JP2009238879A - Method of manufacturing optical semiconductor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an optical semiconductor element in which projections contributing to improvement in extraction efficiency of light are formed uniformly on a light emission surface. <P>SOLUTION: The method of manufacturing the optical semiconductor element includes a preprocessing stage of forming a plurality of projections 401 on the light emission surface and a processing stage of subjecting the light emission surface to anisotropic etching 404. The projections 401 are formed in the preprocessing stage and then can be processed by the anisotropic etching 404 in the processing stage, thereby forming the projections 403 so shaped as to improve the extraction efficiency of light uniformly on the light emission surface. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing an optical semiconductor device, and more particularly, to a method for manufacturing an optical semiconductor device in which a light emitting surface is subjected to uneven processing in order to improve light extraction efficiency.

  In general, an optical semiconductor element has a higher refractive index than the resin or air that seals the optical semiconductor element, so that the light emitted from the inside (active layer) of the optical semiconductor element is totally reflected on the light emitting surface. There are horns. The light that reaches the light emitting surface at a critical angle or more is totally reflected by the light emitting surface, repeats internal reflection in the semiconductor layer, and is absorbed by the metal electrode or the active layer. In order to improve the light extraction efficiency of the light emitting surface, it is known to perform uneven processing on the light emitting surface. By applying unevenness to the light emitting surface, the light that enters the light emitting surface at an angle smaller than the critical angle increases, and the light can be emitted to the outside. As a result, light absorbed inside the semiconductor layer is reduced, so that light extraction efficiency is improved.

  As a method for performing the uneven processing, for example, dry etching such as RIE (reactive ion etching), wet etching using an alkaline solution, and the like are well known. In particular, for nitride semiconductors, a method of anisotropically etching the C minus surface with a KOH solution is known, and hexagonal pyramidal projections can be formed relatively easily. Specifically, Non-Patent Documents 1 and 2 describe a method of immersing an optical semiconductor element in a KOH solution. Patent Document 1 discloses photo-enhanced chemical etching (PEC) in which light is irradiated after being immersed in KOH.

Special table 2007-521441 Fujii et al, Appl. Phys. Lett., Vol. 84, No. 6, (2004), pp.855-857 Hock M. Ng et al, J. Appl. Phys., Vol. 94, No. 1, (2003), pp. 650-653

  In order to improve the light extraction efficiency of the light emitting surface, it is desirable to form the protrusions as densely as possible and reduce the flat portions. However, in the method of immersing the above-described conventional optical semiconductor element in a KOH solution, a flat region in which hexagonal pyramidal projections are not formed is generated, and it is difficult to obtain a dense uneven shape.

  Further, the hexagonal pyramidal projections on the light emitting surface cannot contribute to the improvement of light extraction efficiency unless the size is larger than the emission wavelength. However, the size of the hexagonal pyramidal protrusions formed by the conventional method of immersing in a KOH solution varies, and the protrusions larger than the emission wavelength are only a small part of the hexagonal pyramidal protrusions formed. In addition, there are variations in the shape of the projections formed, for example, there are many projections whose apexes are crushed and those where the angle between the bottom surface and the side surface is out of 52 to 64 ° where light can be extracted efficiently. It was. For this reason, there are few protrusions that can contribute to the improvement of the light extraction efficiency, and it has been difficult to significantly improve the light extraction efficiency by the conventional protrusion formation method.

  In the case of an optical semiconductor device having a structure in which the back surface of the growth substrate is used as a light emitting surface, in order to minimize light absorption by the growth substrate, the growth substrate is usually formed by grinding and polishing to a predetermined thickness (5 Slice to about 200 μm). However, since scratches are formed on the surface of the substrate by grinding and polishing, a crystal plane different from other regions appears at the polishing scratches and the periphery thereof. On different crystal planes, the etching rate with respect to an alkaline solution such as KOH is different from the surroundings. As a result, the density, size, shape, and the like of the hexagonal pyramidal protrusions formed in the vicinity of the wound and the other regions are different, and it is difficult to perform uneven processing uniformly in the substrate surface. For this reason, it has been difficult to significantly improve the light extraction efficiency by wet etching. In addition, if the density, size, shape, etc. of the hexagonal pyramidal projections are affected by scratches, it leads to a decrease in yield and further causes an increase in cost.

  In addition, even when wet etching with an alkaline solution is performed as it is without thinning the growth substrate, the surface of the growth substrate is scratched because the normal growth substrate is subjected to surface treatment such as grinding and polishing before shipment. Remains, and the same problem occurs.

