JP4772314B2 - Nitride semiconductor device - Google Patents

Description

  The present invention relates to a nitride semiconductor device, and more particularly to a nitride semiconductor device using a nitride semiconductor substrate having at least a surface made of a nitride semiconductor.

  Nitride semiconductors such as GaN, AlGaN, GaInN, and AlGaInN have characteristics that they have a large band gap Eg and a direct transition semiconductor material compared to AlGaInAs semiconductors and AlGaInP semiconductors. Therefore, these nitride semiconductors are used as materials for semiconductor light-emitting elements such as semiconductor lasers capable of emitting short-wavelength light from ultraviolet to green and light-emitting diodes capable of covering a wide emission wavelength range from ultraviolet to red. It is attracting attention and is widely considered for high-density optical discs, full-color displays, and environmental and medical fields.

In addition, it has higher thermal conductivity than GaAs-based semiconductors, and is expected to be applied to devices that operate at high temperature and high output. Further, since a material corresponding to arsenic (As) in an AlGaAs-based semiconductor, cadmium (Cd) in a ZnCdSSe-based semiconductor, and its raw material (arsine (AsH ₃ )) are not used, the compound semiconductor material has a low environmental load. Be expected.

  However, conventionally, in the manufacture of a nitride semiconductor laser element, which is one of the nitride semiconductor elements, the ratio of the number of non-defective elements obtained to the number of nitride semiconductor laser elements manufactured on one wafer is shown. There is a problem that the yield value is very low. One of the causes of a drop in yield is the occurrence of cracks. The occurrence of the crack is caused by the substrate and the case where the crack is caused by laminating a nitride semiconductor growth layer composed of a plurality of nitride semiconductor layers (nitride semiconductor thin films) on the substrate. is there.

  Originally, a nitride semiconductor growth layer such as GaN is preferably formed by growing on a GaN substrate because a nitride semiconductor growth layer with good crystallinity and few defects is obtained. However, a high quality GaN single crystal substrate that lattice matches with GaN has not been developed yet. For this reason, an SiC substrate having a relatively small difference in lattice constant may be used, but this SiC substrate is expensive and difficult to increase in diameter, and tensile strain is generated, resulting in cracks. It's easy to do. Furthermore, the conditions required for the substrate material of the nitride semiconductor are required to withstand a high growth temperature of about 1000 ° C. and not to be discolored or corroded in the ammonia gas atmosphere of the raw material.

  For the above reasons, a sapphire substrate is usually used as the substrate on which the nitride semiconductor growth layer is stacked. However, the sapphire substrate has a large lattice mismatch with GaN (about 13%). For this reason, a buffer layer made of GaN or AlN is formed on the sapphire substrate by low temperature growth, and a nitride semiconductor growth film is grown on the buffer layer. However, it is difficult to completely remove the strain, and cracks have occurred depending on the composition and film thickness conditions.

  Moreover, the occurrence of such cracks is not only caused by the substrate. That is, when a nitride semiconductor laser device is manufactured, a nitride semiconductor growth layer is stacked on a substrate, and the nitride semiconductor growth layer is composed of different types of films such as GaN, AlGaN, and InGaN. At this time, the films constituting the nitride semiconductor growth layer have different lattice constants and cause lattice mismatch, and thus cracks are generated. Therefore, a method of reducing cracks by forming a recess without using a processed substrate to grow a nitride semiconductor growth layer and then flattening the surface of the nitride semiconductor growth layer has been proposed (patented). Reference 1). For example, by using the method described in Patent Document 1, it is possible to suppress cracks that are generated due to lattice mismatch of each film constituting the nitride semiconductor growth layer formed on the substrate. However, the technique described in Patent Document 1 has a problem that the flatness of the nitride semiconductor growth layer deteriorates due to the formed depression.

  In response to such a problem that the flatness of the surface of the nitride semiconductor growth layer deteriorates, the present inventor has a digging region composed of about 1 to several stripe-shaped grooves per nitride semiconductor laser element. A hill portion having a width of about 100 μm to 1000 μm sandwiched between adjacent digging regions is formed on a nitride semiconductor substrate, and a nitride semiconductor growth layer is stacked on the nitride semiconductor substrate, thereby cracking We have developed a method that can prevent surface roughness and improve surface flatness within a certain range on the hill surface.

  When a nitride semiconductor laser device is manufactured using the technique developed by the inventor described above, for example, the nitride semiconductor growth layer is configured as shown in FIG.

That is, the nitride semiconductor growth layer 4 formed on the surface of the processed substrate 6 (see FIG. 12) made of etched n-type GaN or the like has an n thickness of 0.2 μm on the surface of the processed substrate 6, for example. N-type Al _0.05 Ga _0.95 N first cladding layer 131 having a thickness of 0.75 μm, and n-type Al _0.08 Ga _0.92 N second cladding having a thickness of 0.1 μm A layer 132, an n-type Al _0.05 Ga _0.95 N third cladding layer 133 having a layer thickness of 1.5 μm, an n-type GaN guide layer 134 having a layer thickness of 0.02 μm, and an InGaN well layer having a layer thickness of 4 nm. A multi-quantum well active layer 135 comprising three layers and four GaN barrier layers having a thickness of 8 nm, a p-type Al _0.3 Ga _0.7 N evaporation preventing layer 136 having a thickness of 20 nm, and a layer thickness of 0.02 μm p-type GaN guide layer 137 and a layer thickness of 0.5 μm a p-type _Al 0.05 _{Ga 0.95} N cladding layer 138, a p-type GaN contact layer 139 having a thickness of 0.1 [mu] m, but is constructed by laminating in this order. The multiple quantum well active layer 135 is formed in the order of barrier layer / well layer / barrier layer / well layer / barrier layer / well layer / barrier layer.

  In addition, when the index indicating the crystal plane or orientation is negative, it is a rule of crystallography to indicate the absolute value with a horizontal line, but in the following, since such notation is not possible, the absolute value A negative sign “−” is added in front of to indicate a negative index.

The “processed substrate” is a nitride semiconductor substrate or a substrate in which a dug region and a hill are formed on the surface of a nitride semiconductor thin film stacked on the nitride semiconductor substrate. Further, a p-type Al _0.3 Ga _0.7 N evaporation preventing layer 136 doped with Mg, a p-type GaN guide layer 137, a p-type Al _0.05 Ga _0.95 N cladding layer 138, a p-type GaN contact layer. Hereinafter, the nitride semiconductor layer obtained by stacking 139 is referred to as a “p layer”.

  By depositing the nitride semiconductor growth layer 4 on the processed substrate 6 surface using the MOCVD (Metal Organic Chemical Vapor Deposition) method, there is a depression on the surface of the nitride semiconductor growth layer 4 as shown in FIG. A nitride semiconductor wafer is formed. In FIG. 12, the plane orientation is also displayed.

An n-type GaN substrate is used as the processed substrate 6 shown in FIG. 12 and is dug in a stripe shape using a dry etching technique such as RIE (Reactive Ion Etching) in the <1-100> direction. Region 2 and hill 1 are formed. The width of the digging region is 5 μm, the depth is 5 μm, and the period with the adjacent digging region is 350 μm. A nitride semiconductor growth layer 4 having a stacked structure as shown in FIG. 13 is formed on the processed substrate 6 subjected to such etching by a growth method such as MOCVD.
JP 2002-246698 A

  However, with the technique developed by the present inventor described above, an n-type GaN substrate is used as the processed substrate 6, and the nitride semiconductor growth layer 4 is epitaxially grown on the n-type GaN substrate using the MOCVD method or the like, thereby nitriding Fabrication of the semiconductor laser device was effective in reducing cracks, but the yield was not significantly improved. That is, using the above-described technique, a plurality of nitride semiconductor laser elements were manufactured, and 100 nitride semiconductor laser elements were randomly taken out from the nitride semiconductor laser elements, and the half widths of the FFP in the horizontal direction and the vertical direction were measured. At this time, when the nitride semiconductor laser element within ± 1 degree with respect to the design value of the half width of the FFP is regarded as a non-defective product, there are 30 nitride semiconductor lasers whose half width of the FFP satisfies the standard, The result was very low yield.

This is because the flatness of the surface of the formed nitride semiconductor growth layer 4 was not sufficiently good. If the surface flatness is not sufficient, the thickness of each layer varies within the nitride semiconductor growth layer 4, the characteristics of each nitride semiconductor laser element differ, and the number of elements that satisfy the characteristics within the standard range decreases. Therefore, in order to improve the yield, it is necessary not only to reduce the generation of cracks but also to further improve the surface flatness of the film.

