JP2004006931A - Semiconductor substrate and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method by which various problems caused by a mask layer used can be avoided, the manufacturing process of a semiconductor substrate can be simplified, and the conventional problem about the difficulty of the selective growth of AlGaN can be solved and, at the same time, the occurrence of warping and cracking can be suppressed when an Si substrate etc., is used. <P>SOLUTION: In the figure, 1 and 2 respectively represent a substrate and a semiconductor crystal grown by the vapor growth method. Protrusions 11 and recesses 12 are formed on the crystal growth surface of the substrate 1 so that crystal growth may be made only from the upside of the protrusions 11. The widths (a) of the projecting sections 11 are controlled to a submicron order of 0<a<1 μm and the ratio of the area occupied by the protrusions 11 to the whole surface of the substrate 1 is adjusted to ≤50 %. <P>COPYRIGHT: (C)2004,JPO

Description

【００４７】
表２に示すように本発明を用い作製したサンプルでは従来例に比べ出力が高く、リーク電流の少ない高品質のＬＥＤが作製できる事がわかった。
【００４８】
［実施例３］
実施例１で作製したＧａＮ結晶を第一結晶とし、その上に第二結晶を成長させた。まずＧａＮ第一結晶にフォトレジストのパターニング（幅：２μｍ、周期：４μｍ、ストライプ方位：ＧａＮ基板の＜１−１００＞）を行い、ＲＩＥ装置で２μｍの深さまで断面方形型にエッチングした。この時のパターニングは基板凸部の上に第一結晶の凹部がくるような配置とした。この時のアスペクト比は１であった。フォトレジストを除去後、ＭＯＶＰＥ装置に基板を装着した。その後、窒素、水素、アンモニア混合雰囲気下で１０００℃まで昇温した。その後、原料としてＴＭＧ・アンモニアを、ドーパントとしてシランを流しｎ型ＧａＮ層を成長した。その時の成長時間は、通常の凹凸の施していない場合のＧａＮ成長における４μｍに相当する時間とした。
【００４９】
成長後の断面を観察すると基板凹部への成長、凸部側面への成長が見られるものの、図２に示すように空洞部を残したまま凹凸部を覆い、平坦になったＧａＮ膜が得られた。続いて得られた膜のピットの評価を行ったところ２×１０^５ｃｍ^−３にピットが減少している事がわかった。このように本実施例を繰り返す事により更なる転位密度低減効果があることが確認できた。
【００５０】
【発明の効果】
以上説明した通りの本発明の半導体基材及びその作製方法によれば、基板に対して凸部を設けておくことで、マスク層を使用することなく低転位領域を形成可能なラテラル成長を行わせることができる。従ってマスク層を形成することに起因する問題点である軸の微小チルティングによるラテラル成長部の合体部分の新たな欠陥の発生の問題やオートドーピングの問題、Ａｌ含有半導体材料が選択成長不可という問題を解消できる。また、基板に凹凸面を設けた後に、一回の成長でバッファ層成長から発光部等の半導体結晶層の成長を連続して行えるので、製造プロセスの簡略化が図れるという利点がある。また貫通転位のもととなる凸部の幅、面積を規定することで低転位密度領域を相対的に広くしたり、凹凸を覆い平坦化するのに用する厚みを薄くできる利点がある。
さらに空洞部の利用による反射率向上や、残留歪の現象などの効果もあり特性向上、低コスト化の面から非常に価値のある発明である。
【図面の簡単な説明】
【図１】本発明に係わる半導体基材の結晶成長状態を説明するための断面図である。
【図２】本発明に係わる半導体基材の結晶成長状態を説明するための断面図である。
【符号の説明】
１　　　基板
１１　　凸部
１２　　凹部
１３　空洞部
２　　半導体層[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor substrate and a method for manufacturing the same, and more particularly to a structure and a method useful when a semiconductor material in which dislocation defects easily occur is used.