  Furthermore, the number and distribution of scratches remaining on the growth substrate differ even with the same type of growth substrate due to differences in the conditions for grinding and polishing of the growth substrate described above, differences in the source of the growth substrate, etc. The subsequent state is also different for each growth substrate, and there is a problem that reproducibility is not good.

  Further, when the light emitting surface is a nitride semiconductor, there is a problem in that wet etching does not easily proceed even when immersed in a relatively strong alkaline solution such as a KOH solution because of its excellent chemical stability. For example, even when the back surface (C minus surface) of a polished GaN substrate is wet etched at 50 ° C. with a 5 mol / L KOH solution for 120 minutes, there are many small hexagonal pyramidal projections that are not effective in light extraction. Many flat surfaces exist and remain unetched. Many are formed in which the angle between the bottom surface and the side surface deviates from 52 to 64 ° at which light can be extracted efficiently.

  An object of the present invention is to provide a method for manufacturing an optical semiconductor element capable of uniformly forming protrusions that contribute to improvement of light extraction efficiency on a light emission surface.

  In order to achieve the above object, the present invention provides the following method for manufacturing an optical semiconductor element. That is, a method for manufacturing an optical semiconductor device having a concavo-convex process on a light emission surface, which includes a pretreatment step for forming a plurality of protrusions on the light emission surface and a processing step for anisotropically etching the light emission surface Is the method. By forming the protrusions in the pretreatment step, the protrusions can be processed by anisotropic etching in the processing step. Therefore, the protrusions having a shape that can contribute to the improvement of the light extraction efficiency are formed on the light emitting surface. It becomes possible to form uniformly.

  The protrusion formed in the pretreatment step preferably has a diameter larger than the emission wavelength of the optical semiconductor element. Thereby, since the diameter of the processus | protrusion processed by anisotropic etching can be made into the light emission wavelength or more, the processus | protrusion of the magnitude | size which can contribute to the improvement of the extraction efficiency of light can be formed.

  In the pretreatment step, a dome-shaped protrusion can be formed. The dome-shaped protrusion can be formed by dry etching. Since dry etching is not easily affected even if there is a scratch or the like on the light emitting surface, it is possible to form protrusions uniformly. As the dry etching, a method of exposing the light emitting surface to plasma containing Si can be used. Since the etching rate changes at the position where Si adheres, Si can be uniformly dispersed on the light emitting surface, and the protrusions can be formed uniformly. For example, the dome-shaped protrusion can be formed by reactive ion etching using plasma containing Si.

It is desirable to form protrusions at a density of 10 ⁷ pieces / cm ² or more and 10 ⁹ pieces / cm ² or less by the pretreatment step.

  The processing step can be a step of processing the projections formed in the pretreatment step into a hexagonal pyramid shape, for example, by wet etching using an alkaline solution. The protrusion formed in the processing step is desirable because it can contribute to the light extraction efficiency when the angle formed by the bottom surface and the side surface is 52 ° or more and 64 ° or less.

The light emitting surface is formed of a nitride semiconductor represented by Al _x In _y Ga _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1). Can be used.

  According to the method for manufacturing an optical semiconductor element of the present invention, before processing the light emitting surface by anisotropic etching, a protrusion is formed in advance by a method that is not easily affected by the state of the light emitting surface. In the isotropic etching step, the protrusion can be processed into a predetermined shape. Therefore, even if there is a scratch or the like on the light emitting surface, a projection having a predetermined shape can be formed uniformly, and the light extraction efficiency can be improved.

  An optical semiconductor device according to an embodiment of the present invention will be described with reference to the drawings.

  In the present invention, the pretreatment process is introduced in advance before the wet etching treatment of the light emitting surface with the alkaline solution, thereby solving the conventional problems and uniformly forming the protrusions that contribute to the improvement of the light extraction efficiency. To do. In the pretreatment step, the protrusions are formed almost uniformly on the light emitting surface by a predetermined method that is not easily affected by the scratches on the light emitting surface such as dry etching. Since this protrusion is processed into a predetermined shape in a later wet etching step, it may have any shape, for example, can be formed in a dome shape. In the wet etching process, the protrusion formed in the pretreatment process may be processed into a protrusion having a predetermined shape that can contribute to light extraction efficiency by anisotropic etching. Thereby, the protrusion of the shape which can contribute to the improvement of the light extraction efficiency can be uniformly formed on the light emission surface.

  In addition, the time required for the entire process is reduced by reducing the time required for the wet etching process.

