JP2004335645A - GaN SUBSTRATE - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a GaN wafer capable of indicating the (11-20) orientation with high accuracy by solving the problem that an orientation indicating means relying upon the orientation flat (OF) has an error as high as 0.5-1° although a circular independent GaN can be produced. <P>SOLUTION: When a linear mask is provided in the (-110) direction on a GaAs substrate and GaN is facet grown thereon, a dislocation is drawn onto the linear mask to produce a defect collective region H. Other part becomes a single crystal region of good quality where dislocation is suppressed. The defect collective region H has a crystal structure different from that of an adjacent single crystal part and also has an optical difference. The GaAs substrate is removed and the mask is also removed, and a parallel defect collective region H grown thereon can be seen with the naked eye. The H is formed in parallel with the cleavage plane which is indicated with high precision by a stripe (defect collective region H). Crystal orientation can thereby be indicated with an error of 0.5° or less or 0.03° or less. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a single-crystal GaN free-standing substrate (wafer) capable of accurately indicating a crystal orientation. Since a single crystal wafer produces various equivalent device chips thereon and cuts into individual chips by cleavage, the crystal orientation must be given accurately. In particular, when a natural cleavage plane is used as a substrate of a laser device used as a resonator, there must be a means capable of accurately indicating the crystal orientation.
[0002]
[Prior art]
In order to indicate the crystal orientation of the wafer, it is common to use an orientation flat method in which an arc-shaped portion of a circular wafer is cut off to expose a surface along the natural cleavage. Since a line segment parallel to the cleavage plane appears around the wafer, the crystal orientation can be determined. A short line segment indicating the direction is called an orientation flat (OF). In the wafer process, various steps are performed by determining the orientation of the wafer based on the OF.
[0003]
In the case of a Si wafer having a diamond structure, there is no distinction between the front and back surfaces, and the cleavage plane is orthogonal to the front and back surfaces. Therefore, the wafer is cut along one of the cleavage planes to obtain an orientation flat. That is, in the case of a Si wafer, only one orientation flat is required. OF indicates a cleavage plane.
[0004]
In the case of a GaAs wafer having a sphalerite structure, since the crystal mesas are different on the front and back, an OF indicating a cleavage plane and an IF indicating the direction of the plane perpendicular to the cleavage plane are provided. If the OF is longer than the IF and is arranged clockwise, such as OF, IF, it is looking at the surface. In the case of a Si or GaAs wafer, the lengths of the OF and IF to be attached thereto are determined according to the SEMI standard according to the diameter of the wafer.
[0005]
In the case of a circular wafer, one or two line segments are attached to the periphery to indicate the crystal orientation or the orientation of the crystal orientation.
The present invention is to newly provide a means for indicating the direction in the case of a GaN substrate. GaN is a high melting point material and does not become a melt even at around 2000 ° C. Therefore, it is difficult to install a single crystal after immersing the seed crystal in the melt or to solidify the melt from one side into a single crystal. So sapphire (α-Al ₂ O ₃ The GaN single-crystal thin film heteroepitaxially grown on the single-crystal substrate is still used as a GaN element (blue InGaN-LED, blue InGaN-LD) substrate.
[0006]
Although GaN on sapphire has an enormous dislocation density, it has nevertheless been proven to produce a long-life, high-brightness blue LED. However, when a GaN buffer layer is mounted on a sapphire substrate and an InGaN active layer is grown on the GaN buffer layer, there is no cleavage, so that chip separation is difficult, and the production of a resonator is troublesome, resulting in a low yield.
[0007]
Therefore, there has always been a demand to use GaN itself instead of sapphire as the substrate of the InGaN element. GaN has a natural cleavage. The cleavage plane is a {1-100} plane. Therefore, chip separation can utilize natural cleavage. In the case of a laser, the cavity surface can also be a cleavage plane, which is convenient.
[0008]
GaN single crystals are produced by a reaction from a gas phase to a solid phase. It has a high dislocation density, good quality, and it is difficult to produce large-diameter ones. With various efforts, it is now possible to manufacture a GaN single crystal wafer having a diameter of about 2 inches.
