JP2013062321A - Nitride semiconductor light-emitting element manufacturing method - Google Patents

Abstract

A method of fabricating a nitride semiconductor light emitting device is provided that enables both formation of an electrode having good physical contact on a semipolar plane and formation of a ridge structure.
In an etching apparatus, a hard mask having a pattern defining a ridge shape is formed. This etching is performed by the ICP-RIE method. Etching is performed at a substrate temperature of 300 degrees Celsius or less. After the hard mask 43 is formed, the mask 41 can be removed. The substrate main surface 11a and the semipolar main surface 13a can be inclined at an angle in a range from 63 degrees to 80 degrees from a plane orthogonal to the reference axis Cx. In this inclination angle range, the semipolar main surface 13a has a step that is easily oxidized. The semiconductor layer 13 and the metal film 33 are etched using the hard mask 43 to form the metal layer 45 and the nitride semiconductor region 47. The nitride semiconductor region 47 includes a semiconductor ridge 49.
[Selection] Figure 4

Description

  The present invention relates to a method for manufacturing a nitride semiconductor light emitting device.

  Patent Document 1 describes that a compound semiconductor laser is manufactured using a GaAs substrate or a GaN substrate. A gallium nitride compound semiconductor laser is fabricated on the c-plane GaN substrate.

JP 2008-98349 A

In the manufacturing method of Patent Document 1, an electrode is formed on the surface of a gallium nitride-based compound semiconductor multilayer structure using lift-off. On the Pd layer, a laminated mask portion in which a Si ₃ N ₄ mask layer, an Al mask layer, and a Si ₃ N ₄ mask layer are sequentially arranged is formed.

  Using a resist mask provided on these mask layers, the three mask layers are sequentially etched to form a lift-off mask and an electrode portion. By this etching, the surface of the gallium nitride compound semiconductor multilayer structure is exposed. The gallium nitride compound semiconductor multilayer structure is etched to form a ridge portion. Next, the Al mask layer is selectively etched using hydrochloric acid to form a recess in the laminated mask portion. Thereafter, an insulating layer is grown over the entire upper surface of the substrate, and the Al mask is removed using a solution containing 50 wt% hydrofluoric acid and 40 wt% ammonium fluoride aqueous solution. As a result, the surface of the electrode part is exposed.

  In Patent Document 1, a complicated mask structure is formed for lift-off and ridge formation. For example, in the mask structure, side etching is caused in the Al layer in the mask structure for lift-off. Further, since lift-off is also used for forming the protective layer, the opening formation of the protective layer is difficult to control independently of the ridge formation. For example, the side-etched Al layer is narrower than the width of the thinned Al layer, and the shape of this mask structure affects the shape of the deposited protective film.

  The present invention has been made in view of such circumstances, and provides a nitride semiconductor light-emitting element that enables both formation of an electrode that makes good contact on a semipolar plane and formation of a ridge structure. It is an object of the present invention to provide a manufacturing method.

  The present invention relates to a method for fabricating a nitride semiconductor light emitting device. This method includes (a) a step of forming a metal film on a semipolar main surface of an epitaxial substrate including a semiconductor stack using growth using an MBE method in a film forming apparatus; and (b) the semiconductor stack. And a step of forming a ridge defining mask on the metal film, and (c) performing etching of the semiconductor stack and the metal film using the mask to form a nitride semiconductor region including a semiconductor ridge, and Forming a metal layer on the semiconductor ridge; and (d) growing an insulating film for a protective layer on the surface of the nitride semiconductor region and on the metal layer after removing the mask; Is provided. The semipolar main surface is made of a group III nitride semiconductor, the semiconductor stack includes an active layer made of group III nitride, and the metal film forms a junction with the semipolar main surface.

  According to a method of manufacturing this nitride semiconductor light emitting device (hereinafter referred to as “manufacturing method”), a process for forming a semiconductor ridge after forming a metal film on a semipolar main surface of a semiconductor stack is performed. As applied, the semipolar major surface is not directly exposed to the process. Further, while protecting the interface between the metal layer and the semipolar main surface, the insulating film for the protective layer can be grown after removing the insulating film mask without using a complicated process of lift-off.

  In the manufacturing method according to the present invention, the semipolar principal surface of the epitaxial substrate is at an angle in a range of 10 degrees to 80 degrees from a plane orthogonal to a reference axis extending along the c-axis of the group III nitride semiconductor. Can be tilted. According to this manufacturing method, the semipolar main surface can be inclined at an angle within the above range.

  The manufacturing method according to the present invention may further include a step of exposing the entire semipolar main surface of the semiconductor stack made of group III nitride to an atmosphere of group III element in the film forming apparatus. The group III nitride preferably includes the group III element as a constituent element.

  According to this manufacturing method, the semipolar main surface is exposed to the group III element atmosphere prior to the formation of the metal film in the film forming apparatus, so that the surface with which the metal film comes into contact is cleaned. Since the metal layer is continuously formed on the cleaned semipolar main surface by the film forming apparatus, contamination at the interface between the metal film and the semipolar main surface can be avoided when forming the ridge.

  In the manufacturing method according to the present invention, the semipolar principal surface is made of a gallium nitride semiconductor, the atmosphere includes gallium, and the step of exposing the semipolar principal surface to the atmosphere is performed at a substrate temperature of 300 degrees Celsius or higher. It is preferable that irradiation of the gallium flux is performed on the semipolar main surface.

  According to this manufacturing method, reduction of the surface oxide is caused by irradiation with the gallium flux, and the oxide on the semipolar main surface made of the gallium nitride semiconductor can be reduced.

  In the manufacturing method according to the present invention, it is preferable that the metal layer includes a gold layer. According to this manufacturing method, the gold layer can provide good electrical contact with the semipolar main surface made of a group III nitride semiconductor.

  The manufacturing method according to the present invention includes a step of forming a resist film on the insulating film, a step of forming a resist mask having an opening provided on the upper surface of the semiconductor ridge from the resist film, and the resist A step of etching the insulating film using a mask to form a protective layer from the insulating film can be provided. The resist film includes a first portion, a second portion, and a third portion, and the first portion, the second portion, and the third portion of the resist film are disposed in this order on the nitride semiconductor region. The second portion of the resist film is located on the upper surface of the semiconductor ridge, and the first portion and the third portion of the resist film are provided apart from the upper surface of the semiconductor ridge, The thickness of the second portion of the resist film is smaller than the thickness of the first portion and the third portion of the resist film, and in the step of forming the resist mask from the resist film, the thickness of the resist film is increased from the surface of the resist film. The resist of the resist film is removed, and the protective layer has an opening that exposes the metal layer on the upper surface of the semiconductor ridge.

  According to this manufacturing method, since the thickness of the second portion of the resist film is thinner than the thickness of the first portion and the third portion of the resist film, the resist film is removed from the surface, thereby opening the upper surface of the semiconductor ridge. A resist mask having can be formed. The protective film can be formed by exposing the metal film on the upper surface of the semiconductor ridge by etching the insulating film using this resist mask.

  In the manufacturing method according to the present invention, the step of forming the resist mask from the resist film includes a step of forming a first resist film on the insulating film and a top surface of the semiconductor ridge using a photolithography method. And forming a first mask layer having an opening exposing the insulating film on the side surface from the first resist film, the nitride semiconductor region, the metal layer, the insulating film, and the first Forming a second resist film on the mask layer; and forming a second mask layer by forming an opening in the second resist film so that the upper surface of the semiconductor ridge is exposed. Can do. The resist film may include the first mask layer and the second resist film, and the resist mask may include the first mask layer and the second mask layer.

  According to this manufacturing method, since the second resist film is formed on the first mask on the upper surface of the semiconductor ridge and in the opening of the first mask, the second resist film is provided on the first region of the nitride semiconductor region. The resist thickness can be different from the resist thickness provided on the second region of the nitride semiconductor region.

