JP4383753B2 - Nitride semiconductor device manufacturing method and nitride semiconductor device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor element in which a semiconductor layer using a nitride semiconductor is provided with a small area (width) electrode, and in particular, a large current driving element (laser diode, high power LED, electronic device such as FET, high frequency Element). Specific examples of the composition include GaN, AlN, InN, or a nitride semiconductor containing AlGaN, InGaN, or AlInGaN which is a mixed crystal thereof.
[0002]
[Prior art]
Nitride semiconductor devices have light emission in a wide wavelength range from an ultraviolet region with a relatively short wavelength to a visible light region including red, and as a material constituting a semiconductor laser (LD), a light emitting diode (LED), and the like. Widely used. In recent years, long life, high reliability, and high output have progressed, and are mainly used for electronic devices such as personal computers and DVDs, medical devices, processing devices, and light sources for optical fiber communication.
[0003]
A nitride semiconductor device is mainly composed of a buffer layer, an n-type contact layer, a crack preventing layer, an n-type cladding layer, an n-type light guide layer, an active layer, a p-type light guide layer, a p-type electron confinement layer, p on a sapphire substrate. It consists of a laminated structure in which a mold cladding layer, a p-type contact layer, and the like are laminated in order. An electrode is provided in such a laminated structure, and the active layer emits light when energized.
[0004]
Of the electrodes provided in such a nitride semiconductor element, an electrode (ohmic electrode) for making ohmic contact with the semiconductor layer is particularly important. In particular, as a material for the p-side electrode, a metal having a large work function is mainly used, and a single layer film, a multilayer film, or an alloy of these metals is used. In the case of a laser element, the element characteristics depend on the characteristics of the ohmic electrode, so that not only the electrode material but also its shape is important. Furthermore, since the current can be efficiently injected by forming the electrode so as to be in contact with the ridge which is the current injection region, the positional accuracy is also important. As a method for forming electrodes on a narrow ridge with high positional accuracy, a self-alignment method is known. This method is a method in which an electrode material on a stripe is formed on a semiconductor plane and etching is performed using the electrode as a mask, and an electrode matched with the width of the ridge can be formed. An electrode material made of a platinum group element is used for the electrode formed by such a self-alignment method because it is necessary to select a material to be a mask for etching the semiconductor layer.
[0005]
[Patent Document 1]
JP 2002-335048 A
[0006]
[Problems to be solved by the invention]
However, when an electrode material made of the above platinum group element is used, ohmic properties are not always excellent depending on the composition of the semiconductor layer. Therefore, a layer of an element other than the platinum group element such as Ni or Au provided on the side in contact with the semiconductor layer, and a layer of the platinum group element can be stacked thereover. However, when the semiconductor layer is etched by the self-alignment method using an electrode having a metal material other than the platinum group element, the resistance is likely to increase, and there is a problem in the lifetime characteristics of the element. Accordingly, in view of the above problems, the present invention provides a nitride semiconductor device that performs etching by a self-alignment method, has a low contact resistance with a semiconductor layer, and has a low lifetime and excellent lifetime characteristics. The purpose is to provide.
[0007]
[Means for Solving the Problems]
  In the method for manufacturing a nitride semiconductor device according to the present invention,Made of alloyable materialA metal layer having a first layer and a second layer made of a platinum group element in contact with the first layer;Lamination processIn a method for manufacturing a nitride semiconductor device including:
  in frontAn alloying step of alloying after laminating the metal layer;
  An etching step of removing a part of the semiconductor layer exposed from the metal layer,
  After the etching step, the alloying step and / orA reaction product removing step of removing the reaction product formed on the end face of the first layer by the etching step is provided.
[0008]
The first metal layer is a material that is alloyed by performing an alloying treatment after film formation, or a material that forms an alloy with the semiconductor layer, and has improved adhesion to the semiconductor layer. Made of a material that In particular, it is made of a multilayer film or mixed film composed of two or more elements that can be alloyed, or a material that can be alloyed with a semiconductor layer by heat treatment or the like even if it is one kind.
[0009]
The alloying treatment of the metal layer is mainly performed by heat treatment. At this time, not only the alloying reaction is performed inside the first layer, but also the reaction proceeds on the surface (interface with the semiconductor layer, interface with the second layer).