[0002]
[Prior art]
When a GaN-based material is crystal-grown, a GaN-based material uses a substrate that does not have a lattice match, such as sapphire, SiC, spinel, or recently, Si because there is no substrate that has a lattice match. However, during the GaN film produced due to the fact that no lattice matching are present 10 ¹⁰ / cm ² things dislocation. In recent years, high-luminance light-emitting diodes, semiconductor lasers, and the like have been realized, but a reduction in dislocation density has been desired in order to improve characteristics.
[0003]
[Problems to be solved by the invention]
As a method of reducing the dislocation density, for example, when a GaN-based semiconductor crystal or the like is vapor-phase grown on a buffer layer and a GaN substrate, a partial mask is provided on the substrate and selectively grown by providing a selective mask. A method has been proposed in which crystal growth is performed to obtain a high-quality crystal with a reduced dislocation density (for example, Japanese Patent Application Laid-Open No. 10-312971).
[0004]
However, according to the above-mentioned method, there is a problem that the c-axis is tilted in the lateral growth direction with a small amount in the laterally grown portion on the mask layer, which causes a new problem that the crystal quality is reduced. (MRS1998 Fall, Meeting G3.1). This can also be confirmed by measuring the incident azimuth dependency of X-ray rocking curve measurement (XRC) (¢ scan). That is, the full width at half maximum (FWHM) of the X-ray rocking curve due to the incident X-rays from the lateral growth direction is larger than the FWHM value due to the X-rays from the stripe direction of the mask layer, and the C axis is slightly tilted (tilted). Indicates that there is orientation dependency. This suggests that a large number of new defects may be induced in the merged portion of the lateral growth on the mask.
[0005]
Although SiO ₂ is commonly used as a mask layer material, there is a problem of so-called auto-doping contamination in which, when a crystal growth layer is stacked thereon, the Si component moves into the crystal growth layer. It turned out that there was.
Furthermore, when a semiconductor material containing Al, for example, AlGaN is grown on a substrate with a SiO ₂ mask layer, there is also a problem that crystals grow on the mask layer, and the selective growth itself cannot be performed effectively.
[0006]
As an attempt to solve such a problem, a substrate in which a buffer layer and a GaN layer are provided on a base substrate of SiC is subjected to stripe groove processing up to the SiC layer to form a convex portion. There has been proposed a method of growing a crystal from a GaN layer that is to be positioned above (MRS 1998 Fall Meeting Preliminary G3.38). According to this method, selective growth can be performed without using a SiO ₂ mask layer, and various problems caused by using the above-described SiO ₂ mask can be solved.
[0007]
In the above method, a sapphire substrate can be used as a base substrate, and a method thereof is also disclosed (for example, JP-A-11-191659). However, the above-described method requires a step of growing a buffer layer material and a GaN-based material on a sapphire base substrate, crystallizing the buffer layer once, removing the groove from the growth furnace, and then performing crystal growth again. There has been a problem that a new inconvenience of complication occurs, the number of working steps increases, and the cost increases.
[0008]
Attempts have also been made to grow a GaN-based material on a Si substrate. However, when a GaN-based crystal is grown, there is a problem in that warpage and cracks occur due to a difference in thermal expansion coefficient, and high-quality crystal cannot be grown.
[0009]
Further, in the case of using the above-described lateral growth technique, it is effective to form the non-mask portion thin in order to reduce threading dislocations from the substrate as much as possible. However, it was difficult to form a fine pattern over the entire surface of the substrate.
[0010]
Therefore, in view of the above problems, it is an object of the present invention to avoid various problems caused by using a mask layer and to simplify a manufacturing process. Another object of the present invention is to solve the problem that selective growth of AlGaN cannot be performed, which has been difficult in the past. It is another object of the present invention to suppress the occurrence of warpage and cracks when using a Si substrate or the like.