  In the manufacturing method according to the present invention, in the step of forming the resist mask from the resist film, the resist film is exposed to a phenomenon liquid to remove the resist on the upper surface of the semiconductor ridge, and the resist mask. Is preferably formed.

  According to this manufacturing method, since the resist film is gradually dissolved from the surface in the resist phenomenon solution, the resist film is subjected to processing such that the upper surface of the semiconductor ridge and the vicinity thereof are exposed from the resist. Is possible.

  In the manufacturing method according to the present invention, the semiconductor ridge and the metal layer form a ridge structure, the upper surface of the semiconductor ridge and the metal layer form a metal-semiconductor junction, and the edge of the metal-semiconductor junction is Located on a side surface of the ridge structure, the protective layer may cover the edge of the metal-semiconductor junction. According to this manufacturing method, the edge of the metal-semiconductor junction is covered with the protective layer.

  The manufacturing method according to the present invention further includes a step of depositing an electrode film on the metal layer and the insulating film after removing the resist mask, and a step of processing the electrode film to form an electrode. Can be provided. The electrode is preferably in contact with the metal layer through the opening of the protective layer, and the electrode film is preferably deposited at a substrate temperature of 300 degrees Celsius or less. According to this manufacturing method, it is possible to avoid the thermal degradation caused by the substrate temperature during electrode film deposition from occurring in the contact resistance.

  In the manufacturing method according to the present invention, it is preferable that the electrode film is deposited by an electron beam evaporation method. According to this manufacturing method, it is possible to reduce the occurrence of thermal degradation at the interface between the metal layer and the group III nitride during the deposition of the electrode film. According to electron beam evaporation, high temperature film formation can be avoided.

  In the manufacturing method according to the present invention, the nitride semiconductor region includes a first groove and a second groove, and a first terrace and a second terrace, wherein the first groove and the second groove define the semiconductor ridge, The semiconductor ridge and the first terrace may define the first groove, and the semiconductor ridge and the second terrace may define the second groove.

  In this manufacturing method, a semiconductor ridge can be manufactured using the first groove and the second groove, and only the semiconductor ridge can be prevented from protruding from the epi plane due to the first terrace, the second terrace, and the semiconductor ridge.

  In the manufacturing method according to the present invention, the step of forming the metal film includes a step of forming a metal region in the film formation apparatus by metal deposition using an MBE method, and etching the metal region to form the semiconductor Forming the metal film on the semipolar main surface of the semiconductor stack and partially exposing the semipolar main surface of the stack. According to this manufacturing method, the metal film can be provided on the semipolar main surface of a part of the semiconductor stack including the part where the semiconductor ridge is to be formed.

  In the manufacturing method according to the present invention, the step of forming the mask includes a step of forming a mask film on the semiconductor stack and the metal layer, and a step of forming the mask by etching the mask film. In addition, the etching is preferably performed at a substrate temperature of 300 degrees Celsius or less. According to this manufacturing method, since the substrate temperature at the time of etching is 300 degrees Celsius or less, the thermal deterioration of the metal-semiconductor junction can be reduced by the substrate temperature during the etching.

  In the manufacturing method according to the present invention, the mask film may include at least one of a tungsten film, a silicon oxide film, and a silicon nitride film. According to this manufacturing method, at least one of a tungsten film, a silicon oxide film, and a silicon nitride film can be used as a mask for etching a group III nitride to form a semiconductor ridge.

  The manufacturing method according to the present invention can further include a step of growing the semiconductor stack on the main surface of the substrate to form the epitaxial substrate. The main surface of the substrate is made of a group III nitride semiconductor, the semiconductor stack includes a first region, a second region, and a third region, and the first region, the second region, and the third region are The second region is located between the first region and the third region, the semiconductor ridge is formed in the second region, and the semiconductor stacked layer is disposed along the main surface of the substrate. Includes a group III nitride semiconductor layer of a first conductivity type, the active layer, and a group III nitride semiconductor layer of a second conductivity type, the epitaxial substrate includes the substrate, and the main surface of the substrate is The group III nitride semiconductor is inclined at an angle in a range of not less than 10 degrees and not more than 80 degrees from a plane orthogonal to a reference axis extending along the c-axis, and the semipolar main surface of the epitaxial substrate is the group III nitride 10 degrees or less from the plane perpendicular to the reference axis extending along the c-axis of the semiconductor It can be inclined at an angle of 80 degrees or less.

  According to this manufacturing method, when the tilt angle is in the range of 10 degrees or more and 80 degrees or less, the semipolar plane of the gallium nitride semiconductor is rich in oxygen bonding. Therefore, it is important to reduce oxygen during the formation of the ohmic electrode.

  In the manufacturing method according to the present invention, the semipolar principal surface of the epitaxial substrate is at an angle in the range of not less than 63 degrees and not more than 80 degrees from a plane orthogonal to a reference axis extending along the c-axis of the group III nitride semiconductor. It is preferable to incline. According to this manufacturing method, the semipolar plane in this angular range has a step that is easily oxidized.

  In the manufacturing method according to the present invention, the epitaxial substrate includes a p-type gallium nitride based semiconductor layer provided on the active layer, the p-type gallium nitride based semiconductor layer includes magnesium as a dopant, and the p-type The main surface of the gallium nitride based semiconductor layer can constitute the semipolar main surface of the epitaxial substrate. According to this manufacturing method, an electrode that makes ohmic contact with the p-type gallium nitride based semiconductor layer can be formed.

  In the manufacturing method according to the present invention, the semiconductor ridge is provided on the light guide layer provided on the active layer, the clad layer provided on the light guide layer, and the clad layer. The semiconductor ridge extends in a first direction, and the light guide layer, the cladding layer, and the contact layer are arranged in a second direction that intersects the first direction. The nitride semiconductor region includes a first region, a second region, and a third region, and the first region, the second region, and the third region are both in the first direction and the second direction. The second region is located between the first region and the third region, the second region includes the semiconductor ridge, the first region, and the second region The surface of the third region consists of the surface of the light guide layer, Protective film can cover the said surface of the first region, wherein the surface of said third region, and a side surface of the semiconductor ridge.

  According to this manufacturing method, the semiconductor ridge includes the light guide layer, the clad layer, and the contour, and the protective film covers the surface of the first region, the surface of the third region, and the side surface of the semiconductor ridge. Current confinement and a good refractive index profile are provided for the light emitting device.

  In the manufacturing method according to the present invention, the active layer may include a gallium nitride based semiconductor layer containing indium as a group III constituent element, and the active layer may have a peak emission wavelength in a wavelength range of 500 nm to 540 nm. .

  According to this manufacturing method, an active layer having a peak emission wavelength in the wavelength range of 500 nm or more and 540 nm or less can be provided to the group III nitride semiconductor light emitting device.

  As described above, according to the present invention, there is provided a method for fabricating a nitride semiconductor light emitting device, which includes both formation of an electrode having good contact on a semipolar plane and formation of a ridge structure. Enable.

FIG. 1 is a drawing schematically showing main steps in a method for producing a nitride semiconductor device according to the present embodiment. FIG. 2 is a drawing schematically showing main steps in the method of manufacturing the nitride semiconductor device according to the present embodiment. FIG. 3 is a drawing schematically showing main steps in the method of manufacturing the nitride semiconductor device according to the present embodiment. FIG. 4 is a drawing schematically showing main steps in the method for producing a nitride semiconductor device according to the present embodiment. FIG. 5 is a drawing schematically showing main steps in the method of manufacturing the nitride semiconductor device according to the present embodiment. FIG. 6 is a drawing schematically showing main steps in the method of manufacturing the nitride semiconductor device according to the present embodiment. FIG. 7 is a drawing schematically showing main steps in the method of manufacturing the nitride semiconductor device according to the present embodiment. FIG. 8 is a drawing schematically showing main steps in the method of manufacturing the nitride semiconductor device according to the present embodiment. FIG. 9 is a drawing showing an example of a nitride semiconductor light emitting device fabricated by the above process. FIG. 10 is a diagram showing the thermal stability of the contact resistance of the p-side electrode. FIG. 11 is a drawing schematically showing a wafer process different from the embodiment. FIG. 12 is a drawing schematically showing a wafer process different from the embodiment. FIG. 13 is a drawing schematically showing a wafer process different from the embodiment.

