JP2007243213A - Surface emitting semiconductor light emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize high performance, high functionality, high reliability, and long lifetime, in a surface emitting semiconductor light emitting element which has a current element layer formed by lateral oxidization. <P>SOLUTION: The element includes a first semiconductor multilayer film mirror 6, a semiconductor active layer 4, and cladding layers 3 and 5 serve as a convex-shaped mesa part. A current constriction part 8 is formed by lateral oxidization of the top layer 2a of a semiconductor multilayer film mirror 2 and the bottom layer 6a of the semiconductor multilayer film mirror 6 from their sides toward the light emitting region 17. These semiconductor multilayer film mirrors 2 and 6 have oxidization anisotropy with a first direction which is easily oxidized to the crystal orientation and a second direction which is not easily oxidized. Distance from the light emitting region to the current constriction part along the first direction is longer than that along the second direction. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a surface emitting semiconductor light emitting device.

  Semiconductor light-emitting elements such as semiconductor lasers and semiconductor light-emitting diodes are used in the field of optical communications, consumer fields such as optical disc systems such as CD (Compact Disc) and DVD (Digital Versatile Disc), and bar code readers, etc. Widely used in fields.

  Among such semiconductor fermenting elements, a surface emitting semiconductor laser has a resonator structure formed by reflecting mirrors provided above and below an active layer, and emits laser light in a direction perpendicular to the substrate. is there.

  This surface-emitting type semiconductor laser attracts a great deal of attention as a key device in the field of optoelectronics in a high-speed optical LAN (Local Area Network), an optical interconnect, and the like because a large number of laser elements can be integrated two-dimensionally on a substrate. ing.

  Features of such a surface emitting semiconductor laser include the following.

  For example, it has a lower threshold value, lower power consumption, higher light emission efficiency, high-speed modulation, less beam divergence, and easier coupling with an optical fiber than an edge-emitting semiconductor laser. It has many advantages such as unnecessary and excellent mass productivity.

  In addition to these features, surface-emitting semiconductor lasers are suitable as light sources for high-speed optical links, and when combined with plastic optical fibers, high-speed optical link light sources are expected to be realized at low cost, and research and development are thriving. Has been done.

  In such a surface emitting semiconductor laser, a current injection part for efficiently injecting a current into the light emitting region is necessary. As a method for forming this current injection portion, a proton injection method and a selective oxidation method are generally used.

  Here, a selective oxidation method that can be formed by simpler process steps will be described.

First, a semiconductor multilayer reflector, a cladding layer, a semiconductor active layer, a cladding layer, a semiconductor multilayer reflector, and a contact layer are sequentially grown on a semiconductor substrate to produce a laser wafer. In this case the semiconductor multilayer reflector, for example, Al _0.95 Ga _0.05 As layer / Al _0.5 Ga _0.5 repetitively laminated structure of As film, also a large Al _x Al composition ratio than film constituting the semiconductor multilayer reflection mirror as the layer to be oxidized It has a Ga _{1 -x} As (x> 0.9) film.

Next, a mesa is formed by etching, and the substrate temperature is heated to 400 ° C. or higher in a water vapor atmosphere. By so doing, the AlGaAs film having a high Al composition ratio among the semiconductor films constituting the semiconductor multilayer mirror is selectively oxidized to become an Al _x O _y film. The oxidation rate varies significantly depending on the Al composition. For example, by setting x = 0.9 to _{1 as} Al _x Ga _1-x As, it is possible to selectively oxidize only the Al high-concentration layer without substantially affecting the cladding layer or the GaAs layer. .

  In this lateral oxidation step, oxidation proceeds from the side surface of the mesa to form a current confinement portion, and a non-oxidized region, that is, an opening portion is formed in the central portion of the mesa. At this time, by appropriately adjusting the temperature and time of the heat treatment, the shape and size of the non-oxidized opening which is a part of the oxidized layer containing Al at a high concentration can be controlled.

  FIG. 5 shows the structure of the surface emitting semiconductor laser formed as described above. 5A is a top view, FIG. 5B is a cross-sectional view in section 1 of FIG. 5A, and FIG. 5C is a cross-sectional view in section 2 of FIG.

  As shown in FIGS. 5B and 5C, this surface-emitting type semiconductor laser includes a semiconductor multilayer reflector 2 in which semiconductor films having different compositions are alternately stacked on a semiconductor substrate 1, a cladding layer 3, and a semiconductor. An active layer 4, a cladding layer 5, a semiconductor multilayer reflector 6 in which semiconductor films having different compositions are alternately stacked, and a contact layer 7 are sequentially stacked.

  As shown in FIG. 5C, at this time, a mesa structure is formed by a part of the semiconductor multilayer reflector 2, the cladding layer 3, the semiconductor active layer 4, the cladding layer 5, the semiconductor multilayer reflector 6, and the contact layer 7. is doing.

  As shown in FIGS. 5A, 5B, and 5C, a recess 16 is formed around the mesa structure. An insulating film 9 such as silicon oxide is formed on the entire element. On the mesa structure, a contact electrode 11 is formed so as to open the light emitting region 17.

  In this mesa structure, the uppermost layer 2a of the semiconductor multilayer film reflecting mirror 2 and the lowermost layer 6a of the semiconductor multilayer film reflecting mirror 6 are oxidizable layers having a high Al composition ratio. Oxidized laterally toward the light emitting region 17 to form a current confinement portion 8.

  The contact electrode 11 is connected to the external connection electrode 12 through the wiring 11a. An electrode 15 is formed on the back surface of the substrate 1.

  In the surface emitting semiconductor laser having such a structure, the structure under the wiring 11a connecting the contact electrode 11 and the external electrode 12 is the same structure as that under the bonding pad 12 without being etched in the mesa formation.

  The current injected from the contact electrode 11 flows in the light emitting region of the semiconductor active layer 3 as shown by an arrow 14 to generate light. However, a part of this current flows from the non-oxidized region below the bonding pad 12 to the active layer 3 via the semiconductor multilayer reflector 6 existing under the wiring 11a as indicated by an arrow 13. There is a problem that this current flows as a leakage current to the outside of the element. For example, this leakage current tends to increase as the diameter of the opening decreases. This is because the smaller the diameter of the opening, the higher the element resistance, and the larger the current that flows to the outside of the mesa structure as indicated by the arrow 13.