[0010]
At the interface (lower surface) with the semiconductor layer, the constituent elements and compounds of the semiconductor layer are formed and alloyed. An alloying reaction with the platinum group element also occurs at the interface (upper surface) with the second layer. However, the alloying of the first layer and the second layer is performed only at the interface. This is because the platinum group element is difficult to be alloyed with other elements, and therefore, a stable interface can be formed. In addition, the second layer can prevent outside air from being excessively mixed into the first layer. Therefore, alloying of the first layer can be performed stably.
[0011]
Thus, the second layer functions as a protective layer during the alloying treatment (heat treatment) of the first layer, but cannot cover the end surface of the first layer. Therefore, the end surface of the first layer is exposed to the outside air, and a reaction product such as oxide or nitride is generated depending on the atmosphere during the heat treatment. Oxide or nitride is mainly an insulator and is used as a protective film such as an end face protective film. However, if it is generated as a secondary material during alloying, the composition is not constant, and There are also problems with film quality. Therefore, if a metal film, an insulating film, or the like is formed so as to cover the surface, problems such as hindering adhesion occur. In the present invention, by removing these, a decrease in adhesion of the functional film can be suppressed and excellent life characteristics can be obtained.
[0012]
In addition, the second layer of the metal layer made of a platinum group element functions as a mask when etching the nitride semiconductor layer in addition to functioning as a layer that blocks the first layer and the outside air as described above. . Therefore, it is made of a material that hardly reacts with the etching gas and maintains a stable surface. On the other hand, the first layer made of the alloying material is not necessarily stable against the etching gas. In particular, as an etching gas for the nitride semiconductor layer, Cl₂, SiCl₄Since a chlorine-based gas such as is used, it reacts with the metal element exposed on the end face of the first layer, so that chloride or the like is easily generated. Further, it reacts with the nitride semiconductor composition (Ga, N) or the like removed by etching to generate a compound. As described above, the reaction product generated in the etching process has a more complicated composition than the reaction product generated by the heat treatment, and the generation region (contamination region) is much larger.
[0013]
Among reaction products obtained by etching, reaction products containing chlorine in particular are problematic because they corrode metal materials. When the reaction product containing chlorine is formed, the reaction proceeds inside the first layer of the metal layer, the reaction product is propagated, and the conductivity of the metal layer is deteriorated. In particular, in the case of a metal material with a small width, there is a possibility that most of the layer will become a reaction product due to the change with time after device operation at the time of device creation, and conduction may be impossible, and it is driven at high current density. In the case of the LD to be used, there is a possibility that serious characteristic deterioration is caused even if conduction is not disabled. In the case where a metal layer is used as an electrode (ohmic electrode), the resistance is increased by a reaction product made of chloride, and the operating voltage is increased. Further, when another metal layer (second metal layer) is formed so as to cover the end face of the first layer, chlorine permeates the second metal layer from the reaction product containing chlorine and changes its quality. As in the present invention, by removing the reaction product due to etching, the resistance can be prevented from being increased and excellent life characteristics can be obtained.
[0014]
  A method for manufacturing a nitride semiconductor device according to claim 2 of the present invention is as follows.The alloying step is a step of alloying by heat treatment and is included before the etching step, and is formed on the end surface of the first layer by the alloying step and the etching step in the reaction product removing step. The reaction product formed is removed. According to a third aspect of the present invention, the nitride semiconductor device manufacturing method further includes a step of covering the insulating film covering at least the first layer after the reaction product removing step.Since the first layer of the metal layer is made of an alloying material composed of one kind, or two or more kinds of multilayer films or mixed films, the film quality has many voids depending on the conditions of film formation. Therefore, the structure may be easily affected by etching. By first heat-treating this first layer, the first layer can be densified to form a more stable end face than during film formation, so that the reaction with the subsequent etching gas can be reduced or the present application can be removed. It can be controlled to a reaction product that can be easily removed in the process.
.
