JP2011114017A - Method of manufacturing nitride semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a nitride semiconductor device in which deterioration of an epitaxial growth film due to a heat treatment during window region formation is suppressed, and a window structure is formed while maintaining basic characteristics of a laser without deterioration in contact resistance between an electrode and a semiconductor layer. <P>SOLUTION: An optical non-absorption window region 14 is formed by diffusing an impurity from a solid-phase diffusion source 8 into a region including an active layer 4 by carrying out the heat treatment in an atmosphere containing oxygen after selectively forming the solid-phase diffusion source 8 in a predetermined region on a p-type GaN contact layer 7 to perform a diffusion treatment for the formation of the window region 14 at a lower diffusion treatment temperature than before, and consequently unnecessary thermal damage due to the window formation to a surface and the inside of crystal can be avoided, thereby forming the window region on a resonator end surface without deteriorating contact characteristics between the p-side electrode 12 and p-type GaN contact layer 7. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a nitride semiconductor device, particularly a semiconductor laser made of a nitride semiconductor.

  A nitride semiconductor laser is used as a semiconductor laser for recording / reading a Blu-ray disc which is a large capacity disc. In order to improve the recording speed and to promote the multi-layer recording for increasing the recording density, it is necessary to further increase the output.

In such a nitride semiconductor laser, as an important technique for realizing a high output operation exceeding 400 mW, the operation voltage by suppressing the end face destruction by reducing the light absorption at the end face of the laser resonator and reducing the resistance of the electrode section Reduction.
In order to prevent end face destruction due to light absorption at the end face of the laser resonator, a red semiconductor laser has so far adopted a window structure that reduces light absorption by widening the band gap of the end face of the resonator. In order to increase the output of the nitride semiconductor laser, it is effective to form a similar window structure.

As a method for widening the band gap, it is common to disorder the multiple quantum well (MQW) of the active layer to obtain a band gap higher than the quantum well level. Similar methods have been proposed for nitride semiconductor lasers.
For example, in Patent Document 1, impurity ions are implanted near the end face of an active layer made of a nitride semiconductor, and then annealed at 1000 ° C., thereby disordering the vicinity of the resonator end face of the active layer and reducing the band gap. A method of forming an expanded window structure is disclosed.
Further, in Patent Document 2, an oxide film containing impurities is formed on the surface of the nitride semiconductor layer, and then annealed at a temperature of about 1000 ° C. in an atmosphere containing nitrogen or ammonia, thereby forming impurity atoms. Has been disclosed to disorder the p-type superlattice cladding layer.

JP 2006-229210 A (page 10) JP 2006-140387 A (page 8)

In order to suppress deterioration over time during high output operation, it is necessary to reduce the operating voltage by suppressing the voltage drop caused by contact between the semiconductor and the electrode, that is, contact resistance. The contact resistance of the p-side electrode greatly depends on the carrier concentration of the contact layer on the outermost surface of the p-type semiconductor layer, the trap concentration of the interface, and the work function of the electrode material.
When a window structure is formed in a crystal such as a nitride semiconductor where diffusion of impurities is not easy, a heat treatment at a high temperature is required. Even in the above-described conventional method for manufacturing a nitride semiconductor device, a heat treatment is performed at a temperature close to 1000 ° C. As a result, nitrogen escape from the semiconductor surface and surface oxidation occur, n-type carriers due to nitrogen defects are generated on the crystal surface, and the contact resistance of the p-side electrode increases due to an increase in trap concentration. There was a problem.
In addition, there is a problem that the laser oscillation characteristics deteriorate due to unnecessary diffusion of dopant impurities by performing heat treatment at a high temperature close to 1000 ° C.

  The present invention has been made in view of such problems, and in the method for manufacturing a nitride semiconductor device, the deterioration of the epitaxially grown film due to the heat treatment at the time of forming the window region is suppressed, and the gap between the electrode and the semiconductor layer is reduced. The present invention provides a method for manufacturing a nitride semiconductor device in which a window structure is formed while maintaining the basic characteristics of a laser without degrading the contact resistance.

  A method for manufacturing a nitride semiconductor device according to the present invention includes: a first conductive type semiconductor layer forming step of stacking a first conductive type nitride semiconductor layer on a substrate; and the first conductive type nitride semiconductor layer on the first conductive type nitride semiconductor layer. A step of forming an active layer and a guide layer made of a nitride semiconductor; a step of forming a second conductivity type semiconductor layer in which a second conductivity type nitride semiconductor layer is stacked on the guide layer; and a step of nitriding the second conductivity type A diffusion source forming step of selectively forming a solid phase diffusion source in a predetermined region on the physical semiconductor layer, and a heat treatment in an atmosphere containing oxygen, whereby the solid phase diffusion source is changed to the region including the active layer. A window region forming step of diffusing impurity atoms to form an optical non-absorbing window region; and a cleaving step of forming a cleaved surface to be an end face of a laser resonator in the optical non-absorbing window region. .