  As described above, in the surface emitting semiconductor laser in which the current confinement portion 8 is formed by the conventional selective oxidation method, the occurrence of leakage current flowing under the wiring 11a is unavoidable, and the threshold current, the device capacity increase, and the high-speed response. There is a problem of deterioration.

Further, in the method of forming the current confinement portion by the selective oxidation method, when an AlAs and Al _x Ga _1-x As layer (x> 0.94) containing Al at a high concentration is oxidized, it follows the <100> axis. Oxidation of the surface has a higher oxidation rate than the surface along the <110> axis, and the oxidation rate differs with respect to the plane orientation. Therefore, the shape of the current confinement portion when the element is viewed from the upper surface is not circular.

  FIG. 6 shows the mesa structure when oxidized from the side of the circular mesa structure.

  As shown in FIG. 6A, the oxidation rate of the oxidized layer in the horizontal (x) direction is lower than that in the vertical (y) direction. The shape of the opening has a problem that the aspect ratio of the square changes depending on the oxidation time, and it is not easy to control the output beam shape and the lateral mode.

  In general, a surface emitting semiconductor laser formed by a method of forming a current confinement portion by a selective oxidation method has a large optical confinement effect with a large difference in refractive index between an oxide layer and a non-oxide layer. For this reason, in order to stabilize the transverse mode, it is necessary to narrow the diameter of the light emitting region, that is, the opening, typically to 5 μm or less.

  However, in the conventional method, the opening (the shape of the current constriction when the element is viewed from above) becomes a distorted square shape that is difficult to control, and therefore the size can be controlled with high accuracy. It has become difficult. Furthermore, in a surface emitting semiconductor laser, an inclined substrate is often used instead of a normal (100) plane substrate for controlling the polarization mode. At this time, anisotropic oxidation depending on the crystal plane orientation is performed. According to the tilt angle, the normal circular mesa structure is further distorted, and the opening as shown in FIG. 6B has a rhombus shape, which makes it difficult to obtain the desired shape and transverse mode characteristics. is doing.

Further, in a surface emitting semiconductor laser formed by a method of forming a current confinement portion by a selective oxidation method, when the AlAs layer and the AlGaAs layer having a high Al concentration are steam-oxidized, the volume of the oxidized layer contracts, and the upper and lower layers are reduced. There is a problem of distortion. This is because the oxide Al _x O _y shrinks in volume by about 30% to 40% compared to the original AlAs layer and the high Al concentration AlGaAs layer.

  Therefore, there is a problem that compressive stress is applied to the light emitting region of the semiconductor active layer after oxidation. In order to effectively perform current constriction, the oxidized layer that becomes the current confinement portion needs to have a certain thickness, but the thicker this layer, the greater the distortion. The strain concentrates on the tip of the oxide layer, but the oxidized layer is provided at a close distance of 0.2 μm from the light emitting region, so this strain affects the region where the current is most concentrated in the light emitting region. There is a problem of reducing the life.

  The present invention has been made in order to solve the above-described problems, and suppresses leakage current to the outside of the device, lowers the threshold value, improves high-speed response, and improves mass productivity. Improve oxidation region, shape of outgoing beam pattern and mode control, relieve compressive stress applied to light emitting region by volume contraction when oxidizing Al high concentration layer, and suppress cracks and breakage at interface An object of the present invention is to provide a surface-emitting type semiconductor light-emitting device capable of enhancing the resistance to a thermal process after the selective oxidation process, improving the reliability of the device, and extending the lifetime.

In order to achieve the above object, the present invention provides:
A substrate having first and second major surfaces;
A first electrode formed on a first main surface of the substrate;
Formed on the second main surface, and formed in a columnar shape surrounded by the concave portion, the peripheral portion, and the concave portion, and partially on the peripheral portion via a high resistance region between the end portions of the adjacent concave portions. A first semiconductor multilayer reflector surface layer formed above the first main surface, and a semiconductor formed above the first semiconductor multilayer reflector surface layer. Oxidized with respect to the crystal direction of the active layer, the second semiconductor multilayer reflector surface layer formed above the semiconductor active layer, and the first semiconductor multilayer reflector surface layer or the second semiconductor multilayer reflector surface layer A current path constriction portion having an oxidation anisotropy that exhibits an easy first direction and a second direction that is difficult to be oxidized, and is formed in the vicinity of the semiconductor active layer, and is provided in the first direction. From the light emitting region along the current path constriction A multilayer structure in which the light emitting region is longer than the distance from the light emitting region along the second direction to the current path constricted portion, and the light emitting region is surrounded by the peripheral portion via the recess. And a second electrode that is provided above the light emitting region, has an opening above the current path narrowing portion, and constitutes a current path that passes through the current path narrowing portion and reaches the first electrode;
A third electrode formed on the periphery of the multilayer structure;
A plurality of conductors formed on the high-resistance region and interconnecting the second and third electrodes;
A surface-emitting type semiconductor light-emitting device that emits light in a direction perpendicular to the substrate is provided.

The present invention also provides:
A substrate having first and second major surfaces;
A first electrode formed on a first main surface of the substrate;
Formed on the second main surface, and formed in a columnar shape surrounded by the concave portion, the peripheral portion, and the concave portion, and partially on the peripheral portion via a high resistance region between the end portions of the adjacent concave portions. A first semiconductor multilayer reflector surface layer formed above the first main surface, and a semiconductor formed above the first semiconductor multilayer reflector surface layer. Oxidized with respect to the crystal direction of the active layer, the second semiconductor multilayer reflector surface layer formed above the semiconductor active layer, and the first semiconductor multilayer reflector surface layer or the second semiconductor multilayer reflector surface layer A current confinement portion having an oxidation anisotropy formed in the vicinity of the semiconductor active layer and having an oxidation anisotropy in a first direction that is easy to be oxidized and a second direction that is difficult to be oxidized; Directed to the high resistance region, The light emitting region is formed on the multilayer structure surrounded by the peripheral portion and the upper surface of the light emitting region, and has an opening above the current path narrowing portion, and passes through the current path narrowing portion. A second electrode constituting a current path to one electrode;
A third electrode formed on the periphery of the multilayer structure;
A plurality of conductors formed on the high-resistance region and interconnecting the second and third electrodes;
A surface-emitting type semiconductor light-emitting device that emits light in a direction perpendicular to the substrate is provided.