[0009]
Next, related prior art will be described.
Patent Document 1 proposes a Si wafer in which a melted hole of 1 mmφ is provided in a Si wafer by a laser beam to replace the OF, since there is a problem such as concentration of thermal stress and occurrence of slip when an OF or IF is attached to the periphery of the wafer. I have.
[0010]
Patent Document 2 proposes a Si wafer in which a small notch is provided around the wafer and the OF and IF are omitted since the wafer may come off during spin coating due to load eccentricity when the OF and IF are formed around the wafer. I have. Patent Literatures 1 and 2 describe an orientation indicating method that does not use OF for a Si wafer.
[0011]
Patent Document 3 proposes a method of growing GaN by ELO by attaching an ELO mask on a GaAs substrate.
Patent Document 4 becomes the present applicant and proposes a facet growth method of a GaN crystal for the first time. Instead of mirror growth, growth is performed while maintaining facets, dislocations are concentrated on the facets, and the remaining portion is made of a high-quality single crystal. As a result, a thick GaN film can be made for the first time.
[0012]
Patent Document 5 was created by the present applicant, in which a dot mask is formed as a base and a facet-growing portion is determined by the mask, and other than that, a high-quality single crystal and a thick free-standing film can be formed.
[0013]
[Patent Document 1]
JP-A-60-167426 (Japanese Patent Application No. 59-23448)
[0014]
[Patent Document 2]
JP-A-2000-331898 (Japanese Patent Application No. 11-141062)
[0015]
[Patent Document 3]
International Patent Publication WO99 / 23693
[0016]
[Patent Document 4]
JP-A-2001-102307 (Japanese Patent Application No. 11-273882)
[0017]
[Patent Document 5]
Japanese Patent Application No. 2002-230925 (filed on August 8, 2002)
[0018]
[Problems to be solved by the invention]
In the case of a GaN wafer, the crystal orientation can be indicated by cutting out a part of the circular peripheral portion along the cleavage and forming an orientation flat OF. As it is, GaN is not as easy as conventional Si and GaAs, because large diameter wafers are still difficult to make.
[0019]
When the orientation flat OF is provided, the crystal orientation can be measured, and a linear portion can be mechanically formed in a certain direction of the wafer by grinding or cutting. Alternatively, the orientation flat may be cut off with tweezers sandwiching the edge of the wafer. It is preferable that the OF is accurately represented on the edge if a natural cleavage plane comes out. For example, if a 60 mmφ disc can be made to secure a 10 mm fold allowance to make a 50 mmφ wafer, the edge can be folded with tweezers without failure and a natural cleavage plane can be obtained. However, in the case of a crystal that is difficult to grow, there is no such margin.
[0020]
Because the fold allowance is not sufficient, it often does not fold well. If it does not break properly, pinch it again with tweezers and apply force to break it. After several attempts, an accurate cleavage plane can be obtained. However, in the case of GaN, it is difficult to produce a large-diameter single crystal, so that the allowance for the cutting cannot be made too wide. At most, there is only a margin of about 1 mm to 2 mm. In this case, the operation of folding the wafer by sandwiching the side circumference with tweezers cannot be repeated many times. Therefore, the error also increases.
[0021]
In the case of the grinding method, sufficient accuracy is not easily obtained. An error exceeding 0.5 degrees may occur. However, since the device is manufactured, it is desired that the error of the orientation of the wafer be 0.5 degrees or less.
[0022]
However, in the case of a GaN circular wafer, the accuracy of the orientation flat is low, and it is not always possible to suppress the error to a required value (0.5 degrees or less).
Since the GaN substrate is manufactured as a substrate for blue LEDs and LDs, the precision of the orientation flat must be suitable for the purpose.
[0023]
When an LED substrate is used, the accuracy of the orientation flat (OF) is not strict. Since the device is a surface light emitting device, there is no relationship between the luminous efficiency and the error of the OF. A slight error may occur in the case of chip separation. But that's not a problem.
