JP2011238884A - Substrate for epitaxial growth, growth method of gan-based semiconductor crystal, semiconductor structure, and gan-based led element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a substrate for epitaxial growth, which can obtain such a structure that a GaN-based semiconductor crystal with low dislocation defect density is grown on a PSS.SOLUTION: A substrate for epitaxial growth comprises: a c-plane sapphire substrate that is capable of performing light diffusion and has an uneven surface on which a GaN-based semiconductor crystal can epitaxially grow; and a growth mask that is partially formed on the uneven surface. The uneven surface includes a first uneven surface that is covered with the growth mask, and a second uneven surface on which the sapphire is exposed.

Description

  The present invention relates to an epitaxial growth substrate, a GaN-based semiconductor crystal growth method, a semiconductor structure, and a GaN-based LED element.

A GaN-based semiconductor is a compound semiconductor represented by the general formula Al _a In _b Ga _1-ab N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1), and is a group III nitride It is also called a semiconductor or a nitride semiconductor. A GaN-based light-emitting diode element (GaN-based LED element) formed by using a GaN-based semiconductor to form a light-emitting structure composed of an n-type conductive layer, a p-type conductive layer, and a light-emitting layer sandwiched between these layers ) Can generate light of near ultraviolet to green wavelengths. A white light emitting diode configured by combining a GaN-based LED element and a phosphor is put into practical use as a light source for a backlight unit of a liquid crystal display or a light source for white illumination.

  A GaN-based LED element is manufactured through a process of epitaxially growing a GaN-based semiconductor crystal on a sapphire substrate by a vapor phase growth method such as MOVPE. Therefore, a GaN-based LED element usually includes a sapphire substrate in its structure, and has a light-emitting structure made of a GaN-based semiconductor on the substrate. Recently, a patterned sapphire substrate (Patterned Sapphire Substrate; hereinafter sometimes abbreviated as “PSS”) is often used as the sapphire substrate.

  The use of PSS contributes to the improvement of the output of the GaN-based LED element through at least one of the improvement of the light extraction efficiency and the quality of the GaN-based semiconductor crystal constituting the light-emitting structure (Patent Document 1, Non-Patent Document 1). ). Non-Patent Document 1 reports a production example of a GaN-based LED element using PSS provided with a patterned surface having a triangular pyramid etched in a hot phosphoric acid-based solution. It has been reported that the area ratio of the c-plane occupying the patterned surface decreases as the pyramid sidewall slope becomes gentler (from 57.4 degrees to 31.6 degrees), and at the same time GaN-based The output of the LED element is increased. On this PSS, since the growth of GaN crystals starts mainly from the c-plane, it is believed that if the area ratio of the c-plane is reduced, the area of crystals with low dislocation defect density formed based on lateral growth will increase. . In addition, it has been found by simulation that the light extraction efficiency increases when the inclination angle of the pyramid sidewall is reduced from 80 degrees to 30 degrees.

International Publication No. WO2002 / 075821 US Pat. No. 6,225,650 US Patent Publication International Publication WO2009 / 020033

Ji-Hao Cheng et al., Applied Physics Letters, 96, 051109 (2010) H. Gao et al., Journal of Applied Physics, 103, 014314 (2008)

  As shown in Non-Patent Document 1, the GaN-based LED element disclosed in Non-Patent Document 1 has achieved the optimization of the PSS uneven surface pattern for the purpose of maximizing the light extraction efficiency of the LED element. Seem. However, there is still room for improvement in the quality of GaN-based semiconductor crystals grown on PSS. That is, if a structure in which a GaN-based semiconductor crystal having a lower dislocation defect density is grown on the PSS can be formed, the output of the GaN-based LED element is expected to be further improved.

  Therefore, the present invention provides an epitaxial growth substrate that provides a structure in which a GaN-based semiconductor crystal having a low dislocation defect density is grown on the PSS, and a method for growing a GaN-based semiconductor crystal having a low dislocation defect density on the PSS. The main purpose is to provide Furthermore, the present invention provides a semiconductor structure having a GaN-based semiconductor crystal with a reduced dislocation defect density on the PSS, and a GaN-based semiconductor having a light emitting layer via the GaN-based semiconductor crystal with a reduced dislocation defect density on the PSS. Providing an LED element is included in its purpose.

According to the first invention, the concavo-convex surface includes a c-plane sapphire substrate having a concavo-convex surface capable of light diffusion and capable of epitaxial growth of a GaN-based semiconductor crystal, and a growth mask partially formed on the concavo-convex surface. There is provided an epitaxial growth substrate having a first irregular surface covered with the growth mask and a second irregular surface from which sapphire is exposed.
The uneven surface capable of diffusing light here is a near-ultraviolet to green wavelength region (a light emission wavelength region of a typical GaN-based LED element having 350 to 550 nm by providing a large number of convex portions and / or concave portions. A surface that can exert a diffusion effect on light having a wavelength within (including range) through scattering, diffraction, refraction, diffuse reflection, and the like. Even when the surface of the c-plane sapphire substrate is such an uneven surface, if the uneven surface includes the sapphire c-plane as at least one of the concave bottom surface or the convex top surface, In addition, GaN-based semiconductor crystals can be epitaxially grown.