  First, the structure of the optical semiconductor element manufactured by the manufacturing method of the embodiment of the present invention will be described with reference to FIG. This optical semiconductor element includes a conductive substrate 10, a semiconductor stacked film 20 mounted on one surface of the substrate 10, an n-type electrode 71 mounted on the other surface 11 of the substrate 10, and the semiconductor stacked film 20. And a p-type electrode 72 mounted on. The semiconductor multilayer film 20 includes an n-type semiconductor layer 21, an active layer 22, and a p-type semiconductor layer 23 that are sequentially stacked from the substrate 10 side.

  The surface 11 of the substrate 10 is a light emission surface, and minute protrusions are uniformly formed. Uniformly formed minute protrusions are hexagonal pyramidal protrusions, which improve the light extraction efficiency of the light emission surface. The size of the hexagonal pyramidal projection is preferably equal to or greater than the wavelength of light in order to improve light extraction efficiency, and more preferably equal to or greater than 1 μm. However, since it may cause a decrease in the adhesion of the n-type electrode 71 if it is too large, the size of the hexagonal pyramidal protrusion is preferably in the range of 3 μm or less from this viewpoint. However, the improvement in the adhesion of the n-type electrode 71 can be solved by other means such as disposing a base layer. In that case, it is not necessary to limit the size of the hexagonal pyramidal projection to 3 μm or less.

  It is desirable that the hexagonal pyramidal projections have a side surface angle of 52 ° or more and 64 ° or less in which light can be extracted efficiently.

For example, an n-type GaN substrate can be used as the substrate 10. In this case, the surface on which the semiconductor multilayer film 20 is mounted is a C plus surface (Ga surface), and the light emitting surface 11 on the back surface side is a C minus surface. Each of the n-type semiconductor layer 21, the active layer 22, and the p-type semiconductor layer 23 is made of Al _x In _y Ga _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1). It is made of a nitride-based semiconductor, and includes Si as an n-type dopant and Mg as a p-type dopant. The n-type electrode 71 and the p-type electrode 72 are composed of a single layer or multiple metal layers. The configuration of the semiconductor stacked film 20 is not limited to the above configuration, and a current diffusion layer, a cladding layer, a contact layer, and the like can be arbitrarily inserted in order to improve the light emission efficiency. It is also possible to configure the active layer 22 with a multilayer film (multiple quantum well structure).

  The substrate 10 is not limited to an n-type GaN substrate, and a lightly doped (n-type) GaN substrate or a non-doped GaN substrate is used for the purpose of preventing output reduction of the optical semiconductor element due to light absorption of the growth substrate. It is also possible.

  Next, a method for manufacturing the optical semiconductor element of this embodiment will be described with reference to FIGS. 2A, 3A to 3C, 3D to 3F, and FIG. To do.

(1) Semiconductor layer growth step 201 (FIG. 2)
First, as the semiconductor growth step 201 in FIG. 2, the semiconductor stacked film 20 is formed on the substrate 10 as shown in FIG. For example, an n-type GaN single crystal substrate is used as the substrate 10, and the n-type semiconductor layer 21, the active layer 22, and the p-type semiconductor layer 23 are sequentially formed on the C plus surface by a known growth method such as MOCVD. Epitaxially grow. At this time, since the substrate 10 is thinned in the next step, a thick substrate can be used.

  The growth method and the type of growth substrate are not particularly limited as long as the semiconductor multilayer film 20 can be epitaxially grown, and known techniques and materials can be used. For example, as a growth method, MBE, HVPE, or the like can be used in addition to MOCVD.

(2) Thinning step (grinding / polishing) 202
Next, the substrate 10 is thinned to a predetermined thickness by grinding or polishing. For example, as shown in FIG. 3B, the upper surface side of the semiconductor laminated film is fixed to the sample holder 30 by fixing means such as wax 40, and the back surface (C minus surface) of the substrate 10 is ground and polished. For example, after thinning to 100 μm by grinding, it is mirror-finished by polishing.

  As a method for thinning the substrate 10, a dry etching method or a wet etching method can be used in addition to mechanical processing such as grinding and polishing. The conditions to be set for dry etching and wet etching differ depending on the chemical properties of the material to be sliced.

The thickness of the substrate 10 after thinning may be arbitrary depending on the purpose, and the thinning step 202 may be omitted if unnecessary. In consideration of light absorption and mechanical strength of the growth substrate 10, the total thickness of the semiconductor laminated film 20 and the substrate 10 is desirably 50 to 200 μm. Furthermore, when a lightly doped (non-doped) GaN growth substrate having an extinction coefficient of 1 cm ⁻¹ or less is used, and the thickness of the growth substrate is thinned to 100 μm or less, the light emission output and light emission of the optical semiconductor element obtained by uneven processing. Most preferable in terms of improving efficiency.