[0015]
  Claims of the invention4The method for producing a nitride semiconductor device described in 1) has a reaction product removal step after the nitride semiconductor layer etching step and an alloying step by heat treatment of the metal layer. Since the nitride semiconductor layer is etched using a chlorine-based gas, the end surface of the first layer of the metal layer has a reaction product made of chloride and a composite product containing the removed components of the nitride semiconductor. Is generated. If heat treatment is carried out without removing these, the composite product will be fixed, making it difficult to remove in a later step. Therefore, after the etching step, it is preferable to remove the reaction product before performing the heat treatment. A reaction product such as an oxide may be formed again by performing a heat treatment after the removal, but it is also preferable to remove this. However, since it does not contain chloride or the like, it can be omitted when an insulating film having a large film thickness is formed on the end face after etching.
[0016]
  Claims of the invention5The method for manufacturing a nitride semiconductor device described in 1) uses an inert gas plasma in the step of removing the reaction product. Reaction products such as oxide, nitride, or chloride generated on the end face of the first layer of the metal layer can be removed by plasma irradiation. Argon (Ar), oxygen, nitrogen, or the like can be used. In particular, when a reaction product is removed by using an inert gas plasma of Ar, another reaction product is newly generated. Can be suppressed. Also, by removing the etching gas components remaining on the surface of the second layer made of platinum group elements, etc., the exposed etching surface damaged by the gas in the previous process (self-alignment), particularly chlorine-based gas. Since the vicinity can be removed by the product removal step, the device can be further improved in reliability.
[0017]
  Claims of the invention6The nitride semiconductor device described in (1) has a metal layer whose outer surface substantially coincides with the upper surface on the upper surface of the convex portion of the nitride semiconductor device having a convex portion,
The metal layer has an alloyed first layer and a second layer that is a surface layer made of a platinum group element in contact therewith,
  The end surface of the first layer recedes inward from the end surface of the second layer.And
An insulating film was formed so as to cover the narrowed part that retreated insideIt is characterized by
[0018]
Various functional films such as a metal layer and an insulating film are formed on the surface of the semiconductor layer. As in the present invention, the end face of the first layer formed below the second layer made of the platinum group element recedes inward so that the end face of the semiconductor layer extends from the end face of the metal layer to the end face of the metal layer. The end surface is not a single plane but a surface having irregularities. That is, the end surfaces of the second layer of the metal layer and the semiconductor layer are substantially the same surface, and the first layer of the metal layer sandwiched between them has a shape that is recessed more than them. By using such a composite end face, a functional film (insulating film or metal film) formed on the end face can be formed with good adhesion.
[0019]
  Claims of the invention7The nitride semiconductor device described in 1 is characterized in that the metal layer is an ohmic contact electrode. In addition to the element driving region (functional region) such as the mesa portion and the LD ridge formed in the mesa portion, the convex portion provided in the semiconductor layer includes an element in order to relieve stress applied when face-down is used. The case where it is provided separately from a drive area | region etc. is mentioned. The metal layer formed in a region other than the element driving region is not an electrode, but a heat radiating part for ensuring heat radiating properties or a reflective film, and has various functions. In the present invention, such a metal layer has a two-layer structure, and a narrowed portion is provided in the first layer, so that an insulating film or the like can be formed with good adhesion. In particular, it is used as an electrode for ohmic contact. Thus, peeling of the insulating film or the like can be suppressed, and an element with excellent reliability can be obtained.
[0020]
  Claims of the invention8The nitride semiconductor device described in (1) is characterized in that the metal layer is formed in an LD device having a ridge composed of convex portions. FIG. 1 is a schematic cross-sectional view of a nitride semiconductor laser device in which a metal layer is formed with a metal layer (electrode) on the upper surface of a convex portion (ridge), and a semiconductor laser device in which a waveguide region is formed by this ridge. It is a schematic diagram which shows (LD). In this way, when the metal layer is used as a p-side electrode (ohmic electrode) provided on the ridge of the LD, an insulating film is formed on both sides of the ridge in order to limit the current injection path to a narrow stripe shape. . At this time, the side surface from the semiconductor layer (ridge) to the metal layer is uneven by making the lower layer (first layer) narrower than the upper layer (second layer) of the metal layer (electrode) as in the present invention. Become a shape. That is, a structure is formed in which the first layer of the metal layer is a recess (constriction) and the semiconductor layer and the second layer of the metal layer are projections. Since the narrowed portion functions as an anchor for the insulating film or metal film formed on the side surface including the narrowed portion, excellent adhesion can be realized.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, although the light emitting element which concerns on embodiment of this invention, and its manufacturing method are demonstrated, this invention is not limited to the element structure shown by embodiment shown below.
