane sapphire. First, a sapphire substrate was mounted facing down on a metal block having wax. The assembly was then mounted on a multi-wire saw. The wire diameter was approximately 160 micrometers, and the wire pitch was 670 micrometers. Diamond slurry was supplied while the wire moved back and forth on the back side of the sapphire substrate. First, the wire was set along the (10-10) plane, and grooves having a depth of about 160 micrometers were formed over the entire rear surface. Through these steps, a sapphire substrate with profile-straight walls and grooves with arc-shaped bottom was fabricated on the backside of the substrate (schematic diagram of FIG. 2). The groove depth was approximately 160 micrometers, the substrate thickness was approximately 430 micrometers, the groove width was approximately 160 micrometers, and the groove pitch was approximately 670 micrometers. The orientation of the grooves is within a reasonable angle error (+/- 5 degrees) from the m-plane. By using multi-wire bows, wide and deep grooves can be formed within one hour.

After the wire bake process, the substrate and metal plate are heated to melt the wax. The substrate is removed from the metal plate and washed with acetone and isopropanol. This cleaning step removes residual wax and diamond slurry from the substrate.

Grooved On the substrate  Growth of thick Group III nitride - Example 3

Similar to the method of Example 1, a thick GaN layer was grown on the grooved sapphire substrate produced in Example 2. [ The GaN layer was grown on the flat, grooved upper surface of the substrate and no GaN was grown on the grooved surface exposed at the bottom of the substrate. The HVPE growth conditions were the same as in Example 1. After growth, the total thickness of GaN was approximately 3600 micrometers.

The GaN layer was spontaneously separated from the sapphire wave during cooling. The bowing of the GaN layer was 138 micrometers in the growth direction (convex), which is greatly reduced at the value in Example 1 (607 micrometers). The bowing was measured as the height difference between the edge and the center of the GaN layer.

Upon self-separation of the GaN layer, the sapphire substrate was broken into several pieces along the grooves, indicating that the grooves induced cracking in the sapphire substrate. Since the groove direction follows the cleavage direction of the sapphire (i.e., m-plane), the grooves helped to cleave or crack the sapphire. In this particular example, scratches in the grooves would also have helped cleavage or cracking, but scratches are not necessary. Substrate cracking and / or cracking can be a spontaneous separation and reduced bowing mechanism.

The cracking along the grooves can be advanced by the abrasive nature of the multi-wire bovine. In addition, the multi-wire cow enables the creation of grooves of uniform depth, width and pitch. This also affects the highly symmetrical configuration of the grooves, particularly the ingots grown due to the grooves disposed along the cleavage planes in the substrate, as well as the effective reduction of stress at the substrate and new growth interface.

In this example, the groove width is 160 micrometers, which is determined by the diameter of the wire. If a wire having a different diameter is used, the groove width can be changed. However, to maintain a certain wire strength, the wire diameter is typically greater than 100 micrometers. In addition, if the groove width is too small, the stress reduction effect will be limited. Conversely, if the width is too large, the substrate becomes excessively fragile. In one example, the groove width is between 100 micrometers and 300 micrometers.

The groove depth in this example is 160 micrometers. The groove depth can easily be changed by adjusting the wire height to the substrate. If the depth is too small, the stress reduction effect will be limited. Conversely, if the depth is too large, the substrate becomes excessively fragile. In one example, the grooves may be between 50 micrometers and 75% of the substrate thickness.

The groove pitch was 670 micrometers, which was determined by the wire pitch of the wire bob. This can be easily changed by using a wire roller having an appropriate groove pitch. If the groove pitch is too large, the stress reduction effect will be limited. Conversely, if the groove pitch is too small, the substrate becomes excessively fragile. In one example, the groove pitch is between 0.1 mm and 5 mm.

The growth conditions including the growth time were the same in the case of Example 1 and Example 3, but in Example 3, the GaN layer thickness was increased remarkably by about 24%. The reduced stress caused by the substrate grooves during growth can advance the crystal growth of GaN and the use of the inventive substrate compared to the same comparative substrate, except that it has no grooves on the second side of the substrate, It can bring speed.

Since the first side of the substrate has the same properties as a standard sapphire substrate, no special growth step is required as required when the grooves are formed on the front side of the substrate to obtain a high quality GaN film. In addition, there is no dislocation agglomeration which causes problems in the CMP process, since the required selective growth for the grooves on the first side is not used.

The obtained 3.6 mm thick free standing GaN was processed by grinding, lapping and CMP to produce a GaN substrate. The final thickness of the GaN substrate was 529 micrometers.

Benefits and Improvements

The substrate having grooves on the back side of the present invention can provide a Group III nitride layer with reduced bowing and additional spontaneous separation. A simple process using multi-wire oxides produces substrates with back grooves. The grooves on the backside of the substrate can reduce bowing of the Group III nitride layer through stress reduction. The grooves may also induce spontaneous separation of the Group III nitride layer from the substrate. The further planar front surface of the substrate enables high quality growth of the Group III nitride on the front surface without requiring special process steps such as that required when the front surface of the substrate is grooved. This feature helps to realize the flat surface of GaN after CMP finish.

