JP5061951B2 - Manufacturing method of optical semiconductor device - Google Patents

Description

  The present invention relates to a method for manufacturing an optical semiconductor device, and more particularly to a method for manufacturing an optical semiconductor device in which a ridge (or mesa) is embedded with a thermosetting resin.

  There is an optical semiconductor device (a light emitting element, a light receiving element, an optical modulator, or the like) in which a “ridge” or “mesa” semiconductor layer is embedded with a thermosetting resin such as benzocyclobutene.

  Such an optical semiconductor device has a small parasitic capacitance and is suitable for high-speed operation because the buried layer supporting the electrode is formed of a thermosetting resin having a low dielectric constant.

  A thermosetting resin used in the manufacture of an optical semiconductor device is cured by heating to change the molecular structure into a network or a three-dimensional structure, but is initially a low molecular weight liquid. Therefore, the optical semiconductor device can be easily flattened simply by applying a liquid thermosetting resin to the substrate surface having ridges and the like where the unevenness is severe and then heating.

  In particular, an optical semiconductor device embedded with benzocyclobutene (hereinafter abbreviated as BCB) has high long-term reliability and excellent flatness of the embedded layer (Patent Documents 1 and 2).

“Ridge” and “mesa” mean a structure in which convex portions provided on a semiconductor substrate extend parallel to the semiconductor substrate. The “ridge” is a convex portion formed by a semiconductor laminated structure that does not include an active layer such as an active layer of a light emitting element or a light absorbing layer of a light receiving element. On the other hand, a “mesa” is a convex portion formed by a semiconductor multilayer structure including such an active layer.
JP 2002-164622 A JP 2004-71713 A

  1 to 6 are process cross-sectional views for explaining a manufacturing procedure of a semiconductor laser device embedded with benzocyclobutene (BCB).

  First, a semiconductor multilayer structure including a buffer layer (not shown), an active layer 4, an upper clad 6, and a contact layer 8 is grown on the semiconductor substrate 2 by metal organic vapor phase epitaxy or the like. Here, the buffer layer also functions as a lower cladding layer.

Next, an etching mask 10 made of, for example, SiO ₂ is formed on the surface of the semiconductor laminated structure, and the openings are opened on both sides of the region where the ridge 12 is to be formed.

  Using this etching mask 10 as a protective film, the semiconductor stacked structure is etched to the vicinity of the active layer by, for example, inductive coupled plasma-reactive ion etching (ICP-RIE) to form a pair of recesses 14 is formed (see FIG. 1A). A region sandwiched between the pair of recesses 14 becomes the ridge 12. 1 to 6 are process sectional views as seen from a direction parallel to the ridge 12.

Next, the etching mask 10 is removed, and a passivation film 16 made of SiO ₂ is formed on the entire surface of the semiconductor substrate 2 on which the ridge 12 is formed. This passivation film 16 is for reducing the surface leakage current of the semiconductor.

  Thereafter, liquid BCB (benzocyclobutene) is applied to the entire surface of the semiconductor substrate 2 covered with the passivation film 16, and then heated and cured at 250 ° C. to form the BCB layer 18 (FIG. 1B). reference).

  Next, a photoresist film 20 is formed on the BCB layer 18 so as to open in the upper part of the region composed of the ridge 12 and the recess 14 (see FIG. 2A).

Next, the photoresist film 20 was used as a protective film, and the reactive ion etching (RIE) using a mixed gas of CF ₄ and O ₂ as a reactive gas was disposed on the ridge 12 and the recess 14. The BCB layer 18 is etched to expose the passivation film 16 that covers the top of the ridge 12. (See FIG. 2 (b)).

  Next, the photoresist film 20 is removed (see FIG. 3A).

  Next, 10: 1 buffer hydrofluoric acid (40% ammonium fluoride aqueous solution for semiconductor (manufactured by Daikin Industries) and 50% hydrofluoric acid aqueous solution for semiconductor (manufactured by Daikin Industries) are mixed at a volume ratio of 10: 1. The passivation film 16 covering the top of the ridge 12, that is, the contact layer 8, is removed by using the chemical solution (hereinafter referred to as 10: 1 BHF) to complete the contact hole 17 (see FIG. 3B).

  Next, a SiN film 28 is formed on the entire surface of the semiconductor substrate 2 in which the contact holes 17 are formed by a P-CVD method (Plasma-enhanced Chemical Vapor Deposition). Thereafter, a photoresist film 20 ′ in which an upper portion of a region including the contact layer 8 is opened is formed on the SiN film 28 (see FIG. 4A).

  The SiN film 28 is used to improve the adhesion between a pad electrode 32 (described later) and the BCB layer 18.

  Next, using the photoresist film 20 ′ as an etching mask, the SiN film 28 is etched to expose the contact layer 8. Thereafter, the photoresist film 20 'is reused to lift off the metal film 22 (to be a contact electrode) on the contact layer 8 (for example, Au / Zn / Au for a P-type contact layer). Form by law. At this time, the metal film 22 is formed so as to protrude from the BCB layer 18 so that the entire surface of the contact layer 8 is reliably covered with the metal film 22. (See FIG. 4 (b)).