  The growth mask is conventionally used for generating ELO (Epitaxial Lateral Overgrowth) of a GaN-based semiconductor crystal. On the surface, the GaN-based semiconductor crystal does not start growing. There are a number of known documents describing ELO of GaN-based semiconductor crystals using a growth mask, and Patent Document 2 and Patent Document 3 are just examples.

  In the epitaxial growth substrate according to the present invention, the concavo-convex surface of the c-plane sapphire substrate has a first concavo-convex surface covered with a growth mask and a second concavo-convex surface from which sapphire is exposed. In vapor phase epitaxial growth of a GaN-based semiconductor crystal using this epitaxial growth substrate, crystal growth is started on the second irregular surface. The initial crystal growth that occurs on the second irregular surface preferably includes lateral growth, but is not limited thereto. Subsequent to crystal growth on the second uneven surface, lateral growth that occurs above the first uneven surface forms a GaN-based semiconductor crystal having a low dislocation defect density. In this lateral growth, a crystal that grows on the second uneven surface is generated as a seed crystal.

  According to the second invention, a step of preparing a c-plane sapphire substrate having a concavo-convex surface capable of diffusing light and allowing epitaxial growth of a GaN-based semiconductor crystal, and by partially forming a growth mask, Providing a first concavo-convex surface covered with a growth mask and a second concavo-convex surface from which sapphire is exposed, and using a vapor phase epitaxial growth method, from above the second concavo-convex surface toward the top of the first concavo-convex surface; A step of laterally growing a GaN-based semiconductor crystal, and a method for growing a GaN-based semiconductor crystal.

  According to the third invention, a c-plane sapphire substrate having a concavo-convex surface on which light diffusion is possible and a GaN-based semiconductor crystal can be epitaxially grown, a growth mask partially formed on the concavo-convex surface, and sandwiching the growth mask A GaN-based semiconductor layer grown so as to cover the uneven surface, and the uneven surface has a first uneven surface covered with the growth mask and a second uneven surface not covered with the growth mask. The GaN-based semiconductor layer is provided with a semiconductor structure including a GaN-based semiconductor crystal laterally grown from the upper portion of the second uneven surface to the upper portion of the first uneven surface.

  According to the fourth invention, a c-plane sapphire substrate having a concavo-convex surface capable of light diffusion and capable of epitaxial growth of a GaN-based semiconductor crystal, a growth mask partially formed on the concavo-convex surface, and sandwiching the growth mask A first GaN-based semiconductor layer grown so as to cover the uneven surface, and an n-type conductive layer, a light-emitting layer, and a p-type layer, each of which is sequentially grown on the first GaN-based semiconductor layer. A first conductive layer, and the uneven surface has a first uneven surface covered with a growth mask and a second uneven surface not covered with the growth mask, and the first GaN-based semiconductor The layer is provided with a GaN-based LED element including a GaN-based semiconductor crystal laterally grown from the upper portion of the second uneven surface toward the upper portion of the first uneven surface.

  According to the present invention, a substrate for epitaxial growth from which a structure in which a GaN-based semiconductor crystal having a low dislocation defect density is grown on a PSS is obtained, a method for growing a GaN-based semiconductor crystal having a low dislocation defect density on a PSS, a dislocation defect Provided are a semiconductor structure having a GaN-based semiconductor crystal with reduced density on a PSS, and a GaN-based LED element having a light emitting layer via a GaN-based semiconductor crystal with reduced dislocation defect density on the PSS.

It is a top view showing the structure of the substrate for epitaxial growth concerning one embodiment of the present invention. It is sectional drawing which shows the structure of the substrate for epitaxial growth which concerns on one Embodiment of this invention. It is sectional drawing which shows the structure of the substrate for epitaxial growth which concerns on one Embodiment of this invention. It is sectional drawing which shows the structure of the substrate for epitaxial growth which concerns on one Embodiment of this invention. It is sectional drawing which shows the structure of the substrate for epitaxial growth which concerns on one Embodiment of this invention. It is a top view showing the structure of the substrate for epitaxial growth concerning one embodiment of the present invention. It is a top view showing the structure of the substrate for epitaxial growth concerning one embodiment of the present invention. It is a top view showing the structure of the substrate for epitaxial growth concerning one embodiment of the present invention. It is a top view showing the structure of the substrate for epitaxial growth concerning one embodiment of the present invention. It is a top view showing the structure of the substrate for epitaxial growth concerning one embodiment of the present invention. It is sectional drawing for demonstrating the growth aspect of the GaN-type semiconductor crystal on the substrate for epitaxial growth which concerns on one Embodiment of this invention. It is sectional drawing which shows the structure of the GaN-type LED element which concerns on one Embodiment of this invention.