[0011]
[Means for Solving the Problems]
The semiconductor substrate of the present invention is a semiconductor substrate comprising a substrate and a semiconductor crystal grown on the substrate by vapor phase, wherein the crystal growth surface of the substrate has an uneven surface, and the semiconductor crystal has the uneven surface. In the semiconductor base material which is exclusively crystal-grown from above the convex portion, the convex portion has a width a in a range of 0 <a <1 μm and occupies the convex portion with respect to the substrate surface. It is characterized in that the area ratio is 50% or less.
[0012]
In the semiconductor substrate as described above, it is preferable that the ratio of the area occupied by the projections to the substrate surface is 2 to 30% from the viewpoint of minimizing dislocation defects.
[0013]
Another semiconductor substrate of the present invention is a semiconductor substrate comprising a substrate and a semiconductor crystal vapor-grown on the substrate, wherein the crystal growth surface of the substrate is an uneven surface, and the semiconductor crystal is In the semiconductor base material which is exclusively crystal-grown from above the convex portion on the concave-convex surface, the convex portion has a width a in a range of 0 <a <1 μm, and the convex portion has a width a in the range of 0 <a <1 μm. The ratio of the occupied area is set to 50 to 70%.
[0014]
Still another semiconductor substrate of the present invention is a semiconductor substrate comprising a substrate and a semiconductor crystal vapor-grown on the substrate, wherein the crystal growth surface of the substrate has an uneven surface, In a semiconductor base material which is exclusively crystal-grown from above the convex portion on the concave-convex surface, the convex portion has a width a in a range of 0 <a <1 μm, and the convex portion has a width a of the concave portion. It has a portion that is equal to or less than the width b.
[0015]
[Action]
The present invention provides a substrate in which lateral growth capable of forming a substantially low dislocation region from the beginning of crystal growth is provided in advance by providing an uneven surface on a substrate in which even a buffer layer or the like is not formed. It is characterized by the fact that That is, in the case of vapor-phase growth, crystal growth can occur on the entire substrate surface in the initial stage of growth, but growth in the upper part of the convex part becomes dominant, and as a result, the raw material hardly diffuses into the concave part, and as a result, the convex part becomes convex. The uneven surface is covered with a layer exclusively grown from the upper part of the part. In the growth of the projections, so-called lateral growth in the direction perpendicular to the C axis occurs, and the formation of a low dislocation region can be substantially achieved without using a mask layer (without using a mask layer as in the related art). . In addition, since this growth can be performed from the crystal growth of a layer (for example, a buffer layer) located immediately above the substrate, there is an advantage that the subsequent growth process can be performed continuously.
[0016]
In addition, according to the first aspect of the present invention, the width a of the convex portion is set in a submicron order of 0 <a <1 μm, and the area occupied by the convex portion with respect to the substrate surface is reduced. Since it is 50% or less, the crystal thickness required until the above-mentioned uneven surface is covered with a layer exclusively grown from the upper part of the convex part can be reduced. As a result, the thermal expansion stress possessed by the crystal is reduced, and the occurrence of warpage can be suppressed.
[0017]
According to the second aspect of the present invention, the ratio of the area occupied by the projections to the substrate surface in the above configuration is particularly set to 2 to 30%, so that the inheritance of dislocation defects is minimized in addition to the above operation. Can be suppressed. In other words, the ratio of the area of the convex portions at which the dislocation lines may extend is set to the minimum necessary for achieving the lateral growth, so that the dislocation defects included in the crystal grown thereon have a minimum value. You can get closer.
[0018]
According to a third aspect of the present invention, the width a of the convex portion is set to be in a range of 0 <a <1 μm, and the purpose of the present invention is to change the viewpoint of the invention exclusively to minimize the crystal thickness. Thus, the area ratio occupied by the projections is set to 50 to 70%. That is, increasing the occupied area ratio of the protrusions results in increasing the density of the protrusions, and when the above-described lateral growth is caused on a substrate having such protrusions, the growth starts. The uneven surface is covered with a layer exclusively grown from above the convex portion in a short time, and as a result, a crystal layer which is thinner and thus has a further improved warpage problem can be obtained.