(3) Pretreatment process 203
The back surface (the surface on which grinding and polishing has been performed) of the substrate 10 on which the thinning step 202 has been completed becomes the light emission surface 11 of the optical semiconductor element of the present embodiment. In the pretreatment process 203, as shown in FIG. 3C, dry etching, for example, reactive ion etching (RIE) is performed on the light emitting surface 11. At this time, by adding Si to the plasma atmosphere 60 of RIE, the dome-shaped protrusion 401 can be uniformly formed on the light emitting surface 11 as shown in FIG. The reason is that Si atoms are dispersed and adhere to the light emission surface 11, and the Si atoms hinder the reaction between the attached portion of the substrate 10 and the reaction gas, thereby reducing the etching rate. As a result, the attached portion of Si atoms remains from the surrounding area, and becomes a dome-shaped protrusion 401. By adjusting dry etching conditions such as the concentration of Si atoms in the gas, the dome-shaped protrusion 401 can be uniformly formed on the light emitting surface 11.

  As a method of adding Si to the atmosphere, not only a method of adding a gas containing Si in a reaction gas but also a method of arranging a material containing Si around the substrate 10 to be processed by RIE is effective. . For example, as shown in FIG. 3C, Si can be added to the atmosphere during plasma processing by using a Si substrate or a SiC substrate as the holding substrate 50 for fixing the substrate 10 with the semiconductor multilayer film 20. is there. As the holding substrate 50 for fixing the substrate 10 in the pretreatment step 203, the sample holder 30 to which the substrate 10 is fixed in the thinning step 202 can be used as it is. In this case, Si can be added to the plasma processing atmosphere by using a Si substrate or a SiC substrate as the sample holder 30.

  Since the dry etching in the pretreatment process 203 includes physical etching, the dry etching is not easily affected by scratches generated on the light emitting surface 11 by the grinding / polishing in the thinning process 202. For this reason, the dome-shaped protrusion 401 is formed of a dome-shaped protrusion having a substantially uniform size, shape, and density within the surface of the substrate 10.

  The conditions for the plasma treatment (RIE) are set so that the diameter R of the base (in the main plane) of the dome-shaped protrusion 401 to be formed is not less than the emission wavelength λ of the optical semiconductor element, preferably not less than twice the emission wavelength. It is desirable to do.

  The reason for setting in this way is as follows. As shown in FIGS. 4A to 4C, the dome-shaped projection 401 is processed into a hexagonal pyramidal projection by the subsequent wet etching process 204. The inventors have clarified that the correspondence is almost one-to-one. For this reason, the diameter R of the dome-shaped protrusion 401 substantially corresponds to the diameter of the base of the hexagonal pyramidal protrusion 403 formed in the subsequent wet etching step 204. When the substrate 10 is a GaN single crystal, the angle formed by the side ridge and the bottom of the hexagonal pyramidal projection 403 is determined to be 58.4 ° due to the crystal anisotropy of the GaN single crystal. Actually, the angle has a distribution centered at 58.4 ° because it is affected by effects other than crystal anisotropy. Therefore, the diameter R of the dome-shaped protrusion 401 is not less than the emission wavelength of the optical semiconductor element, preferably not less than 1 μm, and the height H is not less than the emission wavelength λ, and preferably H ≧ (λ / 2) · tan α ( However, 52 ° ≦ α ≦ 64 °), more preferably H ≧ (R / 2) · tan α (where 52 ° ≦ α ≦ 64 °) can contribute to the light extraction efficiency. It becomes possible to form hexagonal pyramidal projections having a diameter equal to or greater than the wavelength of light and having a side angle of 52 to 64 ° in which light can be efficiently extracted with high probability.

  Specifically, when the emission wavelength of the optical semiconductor element is 450 nm, the dome-shaped protrusion 401 has a base diameter of 0.45 μm or more, preferably 1 μm or more.

The density of the dome-shaped projections 401 is preferably 10 ⁷ pieces / cm ² or more and 10 ⁹ pieces / cm ² or less, and more preferably about 2 × 10 ⁸ pieces / cm ² .

  The diameter R and the density of the dome-shaped protrusion 401 formed in the pretreatment process 203 can be confirmed by observation with a scanning electron microscope (SEM) or an atomic force microscope (AFM), for example.