  It is preferable that a film having a tensile stress is further provided on the surface portion of the multilayer structure.

  It is preferable that a vertical cavity resonator is constituted by the first and second multilayer reflector layers.

  It is preferable that the second electrode is formed in an annular shape in the periphery of the upper surface of the light emitting region, and the third electrode has an annular region surrounding the recess and a pad region for external connection in the peripheral portion.

  It is preferable that the concave portion is disposed symmetrically with respect to the center of the light emitting region.

The present invention also includes a substrate,
A semiconductor active layer having a light emitting region formed on the substrate;
A first semiconductor multilayer film reflecting mirror formed on a side opposite to the substrate with respect to the semiconductor active layer, wherein the semiconductor active layer is sandwiched and a resonator in a direction perpendicular to the substrate is formed, and the semiconductor A second semiconductor multilayer film reflecting mirror formed on the substrate side with respect to the active layer;
A pair of electrodes for injecting a current into the semiconductor active layer through the first semiconductor multilayer reflector and the second semiconductor multilayer reflector respectively;
A current confinement for narrowing the current injected from the pair of electrodes to the light emitting region formed by oxidizing an oxidized layer formed in the vicinity of the semiconductor active layer from the side surface toward the light emitting region. And
Including at least the first semiconductor multilayer film reflector, a recess provided in the oxidized layer, and a mesa portion surrounded by the recess;
The current confinement portion has a direction that is easy to oxidize and a direction that is difficult to oxidize with respect to a crystal direction in the plane of the semiconductor multilayer reflector, and the current confinement portion is formed from the side surface in the direction that is easy to oxidize. A surface-emitting type semiconductor light emitting device characterized in that the distance from the side surface to the light emitting region is short in the direction in which the distance to the light emitting region is long and difficult to oxidize.

    Since the distance to the light-emitting region is changed according to the oxidation speed, distortion of the non-oxidized region due to anisotropic oxidation in the selective oxidation process can be corrected, and the shape and mode characteristics of the outgoing beam pattern can be easily controlled. Become.

The present invention also includes a substrate,
A semiconductor active layer having a light emitting region formed on the substrate;
A first semiconductor multilayer film reflecting mirror formed on a side opposite to the substrate with respect to the semiconductor active layer, wherein the semiconductor active layer is sandwiched and a resonator in a direction perpendicular to the substrate is formed, and the semiconductor A second semiconductor multilayer film reflecting mirror formed on the substrate side with respect to the active layer;
A pair of electrodes for injecting a current into the semiconductor active layer through the first semiconductor multilayer reflector and the second semiconductor multilayer reflector respectively;
A current confinement for narrowing the current injected from the pair of electrodes to the light emitting region formed by oxidizing an oxidized layer formed in the vicinity of the semiconductor active layer from the side surface toward the light emitting region. And
Comprising at least the first semiconductor multilayer film reflector, a recess provided in the oxidized layer, a mesa portion surrounded by the recess, and a peripheral portion formed by being separated from the mesa portion by the recess;
The current confinement portion has a direction that is easy to oxidize and a direction that is hard to oxidize with respect to a crystal direction in the plane of the semiconductor multilayer reflector, and is in a columnar shape in contact with the side surface of the mesa portion in the direction that is easily oxidized. Provided is a surface-emitting type semiconductor light emitting device characterized in that a semiconductor multilayer film is formed.

    Since the columnar semiconductor multilayer film is left in the direction where the oxidation rate is fast so as to prevent oxidation, distortion of the non-oxidized region due to anisotropic oxidation in the selective oxidation process can be corrected, and the output beam pattern can be corrected. The shape and mode characteristics can be easily controlled.

    At this time, a film having a tensile stress is formed on the first semiconductor multilayer film reflecting mirror or the substrate in order to relieve the stress generated by the volume shrinkage caused when the current confinement portion is oxidized. It is preferable.

    The film having tensile stress is preferably made of silicon nitride.

    By doing so, the compressive stress to the light emitting region applied by the volume shrinkage of the Al high concentration layer can be relaxed, cracks and breakage at the interface are suppressed, and the thermal process after the selective oxidation process is suppressed. The durability is also improved, and the reliability of the element can be improved and the lifetime can be extended.

According to the present invention, in a surface-emitting type semiconductor light emitting device in which a current element layer is formed by lateral oxidation, high performance, high functionality, high reliability, and long life can be achieved by a simple and low cost manufacturing method. An element structure that can be realized is obtained.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to the following embodiment, It can be used with various devices.

(Embodiment 1)
1A and 1B are views showing the structure of a surface-emitting type semiconductor light emitting device according to Embodiment 1 of the present invention, in which FIG. 1A is a top view, FIG. FIG. 3 is a cross-sectional view of the cross section 2 of FIG. Here, a surface emitting semiconductor laser will be described.

    This surface emitting semiconductor laser includes a semiconductor active layer 3 having a light emitting region 17 on a substrate 1 and a semiconductor active layer 4 that sandwiches the semiconductor active layer 3 and forms a resonator perpendicular to the substrate 1. The first semiconductor multilayer film reflecting mirror 6 formed on the side opposite to the substrate 1 and the second semiconductor multilayer film reflecting mirror 2 formed on the substrate 1 side with respect to the semiconductor active layer 3 are formed. . Semiconductor clad layers 3 and 5 are formed on both surfaces of the semiconductor active layer 3.

    A contact layer 7 is formed on the first semiconductor multilayer film reflecting mirror 6, and a contact electrode 11 for injecting a current into the light emitting region 17 is formed therethrough. The contact electrode 11 is formed so as to open on the light emitting region 17.

    An electrode 15 is formed on the back surface of the substrate 1, and a current is injected into the light emitting region 17 through the second semiconductor multilayer film reflecting mirror 2.

    The first semiconductor multilayer mirror 6, the semiconductor active layer 4, and the cladding layers 3 and 5 are convex mesa portions. The uppermost layer 2 a of the semiconductor multilayer film reflector 2 and the lowermost layer 6 a of the semiconductor multilayer film reflector 6 are oxidized in the lateral direction from the side surface toward the light emitting region 17, thereby forming a current confinement portion 8. The current confinement portion 8 is for narrowing the current to the light emitting region 17.