[0019]
The invention according to claim 4 is an invention of a specific approach aiming at minimizing dislocation defects. For example, when the convex portions are provided in a parallel stripe shape, the width a of the convex portions is 0 <a <1 μm. And the convex portion is formed so as to have a portion in which the width a of the convex portion is equal to or less than the width b of the concave portion, so that the concave portion having a dislocation line blocking effect is dominant. It becomes a shape, and the inheritability of dislocation defects is suppressed low, and consequently dislocation defects are suppressed.
[0020]
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
1A to 1C are cross-sectional views for explaining a crystal growth state of a semiconductor substrate according to the present invention. In the drawing, reference numeral 1 denotes a substrate, and 2 denotes a semiconductor crystal grown on the substrate 1 by vapor phase. A convex portion 11 and a concave portion 12 are formed on the crystal growth surface of the substrate 1, and the crystal growth is performed exclusively from above the convex portion 11.
[0021]
The substrate in the present invention refers to a substrate serving as a base for growing various semiconductor crystal layers, in which a buffer layer or the like for lattice matching has not been formed yet. As such a substrate, sapphire (C plane, A plane, R plane), SiC (6H, 4H, 3C), GaN, Si, spinel, ZnO, GaAs, NGO, etc. can be used. Other materials may be used as long as they correspond to the above. In addition, those off from these substrates may be used.
[0022]
Various semiconductor materials can be used as the semiconductor crystal grown on the substrate 1, and the composition ratio of x and y is changed in AlXGa 1 -X-YInYN (0 ≦ x ≦ 1, 0 ≦ y ≦ 1). GaN, Al _0.5 Ga _0.05 N, In _0.5 Ga _0.05 N and the like can be exemplified.
[0023]
Above all, in the case of a semiconductor material containing Al such as AlGaN, the conventional mask method has a problem of growing on a SiO ₂ mask layer. However, according to the present invention, such a problem can be solved by masklessness. Lateral growth of AlGaN, which could not be done conventionally, becomes possible, and a high-quality film with low dislocations can be grown directly above the substrate. Therefore, light absorption by the GaN layer, which is a problem in an ultraviolet light emitting element or the like, is eliminated, which is particularly preferable in application.
[0024]
It is effective that the convex portion 11 formed on the crystal growth surface of the substrate 1 has a shape such that crystal growth is performed exclusively from above. “The crystal growth is performed exclusively from the upper part” refers to a state in which crystal growth can be predominantly performed at the apex or the top surface of the convex part 11 and in the vicinity thereof. Although good, it means that the crystal growth of the convex portion 11 becomes dominant eventually. That is, if a low dislocation region is formed by lateral growth starting from the upper part, the same effect as that of the conventional ELO requiring a mask can be obtained. This is a feature of the present invention in that it can be grown without a mask. Hereinafter, this point will be described with reference to FIG.
[0025]
FIG. 1 is a cross-sectional view of a projection 11 formed in a stripe shape.
In the present invention, the width a of the projection 11 is set to 0 <a <1 μm. As described above, the reason why the width a of the convex portion 11 is suppressed to the order of submicron is to reduce the thickness of the crystal required to cover the uneven surface of the substrate and to reduce the thickness of the substrate surface of the convex portion. It is to reduce dislocation defects in combination with the area ratio occupied. From this viewpoint, it is not preferable that the width a of the convex portion 11 is 1 μm or more, since the purpose of reducing the thickness cannot be sufficiently achieved. Therefore, it is desirable that the width a is as narrow as possible. However, considering the workability of unevenness processing, a width that is too narrow is not preferable, and it is desirable to select the width a in the range of about 0.1 <a <0.7 μm. . The “width of the convex portion” in the present invention generally refers to the width of the top surface of the convex portion. However, when the width of the top surface of the convex portion is different from the width of the rising base portion, the base portion width is different. Sometimes it refers to the width of. Further, the groove depth (convex height h) may be appropriately selected within a range in which the effect of the present invention is obtained.