As the plasma treatment (RIE) conditions, for example, any one of Cl ₂ , BCl ₃ , CF ₄ , CCl ₄ , or a mixed gas thereof is used as a reaction gas, and a process pressure is 0.1 Pa to 3 Pa (preferably 0). 1Pa inclusive .5Pa), antenna output 100W, bias output 50 W, C1 ₂ gas flow rate 20 sccm, sets the processing time 240 sec. Under this condition, it is possible to form the dome-shaped protrusions 401 having a base portion having a diameter R in the main plane direction of about 1 μm on the light emitting surface 11 at a density of about 10 ⁷ to 10 ⁹ pieces / cm ² .

(4) Concavity and convexity processing step 204 by wet etching
The substrate 10 on which the dome-shaped protrusions 401 are formed by the pretreatment is wet-etched to form the hexagonal pyramidal protrusions uniformly and densely on the light emitting surface 11. For example, this step 204 is performed by using an alkaline solution as the wet etching solution 3 and immersing the substrate 10 with the semiconductor multilayer film 20 as shown in FIG.

In this step 204, anisotropic etching with an alkaline solution is performed starting from the dome-shaped protrusion 401 (FIG. 4A) formed in the step 203. As shown in FIG. 4B, anisotropic etching proceeds by the sequential appearance of a stable surface 404 ({10-1-1} surface in AlInGaN) with respect to an etchant (alkaline solution). Etching progresses extremely slowly when it collides with the stable surface 404 of the dome-shaped projection 401. As a result, as shown in FIGS. 4C, 5A, and 5B, hexagonal pyramidal projections 403 are formed for each dome-shaped projection 401, and the surface 404 becomes the side surface of the hexagonal pyramidal projections. At this time, since the dome-shaped projections 401 are uniformly distributed on the light emitting surface with a density of 10 ⁷ to 10 ⁹ / cm ² , the diameter R of the base of the dome-shaped projection 401 and the base of the hexagonal pyramidal projection 403 are obtained. The diameter R ′ of each corresponds approximately. Further, the height H ′ of the hexagonal pyramidal projection 403 varies somewhat for each hexagonal pyramidal projection 403, but the height (R ′ / 2) tan 58.4 ° determined depending on the crystal structure is the center. Distributed.

  As the alkaline solution, for example, a KOH solution is used, but not limited to this, an NaOH solution or the like can also be used.

  The wet etching conditions are set such that hexagonal pyramidal protrusions 401 having a size that can contribute to the light extraction efficiency are formed. When a KOH solution is used, the etching rate depends on the concentration and temperature of the KOH solution. The higher the concentration, the faster the etching rate, but there is a tendency that the etching rate does not increase to some extent even if the concentration is higher than a predetermined value. For example, in the case of 50 ° C., the etching rate becomes maximum at about 5 mol / L. The size and shape of the finally formed hexagonal pyramidal projection 403 also varies depending on the temperature and time during etching.

  Specifically, for example, the wet etching condition can be set to a condition of immersing the substrate 10 with the semiconductor multilayer film 20 in a KOH solution at 50 ° C. and 5 mol / L for 120 min. Thereby, the hexagonal pyramidal projections 403 having the same size and shape can be formed uniformly and densely within the light emitting surface 11. In addition, when etching is performed under these conditions, the hexagonal pyramidal protrusions 403 having a wavelength of 1 μm or more that can improve the light extraction efficiency and 3 μm or less are difficult to reduce the adhesion of the n-type electrode 71. The hexagonal pyramidal projection 403 can be formed.

  Since the wet etching with the KOH solution acts only on the C minus surface of the GaN crystal, it does not affect the surface of the semiconductor multilayer film 20 whose outermost surface has the C plus surface. However, when the semiconductor layer has poor crystallinity and a part of the C-minus surface is exposed, or an electrode that is easily eroded by an alkaline solution is formed on the semiconductor laminated film 20 before this step, the back surface of the substrate 10 ( It can be covered with an alkali-resistant protective film except for the light emitting surface 11).

(5) Device fabrication process 205
Next, the board | substrate 10 with the semiconductor laminated film 20 is taken out from an alkaline solution, and element-ization is performed. Specifically, a p-type electrode 72 is formed on the surface of the semiconductor multilayer film 20 and an n-type electrode 71 is formed on the light emission surface 11 of the substrate 10 as shown in FIG. Thereafter, as shown in FIG. 3-2 (f), the substrate 10 with the semiconductor laminated film 20 is subdivided to complete individual optical semiconductor elements.