  Further, when the surface flatness in the nitride semiconductor wafer surface formed as shown in FIGS. 12 and 13 is measured, the measurement result of the surface flatness measured in the <1-100> direction is as shown in FIG. The measurement was performed under the measurement conditions of a measurement length of 600 μm, a measurement time of 3 s, a stylus pressure of 30 mg, and a horizontal resolution of 1 μm / sample. At this time, in the measured region of 600 μm width, the level difference between the highest part and the lowest part of the surface was 300 nm from the graph of FIG. The off-angle of the nitride semiconductor wafer used for this measurement is 0.02 ° or less.

As shown in FIG. 12B, the difference in flatness is due to the fact that the thickness of each layer of the nitride semiconductor growth layer 4 stacked on the surface of the processed substrate 6 varies depending on the position of the wafer. It is. Therefore, the characteristics of the nitride semiconductor laser device vary greatly depending on the in-plane position of the wafer on which the device is manufactured, and the thickness of the p layer doped with Mg that greatly affects the characteristics of the nitride semiconductor laser device (FIG. 13). (Which corresponds to the sum of the thicknesses of the p layers stacked from the p-type Al _0.3 Ga _0.7 N evaporation prevention layer 136 to the p-type GaN contact layer 139) shown in FIG. It becomes.

  Also, when a ridge structure that is a current confinement structure is formed, the ridge portion is left in a stripe shape having a width of 2 μm, and the other portions are etched using a dry etching technique using an ICP (Inductively Coupled Plasma) apparatus or the like. . Therefore, if the p-layer thickness before etching varies depending on the in-plane position of the wafer, the remaining thickness of the p-layer after etching that most affects the characteristics of the nitride semiconductor laser device also varies greatly depending on the in-plane position of the wafer. It becomes. For these reasons, the nitride semiconductor laser elements have different layer thicknesses, and even within a single nitride semiconductor laser element, the p-layer has almost no remaining film thickness and remains significantly. Will be mixed. Thus, if the remaining film thickness of the p layer varies, the lifetime of the nitride semiconductor laser element and characteristics such as the half width of FFP (Far Field Pattern) are affected as described above.

  Thus, a large layer thickness distribution exists in the wafer surface because the growth rate of the film epitaxially grown on the hill portion of the processed substrate including the nitride semiconductor substrate changes due to the influence of the digging region. This is probably because the uniformity in the surface deteriorated.

  That is, when the epitaxial growth is started with respect to the processed substrate 6 in which the digging region 2 is formed as shown in FIG. 15, the digging region 2 is shown in FIG. The digging region in-growth portion 152 made of a nitride semiconductor thin film grown on the bottom surface portion 154 and the side surface portion 156 of the digging region 2 is only partially buried. At this time, the growth of the upper surface growing portion 151 made of a nitride semiconductor thin film growing on the surface of the upper surface portion 153 of the hill 1 proceeds with the surface of the nitride semiconductor thin film being flat.

  When the epitaxial growth of the nitride semiconductor thin film progresses from the state of FIG. 15A described above, the nitride grown on the bottom surface portion 154 and the side surface portion 156 of the digging region 2 as shown in FIG. 15B. The grooving region growth portion 152 made of a thin semiconductor film almost fills the digging region 2, and the upper surface growth portion 151 and the growth portion 155 made of a nitride semiconductor thin film grown on the surface of the upper surface portion 153 of the hill 1. It becomes a connected state. In such a state, the atoms / molecules (Ga atoms and the like) that are the raw materials attached to the surface of the nitride semiconductor thin film grown on the upper surface portion 153 of the hill 1 cause migration or the like by thermal energy, and the growth portion 155 or It moves to the in-digging region growth part 152. The movement of atoms / molecules due to this migration occurs very unevenly in the wafer plane, and the movement distance also takes a different value in the wafer plane. As a result, as shown in FIG. 15B, the flatness of the surface of the upper surface growth portion 151 is deteriorated.

  The flatness of such a nitride semiconductor thin film is due to the non-uniformity of the nitride semiconductor substrate itself such as the off-angle wafer in-plane distribution and the substrate curvature in-wafer distribution, or the epitaxial growth rate in-plane non-uniformity. Further, the non-uniformity in the substrate surface of the digging process influences the <1-100> direction. That is, the time until the digging region 2 is filled varies depending on the <1-100> direction, and the portion that has been buried quickly is an atom that becomes a raw material of the nitride semiconductor thin film by migration or the like from the upper surface growth portion 151 of the hill 1. The molecule moves to the growth part 155 or the in-digging region growth part 152. As a result, the time for forming the nitride semiconductor thin film becomes longer when moved, and as a result, the thickness of the nitride semiconductor thin film formed in the digging region 2 increases. On the other hand, in the portion where the digging region 2 was not filled quickly, the atoms / molecules that are the raw material of the nitride semiconductor thin film do not move from the upper surface growth portion 151 of the hill 1 into the digging region 2, or even if moved, the nitride The time for forming the semiconductor thin film is short. Therefore, the film thickness of the nitride semiconductor thin film formed in the digging region 2 is thinner than the portion where the digging region 2 is buried earlier.

  Also, when the growth rate of the nitride semiconductor thin film is controlled by the flux of atoms / molecules supplied to the wafer surface, the so-called supply-controlled state, the atoms / molecules that are the raw material of the nitride semiconductor thin film migrate When flowing into the digging region 2 by, for example, the upper surface growth in which the nitride semiconductor thin film grows on the upper surface portion 153 of the hill 1 because the flux of atoms and molecules as raw materials supplied to the entire wafer surface is constant. The film thickness of the portion 151 is reduced. In the reverse case, that is, when the atoms / molecules that are the raw material of the nitride semiconductor thin film do not flow into the digging region 2 due to migration or the like, the top growth portion 151 portion where the nitride semiconductor thin film grows on the top surface portion 153 of the hill 1 The film thickness becomes thicker.

  Due to this, the layer thickness of the upper surface growth portion 151 on the upper surface portion 153 of the hill 1 is different within the wafer surface, and as a result, the flatness of the nitride semiconductor thin film surface is deteriorated. That is, in order to improve the flatness, atoms / molecules that are the raw material of the nitride semiconductor thin film move from the upper surface growth portion 151 of the hill 1 to the growth portion 155 or the in-digging region growth portion 152 by migration or the like. It is necessary to suppress the formation of a physical semiconductor thin film.

  Further, as another method for improving the flatness, when atoms / molecules as a raw material of the nitride semiconductor thin film move from the upper surface growth portion 151 of the hill 1 to the in-digging region growth portion 152 by migration or the like, the entire wafer is transferred. A method of uniformly moving can be considered.

  In view of such problems, the present invention provides a nitride semiconductor element such as a nitride semiconductor laser element by laminating a nitride semiconductor growth layer on a substrate having at least a surface formed of a nitride semiconductor. In addition, it prevents the generation of cracks and suppresses the formation of a nitride semiconductor thin film by migration of atoms and molecules, which are the raw material of the nitride semiconductor thin film, to the digging region by migration etc. Nitride with good surface flatness due to the migration of atoms / molecules, which are the raw material of the nitride semiconductor thin film, over the entire wafer due to migration, etc. An object of the present invention is to provide a nitride semiconductor device having a semiconductor growth layer and good characteristics.

  In order to achieve the above object, according to the present invention, at least a surface of a nitride semiconductor substrate composed of a nitride semiconductor is provided with a dug region formed of at least one concave portion and a hill portion which is a non-digged region. A processed semiconductor substrate and a nitride semiconductor growth layer formed by laminating a plurality of nitride semiconductor thin films on the processed substrate, and a {0001} plane as a principal plane orientation on which the nitride semiconductor growth layer is stacked In the nitride semiconductor device used, the first vector and the first vector extending in the normal direction from the surface of the hill and the second vector parallel to the crystal orientation <0001> are the same as the first vector and the The off angle, which is an angle formed with the second vector, is 0.05 ° or more and 4 ° or less.

  In such a nitride semiconductor device, the off-angles of the processed substrate are three axes of the crystal orientation <0001>, the crystal orientation <11-20>, and the crystal orientation <1-100> that are perpendicular to each other. A third vector obtained by projecting the second vector onto the first plane on the first plane composed of two axes of the crystal orientation <0001> and the crystal orientation <1-100> The first vector and the first vector have the same starting point, the first off angle that is an angle formed between the first vector and the third vector, the crystal orientation <0001> that are perpendicular to each other, and the On the second plane constituted by two axes of the crystal orientation <0001> and the crystal orientation <11-20> among the three axes of the crystal orientation <11-20> and the crystal orientation <1-100> Projecting the second vector onto the second plane The fourth vector and the first vector may be the same point, and may be composed of a second off angle that is an angle formed between the first vector and the fourth vector. .

  In such a nitride semiconductor device, | θa | ≧ | θb | may be satisfied, where θa is the first off angle and θb is the second off angle.

  Further, in such a nitride semiconductor device, 0.09 ° ≦ | θa | ° is satisfied.

  Further, such a nitride semiconductor device is characterized in that 3 × | θb | ° <| θa | ° <0.09 ° and 0.05 ° ≦ | θa | °.

  In such a nitride semiconductor device, | θa | ≦ | θb | may be satisfied, where θa is the first off angle and θb is the second off angle.

  In such a nitride semiconductor device, 0.2 ° ≦ | θb | ° is satisfied.

  Further, in such a nitride semiconductor device, the concave portions constituting the digging region extend in a stripe shape, and the direction in which the concave portions extend is parallel or substantially parallel to the crystal orientation <1-100> direction. It does not matter if they are parallel.

  Further, in such a nitride semiconductor device, the recesses constituting the digging region extend in a stripe shape, and the extending direction of the recesses is parallel or substantially parallel to the crystal orientation <11-20> direction. It does not matter as long as the direction is correct.

  Further, in such a nitride semiconductor device, the concave portion constituting the digging region is formed in a grid shape, and one of two perpendicular directions constituting the grid is parallel to the <11-20> direction. Alternatively, it may be substantially parallel and another direction may be parallel or substantially parallel to the <1-100> direction.

  In such a nitride semiconductor device, when the first off angle is θa and the second off angle is θb, the direction parallel to the long side of the hill is parallel to <1-100>. Alternatively, it is substantially parallel and | θa | ≧ | θb |.

  In such a nitride semiconductor device, when the first off angle is θa and the second off angle is θb, the direction parallel to the long side of the hill is parallel to <11-20>. Alternatively, it is substantially parallel and | θa | ≦ | θb |.

  In such a nitride semiconductor device, the square root of the sum of the square of the first off angle and the square of the second off angle is 0.2 ° or more.

  Further, in such a nitride semiconductor device, the width of the hill portion sandwiched between adjacent digging regions may be 100 μm or more and 2000 μm or less.

  In such a nitride semiconductor device, the nitride semiconductor thin film in contact with the processed substrate surface may be GaN having a thickness of 0.5 μm or less.

  Further, in such a nitride semiconductor device, the depth of the concave portion constituting the digging region may be 1.5 μm or more.

  In such a nitride semiconductor device, the total thickness of the nitride semiconductor growth layer formed on the hill portion is T, and the depth of the concave portion constituting the digging region is T / 2 or more. It does not matter as it is.

  Further, in such a nitride semiconductor device, the opening width of the recess constituting the digging region may be 3 μm or more.

  Further, in such a nitride semiconductor device, when forming a nitride semiconductor growth layer formed by laminating a plurality of the nitride semiconductor thin films, the growth conditions of the at least one nitride semiconductor thin film are the growth conditions of the processed substrate. The surface temperature is 1050 ° C. or less, and the number of moles of the flow rate supplied per unit time of the raw material containing the group V atom to the number of moles of the flow rate supplied per unit time of the raw material containing the group III atom. The ratio may be 2250 or more.

  In order to achieve the above object, according to the present invention, at least a surface of a nitride semiconductor substrate composed of a nitride semiconductor is provided with a dug region formed of at least one concave portion and a hill portion which is a non-digged region. In a nitride semiconductor processing substrate in which a {0001} plane is used as a principal plane orientation on which a nitride semiconductor growth layer is stacked, the starting point of the first vector extending in the normal direction from the surface portion of the hill portion and the crystal orientation <0001 The off-angle, which is an angle formed between the first vector and the second vector, with the start point of the second vector parallel to> being the same point, is 0.05 ° or more and 2 ° or less. To

  Further, in such a nitride semiconductor substrate, the off-angles of the processed substrate are three axes of the crystal orientation <0001>, the crystal orientation <11-20>, and the crystal orientation <1-100> that are perpendicular to each other. A third vector obtained by projecting the second vector onto the first plane on the first plane composed of two axes of the crystal orientation <0001> and the crystal orientation <1-100> The first vector and the first vector have the same starting point, the first off angle that is an angle formed between the first vector and the third vector, the crystal orientation <0001> that are perpendicular to each other, and the On the second plane constituted by two axes of the crystal orientation <0001> and the crystal orientation <11-20> among the three axes of the crystal orientation <11-20> and the crystal orientation <1-100> Projecting the second vector onto the second plane The fourth vector and the first vector may be the same point, and may be composed of a second off angle that is an angle formed between the first vector and the fourth vector. .

  Further, in such a nitride semiconductor substrate, when the first off angle is θa and the second off angle is θb, | θa | ≧ | θb | may be satisfied.

  Further, such a nitride semiconductor substrate is characterized by 0.09 ° ≦ | θa | °.

  Further, such a nitride semiconductor substrate is characterized in that 3 × | θb | ° <| θa | ° <0.09 ° and 0.05 ° ≦ | θa | °.

  In such a nitride semiconductor substrate, when the first off angle is θa and the second off angle is θb, | θa | ≦ | θb | may be satisfied.

  Further, such a nitride semiconductor substrate is characterized by 0.2 ° ≦ | θb | °.

  Further, in such a nitride semiconductor substrate, the recesses constituting the digging region extend in a stripe shape, and the extending direction of the recesses is parallel or substantially parallel to the crystal orientation <1-100> direction. It does not matter if they are parallel.

  Further, in such a nitride semiconductor substrate, the recesses constituting the digging region extend in a stripe shape, and the extending direction of the recesses is parallel or substantially parallel to the crystal orientation <11-20> direction. It does not matter as long as the direction is correct.

  Further, in such a nitride semiconductor substrate, the concave portion constituting the digging region is formed in a grid shape, and one of two perpendicular directions constituting the grid is parallel to the <11-20> direction. Alternatively, it may be substantially parallel and another direction may be parallel or substantially parallel to the <1-100> direction.

  In such a nitride semiconductor substrate, when the first off angle is θa and the second off angle is θb, the direction parallel to the long side of the hill is parallel to <1-100>. Alternatively, it is substantially parallel and | θa | ≧ | θb |.

  In such a nitride semiconductor substrate, when the first off angle is θa and the second off angle is θb, the direction parallel to the long side of the hill is parallel to <11-20>. Alternatively, it is substantially parallel and | θa | ≦ | θb |.

  In such a nitride semiconductor substrate, the square root of the sum of the square of the first off angle and the square of the second off angle is 0.2 ° or more.

  Further, in such a nitride semiconductor substrate, the width of the hill portion sandwiched between the adjacent digging regions may be 100 μm or more and 2000 μm or less.

  Further, in such a nitride semiconductor substrate, the depth of the concave portion constituting the digging region may be 1.5 μm or more.

  Further, in such a nitride semiconductor substrate, the total thickness of the nitride semiconductor growth layer formed on the hill portion is T, and the depth of the recess constituting the digging region is T / 2 or more. It does not matter as it is.

  Further, in such a nitride semiconductor substrate, the opening width of the recess constituting the digging region may be 3 μm or more.

  According to the present invention, when a nitride semiconductor growth layer is stacked on a substrate having at least a surface composed of a nitride semiconductor to produce a nitride semiconductor device such as a nitride semiconductor laser device, cracks can be prevented. In addition, the surface of the nitride semiconductor thin film is prevented from diffusing / moving into the digging region due to migration or the like from the upper surface growth part of the hill surface by diffusion and migration into the digging region. A nitride semiconductor growth layer with good flatness can be formed, and a nitride semiconductor device with good characteristics can be obtained.

  In addition, according to the present invention, diffusion / migration due to migration of atoms / molecules as a raw material of the nitride semiconductor thin film from the upper surface growth portion of the hill surface into the digging region is intentionally promoted, and as a result, the nitride semiconductor The atoms and molecules that are the raw material of the thin film are uniformly diffused and moved throughout the wafer, so that a nitride semiconductor growth layer with good surface flatness can be formed, and a nitride semiconductor device with good characteristics can be obtained. .

  First, in this specification, the meaning of some terms will be clarified in advance. First, the “digging region” means, for example, a recess processed into a stripe shape on the surface of the nitride semiconductor substrate as shown in FIG. FIG. 2 is a schematic cross-sectional view of the processed substrate 26 in which the digging process is performed and the digging region 22 and the hill 21 are formed. The cross-sectional shape of the dug region 22 does not necessarily have to be a rectangular shape, and may be a Δ shape or a trapezoidal shape as shown in FIG. Further, the digging region 22 is not necessarily a single concave portion, and may be composed of a plurality of concave portions and a narrow flat portion sandwiched between the concave portions.

  The “hill” is a convex portion that is similarly processed into a stripe shape. The digging region 22 and the hill 21 shown in FIG. 2 have a stripe arrangement processed along one direction, but may be a grid arrangement in which the digging region 22 or the hill 21 intersect each other. Further, the digging region 22 having a different shape and the digging region 22 having different digging depth and width may exist on one substrate. Further, the period in which the dug region 22 is formed on one substrate may be different.

“Nitride semiconductor substrate” means a substrate made of Al _x Ga _y In _z N (0 ≦ x ≦ 1; 0 ≦ y ≦ 1; 0 ≦ z ≦ 1; x + y + z = 1). However, about 10% or less of the nitrogen element of the nitride semiconductor substrate may be substituted with an element of As, P, or Sb (however, the hexagonal system of the substrate is maintained). The nitride semiconductor substrate may be doped with Si, O, Cl, S, C, Ge, Zn, Cd, Mg, or Be. Furthermore, as these n-type nitride semiconductors, Si, O, and Cl are particularly preferable among these doping materials. Further, the C plane {0001} is used as the principal plane orientation of the nitride semiconductor substrate.

  Next, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, a nitride semiconductor laser will be described as an example of a nitride semiconductor device, but the present invention can also be applied to other nitride semiconductor devices. 1 and 3 are schematic views of the processed substrates 16 and 36 before the nitride semiconductor growth layer 4 is grown in the present embodiment. As shown in FIGS. 1 and 3, the processed substrates 16 and 36 have a certain off angle. FIG. 4 is a schematic view of a processed substrate 46 manufactured from a commonly used substrate having an off angle of 0.02 ° or less. In FIGS. 1, 3, and 4, the plane orientation is also displayed. Further, the nitride semiconductor laser device of this embodiment is manufactured by growing the nitride semiconductor growth layer 4 on a processed substrate having an off angle, such as the processed substrates 16 and 36.

  A method of manufacturing the processed substrate 46 from the substrate having the off angle of 0.02 ° or less and the off angle almost zero shown in FIG. 4 will be described. In the present embodiment, n-type GaN substrates are used as the processed substrates 16, 36, and 46.

First, sputter deposited SiO ₂ or the like having a thickness of 1μm on the entire surface of the n-type GaN substrate to form a SiO ₂ film, subsequently, in a general photolithography process, a photoresist pattern of stripes, the resist opening portion It is formed in the <1-100> direction so that the width (hereinafter referred to as the period) in the direction parallel to the <11-20> direction between the stripe central part and the adjacent stripe central part is 350 μm. Next, by using a dry etching technique such as RIE (Reactive Ion Etching) technique, the SiO ₂ film and the n-type GaN substrate are etched to form a digging region 42 having a digging depth of 5 μm and an opening width of 5 μm. Form. Thereafter, SiO ₂ is removed by using HF (hydrofluoric acid) or the like as an etchant, thereby manufacturing a processed substrate 46 having a dug region 42 and a hill 41.

In this embodiment, SiO ₂ is deposited to form the SiO ₂ film on the surface of the n-type GaN substrate. However, the present invention is not limited to this, and other dielectric films and the like are formed on the surface of the n-type GaN substrate. It does not matter as what is formed. Further, the above-described method for forming the SiO ₂ film is not limited to sputtering deposition, and methods such as electron beam deposition and plasma CVD may be used. The period of the resist pattern is not limited to the above-mentioned 350 μm, and may be changed depending on the width of the nitride semiconductor laser element to be manufactured. Furthermore, in the present embodiment, the dry etching technique is used to form the digging region 42, but the present invention is not limited to this method, and a wet etching technique or the like may be used.

  The processed substrate 46 formed in this way may be formed by digging the digging region 42 directly on the surface of the n-type GaN substrate as described above, or other than the n-type GaN substrate or the n-type GaN substrate. A nitride semiconductor thin film such as GaN, InGaN, AlGaN, or InAlGaN may be grown on the nitride semiconductor substrate, and then formed by digging.

  Further, the manufacturing method of the processed substrates 16 and 36 is basically the same as the manufacturing method of the processed substrate 46. However, the substrate used to manufacture the processed substrate 16 has the crystal orientation <11-20> as the rotation axis, and both the crystal orientations <1-100> and <0001> are rotated and inclined by θa °. That is, an off angle θa is assumed between the crystal orientation <0001> and the normal direction of the substrate growth surface. Further, the substrate used to manufacture the processed substrate 36 has the crystal orientation <1-100> direction as the rotation axis, and both the crystal orientations <11-20> and <0001> are rotated and inclined by θb °. That is, it is assumed that there is an off angle θb between the crystal orientation <0001> and the normal direction of the substrate growth surface. The digging regions 12 and 32 and the hills 11 and 31 are formed on each of the substrates having such off angles θa and θb in the same manner as described above. At this time, it is assumed that the off-angle of the substrate is zero and the formation of a photoresist pattern, etching, and the like are performed.

  Further, the inclination direction of the off-angle is not limited to only one direction, as described above, such as only θa or only θb. Each inclination direction and each inclination angle (θa, θb) And may be combined. That is, with the <11-20> direction as the rotation axis, both the crystal orientations <1-100> and <0001> rotate and tilt by θa °, and the crystal orientation <0001> and the normal direction of the substrate growth surface When the rotation angle θa is between, the unit vector (size: 1) in the crystal orientation <0001> direction after the rotation is the end point, and the displacement vector of the unit vector in the crystal orientation <0001> direction before the rotation is the start point The vector is the displacement vector A, the <1-100> direction is the axis of rotation, and both the crystal orientations <11-20> and <0001> rotate and tilt by θb °, and the crystal orientation <0001> and the substrate growth surface A vector having a displacement vector of a unit vector in the crystal orientation <0001> direction before rotation with a unit vector in the crystal orientation <0001> direction after rotation when having an off angle θb with respect to the normal direction When the displacement vector B is used, the displacement vector C is the sum of the displacement vector A and the displacement vector B, and a combined vector D obtained by adding the unit vector in the crystal orientation <0001> direction before the rotation and the displacement vector C is obtained. The end point direction may be the off-angle inclination direction. In the present specification, when the crystal orientation <0001> is inclined by the displacement vector C and the substrate has an off angle, it is indicated by describing both the off angle θa and the off angle θb described above.

<Examination of off-angle>
In describing this embodiment, first, the influence of the off-angle of a substrate when a nitride semiconductor thin film is grown on a processed substrate having a dug region and a hill will be described with reference to the drawings.

  As shown in FIG. 4, in the case of the processed substrate 46 having an off angle of 0.02 ° or less and an off angle of almost zero, the normal direction of the upper surface portion 43 of the hill 41 and the bottom surface portion 44 of the digging region 42 is The crystal orientation <0001> is parallel. The three axes of crystal orientations <0001>, <1-100>, and <11-20> are perpendicular to each other. In such a case, the atoms / molecules 15 which are the raw materials of the nitride semiconductor thin film attached on the upper surface portion 43 of the hill 41 are not necessarily highly diffused in a specific direction, and are isotropic from the attached place. To spread. As a result, the atoms / molecules 15 which are the raw materials of the nitride semiconductor thin film are diffused isotropically by migration or the like in the upper surface portion 43 of the hill 41, and a part thereof moves into the digging region 42, and the nitride semiconductor thin film Is formed.

  In general, when the digging regions 12, 32, and 42 are formed, they are not formed completely uniformly over the entire wafer, but in a photolithography process for forming a photoresist pattern or an etching process for performing dry etching or the like. , Process fluctuations occur. As a result, boundary fluctuation portions 17, 37, 47 that are not straight straight lines are formed at the boundary lines between the digging regions 12, 32, 42 and the hills 11, 31, 41, or the digging region 12, Vertical fluctuation portions 18, 38, 48, etc., in which the angle between the side surface portions 19, 39, 49 of the 32, 42 and the bottom surface portions 14, 34, 44 is not vertical are formed.

  If the shapes of the dug regions 12, 32, 42 and the hills 11, 31, 41 are not uniform over the entire wafer due to such process fluctuations, the upper surface portions 13, 33 of the hills 11, 31, 41 are consequently obtained. 43, the degree to which the atoms / molecules 15 that are the raw material of the nitride semiconductor thin film deposited on 43 are diffused / moved into the dug regions 12, 32, 42 by migration or the like is not uniform on the wafer, but varies depending on the region. Become. That is, in a certain region on the wafer, the atoms / molecules 15 which are the raw materials of the nitride semiconductor thin film deposited on the upper surface portions 13, 33, 43 of the hills 11, 31, 41 are dug regions 12, 32, 42 by migration or the like. In the other region on the wafer, atoms / molecules 15 that are the raw material of the nitride semiconductor thin film deposited on the upper surface portions 13, 33, and 43 of the hills 11, 31, and 41 migrate. It becomes difficult to diffuse and move into the dug areas 12, 32, and 42 by such as.

  As described above, on the wafer, the atoms / molecules 15 which are the raw materials of the nitride semiconductor thin film attached on the upper surface portions 13, 33, 43 of the hills 11, 31, 41 are dug regions 12, 32, If the degree of diffusion / movement into the ridge 42 is different, the flatness of the nitride semiconductor thin film growing on the hills 11, 31, 41 is affected. As a result, the nitride semiconductor thin film growing on the hills 11, 31, 41 The film thickness varies on the wafer and varies depending on the region.

Thus, if the nitride semiconductor thin film grown on the hills 11, 31, 41 varies in thickness, when the nitride semiconductor laser device is formed on the hills 11, 31, 41, the yield is adversely affected. FIG. 5 shows the thickness of the p layer formed on the hill (the thickness of the p layer laminated from the p-type Al _0.3 Ga _0.7 N evaporation prevention layer 136 to the p-type GaN contact layer 139 shown in FIG. 13). This shows the relationship between the standard deviation σ indicating the degree of variation (corresponding to the sum) and the yield. From the graph of FIG. 5, when the standard deviation σ of the p layer thickness is 0.03 μm or less, a very high yield of 90% or more is realized, and when the standard deviation σ of the p layer thickness is larger than 0.03 μm, the yield increases rapidly. It turned out to fall to.

As described above, when the standard deviation σ of the p-layer thickness is larger than 0.03 μm, the cause of the rapid drop in yield is the p-type GaN guide layer 137, the p-type Al _0.05 Ga _0.95 N clad layer 138, etc. This is because if the variation in the layer thickness is too large, the electrical and optical characteristics vary when a nitride semiconductor laser device structure is produced. In addition, when a nitride semiconductor laser device is manufactured in a region where the standard deviation σ of the p layer thickness is large, the generation of a leakage current during energization also causes a decrease in yield.

  Thus, when fabricating a nitride semiconductor laser device, in order to improve the yield, the nitride semiconductor thin film grown on the hill, which is the region where the nitride semiconductor laser device is fabricated, including the p-layer thickness, is improved. Need to be improved. For this purpose, the present inventor has proposed a method for suppressing diffusion / migration of atoms / molecules 15 as a material of the nitride semiconductor thin film into the digging region by migration or the like, and atoms / molecules as a material of the nitride semiconductor thin film. Two methods have been invented, a method of intentionally promoting the diffusion and movement of the molecules 15 into the digging region by migration or the like.

  Of the two methods described above, as shown in FIG. 1, the method of suppressing the diffusion / movement of atoms / molecules 15 that are the material of the nitride semiconductor thin film into the digging region has a crystal orientation <11-20>. Is a substrate in which both crystal orientations <0001> and <1-100> are rotated and inclined by θa °, that is, crystal orientation <0001> after rotation is off with respect to crystal orientation <0001> before rotation. A processed substrate 16 is produced using a substrate having an angle θa, and a nitride semiconductor thin film is grown thereon. When a nitride semiconductor thin film is grown on such a processed substrate 16, the atoms / molecules 15 that are the raw material of the nitride semiconductor thin film attached on the upper surface portion 13 of the hill 11 are compared with the <11-20> direction. , It is known that diffusion and movement due to migration or the like in a direction substantially parallel to the <1-100> direction, that is, a direction parallel to the direction in which the digging region 2 extends, becomes significant. Diffusion / migration due to migration of atoms / molecules 15 serving as a material of the nitride semiconductor thin film attached on the upper surface portion 13 of the hill 11 into the digging region 12 is suppressed. As a result, a nitride semiconductor thin film having good surface flatness is formed on the upper surface portion 13 of the hill 11.

  Of the two methods described above, as shown in FIG. 3, the method of promoting the diffusion / migration of atoms / molecules that are the material of the nitride semiconductor thin film into the digging region is shown in FIG. > As the rotation axis, both the crystal orientation <0001> and <11-20> are rotated and inclined by θb °, that is, the crystal orientation <0001> after the rotation is relative to the crystal orientation <0001> before the rotation. A processed substrate 36 is produced using a substrate having an off angle θb, and a nitride semiconductor thin film is grown thereon. When a nitride semiconductor thin film is grown on such a processed substrate 36, the atoms / molecules 15 that are the raw material of the nitride semiconductor thin film attached on the upper surface portion 33 of the hill 31 are compared with the <1-100> direction. , Diffusion by migration in a direction substantially parallel to the <11-20> direction, that is, a direction perpendicular to the direction in which the digging region 32 extends and a direction parallel to the surface of the upper surface portion 33 of the hill 31 It has been found that the movement becomes remarkable, and as a result, diffusion / diffusion caused by migration of atoms / molecules 15 as raw materials of the nitride semiconductor thin film attached on the upper surface portion 33 of the hill 31 into the dug region 32. The material of the nitride semiconductor thin film adhered to the upper surface portion 33 of the hill 31 evenly throughout the wafer regardless of the presence of the boundary fluctuation portion 37, the vertical fluctuation portion 38, etc. A diffusion-movement is caused by migration to become atoms and molecules 15 engraved regions 32 of the. As a result, a nitride semiconductor thin film having good surface flatness is formed on the upper surface portion 33 of the hill 31.

  In general, it has been found that a nitride semiconductor thin film such as a GaN-based semiconductor thin film has a higher growth rate in the <11-20> direction than in the <1-100> direction. Therefore, a processed substrate 16 is produced using a substrate in which both the crystal orientations <0001> and <1-100> are rotated by θa ° with the crystal orientation <11-20> as the rotation axis, and nitriding is performed on the processed substrate 16. When the semiconductor thin film is grown, the atoms / molecules 15 that are the raw material of the nitride semiconductor thin film attached to the upper surface portion 13 of the hill 11 are substantially parallel to the <1-100> direction, that is, the digging region 12 is Atoms / molecules 15 that promote diffusion and movement by migration in a direction parallel to the extending direction and the nitride semiconductor thin film attached to the upper surface portion 13 of the hill 11 are <11− In order to suppress diffusion and movement into the digging region 12 by migration or the like in a direction parallel to the 20> direction, that is, a direction perpendicular to the direction in which the digging region 2 extends, Large value There is a need to take.

  Here, the relationship between the above-described off angle θa and off angle θb and the standard deviation σ of the p-layer thickness is shown in FIGS. FIG. 6 shows the standard of the off-angle θa and the p-layer thickness formed on the hill when a nitride semiconductor laser device is manufactured using a processed substrate having an absolute value of the off-angle θa equal to or larger than the absolute value of the off-angle θb. The relationship with the deviation σ is shown. FIG. 7 shows the off-angle θb and the thickness of the p layer formed on the hill when a nitride semiconductor laser device is manufactured using a processed substrate having an absolute value of the off-angle θa equal to or smaller than the absolute value of the off-angle θb. Shows the relationship with the standard deviation σ. The sign (±) of the off angles θa and θb on the horizontal axis in FIGS. 6 and 7 defines an arbitrary one of the two directions as + on the used wafer. Are equivalent. Therefore, it is only necessary to pay attention to only the absolute values of the off angles θa and θb.

  From FIG. 6, when using a processed substrate having an absolute value of the off angle θa equal to or larger than the absolute value of the off angle θb, the standard deviation σ of the p layer thickness is as long as the absolute value of the off angle θa is 0.09 ° or greater. When the nitride semiconductor laser device is fabricated, the yield is high (see FIG. 5). Even when the absolute value of the off angle θa is smaller than 0.09 °, the absolute value of the off angle θa is larger than three times the absolute value of the off angle θb, and the absolute value of the off angle θa is 0.05. It was found that the standard deviation σ of the p layer thickness was 0.03 μm or less if it was larger than °. In other cases, the standard deviation σ of the p layer thickness is larger than 0.03 μm, and good surface flatness cannot be obtained on the growth surface, so that a high yield cannot be realized.

  From FIG. 7, when using a processed substrate having an absolute value of the off angle θa equal to or smaller than the absolute value of the off angle θb, the standard deviation σ of the p layer thickness is 0 when the absolute value of the off angle θb is 0.2 ° or more. When the absolute value of the off-angle θb is smaller than 0.2 ° and the absolute value of the off-angle θb is smaller than 0.2 °, the p layer thickness standard deviation σ is larger than 0.03 μm. That is, by setting the absolute value of θb to 0.2 ° or more, good flatness is obtained on the growth surface, and a high yield is realized when a nitride semiconductor laser device is manufactured.

  Further, in the method for obtaining good surface flatness by increasing the absolute value of the off angle θb in this way, both the crystal orientation <0001> and <11-20> are set with the crystal orientation <1-100> as the rotation axis. The processed substrate 36 rotated and inclined by θb ° is used, and the direction of the crystal orientation <0001> is inclined by θb ° with respect to the normal direction of the upper surface portion 33 of the hill 31. Since diffusion / movement due to migration or the like into the digging region 32 occurs in one direction, the surface of the nitride semiconductor thin film grown on the processed substrate 36 is inclined as shown in FIG. In FIG. 8, the surface of the nitride semiconductor thin film grown on the processed substrate 36 is measured by using a surface level meter, and the direction perpendicular to the direction in which the digging region 32 extends (substantially the <11-20> direction). This is a result of scanning in a parallel direction. FIG. 8 shows that the surface of the nitride semiconductor thin film formed on the upper surface portion 33 of the hill 31 is inclined in the direction in which the crystal orientation is inclined. However, the height of the central portion of the hill 31 that is a convex portion for forming the ridge portion of the nitride semiconductor laser element is substantially constant, and the p-layer thickness is also constant, so that the nitride semiconductor laser element is manufactured. It doesn't matter. In the case of using the processed substrate 16 in which both the crystal orientations <0001> and <1-100> are rotated and inclined by θa ° with the crystal orientation <11-20> as the rotation axis, Therefore, when the nitride semiconductor thin film is grown on the processed substrate 16 as described above, it is formed on the upper surface portion 13 of the hill 11. The surface of the nitride semiconductor thin film is not inclined and the surface is flat. Therefore, it is more preferable to use a substrate in which both the crystal orientations <0001> and <1-100> are rotated and inclined by θa ° with the crystal orientation <11-20> as the rotation axis.