[0026]
The ratio of the area occupied by the projections 11 on the substrate surface can be set according to the purpose. First, from the general viewpoint of the present invention that the thickness of the semiconductor crystal 2 is reduced and the dislocation is reduced, the area ratio occupied by the protrusion is set to 50% or less. This is because, in the growth mode in which dislocations from the sapphire substrate extend straight, the number of dislocations inherited decreases as the area ratio occupied by the projections decreases.
[0027]
Therefore, it is preferable that the area ratio occupied by the protrusions is small, and it is preferable that the area ratio be 40% or less, and more preferably 30% or less. In particular, when the content is 30% or less, the object of minimizing dislocation inheritance can be achieved. However, if the area ratio occupied by the projections is extremely reduced, lateral growth itself is unlikely to occur, or it takes a considerable time for the growth. Therefore, it is necessary to secure a projection area of 2% or more. Is desirable. Therefore, from the viewpoint of minimizing the succession of dislocations, the area ratio occupied by the protrusions is preferably 2 to 30%, and more preferably 4 to 20%.
[0028]
On the other hand, from the viewpoint of minimizing the thickness of the semiconductor crystal 2, the area ratio occupied by the convex portions is selected in the range of 50 to 70%. By increasing the density of the projections in this manner, the time during which the crystal growths starting from the upper portions of the respective projections unite with each other can be shortened, and as a result, the thickness of the semiconductor crystal 2 can be minimized. is there. If the area ratio exceeds 70%, the dislocation blocking effect is greatly reduced, which is not desirable.
[0029]
As will be described later, a desirable form of the convex portion 11 is a stripe-shaped convex portion. In the case of such a convex portion, the shape of the convex portion can be defined by the relationship between the width a of the convex portion 11 and the width b of the concave portion 12. That is, on the assumption that the width a of the convex portion 11 is 0 <a <1 μm, the width a of the convex portion is set to be equal to or less than the width b of the concave portion. Can be aimed at. In this case, the relationship between the width a and the width b does not necessarily have to be strictly satisfied over the entire surface of the substrate, and it is sufficient that at least a main portion of the substrate surface is configured as such.
[0030]
Hereinafter, an example will be described in the case of a stripe-shaped convex portion.
FIG. 1A shows a case where the width of the protrusion is 0.5 μm, the area ratio occupying the substrate surface is about 50%, and the height h of the protrusion is also substantially the same. In this case, the source gas can reach the concave portion 12 and the vicinity thereof, so that the growth in the concave portion 12 also occurs. Further, crystal growth also occurs from the upper part of the convex part 11, and as shown in FIG. 1B, crystal units 20 and 21 are generated on the upper part of the convex part 11 and on the surface of the concave part 12, respectively. . Under such circumstances, when the crystal growth continues, the films grown in the lateral direction starting from the upper part of the projection 11 are connected, and eventually cover the uneven surface of the substrate 1 as shown in FIG. In this case, a low dislocation region is formed in the upper part of the concave portion 12, thereby improving the quality of the formed film. At this time, the thickness required until the concave portion was covered and became flat was 0.5 μm.
[0031]
In the present invention, there is no particular limitation as long as such a convex portion 11 is used, and various shapes can be adopted.
Specifically, when the groove depth (projection height) h is larger than the groove width B as described above, when the groove depth (projection height) h is smaller than the groove width B, the groove width is further increased. Various combinations can be performed such as when the groove depth (height of the convex portion) h is very shallow with respect to B, or when the groove width B is very large with respect to the width A of the convex portion 11. In particular, when the groove depth (height of the convex portion) h is deeper than the groove width B, the raw material gas cannot substantially diffuse to the bottom during vapor phase growth, so that the raw material efficiently contributes to the growth of the upper portion of the convex portion 11. preferable. Further, it is preferable that the groove width B is wider than the width A of the convex portion 11 in that the lateral growth region is increased and the low dislocation region is formed wider.