  A known technique can be applied to the configuration and film formation of the electrodes 71 and 72 and the fragmentation method. For example, each electrode material may use various metals, conductive transparent oxide films (transparent electrodes), and the like. When a transparent electrode is used, it is preferable to form a bonding pad for wire bonding on the transparent electrode. Alternatively, a material that efficiently reflects light may be used as the electrode material to form a reflective electrode. For electrode formation, a film forming method such as vapor deposition or sputtering can be used. Various known techniques such as dicing and scribing / breaking can be applied as the subdivision technique.

  As described above, according to the present embodiment, the dome-shaped protrusion 401 can be uniformly and densely formed in advance by introducing the pretreatment process 203 of the wet etching process 204. Thereby, in the wet etching process, the hexagonal pyramidal projections 403 having a size that can contribute to the light extraction efficiency can be formed with high density by processing the dome-shaped projections 401 into the hexagonal pyramidal projections 403. Therefore, an optical semiconductor element with high light extraction efficiency and high light emission output can be provided.

  Further, since the distribution of the hexagonal pyramidal projections 403 can be uniformly formed within the light emitting surface 11 with good reproducibility, the manufacturing yield can be improved.

  Furthermore, since the dome-shaped protrusion 401 is formed in advance, the time required for wet etching can be shortened. As a result, the entire manufacturing time can be shortened and the manufacturing efficiency can be improved.

  In this embodiment, a GaN substrate is used as the substrate 10, and the hexagonal pyramidal projection 403 is formed by using the C minus surface of the thinned substrate 10 as the light emission surface 11. It is also possible to use another substrate such as SiC that allows the semiconductor multilayer film 20 to be epitaxially grown. When used as the substrate 10 of sapphire, SiC, or the like, the dome-shaped protrusion 401 cannot be formed by the pretreatment step 203, and therefore, a step of peeling or removing the substrate 10 is performed instead of the thinning step 202. For example, the substrate 10 is peeled or removed using a technique such as laser lift-off, grinding, wet etching, or dry etching. As a result, the C-minus surface of the n-type semiconductor layer 21 of the semiconductor laminated film 20 is exposed, and the pretreatment step 203 is performed on this surface to form the dome-shaped protrusion 401. When the substrate 10 is peeled or removed, in order to maintain the mechanical strength of the semiconductor laminated film 20 after peeling / removing, the semiconductor laminated film 20 is attached to a support substrate such as a Si substrate through an adhesive layer such as a metal. Metal bonding technology for bonding can be applied.

  As the substrate 10, an insulating substrate such as a lightly doped GaN substrate can be used. In this case, since the n-type electrode 71 cannot be mounted on the substrate 10, a recess reaching the n-type semiconductor layer 21 is provided on the surface of the semiconductor stacked film 20 using a technique such as dry etching. An n-type electrode 71 and an n-pad are formed on the n-type semiconductor layer 21 exposed from the recess. As a result, a lateral or flip chip type optical semiconductor element in which the semiconductor laminated film 20 includes the n-type electrode 71 and the p-type electrode 72 can be obtained.

  The manufacturing method of the present embodiment can be applied to general optical semiconductor elements, particularly nitride-based optical semiconductor elements.

Examples of the present invention will be described below.
The configuration and the manufacturing method of the optical semiconductor element manufactured in this example are the same as the optical semiconductor element configuration in FIG. 1 and the respective manufacturing steps in FIG. 2A described above.

First, an n-type GaN single crystal substrate is used as the substrate 10 and Al _x In _y Ga _1-xy N (0 ≦ x ≦ 1,0) is formed on the C plus surface by a known growth method such as MOCVD. ≦ y ≦ 1, 0 ≦ x + y ≦ 1), which includes an n-type semiconductor layer 21 to which Si or the like is added as an n-type dopant, an active layer 22, and Mg or the like as a p-type dopant. The formed p-type semiconductor layer 23 was sequentially epitaxially grown (step 201 in FIG. 2). As shown in FIG. 3A, the substrate 10 on which the semiconductor multilayer film 20 including the three layers 21, 22, and 23 is mounted is referred to as an optical semiconductor epi-wafer.

  As shown in FIG. 3B, the upper surface of the semiconductor laminated film 20 of the optical semiconductor epiwafer is fixed to the sample holder 30 with wax 40 or the like, and the back surface (C minus surface) of the growth substrate 10 is ground and thinned to 100 μm. Then, a mirror surface was obtained by polishing (thinning step 202).