Possible variants

Although the preferred embodiment describes bulk crystallization of GaN, similar advantages of the present invention can be expected for other Group III nitride nitrides of various compositions such as AlN, AlGaN, InN, InGaN, or GaAlInN.

Although the preferred embodiment describes a sapphire substrate, other materials such as silicon carbide, silicon, quartz, gallium arsenide, gallium phosphide, gallium nitride, aluminum nitride, lithium gallite, lithium aluminate, magnesium gallite, magnesium aluminate have. The substrate may be a dissimilar substrate or a homogeneous substrate.

While the preferred embodiment describes HVPE as a growth method for growth on one side of a substrate, other growth methods, such as MOCVD, MBE, dark thermal, flux, high pressure solution growth, May be used to grow on one side of the substrate or to grow on both sides of the substrate (typically with masking on the back side if grown on both sides).

While the preferred embodiment describes multi-wire bopping, other mechanical, chemical, and physical methods such as dicing, wet etching, and dry etching may be used.

Claims (33)

As a substrate for growing a Group III nitride layer,
(a) a first side adapted for epitaxial growth of a bulk Ill-nitride, and
(b) a second side opposite the first side of the substrate and having a plurality of grooves. The method according to claim 1,
Wherein the widths of the grooves are individually between 100 micrometers and 300 micrometers, and the depths of the grooves are individually 50 micrometers and 75% of the substrate thickness. The method according to claim 1 or 2,
Wherein the pitches of the grooves are individually between 0.1 mm and 5 mm. The method according to any one of claims 1 to 3,
Wherein the grooves follow the crystal orientation of the substrate. The method of claim 4,
Wherein the crystal orientation is the cleavage orientation of the substrate. The method according to any one of claims 1 to 5,
The plurality of grooves are sized and shaped to provide less bowing within the Group III nitride layer formed on the substrate than the same comparative substrate except that the substrate does not have the grooves on the second surface, Lt; / RTI > The method according to any one of claims 1 to 5,
The grooves are sized and shaped to allow the substrate to provide a higher growth rate of the Group III nitride layer on the substrate than the same comparative substrate but not having the grooves on the second surface, A substrate. The method according to any one of claims 1 to 5,
Wherein the grooves are sized and shaped such that when the Group III nitride layer has a thickness greater than 500 micrometers the substrate is completely or partially separated from the grown Group III nitride layer on the first surface of the substrate, A substrate having an arrangement on a surface. The method according to any one of claims 1 to 8,
Wherein the grooves are closer to the center area of the second surface than the edge of the second surface. The method according to any one of claims 1 to 9,
Wherein the substrate is amorphous. The method according to any one of claims 1 to 9,
Wherein the substrate is a single crystal. The method of claim 11,
Wherein the substrate has a wurtzite crystal structure. The method of claim 12,
Wherein the substrate is monocrystalline sapphire or monocrystalline GaN. 14. The method of claim 13,
Wherein the first and second surfaces are c-planes of the single crystal sapphire having a miscut within 5 degrees. 15. The method of claim 14,
Wherein the grooves have a three-fold symmetry along the m-plane of the monocrystalline sapphire or monocrystalline GaN. The method according to any one of claims 1 to 15,
Wherein the grooves are formed using a multiwire element. 18. The method of claim 16,
Wherein the surfaces of the grooves have mechanical scratches along the groove direction. The method according to any one of claims 1 to 17,
Wherein the Group III nitride is GaN. The method according to any one of claims 1 to 18,
Wherein the first surface has no grooves. The method according to any one of claims 1 to 19,
Wherein the substrate has a buffer layer on a first side of the substrate. The method comprising growing a predetermined amount of a Group III nitride layer on a first surface of a substrate having a second surface opposite the first surface, wherein the predetermined amount is such that the thickness of the Group III nitride layer is greater than the thickness of the substrate Lt; RTI ID = 0.0 > III-nitride < / RTI > 23. The method of claim 21,
And spontaneously separating the substrate from the Group III nitride layer. ≪ RTI ID = 0.0 > 11. < / RTI > The method of claim 21 or 22,
Wherein the groove width is between 100 micrometers and 300 micrometers, the groove depth is between 50 micrometers and 75% of the substrate thickness. 23. The method according to any one of claims 21 to 23,
Wherein the pitch of the grooves is between 0.1 mm and 5 mm. 24. The method according to any one of claims 21 to 24,
Wherein the grooves are located along crystal orientations of the substrate. 26. The method according to any one of claims 21 to 25,
Wherein the surfaces of the grooves have mechanical scratches along the grooves. 26. The apparatus according to any one of claims 21 to 26,
Wherein the grooves are formed using a multi-wire ingot. 28. The method according to any one of claims 21 to 27,
Wherein the substrate is a c-plane single crystal sapphire or GaN. 29. The method of claim 28,
Wherein the grooves are configured to have three symmetries along the m-face of monocrystalline sapphire or GaN. 29. The method according to any one of claims 21 to 29,
Wherein the Group-III nitride is GaN. 32. The method according to any one of claims 21 to 30,
Wherein the Group III nitride is grown by hydride vapor phase epitaxy. A Group III nitride ingot manufacturing method comprising growing a predetermined amount of a Group III nitride layer on a first side of a substrate of any one of claims 1 to 20. An ingot formed by the method of any one of claims 21 to 32.

Images