  When the crystal orientation of the substrate is displaced by the above-described displacement vector C, that is, when the inclination of the crystal orientation of the substrate is composed of both the off angle θa and the off angle θb, the square of the off angle θa and the off angle θb If the value of the square root of the sum of the square and the square is 0.2 ° or more, the surface flatness of the nitride semiconductor thin film grown on the processed substrate becomes good.

  In the above description, the direction in which the digging regions 12, 32, and 42 extend is parallel or substantially parallel to the <1-100> direction, but the digging regions 12, 32, and 42 extend. The same effect can be obtained even when the direction to be performed is parallel or substantially parallel to the <11-20> direction. Further, the recessed portion does not extend in only one direction as in the dug regions 12, 32, 42, but the recessed portion extends in parallel or substantially parallel to the <1-100> direction, and the recessed portion A nitride semiconductor thin film having excellent surface flatness can be formed on a hill even when the digging region extends parallel to or substantially parallel to the <11-20> direction and has a grid shape. . In this case, the off-angles θa and θb are set so that atoms / molecules as the raw material of the nitride semiconductor thin film attached on the hill are diffused / moved in the long side direction of the hill divided by the dug region, preferable.

  Thus, the surface flatness of the nitride semiconductor thin film grown on the hill could be improved by changing the tilt angle (off angle) of the crystal orientation of the substrate.

  Further, when the above-described tilt of the crystal orientation of the substrate is an off angle θa, an off angle θb, and an off angle composed of both the off angle θa and the off angle θb, the value of each off angle is set to 0.05 °. Even if it is set to less than that, it is practically difficult to make all the off angles of the substrates to be produced less than 0.05. Further, the laser light emitting end face is generally produced by cleavage, but the end face is inclined such that the cleavage is divided by {11-20} and {1-100} planes along the direction of the {0001} plane. For this reason, when the off angle is larger than 4 °, it is difficult to divide the chip. Therefore, the off angle, which is the tilt angle of the crystal orientation of the substrate, is preferably 0.05 ° or more and 4 ° or less.

  Next, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, a nitride semiconductor laser device will be described as an example of a nitride semiconductor device, but the present invention can also be applied to other nitride semiconductor devices. FIG. 11A is a schematic cross-sectional view of the nitride semiconductor laser device in this example, and FIG. 11B is a top view of FIG. FIG. 9B is a schematic cross-sectional view of the processed substrate 90 before the nitride semiconductor thin film is grown according to the embodiment of the present invention, and FIG. 9A is a top view of FIG. 9B. 9 and 11, the plane orientation is also displayed, but the off angle is displayed as zero. For example, the nitride semiconductor growth layer 4 having the configuration shown in FIG. 13 is stacked on the processed substrate 90 shown in FIG. 9 to obtain the nitride semiconductor laser device shown in FIG.

  First, the processed substrate 90 is manufactured by the same method as that for manufacturing the processed substrates 16, 36, and 46 described above. However, the substrate used to manufacture the processed substrate 90 has an off angle θa of −0.35 ° and an off angle θb of −0.02 °. The opening width X of the digging region 91 is 5 μm, the depth Y is 5 μm, and the period between adjacent digging regions 91 is 350 μm.

A nitride semiconductor growth layer 4 composed of a plurality of nitride semiconductor thin films shown in FIG. 13 is stacked on the fabricated processed substrate 90 by appropriately using a known technique such as MOCVD. At this time, the n-type GaN layer 130 has a growth temperature of 1075 ° C., a V / III ratio of the raw material (a group V atom with respect to the number of moles of the flow rate supplied per unit time of the raw material including the group III atom). The ratio of the number of moles of the flow rate supplied per unit time of the raw material to be contained) was formed under a growth condition of 1200. Subsequently, the n-type Al _0.05 Ga _0.95 N first cladding layer 131, the n-type Al _0.08 Ga _0.92 N second cladding layer 132 and the n-type Al _0.05 Ga _{0 at} a growth temperature of 1075 ° C. _.95 N third cladding layer 133 and n-type GaN guide layer 134 were stacked. Further, the multiple quantum well active layer 135, the p-type Al _0.3 Ga _0.7 N evaporation prevention layer 136, the p-type GaN guide layer 137, the p-type Al _0.05 Ga _0.95 N cladding layer 138, and the p A type GaN contact layer 139 was laminated in order. The growth temperature of the multiple quantum well active layer 135 is approximately 800 ° C., and the p-type Al _0.3 Ga _0.7 N evaporation prevention layer 136, the p-type GaN guide layer 137, and the p-type Al _0.05 Ga _0. The growth temperature of the ₉₅ N clad layer 138 and the p-type GaN contact layer 139 is approximately 1030 ° C.

  As described above, the nitride semiconductor growth layer 4 made of a plurality of nitride semiconductor thin films is stacked on the processing substrate 90 having the digging region 91 and the hills 92. The opening width of the digging region 91 and the like are described above. It is not limited to the value of. Further, if the opening width X of the digging region 91 is less than 3 μm, the digging region 91 is easily buried when the nitride semiconductor growth layer 4 is formed, and the nitride semiconductor growth layer 4 Not only are the strains contained therein not released, but the atoms / molecules that are the raw material of the nitride semiconductor thin film deposited on the hill 92 diffuse and move into the digging region 91 due to migration or the like, and are thus stacked on the hill 92. The surface flatness of the nitride semiconductor growth layer 4 is deteriorated, which is not preferable. Also, regarding the depth Y of the digging region 91, if the value is less than 1.5 μm, the digging region 91 is easily buried when the nitride semiconductor growth layer 4 is formed, which is not preferable. Therefore, the opening width X of the digging region 91 is preferably 3 μm or more, and the depth Y of the digging region 91 is preferably 1.5 μm or more. Further, when the total thickness of the nitride semiconductor growth layer 4 formed on the processed substrate 90 is larger than twice the depth Y of the digging region 91, the nitride semiconductor growth layer 4 is stacked on the processed substrate 90. In this case, the digging area 91 is easily filled, which is not preferable. Therefore, the depth Y of the digging region 91 is preferably larger than ½ of the total thickness of the nitride semiconductor growth layer 4 formed on the processed substrate 90.

  Further, the width of the hill 92 between the adjacent digging regions 91 in the direction substantially parallel to the <11-20> direction, that is, the direction perpendicular to the direction in which the digging region 91 extends and parallel to the surface of the hill 92. If (the width of the hill 92) is less than 100 μm, the strain included in the nitride semiconductor growth layer 4 is not released, so that not only cracks are likely to occur, but also the nitride semiconductor laser element on the hill 92 It becomes difficult to produce. If the width of the hill 92 is larger than 2000 μm, the effect of preventing the occurrence of cracks in the nitride semiconductor growth layer 4 is lost. Therefore, the width of the hill 92 is preferably 100 μm or more and 2000 μm or less.

  Further, in the nitride semiconductor growth layer 4, the n-type GaN layer 130 (see FIG. 13) formed on the surface of the processed substrate 90 is very migrated and easily diffuses and moves as compared with the AlGaN layer or the like. For this reason, when the layer thickness of the n-type GaN layer 130 is larger than 0.5 μm, the n-type GaN layer 130 grown on the hill 92 easily flows into the digging region 91. Further, since the entire thickness of the nitride semiconductor growth layer 4 is increased, it is easy to create a situation in which the digging region 91 is easily filled with the nitride semiconductor growth layer 4 as a result. Therefore, the layer thickness of the n-type GaN layer 130 is preferably 0.5 μm or less.

  Furthermore, when the nitride semiconductor growth layer 4 composed of a plurality of nitride semiconductor thin films is laminated, depending on the growth conditions of the respective nitride semiconductor thin films, diffusion / migration due to migration of atoms / molecules as the raw material of the nitride semiconductor thin films occurs. We know that ease is different. In order to improve the surface flatness of the nitride semiconductor growth layer 4 formed on the hill 92, each nitride semiconductor thin film is formed under the condition that suppresses migration of atoms / molecules as a raw material of the nitride semiconductor thin film. Need to grow. As such growth conditions, the surface temperature of the processed substrate is 1050 ° C. or less, and the V / III ratio (including atoms belonging to Group V relative to the number of moles of the flow rate supplied per unit time of the raw material including atoms belonging to Group III) The ratio of the number of moles of the flow rate supplied per unit time of the raw material) is preferably 2250 or more.