    A recess 16 is provided around the mesa portion including the first semiconductor multilayer mirror 6 and the semiconductor active layer 3. A peripheral portion 18 is formed by the recess so as to be separated from the mesa portion. This peripheral portion also has the same laminated structure as the mesa structure. The surface of the mesa portion and the surface of the peripheral portion are formed at substantially the same height.

    A peripheral electrode 11 b is formed on the peripheral portion 18. The contact electrode 11 and the peripheral electrode 11b are connected by a wiring part 11a. A cavity 20 is provided below the wiring portion 11a. Reference numeral 9 denotes a film having a tensile stress formed on the surface, for example, a film made of a silicon nitride film, which is used not only as a stress control but also as an etching mask film for pattern formation, and the contact electrode 11 and the peripheral electrode 11b are formed. Under the connecting wiring part 11a, it is also a bridge for the cavity 20.

    Such a surface-emitting type semiconductor laser can emit light by injecting a current from the contact electrode 11 into the light emitting region 17 through the first semiconductor multilayer film reflecting mirror 6 as indicated by an arrow 14.

    At this time, since the cavity layer 20 is formed in the lower layer of the wiring portion 11 a that connects the contact electrode 11 and the peripheral electrode 11 b, the current path as indicated by the arrow 13 cannot flow through the empty window 20. Therefore, in this surface-emitting type semiconductor laser, current can flow only by the path indicated by the arrow 14, current can be confined very efficiently, and low threshold value, high speed response, and mass productivity can be improved. Become.

    Next, a method for manufacturing such a surface emitting semiconductor laser will be specifically described.

    First, an n-type semiconductor multilayer mirror 2, an oxidized layer 2a, a cladding layer 3, a semiconductor active layer 4, and a cladding layer are formed on a cleaned 3-inch n-type GaAs substrate 1 having a thickness of 400 μm using an MOCVD apparatus. 5. Oxidized layer 6a, semiconductor multilayer film reflecting mirror 6, and contact layer 7 are formed.

    Here, a structure in which the semiconductor multilayer reflectors 2 and 6 are arranged above and below the resonator composed of the semiconductor active layer 4 and the cladding layers 3 and 5 has a basic structure, and is designed as a 650 nm band red InGaAlP surface emitting semiconductor laser. Produced.

The semiconductor multilayer reflector 2 was an AlGaAs semiconductor multilayer reflector into which n-type impurities were introduced at 1 × 10 ¹⁸ / cm ³ . The clad layer 3 was made of n-type In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P. The semiconductor active layer 4 has a quantum well structure composed of In _x Ga _1-x P / In _0.5 (Ga _0.5 Al _0.5 ) _0.5 P adjusted so that the emission peak wavelength is 650 nm. The structure was such that five InGaAlP layers were formed. The clad layer 5 was made of p-type In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P. The semiconductor multilayer mirror 6 is an AlGaAs-based semiconductor multilayer mirror in which 1 × 10 ¹⁸ / cm ^{3 of} p-type impurities are introduced.

As the oxidized film 2 a, Al _x Ga _1-x As (x> 0.98), which is formed immediately below the cladding layer 3 and has an Al composition ratio larger than that of AlGaAs constituting the semiconductor multilayer film reflecting mirror 2, was used. As the oxidized film 6 a, Al _x Ga _1-x As (x> 0.98), which is formed immediately above the cladding layer 5 and has a larger Al composition ratio than AlGaAs constituting the semiconductor multilayer film reflecting mirror 6, was used. The contact layer 7 is made of GaAs.

Here, in the AlGaAs-based semiconductor multilayer mirrors 2 and 6, an Al _0.95 Ga _0.05 As layer and an Al _0.5 Ga _0. A structure in which ₅ As layers were alternately stacked was used.

Next, a film 9 having a tensile stress is formed. Here, a Si ₃ N ₄ film was formed by PECVD (Plasma Enhanced Chemical Vapor Deposition). At this time, the film stress was controlled by adjusting the pressure and flow rate of the raw material gases SiH ₄ , NH ₃ , and N ₂ to form a film having a tensile stress of 150 MPa.

The value of the tensile stress of the film 9 was determined by the following equation in consideration of the thermal stress σ _T generated between the film 19 and the GaAs substrate 1.

σ _T = E _F (α _F -α _S ) ΔT
Where α _F , α _S : thin film, coefficient of thermal expansion of the substrate 1, E _F : Young's modulus of the thin film, ΔT: temperature rise When the steam oxidation process temperature is set to 420 ° C., ΔT = 400K. For thin film Si ₃ N ₄ (E _F = 160 GPa, α _F = 2.7 × 10 ⁻⁷ / K) and substrate GaAs (α _S = 6.0 × 10 ⁻⁶ / K), σ _T = −158 MPa Compressive stress is generated.

Therefore, in this embodiment, in order to relieve this compressive stress, the film | membrane 9 which has a tensile stress is formed, the compressive stress applied to the semiconductor active layer 4 is relieve | moderated, and heat resistance is improved. On the other hand, in the case of the etching mask film often used in the conventional example, the thin film SiO ₂ (E _F = 74 GPa, α _F = 0.4 × 10 ⁻⁶ / K), the substrate GaAs (α _S = 6.0 × 10). ⁻⁶ / K), in addition to α _T = −124 MPa (compressive stress), the film-forming stress tends to be a film having a compressive stress of about −200 MPa. Therefore, the compressive stress applied to the semiconductor active layer 4 is further increased and the heat resistance is also weak.

    Next, a commercially available photoresist is spin-coated with a spin coater. Next, a baking process is performed using a hot plate to form a 350 nm-thick photosensitive film. Next, the mask pattern is exposed and transferred using a stepper.

    In this step, first, marks for alignment of various patterns are exposed and transferred, developed and baked to form a pattern on the photosensitive film.

    Next, etching is performed based on the photosensitive film pattern to form a mark pattern for alignment on the stress-controlled etching mask film 9. The photosensitive film is removed by oxygen plasma ashing.

Thereafter, only the contact layer 7 under the etching mask film 9 is subjected to the etching of the mark pattern by a wet etching process using a NH ₃ / H ₂ O ₂ mixed solution.