Next, the sample holder 30 was removed, and the Si substrate was fixed as the holding substrate 50. The back surface (C minus surface) of the growth substrate 10 was plasma-processed by RIE (pretreatment step 203). Since a Si substrate is used as the holding substrate 50, Si atoms are released from the holding substrate 50 into the atmosphere during RIE, and RIE can be performed in an atmosphere containing Si. Conditions of the RIE, reactive gas species _Cl 2, C1 ₂ gas flow rate 20 sccm, process pressure 0.1～3Pa (preferably 0.5～1Pa), antenna output 100W, bias output 50 W, and a processing time 240 sec.

  As a result, a dome-shaped protrusion was formed on the back surface of the substrate 10. An SEM photograph of the obtained sample is shown in FIG. The sample shown in FIG. 6A-1 is a plasma-treated sample under the RIE condition.

  Further, FIG. 6B-1 shows a photograph of a sample in which an Al substrate is used as the holding substrate 50 and the pretreatment process 203 is performed without adding Si in the atmosphere.

In the sample shown in FIG. 6A-1 of this example, a dome-shaped protrusion 401 was formed on the back surface (C minus surface) of the growth substrate 10. Its size, shape, and density were almost uniform in the main plane, and no effect of scratches due to grinding / polishing was observed. Specifically, the dome-shaped protrusions 401 having a diameter of about 1 μm are formed at a density of about 10 ⁷ to 10 ⁹ pieces / cm ² , and the uneven processing 204 later contributes to the improvement of the light emission efficiency. The shape was suitable for processing into a hexagonal pyramidal projection.

According to the experiments by the inventors, the dome-shaped protrusion 401 has a width of 0.5 to 1.5 μm, a height of 0.3 to 0.6 μm, and a density of about 2 × 10 ⁸ pieces / cm ^2. This state is preferable for performing the subsequent unevenness processing step 204.

  On the other hand, in the sample of FIG. 6B-1 in which the pretreatment step 203 was performed without adding Si, although the protrusion was formed, the diameter of the base of the formed protrusion was small. ) In a shape close to a needle shape.

  Next, the unevenness processing step 204 was performed on the back surface (C minus surface) of the growth substrate 10 by immersing the optical semiconductor epiwafer of FIGS. 6A-1 and 6B-1 in an alkaline solution and performing wet etching. . Specifically, the optical semiconductor epiwafer was immersed in a KOH solution at 50 ° C. and 5 mol / L for 120 min. SEM photographs of the obtained sample are shown in FIGS. 6 (a-2) and (b-2), respectively.

  The sample of FIG. 6A-1 added with Si in the pretreatment step 203 has substantially the same size and shape on the back surface (C minus surface) of the growth substrate 10, as can be seen from FIG. 6A-2. The hexagonal pyramidal protrusions were uniformly and densely formed in the plane. The size of the base was 0.5 to 1.5 μm, which was larger than the emission wavelength (450 nm). Moreover, about the shape of the formed hexagonal pyramid structure, it was distributed in the range of the angle of 45-65 degrees which a side surface and a bottom face comprise, and there were most things which have about 58 degrees. For this reason, most of the hexagonal pyramidal projections are within the range of 52 to 64 ° in which the angle formed between the side surface and the bottom surface can contribute to the light extraction efficiency. Therefore, most of the hexagonal pyramidal projections have a shape that can improve the light extraction efficiency.

  On the other hand, in the sample of FIG. 6B-2 in which the pretreatment step 203 was performed without adding Si, the diameter of the protrusion formed in the pretreatment step 203 was small. There were many small things. Moreover, compared with the sample of FIG. 6 (a-2), there were few hexagonal pyramidal protrusions sufficiently larger than the emission wavelength.

  For these reasons, in order to uniformly distribute hexagonal pyramidal projections sufficiently larger than the emission wavelength by wet etching in the unevenness processing step 204, it is preferable to perform in an atmosphere containing Si during the plasma processing in the pretreatment step 203. It became clear that.

  Thereafter, the semiconductor epi-wafer was taken out of the alkaline solution and formed into an element (step 205). Specifically, after forming the p-type electrode 72 and the n-type electrode 71 on the surface of the semiconductor laminated film 20 and the back surface of the growth substrate 10 that has been processed to be concavo-convex, individual optical semiconductors are used by using existing techniques such as scribe / break. Subdivided into elements.