1. Epitaxial Growth Substrate FIGS. 1 and 2 schematically show the structure of an epitaxial growth substrate according to an embodiment of the present invention. 1 is a plan view, and FIG. 2 is a cross-sectional view taken along line XX in FIG. The substrate 10 for epitaxial growth is composed of a c-plane sapphire substrate 11 whose upper surface is made uneven by etching, and a growth mask 12 partially formed on the uneven surface.

  As shown in each enlarged view of FIG. 1 and FIG. 2, the upper surface of the c-plane sapphire substrate 11 is an uneven surface. The convex portion is a triangular pyramid, and the uneven surface has a repeating pattern in which the triangular pyramids are evenly arranged. In the partially enlarged view of FIG. 1, the hatched triangular area is the bottom surface of the recess, and each is surrounded by three triangular pyramids. The bottom surface of the recess is a sapphire c-plane, from which epitaxial growth of a GaN-based semiconductor crystal can be started. Note that it is not essential that the bottom surface of the recess is exactly coincident with the sapphire c-plane. This is because the GaN-based semiconductor crystal can be epitaxially grown even from a surface slightly inclined with respect to the sapphire c-plane.

  The uneven surface pattern provided on the c-plane sapphire substrate 11 is not limited to that shown in FIG. For example, the bottom surface of the triangular pyramid may have a rounded shape (a bulging regular triangle). In that case, the area of the bottom surface of the recess is smaller. Alternatively, the triangular pyramids can be completely separated from each other. Instead of the triangular pyramid, the convex portion may be a quadrangular pyramid, a hexagonal pyramid, or a cone.

  In one embodiment, as shown in a cross-sectional view in FIG. 3, the uneven surface provided on the c-plane sapphire substrate 11 may have a convex portion having a trapezoidal cross section. Examples of the convex portion having such a cross section include a truncated pyramid, a truncated cone, and a ridge having a top surface. Such a protrusion may have a sapphire c-plane as the top surface, and in that case, the GaN-based semiconductor crystal can be epitaxially grown from the top surface.

In one embodiment, as shown in a sectional view in FIG. 4, the uneven surface provided on the c-plane sapphire substrate 11 may have a convex portion having a semicircular cross section. The convex portion having such a cross section includes a hemisphere and a ridge with a rounded surface.
In one embodiment, as shown in a cross-sectional view in FIG. 5, the uneven surface provided on the c-plane sapphire substrate 11 may have a concave portion having a V-shaped cross section. The concave portion having such a cross section includes a pit having a triangular pyramid shape, a quadrangular pyramid shape, a hexagonal pyramid shape, a conical shape, or a V-groove. In this case, the top surface is a sapphire c-plane so that epitaxial growth of the GaN-based semiconductor crystal can be started from the top surface of the convex portion.

  The common feature of the concavo-convex surface pattern exemplified above is that the cross-sectional area of the convex portion included in the concavo-convex surface becomes smaller from the base portion toward the upper portion. The cross-sectional area referred to here is an area of a cross section formed by cutting along a plane parallel to the sapphire c-plane. Since the concavo-convex surface having such convex portions includes many inclined surfaces, it is excellent in the effect of improving the light extraction efficiency of the GaN-based LED element. Referring to the teaching of Non-Patent Document 1, this effect is particularly strong when the inclination angle of the convex side wall is close to 30 degrees. Therefore, the inclination angle of the convex side wall on the irregular surface is preferably 20 degrees or more and 60 degrees or less, more preferably 25 degrees or more and 45 degrees or less. In the case of a convex portion having a rounded side wall, such as a hemisphere, the portion where the inclination angle is included in this preferable range may be increased as much as possible.

In addition, on the concavo-convex surface having a convex portion whose cross-sectional area decreases from the base portion toward the upper portion, the raw material easily diffuses to the bottom portion of the concave portion during epitaxial growth of the GaN-based semiconductor crystal. For this reason, it is difficult to form a gap between the concavo-convex surface and the GaN-based semiconductor crystal grown on the upper surface. This is extremely preferable for preventing a decrease in thermal conductivity inside the LED element. The most preferable inclination angle of the convex side wall on the concave and convex surface viewed from this viewpoint is 20 degrees or more and 45 degrees or less.

  In order for the concavo-convex surface provided on the c-plane sapphire substrate 11 to exhibit light diffusibility, the height difference between the concave portion and the convex portion, that is, the height from the deepest portion of the concave portion to the uppermost portion of the convex portion is at least the substrate. The wavelength of the light emitted from the light emitting element using the GaN-based semiconductor may be the same as that inside the GaN-based semiconductor. Taking a blue light emitting device having an emission peak wavelength of 460 nm as an example, in GaN having a refractive index of 2.4, the wavelength of light emitted by this device is 192 nm, and therefore the above height difference should be at least 0.2 μm. . If the light emission wavelength of the light emitting element is in the range of 350 to 550 nm, the above height difference is preferably 0.5 μm or more in order to sufficiently increase the light diffusion effect by the uneven surface. More preferably. On the other hand, if this height difference is made too large, it will be difficult to form a high-quality light-emitting element structure by growing a GaN-based semiconductor crystal on the uneven surface so that the surface becomes flat. Therefore, this height difference is preferably 2.5 μm or less, more preferably 2.0 μm or less.