  Embodiments relating to a method for manufacturing a nitride semiconductor device, a method for forming a semiconductor ridge, and a method for forming an electrode will be described. Where possible, the same parts are denoted by the same reference numerals. In the following description, a nitride semiconductor light emitting device as a nitride semiconductor device, a method for forming a semiconductor ridge, and a method for forming an electrode will be described.

  1 to 8 are drawings schematically showing main steps in a method for manufacturing a nitride semiconductor device, a method for forming a semiconductor ridge, and a method for forming an electrode according to the present embodiment. In the schematic diagrams of FIGS. 1 to 8, a rectangular substrate is drawn, but the shape of the substrate is not limited to this. In order to facilitate understanding, in the following description, a procedure for forming a nitride semiconductor light-emitting element on a single-sized substrate will be described.

  In the first step, a substrate (reference numeral “11” shown in FIG. 1A) is prepared. The substrate 11 has a main surface 11a made of a group III nitride semiconductor. Main surface 11a is inclined with respect to a plane orthogonal to a reference axis (indicated by vector VC in FIG. 1A) extending in the c-axis direction of the group III nitride semiconductor. Here, the vector VC indicates the <0001> direction. The main surface 11a of the substrate 11 is semipolar. The group III nitride semiconductor of the substrate 11 can be made of, for example, GaN.

  As shown in FIG. 1A, in the next step, a semiconductor stack 13 for a semiconductor light emitting device is grown on a main surface 11a of a substrate 11 in a growth furnace 10a to form an epitaxial substrate E. . The epitaxial substrate E includes a substrate 11 and a semiconductor stack 13.

  One embodiment will be described. As the growth method for the growth furnace 10a, for example, a metal organic chemical vapor deposition method can be used. After the substrate 11 is placed in the growth furnace 10a, ammonia and hydrogen are supplied to the growth furnace 10a to perform thermal cleaning of the main surface 11a of the substrate 11. Thereafter, in the growth furnace 10a, a plurality of group III nitride semiconductor layers are grown in order on the main surface 11a of the substrate 11.

  The semiconductor stack 13 includes a first conductivity type group III nitride semiconductor layer such as an n-type group III nitride semiconductor region 15, an n-side light guide layer 16, an active layer 17, a p-side light guide layer 18, and a p-type group III group. A group III nitride semiconductor layer of the second conductivity type such as the nitride semiconductor region 19 is included. The n-type group III nitride semiconductor region 15 can be made of, for example, GaN, AlGaN, InAlGaN, or the like. The n-type group III nitride semiconductor region 15 can include an n-type cladding layer. The p-type group III nitride semiconductor region 19 can be made of, for example, GaN, AlGaN, InAlGaN, or the like, and can include a p-type cladding layer and a p-type contact layer. The p-type group III nitride semiconductor region 19 can include an electron blocking layer, if necessary. The p-type group III nitride semiconductor region 19 includes a p-type gallium nitride semiconductor layer serving as a p-type contact layer, and the main surface of the p-type gallium nitride semiconductor layer constitutes the semipolar main surface 13a of the epitaxial substrate E. can do. The p-type gallium nitride based semiconductor layer can contain magnesium as a dopant, and an electrode that forms ohmic contact with the p-type gallium nitride based semiconductor layer can be formed.

  The active layer 17 has, for example, a quantum well structure 21, and the quantum well structure 21 can include alternately arranged barrier layers 23 and well layers 25. The band gap of the barrier layer 23 is larger than the band gap of the well layer 25. The barrier layer 23 can be made of, for example, GaN, InGaN, InAlGaN, or the like, and the well layer 25 can be made of, for example, GaN, InGaN, InAlGaN, or the like.

  The peak emission wavelength of the emission spectrum of the active layer 17 can be in the wavelength range of 360 nm to 600 nm. The active layer 17 preferably includes a gallium nitride based semiconductor layer containing indium. After the growth of the stacked layer 13 is completed, the epitaxial substrate E is taken out from the growth furnace 10a. The main surface of the nitride semiconductor region of the epitaxial wafer E takes on the plane orientation of the substrate main surface 11a and exhibits semipolarity. The nitride semiconductor region of the epitaxial substrate E includes an active layer 17, and the active layer 17 also has a property according to semipolarity. Taking advantage of this semipolar property, it is preferable to provide a light-emitting element having a peak wavelength of an emission spectrum within a wavelength range of 500 nm or more and 540 nm or less.

  In this step, the semiconductor stack 13 is grown on the main surface 11a of the substrate 11 to form the epitaxial substrate E. In a preferred embodiment, a p-type contact layer is exposed on the outermost surface of the epitaxial substrate E. The p-type contact layer can be made of, for example, a gallium nitride based semiconductor, and the gallium nitride based semiconductor is made of, for example, GaN. In the formation of the epitaxial substrate E, the main surface 11a of the substrate 11 can be inclined at an angle Angle in the range of not less than 10 degrees and not more than 80 degrees from the plane Sc orthogonal to the reference axis Cx. The reference axis Cx extends along the c-axis of the group III nitride semiconductor. In addition, the main surface of the epitaxial substrate E is preferably inclined at an angle in the range of 10 degrees or more and 80 degrees or less from the plane orthogonal to the reference axis Cx. When these inclination angles are in the range of 10 degrees or more and 80 degrees or less, the semipolar plane of the gallium nitride-based semiconductor is rich in oxygen bonding. Therefore, it is important to reduce oxygen during the formation of the ohmic electrode. Further, it is preferable that the inclination angle of the main surface of the epitaxial substrate E is inclined at an angle in the range of 63 degrees or more and 80 degrees or less from a plane orthogonal to the reference axis extending along the c-axis of the group III nitride semiconductor. is there. The semipolar plane in this angular range has a step that is susceptible to oxidation.

  When the epitaxial substrate E is taken out from the growth furnace 10a, the epitaxial substrate E is exposed to an atmosphere containing oxygen. As a result, a group III element natural oxide (eg, gallium oxide) is formed on the gallium nitride based semiconductor surface exposed on the surface of the epitaxial substrate E.

  After removing the epitaxial substrate E from the growth furnace 10a, the epitaxial substrate E is placed in the film forming apparatus 10b. By using the growth using the MBE method in the film forming apparatus 10b, a metal film (reference numeral “29” in FIG. 2A) is formed on the semipolar main surface 13a of the epitaxial substrate E including the semiconductor stack 13. Form).

  The formation of the metal film 29 using the growth using the MBE method in the film forming apparatus 10b is performed as follows, for example. As shown in FIG. 1B, in this step, an atmosphere containing gallium is formed in the chamber of the film forming apparatus 10b, and the semipolar surface 13a of the epitaxial substrate E is exposed to this atmosphere. If necessary, the epitaxial substrate E can be heated by the film forming apparatus 10b prior to this treatment. In one example of the heating conditions, the heating temperature is, for example, 750 degrees Celsius, the heat treatment time is about 30 minutes, and the heat treatment atmosphere is, for example, an atmosphere containing a group III constituent element gallium. This temperature range can be, for example, 300 degrees Celsius or higher. When the temperature is higher than this temperature, gallium oxide on the surface of the epitaxial substrate E is easily reduced to a composition of gallium oxide exhibiting a high vapor pressure. Irradiation of gallium flux causes reduction of the surface oxide, and the oxide of the semipolar main surface 13a made of a gallium nitride semiconductor can be reduced. Also, this temperature range can be, for example, a range of 900 degrees Celsius or less, in order to avoid damage to the active layer 17.