    Thereafter, a commercially available photoresist is spin-coated and baked using a hot plate to form a 350 nm-thick photosensitive film. Next, the contact hole pattern is exposed and transferred using a stepper and developed with a developer. Next, post-baking is performed to form a contact hole pattern in the photosensitive film. Next, etching is performed based on the photosensitive film pattern to form a contact pattern on the etching mask film 9. Next, the photosensitive film is removed by oxygen plasma ashing.

    Similarly, a commercially available photoresist is spin-coated and baked using a hot plate. Next, a 350 nm-thick photosensitive film is formed, and the pattern is exposed and transferred to the surface p-side contact electrode 11, bonding pad 12, wiring 11a, and peripheral electrode 11b together using a stepper. Next, it develops with a developing solution and performs post-baking. In this way, a pattern of the p-side contact electrode 11, the bonding pad 12, the wiring 11a, and the peripheral electrode 11b is formed on the photosensitive film.

    Next, a Ti / Pt / Au film is formed on the photosensitive film pattern by an electron gun vapor deposition apparatus, and a contact electrode 11 is formed by lift-off and sintering.

    Thereafter, the GaAs contact layer 7 is subjected to pattern etching as a step of opening the window region of the laser beam. Thereafter, a commercially available photoresist is spin-coated and baked using a hot plate. Next, a 350 nm-thick photosensitive film is formed, and a mesa structure forming pattern is exposed and transferred using a stepper. Next, it develops with a developing solution and performs post-baking. Next, a mesa structure forming pattern is formed on the photosensitive film, and etching is performed based on the photosensitive film pattern. Next, a mesa structure forming pattern is formed on the etching mask film 9.

    Next, plasma dry etching with a chlorine-based gas is performed based on the pattern formed on the etching mask film 9 to form a mesa portion. Next, the photosensitive film is removed by oxygen plasma ashing.

    In the plasma etching for forming the mesa structure at this time, etching is performed until the end portions of the oxidized layers 6a and 2a are exposed to the side surfaces of the mesa structure as shown in FIG. At this time, etching is performed so that the mesa etch region (concave portion) is divided into a plurality of portions.

    Next, heat treatment is performed at 400 ° C. to 500 ° C. in a water vapor atmosphere to selectively oxidize the oxidized layers 6a and 2a in the lateral direction.

    FIG. 2A shows the shape (non-oxidized region) and mesa-etched region (recessed portion) of the light-emitting region that remains without being oxidized in the mesa structure.

    In this embodiment, the oxidized layers 6a and 2a (see FIG. 1C) under the cavity 20 are formed in a direction that is easily oxidized (that is, the oxidation rate is high) with respect to the oxidized layers 6a and 2a. Yes. In addition, the other side faces are less likely to be oxidized (that is, the oxidation rate is slower) than this.

    Further, the distance from the side surfaces of the oxidized layers 6a and 2a under the cavity 20 to the light emitting region is long, and the distance from the side surfaces of the other oxidized layers 6 and 2a to the light emitting region is short. That is, in the direction in which the oxidized layers 6a and 2a are easily oxidized, the distance to be oxidized is long, and in the direction that is not easily oxidized, the distance to be oxidized is short. As a result, the opening has a more circular shape (for comparison, FIG. 6A).

    This is because the internal oxidation can be delayed compared to the inside of the mesa etch 16 at the boundary portion of the mesa etch (concave portion) 16 that is divided into a plurality and arranged at symmetrical positions. Thus, the non-oxidized region 30 can be controlled to an arbitrary shape.

    FIG. 2B shows a case where the mesa etch 16 portion is further subdivided. By further subdividing in this way, it is possible to make the shape of the non-oxidized region 30 closer to a circle.

    Further, as shown in FIG. 2 (c), the shape of the non-oxidized region 30 can be reduced by cutting the mesa structure that is difficult to be laterally oxidized, and by controlling the distance between the side surface and the light emitting region to be short. Furthermore, it is possible to make it close to a circle.

    In the present embodiment, an inclined substrate may be used as the substrate 1 in order to control the polarization mode.

    FIG. 3 shows the shape of the light emitting region (non-oxidized region) left unoxidized in the mesa structure at this time.

    First, the oxidation rate of the plane orientation with respect to the tilt angle of the tilted substrate is obtained, and when the mesa etch regions shown in FIGS. 3 (a), (b), and (c) are arranged, desired square, rectangular, and circle shapes are obtained. It was shown that This method is described below.

    First, in the present embodiment, the electrode wiring to the center of the element was performed as a thin path wiring having symmetry, with a pattern having a path line width of 1 to 5 μm. In the shape control of the non-oxidized region, if the desired shape is a square or a rectangle, the narrower width at the junction with the mesa region is more suitable for preventing the non-oxidized region from being diversified. is there.

Here, the line width of the wiring path is reduced in the internal direction of the element. When forming a rectangular or square non-oxidized shape of length l, m, the oxidation rate of the surface along the <100> axis at a temperature T ° C. of Al _x Ga _1-x As (x> 0.94) is expressed as a (x, T), where the oxidation rate of the surface along the <110> axis is b (x, T), and the lengths of the mesa portions in the oxidation progress direction are R ₁ and R ₂ , respectively.
R ₂ = m + b (x, T) x (R ₁ -l) / a (x, T)
When an elliptical or circular mesa structure having the diameters R ₁ and R ₂ that satisfies the relationship is satisfied, a rectangular or square non-oxidized shape having a desired length l and m can be formed.

    Further, in the inclined substrate, the mesa-etched region 16 is divided into mesa-etched pattern shapes and pattern arrangements that are close to or away from the element center according to the surface direction oxidation rate, thereby obtaining a desired non-oxidized region shape, The size can be controlled.

Here, the oxidation rate is corrected by f ₁ (x, T, θ), f ₂ (x, T, θ) for a (x, T), and f ₃ ( x, T, θ), f ₄ (x, T, θ)
R ₂ = m + b (x, T) × (R ₁ -l) / a (x, T) × (f ₃ (x, T, θ) + f ₄ (x, T, θ)) / (f ₁ (x, T, θ) + f ₂ (x, T, θ))
When the elliptical or circular pseudo-mesa structure having the diameters R ₁ and R ₂ that satisfies the relationship is satisfied, a rectangular or square non-oxidized shape having a desired length l and m can be formed.