  In order to increase the light diffusibility of the uneven surface provided on the c-plane sapphire substrate 11, the inclination angle of the side wall of the convex portion is within the above preferable range, and the height difference between the concave portion and the convex portion is within the above preferable range. In addition, it is desirable to form the convex portions or the concave portions with as high a density as possible. Therefore, it is preferable to adopt a repeating pattern in which the convex portions are arranged uniformly on the concave-convex surface having dot-shaped convex portions such as pyramids, cones, truncated cones, and hemispheres. The repeated pattern in which the convex portions are uniformly arranged is a pattern in which each of the many convex portions is arranged at the lattice position of the triangular lattice when the concave and convex surface is viewed from the sapphire c-axis direction. Regardless of the repetitive pattern employed, the repetitive pattern pitch is made as small as possible within a range in which the area of the sapphire c surface, which is the surface on which the growth of the GaN-based semiconductor crystal starts, does not become too small. The ratio of the area occupied by the sapphire c-plane is preferably not less than 5% when the concavo-convex surface is viewed from the sapphire c-axis direction. The same can be said for the arrangement pattern of the concave portions on the concave and convex surface having dot-shaped concave portions (pits) and the pitch setting in the repeated pattern. The same applies to the pitch setting on the concavo-convex surface adopting a repeated pattern in which ridges (convex portions) and grooves (concave portions) are alternately arranged.

In one embodiment, the concavo-convex surface provided on the c-plane sapphire substrate 11 may be an concavo-convex surface in which a large number of concave portions or convex portions are irregularly arranged.
The growth mask 12 is patterned so as to partially cover the uneven surface of the c-plane sapphire substrate 11. In other words, it can be said that the uneven surface includes the first uneven surface 11a covered with the growth mask 12 and the second uneven surface 11b from which sapphire is exposed. During vapor phase epitaxial growth of a GaN-based semiconductor crystal on the epitaxial growth substrate 10, crystal growth is started on the second uneven surface 11b.

As the material of the growth mask 12, a material capable of generating ELO of a GaN-based semiconductor crystal and weakly absorbing light in the near ultraviolet to green wavelength region (including a range of 350 to 550 nm) is used. Preferable examples are oxides, nitrides or oxynitrides of various metals, and particularly those having insulating properties. Particularly preferred are oxides, nitrides or oxynitrides of Si, Ti, Ta or Zr, especially SiO ₂ , SiN _x , SiO _x N _1-x , TiO ₂ and ZnO ₂ .

The thickness of the growth mask 12 may be set within a range where the effect is produced, and is usually within a range of 0.01 to 1 μm. Preferably, the growth mask 12 is formed conformally with respect to the first concavo-convex surface 11a of the c-plane sapphire substrate 11, as shown in partial enlarged views of FIGS. By doing so, the lower surface of the GaN-based semiconductor crystal that laterally grows on the top of the growth mask 12 becomes an uneven surface reflecting the shape of the first uneven surface 11a, so that the GaN-based LED formed using the epitaxial growth substrate 10 The light extraction efficiency of the element is increased. For this reason, the thickness of the growth mask 12 should be smaller than the height difference between the concave and convex portions on the first uneven surface 11a, preferably less than half of the height difference, more preferably 4 minutes. 1 or less.

  In the epitaxial growth substrate 10 shown in FIG. 1, the growth mask 12 is formed so as to form a repetitive pattern in which a plurality of circular openings are evenly arranged. The second uneven surface 11b of the c-plane sapphire substrate 11 is exposed in this opening. The diameter of the opening is preferably set to 1.5 times or more, more preferably 2 times or more of the repetition period of the concavo-convex pattern, so that the second concavo-convex surface 11b surely includes the sapphire c-plane. The area ratio of the second concavo-convex surface 11b to the sum of the areas of the first concavo-convex surface 11a and the second concavo-convex surface 11b is preferably 70% or less, so that the region where the lateral growth of the GaN-based semiconductor crystal occurs is not too small. Preferably it is 50% or less, and may be 30% or less. On the other hand, if the area of the second concavo-convex surface 11b is made too small, the time required for the GaN-based semiconductor crystal that laterally grows during epitaxial growth to completely cover the region on the first concavo-convex surface 11a becomes long, and the manufacturing efficiency decreases. there's a possibility that. Therefore, the area ratio is preferably 5% or more, and more preferably 10% or more.

The shape of the opening provided in the growth mask 12 is not limited to a circle. In one example, it may be a regular triangle as in the example shown in FIG. 6, a parallelogram as in the example shown in FIG. 7, or a regular hexagon as in the example shown in FIG. May be. In any of the examples shown in these drawings, the growth mask 12 is provided with openings having the same size and shape so as to form a repeated pattern. The reason is that a region where lateral growth of the GaN-based semiconductor crystal, that is, a region on the first uneven surface 11a is uniformly distributed in the crystal growth surface of the epitaxial growth substrate 10. (In FIG. 6, FIG. 7, and FIG. 8, illustration of the concave / convex pattern exhibited by the second concave / convex surface is omitted. The same applies to FIG. 9 and FIG. 10).
Furthermore, the shape of the opening provided in the growth mask 12 can be a stripe as in the example shown in FIG. In the examples shown in FIGS. 1, 6, 7 and 8, the pattern formed by the growth mask and the pattern formed by the opening can be interchanged. FIG. 10 shows an example thereof. In the example shown in FIG. 1, the pattern formed by the growth mask and the pattern formed by the opening are interchanged, and the growth mask 12 has a circular shape.

  When the shape of the opening provided in the growth mask 12 is a polygon, each side of the polygon is preferably orthogonal to the M-axis of sapphire. The same applies to the longitudinal direction of the stripe when the shape of the opening is a stripe. This is because the lateral growth rate of the GaN-based semiconductor crystal generated from the upper part of the second uneven surface 11b toward the upper part of the first uneven surface 11a increases. This phenomenon is related to the fact that the A-axis of the GaN-based semiconductor crystal epitaxially grown on the sapphire c-plane is parallel to the M-axis of sapphire.

Next, a method for manufacturing the epitaxial growth substrate 10 will be described.
First, as a starting material, a normal c-plane sapphire substrate, that is, a c-plane sapphire substrate having a mirror-finished flat surface that can be used for epitaxial growth of a GaN-based semiconductor crystal is prepared. The c-plane sapphire substrate may be given an off angle.
Next, the flat surface of the prepared c-plane sapphire substrate is processed by etching to form an uneven surface. In the wet etching technique, a SiO ₂ film having a thickness of about 100 to 500 nm is used as an etching mask, and a solution in which sulfuric acid (H ₂ SO ₄ ) and phosphoric acid (H ₃ PO ₄ ) are mixed is used as an etchant. The mixing ratio is preferably 3: 1 by volume (H ₂ SO ₄ : H ₃ PO ₄ = 3: 1). The formation and patterning of the SiO ₂ mask may be performed using a well-known thin film formation technique and photolithography technique.

As disclosed in International Publication No. WO2009 / 020033 (Patent Document 4), when the sapphire c surface protected by a circular SiO ₂ mask is wet-etched with the above mixed acid, the bottom surface of the protected portion is substantially omitted. A substantially triangular frustum-shaped convex portion having a triangular shape and a substantially circular upper surface is formed. As disclosed in Non-Patent Document 2, this protrusion can be formed into a triangular pyramid by performing an additional wet etching process after removing the SiO ₂ mask. Therefore, in order to form an uneven surface in which triangular pyramids are densely arranged, the SiO ₂ mask formed on the sapphire c surface may be formed in a repeating pattern in which circular patterns are uniformly arranged. The height of the triangular pyramid, the inclination angle of the side wall, and the area of the bottom surface of the recess can be adjusted by the time of an additional wet etching process performed after removing the SiO ₂ mask.

  When dry etching techniques such as RIE (reactive ion etching) and plasma etching are used, it is possible to form an uneven pattern corresponding to the pattern of the etching mask on the c-plane sapphire substrate. Therefore, the degree of freedom in designing the concavo-convex pattern becomes higher. The inclination of the side wall of the convex portion can be controlled based on the etching rate ratio between the etching mask and sapphire. When the etching rate of the etching mask is relatively high, as the sapphire etching proceeds, the etching mask disappears from the peripheral portion and the area is reduced, so that the slope of the side wall of the formed convex portion becomes gentle. This effect is more prominent when an etching mask (an etching mask having a tapered end face) with a smaller film thickness at the periphery than at the center is used. The material of the etching mask is, for example, a photoresist. The end face of the photoresist film can be tapered by post baking after patterning.

It is also possible to use both dry etching and wet etching. For example, an uneven surface with a large inclination angle of the convex side wall is first formed by dry etching, and then a crystal plane with a small inclination angle is exposed on the convex side wall by wet etching. In this method, if necessary, the bottom surface of the recess made of the sapphire c surface formed in the dry etching process may be protected with a SiO ₂ mask before the wet etching process.

After the formation of the uneven surface, a growth mask is partially formed on the uneven surface. There is no limitation on the method of forming the growth mask, and it may be appropriately selected from known thin film forming methods depending on the material. If the growth mask is formed of a metal oxide, nitride, or oxynitride, a plasma CVD method, a vacuum evaporation method, or a sputtering method can be preferably used.
The growth mask can be patterned using a lift-off method. Further, after the growth mask is formed so as to cover the entire concavo-convex surface, it is possible to perform patterning by removing unnecessary portions by using photolithography and etching techniques.

The epitaxial growth substrate 10 can be manufactured by the method described above.
2. Epitaxial growth of GaN-based semiconductor crystal As a method of epitaxially growing a GaN-based semiconductor crystal on the substrate 10 for epitaxial growth, there are MOVPE, HVPE, MBE, sputtering, reactive sputtering, and other epitaxial growth of GaN-based semiconductor crystals. Any method known to be usable can be used. The most preferred method is the MOVPE method.

As is usually done, it is desirable to provide a buffer layer at the interface between sapphire and the GaN-based semiconductor crystal. This buffer layer may be a known low-temperature buffer layer. The low-temperature buffer layer is a buffer layer made of a GaN-based semiconductor material such as GaN, AlGaN, or AlN, which is formed at a lower temperature, for example, 400 to 600 ° C., than when a single crystal thin film is grown using the MOVPE method. is there. As the buffer layer, a GaN-based semiconductor thin film formed by sputtering or reactive sputtering can also be used.

  The growth mode of the GaN-based semiconductor crystal on the epitaxial growth substrate according to the present invention is generally as shown in FIG. FIG. 11A is a cross-sectional view of the epitaxial growth substrate according to the present invention as viewed from a direction perpendicular to the c-axis of sapphire. The epitaxial growth substrate 10 is composed of a c-plane sapphire substrate 11 (unshown of concavo-convex illustration) whose upper surface is a concavo-convex surface, and a growth mask 12 formed on the concavo-convex surface. By partially forming the growth mask 12, the uneven surface is divided into a first uneven surface 11a covered with the growth mask and a second uneven surface 11b from which sapphire is exposed.

  In the process of growing the GaN-based semiconductor layer 21 on the epitaxial growth substrate 10 via the buffer layer, first, as shown in FIG. 11B, crystal growth is performed from the second uneven surface 11b of the c-plane sapphire substrate 11. Be started. When the height of the crystal exceeds the thickness of the growth mask 12, as shown in FIG. 11C, lateral growth using crystals grown on the second uneven surface 11b as seeds starts from above the second uneven surface 11b. It occurs toward the first uneven surface 11a. If the growth is further continued, as shown in FIG. 11 (d), the laterally grown crystals are fused together, and the GaN-based semiconductor crystal forms one layer on the c-plane sapphire substrate 11. That is, the semiconductor structure 20 is formed in which the GaN-based semiconductor layer 21 covers the entire upper surface of the c-plane sapphire substrate 11 with the growth mask 12 interposed therebetween.

3. GaN-based LED element FIG. 12 shows a cross-sectional structure of a GaN-based LED element according to an embodiment of the present invention. The GaN-based LED element 30 includes a c-plane sapphire substrate 11 having a concavo-convex surface (the concavo-convex illustration is omitted) on which the entire upper surface can diffuse light, and a growth mask 12 partially formed on the concavo-convex surface. And a GaN-based semiconductor layer 21 grown so as to cover the uneven surface with the growth mask 12 interposed therebetween. Since the growth mask 12 is partially formed, the upper surface of the c-plane sapphire substrate 11 has a first uneven surface 11 a covered with the growth mask 12 and a second uneven surface 11 b not covered with the growth mask 12. It is divided into and. The GaN-based semiconductor layer 21 includes a GaN-based semiconductor crystal laterally grown from the upper portion of the second uneven surface 11b toward the upper portion of the first uneven surface 11a.

  The GaN-based LED element 30 further includes an n-type contact layer 32, a light emitting layer 33, and a p-type contact layer 34, which are sequentially formed by epitaxially growing a GaN-based semiconductor crystal on the GaN-based semiconductor layer 21. Yes. An n-electrode E <b> 1 is formed on the partially exposed surface of the n-type contact layer 32. A p-electrode E2 is formed on the upper surface of the p-type contact layer 33, and an electrode pad E3 is formed on a part of the p-electrode E2.

The GaN-based semiconductor layer 21 is formed of n-type GaN to which undoped GaN or Si is added. The n-type contact layer 32 is formed of n-type GaN to which Si is added at a concentration of 1 × 10 ¹⁸ cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ . By adding Si to the GaN-based semiconductor layer 21 at such a concentration, the GaN-based semiconductor layer 21 and the n-type contact layer 31 can be integrated. The light emitting layer 32 is a multiple quantum well layer in which a well layer made of a GaN-based semiconductor containing In and a barrier layer having a larger band gap energy than the well layer are alternately stacked. The p-type contact layer 33 is made of p-type GaN to which Mg is added at a concentration of 5 × 10 ^{19 to} 5 × 10 ²⁰ .