  Further, when the epitaxial substrate E is heated, without breaking the vacuum, as already described, in the film forming apparatus 10b, as shown in FIG. The entire polar main surface 13a is exposed to an atmosphere of a group III element. The group III nitride on the surface of the semiconductor stack 13 includes a group III element as a constituent element. Prior to the formation of the metal film 29 in the film forming apparatus 10b, the semipolar main surface 13a is exposed to the group III element atmosphere, so that the surface with which the metal film 29 comes into contact is cleaned. In the film forming apparatus 10b, since the metal film 29 is continuously formed on the cleaned semipolar main surface, contamination on the interface between the metal film 29 and the semipolar main surface can be avoided.

  When the semipolar main surface 13a is made of a gallium nitride semiconductor, an atmosphere 27 containing gallium is formed in the chamber of the film forming apparatus 10b, and the surface 13a of the epitaxial substrate E is exposed to the atmosphere 27. The atmosphere 27 preferably does not contain nitrogen in order to avoid the growth of a gallium nitride based semiconductor. The substrate temperature range in this process can be, for example, 300 degrees Celsius or more. When this temperature is exceeded, the natural oxide film is promoted to change to gallium oxide having a higher vapor pressure (for example, reduction). Also, this temperature range can be, for example, a range of 900 degrees Celsius or less, in order to avoid damage to the active layer 17. The duration for this heat treatment is, for example, about 0.5 hours.

In one embodiment of this process, exposing the surface 13a of the epitaxial substrate E is possible by irradiating the surface 13a with gallium flux. There are various compositions of compounds of gallium and oxygen. These gallium oxides have various melting points. By utilizing this difference in melting point, the oxygen concentration on the semipolar main surface can be reduced. Examples of gallium oxide include the following. The melting point of Ga ₂ O ₃ (eg, 1725 degrees Celsius, 1 atmosphere, RT) is relatively high, but the melting point of Ga ₂ O (eg, 500 degrees Celsius, 1 × 10 ⁻⁶ Torr) is relatively low.

  In the process so far, after the epitaxial substrate E is disposed in the vacuum chamber of the film forming apparatus 10b, the modification process by heating and / or Ga irradiation has been performed. Thereafter, if necessary, a new epitaxial substrate E can be formed by growing a gallium nitride based semiconductor layer on the semiconductor stack 13. It is preferable to add a desired conductivity type dopant, for example, a p-type dopant such as magnesium, to the gallium nitride based semiconductor layer. According to this method, the oxygen concentration of the group III nitride semiconductor grown by this film formation can be reduced.

  As shown in FIG. 2A, in the next step, after removing the gallium atmosphere, the entire surface of the semipolar main surface 13a of the epitaxial substrate E is broken without breaking the vacuum in the vacuum chamber of the film forming apparatus 10b. Next, a metal film 29 is formed in the vacuum chamber of the film forming apparatus 10b. Since the vacuum is not broken, the substrate product SP1 is formed by forming the metal film 29 on the surface cleaned by flux irradiation. The metal film 29 of the substrate product SP is bonded to the semipolar main surface 13a. According to this manufacturing method, the metal film 29 which makes a low resistance contact with the p-type gallium nitride based semiconductor layer can be formed. The metal film 29 is, for example, 3 nm or more and can be 1000 nm or less. The metal film 29 preferably includes a gold (Au) layer, and the gold (Au) layer can provide good electrical contact with the semipolar principal surface 13a. The thickness of Au is, for example, 200 nm.

  In the step of forming the metal film 29, if necessary, a metal film can be provided on the upper surface of the semiconductor ridge when a semiconductor ridge is formed in a later step. This process is performed as follows, for example. As shown in part (b) of FIG. 2, after forming a metal region (corresponding to the metal film 29) by metal deposition using the MBE method in the film forming apparatus 10b, a mask 31 is used in the etching apparatus 10c. The metal region can be etched to partially expose the semipolar main surface 13a of the semiconductor stack 13 and to form the metal film 33 on the semipolar main surface 13a of the semiconductor stack 13. The mask 31 can be made of a resist, for example. The mask 31 is formed on the semiconductor stack 13 and the metal film 29. When the metal region is made of Au, the etching can be performed by a wet process using aqua regia as an etchant. As a result, the metal film 33 can be provided on the semipolar main surface 13a of a part of the semiconductor stack 13 including the portion where the semiconductor ridge is to be formed. In the present embodiment, the metal film 33 has a stripe shape. The stripe width is larger than the width of the upper surface of the semiconductor ridge and smaller than the sum of the width of the semiconductor ridge and the width of the pair of grooves on both sides. In the subsequent process, the metal film 29 covering the entire semipolar main surface 13 a of the semiconductor stack 13 is used in place of the metal film 33.

  In the next step, as shown in part (a) of FIG. 3, the mask 31 is removed using the processing apparatus 10d to obtain a substrate product SP2. In the subsequent step, after the mask 31 is removed, a mask for defining the ridge (reference numeral “43” shown in FIG. 4A) is formed. The mask 43 is formed as follows, for example. As shown in part (b) of FIG. 3, a mask film 35 for a hard mask is formed on the semipolar main surface 13 a and the metal film 33 of the semiconductor stack 13 by the film forming apparatus 10 e. The mask film 35 is formed by, for example, an electron beam evaporation method. This film formation is preferably performed at a substrate temperature of 150 degrees centigrade or less in order to protect the interface between the already formed metal film 33 and the semipolar surface 13a. The mask film 35 can include at least one of a tungsten film, a silicon oxide film, a silicon nitride film, and the like. As the hard mask, at least one of a tungsten film, a silicon oxide film, and a silicon nitride film can be used.

  In the next step, a mask 41 for forming a pattern on the mask film 35 is formed on the mask film 35. The mask 41 has a pattern that defines a ridge shape. The mask 41 can be made of a resist, for example. As shown in part (a) of FIG. 4, in the etching apparatus 10 f, the mask film 35 is etched using the mask 41 to form the hard mask 43. The hard mask 43 has a pattern that defines a ridge shape. This etching is preferably performed, for example, by an inductive coupling plasma reactive ion etching method (ICP-RIE method). According to this etching method, anisotropy in etching can be realized. After the hard mask 43 is formed, the mask 41 can be removed. Etching is performed at a substrate temperature of 300 degrees Celsius or lower, and the substrate temperature is preferably 150 degrees Celsius or lower.

  As shown in FIG. 4A, in the epitaxial substrate E, the semiconductor stack 13 includes a first region 13c, a second region 13d, and a third region 13e. The first region 13c, the second region 13d, and the third region 13e are disposed along the main surface 11a of the substrate 11. The second region 13d is located between the first region 13c and the third region 13e. A semiconductor ridge 49 is formed in the second region 13d. The semiconductor stack 13 may include a fourth region 13f and a fifth region 13f, and the first region 13c, the second region 13d, and the third region 13e are between the fourth region 13f and the fifth region 13f. Arranged.

  When the main surface 11a of the substrate 11 is inclined at an angle in the range of 10 degrees to 80 degrees from a plane orthogonal to the reference axis Cx extending along the c-axis of the group III nitride semiconductor, the semipolar main surface of the epitaxial substrate E The surface 13a is also inclined at an angle in the range of 10 degrees to 80 degrees from the surface orthogonal to the reference axis Cx. When these inclination angles are in the range of 10 degrees or more and 80 degrees or less, the semipolar plane of the gallium nitride-based semiconductor is rich in oxygen bonding. Therefore, it is important to reduce oxygen during the formation of the ohmic electrode.

  The substrate main surface 11a and the semipolar main surface 13a can be inclined at an angle in a range from 63 degrees to 80 degrees from a plane orthogonal to the reference axis Cx. In this inclination angle range, the semipolar main surface 13a has a step that is easily oxidized. The semipolar main surface 13a of the epitaxial substrate E also has a step that is easily oxidized.

  In the next step, as shown in FIG. 4B, the semiconductor layer 13 and the metal film 33 are etched using the hard mask 43 to form the metal layer 45 and the nitride semiconductor region 47. . The nitride semiconductor region 47 includes a semiconductor ridge 49. The metal layer 45 is located on the upper surface 49 a of the semiconductor ridge 49. For the etching of the metal film 33, for example, argon (Ar), nitrogen (N2), or the like can be used. Etching using argon (Ar) is not reactive, but is anisotropic. For example, chlorine or boron trichloride can be used for etching the semiconductor stack 13. In an embodiment, the semiconductor ridge height HR is, for example, 0.2 μm or more, for example, 2.0 μm or less. This etching is preferably performed by, for example, an ICP-RIE method. According to this etching method, anisotropy in etching and a desired ridge height can be realized. After the etching is completed, the hard mask 43 is removed. This etching is performed at a substrate temperature of 300 degrees centigrade or less and preferably at a substrate temperature of 150 degrees centigrade or less in order to protect the interface between the metal film 33 already formed and the semipolar surface 13a.

  The nitride semiconductor region 47 includes a first groove 51 and a second groove 53, and a first terrace 55 and a second terrace 57. The first terrace 55, the first groove 51, the semiconductor ridge 49, the second groove 53, and the second terrace 57 are perpendicular to both the normal direction of the upper surface 49 a of the semiconductor ridge 49 and the extending direction of the semiconductor ridge 49. Are arranged in this order. The first groove 51 and the second groove 53 define a semiconductor ridge 49. The semiconductor ridge 49 and the first terrace 55 define a first groove 51. The semiconductor ridge 49 and the second terrace 57 define a second groove 53. According to this structure, the semiconductor ridge 49 can be formed by using the first groove 51 and the second groove 53, and only the semiconductor ridge 49 is formed by the first terrace 55, the second terrace 57, and the semiconductor ridge 49. 51 and the bottom surface (epi surface) 51a, 53a of the second groove 53 can be avoided from projecting.

  The nitride semiconductor region 47 includes a first region 47c, a second region 47d, and a third region 47e, and the first region 47c, the second region 47d, and the third region 47e are respectively the first region 13c of the semiconductor stacked layer 13. , Corresponding to the second region 13d and the third region 13e. The nitride semiconductor region 47 can also include a fourth region 47f and a fifth region 47f, and the first region 47c, the second region 47d, and the third region 47e include the fourth region 47f and the fifth region 47f. Are arranged in between. The fourth region 47f and the fifth region 47f correspond to the fourth region 13f and the fifth region 13f of the semiconductor stacked layer 13, respectively.

  The first region 47 c includes a semiconductor ridge 49. The second region 47d and the third region 47e include a first groove 51 and a second groove 53, respectively. The fourth region 47f and the fifth region 47f include a first terrace 55 and a second terrace 57, respectively.

After the hard mask 43 is removed, as shown in FIG. 5A, an insulating film 59 is grown on the surface of the nitride semiconductor region 47 and the metal layer 45 in the film forming apparatus 10h. Thereby, the substrate product SP3 is formed. The film formation apparatus 10h can apply film formation by, for example, an electron beam evaporation method, a plasma film formation method, a sputtering film formation method, or the like. For example, the insulating film 59 can include a silicon-based inorganic insulating film, a zirconia-based inorganic insulating film, and the like grown by an electron beam evaporation method. This silicon-based inorganic insulating layer can be made of, for example, silicon oxide (specifically, SiO ₂ ), zirconia oxide, or the like. In order to protect the interface between the already formed metal layer 45 and the semipolar surface 13a, the film forming process is performed at a substrate temperature of 300 degrees Celsius or less, and preferably at a substrate temperature of 150 degrees Celsius or less. .

  According to the manufacturing method including the steps of the above example, since the process for forming the semiconductor ridge 49 is applied after the metal film 33 is formed on the semipolar main surface 13a of the semiconductor stack 13, the semipolar main The surface 13a is not directly exposed to the process atmosphere. In addition, while protecting the interface between the metal layer 45 and the semipolar main surface 13a, the insulating film 59 for the protective layer is grown after removing the hard mask 43 without using lift-off consisting of a complicated series of steps. It can be carried out.

  Next, an opening is formed in the insulating film 59 on the upper surface of the semiconductor ridge 49 to form a protective film. For this purpose, as shown in part (b) of FIG. 5, a resist film 61 is formed using several apparatuses 10i. The resist film 61 includes a first portion 61a, a second portion 61b, and a third portion 61c. The first portion 61 a, the second portion 61 b and the third portion 61 c of the resist film 61 are arranged in this order on the nitride semiconductor region, and the second portion 61 b is on the upper surface 49 a of the semiconductor ridge 49 in the nitride semiconductor region 47. Provided. In the present embodiment, the first portion 61 a and the third portion 61 c are provided on the terrace 55 and the terrace 57. The first portion 61 a and the third portion 61 c of the resist film 61 are provided apart from the upper surface 49 a of the semiconductor ridge 49. The thickness D61b of the second portion 61b of the resist film 61 is thinner than the thicknesses D61a and D61c of the first portion 61a and the third portion 61c of the resist film 61.

  Next, a resist mask (indicated by reference numeral “63” in FIG. 7B) is formed from the resist film 61 for removing the insulating film 59 on the top surface of the ridge shown in FIG. . The resist mask 63 has an opening 63 a provided in the upper surface 49 a of the semiconductor ridge 49. In order to form the resist mask 63 from the resist film 61, the resist is gradually removed from the surface of the resist film 61 using the processing apparatus 10j until the metal layer 45 on the upper surface 49a of the semiconductor ridge 49 is exposed from the resist. I will do it. In these processes, treatments such as coating, baking, and removal are performed at a substrate temperature of 300 degrees Celsius or lower in order to protect the interface that has already been formed (the interface between the semipolar surface of the ridge upper surface and the metal layer 45). The substrate temperature is preferably 150 degrees Celsius or less.

  According to this manufacturing method, as shown in FIG. 5B, the thickness D61b of the second portion 61b of the resist film 61 is equal to the thickness D61a of the first portion 61a and the third portion 61c of the resist film 61. The resist mask 63 having an opening 63a on the upper surface 49a of the semiconductor ridge 49 can be formed by removing the resist of the resist film 61 from the surface thereof. In the subsequent process, as shown in FIG. 7B, the insulating film 59 is etched using the resist mask 63 to expose the metal layer 45 on the upper surface 49a of the semiconductor ridge 49. Thus, the protective layer 75 can be formed.

  The resist film 61 in which the thickness D61b of the second portion 61b is thinner than the thicknesses D61a and D61c of the first portion 61a and the third portion 61c is produced, for example, as follows. As shown in FIG. 6B, a resist is applied to the entire surface of the substrate product Sp3 using the processing apparatus 10k to form a first resist film 65. As shown in part (b) of FIG. 6, a first mask layer 67 is formed from the first resist film 65 by using a photolithography method. The first mask layer 67 has an opening 67 a that exposes the insulating film 59 on the upper surface 49 a and the side surfaces 49 b and 49 c of the semiconductor ridge 49. Next, as shown in FIG. 5A, a second resist film 69 is formed on the nitride semiconductor region 47, the metal layer 45, the insulating film 59, and the first mask layer 67. The first mask layer 67 and the second resist film 69 constitute a resist film 61. Subsequently, as shown in FIG. 7A, an opening is formed in the second resist film 69 so that the metal layer 45 on the upper surface 49a of the semiconductor ridge 49 is exposed, and the second mask layer 73 is formed. Form. The first mask layer 67 and the second mask layer 73 can constitute a resist mask 63.

  According to this manufacturing method, since the second resist film 69 is formed on the first mask layer 67 on the upper surface 49 a of the semiconductor ridge 49 and the opening 67 a of the first mask layer 67, the nitride semiconductor region 47 is formed. The resist thickness provided on the second region 47 b can be different from the resist thickness provided on the region of the nitride semiconductor region 47 away from the second region 47 b.