  When the surface flatness of the surface of the processed substrate 90 on which the nitride semiconductor growth layer 4 was thus formed was measured, the direction substantially parallel to the <1-100> direction, that is, the direction in which the digging region 91 extends. FIG. 10 shows the measurement result of the surface flatness measured in the direction parallel to the surface. The measurement position is the center of the hill 92. At this time, in the measured 600 μm wide region, the step between the highest and lowest portions of the surface is approximately 20 nm from the graph of FIG. 10, and the wafer whose off angle is almost zero (0.02 ° or less). Compared with the measured value (300 nm) in the case where the processed substrate 6 is produced using the substrate and the nitride semiconductor growth layer 4 is formed, a good surface flatness is obtained.

Further, by forming the nitride semiconductor growth layer 4 on the processed substrate 90 in this manner, the nitride semiconductor laser device shown in FIG. 11 is manufactured. In the nitride semiconductor laser element, a laser stripe 93 as a laser waveguide and a laser stripe 93 are sandwiched between the surfaces of the nitride semiconductor growth layer 4 formed on the hill 92 of the processed substrate 90 including the digging region 91. Thus, a SiO ₂ film 94 for current confinement is formed. A p-side electrode 95 is formed on the surface of the laser stripe 93 and the SiO ₂ film 94, and an n-side electrode 96 is formed on the back surface of the processed substrate 90. Further, the convex portion on the surface of the p-side electrode 95 immediately above the laser stripe 93 is defined as a stripe 97.

Such a nitride semiconductor laser device having a ridge structure is manufactured by appropriately using a well-known technique after the nitride semiconductor growth layer 4 is stacked on the processing substrate 90. Description of is omitted. The nitride semiconductor growth layer 4 is laminated to divide a plurality of nitride semiconductor laser elements formed on the processed substrate 90 (wafer) into individual elements. At this time, first, a part of the processed substrate 90 is removed, and the thickness of the wafer is reduced to about 100 μm. Thereafter, Hf / Al is formed as the n-side electrode 96 on the back side of the processed substrate 90 from the side close to the processed substrate 90. Subsequently, the resonator is cleaved along the direction substantially parallel to the <11-20> direction, that is, the direction perpendicular to the direction in which the digging region 91 extends and the direction parallel to the surface of the hill 92. An end face is formed, and a bar-like one (not shown) provided with a plurality of nitride semiconductor laser elements is formed. In the case of this example, the cleavage surface of the nitride semiconductor is {11-20}, but since it is inclined by the off angle θa °, it is difficult to break during cleavage, and a good cleavage surface cannot be obtained. There was concern. However, in practice, if the off angle is 4 ° or less, a good cleavage plane can be obtained, and it has been confirmed that there is no problem as an end face of the nitride semiconductor laser. At this time, the cavity length of the nitride semiconductor laser element is preferably 300 μm or more and 1200 μm or less. In this example, the resonator length was 600 μm. In addition, a dielectric film made of SiO ₂ and TiO ₂ is alternately deposited on the end face of the resonator formed by cleaving the wafer as described above by using an electron beam deposition method, etc. Form. The dielectric material for forming the dielectric multilayer film is not limited to SiO ₂ / TiO ₂ , and for example, SiO ₂ / Al ₂ O ₃ may be used. In addition, the material used for the n-side electrode 96 is not limited to the above-described materials, and Hf / Al / Mo / Au, Hf / Al / Pt / Au, Hf / Al / W / Au, Hf / Au, Hf / Mo / Au, etc. may be used.

In the nitride semiconductor laser device as shown in FIG. 11, the p-side electrode 95 is only Mo / Au, Mo / Pt / Au, or Au single layer from the side close to the nitride semiconductor growth layer 4. Formed from. In this embodiment, the SiO ₂ film 94 is used as an insulating film for current confinement, but ZrO, TiO ₂ , Si ₂ N ₄ or the like may be used as an insulating film material.

  Individual nitride semiconductor laser elements are obtained by dividing the bar thus obtained into chips. Since this dividing step is performed using a known technique, a detailed description thereof will be omitted.

  In the nitride semiconductor laser device thus fabricated, no cracks were observed. In addition, a plurality of nitride semiconductor laser elements in this example are manufactured, and 100 nitride semiconductor laser elements are randomly taken out from the nitride semiconductor laser elements, and the full width at half maximum of FFP (Far Field Pattern) in the horizontal and vertical directions is measured. did. At this time, when the nitride semiconductor laser element within ± 1 degree with respect to the design value of the half width of the FFP is regarded as a non-defective product, there are 94 nitride semiconductor lasers whose half width of the FFP satisfies the standard. The result was very high yield.

  That is, as described above, the nitride semiconductor growth layer 4 is formed by growing a plurality of nitride semiconductor thin films on the processed substrate 90 having the off angle θa and the off angle θb, thereby suppressing variations in p layer thickness. As a result, the flatness of the nitride semiconductor thin film became good, and further, the generation of cracks was suppressed, and a nitride semiconductor laser device with good characteristics could be produced with a good yield.

  The processed substrate in this example is manufactured by the same method as in Example 1. However, the substrate used for manufacturing the processed substrate has an off angle θa of −0.05 ° and an off angle θb of −0.39 °. The opening width of the digging region is 80 μm, and the period between the adjacent digging regions is 300 μm. Other than that, a nitride semiconductor laser device was fabricated in the same manner as in Example 1.

  Further, in this example, similarly to Example 1, after the nitride semiconductor growth layer 4 was laminated on the processed substrate, the surface flatness of the surface of the nitride semiconductor growth layer 4 formed on the hill was measured. At this time, in the measured region having a width of 600 μm, the level difference between the highest part and the lowest part of the surface is 24 nm or less, and good surface flatness is obtained.

  Also, a plurality of nitride semiconductor laser elements in this example were fabricated, and 100 nitride semiconductor laser elements were randomly taken out from the nitride semiconductor laser elements, and the half widths of the FFP in the horizontal direction and the vertical direction were measured. At this time, when the nitride semiconductor laser element within ± 1 degree with respect to the design value of the half width of the FFP is regarded as a non-defective product, there are 91 nitride semiconductor lasers whose half width of the FFP satisfies the standard. The result was very high yield.

  The processed substrate in this example is manufactured by the same method as in Example 1. However, the substrate used for manufacturing the processed substrate has an off angle θa of 0.21 ° and an off angle θb of −0.21 °. Other than that, a nitride semiconductor laser device was fabricated in the same manner as in Example 1.

  Further, in this example, similarly to Example 1, after the nitride semiconductor growth layer 4 was laminated on the processed substrate, the surface flatness of the surface of the nitride semiconductor growth layer 4 formed on the hill was measured. At this time, in the measured region having a width of 600 μm, the level difference between the highest part and the lowest part of the surface is 10 nm or less, and good surface flatness is obtained.

  Also, a plurality of nitride semiconductor laser elements in this example were fabricated, and 100 nitride semiconductor laser elements were randomly taken out from the nitride semiconductor laser elements, and the half widths of the FFP in the horizontal direction and the vertical direction were measured. At this time, when the nitride semiconductor laser element within ± 1 degree with respect to the design value of the half width of the FFP is regarded as a non-defective product, there are 97 nitride semiconductor lasers whose half width of the FFP satisfies the standard, The result was very high yield.

The processed substrate in this example is manufactured by the same method as in Example 1. However, the substrate used for manufacturing the processed substrate has an off angle θa of 0.10 ° and an off angle θb of −0.02 °. Further, the n-type GaN layer 130, the n-type Al _0.05 Ga _0.95 N first cladding layer 131 and the n-type Al _0.08 Ga _0.92 N second cladding layer 132 constituting the nitride semiconductor growth layer 4. The n-type Al _0.05 Ga _0.95 N third cladding layer 133 and the n-type GaN guide layer 134 have a growth temperature of 1030 ° C., and the n-type GaN layer 130 and the n-type GaN guide layer 134 are grown. Was formed under the growth conditions where the V / III ratio of the raw material was 4500. Other than that, a nitride semiconductor laser device was fabricated in the same manner as in Example 1.

  Further, in this example, similarly to Example 1, after the nitride semiconductor growth layer 4 was laminated on the processed substrate, the surface flatness of the surface of the nitride semiconductor growth layer 4 formed on the hill was measured. At this time, in the measured region having a width of 600 μm, the step difference between the highest part and the lowest part of the surface is 28 nm or less, and good surface flatness is obtained.

  Also, a plurality of nitride semiconductor laser elements in this example were fabricated, and 100 nitride semiconductor laser elements were randomly taken out from the nitride semiconductor laser elements, and the half widths of the FFP in the horizontal direction and the vertical direction were measured. At this time, when the nitride semiconductor laser element within ± 1 degree with respect to the design value of the half width of the FFP is regarded as a non-defective product, there are 90 nitride semiconductor lasers whose half width of the FFP satisfies the standard. The result was very high yield.

Thus, this example has a smaller substrate off-angle value than Examples 1 to 3. However, the n-type GaN layer 130, the n-type Al _0.05 Ga _0.95 N first cladding layer 131, and the n-type Al _0.08 Ga _0.92 N second cladding layer 132 constituting the nitride semiconductor growth layer 4. And the growth conditions of the n-type Al _0.05 Ga _0.95 N third cladding layer 133 and the n-type GaN guide layer 134 are such that the migration is suppressed, so that a nitride semiconductor laser device with good characteristics can be obtained. We were able to make well.

It is the schematic of the process board | substrate which has off angle (theta) a in embodiment of this invention. It is a schematic sectional drawing of the process board | substrate with which the digging area | region of various shapes was formed. It is the schematic of the process board | substrate which has off angle (theta) b degree in embodiment of this invention. It is the schematic of the process board | substrate which does not have an off angle. It is a correlation diagram between the standard deviation σ of the p layer thickness and the yield. FIG. 4 is a correlation diagram between an off angle θa and a standard deviation σ of p layer thickness. It is a correlation diagram of off-angle (theta) b and standard deviation (sigma) of p layer thickness. It is a surface level | step difference plot figure of the wafer which laminated | stacked the nitride semiconductor growth layer on the process board | substrate which has off angle (theta) bdegree in embodiment of this invention. It is the schematic of the processed substrate in Example 1- Example 4 of this invention. It is a surface level | step difference plot figure of the wafer which laminated | stacked the nitride semiconductor growth layer on the process board | substrate in Example 1 of this invention. It is the schematic of the nitride semiconductor laser element in Example 1- Example 4 of this invention. It is the schematic of the wafer which laminated | stacked the nitride semiconductor growth layer on the conventional process board | substrate. It is a schematic sectional drawing of a nitride semiconductor growth layer. It is the surface level | step difference plot figure of the wafer which laminated | stacked the nitride semiconductor growth layer on the conventional process board | substrate. It is explanatory drawing explaining the model of flatness deterioration.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hill 2 Excavation area 4 Nitride semiconductor growth layer 6 Processed substrate 11 Hill 12 Excavation area 13 Upper surface part 14 Bottom surface part 15 Atom and molecule 16 Processed substrate 17 Boundary line fluctuation part 18 Vertical fluctuation part 19 Side part 21 Hill 22 Excavation area 26 Processed substrate 31 Hill 32 Excavation area 33 Upper surface part 34 Bottom surface part 36 Processed substrate 37 Boundary line fluctuation part 38 Vertical fluctuation part 39 Side surface part 41 Hill 42 Excavation area 43 Upper surface part 44 Bottom surface part 46 Process substrate 47 Boundary line fluctuation portion 48 Vertical fluctuation portion 49 Side surface portion 90 Work substrate 91 Excavation region 92 Hill 93 Laser stripe 94 SiO ₂ film 95 P-side electrode 96 N-side electrode 97 Stripe 130 n-type GaN layer 131 n-type Al _0.05 Ga _0.95 N first cladding layer 132 n-type Al _0.08 Ga _0.92 N second cladding layer 133 n-type Al _0.05 Ga _0.95 N third cladding layer 134 n-type GaN guide layer 135 multiple quantum well active layer 136 p-type Al _0.3 Ga _0.7 N evaporation preventing layer,
137 p-type GaN guide layer 138 p-type Al _0.05 Ga _0.95 N clad layer 139 p-type GaN contact layer 151 upper surface growth portion 152 digging region growth portion 153 upper surface portion 154 bottom surface portion 155 growth portion 156 side surface portion

Claims (19)

A processed substrate in which at least a surface is made of a nitride semiconductor, a processed substrate provided with a dug region formed of at least one concave portion and a hill portion which is an unexcavated region on the surface of the nitride semiconductor substrate, and a plurality of the processed substrate on the processed substrate A nitride semiconductor growth layer formed by laminating the nitride semiconductor thin film, and a nitride semiconductor element in which a {0001} plane is used as a principal plane orientation on which the nitride semiconductor growth layer is laminated,
The digging region is not filled with the nitride semiconductor thin film,
The first vector extending from the surface of the hill portion in the normal direction and the starting point of the second vector parallel to the crystal orientation <0001> are defined as the same point between the first vector and the second vector. The nitride semiconductor device, wherein an off angle, which is an angle formed, is 0.05 ° or more and 4 ° or less. The off-angle of the processed substrate is
Of the three axes of the crystal orientation <0001>, crystal orientation <11-20>, and crystal orientation <1-100> that are perpendicular to each other, two of the crystal orientation <0001> and the crystal orientation <1-100> On the first plane constituted by the axes, the start point of the third vector obtained by projecting the second vector onto the first plane and the first vector are the same point, and the first vector and the first vector A first off angle that is an angle formed between the three vectors;
Of the three axes of the crystal orientation <0001>, the crystal orientation <11-20>, and the crystal orientation <1-100> that are perpendicular to each other, the crystal orientation <0001> and the crystal orientation <11-20> On the second plane composed of the two axes, the fourth vector obtained by projecting the second vector onto the second plane and the first vector have the same starting point, and the first vector and A second off angle that is an angle formed between the fourth vector and the fourth vector;
The nitride semiconductor device according to claim 1, comprising: When the first off angle is θa and the second off angle is θb,
The nitride semiconductor device according to claim 2, wherein | θa | ≧ | θb |.   The nitride semiconductor device according to claim 3, wherein 0.09 ° ≦ | θa | °. The nitride semiconductor device according to claim 3, wherein 3 × | θb | ° <| θa | ° <0.09 ° and 0.05 ° ≦ | θa | °. When the first off angle is θa and the second off angle is θb,
The nitride semiconductor device according to claim 2, wherein | θa | ≦ | θb |.   The nitride semiconductor device according to claim 6, wherein 0.2 ° ≦ | θb | °.   2. The concave portion constituting the digging region extends in a stripe shape, and a direction in which the concave portion extends is parallel or substantially parallel to a crystal orientation <1-100> direction. The nitride semiconductor device according to claim 7.   The concave portion constituting the digging region extends in a stripe shape, and a direction in which the concave portion extends is parallel or substantially parallel to a crystal orientation <11-20> direction. The nitride semiconductor device according to any one of claims 1 to 7.   The concave portion constituting the digging region is formed in a grid shape, and one of two perpendicular directions constituting the grid is parallel or substantially parallel to the <11-20> direction and another one direction The nitride semiconductor device according to claim 2, wherein is parallel to or substantially parallel to the <1-100> direction. When the first off angle is θa and the second off angle is θb,
11. The nitride semiconductor according to claim 10, wherein a direction parallel to a long side of the hill portion is parallel or substantially parallel to the <1-100> and | θa | ≧ | θb |. element. When the first off angle is θa and the second off angle is θb,
11. The nitride semiconductor according to claim 10, wherein a direction parallel to a long side of the hill portion is parallel or substantially parallel to the <11-20> and is | θa | ≦ | θb |. element.   The nitride according to any one of claims 2 to 12, wherein a square root of a sum of the square of the first off angle and the square of the second off angle is 0.2 ° or more. Semiconductor element.   14. The nitride semiconductor device according to claim 1, wherein a width of the hill portion sandwiched between adjacent digging regions is not less than 100 μm and not more than 2000 μm.   The nitride semiconductor element according to claim 1, wherein the nitride semiconductor thin film in contact with the processed substrate surface is GaN having a thickness of 0.5 μm or less.   The nitride semiconductor device according to any one of claims 1 to 15, wherein a depth of the concave portion constituting the digging region is 1.5 µm or more. The total thickness of the nitride semiconductor growth layer formed on the hill is T,
The depth of the said recessed part which comprises the said digging area | region is T / 2 or more, The nitride semiconductor element in any one of Claims 1-16 characterized by the above-mentioned.   18. The nitride semiconductor device according to claim 1, wherein an opening width of the concave portion constituting the digging region is 3 μm or more.   When forming a nitride semiconductor growth layer formed by laminating a plurality of the nitride semiconductor thin films, as a growth condition of at least one nitride semiconductor thin film, the surface temperature of the processed substrate is 1050 ° C. or lower, and a group III The ratio of the number of moles of the flow rate supplied per unit time of the raw material containing atoms belonging to Group V to the number of moles of the flow rate supplied per unit time of the raw material containing atoms is 2250 or more. The nitride semiconductor device according to any one of claims 1 to 18.

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