An n-type cladding layer (carrier block layer) including an AlGaN layer may be provided between the n-type contact layer 31 and the light emitting layer 32. Further, a p-type cladding layer (carrier block layer) including an AlGaN layer may be provided between the light emitting layer 32 and the p-type contact layer 33. These carrier block layers may be superlattice layers. In addition, a layer having a strain relaxation function or the like can be appropriately provided above and below the light emitting layer 32.

The n-electrode E1 serves both as an ohmic electrode and an electrode pad, and has an ohmic contact layer made of a simple substance or alloy of Al, Ti, Cr, TCO (transparent conductive oxide) or the like at a portion in contact with the n-type contact layer. is doing. The outermost layer of the n electrode E1 is preferably an Au layer.
The p electrode E2 is a translucent electrode made of TCO. An indium oxide-based TCO such as ITO or a zinc oxide-based TCO can be preferably used as the material of the p-electrode E2. The electrode pad E3 is made of a metal having good adhesion to the TCO at the portion in contact with the p electrode E2, and the outermost layer is preferably made of Au.

  When the GaN-based LED element 30 is manufactured, first, an epitaxial growth substrate is prepared in which a growth mask 12 is partially formed on the concavo-convex surface of a c-plane sapphire substrate 11 whose upper surface is processed into a concavo-convex surface. Next, a GaN-based semiconductor layer 21, an n-type contact layer 31, a light-emitting layer 32, and a p-type contact layer 33 are sequentially epitaxially grown on the epitaxial growth substrate via a buffer layer to produce a semiconductor wafer. In this step, the MOVPE method or the reactive sputtering method can be preferably used as the vapor phase epitaxial growth method. Thereafter, an n-electrode E1, a p-electrode E2, and an electrode pad E3 are respectively formed at portions corresponding to the individual elements in the semiconductor wafer, and then the semiconductor wafer is divided into individual elements.

  Preferably, prior to the step of dividing the semiconductor wafer into individual elements, a modified region along the dividing line is formed inside the c-plane sapphire substrate 11 using a laser processing technique, and this modified region is formed in the dividing step. The semiconductor wafer is broken starting from. In the step of forming the modified region, there is a possibility that part of the laser beam for processing is scattered by the uneven surface provided on the c-plane sapphire substrate 11. When absorbed by E2 or E3), heat is generated and one or both of the electrode and the GaN-based semiconductor deteriorate. In order to prevent this, it is desirable to perform a step of forming an electrode after the step of forming the modified region in the c-plane sapphire substrate by laser processing.