  Further, in order to form an opening in the second resist film 69 so that the upper surface 49a of the semiconductor ridge 49 is exposed, the resist film 61 is exposed to a phenomenon solution, and the resist on the upper surface 49a of the semiconductor ridge 49 is removed. The resist mask 63 is preferably formed. In this manufacturing method, since the resist film 61 is gradually dissolved from the surface thereof in the resist phenomenon solution, the resist film 61 is processed so that the upper surface 49a of the semiconductor ridge 49 and its vicinity are exposed from the resist. It becomes possible to apply.

  The processing such as development and baking in this step is performed at a substrate temperature of 300 degrees Celsius or less in order to protect the interface between the metal film 33 and the semipolar surface 13a that has already been formed, and the substrate temperature is 150 degrees Celsius or less. Preferably there is.

  In the subsequent steps, as shown in FIG. 7B, the insulating film 59 is etched using the resist mask 73 using the etching apparatus 10m, and the protective layer 75 is formed from the insulating film 59. . The protective layer 75 has an opening 75a that exposes the metal layer 45 on the upper surface 49a of the semiconductor ridge 49a. This etching is preferably performed by, for example, an ICP-RIE method. According to this etching method, anisotropy in etching can be realized. The treatment in this step is performed at a substrate temperature of 300 degrees centigrade or less in order to protect the already formed metal layer-semiconductor interface, and the substrate temperature is preferably 150 degrees centigrade or less.

  In a step after the etching, the resist mask 73 is removed. As shown in FIG. 8A, the semiconductor ridge 49 and the metal layer 45 form a ridge structure. The upper surface 49 a of the semiconductor ridge 49 and the metal layer 45 form a metal-semiconductor junction 77. The edge 77 a of the metal-semiconductor junction 77 is located on the side surface of the ridge structure, and the protective layer 75 covers the edge 77 a of the metal-semiconductor junction 77. According to this manufacturing method, since the edge 77a of the metal-semiconductor junction 77 is covered with the protective layer 75, the p layer can be protected from oxygen ashing using O2 which is also an n layer donor. Processing such as film formation is performed at a substrate temperature of 300 degrees centigrade or less, and the substrate temperature is preferably 150 degrees centigrade or less.

  In the subsequent process, an electrode film is deposited on the metal layer 45 and the protective film 75 as shown in FIG. The electrode film is deposited at a substrate temperature of 300 degrees centigrade or less, and more preferably at a substrate temperature of 150 degrees centigrade or less. According to this film formation method, it is possible to avoid the thermal degradation caused by the substrate temperature during electrode film deposition from occurring in the contact resistance. The electrode film is preferably deposited by electron beam evaporation. Next, this electrode film is processed to form an electrode 79a. This processing is performed, for example, by a photolithography lift-off method. The electrode 79 a is in contact with the metal layer 45 through the opening 75 a of the protective layer 75. The electrode 79a is formed on the metal layer 45 and the protective layer 75 and includes a pad electrode. The electrode 79a can be made of, for example, Au, Ti, Pt, or the like.

  Further, as shown in FIG. 8B, after the pad electrode is formed, the electrode 79b is formed. If necessary, after polishing a back surface of the substrate 11 to form a polished substrate (referred to as “11” here), an electrode 79b is formed on the polishing surface 11b of the substrate. After these steps, a nitride semiconductor light emitting element such as a nitride semiconductor laser is formed by performing steps such as laser bar fabrication, dielectric multilayer film formation, and chip separation.

  FIG. 9 is a drawing showing an example of a nitride semiconductor light emitting device fabricated by the above process. The nitride semiconductor light emitting element LD can be, for example, a semiconductor laser. The nitride semiconductor light emitting element LD includes a substrate 83, a first electrode 85, a nitride semiconductor region 87, a protective film 89, a second electrode 91, and a dielectric multilayer film 93. Nitride semiconductor region 87 is in contact with main surface 83 a of substrate 83. The first electrode 85 is in contact with the semipolar main surface 87 a of the nitride semiconductor region 87 through the stripe opening of the protective film 89. The second electrode 91 is in contact with the back surface 83 a of the substrate 83. On the substrate 83, a vector VC indicating the inclination of the c-axis is shown. The nitride semiconductor light emitting element LD has end faces 81a and 81b.

  The nitride semiconductor region 87 includes a first region 87c, a second region 87d, and a third region 87e, and the first region 87c, the second region 87d, and the third region 87e are the first region of the nitride semiconductor region 47, respectively. This corresponds to the region 47c, the second region 47d, and the third region 47e. The nitride semiconductor region 87 can also include a fourth region 87f and a fifth region 87f, and the first region 87c, the second region 87d, and the third region 87e include the fourth region 87f and the fifth region 87f. Are arranged in between. The fourth region 87f and the fifth region 87f correspond to the fourth region 47f and the fifth region 47f of the nitride semiconductor region 47, respectively.

  The first region 87c includes a semiconductor ridge 95a. The second region 87d and the third region 87e include a first groove 95b and a second groove 95c, respectively. The fourth region 87f and the fifth region 87f include a first terrace 95d and a second terrace 95e, respectively. The pad electrode 99 is provided on the semiconductor ridge 95a, the first groove 95b, the second groove 95c, the first terrace 95d, and the second terrace 95e.

  The nitride semiconductor region 87 includes an n-type cladding layer 97a, an n-side light guide layer 97b, an active layer 97c, a p-side light guide layer 97d, a p-type cladding layer 97e, and a p-type contact layer 97f. The p-side light guide layer 97d can include an electron blocking layer if necessary. In this embodiment, the semiconductor ridge 95a includes a part of the p-side light guide layer 97d, a p-type cladding layer 97e, and a p-type contact layer 97f. The semiconductor ridge 95a includes a part of the p-side light guide layer 97d, the p-type cladding layer 97e, and the p-type contact layer 97f extending in the waveguide direction from the end surface 81a to the end surface 81b on the main surface 83a of the substrate 83. Are arranged in the direction of the normal line Nx of the main surface 83 a of the substrate 83. The first region 87c, the second region 87d, and the third region 87e of the nitride semiconductor region 87 are arranged along a direction that intersects both the direction of the normal line Nx and the waveguide direction. In the present embodiment, the surfaces of the first region 87c and the third region 87e are composed of the surface of the p-side light guide layer 97d, and the protective film 89 includes the surface of the first region 87c, the surface of the third region 87e, and the semiconductor ridge 95a. , The surface of the fourth region 87f, and the surface of the fifth region 87f. Since the semiconductor ridge 95a includes the light guide layer 97d, the cladding layer 97e, and the contact layer 97f, and the protective film 89 covers the surface of the first region 87c, the surface of the third region 87e, and the side surface of the semiconductor ridge 95a. Good current confinement and good refractive index profile are provided for the light emitting device.

Example 1
According to the knowledge of the inventors, a low resistance electrode (MBE electrode) can be formed on the semipolar surface by forming an electrode by the MBE method. A nitride semiconductor laser having a ridge structure is formed so as not to impair the characteristics of the metal film thus grown.

  A GaN substrate having a principal surface whose c-plane is inclined at an angle of 75 degrees in the m-axis direction is prepared. This GaN substrate has a semipolar surface. First, an n-type GaN buffer layer, an n-type AlGaN cladding layer, an n-type and undoped InGaN guide layer, an InGaN active layer, a p-type AlGaN electron block layer, an undoped and p-type InGaN guide layer, p on the semipolar surface of the GaN substrate An epitaxial substrate having a laser structure is fabricated by sequentially epitaxially growing a p-type GaN contact layer and a p-type GaN contact layer.

An Au film (MBE electrode) was formed on the p-type GaN contact layer with an MBE apparatus. The Au film is patterned by lithography to form a stripe-shaped Au layer having a width wider than that of the ridge structure on a part of the surface of the epitaxial substrate. The stripe shape has a width of 20 μm. This Au layer is left on a part of the surface of the epitaxial substrate (area to be the surface of the semiconductor ridge) by etching using a resist mask. Aqua regia is used as an etchant for the Au layer, and the resist is removed by organic cleaning after etching. Subsequently, a SiO ₂ film (thickness 300 nm) for forming a ridge forming mask is formed by electron beam evaporation. A resist mask for ridge formation (ridge width 2 μm, groove opening width 20 μm) is formed on the SiO ₂ film. Using a resist mask with an ICP-RIE apparatus, the SiO ₂ film is etched using an etchant CHF ₃ gas to form a SiO ₂ mask. In the same ICP-RIE apparatus, the Au layer is etched with Ar gas using a resist mask / SiO ₂ mask. Next, in the same ICP-RIE apparatus, the gallium nitride based semiconductor layer is etched by etchant BCl ₃ and / or Cl ₂ gas using a resist mask / SiO ₂ mask to form a semiconductor ridge and a pair of grooves. After these dry etching is finished, the SiO ₂ mask is removed with hydrofluoric acid. Thereafter, a SiO ₂ film (thickness: 300 nm to 400 nm) for filling is formed by electron beam evaporation.

Subsequently, in order to expose the surface of the p-electrode, a resist having an opening exposing a part of the semiconductor ridge and the grooves on both sides thereof is formed. On this resist, another resist having a small thickness is applied on the entire surface to form a resist multilayer film. The ridge structure is covered only with another resist of the resist multilayer film. Next, the resist multilayer film is developed while adjusting the time so that the upper portion of the ridge structure appears slightly. When the upper part of the ridge structure appears, the development is finished. Using a resist mask with an ICP-RIE apparatus, the SiO ₂ film is etched using an etchant CHF ₃ gas to expose the p-side electrode. After this dry etching, organic cleaning is performed to remove the resist multilayer film. Next, Au / Pt / Au / Pt / Ti (300 nm / 30 nm / 450 nm / 30 nm / 20 nm) is deposited in a vacuum deposition furnace to form a metal film for the p-side pad electrode, and then lifted off to form a pad electrode. Form. After the electrode process is completed, the back surface of the substrate is polished, the back surface of the substrate is polished to a thickness of 80 μm, and the back surface, which is the polishing surface, is etched with an etchant BCl ₃ and / or Cl ₂ gas, and the damaged damage layer is etched. Remove. Au / Ti / Al (600 nm / 50 nm / 500 nm) is deposited on the etched back surface in a vacuum deposition furnace. After this wafer process, the substrate product is completed. The substrate product is separated to form a chip to obtain a laser chip.

  In this wafer process, an electrode metal film (for example, an Au film) formed by the MBE method is likely to deteriorate due to the influence of heat received after the formation. For this reason, it is preferable that the substrate temperature is set so as not to exceed 300 degrees Celsius in all steps performed after the metal film for the electrode is formed. The wafer process in this embodiment can be performed so as not to exceed 150 degrees Celsius. In particular, care should be taken not to exceed 150 degrees Celsius during ICP-REI dry etching, electrode formation, and insulating film formation.

  FIG. 10 is a diagram showing the thermal stability of the contact resistance of the p-side electrode. The Au electrode and the Pd electrode can provide good contact resistance with respect to the semipolar plane. The Au electrode is more excellent in thermal stability than the Pd electrode.

11, 12, and 13, an epitaxial in which an electrode is formed after the semipolar plane of the semiconductor ridge is exposed to the atmosphere (a process different from the wafer process in the above embodiment) is produced in the same manner as described above. An example applied to a substrate will be described. As shown in part (a) of FIG. 11, SiO ₂ / Ti / Al (300 nm / 50 nm / 100 nm) is deposited on the epitaxial substrate in a vacuum deposition furnace. As shown in FIG. 11B, a resist mask having a 2 μm wide pattern for ridge formation is formed thereon.

As shown in part (c) of FIG. 11, the SiO ₂ film is etched using an etchant CHF ₃ gas with an ICP-RIE apparatus using a resist mask. In the same ICP-RIE apparatus, the Ti / Al / gallium nitride based semiconductor layer is etched by etchant BCl ₃ and / or Cl ₂ gas using a resist mask / SiO ₂ mask. After these dry etching is finished, the SiO ₂ mask is removed with hydrofluoric acid.

As shown in FIG. 12A, side etching is performed on the Al layer with hydrochloric acid so that SiO _{2 to} be deposited next is not deposited on the Al layer, which is a sacrificial layer. Thereafter, as shown in part (b) of FIG. 12, SiO ₂ (thickness: 300 nm to 400 nm) for embedding is formed. After the SiO ₂ deposition, as shown in FIG. 12C, lift-off is performed by etching with hydrochloric acid in order to remove the SiO ₂ on the ridge.

Subsequently, in order to deposit the p-side electrode, as shown in FIG. 13A, after forming a resist mask having an opening in the ridge portion, a Pd film having a thickness of 30 nm is formed for the p-electrode. Vapor deposition in a vacuum deposition furnace. Thereafter, as shown in FIG. 13B, a p-electrode is formed by lift-off of the Pd film. After forming a metal film for the p-side pad electrode by depositing Au / Pt / Au / Pt / Ti (300 nm / 30 nm / 450 nm / 30 nm / 20 nm) in a vacuum evaporation furnace to form a p-pad. A pattern is formed on the metal film to form pad electrodes as shown in FIG. 13 (c). After the electrode process is completed, the back surface of the substrate is polished, the back surface of the substrate is polished to a thickness of 80 μm, and the back surface, which is the polishing surface, is etched with an etchant BCl ₃ and / or Cl ₂ gas, and the damaged damage layer is etched. Remove. As shown in part (d) of FIG. 13, Au / Ti / Al (600 nm / 50 nm / 500 nm) is deposited on the etched back surface in a vacuum deposition furnace. After this wafer process, the substrate product is completed. The substrate product is separated to form a laser bar, and a semiconductor laser chip is obtained from the laser bar.

  In this example, since the metal film for the electrode is formed on the upper surface of the semiconductor ridge after the semiconductor ridge is exposed, the influence of the surface oxide is inevitable. In addition, since the width of the electrode to be formed is as thin as several μm, it is difficult to control the etching using an acid or alkali solution, and the side surface of the etching surface is disturbed.

  The present invention is not limited to the specific configuration disclosed in the present embodiment.

  According to an embodiment of the present invention, there is provided a method for fabricating a nitride semiconductor light emitting device that enables both formation of an electrode having good physical contact on a semipolar plane and formation of a ridge structure. The

DESCRIPTION OF SYMBOLS 11 ... Board | substrate, 11a ... Substrate main surface, 13 ... Semiconductor lamination, 13a ... Semipolar main surface, 13c ... 1st area | region, 13d ... 2nd area | region, 13e ... 3rd area | region, 13f ... 4th area | region, 13f ... 5th 15 ... n-type group III nitride semiconductor region, 16 ... n-side light guide layer, 17 ... active layer, 18 ... p-side light guide layer, 19 ... p-type group III nitride semiconductor region, 21 ... quantum well structure , 23 ... barrier layer, 25 ... well layer, E ... epitaxial substrate, 27 ... atmosphere, 29 ... metal film, 35 ... mask film, 41 ... mask, 43 ... hard mask, 47 ... nitride semiconductor region, 47c ... first Region 47d ... Second region 47e ... Third region 47f ... Fourth region 47f ... Fifth region 49 ... Semiconductor ridge 49a ... Semiconductor ridge upper surface 49b, 49c Semiconductor ridge side surface 51 ... First groove 53 ... 2nd groove, 55 ... 1st terra , 57 ... second terrace, 59 ... insulating film, 61 ... resist film, 63 ... resist mask, 65 ... first resist film, 67 ... first mask layer, 69 ... second resist film, 73 ... second mask Layer, 75 ... protective layer, 75a ... opening, 77 ... metal-semiconductor junction, 77a ... metal-semiconductor junction edge, 79a, 79b ... electrode.

Claims (19)

A method for producing a nitride semiconductor light emitting device, comprising:
Forming a metal film on a semipolar main surface of an epitaxial substrate including a semiconductor stack using growth using an MBE method in a film forming apparatus;
Forming a ridge defining mask on the semiconductor stack and the metal film;
Etching the semiconductor stack and the metal film using the mask to form a nitride semiconductor region including a semiconductor ridge and a metal layer on the semiconductor ridge;
Growing an insulating film for a protective layer on the surface of the nitride semiconductor region and the metal layer after removing the mask;
With
The semipolar main surface is made of a group III nitride semiconductor,
The semiconductor stack includes an active layer made of group III nitride,
A method for producing a nitride semiconductor light emitting device, wherein the metal film forms a junction with the semipolar main surface.   2. The semipolar main surface of the epitaxial substrate is inclined at an angle in a range of 10 degrees to 80 degrees from a plane orthogonal to a reference axis extending along the c-axis of the group III nitride semiconductor. A method for fabricating a nitride semiconductor light emitting device. In the film forming apparatus, further comprising the step of exposing the entire semipolar main surface of the semiconductor stack to an atmosphere of a group III element,
The semipolar main surface of the semiconductor stack is made of group III nitride,
The method for producing a nitride semiconductor light emitting device according to claim 1, wherein the group III nitride includes the group III element as a constituent element. The semipolar principal surface of the semiconductor stack is made of a gallium nitride based semiconductor,
The atmosphere includes gallium;
The said process which exposes the said semipolar principal surface to the said atmosphere WHEREIN: Irradiation of a gallium flux is performed to the said semipolar principal surface at the substrate temperature of 300 degreeC or more. A method for fabricating a nitride semiconductor light emitting device.   4. The method for producing a nitride semiconductor light emitting device according to claim 1, wherein the metal film includes gold grown by an MBE method. 5. Forming a resist film on the insulating film;
Forming a resist mask having an opening provided on the upper surface of the semiconductor ridge from the resist film;
Etching the insulating film using the resist mask to form a protective layer from the insulating film;
With
The protective layer has an opening exposing a metal layer on the top surface of the semiconductor ridge;
The resist film includes a first portion, a second portion, and a third portion,
The first portion, the second portion, and the third portion of the resist film are disposed in this order on the nitride semiconductor region,
The second portion of the resist film is located on an upper surface of the semiconductor ridge;
The first portion and the third portion of the resist film are provided apart from the semiconductor ridge,
The thickness of the second portion of the resist film is thinner than the thickness of the first portion and the third portion of the resist film,
The nitride according to any one of claims 1 to 5, wherein, in the step of forming the resist mask from the resist film, the resist of the resist film is removed from the surface of the resist film. A method of manufacturing a semiconductor light emitting device. The step of forming the resist mask from the resist film includes:
Forming a first resist film on the insulating film;
Forming a first mask layer from the first resist film having an opening exposing the insulating film on the top and side surfaces of the semiconductor ridge using a photolithography method;
Forming a second resist film on the nitride semiconductor region, the metal layer, the insulating film, and the first mask layer;
Forming an opening in the second resist film to expose the upper surface of the semiconductor ridge and forming a second mask layer;
With
The resist film includes the first mask layer and the second resist film,
The method for producing a nitride semiconductor light emitting device according to claim 6, wherein the resist mask includes the first mask layer and the second mask layer.   The step of forming the resist mask from the resist film, the resist film is exposed to a phenomenon solution, the resist on the upper surface of the semiconductor ridge is removed, and the resist mask is formed. The method for producing a nitride semiconductor light emitting device according to claim 7. The semiconductor ridge and the metal layer form a ridge structure;
The upper surface of the semiconductor ridge and the metal layer form a metal-semiconductor junction;
An edge of the metal-semiconductor junction is located on a side surface of the ridge structure;
The method for producing a nitride semiconductor light-emitting device according to claim 6, wherein the protective layer covers the edge of the metal-semiconductor junction. Depositing an electrode film on the metal layer and the insulating film after removing the resist mask;
Processing the electrode film to form an electrode;
Further comprising
The electrode is in contact with the metal layer through the opening of the protective layer;
The method for producing a nitride semiconductor light emitting element according to claim 6, wherein the electrode film is deposited at a substrate temperature of 300 degrees Celsius or less.   The method for producing a nitride semiconductor light emitting device according to claim 10, wherein the electrode film is deposited by an electron beam evaporation method. The nitride semiconductor region includes a first groove and a second groove, and a first terrace and a second terrace,
The first groove and the second groove define the semiconductor ridge;
The semiconductor ridge and the first terrace define the first groove;
The method of manufacturing a nitride semiconductor light emitting device according to claim 1, wherein the semiconductor ridge and the second terrace define the second groove. The step of forming the metal film includes:
Forming a metal region in the film forming apparatus by metal deposition using an MBE method;
Etching the metal region to partially expose the semipolar main surface of the semiconductor stack and forming the metal film on the semipolar main surface of the epitaxial substrate;
The method of producing the nitride semiconductor light-emitting device as described in any one of Claims 1-12 containing this. The step of forming the mask includes:
Forming a mask film on the semiconductor stack and the metal layer;
Forming the mask by etching the mask film;
Including
The method for producing a nitride semiconductor light emitting device according to claim 1, wherein the etching is performed at a substrate temperature of 300 degrees Celsius or less.   The method for manufacturing a nitride semiconductor light emitting device according to claim 14, wherein the mask film includes at least one of a tungsten film, a silicon oxide film, and a silicon nitride film. Further comprising the step of growing the semiconductor stack on the main surface of the substrate to form the epitaxial substrate;
The main surface of the substrate is made of a group III nitride semiconductor,
The semiconductor stack includes a first conductivity type group III nitride semiconductor layer, the active layer, and a second conductivity type group III nitride semiconductor layer,
The epitaxial substrate includes the substrate,
The main surface of the substrate is inclined at an angle in the range of 10 degrees to 80 degrees from a plane orthogonal to a reference axis extending along the c-axis of the group III nitride semiconductor,
The main surface of the epitaxial substrate is inclined at an angle in a range of 10 degrees to 80 degrees from a plane orthogonal to a reference axis extending along the c-axis of the group III nitride semiconductor,
The semiconductor stack includes a first region, a second region, and a third region,
The first region, the second region, and the third region are disposed along the main surface of the substrate;
The second region is located between the first region and the third region;
The method for producing a nitride semiconductor light emitting device according to claim 1, wherein the semiconductor ridge is formed in the second region.   The semipolar main surface of the epitaxial substrate is inclined at an angle in the range of 63 degrees to 80 degrees from a plane orthogonal to a reference axis extending along the c-axis of the group III nitride semiconductor. Item 19. A method for producing the nitride semiconductor light emitting device according to any one of Items 16. The semiconductor ridge includes a light guide layer provided on the active layer, a clad layer provided on the light guide layer, and a contact layer provided on the clad layer,
The semiconductor ridge extends in a first direction;
The light guide layer, the cladding layer, and the contact layer are arranged in a second direction intersecting the first direction,
The nitride semiconductor region includes a first region, a second region, and a third region,
The first region, the second region, and the third region are arranged along a third direction that intersects both the first direction and the second direction;
The second region is located between the first region and the third region;
The second region includes the semiconductor ridge;
The surfaces of the first region and the third region are the surfaces of the light guide layer,
The nitride semiconductor light emitting device according to claim 1, wherein the protective layer covers the surface of the first region, the surface of the third region, and a side surface of the semiconductor ridge. A method for manufacturing an element. The active layer includes a gallium nitride based semiconductor layer containing indium as a group III constituent element,
The method for producing a nitride semiconductor light emitting element according to any one of claims 1 to 18, wherein the active layer has a peak emission wavelength in a wavelength range of 500 nm or more and 540 nm or less.

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