[0022]
In producing a light emitting device using the manufacturing method according to the present invention, the reaction product formed mainly on the end face of the first layer of the metal layer by the alloying (heat treatment) process or the etching process is removed by the reaction product. Can be any process that can be removed, and is preferably carried out in such a way that it does not produce any further reaction products. For example, it can be removed by a chemical or physical method using wet etching or dry etching, and a preferable one can be selected depending on the composition of the reaction product. In particular, it is preferably removed by plasma irradiation with an inert gas such as argon (Ar).
[0023]
The reaction product removal step may be performed in any step after the reaction product is generated and before a new functional film (insulating film or metal film) is formed on the upper surface or end surface of the metal layer. Can do. Preferably, it is performed immediately before forming the functional film. Further, the removing step may be performed by dividing it into a plurality of steps. In that case, different means may be used as the removing means (type of gas used, apparatus, etc.), or the same means may be used.
[0024]
Moreover, the temperature at the time of reaction product removal should just be below the temperature which has a bad influence on an element, such as a nitride semiconductor layer decomposing | disassembling. Further, if the time required for the removal becomes longer, other parts are liable to be adversely affected. Therefore, it is preferable to select a means in consideration of the composition of the reaction product.
[0025]
(Stenosis)
In this manufacturing method, the end product of the first layer is depressed and a constriction is formed by removing the reaction product generated mainly on the end surface of the first layer of the metal layer. If the reaction product is a modified metal layer, it can be removed to form a narrowed portion. The constriction is mainly formed on the end face of the first layer, but the shape varies depending on the state of reaction product generation. It also depends on the removal means. The shape is not limited to the shape in which the vicinity of the center of the layer shown in FIG. 1 is most depressed, and various shapes such as a plurality of fine recesses are formed. Further, since the formation region depends on the region where the reaction product is generated, it is formed uniformly or non-uniformly on the entire end face.
[0026]
The shape of the narrowed portion may change by performing another process after the narrowed portion is formed. For example, if a reaction product is removed after the etching process to form a constricted portion, and then heat treatment is performed, the end surface that becomes the constricted portion is changed in a direction to reduce the surface area by surface tension. That is, it changes so that it may become a flat surface. Even in such a case, flattening is unlikely to occur at all, so that the constriction portion remains formed.
[0027]
As described above, by removing the reaction product, a narrowed portion is formed so as to recede inward from the end face. However, the surface area of the end face can be increased even in the following cases, so that an insulating film or the like can be formed. Adhesiveness can be improved.
[0028]
A form in which a part of the end surface of the metal layer protrudes from the end surface of the nitride semiconductor of the convex portion more than the other end surface may increase the surface area. For example, a reaction product formed by heat treatment or etching treatment may float in the system and reattach to a position different from the original. In particular, at the time of etching, since the nitride semiconductor layer is scraped, semiconductor constituents exist in the system, and a relatively stable reaction product may be formed. In this way, reaction products are generated through device processes such as heat treatment and etching, and are attached to or removed from the protrusions of the semiconductor layer and the metal formed thereon. Unlike the single plane at the time of formation, the end face of the layer becomes a composite end face having irregularities. Thereby, a bonding area with an insulating film etc. can be enlarged and adhesiveness can be improved.