4). Preferred Embodiments Preferred embodiments of the present invention are described below.
(1) A c-plane sapphire substrate having a concavo-convex surface on which light diffusion is possible and a GaN-based semiconductor crystal can be epitaxially grown, and a growth mask partially formed on the concavo-convex surface, the concavo-convex surface serving as the growth mask An epitaxial growth substrate having a covered first uneven surface and a second uneven surface from which sapphire is exposed.
(2) The epitaxial growth according to (1) above, wherein the convex portion included in the concavo-convex surface has an area of a cross section formed by cutting along a plane parallel to the sapphire c-plane, and decreases from the base toward the top. Substrate.
(3) The substrate for epitaxial growth according to (2) above, wherein the convex portion included in the concave-convex surface has a portion whose side wall has an inclination angle of 20 degrees or more and 60 degrees or less.
(4) The substrate for epitaxial growth according to (3), wherein the uneven surface has a height difference between a concave portion and a convex portion of 0.5 μm or more and 2.5 μm or less.
(5) The substrate for epitaxial growth according to (4), wherein the ratio of the area occupied by the sapphire c-plane is 5% or more when the concavo-convex surface is viewed from the sapphire c-axis direction.
(6) The epitaxial growth substrate according to any one of (1) to (5), wherein the growth mask is formed conformally with respect to the first uneven surface.
(7) When the uneven surface is viewed from the sapphire c-axis direction, the area ratio of the second uneven surface to the sum of the areas of the first uneven surface and the second uneven surface is 5% or more and 70% or less. The substrate for epitaxial growth according to any one of (1) to (6) above.
(8) A step of preparing a c-plane sapphire substrate having a concavo-convex surface on which light diffusion is possible and a GaN-based semiconductor crystal can be epitaxially grown, and a growth mask is partially formed to cover the concavo-convex surface with the growth mask. Providing a first concavo-convex surface and a second concavo-convex surface from which sapphire is exposed, and using a vapor phase epitaxial growth method, a GaN-based semiconductor crystal is formed from the upper portion of the second concavo-convex surface toward the upper portion of the first concavo-convex surface. A step of laterally growing the GaN-based semiconductor crystal.
(9) A c-plane sapphire substrate having a concavo-convex surface on which light diffusion is possible and a GaN-based semiconductor crystal can be epitaxially grown, a growth mask partially formed on the concavo-convex surface, and the concavo-convex surface sandwiching the growth mask A GaN-based semiconductor layer grown so as to cover the concavo-convex surface, the concavo-convex surface having a first concavo-convex surface covered with the growth mask and a second concavo-convex surface not covered with the growth mask, A semiconductor structure including a GaN-based semiconductor crystal laterally grown from an upper portion of the second uneven surface toward an upper portion of the first uneven surface;
(10) A c-plane sapphire substrate having a concavo-convex surface on which light diffusion is possible and a GaN-based semiconductor crystal can be epitaxially grown, a growth mask partially formed on the concavo-convex surface, and the concavo-convex surface sandwiched by the growth mask A first GaN-based semiconductor layer grown so as to cover, an n-type conductive layer, a light-emitting layer, and a p-type conductive layer, each of which is sequentially grown on the first GaN-based semiconductor layer, and made of a GaN-based semiconductor; The uneven surface has a first uneven surface covered with a growth mask and a second uneven surface not covered with the growth mask, and the first GaN-based semiconductor layer includes the second uneven surface. A GaN-based LED element comprising a GaN-based semiconductor crystal that is laterally grown from the top of the concavo-convex surface toward the top of the first concavo-convex surface.
(11) The GaN as described in (10) above, wherein the convex portion included in the concave-convex surface has a cross-sectional area that is reduced when cutting along a plane parallel to the sapphire c-plane as it goes from the base toward the top. LED element.
(12) The GaN-based LED element according to (11), wherein the convex portion included in the concave-convex surface has a portion whose side wall has an inclination angle of 20 degrees to 60 degrees.
(13) The GaN-based LED element according to (12), wherein the uneven surface has a height difference between a concave portion and a convex portion of 0.5 μm or more and 2.5 μm or less.
(14) The GaN-based LED element according to any one of (10) to (13), wherein the growth mask is formed conformally with respect to the first uneven surface.
(15) When the uneven surface is viewed from the sapphire c-axis direction, the area ratio of the second uneven surface to the sum of the areas of the first uneven surface and the second uneven surface is 5% or more and 70% or less. The GaN-based LED element according to any one of (10) to (15) above.
(16) A wafer preparation step of preparing a semiconductor wafer including a sapphire substrate having an uneven surface capable of diffusing light and a GaN-based semiconductor formed on the sapphire substrate and having a light emitting structure, and each of the semiconductor wafers in the semiconductor wafer An electrode forming step of forming an electrode in a portion corresponding to the element; a dividing step of dividing the semiconductor wafer into individual elements after the electrode forming step; and the semiconductor using laser processing technology prior to the electrode forming step Forming a modified region along a dividing line inside a sapphire substrate included in the wafer, and in the dividing step, the semiconductor wafer is broken starting from the modified region. Production method.
The present invention is not limited to the embodiments or examples explicitly described in the specification and drawings, and various modifications can be made without departing from the spirit of the invention.

DESCRIPTION OF SYMBOLS 10 Epitaxial growth substrate 11 c surface sapphire substrate 11a 1st uneven surface 11b 2nd uneven surface 12 Growth mask 20 Semiconductor structure 21 GaN-based semiconductor layer 30 GaN-based LED element 31 n-type contact layer 32 Light-emitting layer 33 p-type contact layer E1 n Electrode 26
E2 p-electrode 27
E3 electrode pad

International Publication No. WO2002 / 075821 US Pat. No. 6,225,650 US Pat. No. 6,252,261 International Publication WO2009 / 020033

Claims (7)

  A c-plane sapphire substrate having a concavo-convex surface capable of light diffusion and capable of epitaxial growth of a GaN-based semiconductor crystal, and a growth mask partially formed on the concavo-convex surface, the concavo-convex surface covered by the growth mask An epitaxial growth substrate having a first uneven surface and a second uneven surface from which sapphire is exposed.   2. The epitaxial growth substrate according to claim 1, wherein an area of a cross section formed when the convex portion included in the concave-convex surface is cut along a plane parallel to the sapphire c-plane decreases from the base toward the top.   The substrate for epitaxial growth according to claim 2, wherein the convex part included in the uneven surface has a part having an inclination angle of the side wall of 20 degrees or more and 60 degrees or less.   The substrate for epitaxial growth according to claim 3, wherein the uneven surface has a height difference between a concave portion and a convex portion of 0.5 μm or more and 2.5 μm or less.   The epitaxial growth substrate according to claim 4, wherein a ratio of the area occupied by the sapphire c-plane is 5% or more when the uneven surface is viewed from the sapphire c-axis direction.   The epitaxial growth substrate according to claim 1, wherein the growth mask is formed conformally with respect to the first uneven surface.   The area ratio of the second uneven surface with respect to the sum of the areas of the first uneven surface and the second uneven surface when the uneven surface is viewed from the sapphire c-axis direction is 5% or more and 70% or less. The substrate for epitaxial growth as described in any one of 1-6.

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