(Comparative example)
As a comparative example, as shown in FIG. 2B, the pretreatment step 203 was not performed, and the other steps 201, 202, 204, and 205 were prepared in the same manner as in the example. FIG. 7 shows an SEM photograph of the back surface of the growth substrate 10 after the unevenness processing step 204 is completed. There was a flat region where hexagonal pyramidal projections were not formed, and hexagonal pyramidal projections could not be formed uniformly. In addition, the size of the hexagonal pyramidal projections varied, and the shape also varied, such as the apexes being crushed. Furthermore, most of the hexagonal pyramidal projections have an angle between the bottom surface and the side surface of 30 ° to 40 °, and many cannot contribute to the improvement of light extraction efficiency.

Sectional drawing of the optical-semiconductor element manufactured with the manufacturing method of this Embodiment. (A) Explanatory drawing which shows the process of the manufacturing method of this Embodiment. (B) Explanatory drawing which shows the process of the manufacturing method of a comparative example. (A)-(c) Explanatory drawing explaining the semiconductor growth process of this Embodiment, a thinning process, and a pre-processing process, respectively. (D)-(f) Explanatory drawing explaining the uneven | corrugated processing process of this Embodiment, an element formation process (an electrode formation process and a chip | tip subdivision process, respectively. (A) In the manufacturing method of this Embodiment, explanatory drawing which shows the dome-shaped protrusion 401 formed at a pre-processing process, (b) and (c) The dome-shaped protrusion 401 is a hexagonal pyramid shape by wet etching at an uneven | corrugated processing process. Explanatory drawing which shows the state processed into the processus | protrusion 403. FIG. The (a) top view of the hexagonal cone-shaped protrusion 403 formed at the uneven | corrugated processing process of this Embodiment, (b) Sectional drawing. (A-1) SEM photograph of the sample subjected to the RIE (pretreatment) step in the atmosphere to which Si was added in this example, (b-1) RIE (pretreatment) step in the atmosphere in which Si was not added in this example. SEM photograph of the sample subjected to the above, (a-2) and (b-2) SEM photograph of the sample obtained by wet etching (unevenness processing step) the above samples (a-1) and (b-1). The SEM photograph of the sample after the uneven | corrugated processing process of a comparative example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Board | substrate, 11 ... Light emission surface, 20 ... Semiconductor laminated film, 21 ... N-type semiconductor layer, 22 ... Active layer, 23 ... P-type semiconductor layer, 71 ... N-type electrode, 72 ... P-type electrode, 30 ... Sample Holder: 40 Wax, 60: Plasma atmosphere, 401: Domed projection, 403: Hexagonal projection, 404: Etching surface.

Claims (10)

A method of manufacturing an optical semiconductor element having irregularities on a light emitting surface,
A pretreatment step of forming a plurality of protrusions on the light emitting surface;
And a processing step of anisotropically etching the light emitting surface.   2. The method of manufacturing an optical semiconductor device according to claim 1, wherein the protrusion formed in the pretreatment step has a diameter larger than an emission wavelength of the optical semiconductor device.   3. The method of manufacturing an optical semiconductor element according to claim 1, wherein the pretreatment step forms a dome-shaped protrusion as the protrusion.   4. The method of manufacturing an optical semiconductor device according to claim 1, wherein the pretreatment step is a step of dry etching the light emitting surface.   5. The method of manufacturing an optical semiconductor device according to claim 4, wherein the pretreatment step is a step of forming the protrusion by exposing the light emitting surface to plasma containing Si. Production method.   6. The method of manufacturing an optical semiconductor device according to claim 5, wherein the pretreatment step is reactive ion etching using plasma containing Si. 7. The method of manufacturing an optical semiconductor device according to claim 1, wherein the pretreatment step forms the protrusions at a density of 10 ⁷ pieces / cm ² or more and 10 ⁹ pieces / cm ² or less. A method of manufacturing an optical semiconductor element characterized by the above.   8. The method of manufacturing an optical semiconductor device according to claim 1, wherein the processing step processes the protrusion formed in the pretreatment step into a hexagonal pyramid shape by wet etching using an alkaline solution. A method of manufacturing an optical semiconductor element, which is a process.   9. The method of manufacturing an optical semiconductor device according to claim 1, wherein an angle formed between a bottom surface and a side surface of the protrusion formed in the processing step is 52 ° or more and 64 ° or less. A method for manufacturing an optical semiconductor element. 10. The method for manufacturing an optical semiconductor device according to claim 1, wherein the light emitting surface is formed of Al _x In _y Ga _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1). , 0 ≦ x + y ≦ 1). A method for manufacturing an optical semiconductor element, characterized by comprising: