JP3791246B2 - Nitride semiconductor growth method, nitride semiconductor device manufacturing method using the same, and nitride semiconductor laser device manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a nitride semiconductor (In_XAl_YGa_1-XYN, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1), and more particularly to a method for growing a substrate made of a nitride semiconductor with few dislocations. The present invention also provides a nitride semiconductor (In) used in a light-emitting element such as a light-emitting diode or a laser diode, or a light-receiving element such as a solar cell or an optical sensor, using the substrate made of the nitride semiconductor._XAl_YGa_1-XYN, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1)Manufacturing methodAbout.
[0002]
[Prior art]
  In recent years, SiO made of a material in which a nitride semiconductor does not grow or is difficult to grow on a heterogeneous substrate different from a nitride semiconductor such as sapphire, spinel, or silicon carbide, or on a nitride semiconductor grown on a heterogeneous substrate.₂A variety of nitride semiconductor growth methods [ELOG (Epitaxially laterally overgrown GaN) growth methods] that can reduce dislocations by growing a protective film such as the like and selectively growing a nitride semiconductor thereon are known. .
[0003]
  For example, SiO₂As a growth method of ELOG when using a protective film such as Jpn. J. et al. Appl. Phys. Vol. 37 (1998) p. L309-L312 (hereinafter simply referred to as J.J.A.P. literature) on a nitride semiconductor grown on sapphire.₂It is described that a nitride semiconductor with few dislocations is obtained by partially forming a mask such as a stripe shape and then growing a nitride semiconductor thereon.
  In the ELOG growth, a mask is formed and GaN is intentionally grown in the lateral direction so as to cover the mask, so that almost no dislocation is observed in the nitride semiconductor grown on the upper part of the mask. In other words, when a nitride semiconductor grows laterally so as to cover the mask, dislocations also propagate in the lateral direction along with the growth of the nitride semiconductor, and the dislocations once propagated in the lateral direction again become longitudinal (nitride semiconductor In this case, dislocations are hardly observed in the nitride semiconductor grown on the upper portion of the mask.
  The surface of GaN grown on the portion where the mask is not formed is almost 1 × 10⁷/ Cm²However, almost no dislocation is observed on the surface of GaN grown on the upper part of the mask. As described above, since it is possible to obtain a nitride semiconductor substrate with few dislocations, the lifetime characteristics of the nitride semiconductor device can be improved.
[0004]
  However, J. J. et al. A. P. Although the ELOG growth method described in the above document can reduce dislocations and obtain a device having good lifetime characteristics, it is possible to obtain SiO2 by heat during growth.₂May break down. SiO₂When SiO decomposes, SiO₂The nitride semiconductor may grow abnormally from above, or decomposed Si or O may enter the nitride semiconductor and contaminate GaN, leading to a decrease in crystallinity.
[0005]
  In contrast, SiO₂As a method for growing ELOG when a protective film such as the above is not used, an amorphous GaN film is grown on a heterogeneous substrate in Japanese Patent Application Laid-Open No. 8-64791, and then the amorphous GaN film is striped. By etching and further growing a nitride semiconductor on this, dislocations of the nitride semiconductor grown from other than the amorphous GaN film portion concentrate on a specific nitride semiconductor portion growing on the amorphous GaN film, and the amorphous film It is described that dislocations of nitride semiconductors grown other than at the top can be reduced.
[0006]
[Problems to be solved by the invention]
  However, in the method described in JP-A-8-64791, dislocations tend to concentrate on a specific part growing on top of the amorphous GaN film, but dislocations cannot be sufficiently concentrated on the amorphous film, Reduction of dislocations in nitride semiconductors grown from other than stripe-like amorphous is not sufficient.
  Such SiO₂In the ELOG growth method that does not use a protective film such as a nitride semiconductor, it is impossible to obtain a nitride semiconductor with dislocations reduced to a satisfactory degree. In order to fabricate a nitride semiconductor device with good lifetime characteristics, it is desirable to obtain a nitride semiconductor substrate with few dislocations, but it is difficult to reduce dislocations to such an extent that the above-mentioned conventional method has sufficient lifetime characteristics. .
[0007]
  Therefore, the object of the present invention is to provide SiO₂It is an object of the present invention to provide a method of growing a nitride semiconductor that can obtain a nitride semiconductor with good crystallinity and reduced dislocation without using a protective film such as the above.
  Furthermore, the present invention relates to a nitride semiconductor device using a nitride semiconductor having good crystallinity and few dislocations as a substrate.Manufacturing methodIs to provide.
[0008]
[Means for Solving the Problems]
  That is, the object of the present invention can be achieved by the following configurations (1) to (9).
(1) a first step of growing a first nitride semiconductor on a heterogeneous substrate made of a material different from the nitride semiconductor;
After the first step, the surface of the first nitride semiconductor is partially modified by dry etching so that the nitride semiconductor is difficult to grow or does not grow, and is applied to the surface of the first nitride semiconductor. A second step of imparting selectivity to the growth of the nitride semiconductor;
After the second step, the nitride semiconductor has at least a third step of growing a second nitride semiconductor on the first nitride semiconductor whose surface is partially modified Growth method.
(2) In the second step, after a protective film is partially formed on the first nitride semiconductor grown on the heterogeneous substrate, a portion where the protective film is not formed is subjected to the dry etching. The nitride semiconductor according to (1) is a step of forming an N deficient portion by partially modifying the surface of the first nitride semiconductor and then removing the protective film. Growth method.
(3) The dry etching is performed with noble gas and O.₂The method for growing a nitride semiconductor according to (1) or (2), wherein at least one kind of gas is used.
(4) After the third step, the nitride semiconductor is difficult to grow by dry etching on the surface of the second nitride semiconductor and on the upper portion of the first nitride semiconductor other than the surface modified portion. Or a fourth step of selectively modifying the surface of the second nitride semiconductor so that the nitride semiconductor is selectively grown on the surface of the second nitride semiconductor;
  After the fourth step, the method includes (5) a fifth step of growing a third nitride semiconductor on the second nitride semiconductor whose surface has been partially modified. The method for growing a nitride semiconductor according to any one of (3) to (3).
(5) The method for growing a nitride semiconductor according to any one of (1) to (4), wherein the dissimilar substrate has a C-plane of sapphire that is off-angled stepwise.
(6) The nitride semiconductor growth method according to (5), wherein an off-angle angle of the sapphire substrate that is off-angled in a step shape is 0.1 ° to 0.5 °.
(7) The above (5) or (6), wherein a direction (step direction) along the step of the sapphire substrate that is off-angled in a step shape is formed perpendicular to the A surface of sapphire. The method for growing a nitride semiconductor as described in 1).
(8) The method for growing a nitride semiconductor according to any one of (1) to (7)A first step of growing the substrate by the method, and the substrateAt least an n-type nitride semiconductor, an active layer, and a p-type nitride semiconductor having an element structure thereonHaving a second step of formingNitride semiconductor device characterized in thatManufacturing method.
(9) The method for growing a nitride semiconductor according to any one of (1) to (7)A first step of growing the substrate by the method, and the substrateAt least an n-type nitride semiconductor, an active layer, and a p-type nitride semiconductor having an element structure thereonA second step of formingA stripe shape or a ridge shape for guiding the light of the nitride semiconductor laser device on the modified portion formed in the first nitride semiconductor of the nitride semiconductor substrateTheFormationYouRuHaving a third stepthingTheNitride semiconductor laser deviceManufacturing method.
[0009]
  In other words, the nitride semiconductor growth method of the present invention partially modifies the surface of the first nitride semiconductor grown on the heterogeneous substrate so that the nitride semiconductor is difficult to grow. The growth of the second nitride semiconductor on the modified portion is suppressed, and the selectivity of the growth of the nitride semiconductor on the surface of the first nitride semiconductor is generated.₂As in the case where a protective film such as is used, the modified portion acts like a protective film, so that the second nitride semiconductor grown above the modified portion hardly sees dislocations. .
[0010]
  Conventional SiO₂In the method of growing ELOG without using₂Since selectivity cannot be obtained in the growth of a nitride semiconductor as in the case of using N, the nitride semiconductor cannot be intentionally grown in the lateral direction.
  In addition, SiO₂In the conventional technique using Nb, selectivity for growth of a nitride semiconductor can be obtained and a part having almost no dislocation can be formed.₂There is a concern that the crystallinity may be reduced due to contamination due to decomposition of the.
[0011]
  On the other hand, the nitride semiconductor growth method of the present invention is, as described above, SiO 2₂Even without using a mask such as the above, the nitride semiconductor growth can be made selective by partially modifying the surface of the nitride semiconductor. Thereby, the nitride semiconductor can be intentionally grown in the lateral direction toward the modified portion, and as a result, dislocations can be reduced.
  In the present invention, the growth of the nitride semiconductor is suppressed in the modified portion, and the nitride semiconductor grows from other than the modified portion. The nitride semiconductor that has begun to grow grows into a thick film intentionally in the lateral direction in the direction of the modified portion where growth is suppressed, and at the same time, dislocations also move in the direction of the modified portion. Propagate horizontally. As a result, almost no dislocation is observed in the second nitride semiconductor grown above the modified portion.
[0012]
  Dislocations have the property of propagating in a direction substantially similar to the direction of nitride semiconductor growth, but promote lateral growth as compared to nitride semiconductor vertical growth (intentionally lateral growth). Tend to promote lateral growth) and tend to propagate laterally. Dislocations that have once propagated in the horizontal direction tend to be less likely to propagate in the vertical direction (above the reformed portion), even if the growth in the vertical direction is promoted again, compared to the growth in the horizontal direction again. As a result, almost no dislocation is observed in the nitride semiconductor portion intentionally grown laterally toward the modified portion.
[0013]
  In addition, when an element structure is formed using a second nitride semiconductor having a portion in which dislocations are hardly observed as a substrate, a nitride semiconductor element having excellent lifetime characteristics can be obtained. In this case, it is preferable that the waveguide of the element is formed above a portion where dislocations are hardly observed from the viewpoint of improving the life characteristics.
[0014]
  Further, in the present invention, after the second step, a protective film is partially formed on the first nitride semiconductor grown on the heterogeneous substrate, and then the portion where the protective film is not formed is dried. Etching forms an N deficient portion to partially modify the surface of the first nitride semiconductor, and then removes the protective film, thereby improving the growth of the nitride semiconductor to the modified portion It is preferable from the viewpoint of reducing dislocations by making the lateral growth of the nitride semiconductor grown from other than the modified portion good.
  In this case, when the portion where the protective film is not formed is dry-etched, an N deficient portion is formed, and the nitride semiconductor does not grow or is difficult to grow on the surface of the nitride semiconductor that has become the N deficient.
  Furthermore, in the present invention, dry etching is performed with noble gases and O.₂It is preferable to use at least one kind of gas from the standpoint that dry etching is performed only by sputtering and that it can be effectively modified. On the surface of the first nitride semiconductor where the protective film is not formed, when the dry etching is performed with the gas as described above, the nitride semiconductor is hardly scraped and only the quality of the nitride semiconductor is changed. Therefore, the surface of the first nitride semiconductor having the modified portion can be easily covered with the second nitride semiconductor.
[0015]
  The second step is a step of partially modifying the surface of the first nitride semiconductor by partially diffusing impurities on the first nitride semiconductor grown on the different substrate. Therefore, it is possible to satisfactorily suppress the growth of the nitride semiconductor on the modified portion, and to improve the lateral growth of the nitride semiconductor grown from other than the modified portion, which is preferable in terms of reducing dislocations.
  Furthermore, it is preferable that the impurity is an element other than the 3B group and 5B group of the periodic table because the growth of the nitride semiconductor in the impurity diffusion portion can be satisfactorily suppressed. In the impurity diffusion portion, the nitride semiconductor does not grow or is difficult to grow.
[0016]
  Further, in the method of modifying the surface of the first nitride semiconductor in the method of the present invention, the second nitride semiconductor that grows from other than the modified portion does not have a significant step on the surface of the first nitride semiconductor. There is a tendency that the modified portion is easily covered well. The tendency to easily cover the modified portion is that dislocations can be reduced satisfactorily even when the second nitride semiconductor film is grown as a relatively thin film. When it is performed repeatedly, the operation can be simplified such as shortening the growth time, which is preferable.
[0017]
  Furthermore, in the present invention, the dislocation can be further reduced by repeating the second step and the third step after growing the second nitride semiconductor into a thick film. However, the second process to be repeated is such that the modified portion formed on the surface of the second nitride semiconductor is positioned above the modified portion formed on the surface of the first nitride semiconductor. In addition, the surface of the second nitride semiconductor is partially modified. The second and third steps may be repeated twice or more.
  As described above, when the modified portion of the surface of the first nitride semiconductor and the modified portion of the surface of the second nitride semiconductor are alternated as described above, a thickness is formed above the modified portion. Since almost no dislocation is observed in the nitride semiconductor grown on the film, almost no dislocation is observed on the entire surface of the nitride semiconductor grown on the second nitride semiconductor having the modified portion. Thus, it is preferable to grow a device structure using a nitride semiconductor with reduced dislocations as a whole as a substrate when mass-producing devices having good lifetime characteristics.
[0018]
  Furthermore, in the growth method of the present invention, when the heterogeneous substrate is one in which the C-plane of sapphire is off-angled stepwise, when forming an element structure using the obtained nitride semiconductor as a substrate, one chip is formed. It is preferable that a nitride semiconductor substrate having a flat surface with a width equivalent to the size of the above can be obtained, and an element having good life characteristics can be easily selected. Furthermore, when the angle is off-stepped, the threshold value decreases in the laser element, and the light emission output tends to increase by 20 to 30% in the LED.
  Furthermore, in the present invention, when the off-angle angle of the sapphire substrate which is off-angled stepwise is 0.1 ° to 0.5 °, the surface property of the portion that becomes the above-described good plane becomes good. It is preferable to form a device in which the life characteristics can be improved. Further, it is preferable that the off-angle is in the above range because the threshold value is further lowered and the light emission output is further improved.
  Furthermore, in the present invention, when the direction along the step (step direction) of the sapphire substrate that is off-angled in a step shape is formed perpendicular to the A plane of sapphire, the nitride with respect to the A plane of sapphire If the second nitride semiconductor is grown so that the M-plane of the semiconductor is parallel and a ridge-shaped stripe, for example, is formed in parallel to the step direction, the M-plane is easily cleaved and a good resonance surface is obtained. preferable.
[0019]
  In the present invention, a nitride semiconductor obtained by the nitride semiconductor growth method of the present invention is used as a substrate, and at least an n-type nitride semiconductor, an active layer, and a p-type nitride semiconductor forming an element structure are formed thereon. By doing so, a nitride semiconductor device with good lifetime characteristics can be obtained.
  Further, in the present invention, when a nitride semiconductor laser device having a ridge-shaped stripe is manufactured, the device is manufactured so that the ridge-shaped stripe is positioned above the portion modified by the nitride semiconductor growth method. Then, a laser element having better life characteristics is obtained and preferable. Further, when the second and third steps are repeated by the method of the present invention, the position where the ridge-shaped stripe is formed need not be taken into consideration.
  It is preferable to form a nitride semiconductor element in a portion with few dislocations because it has good element characteristics.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, the present invention will be described in more detail with reference to the drawings.
  FIG. 1 to FIG. 4 are schematic views showing an embodiment of the nitride semiconductor growth method of the present invention step by step.
[0021]
  As an embodiment of the nitride semiconductor growth method of the present invention, first, in the first step of FIG. 1, the first nitride semiconductor 2 is grown on the heterogeneous substrate 1, and the second step of FIG. , The surface of the first nitride semiconductor 2 is partially modified so that the nitride semiconductor is difficult to grow or does not grow, and is selected for the growth of the nitride semiconductor on the surface of the first nitride semiconductor 2 Then, in the third step of FIG. 3, the second nitride semiconductor 3 is grown on the partially modified first nitride semiconductor 2.
[0022]
  Hereinafter, each step will be described in more detail with reference to the drawings.
(First step)
  FIG. 1 is a schematic step view in which a first step of growing a first nitride semiconductor 2 on a heterogeneous substrate 1 is performed.
  In this first step, examples of the heterogeneous substrate that can be used include sapphire and spinel (MgA1) whose principal surface is any one of the C-plane, R-plane, and A-plane.₂O_Four) Such as an insulating substrate, SiC (including 6H, 4H, 3C), ZnS, ZnO, GaAs, Si, and an oxide substrate lattice-matched with a nitride semiconductor, etc. Substrate material can be used. Preferable heterogeneous substrates include sapphire and spinel.
[0023]
  In the first step, a buffer layer (not shown) may be formed on the heterogeneous substrate 1 before growing the first nitride semiconductor 2 on the heterogeneous substrate 1. As the buffer layer, AlN, GaN, AlGaN, InGaN or the like is used. The buffer layer is grown at a temperature of 900 ° C. or lower and 300 ° C. or higher with a film thickness of 0.5 μm to 10 Å. Thus, when the buffer layer is formed on the heterogeneous substrate 1 at a temperature of 900 ° C. or less, the lattice constant irregularity between the heterogeneous substrate 1 and the first nitride semiconductor 2 is alleviated, and the crystal defects of the first nitride semiconductor 2 are reduced. Tend to decrease.
[0024]
  In the first step, the first nitride semiconductor 2 formed on the heterogeneous substrate 1 is doped with n-type impurities such as GaN, Si, Ge, and S which are undoped (undoped). GaN can be used.
  The first nitride semiconductor 2 is grown on the heterogeneous substrate 1 at a high temperature, specifically, higher than about 900 ° C. to 1100 ° C., preferably 1050 ° C. When grown at such a temperature, the first nitride semiconductor 2 becomes a single crystal. The film thickness of the first nitride semiconductor 2 is not particularly limited, but is preferably such that the surface of the first nitride semiconductor can be satisfactorily modified, for example, 500 angstroms to 10 micrometers is preferable and 2.5 micrometers-5 micrometers are more preferable. Within the above range, warpage is prevented and crystallinity is improved, which is preferable.
[0025]
(Second step)
  Next, in FIG. 2, after the first nitride semiconductor 2 is grown on the heterogeneous substrate 1, the surface of the first nitride semiconductor 2 is partially modified so that the nitride semiconductor is difficult to grow or does not grow. FIG. 2 is a schematic cross-sectional view obtained by giving selectivity to the growth of a nitride semiconductor on the surface of the first nitride semiconductor 2.
[0026]
  In the second step, partially modifying the surface means changing the property of the surface of the nitride semiconductor so that the nitride semiconductor does not grow on at least the surface of the first nitride semiconductor 2, thereby improving the nitride. It is to suppress the growth of the semiconductor.
  In addition, the shape of the modified portion formed on the surface of the first nitride semiconductor 2 is not particularly limited, but the shape of the first nitride semiconductor 2 viewed from directly above is, for example, random. , Stripes, grids, and dots. A preferred shape is a stripe shape, and this shape is preferable because it has less abnormal growth and is buried more flatly.
[0027]
  When the shape of the modified portion is a stripe shape, the shape of the stripe is not particularly limited. For example, the stripe width of the modified portion is 1 to 30 μm, preferably 10 to 20 μm, and the portion other than the modified portion The stripe spacing of 1 to 30 μm, preferably 2 to 20 μm can be formed.
  Having such a stripe shape is preferable in terms of reducing dislocations and improving the surface state.
[0028]
  In the present invention, the modification of the surface of the first nitride semiconductor 2 is not particularly limited as long as at least the growth of the nitride semiconductor is suppressed. Method of modifying a portion where the protective film is not formed by dry etching after forming the protective film [However, the protective film is removed by isotropic etching (dry etching or wet etching) after the modification] (Refer to a-1 to a-3 in FIG. 2) and a method for modifying by modifying impurities (elements other than 3B group and 5B group in the periodic table) (see b-1 to b-3 in FIG. 2) ). In the following, these preferred methods of modification will be described.
[0029]
  First, a method for modifying by dry etching shown in (a-1) to (a-3) of FIG. 2 will be described.
  A protective film is partially formed on the surface of the first nitride semiconductor 2 as shown in FIG. Thereafter, as shown in FIG. 2A-2, dry etching is performed on the first nitride semiconductor 2 on which the protective film is formed, so that the first nitride semiconductor in a portion where the protective film is not formed is formed. 2 The surface of the first nitride semiconductor 2 is partially modified by forming an N deficient portion on the surface. After the modification, as shown in FIG. 2A-3, the protective film is removed by isotropic etching (dry etching or wet etching).
[0030]
  The protective film formed on the first nitride semiconductor 2 is not particularly limited, and can protect the first nitride semiconductor when the surface of the first nitride semiconductor is modified by dry etching. The material is not particularly limited, and examples thereof include oxides, metals, fluorides, and nitrides. For example, specifically silicon oxide (SiO_X), Silicon nitride (Si_XN_Y), Titanium oxide (TiO_X), Zirconium oxide (ZrO)_X) And the like, and multilayer films and metals thereof can be used. As a preferable protective film material, SiO₂And SiN. Use of such a protective film is preferable in terms of selection during dry etching and not diffusion into the nitride semiconductor.
[0031]
  As a method for forming the protective film as described above on the surface of the first nitride semiconductor 2, for example, vapor deposition techniques such as vapor deposition, sputtering, and CVD can be used. Further, in order to form partially (selectively), a photomask having a predetermined shape is produced by using a photolithography technique, and the material is vapor-deposited through the photomask. A protective film having a predetermined shape can be formed. The shape of the protective film is not particularly limited. For example, the protective film can be formed in the shape of dots, stripes, and a grid surface. Is done. The surface area where the protective film is formed is smaller than the surface area of the portion where the protective film is not formed, so that dislocation can be prevented and a nitride semiconductor substrate having good crystallinity can be obtained.
  The width of the protective film is adjusted by the width of the portion other than the above-described modified portion, and the width between the protective film and the protective film is adjusted by the width of the above-described modified portion. Further, the shape of the protective film is appropriately adjusted so that the shape of the modified portion is, for example, a stripe shape as described above.
[0032]
  Described below is dry etching for forming an N deficient portion after the protective film is partially formed on the surface of the first nitride semiconductor 2 as described above.
  The dry etching is anisotropic dry etching, and non-reactive dry etching is preferable. Gases used for etching include rare gases such as He, Ne, Ar, and Xe, and O₂At least one gas such as a gas can be used.
  Use of such a gas is preferable in that dry etching is performed only by sputtering, and it can be effectively modified. The modified part has N deficiency, and this part has a crystal plane with such a property that the nitride semiconductor does not grow.
  Further, when the surface of the first nitride semiconductor where the protective film is not formed is dry-etched with the gas as described above, the nitride semiconductor is hardly shaved and only the quality of the nitride semiconductor is changed. Therefore, the surface of the first nitride semiconductor having the modified portion can be easily covered with the second nitride semiconductor.
  After forming the modified portion as described above, the protective film is removed from the surface of the first nitride semiconductor 2, and the second nitride semiconductor 3 is grown thereon.