[0032]
Examples of the mode of forming such a concavo-convex surface include island-shaped dotted projections, stripe-shaped projections, lattice-shaped projections, and projections in which the lines forming these are curved. Can be exemplified.
Among these convex portions, those having a stripe-shaped convex stripe are preferable in that the production process can be simplified and a regular pattern can be easily produced. The longitudinal direction of the stripe may be arbitrary, but if the material to be grown on the substrate is GaN and the <1-100> direction of the GaN-based material is used, it is difficult to form oblique facets such as {1-101} planes. Lateral growth (lateral growth) is faster. As a result, it is particularly preferable that the uneven surface is quickly covered.
[0033]
As in the embodiment shown in FIG. 1, when the concave and convex surface of the substrate 1 is buried while the cavity 13 is left, and then the light emitting portion is grown thereon to produce a light emitting element, the refraction of the interface between the cavity and the semiconductor is made. A large rate difference can be obtained. As a result, the rate at which light directed downward from the light emitting portion is reflected at this interface increases. For example, when the LED is die-bonded with the sapphire substrate surface facing down, it is preferable because the amount of light that can be taken out increases.
[0034]
Further, burying the cavity 13 while leaving it intact means that the contact area between the substrate 1 and the semiconductor layer grown thereon can be reduced. It is preferable in terms of reducing the amount. This reduction in strain has the effect of reducing the warpage that occurs when a GaN-based material is grown thick on sapphire. In particular, in the conventional method, when a GaN-based material is crystal-grown on a Si substrate, there is a problem that warpage and cracks are generated due to a difference in thermal expansion coefficient and high-quality crystal growth cannot be performed. Eliminate problems.
[0035]
Further, by utilizing the fact that the contact area between the substrate 1 and the semiconductor layer 2 grown thereon can be reduced, when the semiconductor layer 2 grows thick, stress concentrates on this small contact portion, and the substrate 1 and the semiconductor layer 2 can be separated. By applying this, a substrate such as GaN can be manufactured.
[0036]
As described above, the case where only one semiconductor layer 2 is grown on the substrate 1 has been described. However, in order to further reduce dislocation defects, a similar process may be repeated twice. That is, as shown in FIG. 2, after the crystal growth of the first semiconductor layer 2a is performed so as to cover the uneven surface of the substrate 1 by the same method as described above, the surface of the first semiconductor layer 2a is The second semiconductor crystal 2b can also be formed on the first semiconductor layer 2a by crystal growth exclusively from above the convex portion of the first semiconductor layer 2a by vapor phase growth. In this case, if the convex portion 11 of the substrate 1 and the position of the convex portion 11a formed on the first semiconductor layer 2a are shifted in the vertical direction, the first semiconductor Many dislocations above the protrusions 11a of the layer 2a will not propagate. That is, with such a configuration, the entire region of the second semiconductor layer 2b can be a low dislocation region, and a higher quality semiconductor layer can be obtained.
[0037]
Further, the surface of the second semiconductor crystal 2b may be made more uneven, and a third semiconductor layer similarly formed by a vapor phase growth method may be formed thereon. Alternatively, a similar process may be repeated to form a plurality of semiconductor layers in a multiplex manner. With such a configuration, dislocations that propagate each time the layers are stacked can be gradually reduced without intentionally adjusting the position of the upper and lower convex portions as described above.
[0038]
The projections can be formed, for example, by patterning the projections according to the shape of the projections using a normal photolithography technique, and performing etching using an RIE technique or the like.
[0039]
HVPE, MOCVD, MBE, or the like may be used as a method for growing a semiconductor layer on a substrate. When forming a thick film, the HVPE method is preferable, but when forming a thin film, the MOCVD method is preferable.