[0029]
(Metal layer)
The first layer of the metal layer is made of an alloyable material (alloying material) and is alloyed mainly by heat treatment. Preferred materials for the first layer (alloying layer) of the metal layer include Ni, Co, Fe, Cu, Au, W, Mo, Ta, Ag, Al, Cr, Pt, Pd, Rh, Ir, Ru, Os. , V, Cr, Ta and oxides and nitrides thereof, and particularly preferably, at least one selected from the group consisting of Ni, Co, Fe, Ti, Cu, Al, and Au, or two or more A multilayer film or an alloy film. When this metal layer is used as an electrode for ohmic contact with the p-type nitride semiconductor layer, it is preferable to use Ni or a material containing Ni and Au. When the metal layer is an electrode for ohmic contact with the n-type nitride semiconductor layer, it is preferable to use a material containing Ti and Al. These electrode materials are alloyed by heat treatment, and good ohmic contact with the semiconductor layer can be obtained. The heat treatment temperature is preferably in the range of 350 ° C to 1200 ° C, more preferably 400 ° C to 700 ° C, and particularly preferably in the range of 450 ° C to 650 ° C.
[0030]
The second layer of the metal layer formed on the first layer which is an alloying layer is made of one or more alloys of platinum group elements (Pt, Pd, Ph, Ir, Ru, Os). Among them, Pt is particularly preferable among them. Two kinds of platinum group elements may be used. The platinum group element is suitable as a mask material when a part of the nitride semiconductor layer is removed by etching. By forming the platinum group element so as to have a desired mesa shape (ridge), it substantially matches the shape of the mesa portion. A metal layer having a shape to be formed can be formed.
[0031]
When a metal layer is used as an electrode, the preferable film thickness is preferably 300 to 5000 mm in terms of the total film thickness of the first layer and the second layer. By setting the total film thickness to 300 to 5000 mm, the sheet resistance can be lowered. The film thickness of the second layer is preferably 100 to 5000 mm, more preferably 500 to 3000 mm, and particularly preferably 1000 to 2500 mm. If the thickness of the second layer is less than 100 mm, it is difficult to block outside air during the alloying process of the first layer, and the adhesion may be deteriorated, which is not preferable. On the other hand, if the thickness of the second layer exceeds 5000 mm, the ohmic characteristics are impaired, which is not preferable. The film thickness of the first layer is preferably 200 to 4000 mm, more preferably 500 to 3000 mm, and particularly preferably 1000 to 2000 mm. If the thickness of the first layer is out of the above range, the ohmic characteristics are deteriorated, which is not preferable.
[0032]
【Example】
In the present invention, the device structure of the p-type nitride semiconductor layer, the active layer, and the n-type nitride semiconductor layer constituting the nitride semiconductor layer is not particularly limited, and various layer structures can be used. As a specific structure of the device, for example, a device structure described in Examples described later can be given. As a specific example of the nitride semiconductor, a nitride semiconductor such as GaN, AlN, or InN, or a III-V group nitride semiconductor that is a mixed crystal thereof can be used. Further, a nitride semiconductor partially substituted with B, P, or the like can be used. Nitride semiconductor growth is known to grow nitride semiconductors such as MOVPE, MOCVD (metal organic chemical vapor deposition), HVPE (halide vapor deposition), MBE (molecular beam vapor deposition). All methods are applicable.
[0033]
[Example 1]
A sapphire substrate having a C-plane as the main surface is used as the substrate. On top of that, Si-doped Al_0.02Ga_0.98A buffer layer made of N is grown to a thickness of 1 μm. Next, an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer are stacked in this order. The n-type nitride semiconductor layer is made of Si-doped n-Al._0.02Ga_0.98N-type contact layer (3.5 μm) made of N, Si-doped n-In_0.05Ga_0.95Crack prevention layer made of N (0.15 μm), undoped Al_0.05Ga_0.095An n-type cladding layer composed of a multilayer film (superlattice structure) having a total film thickness of 1.1 μm and an n-type light composed of undoped GaN by alternately stacking N layers (50 Å) and Si-doped GaN layers (50 Å) A guide layer (0.15 μm) is sequentially laminated.
[0034]
As the active layer, Si-doped In_0.02Ga_0.98A barrier layer made of N (140 cm) and undoped In_0.1Ga_0.9A well layer (70 cm) made of N is repeatedly stacked twice, and finally Si-doped In_0.02Ga_0.98A barrier layer (140 Å) made of N is grown to form an active layer of a multiple quantum well structure (MQW) with a total film thickness of 560 Å.
[0035]
As a p-type nitride semiconductor layer grown next to the active layer, Mg-doped Al_0.25Ga_0.75First p-type electron confinement layer (100Å) made of N, p-type light guide layer (0.15 μm) made of undoped GaN, undoped Al_0.08Ga_0.92A p-type cladding layer made of a multilayer film (superlattice structure) having a total film thickness of 0.45 μm, in which N (80Å) and Mg-doped GaN (80Å) are alternately laminated, and a p-type contact layer made of Mg-doped GaN ( 150Å) are laminated in order.
[0036]
After completion of the reaction, the wafer is heat-treated at 700 ° C. in a nitrogen atmosphere in the reaction vessel to further reduce the resistance of the p-type layer. Note that the optimum atmosphere and heat treatment temperature for the p-type can be selected depending on the composition of the p-type contact layer and the like.
[0037]
(Metal layer: p-side ohmic electrode)
A resist having a stripe-shaped opening having a width of 1.6 μm is formed on the upper surface of the p-type contact layer, and a metal layer is formed on the entire surface of the wafer. As the metal layer, a first layer made of Ni / Au (2000 Å) and a second layer made of Pt (1500 Å) are formed thereon. Next, a stripe-shaped metal layer having a width of 1.6 μm is formed by lifting off. Next, a p-side ohmic electrode is obtained by heat treatment (alloying) at 600 ° C. in a mixed atmosphere of oxygen and nitrogen.
[0038]
(Ridge formation)
Next, etching is performed by a self-alignment method using the p-side ohmic electrode as a mask to form a ridge stripe as shown in FIG. Etching gas is Cl₂Etching is performed using gas to a depth at which the p-type guide layer is exposed. After the etching, as shown in FIG. 2C, an altered portion (reaction product) is formed on the end face of the p-side ohmic electrode.
[0039]
The ridge is not limited to the forward mesa shape in which the width on the bottom side of the convex portion is wide and the stripe width decreases as it approaches the upper surface, but on the contrary, the reverse mesa shape in which the width of the stripe decreases as it approaches the plane of the convex portion may be used. Further, it may be a stripe having a side surface perpendicular to the laminated surface, or a shape in which these are combined. Also, the striped waveguides need not have the same width.
[0040]
(Reaction product removal)
Next, the reaction product on the side surface of the first layer of the p-side ohmic electrode is removed by irradiation with inert gas (Ar) plasma, and the width of the first layer is the second layer as shown in FIG. The p-side ohmic electrode has a cross-sectional shape smaller than the width of.
[0041]
(First insulating film)
Next, SiO on the entire wafer surface₂An adhesion layer made of Si is further formed thereon. The thickness of the adhesion layer at this time may be a thickness that can ensure insulation, and is preferably formed lower than the upper surface of the ridge. When forming higher than the ridge upper surface, a conduction path is secured by forming an opening in the upper part of the ridge. Next, a resist is formed on the entire surface of the adhesion layer. Then O₂Etching with gas and SiO on top of ridge₂Alternatively, the Si layer is exposed and CF₄Or CHF₃SiO exposed using gas₂Alternatively, Si is removed. Finally, the resist is removed by lift-off, so that SiO is formed on the p-type semiconductor layer on both sides of the ridge from the ridge side as shown in FIG.₂A first insulating film made of Si and an adhesion layer made of Si are formed. Only the end surface of the first layer may be covered with the first insulating film, or the end surfaces of the second layer and the first layer may be covered with the first insulating film.
[0042]
As a material for the first insulating film, in addition to Si, an oxide containing at least one element selected from the group consisting of Ti, Al, V, Zr, Nb, Hf, and Ta, SiN, BN, SiC, It is desirable to use at least one of AlN and AlGaN, and among these, it is particularly preferable to use oxides of Si, Al, Zr, and Hf, BN, AlN, and AlGaN. The film thickness of the first insulating film is specifically in the range of 100 to 1 μm, preferably in the range of 500 to 5000 μm. The reason is that if the thickness is less than 100 mm, it is difficult to ensure sufficient insulation at the time of electrode formation, and if it is 1 μm or more, the uniformity of the protective film is lost, and a good insulating film is not obtained. . Moreover, by being in the preferred range, a uniform film having a good refractive index difference between the ridge and the ridge can be formed on the side surface of the ridge.
[0043]
(Mesa formation: n-type layer exposure)
Next, a resist is formed so that the p-type semiconductor layer including the ridge portion is exposed, and a second metal layer made of Ti / Pt (2000 mm) is formed with a width of about 160 μm and lifted off. Using this metal layer as a mask, CHF₃SiO2 using gas₂Etch and Si to expose the p-type semiconductor layer, followed by ClE using RIE (Reactive Ion Etching)₂The semiconductor layer is etched with gas to expose the n-type contact layer. The n-side ohmic electrode is made of Ti / Al (200/8000) and is formed in stripes parallel to the ridge and having the same length.
[0044]
(P-side pad electrode, n-side pad electrode)
A resist is formed so that the region including the ridge portion of the p-side ohmic electrode is exposed, and a metal layer made of Ti / Pt / Au (1000 Å / 1000 Å / 6000 Å) is laminated. Thereafter, a p-type pad electrode is formed by lift-off. At this time, a p-side pad electrode and an n-side pad electrode are formed simultaneously by using a resist having an opening on the n-side ohmic electrode.
[0045]
(Second insulating film)
Next, a resist having an opening between the p-side ohmic electrode on the ridge and the n-side ohmic electrode is formed, and SiO 2₂A second insulating film made of is formed on almost the entire surface and lifted off, thereby forming a protective film with a thickness of 5000 mm between the p-side ohmic electrode and the n-side ohmic electrode above the ridge. At this time, in consideration of the subsequent division, the first and second insulating films and electrodes are not formed in the stripe-shaped range having a width of about 10 μm across the division position in the direction perpendicular to the ridge. May be. As another method of forming the second insulating film, almost the entire surface is made of SiO.₂The second insulating film may be formed, a resist is formed except for the upper portions of the p-side and n-side ohmic electrodes, and the second protective film on the ohmic electrodes is removed by etching.
[0046]
The second insulating film can be formed before the pad electrode is formed, or may be provided on a side surface other than between the p-side electrode and the n-side electrode. Preferred materials for the second insulating film include oxides containing at least one element selected from the group consisting of Si, Ti, Al, V, Zr, Nb, Hf, and Ta, SiN, BN, SiC, AlN, It is desirable to form at least one of AlGaN, and among these, as a particularly preferable material, SiO₂, Al₂O₃, ZrO₂TiO₂And a single layer film or a multilayer film.
[0047]
(Cleavage and resonator surface formation)
Next, the substrate is polished and adjusted to have a film thickness of about 150 μm, and then a scribe groove is formed on the back surface of the substrate, braked from the nitride semiconductor layer side, and cleaved to obtain a bar-shaped laser. The cleavage surface of the nitride semiconductor layer is the M-plane (1-100 plane) of the nitride semiconductor, and this plane is the resonator plane. The resonator surface may be the A surface of a nitride semiconductor, or may be formed by etching instead of cleaving. When formed by etching, the n-type layer can be formed without increasing the number of steps by forming it simultaneously.
[0048]
(End face protection film formation)
On the resonator surface formed as described above, the end face protective film or the reflective film is made of SiO.₂And ZrO₂A dielectric multilayer film is formed. On the resonator surface on the light reflection side (monitor side), ZrO is used by using a sputtering device.₂A protective film consisting of₂And ZrO₂Are alternately stacked to form a highly reflective film. Here, the protective film and the SiO constituting the highly reflective film₂Membrane and ZrO₂The thickness of the film can be set to a preferable thickness according to the emission wavelength from the active layer. In addition, it is not necessary to provide anything on the resonator surface on the light emitting side, and ZrO may be used by using a sputtering apparatus.₂, Nb₂O₅, Al₂O₃, ZrO₂A first low reflection film comprising SiO2 and₂A second low reflection film may be formed.
[0049]
Preferred materials for the end face protective film include Si, Mg, Al, Hf, Nb, Zr, Sc, Ta, Ga, Zn, Y, B, Ti, and compounds such as oxides, nitrides and fluorides. Those selected from any one selected from can be used. These may be used alone, or may be used as a compound or a multilayer film in which a plurality of them are combined. A semiconductor such as AlN, AlGaN, or BN can also be used.
[0050]
Finally, the groove is formed by scribing so as to be substantially parallel to the ridge stripe, and the bar is cut to obtain the nitride semiconductor device of the present invention. The nitride semiconductor device obtained as described above has a low operating voltage and operating power, and a threshold current density of 2.9 kA / cm at room temperature.², Capable of continuous oscillation with an oscillation wavelength of 405 nm at a high output of 30 mW.
[0051]
[Example 2]
In Example 2, after the p-side ohmic electrode (metal layer) of Example 1 was formed, the semiconductor layer was etched using this as a mask to form a ridge, and Ar plasma was irradiated to remove reaction products, followed by heat treatment. A nitride semiconductor device of the present invention is obtained in the same manner as in Example 1 except that (alloying) is performed and then Ar plasma is irradiated again to remove the reaction product. The resulting nitride semiconductor device has a low operating voltage and operating power, and a threshold current density of 2.9 kA / cm at room temperature.², Capable of continuous oscillation with an oscillation wavelength of 405 nm at a high output of 30 mW.
[0052]
【The invention's effect】
The nitride semiconductor device manufacturing method of the present invention suppresses deterioration of device characteristics due to alloying (heat treatment) and reaction products formed during etching when a semiconductor layer is etched by a self-alignment method using a metal layer as a mask. can do. Further, by removing the reaction product, a metal layer having a unique cross-sectional shape can be obtained, and the adhesion of a protective film and the like can be improved, and an element having excellent reliability can be realized.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view illustrating an embodiment of the present invention.
FIG. 2 is a schematic cross-sectional view illustrating the manufacturing method of the present invention.
[Explanation of symbols]
101... Substrate
102 ... n-type nitride semiconductor layer,
103 ... p-type nitride semiconductor layer,
104 ... active layer,
105a, 205a ... the first layer of the metal layer (p-side ohmic electrode),
105b, 205b ... the second layer of the metal layer (p-side ohmic electrode),
106... P-side pad electrode,
107 ... second metal layer,
108, 208 ... first insulating film,
109 ... second insulating film,
110 ... n-side ohmic electrode,
111... N-side pad electrode,
212 ... Reaction product.

Claims (8)

In the method for manufacturing a nitride semiconductor device, the method includes a step of laminating a metal layer having a first layer made of an alloyable material and a second layer made of a platinum group element in contact with the first layer made of an alloyable material on the surface of the semiconductor layer.
And alloying step of alloying after laminating the pre Symbol metal layer,
An etching step of removing a part of the semiconductor layer exposed from the metal layer,
A nitride semiconductor comprising a reaction product removal step of removing a reaction product formed on an end surface of the first layer by the alloying step and / or the etching step after the etching step. Device manufacturing method. The alloying step is a step of alloying by heat treatment and is included before the etching step, and is formed on the end surface of the first layer by the alloying step and the etching step in the reaction product removing step. The method for producing a nitride semiconductor device according to claim 1, wherein the reaction product is removed . The method for manufacturing a nitride semiconductor device according to claim 2, further comprising a step of forming an insulating film covering at least the first layer after the reaction product removing step.   The alloying step is a step of alloying by heat treatment, and is included after the etching step, and the reaction product removing step is included between the etching step and the alloying step. The manufacturing method of the nitride semiconductor element of description. In said reaction product removing step, the method of manufacturing the nitride semiconductor device according to any one of claims 1 to 4 wherein using an inert gas plasma. A nitride semiconductor element having a convex portion, the upper surface of the convex portion has a metal layer whose outer surface substantially coincides with the upper surface;
The metal layer has an alloyed first layer and a second layer that is a surface layer made of a platinum group element in contact therewith,
The end surface of the first layer is recessed inward from the end surface of the second layer ;
A nitride semiconductor device, characterized in that an insulating film is formed so as to cover a constricted portion receding inside . The nitride semiconductor device according to claim 6 , wherein the metal layer is an ohmic contact electrode. The nitride semiconductor device according to claim 6 , wherein the nitride semiconductor device is a laser device having a ridge formed of a convex portion.

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