  In the present invention, the modified portion by dry etching is the SiO 2 of the prior art.₂SiO in the growth method of ELOG when using₂Works the same as
[0033]
  next,As a reference exampleA method of modifying by impurity diffusion shown in (b-1) to (b-3) of FIG. 2 will be described.
  As shown in FIG. 2 (b-1), an element to be an impurity is partially formed on the first nitride semiconductor 2, and subsequently, as shown in FIG. 2 (b-2), heat treatment is performed. To diffuse the element near the surface of the first nitride semiconductor 2, and then remove the element as an impurity from the surface of the first nitride semiconductor 2 as shown in FIG. 2 (b-3). Impurities are diffused in the portion where the element has been formed, and the surface of the portion becomes a crystal plane with such a property that the growth of the nitride semiconductor is suppressed, and is modified.
[0034]
  Although it does not specifically limit as an element used as said impurity, For example, as a preferable element, elements other than 3B group and 5B group are mentioned, More preferably, elements other than 3B group and 5B group have an electronegativity, Ga Larger elements. As a more preferable specific example, any one or more elements of Ni, Au, Co, Cr, Fe and Cu can be used. When such an element is used, there is little diffusion to other than the modified portion, the surface of the first nitride semiconductor 2 can be partially modified, and the dislocation of the second nitride semiconductor 3 grown after the modification can be reduced. It can be reduced well and is preferable.
  The shape in which the element which becomes an impurity is formed, the width of the portion where the element is not formed, and the like are the same as the shape of the modified portion and portions other than the modified portion.
  Further, the film thickness at the time of formation of the element which becomes an impurity is not particularly limited as long as the surface of the first nitride semiconductor 2 is modified. For example, a preferable film thickness is 10 angstroms to 5 μm. The thickness is preferably 100 angstroms to 1 μm. A film thickness in the above range is preferable in terms of the modification of the first nitride semiconductor and the formation and removal of the element that becomes an impurity.
[0035]
  The heat treatment after the above elements are formed on the surface of the first nitride semiconductor 2 is heat-treated at a temperature at which the elements are diffused. Specifically, for example, 200 to 800 ° C., preferably 400 to 700 ° C. The element is diffused into the first nitride semiconductor by heating to the extent. Heat treatment at a temperature in the above range is preferable in terms of modification of the surface of the first nitride semiconductor 2 because the element which becomes an impurity is diffused well.
[0036]
  After the heat treatment, the element is removed from the surface of the first nitride semiconductor 2. As a removal method, for example, it is removed by treatment with aqua regia, hydrofluoric acid or the like. Then, the element is diffused on the surface of the first nitride semiconductor 2 from which the element has been removed, and this portion becomes a crystal plane having such a property that the growth of the nitride semiconductor is suppressed and is modified. ing.
[0037]
(Third step)
  Next, FIG. 3 is a schematic cross-sectional view in which a third step of growing the second nitride semiconductor 3 on the first nitride semiconductor 2 whose surface is partially modified is performed.
  As the second nitride semiconductor 3, the same one as the first nitride semiconductor 2 can be used. The growth temperature of the second nitride semiconductor 3 is the same as in the case where the first nitride semiconductor 2 is grown.
  The film thickness of the second nitride semiconductor 3 is not particularly limited, but may be a film thickness that can satisfactorily cover at least the modified portion of the surface of the first nitride semiconductor 2. Specifically, it is 5 to 30 μm, preferably 10 to 15 μm. When grown with such a film thickness, the surface of the first nitride semiconductor 2 having the modified portion can be satisfactorily covered, and a good second nitride semiconductor 3 with reduced dislocations can be obtained. it can.
[0038]
  The second nitride semiconductor 3 is first grown from the surface of the first nitride semiconductor 2 other than the modified portion, and in the process of growing, grows laterally toward the modified portion. Cover the modified part. Then, when grown to a thick film, the modified portion has the property that the nitride semiconductor does not grow, but the second portion as shown in FIG. 4 is as if the nitride semiconductor has grown in the modified portion. The nitride semiconductor 3 grows. In addition, as shown in FIG. 4, a slight gap may be formed in the modified portion.
[0039]
  Further, when the second nitride semiconductor 3 is grown, it is grown by doping with impurities (for example, Si, Ge, Sn, Be, Zn, Mn, Cr, Mg, etc.) and grown under reduced pressure conditions. Or, the growth in the lateral direction is promoted compared to the growth in the vertical direction by adjusting the molar ratio (III / V molar ratio) of the group III and group V components, which are the raw materials of the nitride semiconductor. It is preferable at the point which reduces. Such reaction conditions can be applied when a nitride semiconductor is intentionally grown in the lateral direction in order to reduce dislocations.
[0040]
  Further, in the present invention, when the second and third steps are repeated, the second nitride semiconductor 3 is formed above the modified portion of the surface of the first nitride semiconductor 2 as shown in FIG. The surface of the second nitride semiconductor 3 is located on the surface of the first nitride semiconductor 2 so that a portion other than the modified portion that is partially formed on the surface is positioned above the portion other than the modified portion of the surface of the first nitride semiconductor 2. The surface of the second nitride semiconductor 3 is partially modified so that the modified portion is located. Then, the third nitride semiconductor 4 is grown on the second nitride semiconductor 3 having the modified portion.
  The third nitride semiconductor 4 is preferably a nitride semiconductor with less dislocations on the entire surface. Examples of the third nitride semiconductor 4 include those similar to the second nitride semiconductor. Further, the film thickness of the third nitride semiconductor 4 is not particularly limited, but may be a film thickness that can satisfactorily cover at least the modified portion of the second nitride semiconductor 3.
[0041]
  In addition, the second nitride semiconductor 3 serves as a substrate for growing a nitride semiconductor having an element structure thereon, and the element structure is formed after removing a different substrate in advance. There are cases in which a different substrate or the like is left behind. In some cases, the heterogeneous substrate is removed after the element structure is formed.
  The thickness of the second nitride semiconductor 3 when removing the heterogeneous substrate or the like is 50 μm or more, preferably 100 μm or more, preferably 500 μm or less. Within this range, it is preferable that the second nitride semiconductor 3 is hard to break and easy to handle even if the foreign substrate, the protective film, and the like are polished and removed.
[0042]
  In addition, the thickness of the second nitride semiconductor 3 in the case of leaving the heterogeneous substrate or the like is not particularly limited, but is 100 μm or less, preferably 50 μm or less, more preferably 20 μm or less. Within this range, the wafer can be prevented from warping due to the difference in thermal expansion coefficient between the dissimilar substrate and the nitride semiconductor, and the nitride semiconductor as the element structure can be satisfactorily grown on the second nitride semiconductor 5 as the element substrate. Can be made.
[0043]
  In the nitride semiconductor growth method of the present invention, the method for growing the first nitride semiconductor 2, the second nitride semiconductor 3 and the like is not particularly limited, but MOVPE (metal organic chemical vapor deposition), All methods known to grow nitride semiconductors such as HVPE (halide vapor phase epitaxy), MBE (molecular beam epitaxy), MOCVD (metal organic chemical vapor deposition) can be applied. As a preferable growth method, when the film thickness is 50 μm or less, the growth rate can be easily controlled by using the MOCVD method. When the film thickness is 50 μm or less, HVPE has a high growth rate and is difficult to control.
[0044]
  In the present invention, since the nitride semiconductor having the element structure can be formed on the second nitride semiconductor 3, the second nitride semiconductor 3 is referred to as an element substrate or a nitride semiconductor substrate in the specification. May say.
[0045]
  Further, it is preferable to use a substrate in which the main surface of the material to be the heterogeneous substrate in the first step is off-angled, and further a substrate in which a step-off angle is formed. When an off-angle substrate is used, three-dimensional growth is not seen on the surface, step growth appears and the surface tends to be flat. Furthermore, when the direction along the step (step direction) of the sapphire substrate that is off-angled stepwise is formed perpendicular to the A-plane of sapphire, the step surface of the nitride semiconductor is aligned with the laser cavity direction. It is preferable that the laser light is less diffusely reflected by the surface roughness.
[0046]
  As a more preferable heterogeneous substrate, sapphire whose main surface is the (0001) plane [C plane], sapphire whose main plane is the (112-0) plane [A plane], or spinel whose main plane is the (111) plane. It is. Here, when the heterogeneous substrate is sapphire whose main surface is the (0001) plane [C plane], the stripe shape of the modified portion formed in the first nitride semiconductor or the like is the (112− 0) It is preferable to have a stripe shape perpendicular to the plane [A plane] [to form a stripe in a direction parallel to the (101-0) [M plane] of the nitride semiconductor] and off The off angle θ of the angle (θ shown in FIG. 11) is 0.1 ° to 0.5 °, preferably 0.1 ° to 0.2 °. Further, when the sapphire has a (112-0) plane [A plane] as a main surface, the stripe shape of the modified portion is a stripe shape perpendicular to the (11-02) plane [R plane] of the sapphire. When the spinel has a (111) plane as a main surface, the stripe shape of the modified portion has a stripe shape perpendicular to the (110) plane of the spinel. It is preferable.
  Here, the case where the modified portion has a stripe shape has been described. However, in the present invention, since the nitride semiconductor easily grows laterally on the A and R surfaces of sapphire and the (110) surface of spinel, The shape is preferably formed in consideration of these surfaces.
[0047]
  The different types of substrates used in the present invention will be described in more detail with reference to the drawings. FIG. 6 is a unit cell diagram showing the crystal structure of sapphire, illustrating the following surfaces of sapphire.
  First, in the method of the present invention, a case where sapphire having a C-plane as a main surface is used and the modified portion has a stripe shape perpendicular to the sapphire A-plane will be described. For example, FIG. 7 is a plan view of a sapphire substrate on the main surface side. In FIG. 7, the sapphire C surface is the main surface, and the orientation flat (orientation flat) surface is the A surface. As shown in this figure, the stripes of the modified portion are formed in a direction perpendicular to the A plane and parallel to each other. As shown in FIG. 7, when a nitride semiconductor is selectively grown on the sapphire C plane, the nitride semiconductor tends to grow in a direction parallel to the A plane in the plane and hardly grow in a vertical direction. It is in. Therefore, when a stripe is provided in a direction perpendicular to the A plane, the nitride semiconductor between the stripes is connected and easily grown, and crystal growth as shown in FIGS. 1 to 4 can be easily performed. It is possible, but details are not clear.
[0048]
  Next, when a sapphire substrate having an A surface as a main surface is used, as in the case where the C surface is used as a main surface, for example, when an orientation flat surface is an R surface, they are parallel to each other in a direction perpendicular to the R surface. By forming a simple stripe, the nitride semiconductor tends to grow in the stripe width direction, so that a nitride semiconductor layer with few crystal defects can be grown.
[0049]
  Next, spinel (MgAl₂O_Four), The growth of the nitride semiconductor is anisotropic. When the growth surface of the nitride semiconductor is the (111) plane and the orientation flat surface is the (110) plane, the nitride semiconductor is the (110) plane. On the other hand, it tends to grow in a parallel direction. Therefore, when a stripe is formed in a direction perpendicular to the (110) plane, the nitride semiconductor layer and the adjacent nitride semiconductor are connected to each other at the upper portion of the protective film, so that a crystal with few crystal defects can be grown. Spinel is not particularly shown because it is tetragonal.
[0050]
  Hereinafter, a case where the direction along the step of the off-angled sapphire substrate is formed perpendicular to the A surface of the sapphire substrate will be described with reference to FIG.
  A heterogeneous substrate such as sapphire which is off-angled in a step shape has a substantially horizontal terrace portion A and a step portion B as shown in FIG. The terrace portion A has few surface irregularities and is formed almost regularly. The stepped portion having such an off angle θ is desirably formed continuously over the entire substrate, but may be formed particularly partially. As shown in FIG. 11, the off angle θ represents an angle between a straight line connecting the bottoms of a plurality of steps and a horizontal plane of the uppermost step.
  The different substrate has an off angle of 0.1 ° to 0.5 °, preferably 0.1 ° to 0.2 °. When the off-angle is in the above range, the surface of the first nitride semiconductor 2 has a fine streak morphology, and the epitaxial growth surface (the surface of the second nitride semiconductor 3) has a wave-like morphology, which can be obtained using this substrate. The nitride semiconductor device is smooth and has characteristics that have a long life, high efficiency, high output, and improved yield.
[0051]
  The nitride semiconductor device of the present invention (hereinafter sometimes referred to as the device of the present invention) will be described below.
  The nitride semiconductor device of the present invention has at least an n-type and a p-type of device structure on the second nitride semiconductor 3 (nitride semiconductor substrate) obtained by the above-described nitride semiconductor growth method of the present invention. A nitride semiconductor or the like is formed. In the present invention, when an element structure is formed on a nitride semiconductor obtained by the growth method of the present invention, a light emitting region or the like (for example, a ridge-shaped stripe in a laser element) is positioned above the modified portion. It is preferable to form an element structure in order to obtain an element having good element characteristics such as lifetime characteristics.
  The nitride semiconductor constituting the nitride semiconductor element of the present invention is not particularly limited, and it is sufficient that at least an n-type nitride semiconductor, an active layer, and a p-type nitride semiconductor are stacked. For example, an n-type nitride semiconductor layer having an n-type nitride semiconductor layer having a superlattice structure as an n-type nitride semiconductor layer and capable of forming an n-electrode on the n-type layer having the superlattice structure is formed. And the like. Examples of the active layer include an active layer having a multiple quantum well structure containing InGaN.
  Further, any other configuration such as an electrode and a shape of the element may be applied to the other structure forming the nitride semiconductor element structure. Although one embodiment of the nitride semiconductor device of the present invention has been shown as an example, the present invention is not limited to this.
[0052]
  A method for growing a nitride semiconductor having the nitride semiconductor element structure of the present invention is not particularly limited, but MOVPE (metal organic vapor phase epitaxy), HVPE (halide vapor phase epitaxy), MBE (molecular beam epitaxy), All methods known to grow nitride semiconductors such as MOCVD (metal organic chemical vapor deposition) can be applied. A preferred growth method is the MOCVD method, and the crystal can be grown neatly. However, since the MOCVD method takes time, it is preferable to perform the method with a short time when the film thickness is large. In addition, it is preferable to grow nitride semiconductors by appropriately selecting various nitride semiconductor growth methods depending on the purpose of use.
[0053]
【Example】
  Examples of the present invention will be described below to explain the present invention in more detail. However, the present invention is not limited to this.
[Example 1]
  Each process in Example 1 is shown using FIGS. In addition, Example 1 was performed using the MOCVD method.
[0054]
(First step)
  As a heterogeneous substrate 1, a sapphire substrate 1 having a 2 inch φ, C-plane as a main surface and an orientation flat surface as an A-plane is set in a reaction vessel, the temperature is set to 510 ° C., hydrogen as a carrier gas, and ammonia as a source gas And TMG (trimethylgallium) are used to grow a buffer layer (not shown) made of GaN on the sapphire substrate 1 to a thickness of about 200 Å.
  After growing the buffer layer, only TMG is stopped and the temperature is raised to 1050 ° C. When the temperature reaches 1050 ° C., TMG and ammonia are used as the source gas, and the first nitride semiconductor layer 2 made of undoped GaN is grown to a thickness of 2.5 μm (FIG. 1).
[0055]
(Second step)
  After the growth of the first nitride semiconductor layer 2, SiO 2 is formed on the first nitride semiconductor layer 2 by a CVD apparatus.₂And a stripe width of 10 μm in the portion where the protective film is not formed (modified portion) through the stripe-shaped photomask by photolithography, and the stripe interval of the portion where the protective film is formed (portion other than the modified portion) SiO patterned to be 10 μm₂A protective film made of a film is formed (a-1 in FIG. 2), and subsequently sputtered with Ar gas (dry etching) by an RIE apparatus, so that a portion of the first nitride semiconductor layer where the protective film is not formed is formed 2 The surface is modified with N deficiency (a-2 in FIG. 2). After the modification, the protective film is removed (a-3 in FIG. 2).
  And SiO₂N deficiency occurs on the surface of the first nitride semiconductor in a portion where no is formed, and the nitride semiconductor does not grow or is difficult to grow in this portion (a-3 in FIG. 2).
  The stripe direction is formed in a direction perpendicular to the orientation flat surface as shown in FIG.
[0056]
(Third step)
  Next, a wafer in which the surface of the first nitride semiconductor layer 2 is partially formed with a modified portion is set in a reaction vessel, TMG and ammonia are used as source gases, and a second layer made of undoped GaN. The nitride semiconductor layer 3 is grown to a thickness of 15 μm (FIGS. 3 and 4).
[0057]
  After the second nitride semiconductor layer 3 is grown, the wafer is taken out of the reaction vessel to obtain a nitride semiconductor substrate made of undoped GaN.
[0058]
  When the obtained second nitride semiconductor layer 3 (nitride semiconductor substrate of the present invention) was observed by a CL (cathode luminescence) method, the dislocation density was slightly higher in the upper part other than the modified part. However, almost no dislocation is observed in the upper part of the modified portion, and the crystal has good crystallinity.
[0059]
[Reference example 1]
  In the first embodiment, the second nitride semiconductor 3 is grown in the same manner except that the second step is as follows.
(Second step)
  After the first nitride semiconductor layer 2 is grown, the Ni is modified with a thickness of 1000 Å so that the stripe width of the modified portion is 10 μm and the stripe interval other than the modified portion is 10 μm. (B-1 in FIG. 2).
  Next, heat treatment is performed at 600 ° C. to diffuse Ni into the surface portion of the first nitride semiconductor layer 2 (b-2 in FIG. 2). Thereafter, the striped Ni is removed, and a modified surface in which Ni is diffused is formed on the surface of the first nitride semiconductor layer 2 (b-3 in FIG. 2). On the surface of the first nitride semiconductor 2 where Ni is diffused as an impurity, the nitride semiconductor does not grow or is difficult to grow.
  The stripe direction is formed in a direction perpendicular to the orientation flat surface as shown in FIG.
[0060]
  When the second nitride semiconductor 3 obtained as described above is observed in the same manner as in Example 1, almost no dislocation is observed in the upper portion of the modified portion, and a good result equivalent to that in Example 1 is obtained. It was.
[0061]
[Example2]
  The second step and the third step of Example 1 are repeated on the surface of the second nitride semiconductor 3 obtained in Example 1.
(Second step to be repeated)
  First, as shown in FIG. 5, a portion other than the modified portion formed on the surface of the second nitride semiconductor 3 is positioned above the modified portion of the surface of the first nitride semiconductor 2. Furthermore, the second nitride semiconductor is arranged such that the modified portion formed on the surface of the second nitride semiconductor 3 is located above the portion other than the modified portion on the surface of the first nitride semiconductor 2. On layer 3, SiO is deposited by a CVD apparatus.₂And a stripe width of 10 μm in the portion where the protective film is not formed (modified portion) and the interval between the portions where the protective film is formed (portion other than the modified portion) through a striped photomask by photolithography SiO patterned to 10 μm₂A protective film made of a film is formed, followed by sputtering with Ar gas by a RIE apparatus (dry etching) to modify the surface of the second nitride semiconductor layer 3 where the protective film is not formed as an N defect. To do. After the modification, the protective film is removed. SiO₂Similar to the modified portion formed on the surface of the first nitride semiconductor of Example 1, the nitride semiconductor is less likely to grow on the removal surface of the film.
(Repeated third step)
  Next, a third nitride semiconductor 4 made of undoped GaN is grown to a thickness of 15 μm on the second nitride semiconductor 3 having the modified portion (FIG. 5).
[0062]
  When the third nitride semiconductor 4 obtained as described above is observed by the CL method, a nitride semiconductor with reduced dislocations as a whole can be obtained.
[0063]
[Example3]
  In the following, referring to FIG.3Will be explained. FIG. 8 is a schematic cross-sectional view showing the structure of a laser device according to an embodiment of the present invention, in which a device structure is formed using the second nitride semiconductor obtained in Example 1 of the present invention as a substrate. .
  Using the second nitride semiconductor 3 obtained in Example 1 as a nitride semiconductor substrate, the following element structure is grown in layers.
[0064]
(Undoped n-type contact layer) [not shown in FIG. 8]
  On the nitride semiconductor substrate 1, undoped Al using TMA (trimethylaluminum), TMG, and ammonia gas as source gases at 1050 ° C._0.05Ga_0.95An n-type contact layer made of N is grown to a thickness of 1 μm.
[0065]
(N-type contact layer 32)
  Next, at the same temperature, TMA, TMG, and ammonia gas are used as source gas, and silane gas (SiH) is used as impurity gas._Four) And Si 3 × 10¹⁸/ Cm^ThreeDoped Al_0.05Ga_0.95An n-type contact layer 2 made of N is grown to a thickness of 3 μm.
[0066]
(Crack prevention layer 33)
  Next, the temperature is set to 800 ° C., TMG, TMI (trimethylindium) and ammonia are used as source gas, silane gas is used as impurity gas, and Si is 5 × 10 5.¹⁸/ Cm^ThreeDoped In_0.08Ga_0.92A crack prevention layer 33 made of N is grown to a thickness of 0.15 μm.
[0067]
(N-type cladding layer 34)
  Next, the temperature is set to 1050 ° C., TMA, TMG, and ammonia are used as source gases, and undoped Al_0.14Ga_0.86An A layer made of N is grown to a thickness of 25 Å, then TMA is stopped, silane gas is used as an impurity gas, and Si is 5 × 10 5¹⁸/ Cm^ThreeA B layer made of doped GaN is grown to a thickness of 25 Å. This operation is repeated 160 times, and the A layer and the B layer are laminated to grow an n-type cladding layer 34 composed of a multilayer film (superlattice structure) having a total film thickness of 8000 angstroms.
[0068]
(N-type guide layer 35)
  Next, at the same temperature, an n-type guide layer 35 made of undoped GaN is grown to a thickness of 0.075 μm using TMG and ammonia as source gases.
[0069]
(Active layer 36)
  Next, the temperature is set to 800 ° C., TMI, TMG, and ammonia are used as source gases, silane gas is used as an impurity gas, and Si is 5 × 10 5.¹⁸/ Cm^ThreeDoped In_0.01Ga_0.99A barrier layer made of N is grown to a thickness of 100 Å. Subsequently, silane gas was turned off and undoped In_0.11Ga_0.89A well layer made of N is grown to a thickness of 50 Å. This operation is repeated three times, and finally, an active layer 36 having a multi-quantum well structure (MQW) having a total film thickness of 550 Å, on which barrier layers are stacked, is grown.
[0070]
(P-type electron confinement layer 37)
  Next, at the same temperature, TMA, TMG and ammonia are used as source gases, and Cp is used as an impurity gas.₂Mg (cyclopentadienylmagnesium) is used and Mg is 1 × 10¹⁹/ Cm^ThreeDoped Al_0.4Ga_0.6A p-type electron confinement layer 37 made of N is grown to a thickness of 100 Å.
[0071]
(P-type guide layer 38)
  Next, the temperature is set to 1050 ° C., TMG and ammonia are used as the source gas, and the p-type guide layer 8 made of undoped GaN is grown to a thickness of 0.075 μm.
  The p-type guide layer 8 is grown as undoped, but due to the diffusion of Mg from the p-type electron confinement layer 37, the Mg concentration is 5 × 10 5.¹⁶/ Cm^ThreeAnd p-type.
[0072]
(P-type cladding layer 39)
  Next, at the same temperature, TMA, TMG and ammonia are used as source gases, and undoped Al_0.1Ga_0.9An A layer made of N is grown to a film thickness of 25 Å, and then TMA is stopped and Cp is used as an impurity gas.₂Mg is used, and Mg is 5 × 10¹⁸/ Cm^ThreeA B layer made of doped GaN is grown to a thickness of 25 Å. This operation is repeated 100 times, and the A layer and the B layer are laminated to grow a p-type cladding layer 39 made of a multilayer film (superlattice structure) having a total film thickness of 5000 angstroms.
[0073]
(P-type contact layer 40)
  Next, at the same temperature, TMG and ammonia are used as the source gas, and Cp is used as the impurity gas.₂Mg is used, and Mg is 1 × 10²⁰/ Cm^ThreeA p-type contact layer 40 made of doped GaN is grown to a thickness of 150 Å.
[0074]
  After the completion of the reaction, the wafer is annealed in a reaction vessel at 700 ° C. in a nitrogen atmosphere to further reduce the resistance of the p-type layer.
  After annealing, the wafer is taken out of the reaction vessel, and SiO is deposited on the surface of the uppermost p-side contact layer.₂A protective film is formed, and SiCl is formed using RIE (reactive ion etching)._FourEtching with a gas exposes the surface of the n-side contact layer 32 where an n-electrode is to be formed, as shown in FIG.
  Next, as shown in FIG. 9A, Si oxide (mainly SiO 2) is formed on almost the entire surface of the uppermost p-side contact layer 40 by a PVD apparatus.₂) Is formed to a thickness of 0.5 μm, a mask having a predetermined shape is put on the first protective film 61, and a third protective film 63 made of photoresist is formed. The stripe width is 1.8 μm and the thickness is 1 μm.
  Next, as shown in FIG. 9B, after the formation of the third protective film 63, CF is performed by an RIE (reactive ion etching) apparatus._FourUsing gas, the first protective film is etched using the third protective film 63 as a mask to form stripes. Thereafter, the first protective film 61 having a stripe width of 1.8 μm can be formed on the p-side contact layer 40 as shown in FIG.
[0075]
  Further, as shown in FIG. 9D, after the first protective film 61 having a stripe shape is formed, SiCl is again performed by RIE._FourThe p-side contact layer 40 and the p-side cladding layer 39 are etched using gas to form a ridge-shaped stripe having a stripe width of 1.8 μm. However, as shown in FIG. 8, the ridge-shaped stripe is formed so as to reach the upper part of the recess formed in the first nitride semiconductor.
  After forming the ridge stripe, the wafer is transferred to a PVD apparatus, and as shown in FIG. 9 (e), Zr oxide (mainly ZrO₂The second protective film 62 is formed continuously on the first protective film 61 and on the p-side cladding layer 39 exposed by etching with a thickness of 0.5 μm. The formation of the Zr oxide in this manner is preferable because the transverse mode can be stabilized because the pn plane is insulated.
  Next, the wafer is immersed in hydrofluoric acid, and as shown in FIG. 9F, the first protective film 61 is removed by a lift-off method.
[0076]
  Next, as shown in FIG. 9G, the p-electrode 20 made of Ni / Au is formed on the surface of the p-side contact layer exposed by removing the first protective film 61 on the p-side contact layer 40. To do. However, the p electrode 20 has a stripe width of 100 μm and is formed over the second protective film 62 as shown in FIG.
  After the formation of the second protective film 62, an n electrode 21 made of Ti / Al is formed in a direction parallel to the stripes on the exposed surface of the n-side contact layer 2 as shown in FIG.
[0077]
  As described above, after polishing the sapphire substrate of the wafer on which the n-electrode and the p-electrode are formed to 70 μm, the substrate is cleaved in a bar shape from the substrate side in a direction perpendicular to the stripe-shaped electrode. A resonator is formed on the 11-00 plane, a plane corresponding to the side surface of the hexagonal columnar crystal = M plane). SiO on the resonator surface₂And TiO₂A dielectric multilayer film is formed, and finally the bar is cut in a direction parallel to the p-electrode to obtain a laser element as shown in FIG. The resonator length is preferably 300 to 500 μm.
  The obtained laser element was placed on a heat sink, and each electrode was wire-bonded to attempt laser oscillation at room temperature.
  As a result, the threshold value is 2.5 kA / cm at room temperature.²Continuous oscillation at an oscillation wavelength of 400 nm was confirmed at a threshold voltage of 5 V, and the lifetime was 10,000 hours or more at room temperature. In addition, since the surface state of the second nitride semiconductor is good, a laser device having good device characteristics can be obtained with a high yield.
[0078]
[Example4]
  Hereinafter, an example based on FIG.4Will be described. FIG. 10 is a schematic cross-sectional view showing the structure of a laser device according to an embodiment using a nitride semiconductor layer obtained by the growth method of the present invention as a substrate.
[0079]
  In Example 1, when the second nitride semiconductor 3 is grown, 1 × 10 Si is used.¹⁸/ Cm^ThreeThe Si-doped second nitride semiconductor 3 is obtained in the same manner except that the film thickness is 150 μm. The sapphire substrate or the like of the obtained wafer is polished and removed to form the second nitride semiconductor 3 alone.
[0080]
  Next, a wafer whose main surface is the second nitride semiconductor layer 3 (Si-doped GaN) on the surface opposite to the surface from which the sapphire substrate is removed is set in the reaction vessel of the MOVPE apparatus, and this second nitridation is performed. The following layers are formed on the physical semiconductor layer 3.
[0081]
(N-side cladding layer 43)
  Next, Si is 1 × 10¹⁹/cm^ThreeDoped n-type Al_0.2Ga_0.8A superlattice structure with a total film thickness of 0.4 μm is formed by alternately stacking 100 first layers of N, 20 Å, and second layers of 20 Å of undoped GaN.
[0082]
(N-side light guide layer 44)
  Then, Si is 1 × 10¹⁷/cm^ThreeAn n-type light guide layer 44 made of doped n-type GaN is grown to a thickness of 0.1 μm.
[0083]
(Active layer 45)
  Next, Si is 1 × 10¹⁷/cm^ThreeDoped In_0.2Ga_0.8Well layer made of N, 25 Å, and 1 × 10 Si¹⁷/cm^ThreeDoped In_0.01Ga_0.95An active layer 45 of a multiple quantum well structure (MQW) having a total film thickness of 175 Å formed by alternately laminating N barrier layers and 50 Å is grown.
[0084]
(P-side cap layer 46)
  Next, the band gap energy is larger than that of the p-side light guide layer 47 and larger than that of the active layer 45.²⁰/cm^ThreeDoped p-type Al_0.3Ga_0.9A p-side cap layer 46 made of N is grown to a thickness of 300 angstroms.
[0085]
(P-side light guide layer 47)
  Next, the band gap energy is smaller than the p-side cap layer 46, and Mg is 1 × 10.¹⁸/cm^ThreeA p-side light guide layer 47 made of doped p-type GaN is grown to a thickness of 0.1 μm.
[0086]
(P-side cladding layer 48)
  Next, Mg is 1 × 10²⁰/cm^ThreeDoped p-type Al_0.2Ga_0.8A first layer of N, 20 Å, and 1 × 10 Mg²⁰/cm^ThreeA p-side cladding layer 48 made of a superlattice layer having a total thickness of 0.4 μm is formed by alternately laminating a second layer made of doped p-type GaN and 20 Å.
[0087]
(P-side contact layer 49)
  Finally, Mg 2 × 10²⁰/cm^ThreeA p-side contact layer 49 made of doped p-type GaN is grown to a thickness of 150 Å.