Further, as shown in FIG. 3A, in the case of the mesa etch region divided into four, the distance from the mesa center point to each mesa etch region is represented by r ₁ , r ₂ , r ₃ , r ₄ ,
r ₁ = l / 2 + f ₁ (x, T, θ) × (R ₁ -l) / (f ₁ (x, T, θ) + f ₂ (x, T, θ))
r ₂ = l / 2 + f ₂ (x, T, θ) × (R ₁ -l) / (f ₁ (x, T, θ) + f ₂ (x, T, θ))
r ₃ = m / 2 + b (x, T) × f ₃ (x, T, θ) × (R ₁ -l) / (f ₁ (x, T, θ) + f ₂ (x, T, θ) )
r ₄ = m / 2 + b (x, T) × f ₄ (x, T, θ) × (R ₁ -l) / (f ₁ (x, T, θ) + f ₂ (x, T, θ) )
R ₁ = r ₁ + r ₂ , R ₂ = r ₃ + r ₄
If an elliptical or circular pseudo mesa structure satisfying the above relationship is formed, a rectangular or square non-oxidized shape having a desired length l and m can be formed at the mesa center.

    Next, after forming a current confinement portion by steam oxidation, a commercially available photoresist is spin-coated and baked using a hot plate. Next, a photosensitive film having a thickness of 350 nm is formed, and exposure and transfer for isolation are performed using a stepper. Next, it develops with a developing solution and performs post-baking. Next, an isolation pattern is formed on the photosensitive film, and the etching time is adjusted with a mixed solution of sulfuric acid / hydrogen peroxide solution with respect to the width 1 μm to 5 μm of the wiring 11a based on the photosensitive film pattern. By performing the etching process, the GaAs (contact) layer 7 and the semiconductor multilayer film reflecting mirror 6 under the wiring 11a are removed by etching, and a cavity 20 is formed.

    At this time, the mesa region protected by the resist and the lower layer region below the oxidized layer 6a protected by the oxide layer are hardly etched even under the wiring 11a.

    In this way, as shown in FIG. 1, the cavity 20 is formed under the wiring 11a, and the leakage current outside the mesa region is completely prevented. Here, the line width of the wiring 11a is not particularly limited as long as a part of the lower layer of the wiring 11a can be removed and the cavity 20 can be formed. In particular, when the side surface of the mesa region (element portion) is protected with a resist, the line width is not a problem at all.

    On the other hand, when the side surface of the mesa region (element portion) is not protected by the resist, the lower contact layer and the semiconductor multilayer reflector 2 are also etched away on the side surface of the mesa region, so that the cavity 20 is formed. Therefore, it is necessary to make the line width less than the oxidation width of the oxidized layer so that the etching does not proceed to the non-oxidized region inside the element by the isolation process.

    Next, after the isolation process, the photosensitive film is removed by oxygen plasma ashing, and the back surface is polished to a substrate thickness of 120 μm. Next, an AuGe / Ni / Au film is deposited on the back surface of the substrate 1 as the n-side contact electrode 15 and sintered to complete the device.

    In the surface-type semiconductor laser fabricated in this way, continuous oscillation at room temperature was obtained at a wavelength of 650 nm, and leakage current to the outside of the element was completely blocked by the cavity 20, so that low threshold current oscillation and high-speed response were achieved. An improvement was seen.

    Further, since the contact electrode 11 and the peripheral electrode 11b and the wiring 11a connecting them are formed at substantially the same level, a surface emitting semiconductor laser having no step breakage and excellent in mass productivity can be provided. Therefore, it is possible to provide a low-cost and highly reliable element.

    In addition, the shape of the non-oxidized region and the outgoing beam pattern generated by anisotropic oxidation is improved, a desired beam pattern shape is obtained, and mode control is facilitated.

    Furthermore, by forming a film having tensile stress as an etching mask film, the compressive stress applied to the active layer and mesa structure center applied by volume shrinkage accompanying the oxidation of the Al high concentration layer is relieved, and at the interface. Improvements in device reliability and longer life can be expected by suppressing cracks and breakage and increasing resistance to thermal processes after selective oxidation.

In this embodiment, the Si ₃ N ₄ film is used as the film having the tensile stress. However, the composition ratio is not limited to the composition of 3: 4, and the silicon nitride film having another composition ratio is used. Need only have the same tensile stress. In addition, the SiN film is suitable from the viewpoint of etching processability and stress control, but the same effect is obtained for other compounds such as SiON, SiC, diamond, nitride film semiconductors, nitride semiconductors, and compound materials containing nitrogen. There is.

    Further, even if the film having stress is formed as a buried film or a heat dissipation film, the same effect can be obtained.

    Further, although the PECVD apparatus is used for forming the tensile stress film, it is also possible to use a film forming apparatus such as an rf sputtering apparatus.

    Furthermore, the quantum well active layer is not limited to the InGaAlP system, and various materials such as an AlGaAs system and an InGaAsP system can also be used.

    The clad layer is not limited to the InGaAlP system, and various materials such as a ZnSSe system and a ZnMgSSe system can also be used.

    Moreover, although the case where the layer to be oxidized is two layers has been described, the same effect can be obtained when the layer is a single layer.

(Embodiment 2)
4A and 4B are configuration diagrams of a surface-emitting type semiconductor laser according to a second embodiment of the present invention, in which FIG. 4A is a top view, FIG. 4B is a cross-sectional view in section 1 of FIG. FIG.

    In the present embodiment, the point that the high resistance region 30 is formed under the wiring 11a by ion implantation instead of the cavity is substantially the same as in the first embodiment. Description is omitted.

    As shown in FIGS. 4B and 4C, the peripheral portion 18 excluding the mesa structure and the layer structure under the wiring portion 11a are increased in resistance by ion implantation to form a high resistance region 30. By doing so, the leakage current indicated by the arrow 13 is suppressed, and the same effect as in the first embodiment is produced.

    Next, a method for manufacturing this surface emitting semiconductor laser will be specifically described.

    First, on a cleaned 3 inch n-type GaAs substrate 1 having a thickness of 400 μm, a semiconductor multilayer mirror 2, an oxidized layer 2a, a cladding layer 3, a semiconductor active layer 4, a cladding layer 5, An oxide layer 6a, a semiconductor multilayer mirror 6 and a contact layer 7 are formed.

    The basic structure is such that semiconductor multilayer reflectors 2 and 6 are arranged above and below a resonator composed of the semiconductor active layer 4 and the cladding layers 3 and 5. Moreover, it designed and manufactured as a 650 nm band red InGaAlP type surface emitting semiconductor laser.

Here, the semiconductor multilayer reflector 2 is an AlGaAs-based semiconductor multilayer reflector into which an n-type impurity is introduced at 1 × 10 ¹⁸ / cm ³ , and the cladding layer 3 is an n-type In _0.5 (Ga _0.3 Al _{0. 7} ) It was formed at _0.5 P. The semiconductor active layer 4 has a quantum well structure made of In _x Ga _1-x P / In _0.5 (Ga _0.5 Al _0.5 ) _0.5 P adjusted so that the emission peak wavelength is 650 nm. . The clad layer 5 was formed of p-type In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P. The semiconductor multilayer mirror 6 is an AlGaAs-based semiconductor multilayer mirror in which p-type impurities are introduced at 1 × 10 ₁₈ / cm ₃ . As the oxidized layer 2 a, Al _x Ga _1-x As (x> 0.98), which is formed immediately below the cladding layer 3 and has an Al composition ratio larger than that of AlGaAs constituting the n-type semiconductor multilayer mirror 2. As the specific acid lower layer 6 a, Al _x Ga _1-x As (x> 0.98), which is formed immediately above the cladding layer 5 and has an Al composition ratio larger than that of AlGaAs constituting the p-type semiconductor multilayer mirror 6. The contact layer 7 is a GaAs layer.

Here, Al _0.95 Ga _0.05 As and Al _0.5 Ga _0.5 As are used for the AlGaAs-based semiconductor multilayer mirror so that the optical film thickness becomes 1/4 of the resonance wavelength. An alternately stacked structure is used.

    First, the etching mask film 9 having a tensile stress of 150 MPa is formed as in the first embodiment.

    Next, a commercially available photoresist is spin-coated by a spin coater and a baking process is performed using a hot plate to form a 350 nm-thick photosensitive film. Next, the mask pattern is exposed and transferred using a stepper.

    First, marks for aligning various patterns are exposed and transferred. Next, it develops with a developing solution, performs post-baking, and forms a pattern in a photosensitive film. Next, etching is performed based on the photosensitive film pattern to form a mark pattern for alignment on the etching mask film 9. Next, the photosensitive film is removed by oxygen plasma ashing.

Thereafter, the mark pattern is etched only in the contact layer under the etching mask film 9 by PA treatment using a NH ₃ / H ₂ O ₂ mixed solution. Thereafter, a commercially available photoresist is spin-coated and baked using a hot plate to form a photosensitive film having a thickness of 5 μm.

    Next, in order to form a pattern for isolation by proton injection using a stepper, exposure / transfer and development with a developer are performed. Next, post-baking is performed to form an isolation pattern by proton implantation in the photosensitive film.

    Next, etching is performed based on the photosensitive film pattern to form an isolation pattern by proton implantation in the etching mask film 9.

Next, the ion implantation apparatus irradiates the outer peripheral portion of the element with acceleration voltages of 100, 200, and 300 kV and a dose of 1E15 / cm ² to inject protons. Thus, the high resistance region 30 is formed.

    At this time, it is uniformly distributed as a peak in a depth range of 0.5 to 2.5 μm, and the resistance is increased to a depth of about 3 μm. At this time, the distance from the surface to the semiconductor active layer 4 was about 3 μm. Further, since the resist forming portion (element internal position) is formed with a film thickness of 5 μm, all protons are injected into the resist film.

    Thereafter, the photosensitive film is removed by oxygen plasma ashing, and the etching mask film 9 is removed by wet etching.

    Next, an etching mask film 9 having a tensile stress of 150 MPa is formed again. Next, a commercially available photoresist is spin-coated on the film and baked using a hot plate to form a 350 nm-thick photosensitive film. Next, the contact hole pattern is exposed and transferred using a stepper. Next, development is performed with a developer and post-baking is performed to form a contact hole pattern in the photosensitive film.

    Next, etching is performed based on the photosensitive film pattern to form a contact pattern on the etching mask film 9. Next, the photosensitive film is removed by oxygen plasma ashing.

    Next, a commercially available photoresist is spin-coated and baked using a hot plate to form a 350 nm-thick photosensitive film. Next, the electrode pattern is exposed and transferred using a stepper, developed with a developer, and post-baked. In this way, patterns of the p-side contact electrode 11, the bonding pad 12, the wiring 11a, and the peripheral wiring 11b are formed.

    Next, a Ti / Pt / Au film is formed on the photosensitive film pattern of the p-side contact electrode 11 and the like by an electron gun vapor deposition apparatus. Next, electrodes and wiring patterns are formed by lift-off and sintering.

    Thereafter, the window region 17 of the laser beam is opened and the GaAs contact layer 7 is subjected to pattern etching. Next, a commercially available photoresist is spin-coated and baked using a hot plate to form a 350 nm-thick photosensitive film. Next, using a stepper, exposure and transfer for mesa structure formation, development with a developer, and post-baking are performed. Next, a mesa structure forming pattern is formed on the photosensitive film, and the mesa structure forming pattern is formed on the etching mask film 9 by performing etching based on the photosensitive film pattern.

    Next, plasma dry etching using a chlorine-based gas is performed based on the etching mask film 9 to form a mesa structure. Next, the photosensitive film is removed by oxygen plasma ashing.

    Next, heat treatment is performed at 400 ° C. to 500 ° C. in a water vapor atmosphere to selectively oxidize the oxidized layers 6a and 2a in the lateral direction. Thus, similarly to the first embodiment, the mesa structure and the tensile stress film are formed to control the shape of the non-oxidized region to a desired shape and relieve the compressive stress applied to the semiconductor active layer.

    Next, after the steam oxidation treatment, the substrate 1 is polished from the back surface so as to have a thickness of 120 μm. Next, an AuGe / Ni / Au film is deposited as an n-side contact electrode 15 on the back surface of the substrate 1 and subjected to a sintering process to complete device fabrication.

    In the surface emitting semiconductor laser manufactured according to this embodiment, a high resistance region formed by proton implantation is formed in the lower layer of the wiring 11a, so that the leakage current outside the mesa region is completely eliminated as indicated by an arrow 13. To be blocked.

  According to the above embodiment, the leakage current to the outside of the device is suppressed, the threshold is lowered, the high speed response, the mass productivity is improved, the non-oxidized region caused by anisotropic oxidation, the shape of the outgoing beam pattern, Improve mode control, relieve compressive stress applied to the light emitting region by volume shrinkage when oxidizing Al high-concentration layer, suppress cracks and breakage at the interface, and heat treatment after selective oxidation process Accordingly, it is possible to provide a surface-emitting type semiconductor light-emitting device that can improve the resistance to the device, improve the reliability of the device, and extend the lifetime.

BRIEF DESCRIPTION OF THE DRAWINGS It is a block diagram of the surface emitting semiconductor element concerning Embodiment 1 of this invention, (a) is a top view, (b) (c) is sectional drawing. The top view of the shape (non-oxidation area | region) of the light emission area | region which remained without being oxidized in the mesa structure of this invention, and a mesa etch area | region (recessed part). The top view of the shape (non-oxidation area | region) of the light emission area | region which remained without being oxidized in the mesa structure of this invention, and a mesa etch area | region (recessed part). It is a block diagram of the surface emitting semiconductor element concerning Embodiment 2 of this invention, (a) is a top view, (b) (c) is sectional drawing. It is a block diagram of the conventional surface emitting semiconductor element, (a) is a top view, (b) (c) is sectional drawing. The top view of the shape (non-oxidation area | region) of the light emission area | region which remained without being oxidized in the conventional mesa structure, and a mesa etch area | region (recessed part).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Semiconductor multilayer reflective mirror 3 ... Cladding layer 4 ... Semiconductor active layer 5 ... Cladding layer 6 ... Semiconductor multilayer reflective mirror 7 ... Contact layer 8 .. Current confinement part 9 ... Insulating film 11 ... Contact electrode 11a ... Wiring part 11b ... Peripheral electrode 12 ... Bonding electrode 15 ... Contact electrode 16 ... Mesa etch region (concave part)
DESCRIPTION OF SYMBOLS 17 ... Light emission area | region 18 ... Peripheral part 19 ... Film | membrane which has a tensile stress 20 ... Cavity

Claims (10)

A substrate having first and second major surfaces;
A first electrode formed on a first main surface of the substrate;
Formed on the second main surface, and formed in a columnar shape surrounded by the concave portion, the peripheral portion, and the concave portion, and partially on the peripheral portion via a high resistance region between the end portions of the adjacent concave portions. A first semiconductor multilayer reflector surface layer formed above the first main surface, and a semiconductor formed above the first semiconductor multilayer reflector surface layer. Oxidized with respect to the crystal direction of the active layer, the second semiconductor multilayer reflector surface layer formed above the semiconductor active layer, and the first semiconductor multilayer reflector surface layer or the second semiconductor multilayer reflector surface layer A current path constriction portion having an oxidation anisotropy that exhibits an easy first direction and a second direction that is difficult to be oxidized, and is formed in the vicinity of the semiconductor active layer, and is provided in the first direction. From the light emitting region along the current path constriction A multilayer structure in which the light emitting region is longer than the distance from the light emitting region along the second direction to the current path constricted portion, and the light emitting region is surrounded by the peripheral portion via the recess. And a second electrode that is provided above the light emitting region, has an opening above the current path narrowing portion, and constitutes a current path that passes through the current path narrowing portion and reaches the first electrode;
A third electrode formed on the periphery of the multilayer structure;
A plurality of conductors formed on the high-resistance region and interconnecting the second and third electrodes;
A surface-emitting semiconductor light-emitting element that emits light in a direction perpendicular to the substrate.   2. The surface-emitting type semiconductor light emitting device according to claim 1, further comprising a film having a tensile stress on a surface portion of the multilayer structure.   3. The surface-emitting type semiconductor light emitting device according to claim 1, wherein the first and second multilayer reflecting mirror surface layers constitute a vertical cavity resonator.   The second electrode is formed in an annular shape around the upper surface of the light emitting region, and the third electrode has an annular region surrounding the recess and a pad region for external connection in the peripheral portion. The surface-emitting type semiconductor light-emitting device according to claim 1.   5. The surface-emitting type semiconductor light emitting device according to claim 1, wherein the recesses are arranged symmetrically with respect to the center of the light emitting region. A substrate having first and second major surfaces;
A first electrode formed on a first main surface of the substrate;
Formed on the second main surface, and formed in a columnar shape surrounded by the concave portion, the peripheral portion, and the concave portion, and partially on the peripheral portion via a high resistance region between the end portions of the adjacent concave portions. A first semiconductor multilayer reflector surface layer formed above the first main surface, and a semiconductor formed above the first semiconductor multilayer reflector surface layer. Oxidized with respect to the crystal direction of the active layer, the second semiconductor multilayer reflector surface layer formed above the semiconductor active layer, and the first semiconductor multilayer reflector surface layer or the second semiconductor multilayer reflector surface layer A current confinement portion having an oxidation anisotropy formed in the vicinity of the semiconductor active layer and having an oxidation anisotropy in a first direction that is easy to be oxidized and a second direction that is difficult to be oxidized; Directed to the high resistance region, The light emitting region is formed on the multilayer structure surrounded by the peripheral portion and the upper surface of the light emitting region, and has an opening above the current path narrowing portion, and passes through the current path narrowing portion. A second electrode constituting a current path to one electrode;
A third electrode formed on the periphery of the multilayer structure;
A plurality of conductors formed on the high-resistance region and interconnecting the second and third electrodes;
A surface-emitting semiconductor light-emitting element that emits light in a direction perpendicular to the substrate.   The surface emitting semiconductor light emitting device according to claim 6, further comprising a film having a tensile stress on a surface portion of the multilayer structure.   8. The surface-emitting type semiconductor light emitting device according to claim 6, wherein the first and second multilayer reflecting mirror surface layers constitute a vertical cavity resonator.   The second electrode is formed in an annular shape around the upper surface of the light emitting region, and the third electrode has an annular region surrounding the recess and a pad region for external connection in the peripheral portion. The surface-emitting type semiconductor light-emitting device according to claim 6.   The surface-emitting type semiconductor light-emitting device according to claim 6, wherein the recesses are arranged symmetrically with respect to the center of the light-emitting region.

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