[0024]
The problem is in the case of using a semiconductor laser substrate. In that case, an advantage over the sapphire substrate was that the cleavage could be used as a resonator mirror. Ideally, the stripe of the laser chip is perpendicular to the resonance plane (cleavage plane). However, if the stripe of the laser deviates from the cleavage plane, the reflection efficiency decreases, the threshold value of laser oscillation increases, and the luminance is poor. . FIG. 1 shows the relationship between the laser chip 2 and the active layer 3 inclined in the longitudinal direction. The active layer 3 of the laser is an elongated portion extending in the longitudinal direction and is called a stripe. However, in the present invention, the term "stripe" will be used for other concepts later, and the laser active layer will be referred to as the linear active layer 3 to avoid confusion.
[0025]
Current is injected vertically in the linear active layer 3, which generates photons. Photons are amplified by reciprocating in the linear active layer and emitted as a beam from one end face. Both ends of the linear active layer are mirrors 4 and 4. Since the parallel mirrors 4 and 4 face each other, it is called a resonator. The width d of the linear active layer 3 is as thin as about 2 to 3 μm. The length of the linear active layer 3 is equal to the length L of the chip. If the end face of the linear active layer 3 is completely perpendicular to the longitudinal direction of the linear active layer 3, what is reflected on one end face can go to the other end face and repeats multiple reflection.
[0026]
However, if the end surface is slightly inclined (the inclination angle is defined as Υ), it may not be possible to repeatedly reflect. Since the tilt of the beam increases by 2 ° in one reflection, the beam running at the end of the linear active layer 3 is reflected by the end face and returned, and remains in the active layer at the other end face. No. The width of the linear active layer 3 is d = 2 to 3 μm, and the chip length is L = about 300 to 600 μm. The condition for returning the reflected light is Υ ≦ d / 2L, so the narrower the width d and the longer L, the more severe the condition for Υ.
[0027]
At present, the shortest length is about 300 μm. However, even if a device having a length of 200 μm is created in the future due to technological progress in a reading device or the like, if d = 3 μm and L = 200 μm, {≦ 0.5}. It becomes. Therefore, the maximum allowable angle of Υ is about 0.5 で も in view of future technological progress. At present, since L is about 500 μm, {≦ 0.2} when d = 3 μm. Even better, it is possible to reciprocate the linear active layer not only once but also many times. The condition that the beam traveling at the end of the linear active layer remains on the linear active layer even after being reflected m times is Υ ≦ d / 2 mL, but d = 3 μm, L = 500 μm, m = 6, and Υ ≦ 0.03 degrees.
[0028]
The limitation of the angle of deviation Υ of the end face with respect to the linear active layer 3 is given not only by the reflection condition but also by the chip cleavage yield. FIG. 2 shows a state in which, when a large number of chips 2 are cut out from the wafer 5, the direction perpendicular to the cleavage is different from the chip cutting line. If there is a discrepancy in the orientation Υ, the mirror state of the cleavage plane deteriorates, and the cleavage yield decreases.
[0029]
FIG. 9 shows the relationship between the inclination angle of the linear active layer and the number of chip chips obtained when the width of the stripe core (defect accumulating region H) is 50 μm, the interval between the stripe cores is 400 μm, and the chip size is 600 μm × 400 μm. It is a graph. FIG. 7 is a graph showing the relationship between the inclination angle の of the linear active layer and the cleavage yield under the same conditions. The result that the cleavage yield is close to 100% is obtained when Υ is within 0.03 degrees. The number of chips in the wafer surface is as follows. If the angle of deviation of the end face is large, the percentage of chips that can be obtained from one GaN wafer decreases. On the other hand, considering the chip yield due to the parallelism shift (θ ゜) between the stripe core and the linear active layer, 100% is obtained when θ = 0 ° and 100% when θ is 0 to 0.2 °. You can take a tip. However, when θ exceeds 0.2 degrees, the number of chips obtained is reduced to 76.2%. The spacing between the stripe cores is 350 μm, but the linear active layer is preferably located exactly in the middle. However, since θ is finite, the linear active layer is shifted from the center (175 μm) of the stripe core at the end of the chip. If the deviation from the center exceeds 90 μm, it is a defective product. Since the wafer is a 2-inch wafer (having a radius of 25 mm), assuming that the linear active layer is at the center of the stripe core at the center and 90 μm away from the center at the periphery, the angle of deviation in that case is tan. ^-1 (0.09 / 25) = 0.2 degrees. If the angle is exceeded, the chips in the left and right peripheral portions become defective, and the yield of non-defective products is reduced to 76.2%.
[0030]
The deviation angle is also related to the characteristics of the laser when the laser is fabricated on a GaN wafer. There are various characteristics, but here, the oscillation current threshold value Ith will be described. FIG. 8 is a schematic diagram showing the relationship between the deviation angle Υ of the crystal orientation from the linear active layer and the oscillation current threshold value Ith. It can be seen that when the deviation angle Υ increases, the threshold current increases and the laser characteristics deteriorate. .
[0031]
[Means for Solving the Problems]
According to the present invention, a parallel mask having a crystal orientation different from the surroundings exists in a GaN single crystal which is provided with a parallel mask on a substrate and has a crystal orientation different from its surroundings along the mask in a facet-grown GaN single crystal. The angle α formed between the portion (stripe: defect accumulating region H) and the (1-100) plane ([11-20] direction) of the single crystal is 0.5 degrees or less, and the crystal orientation differs from the surroundings. The straight line portion (the defect accumulating region H) is used as an orientation marker. More preferably, the angle α between the straight portion (defect gathering region H) having a different crystal orientation and the (1-100) plane direction is 0.2 degrees or less, and the linear portion having different crystal orientations (defect gathering region H). Is used as the direction method. More preferably, the angle α formed between the crystal orientation difference linear portion (defect accumulating region H) and the (1-100) plane direction is 0.03 degrees or less.
[0032]
Alternatively, it is rotated by 90 ° so as to take a stripe (defect accumulating region H) in the (11-20) plane ([-1100] direction), and the angle α formed between them is 0.5 ° or less and 0 °. .2 ° or less, or 0.03 ° or less.
[0033]
That is, in the present invention, a portion having a different crystal orientation in a transparent crystal is used as a mark of the (1-100) plane direction or the (11-20) plane instead of the OF. It is an unprecedented means of indicating the crystal orientation. If the orientation of single-crystal GaN can be specified with high accuracy, the device characteristics are improved, and the number of device chips that can be obtained from one wafer increases.
[0034]
BEST MODE FOR CARRYING OUT THE INVENTION
Since a large seed crystal does not exist in a GaN crystal, it is grown on another type of single crystal substrate by a vapor phase growth method. If GaN is grown on the entire surface of another type of substrate, a strong single-crystal cannot be obtained due to strong mismatch due to strong mismatch. Therefore, a mask having fine windows is attached to another type of substrate so that GaN crystal growth starts from an isolated window. It is called a lateral growth method (ELO; Epitaxy Lateral Overgrowth). Patent Document 3 describes GaN ELO. GaN ELO is a technique developed as a method for growing a thin film of about several μm. With that alone, there are too many dislocations and the internal stress is also strongly separated to form a thick film.
[0035]
The present inventor has devised a facet growth method in which a facet (a low index surface inclined with respect to the growth surface) is intentionally formed on the growth surface and grown while maintaining the growth conditions so that the facet does not disappear. The facet growth method is described in US Pat. GaN is a hexagonal system, and when grown in the c-plane (0001) direction, pits (recesses) of regular hexagonal pyramid or regular dodecagonal pyramid are generated depending on conditions. As the facet surface is open upward and grows, dislocations converge on the facet boundary surface and converge on the pyramid axis (pit axis) as it grows. 10 on the pit axis ³ -10 ⁴ Since such dislocations are concentrated, the other portions become a single crystal having few dislocations. Only the pit portion becomes a defect accumulating region H where a large number of defects are gathered, which is unavoidable.
[0036]
It is inconvenient, however, because where the facets occur is not predetermined. It is better to be able to predefine where the facets occur. The inventor made trial and error what to do. In order to solve the problem, a SiO.sub. ₂ When GaN is facet-grown on a mask (covering portion) such as circular, square, or linear with SiN or the like under the condition that the facet can be maintained, a facet is generated on the mask (covering portion). And found that faceting could not be done on other parts. It is described in US Pat.
[0037]
In this case, the mask for determining the facet growth position is a mask having a much larger period than the above-described ELO mask. The mask can be used together with ELO. The ELO has a wide covering portion, narrow windows, dotted windows, a cycle of about ten and several micrometers, and uses a fine mask.
[0038]
The facet-grown mask created by the present inventors has a size (diameter and width) of about 20 μm to 200 μm (preferably 50 μm), and has a wide exposed portion and a narrow covered portion.
To avoid confusion, an ELO mask is referred to as an ELO mask to distinguish the two types of masks, and a mask for designating facets for facet growth is referred to as a facet mask.
[0039]
The facet mask can provide the covering portion as a set of isolated points (dot type) or the covering portion as a parallel straight line (stripe type). In each case, a facet grows on the covering portion, and a single crystal grows on the substrate exposed portion (uncovered portion). Thereby, the position where the facet is generated can be specified in advance.
[0040]
FIG. 3 shows the steps of the facet mask method, and the facet mask growth method will be briefly described below. FIG. 3A shows a base substrate. It is not a GaN substrate. The base substrate is a GaAs substrate 6 here. A mask 7 having a size larger than ELO (about ten and several μm) is formed on the GaAs substrate 6 (FIG. 3B). The mask 7 is made of SiO ₂ , SiN, AlN or the like. The size of the mask 7 may be about 20 μm to 100 μm, and may be an isolated dot shape or a parallel linear band shape.
[0041]
GaN is vapor-phase grown thereon by any of HVPE, MOC, MOCVD, and sublimation. The GaN crystal nuclei selectively grow on the exposed base portion 8 and do not occur on the mask. Then, as the crystal 9 grows, it rises from the exposed base portion 8 and protrudes onto the mask. However, it is difficult to grow on the mask and the growth is delayed (FIG. 3 (3)). So a diagonal surface comes out on the mask. That is the facet plane F. They are {-1-122}, {1-101}, etc., whose surface indices are relatively low.
[0042]
When the growth of GaN is further continued, the crystal layers are stacked more and more as shown in FIG. 3D, but the crystals are deposited relatively quickly on the exposed portions 8 and grow slowly on the mask. As the facet faces are formed inward, dislocations are drawn inward by the facet faces. Therefore, the dislocations are concentrated on the growing portion on the mask. The portion on the mask where the dislocations are gathered is called a defect gathering region H. It has been found for the first time by the present applicant and is described in Patent Documents 4 and 5.
[0043]
If the mask is too small, the defect accumulating region H will disappear on the way. When a large mask 7 having a size of about 20 μm to 200 μm is used, the mask 7 does not disappear halfway, and the defect accumulating region H is slightly reduced at the same position as the mask and is continuously generated. A preferred mask width is 50 μm.
[0044]
In the defect accumulating region H, dislocations are present at a high density, but the remaining portion has fewer dislocations and becomes a low dislocation single crystal. Although it becomes a single crystal, two types of parts are distinguished. The portion immediately below the facet is a single crystal Z (single crystal low dislocation accompanying region) having high electric conductivity and few dislocations, and the portion immediately below the flat surface (the C plane) between the facet and the facet is electrically conductive. Is a single crystal Y having a small number of dislocations and a low dislocation single crystal region. Therefore, they are arranged as shown in FIG. 3 (4)... HZYZHZYZHZYZH.
[0045]
When GaN is grown to a sufficient thickness, the GaN is removed from the growth apparatus, and the facet portion is ground and processed flat. The result is as shown in FIG. Further, the GaAs base substrate 6 is removed. At the same time, the mask 7 is also removed. Polish the back surface evenly.
[0046]
The remaining one is a flat and smooth GaN crystal as shown in FIG. Y and Z are low dislocation single crystals, while H is a defect accumulating region with many dislocations. There are various types such as a polycrystal, a single crystal having a misaligned orientation, and a single crystal having an inverted orientation. The most common is a single crystal having an inverted orientation.
[0047]
Either one may be used, but when looking at the transparent GaN substrate, the Y + Z portion and the H portion can be clearly distinguished. Since H grows on the mask, it has a relationship as if the shape and dimensions of the mask were transferred. An arbitrary defect accumulating region H can be freely provided depending on the shape, size, and arrangement of the mask.
[0048]
The mask 7 for facet growth can be formed on the underlying substrate 6 in any manner. As such, there is no force to determine the orientation of the GaN crystal to be grown. It is the orientation of the underlying substrate that determines the orientation of the GaN crystal. Such properties are not obvious, but have been found by the present inventor when GaN is repeatedly grown on GaAs heterogeneous substrates by ELO and facet mask growth.
[0049]
When GaN is grown with a mask on the underlying substrate, the underlying substrate is removed. Therefore, it becomes a film consisting only of GaN. If it has a sufficient thickness, it becomes a free-standing film. It is a transparent film. Although it is transparent, if you look closely, you can visually distinguish the part where the facet mask was and the other part.
[0050]
The other portion was a single crystal having a (0001) crystal orientation, but it was found that the orientation of the portion grown on the mask was often inverted. That is, the portion grown on the mask is often (000-1). In addition, the upper portion of the mask may be polycrystalline or single crystal, but the orientation may be oblique. In any case, it has been found that the upper portion of the mask has many defects and has different orientations, so that it can be visually distinguished from other portions.
[0051]
The present invention seeks to determine the crystal orientation using such optical differences. The orientation of the underlying substrate determines the orientation of the GaN single crystal grown thereon. Therefore, the facet mask is arranged in a direction such that it becomes the <1-100> direction when GaN is grown.
[0052]
When GaAs is used as a base substrate, a single crystal wafer having a (111) plane is cut out and used as a substrate because GaAs is cubic. Since it has a three-fold symmetry, it matches the three-fold symmetry of the (0001) plane of GaN. In addition, due to the similarity of lattice constant, (111) GaAs is used as the substrate. When GaAs is used as a base substrate, a (111) Ga plane and a (111) As plane are distinguished. GaN can be facet grown on either surface as a base.
[0053]
In this case, the GaAs [11-2] direction and the [-110] direction exist on the (111) plane as directions orthogonal to each other. Here, those with square brackets [11-2] are expressions of individual directions, and <11-2> with brackets is a comprehensive expression indicating directions. The [11-2] and [-110] directions included in the GaAs individual planes (111) are orthogonal to each other.
[0054]
This is the orientation of GaAs. When GaN is grown on GaAs, a single crystal of (0001) plane grows on GaN. The orientation in the horizontal direction is determined by the underlying substrate. Since GaN is hexagonal, there are four plane indices (hkmn). The sum of the first three is always 0 (h + k + m = 0).
[0055]
As shown in FIG. 4, the [11-2] direction and the [-110] direction of GaAs exist on the (111) plane. When GaN is grown thereon, a crystal having a (0001) plane grows. The [-1100] direction of GaN grows in the [11-2] direction of GaAs, and the [11-20] direction of GaN grows in the [-110] direction of GaAs. Looking only at the preceding three surface indices, the relationship is as if rotated 90 °.
[0056]
The relationship is high precision, and there is little inconsistency. The present invention takes advantage of that property.
The cleavage plane of GaN is the (-1100) plane, which is parallel to the [11-20] direction. It is known that the [11-20] direction of GaN is generated parallel to the [-110] direction of the GaAs base.