[0088]
  After the completion of the reaction, the wafer is annealed in a reaction vessel at 700 ° C. in a nitrogen atmosphere to further reduce the resistance of the p-type layer. After annealing, the wafer is taken out of the reaction vessel, and as shown in FIG. 10, the uppermost p-type contact layer 49 and p-type cladding layer 48 are etched by an RIE apparatus to form a ridge shape having a stripe width of 4 μm. Then, a p-electrode 51 made of Ni / Au is formed on the entire surface of the ridge.
[0089]
  Next, as shown in FIG. 10, the surface of the p-side cladding layer 48 and the contact layer 49 excluding the p-electrode 51 is made of SiO.₂An insulating film 50 is formed, and a p-pad electrode 52 electrically connected to the p-electrode 51 through the insulating film 50 is formed.
[0090]
  After forming the p-side electrode, an n-electrode 53 made of Ti / Al is formed to a thickness of 0.5 μm on the entire surface of the second nitride semiconductor layer 3 where the element structure is not formed, and a heat sink and A thin film made of Au / Sn is formed for metallization.
[0091]
  Thereafter, scribing is performed from the n-electrode side 53, and the second nitride semiconductor layer 5 is cleaved at the M-plane of the second nitride semiconductor layer 3 (11-00, the plane corresponding to the side of the hexagonal column in FIG. 6). A resonant surface is produced. SiO on both or one of the resonant surfaces₂And TiO₂A dielectric multilayer film was formed, and finally a bar was cut in a direction parallel to the p-electrode to obtain a laser chip. Next, the chip was placed face-up (with the substrate and the heat sink facing each other) on the heat sink, the p-pad electrode 52 was wire-bonded, and laser oscillation was attempted at room temperature. The threshold current density was 2.5 kA at room temperature. /cm²Continuous oscillation with an oscillation wavelength of 405 nm was confirmed at a threshold voltage of 4.5 V, and a lifetime of 10,000 hours or more was shown.
[0092]
[Example5]
  Example2Example using the third nitride semiconductor 4 obtained in step 1 as a substrate3A laser device was fabricated by forming the same device structure as in FIG.
  The obtained laser device has good life characteristics as in Example 3. Even if the position where the ridge-shaped stripe is formed is formed on the upper portion of the second nitride semiconductor 3 other than the modified portion, good characteristics are exhibited.
[0093]
[Example6]
  In Example 1, the sapphire substrate 1 has a step of 2 inches φ, an off-angle angle θ = 0.2 °, a step difference (height) of about 1 atomic layer, a terrace width W of about 40 Å, and a C plane. The second nitride semiconductor is similar to the above except that a sapphire substrate is used in which the orientation plane is the A plane and the direction along the step, that is, the direction of the step is perpendicular to the A plane. Grow 3
  Example using the obtained second nitride semiconductor 3 as a substrate3A laser element is manufactured by forming an element structure similar to the above.
  The obtained laser device is an example.3The threshold value is lowered, and the life characteristics are better.
[0094]
【The invention's effect】
  As described above, the present inventionSiO ₂ Without using a mask such asBy partially modifying the surface of the nitride semiconductor, the modified portion becomes the SiO used in the case of conventional ELOG growth.₂Intentionally promotes lateral growth of nitride semiconductors in much the same waycan do.Thereby,The present inventionDislocationTheReducedSet,And,It is possible to provide a nitride semiconductor growth method capable of obtaining a nitride semiconductor with good crystallinity.
  Furthermore, the present invention provides a nitride semiconductor device having good lifetime characteristics using a nitride semiconductor having good crystallinity and few dislocations as a substrate.Manufacturing methodCan be provided.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing the structure of a nitride semiconductor wafer obtained in each step of the method of the present invention.
FIG. 2 is a schematic cross-sectional view showing the structure of a nitride semiconductor wafer obtained in each step of the method of the present invention.
FIG. 3 is a schematic cross-sectional view showing the structure of a nitride semiconductor wafer obtained in each step of the method of the present invention.
FIG. 4 is a schematic cross-sectional view showing the structure of a nitride semiconductor wafer obtained in each step of the method of the present invention.
FIG. 5 is a schematic cross-sectional view showing the structure of a nitride semiconductor wafer obtained in each step of the method of the present invention.
FIG. 6 is a unit cell diagram showing the surface orientation of sapphire.
FIG. 7 is a plan view of the main surface side of the substrate for explaining the stripe direction of the protective film.
FIG. 8 is a schematic cross-sectional view showing one structure of a nitride semiconductor LD device using a substrate according to the method of the present invention.
FIG. 9 is a schematic cross-sectional view showing a partial structure of a wafer in each step of a method which is an embodiment of forming a ridge-shaped stripe.
FIG. 10 is a schematic cross-sectional view showing one structure of a nitride semiconductor LD device using a substrate according to the method of the present invention.
FIG. 11 is a schematic cross-sectional view showing an enlarged part of a substrate according to the method of the present invention.
[Explanation of symbols]
  1 ... Different substrates
  2... First nitride semiconductor
  3. Second nitride semiconductor
  4... Third nitride semiconductor

Claims (9)

A first step of growing a first nitride semiconductor on a heterogeneous substrate made of a material different from the nitride semiconductor;
After the first step, the surface of the first nitride semiconductor is partially modified by dry etching so that the nitride semiconductor is difficult to grow or does not grow, and is applied to the surface of the first nitride semiconductor. A second step of imparting selectivity to the growth of the nitride semiconductor;
After the second step, the nitride semiconductor has at least a third step of growing a second nitride semiconductor on the first nitride semiconductor whose surface is partially modified Growth method.   In the second step, after a protective film is partially formed on the first nitride semiconductor grown on the heterogeneous substrate, a portion where the protective film is not formed is subjected to N deficiency by the dry etching. 2. The method for growing a nitride semiconductor according to claim 1, wherein the method is a step of partially modifying the surface of the first nitride semiconductor by forming a portion and then removing the protective film. 3. The method for growing a nitride semiconductor according to claim 1, wherein the dry etching uses at least one kind of gas of noble gas and O ₂ gas. After the third step, the nitride semiconductor is difficult to grow or grows by dry etching on the surface of the second nitride semiconductor and the upper portion of the first nitride semiconductor other than the surface modified portion. A fourth step of partially modifying so as not to cause selectivity to growth of the nitride semiconductor on the surface of the second nitride semiconductor;
2. The method according to claim 1, further comprising a fifth step of growing a third nitride semiconductor on the second nitride semiconductor having the surface partially modified after the fourth step. 4. The method for growing a nitride semiconductor according to any one of 3 above.   5. The method for growing a nitride semiconductor according to claim 1, wherein a C surface of sapphire is off-angled stepwise in the dissimilar substrate.   The nitride semiconductor growth method according to claim 5, wherein an off-angle angle of the sapphire substrate that is off-angled in a step shape is 0.1 ° to 0.5 °.   The nitride according to claim 5 or 6, wherein a direction (step direction) along the step of the sapphire substrate that is off-angled in a step shape is formed perpendicular to the A-plane of sapphire. Semiconductor growth method. A first step of growing a substrate by the nitride semiconductor growth method according to any one of claims 1 to 7, at least an n-type nitride semiconductor having an element structure on the substrate , an active layer, and A method for manufacturing a nitride semiconductor device , comprising a second step of forming a p-type nitride semiconductor. A first step of growing a substrate by the nitride semiconductor growth method according to any one of claims 1 to 7, at least an n-type nitride semiconductor having an element structure on the substrate , an active layer, and a second step of forming a p-type nitride semiconductor, and a stripe shape for guiding light of the nitride semiconductor laser device on the modified portion formed in the first nitride semiconductor of the nitride semiconductor substrate; manufacturing method of the nitride semiconductor laser device characterized by having a third step that form a ridge.

Images