  Further, a metal film (for example, AuGe / Ni / Au for an N-type substrate) to be a back electrode (not shown) is deposited on the back surface of the semiconductor substrate 2. Thereafter, for example, the semiconductor substrate 2 is heated to 350 ° C., and the respective metal films and the semiconductor layer are reacted to form the contact electrode 26 and the back electrode 27 (FIG. 5A).

  Next, a metal film (not shown) made of, for example, Au is deposited on the entire surface of the semiconductor substrate 2 on which the contact electrode 26 and the insulating film 28 are formed to form a plating electrode. Thereafter, a plating photoresist film 30 opened in a region where the pad electrode is to be formed is formed on the plating electrode (FIG. 5B).

  The pad electrode 32 is connected to a lead wire through which a drive current flows after the completion of the semiconductor laser device.

  Next, for example, Au is plated on the plating electrode not covered with the plating photoresist film 30 to form the pad electrode 32. Thereafter, the plating electrode protruding from the plating photoresist film 30 and the pad electrode 32 is removed (FIG. 6).

  Finally, the semiconductor substrate 2 is cleaved to form the end face of the optical resonator, thereby completing the semiconductor laser device.

  According to the above procedure, an optical semiconductor device in which a ridge (or mesa) is embedded with a thermosetting resin is manufactured.

  By the way, in the etching process of the BCB layer 18 described with reference to FIG. 2B, the etching is continued for a while after the passivation film 16 is exposed so that the subsequent process is not hindered. The passivation film 16 is completely exposed. That is, overetching is performed. Therefore, the surface of the BCB layer 18 adjacent to the ridge 12 is slightly lower than the top 19 of the ridge 12 (the surface of the contact layer 8), as shown in FIG.

  Thereafter, as described with reference to FIG. 3B, the passivation film 16 covering the top 19 of the ridge 12 is removed with an etching solution such as 10: 1 BHF. At this time, the surface of the contact layer 8 is completely removed. The passivation film 16 is over-etched so as to be exposed.

  Due to the overetching of the BCB layer 18 described above, the upper end of the passivation film 16 covering the side surface of the ridge 12 is exposed on the BCB layer 18 as shown in FIG. The exposed passivation film 16 is completely removed by subsequent over-etching with 10: 1 BHF or the like, and further, a portion buried in the BCB layer 18 is also partially removed. For this reason, the upper side surface 34 of the ridge 12 is bare (see FIG. 3B).

  The naked upper side surface 34 is exposed to various chemical solutions in the subsequent process. For example, in the step of forming the contact electrode 26 described with reference to FIGS. 4A to 5A, the surface of the contact layer 8 is coated with a chemical solution such as hydrochloric acid or sulfuric acid before the metal film 22 is deposited. Wash with. At this time, the upper side surface 34 of the bare ridge 12 is also exposed to these chemicals.

  Further, in the step of forming the plating photoresist film 30 described with reference to FIG. 5B, the upper side surface 34 of the ridge 12 is exposed to an alkaline photoresist removing solution.

  The upper side surface 34 of the ridge 12 is gradually eroded by these chemicals, and finally, as shown in FIG. 5B, the tip of the ridge 12 including the contact layer 8 (the top and the vicinity thereof) is thinned. (So-called etch-off phenomenon). Accordingly, degradation of the device characteristics such as an increase in device resistance occurs.

  Such an etch-off phenomenon is particularly remarkable in an optical semiconductor device (GaAs optical semiconductor device) formed of a semiconductor material containing GaAs as a main component. However, even in an optical semiconductor device formed of a semiconductor material containing other semiconductor as a main component such as an optical semiconductor device (InP-based optical semiconductor device) formed of a semiconductor material containing InP as a main component, this etch-off phenomenon is To express.

  2B to FIG. 3A, the reason that the BCB layer 18 and the passivation film 16 are over-etched is that when they remain on the surface of the contact layer 8, the contact electrode 26 This is because the formation of is hindered and the device resistance increases.

  As is clear from the above description, if the disappearance of the passivation film 16 covering the upper side surface 34 of the ridge 12 due to the over-etching can be avoided, the above-described etch-off phenomenon can be prevented. Therefore, an increase in device resistance can be avoided.

  In order to prevent the etching of the passivation film 16 on the ridge upper side surface 34, a dry etching method is effective in which ions in the reaction gas converted into plasma are accelerated by an electric field and incident on an etching target. According to such a dry etching method, the passivation film 16 is preferentially etched at the top 19 of the ridge 12 perpendicular to the electric field, and the passivation film 16 is hardly etched on the upper side surface 34 thereof.

  In many dry etching methods, an etching target is chemically etched by a reaction gas activated by plasmatization, and ions in the plasma are accelerated by an electric field and collide with the etching target. It is physically etched. Therefore, etching becomes significant in the direction in which ions in the plasma are accelerated, that is, in the direction perpendicular to the semiconductor substrate 2, and the passivation film 16 is etched substantially only at the top 19 of the ridge 12.

  As a dry etching method capable of such anisotropic etching, there is, for example, reactive ion etching in which the potential of an etching target is negative with respect to plasma.

  Therefore, according to such a dry etching method, it is possible to remove the passivation film 16 from the top of the ridge 12 while avoiding the etching of the passivation film 16 covering the upper side surface of the ridge 12.

  However, when the passivation film 16 is etched by the dry etching method, the contact layer 8 disposed on the top of the ridge 12 may be damaged and deteriorated by ion bombardment received from plasma. For this reason, since the metal film 22 deposited on the contact layer 8 and the contact layer 8 react appropriately by the heat treatment to prevent an ohmic electrode from being formed, lowering the resistance of the contact electrode is hindered. Therefore, there is a concern about applying the dry etching method to the final procedure of removing the passivation film 16 covering the top of the ridge, that is, forming the contact hole 17.

  If the upper side surface 34 of the ridge 12 is covered with the metal film 22 in the process of forming the contact electrode 26 described with reference to FIGS. The erosion of the upper side surface 34 of the ridge 12 by various chemical solutions can be mitigated. However, as shown in FIG. 3B, the upper side surface 34 of the ridge is cut perpendicularly to the adjacent BCB layer 18 to form a step. Therefore, it is difficult for the upper side surface 34 of the ridge 12 to be covered with the metal film 22. Therefore, protection of the ridge upper side surface by the metal film 22 cannot be expected.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to make an optical semiconductor device manufacturing method in which a ridge (or mesa) is embedded with a thermosetting resin so that the tip portion (the top and the vicinity thereof) of the ridge 12 is eroded by a chemical solution and becomes thin. It is an object of the present invention to provide a method of manufacturing an optical semiconductor device that prevents deterioration of device characteristics such as an increase in device resistance.

  In order to achieve the above object, the present manufacturing method etches a semiconductor laminated structure formed on a semiconductor substrate using a mask made of a first insulating film, thereby providing a convex portion provided on the semiconductor substrate. Forming a structure extending in parallel with the semiconductor substrate, and forming a second insulating film on the surface of the semiconductor substrate on which the structure is formed, leaving the first insulating film. Forming a second step of covering the top and side surfaces of the structure with the second insulating film; and covering the surface of the semiconductor substrate on which the second insulating film is formed with a thermosetting resin. 3, a fourth step of etching the thermosetting resin covering the top of the structure to expose the surface of the second insulator covering the top, and the top by the dry etching method. A fifth step of exposing the first insulating film covering the substrate; A sixth step of selectively etching the first insulating film with respect to the second insulating film with a etching solution to expose the top, and a seventh step of forming a contact electrode on the exposed top. The process is comprised.

  In the present manufacturing method, since the second insulating film covering the structure (ridge or mesa) is etched by a dry etching method, the structure without losing the second insulator covering the side surface of the structure. A first insulator covering the top of the substrate can be exposed. Thereafter, the first insulator is selectively removed by an etching solution, so that the top can be exposed without damaging the semiconductor layer (contact layer) included in the structure.

  That is, according to the present manufacturing method, the step after the removal of the first insulator can be performed without damaging the contact layer and protecting the side surface of the structure with the second insulating film. it can.

  Therefore, according to this manufacturing method, in the method of manufacturing an optical semiconductor device in which the structure (ridge or mesa) is embedded with a thermosetting resin, the thinning of the tip of the structure with the chemical used in the manufacturing process is performed. Therefore, it is possible to avoid deterioration of device characteristics such as increase in device resistance.

  In the disclosed manufacturing method, the second insulating film covering the first insulator disposed on the top of the ridge (or mesa) is etched by the dry etching method, so that the second surface covering the side surface of the ridge (or mesa) is etched. The first insulator can be exposed on the top of the ridge (or mesa) without losing the insulator. Thereafter, since the first insulator is selectively removed by a chemical etching solution, the top of the ridge (or mesa) can be exposed without damaging the contact layer included in the ridge (or mesa). it can.

  That is, according to the disclosed manufacturing method, the first insulating layer is not damaged in the contact layer included in the ridge (or mesa) and the side surface of the ridge (or mesa) is protected by the second insulating film. The manufacturing process after removing the insulating film can be performed. Therefore, according to the disclosed manufacturing method, the thinning of the tip of the ridge (or mesa) due to the chemical can be prevented in the step after the first insulator removal.

  Therefore, according to the disclosed manufacturing method, it is possible to avoid degradation of device characteristics such as increase in device resistance in a method of manufacturing an optical semiconductor device in which a ridge (or mesa) is embedded with a thermosetting resin. become.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the technical scope of the present invention is not limited to these embodiments, but extends to the matters described in the claims and equivalents thereof.
(Embodiment 1)
In the method of manufacturing an optical semiconductor device in which the ridge is embedded with a thermosetting resin, the present embodiment prevents the tip portion (the top and the vicinity thereof) of the ridge 12 including the contact layer 8 from thinning, The present invention relates to a method of manufacturing an optical semiconductor device that avoids deterioration of device characteristics such as an increase in resistance.

  As shown in FIG. 13B, the optical semiconductor device manufactured according to the present embodiment has a ridge 12 composed of an upper clad 6 and a contact layer 8, and a benzocyclobutene layer (BCB layer 18) in which the ridge 12 is embedded. Consists of.

  A method for manufacturing the optical semiconductor device according to the present embodiment will be described below with reference to FIGS. FIG. 7 is a flowchart illustrating the manufacturing procedure of the optical semiconductor device according to the present embodiment. On the other hand, FIGS. 8 to 13 are process cross-sectional views illustrating the manufacturing procedure of the semiconductor laser device according to the present embodiment.

  First, a semiconductor multilayer structure including a buffer layer (not shown), an active layer 4, an upper clad 6, and a contact layer 8 is grown on the semiconductor substrate 2 by metal organic vapor phase epitaxy (step). S1). The buffer layer also functions as a lower cladding layer.

  Thereafter, a SiN film having a thickness of 400 nm is deposited on the surface of the semiconductor laminated structure at about 300 ° C. by, for example, a plasma CVD method (P-CVD method).

  Further, a photoresist film having openings on both sides of the region to be the ridge 12 is formed on the SiN film. Thereafter, the SiN film is etched by 100: 1 BHF to form an SiN etching mask 10 ′ having openings on both sides of the region to be the ridge 12 (step S 2).

  Thereafter, using the SiN etching mask 10 'as a protective film, the semiconductor stacked structure is etched to the vicinity of the active layer by, for example, inductively coupled reactive ion etching (ICP-RIE) to form a pair of recesses 14. To do. A region sandwiched between the pair of recesses 14 becomes the ridge 12 (step S3; see FIG. 8A).

  8 to 13 are process cross sections each having a cross section perpendicular to the ridge 12.

Next, a SiO ₂ passivation film 16 ′ having a thickness of 400 nm is formed on the surface of the semiconductor substrate 2 on which the ridge 12 is formed, while leaving the SiN etching mask 10 ′. The side surface is covered (step S4).

This SiO ₂ is deposited by, for example, a thermal CVD method (Thermal Chemical Vapor Deposition). Here, the passivation film 16 'is for reducing the surface leakage current of the semiconductor.

  Thereafter, liquid BCB (benzocyclobutene) is applied to the entire surface of the semiconductor substrate 2 covered with the passivation film 16 '. Thereafter, the BCB is heated to 250 ° C. and cured to form the BCB layer 18 (step S5; see FIG. 8B).

  Next, a photoresist film 20 is formed on the BCB layer 18 so as to open above the region having the ridge 12 and the recess 14 (see FIG. 9A).

Next, the BCB layer 18 disposed on the ridges 12 and the recesses 14 is formed by reactive ion etching (RIE) using the photoresist film 20 as a protective film and a mixed gas of CF ₄ and O ₂ as a reaction gas. Etching exposes the passivation film 16 ′ covering the top of the ridge 12. (Step S6; see FIG. 9B).

Next, the photoresist film 20 is removed (see FIG. 10A). Thereafter, the passivation film 16 ′ made of SiO _{2 is} etched by a dry etching method, for example, RIE using CF ₄ as a reactive gas to expose the etching mask 10 ′ made of SiN covering the top of the ridge 12 (step S7). ; See FIG. 10 (b)).

  As described above, in the dry etching method, the etching rate in the direction perpendicular to the main surface of the semiconductor substrate 2 is higher than the etching rate in the direction horizontal to the main surface. Therefore, unlike the related art described with reference to FIG. 3B, according to the present embodiment, the entire side surface of the ridge 12 can be kept covered with the passivation film 16 ′.

In addition, in this embodiment, since the top of the ridge 12 is protected by the SiN etching mask 10 ′, even if the SiO ₂ passivation film 16 ′ is removed by dry etching, the contact layer 8 by ion bombardment is used. Will not take damage.

Note that the etching rate of SiO ₂ by RIE is substantially the same as the etching rate of SiN. Accordingly, in the above-described step of exposing the etching film 10 ′ described with reference to FIG. 10B, the etching time is adjusted so that only the passivation film 16 ′ is etched.

  Next, the etching mask 10 'made of SiN is selectively etched using 100: 1 BHF to complete the contact hole 17 (step S8; see FIG. 11A).

The etching rate of the SiN film deposited by plasma CVD with respect to 100: 1 BHF can be 200 nm / min at room temperature (25 ° C.) by the film forming method. On the other hand, the etching rate (room temperature) of the SiO ₂ film deposited by thermal CVD can be made 20 nm / min, which is only 1/10 of the etching rate of the SiN film, by the film forming method. Therefore, the selective etching as described above is possible.

  As shown in FIG. 10A, according to the above steps (steps S6 to S8), the entire side surface of the ridge 12 is covered and protected by the passivation film 16 ′. Therefore, unlike the related art (see FIG. 5B), the tip of the ridge 12 is not eroded and thinned by the chemical used in the subsequent steps.

  Next, a SiN film 28 is formed on the entire surface of the semiconductor substrate 2 in which the contact holes 17 are formed by a P-CVD method. Thereafter, a photoresist film 20 ′ is formed on the SiN film 28 so as to open in the upper part of the region including the contact layer 8 (see FIG. 11B).

  The SiN film 28 is used to improve the adhesion between a pad electrode 32 (described later) and the BCB layer 18.

  Next, using the photoresist film 20 ′ as an etching mask, the SiN film 28 is etched to expose the contact layer 8. Thereafter, the photoresist film 20 'is reused to form a metal film 22 (to be a contact electrode) (for example, Au / Zn for a P-type contact layer) on the contact layer 8 by a lift-off method. To do. At this time, the metal film 22 is formed so as to protrude into the BCB layer 18 so that the entire surface of the contact layer 8 is surely covered with the metal film 22. (See FIG. 12 (a)).

  Further, a metal film (for example, AuGe / Ni / Au for an N-type substrate) to be a back electrode (not shown) is deposited on the back surface of the semiconductor substrate 2. Thereafter, for example, the semiconductor substrate 2 is heated to 350 ° C. to cause the respective metal films and the semiconductor layer to react to form the contact electrode 26 and the back electrode 27 (step S9; FIG. 12B).

  Next, a metal film (not shown) made of, for example, Au is deposited on the entire surface of the semiconductor substrate 2 on which the contact electrode 26 and the insulating film 28 are formed to form a plating electrode. Thereafter, a plating photoresist film 30 having an opening in a region where a pad electrode is to be formed is formed (see FIG. 13A). After the completion of the semiconductor laser device, a lead wire is connected to the pad electrode 32, and a drive current is supplied to the semiconductor laser device via this lead wire.

  Next, using the plating electrode as an electrode, for example, Au is plated in a region not covered with the plating photoresist film 30 to form a pad electrode 32. Thereafter, the plating photoresist film 30 is removed, and the plating electrode is removed from the portion where the pad electrode 32 is not formed, thereby completing the pad electrode 32 (step S10; see FIG. 13B). .

  Thereafter, the semiconductor substrate 2 is cleaved to form the end face of the optical resonator, thereby completing the semiconductor laser device (step S11).

  As shown in FIG. 11A, according to the method for manufacturing the optical semiconductor device according to the present embodiment, the entire side surface of the ridge 12 is covered with the passivation film 16 ′. The tip of the ridge 12 is not eroded by the chemical used for forming the ridge. Therefore, the tip of the ridge 12 is not tapered, and the device resistance of the optical semiconductor device is not increased.

  The main parts of the method of manufacturing the optical semiconductor device described with reference to FIGS. 7 to 13 are summarized as follows.

  That is, in the present embodiment, first, a semiconductor stacked structure (active layer 4) including a semiconductor layer (contact layer 8) formed on the semiconductor substrate 2 and scheduled to be in electrical contact with the contact electrode 26. And the upper clad 6 and the semiconductor laminated structure comprising the contact layer 8) are provided on the semiconductor substrate by etching using a mask made of the first insulating film (SiN film; etching mask 10 ′). A structure (ridge 12) having a convex portion extending in parallel with the semiconductor substrate is formed (see FIG. 8A).

Next, in the present embodiment, the second insulating film (SiN film; etching mask 10 ') is left on the surface of the semiconductor substrate 2 on which the structure (ridge 12) is formed, while the first insulating film (SiN film; etching mask 10') is left. An insulating film (SiO ₂ film; passivation film 16 ′) is formed, and the top and side surfaces of the structure (ridge 12) are covered with the second insulating film (SiO ₂ film; passivation film 16 ′).

Further, in the present embodiment, the surface of the semiconductor substrate 2 on which the second insulator (SiO ₂ film; passivation film 16 ′) is formed is covered with the thermosetting resin (BCB; BCB layer 18). (See FIG. 8 (b)).

Next, in the present embodiment, the thermosetting resin (BCB; BCB layer 18) covering the upper portion of the structure (ridge 12) is etched, and the second insulator (SiO ₂ ) covering the top. The surface of the film (passivation film 16 ') is exposed (see FIGS. 9A to 10A).

Next, in the present embodiment, the second insulating film (SiO 2) is etched by a dry etching method in which the etching rate in the direction perpendicular to the main surface of the semiconductor substrate 2 is larger than the etching rate in the direction horizontal to the main surface. ₂ film; passivation film 16 ′) is etched to cover the top without damaging the second insulating film (SiO ₂ film; passivation film 16 ′) covering the side surface of the structure (ridge 12). The first insulating film (SiN film; etching mask 10 ′) is exposed (see FIG. 10B).

Next, in the present embodiment, the first insulating film (SiN film; etching mask 10 ′) is selectively used with respect to the second insulating film (SiO ₂ film; passivation film 16 ′) by an etching solution. Etching is performed to expose the top (see FIGS. 11A to 13A).

  In this embodiment, the contact electrode 26 is formed on the exposed top (see FIG. 11B).

As described above, in this embodiment, the top and side surfaces of the ridge 12 are formed on the second insulating film (SiO ₂ ) while the first insulating film (SiN film), that is, the etching mask 10 ′ is left on the top of the ridge 12. Film), that is, a passivation film 16 '.

Therefore, even if the second insulating film (SiO ₂ film) covering the top of the ridge 12 is etched by dry etching, the first insulating film (SiN film) serves as a protective layer and is disposed on the top of the ridge 12. The contact layer 8 is not damaged.

Furthermore, since the second insulating film (SiO ₂ film) is etched by dry etching, never second insulating film covering the side surfaces of the ridge 12 (SiO ₂ film) is impaired (Fig. 10 (b) reference).

  Further, only the first insulating film (SiN film) exposed by the dry etching is selectively etched with a chemical etching solution to complete the contact hole 17 (see FIG. 11A).

Therefore, since all the side surfaces of the ridge are still covered with the _second insulating film (SiO ₂ film), the tip portion is not eroded by the chemical solution and thinned in the subsequent steps.

Therefore, according to the present embodiment, the tip of the ridge 12 is not eroded and thinned, so that the contact resistance (that is, the device resistance) of the optical semiconductor device is increased and the device characteristics are deteriorated. There is no.
(Embodiment 2)
In the present embodiment, in the method of manufacturing an optical semiconductor device according to the first embodiment, the surface of the BCB layer 18 is aligned substantially on the same plane as the top of the ridge 12 so that the contact electrode 26 is not divided (stepped). The present invention relates to a method for manufacturing an optical semiconductor device.

  In step S6 of the manufacturing method according to the first embodiment, that is, the step of etching the BCB layer 18 to expose the passivation film 16 'covering the top of the ridge 12 (see FIG. 9B), the BCB layer 18 is over-etched. This is to prevent the BCB layer 18 from remaining on the passivation film 16 'so as not to hinder subsequent processes. However, this over-etching causes the surface of the BCB layer 18 to be lower than the top of the ridge 12 in a region adjacent to the ridge 12 (see FIG. 9B).

  Due to the step between the surface of the BCB layer 18 formed at this time and the top of the ridge 12, the metal film 22 deposited in the step of forming the contact electrode 26 and the like (Step S 9) is between the ridge 12 and the BCB layer 18. It will be divided (see FIG. 12 (a)). Therefore, the contact electrode 26 (formed by reacting the metal film 22 with the contact layer 8) is also divided and its width is narrowed (see FIG. 12B), and as a result, the device resistance may be increased.

  Therefore, in the present embodiment, the etching mask 10 ′ disposed between the top of the ridge 12 and the passivation film 16 ′ is thickened (see FIG. 15B), and after overetching (adjacent to the ridge 12). The surface of the BCB layer 18 (in the region) is aligned approximately flush with the top of the ridge 12. In this way, the contact electrode 26 is not divided (see FIG. 19B), and the device resistance does not increase.

  Hereinafter, a method for manufacturing an optical semiconductor device according to the present embodiment will be described with reference to FIGS. However, detailed description of the same steps as those in Embodiment 1 is omitted.

  FIG. 14 is a flowchart illustrating the manufacturing procedure of the optical semiconductor device according to the present embodiment. On the other hand, FIGS. 15 to 20 are process cross-sectional views illustrating the manufacturing procedure of the semiconductor laser device according to the present embodiment.

  First, in the same manner as in the first embodiment, a semiconductor multilayer structure is grown using an organic metal growth method (step S1).

  Next, as in the first embodiment, a SiN film is deposited on the semiconductor multilayer structure including the active layer 4 and the like. Thereafter, this SiN film is processed by photolithography and wet etching to form an etching mask 10 '(step S2).

  However, the thickness of the SiN film is set to 800 nm which is thicker than the SiN film deposited in the first embodiment.

  Next, using the etching mask 10 'as a protective film, the semiconductor stacked structure is etched by ICP-RIE to form the ridge 12 (step S3; see FIG. 15A).

Next, a passivation film 16 ′ made of SiO ₂ having a thickness of 400 nm is formed on the surface of the semiconductor substrate 2 on which the ridge 12 is formed, leaving the etching mask 10 ′ made of SiN film (step S4).

  Next, the BCB layer 18 is formed on the surface of the semiconductor substrate 2 covered with the passivation film 16 ′ (step S5; see FIG. 15B).

  Next, a photoresist film 20 is formed on the surface of the BCB layer 18 so as to open in the upper part of the region composed of the ridge 12 and the recess 14 (see FIG. 16A). Thereafter, the BCB layer 18 is etched by RIE using the photoresist film 20 as a protective film to expose the passivation film 16 ′ covering the top of the ridge 12 (step S 6; see FIG. 16B).

  At this time, even after the passivation film 16 ′ appears, the etching of the BCB layer 18 is continued and the BCB layer 18 is etched by an extra 1200 nm.

  Incidentally, as described above, an etching mask 10 'having a thickness of 800 nm and a passivation film 16' having a thickness of 400 nm are stacked on the top of the ridge 12 (the surface of the contact layer 8) (see FIG. 16B). . Therefore, the surface of the passivation film 16 ′ is positioned 1200 nm (= 400 nm + 800 nm) above the top of the ridge 12. Therefore, the surface of the BCB layer 18 after over-etching is aligned with the top 19 of the ridge 12 (the surface of the contact layer 8) in a region adjacent to the ridge 12 (see FIG. 17A).

Next, the passivation film 16 ′ made of SiO _{2 is} etched by a dry etching method to expose the etching mask 10 ′ made of SiN covering the top of the ridge 12 (step S7; see FIG. 17B).

  Next, the etching mask 10 ′ made of SiN is selectively removed using 100: 1 BHF. Further, the contact hole 17 without a step is completed by performing additional etching of the passivation film 16 'with the etching time adjusted using, for example, 10: 1 BHF (step S8; see FIG. 18A).

  Next, in the same manner as in the first embodiment, the SiN film 28, the metal film 22, and the back electrode metal film (not shown) are formed (see FIGS. 18B to 19A). Thereafter, the semiconductor substrate 2 on which the metal film 22 and the like are formed is heat-treated to form the metal contact electrode 26 and the back electrode 27 (step S9; see FIG. 19B).

  Next, in the same manner as in the first embodiment, a plating electrode (not shown) and a plating photoresist film 30 are formed (see FIG. 20A). Thereafter, Au is plated to form the pad electrode 32 (step S10; see FIG. 20B).

  Next, the semiconductor substrate 2 is cleaved to form the end face of the optical resonator, thereby completing the semiconductor laser device (step S11).

  As described with reference to FIG. 15A, in the method of manufacturing the optical semiconductor device according to the present embodiment, the etching mask 10 ′ is deposited thick. Therefore, even if the BCB layer 18 is over-etched, the surface of the BCB layer 12 adjacent to the ridge 12 can be aligned on the same plane as the top of the ridge 12. Therefore, since the contact electrode 26 is not divided and the width thereof is not narrowed, the device resistance of the optical semiconductor device is not increased (see FIG. 20B).

  The main parts of the method of manufacturing the optical semiconductor device described with reference to FIGS. 14 to 20 are summarized as follows.

  That is, in the present embodiment, in the method of manufacturing the optical semiconductor device described in the first embodiment, the step of forming the contact electrode 26 and the like (step S9) in the step of forming the semiconductor multilayer structure (step S1). ) Is extended to the surface of the thermosetting resin 18 adjacent to the structure (ridge 12), the contact electrode 26 is formed on the surface and the top 19 of the structure (ridge 12). The surface of the thermosetting resin 18 after being etched by the step of exposing the passivation film 16 'covering the top (step S4) and the top are on the same plane so that the top is not divided. The first insulating film (etching mask 10 ') whose film thickness is set so as to be aligned is used.

  Therefore, according to this embodiment, since the contact electrode 26 is not divided between the ridge 12 and the BCB layer 18, the device resistance is not increased.

  In the first and second embodiments described above, the method for manufacturing an optical semiconductor device embedded with a thermosetting resin has been described using the semiconductor laser device as an example. However, the optical semiconductor device to which the present invention can be applied is not limited to a semiconductor laser device. For example, other semiconductor light emitting devices (edge-emitting light emitting diode devices and traveling wave semiconductor optical amplifiers), semiconductor photodetectors It is also possible to apply to (waveguide type semiconductor photodetector, etc.) and semiconductor optical modulator.

  In the first and second embodiments, no particular reference is made to the semiconductor material forming the optical semiconductor device. However, the first and second embodiments can be applied to optical semiconductor devices formed of various semiconductor materials such as a semiconductor material containing GaAs as a main component and a semiconductor material containing InP as a main component.

  Moreover, in the above example, the manufacturing method of the optical semiconductor device which the convex part formed on the semiconductor substrate consists of what is called a ridge without an active layer was demonstrated. However, the scope of application of the present invention is not limited to such an optical semiconductor device manufacturing method. For example, the present invention can also be applied to a method of manufacturing an optical semiconductor device in which the convex portion is a so-called mesa including an active layer.

  In the above example, BCB has been described as a thermosetting resin covering the ridge (or mesa). However, the ridge (or mesa) may be embedded with another thermosetting resin such as polyimide.

  In the above example, the case where the uppermost portion of the semiconductor multilayer structure forming the ridge 12 is formed of the contact layer 8 has been described. However, for example, a thin semiconductor layer for preventing contamination is formed on the contact layer 8. It may be laminated. In this case, the semiconductor layer may be removed with an etching solution before depositing the metal film to be the contact electrode.

Further, although the SiN film is exemplified as the first insulating film and the SiO ₂ is exemplified as the second insulating film, the first and second insulating films are not limited to these. If the combination of the insulating films satisfies the condition that the etching rate of the first insulating film> the etching rate of the second insulating film with respect to an etching solution (for example, BHF) having the same composition, a combination of other insulating films May be used.

  In the above-described example, the vicinity of both sides of the region to be the ridge 12 (or mesa) is etched to form the ridge 12 (or mesa) surrounded by the pair of recesses 14 (FIG. 8 ( a)). However, the shape of the ridge (or mesa) is not limited to this. For example, as shown in FIG. 21, a ridge 12 ′ (or mesa) protruding on the semiconductor substrate 2 may be formed by etching all other regions while leaving a region to be the ridge 12 (or mesa).

  In the above-described example, the case where the contact layer 8 and the semiconductor substrate 2 are formed of a p-type semiconductor and an n-type semiconductor has been described. However, the contact layer 8 and the semiconductor substrate 2 may be formed of an n-type semiconductor and a p-type semiconductor, respectively (in this case, a metal film such as AuGe / Ni / Au is formed on the n-type contact layer). On the other hand, a metal film such as Au / Zn is deposited on the p-type substrate).

It is process sectional drawing explaining the manufacturing procedure of the semiconductor laser apparatus embedded with the benzocyclobutene (BCB) (the 1). It is process sectional drawing explaining the manufacturing procedure of the semiconductor laser apparatus embedded with the benzocyclobutene (BCB) (the 2). It is process sectional drawing explaining the manufacturing procedure of the semiconductor laser apparatus embedded with the benzocyclobutene (BCB) (the 3). It is process sectional drawing explaining the manufacturing procedure of the semiconductor laser apparatus embedded with the benzocyclobutene (BCB) (the 4). It is process sectional drawing explaining the manufacturing procedure of the semiconductor laser apparatus embedded with the benzocyclobutene (BCB) (the 5). It is process sectional drawing explaining the manufacturing procedure of the semiconductor laser apparatus embedded with the benzocyclobutene (BCB) (the 6). FIG. 6 is a flowchart illustrating a manufacturing procedure of the optical semiconductor device according to the first embodiment. FIG. 6 is a process cross-sectional view illustrating the manufacturing procedure of the semiconductor laser device according to the first embodiment (No. 1). FIG. 6 is a process cross-sectional view illustrating the manufacturing procedure of the semiconductor laser device according to the first embodiment (No. 2). FIG. 9 is a process cross-sectional view illustrating the manufacturing procedure of the semiconductor laser device according to the first embodiment (No. 3). FIG. 8 is a process cross-sectional view illustrating the manufacturing procedure of the semiconductor laser device according to the first embodiment (No. 4). FIG. 6 is a process cross-sectional view illustrating the manufacturing procedure of the semiconductor laser device according to the first embodiment (No. 5). FIG. 6 is a process cross-sectional view illustrating the manufacturing procedure of the semiconductor laser device according to the first embodiment (No. 6). FIG. 11 is a flowchart illustrating a manufacturing procedure of the optical semiconductor device according to the second embodiment. FIG. 11 is a process cross-sectional view illustrating the manufacturing procedure of the semiconductor laser device according to the second embodiment (No. 1). FIG. 11 is a process cross-sectional view illustrating the manufacturing procedure of the semiconductor laser device according to the second embodiment (No. 2). FIG. 13 is a process cross-sectional view illustrating the manufacturing procedure of the semiconductor laser device according to the second embodiment (No. 3). FIG. 11 is a process cross-sectional view illustrating the manufacturing procedure of the semiconductor laser device according to the second embodiment (No. 4). FIG. 11 is a process cross-sectional view illustrating the manufacturing procedure of the semiconductor laser device according to the second embodiment (No. 5). FIG. 11 is a process cross-sectional view illustrating the manufacturing procedure of the semiconductor laser device according to the second embodiment (No. 6). It is sectional drawing explaining the other form of a ridge (or mesa).

Explanation of symbols

2 ... Semiconductor substrate 4 ... Active layer 6 ... Upper clad 8 ... Contact layer 10, 10 '... Etching mask 12, 12' ... Ridge 14 ... Recess 16, 16, 16 ' ... Passivation film 17 ... Contact hole 18 ... BCB layer 19 ... Top 20 of ridge ... Photoresist film 22 ... Metal film 26 ... Contact electrode 27 ... Back electrode 28 ... SiN film 30 ... Plating photoresist film 32 ... Pad electrode 34 ... Upper side of ridge

Claims (4)

A semiconductor laminated structure formed on a semiconductor substrate
Etching using a mask made of the first insulating film,
A first step of forming a structure in which convex portions provided on the semiconductor substrate extend parallel to the semiconductor substrate;
A second insulating film is formed on the surface of the semiconductor substrate on which the structure is formed, leaving the first insulating film, and the top and side surfaces of the structure are covered with the second insulating film. A second step;
A third step of covering the surface of the semiconductor substrate on which the second insulating film is formed with a thermosetting resin;
Etching the thermosetting resin covering the top of the structure to expose the surface of the second insulator covering the top; and
Etching the second insulating film by dry etching,
A fifth step of exposing the first insulating film covering the top;
A sixth step of selectively etching the first insulating film with respect to the second insulating film to expose the top;
A seventh step of forming a contact electrode on the exposed top;
A method of manufacturing an optical semiconductor device, comprising: In the manufacturing method of the optical semiconductor device according to claim 1,
The thermosetting resin is made of benzocyclobutene,
A method for manufacturing an optical semiconductor device. In the manufacturing method of the optical semiconductor device according to claim 1 or 2,
The optical semiconductor device, wherein the semiconductor multilayer structure includes an active layer. In the manufacturing method of the optical semiconductor device according to any one of claims 1 to 3,
The optical semiconductor device is any one of a semiconductor light emitting device, a semiconductor photodetector, and a semiconductor optical modulator,
A method for manufacturing an optical semiconductor device.

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