[0057]
Therefore, in the present invention, the facet mask 7 is provided on the (111) GaAs base so as to be parallel to the [-110] direction. When GaN is grown on such GaAs by the facet growth method, a parallel-line-shaped defect accumulating region H extends over the mask as shown in FIG. Since it is a parallel line, it is called a stripe here.
[0058]
Therefore, a stripe (defect collection region) H extending in the same direction at the same position as the mask 7 is formed. In FIG. 4, the mask 7 and the stripe (defect collection region) H overlap. When the substrate is removed, the mask disappears, but the stripes (defect collection regions) H remain, and the stripes (defect collection regions) H and the single crystal regions Y + Z can be distinguished by the naked eye.
[0059]
Therefore, if a mask 7 that is strictly parallel to the [-110] direction of GaAs is attached first, when the GaN self-standing crystal is formed, the extension direction Q ([11-20]) of the cleavage plane (-1100) is obtained. And the stripe α (defect accumulating region) H should be 0 °. FIG. 5 shows the relationship. Q is the cleavage plane extension direction [11-20], and forms an angle of α with a stripe (defect accumulating region) H provided in parallel. The orientation of the GaAs undersubstrate can be accurately determined by X-ray diffraction.
[0060]
Therefore, the angle α between the mask extension direction and the cleavage plane extension direction can be easily reduced to 0.5 ° or less depending on the accuracy of mask generation on the GaAs substrate. Also, it can be less than 0.2 °. Further, it can be 0.03 ° or less.
[0061]
Normal OF is determined to be parallel to the cleavage plane because the edge of the crystal is cut off. However, in the case of the present invention, since the edge of the crystal is not cut off, it is not necessary to determine the orientation as the cleavage plane. . In the above description, stripes parallel to the extension direction [11-20] of the cleavage plane (-1100) are provided, but not limited thereto. By rotating by 90 °, stripes parallel to the direction [-1100] perpendicular to the cleavage plane (-1100) may be provided. In that case, a mask may be formed so as to be parallel to [11-2] of the underlying GaAs (111). Since cleavage is not used, the orientation to be displayed may be the cleavage direction or a direction perpendicular to it.
[0062]
【Example】
Fourteen wafers showing the orientation of the GaN wafer were produced by the conventional OF method, and 14 wafers showing the orientation by the defect accumulating region H of the stripe facet growth method of the present invention were produced, and the [11-20] direction was determined. Was measured, and its variation was examined.
[0063]
In the case of the OF method, the orientation is determined not by natural cleavage but by X-rays, and a short bow-shaped portion is removed by grinding to form an OF. According to this, the variation of α varied from about 0.2 ° to 1 °, the average value was 0.5 °, and the standard deviation σ was as large as σ = 0.4 °.
[0064]
According to the present invention, the minimum value of α was 0.00 °, the maximum value was 0.1 °, and the average value was 0.03 °, four of which were 0.03 ° or less. The standard deviation was σ = 0.04 °. It can be seen that the wafer of the present invention specifies the orientation more precisely.
[0065]
【The invention's effect】
Since a large GaN single crystal cannot be obtained yet and a sufficient allowance for bending cannot be obtained, the OF by mechanical grinding or manual cleavage often deviates from the [11-20] direction by 1 ° to 0.5 ° in many cases. .
[0066]
According to the present invention, the orientation of a defect accumulating region H grown on a facet mask that can be visually discriminated in a transparent wafer is not used as a measure of the orientation in which the edge of the GaN circular substrate is naturally cleaved. 11-20] direction.
[0067]
The azimuth is indicated by stripes (defect accumulating regions H) having slightly different brightness generated by growing the inside of the wafer by the facet mask method without processing the edge of the wafer. The stripes (defect accumulating regions H) are generated in parallel to the facet mask, and the facet mask can be accurately attached so as to face a specific direction of the underlying substrate. Since it is determined, the facet mask line can be formed so as to accurately indicate the [11-20] direction.