[0040]
The growth conditions (gas type, growth pressure, growth temperature, and the like) for growing a semiconductor layer on a substrate may be appropriately selected depending on the purpose as long as the effects of the present invention are obtained.
[0041]
【Example】
[Example 1]
A photoresist is patterned on the c-plane sapphire substrate (width: 0.3 μm, period: 4 μm, stripe orientation: stripe extending direction is <11-20> direction of the sapphire substrate), and 3 μm by RIE (Reactive Ion Etching) apparatus. Was etched in a square cross section to a depth of. After removing the photoresist, the substrate was mounted on a MOVPE apparatus. Thereafter, the temperature was increased to 1100 ° C. in a hydrogen atmosphere, and thermal etching was performed. Thereafter, the temperature was lowered to 500 ° C., and trimethylgallium (hereinafter, TMG) was used as a Group 3 raw material, and ammonia was flowed as an N raw material, to grow a GaN low-temperature buffer layer. Subsequently, the temperature was raised to 1000 ° C., and TMG / ammonia was flowed as a raw material and silane was flowed as a dopant to grow an n-type GaN layer. The growth time at that time was set to a time corresponding to 4 μm in the GaN growth in the case where the normal unevenness was not applied.
[0042]
Observation of the cross section after the growth shows that the growth has occurred in the concave portions of the substrate, but as shown in FIG. 1C, the concave and convex portions were covered while leaving the hollow portions 13 in the concave portions, and a flat GaN film was obtained. .
On this film, pits (corresponding to dislocations) appearing when InGaN (InN mixed crystal ratio = 0.2, 100 nm thickness) was continuously grown were counted to evaluate the dislocation density. ^The dislocation density was ⁶ cm ⁻³ , which was lower than that of the normal reported example.
[0043]
For comparison, a GaN layer and an InGaN layer were formed on a normal c-plane sapphire substrate under the same growth conditions and evaluated. The result was 2 × 10 ⁹ cm ^−3, which was ^{almost the} same as that of the normal report example, and was much larger than that of Example-1.
[0044]
An attempt was made to compare with Example-1 by the ordinary ELO method. First, a GaN layer having a thickness of 1.5 μm was formed on a sapphire substrate via a buffer layer. Thereafter, a resist for forming an SiO ² film by lift-off was applied, and exposure was attempted. However, although a 0.5 μm stripe was formed at the center of the wafer, no pattern was formed at the periphery of the wafer. It has been found that this is because the distance between the mask and the wafer fluctuates in the plane due to the warpage of the wafer. Therefore, pattern formation of 0.3 μm was abandoned.
[0045]
[Example 2]
An n-type AlGaN cladding layer, an InGaN light-emitting layer, a p-type AlGaN cladding layer, and a p-type GaN contact layer were sequentially formed on the film obtained in Example 1 to produce an ultraviolet LED wafer having an emission wavelength of 370 nm.
Thereafter, electrode formation and element separation were performed to obtain an LED element. The average value of the output of the LED chips collected over the entire wafer and the reverse current characteristics were evaluated. As an object to be compared, there is an ultraviolet LED chip having the above structure manufactured using a normal sapphire substrate. Table 1 shows the evaluation results.
[0046]
[Table 1]

[0047]
As shown in Table 2, it was found that a sample manufactured using the present invention has a higher output and a higher quality LED with less leakage current than the conventional example.
[0048]
[Example 3]
The GaN crystal produced in Example 1 was used as a first crystal, and a second crystal was grown thereon. First, the GaN first crystal was patterned with a photoresist (width: 2 μm, period: 4 μm, stripe orientation: <1-100> of the GaN substrate), and etched by a RIE apparatus into a square cross section to a depth of 2 μm. At this time, the patterning was performed so that the concave portion of the first crystal came on the convex portion of the substrate. The aspect ratio at this time was 1. After removing the photoresist, the substrate was mounted on a MOVPE apparatus. Thereafter, the temperature was raised to 1000 ° C. in a mixed atmosphere of nitrogen, hydrogen and ammonia. Thereafter, TMG / ammonia was flowed as a raw material and silane was flowed as a dopant to grow an n-type GaN layer. The growth time at that time was set to a time corresponding to 4 μm in the GaN growth in the case where the normal unevenness was not applied.
[0049]
Observation of the cross-section after growth reveals growth on the concave portions of the substrate and growth on the side surfaces of the convex portions. However, as shown in FIG. 2, a flat GaN film is obtained that covers the concave and convex portions while leaving the hollow portions. Was. Subsequently, when the pits of the obtained film were evaluated, it was found that the pits were reduced to 2 × 10 ⁵ cm ⁻³ . Thus, it was confirmed that the effect of reducing the dislocation density was further obtained by repeating this example.
[0050]
【The invention's effect】
According to the semiconductor substrate of the present invention and the method for manufacturing the same as described above, by providing the substrate with a convex portion, lateral growth capable of forming a low dislocation region without using a mask layer is performed. Can be made. Therefore, the problems caused by the formation of the mask layer, such as the problem of generation of new defects in the united portion of the lateral growth portion due to the micro tilting of the axis, the problem of autodoping, and the problem that the Al-containing semiconductor material cannot be selectively grown Can be eliminated. In addition, since the growth of the buffer layer and the growth of the semiconductor crystal layer such as the light-emitting portion can be continuously performed in one growth after providing the uneven surface on the substrate, there is an advantage that the manufacturing process can be simplified. In addition, by defining the width and the area of the convex portion that is the source of threading dislocation, there is an advantage that the low dislocation density region can be relatively widened, and the thickness used for covering the unevenness and flattening can be reduced.
Furthermore, the use of the cavity has the effect of improving the reflectance and the phenomenon of residual strain, and is a very valuable invention in terms of improving characteristics and reducing costs.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view for explaining a crystal growth state of a semiconductor substrate according to the present invention.
FIG. 2 is a cross-sectional view for explaining a crystal growth state of a semiconductor substrate according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Substrate 11 Convex part 12 Concavity 13 Cavity part 2 Semiconductor layer

Claims (4)

A semiconductor substrate comprising a substrate and a semiconductor crystal vapor-grown on the substrate, wherein a crystal growth surface of the substrate is an uneven surface, and the semiconductor crystal is exclusively formed from an upper portion of a convex portion in the uneven surface. In the semiconductor substrate on which the crystal has been grown, the protrusion has a width a in a range of 0 <a <1 μm and a ratio of an area occupied by the protrusion to the substrate surface is 50% or less. A semiconductor substrate characterized in that: 2. The semiconductor substrate according to claim 1, wherein a ratio of an area occupied by the projection to the substrate surface is 2 to 30%. A semiconductor substrate comprising a substrate and a semiconductor crystal vapor-grown on the substrate, wherein a crystal growth surface of the substrate is an uneven surface, and the semiconductor crystal is exclusively formed from an upper portion of a convex portion in the uneven surface. In the semiconductor substrate on which the crystal has been grown, the protrusion has a width a in a range of 0 <a <1 μm, and a ratio of an area occupied by the protrusion to the substrate surface is 50 to 70%. A semiconductor substrate characterized in that: A semiconductor substrate comprising a substrate and a semiconductor crystal vapor-grown on the substrate, wherein a crystal growth surface of the substrate is an uneven surface, and the semiconductor crystal is exclusively formed from an upper portion of a convex portion in the uneven surface. In the semiconductor substrate on which the crystal is grown, there is a portion in which the width a of the protrusion is in the range of 0 <a <1 μm, and the width a of the protrusion is equal to or less than the width b of the recess. A semiconductor substrate, characterized in that:

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