[0068]
Thereby, the discrepancy between the facet mask line and the [11-20] direction can be made 0.5 ° or less. It can be further reduced to 0.2 ° or less. As described above, if the deviation in the reference direction is 0.2 ° or less, the number of device chips removed from the wafer can be 76.2% or more. The yield can be increased. Further, the direction can be indicated with an error of 0.03 ° or less. Then, the number of chips obtained from the wafer becomes almost 100%.
[0069]
Even when a laser chip is manufactured on a wafer, variations in characteristics (threshold current Ith and the like) are small, and more stable laser elements can be manufactured.
Since there is no OF or IF, chipping does not occur from the edge of the wafer. There is no eccentricity when spin coating.
[0070]
However, in order to show the front and back, things such as OF and IF may be added. FIG. 6 shows such a wafer. That is, only the front and back sides are shown, and the orientation is indicated by stripes (defect accumulating regions H).
[Brief description of the drawings]
FIG. 1 is a laser plan view for explaining that light reflected on a mirror surface shifts from a linear active layer when a linear active layer of a laser chip and mirror surfaces at both ends thereof are staggered by an angle Υ. .
FIG. 2 is a diagram for explaining that when a large number of laser elements formed on a wafer are cut into individual chips, the number of picked-up chips decreases if the orientation is shifted by Δ.
FIG. 3 shows a case where a mask is formed on an undersubstrate and GaN is grown on the underlying substrate in a vapor phase while maintaining a facet. Is a cross-sectional view for explaining that a high-quality single crystal (Z + Y) having a fixed orientation grows in a portion of FIG. (1) is an undersubstrate, (2) is a substrate provided with a mask, (3) is a state when GaN is started to grow, and (4) is a state where GaN growth continues and follows the mask. This indicates that a stripe (defect collection region) H is formed, and that a facet is present thereon. (5) is obtained by grinding and dropping the upper facet-rich portion after crystal growth is completed, and (6) is obtained by removing the underlying substrate and the mask to form a GaN free-standing film.
FIG. 4 is a view showing a state in which GaN is grown on a GaAs (111) base substrate so that a GaN [11-20] direction is generated in parallel with GaAs [-110]. FIG. 9 is a view for explaining that a mask is attached so that a formed GaN stripe (defect accumulating region) H is parallel to [11-20].
FIG. 5 is a diagram showing a definition of a shift α between a direction of a stripe (defect accumulating region) H and a direction of GaN [11-20] in a GaN free-standing film after crystal growth.
FIG. 6 is a view of a wafer having an OF and an IF for indicating that a stripe (defect accumulating region) H is used as an index of an azimuth, but that an OF and an IF may be added to indicate front and back.
FIG. 7 is a graph showing a relationship between a deviation angle Υ of a linear active layer and a device cleavage yield in a laser chip.
FIG. 8 is a graph showing a relationship between a deviation angle の of a linear active layer in a laser chip and element characteristics (laser oscillation threshold current (Ith)).
FIG. 9 is a graph showing the relationship between the inclination angle θ of a linear active layer and the number of chip chips obtained in a laser chip.
[Explanation of symbols]
2 chips
3 Linear active layer
4 Reflection mirror
5 GaN wafer
6 Base substrate (GaAs)
7 Mask
8 Exposed part
9 GaN crystal
H defect accumulating area
Z single crystal low dislocation associated region
Y single crystal low dislocation extra region
F facet surface

Claims (3)

It has a single crystal portion having the same crystal orientation and a stripe portion having a crystal orientation different from that of the single crystal portion and continuing in a parallel line shape. A GaN substrate having an angle α with respect to an extension direction of a stripe portion of 0.5 degrees or less. It has a single crystal portion having the same crystal orientation and a stripe portion having a different crystal orientation from the single crystal portion and continuing in a parallel line shape. A GaN substrate, wherein an angle α formed between the GaN substrate and the extending direction of the stripe portion is 0.2 degrees or less. It has a single crystal portion having the same crystal orientation and a stripe portion having a different crystal orientation from the single crystal portion and continuing in a parallel line shape. A GaN substrate, wherein an angle α formed between the GaN substrate and the extending direction of the stripe portion is 0.03 degrees or less.

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