  According to the present invention, since the diffusion treatment temperature at the time of forming the window region can be performed at a lower temperature than before, the crystal surface and the inside of the crystal can be avoided from the thermal damage due to the window formation more than necessary. The window region can be formed on the resonator end face without deteriorating the contact characteristics between the layers. Therefore, it is possible to obtain a long-lived high-power laser without degrading basic laser characteristics.

1 is a cross-sectional view showing the structure of a nitride semiconductor device in Embodiment 1 of the present invention. It is sectional drawing which shows the manufacturing process of the nitride semiconductor device in Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing process of the nitride semiconductor device in Embodiment 1 of this invention. It is a figure which shows the result of having measured the diffusion profile of the impurity atom in the nitride semiconductor when heat processing is performed in the atmosphere containing oxygen by SIMS analysis. It is sectional drawing which shows the manufacturing process of the nitride semiconductor device in Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing process of the nitride semiconductor device in Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing process of the nitride semiconductor device in Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing process of the nitride semiconductor device in Embodiment 1 of this invention. It is a figure which shows the electric current-output characteristic of the nitride semiconductor device in Embodiment 1 of this invention with a comparative example. FIG. 10 is a cross sectional view showing a modification of the manufacturing process of the nitride semiconductor device in the first embodiment of the present invention. It is sectional drawing which shows the manufacturing process of the nitride semiconductor device in Embodiment 2 of this invention. It is sectional drawing which shows the manufacturing process of the nitride semiconductor device in Embodiment 3 of this invention. It is sectional drawing which shows the manufacturing process of the nitride semiconductor device in Embodiment 3 of this invention. It is sectional drawing which shows the manufacturing process of the nitride semiconductor device in Embodiment 3 of this invention. It is sectional drawing which shows the manufacturing process of the nitride semiconductor device in Embodiment 3 of this invention.

Embodiment 1 FIG.
FIG. 1 is a cross-sectional view showing a configuration of a nitride semiconductor device according to the first embodiment. FIG. 1 (a) is a cross-sectional view in the resonator direction, and FIG. 1 (b) is an AA line in FIG. 1 (a). It is a figure which shows the cross section in.
First, the configuration of the semiconductor laser according to the present embodiment will be described with reference to FIG.

In FIG. 1, a semiconductor laser 100 which is a nitride semiconductor device is a gallium nitride (GaN) based semiconductor laser that generates blue-violet laser light having a wavelength of 405 nm, for example. As shown in FIG. On an n-type GaN substrate 1 that is a physical semiconductor substrate, an n-type AlGaN cladding layer 2, an n-type GaN guide layer 3, and an undoped layer In _x Ga _1-x N / In _y Ga _1-y N (x>, y ≧ 0) A multiple quantum well (MQW) active layer 4, an undoped AlGaN guide layer 5, a p-type AlGaN cladding layer 6, and a p-type GaN contact layer 7 are sequentially stacked. As shown in FIG. 1B, a stripe-shaped ridge 15 is formed on a part of the p-type AlGaN cladding layer 6 and the p-type GaN contact layer 7. The ridge 15 is disposed at a substantially central portion in the width direction of the cleaved end surface serving as the resonator end surface of the semiconductor laser 100, and extends between both cleaved surfaces serving as the resonator end surface. A p-side electrode 12 is stacked on the side wall of the ridge portion 15 with the insulating film 11 interposed therebetween.

  An n-side electrode 13 is formed on the back surface of the n-type GaN substrate 1. As shown in FIG. 1A, impurity diffusion regions 9 are formed on both end portions of the semiconductor laser 100 from the surface of the p-type GaN contact layer 7 to a partial region of the n-type GaN guide layer 3. Has been. By forming the impurity diffusion region 9 in both end portions of the semiconductor laser 100 in this manner, the active layer 4 is disordered, and an optical non-absorption window region 14 having a band gap wider than that of the active layer 4 is formed. .

In the above description, the expression “AlGaN” means an Al _x Ga _1-x N (0 ≦ x <1) type mixed crystal, and x is a value not less than 0 and less than 1. It is something to take. Unless x is specified, each AlGaN assumes a different value of x.

Next, a method for manufacturing the semiconductor laser 100 will be described with reference to FIGS.
2 to 8, (a) is a cross-sectional view perpendicular to the resonator direction, and (b) is a cross-sectional view in the resonator direction. Each figure is shown.

(N-type semiconductor layer forming step, undoped layer forming step)
First, in the process shown in FIG. 2, for example, MOCVD (Metal Organic Chemical Vapor Deposition) is formed on the Ga surface of the first conductivity type n-type GaN substrate 1 whose surface has been previously cleaned by thermal cleaning or the like. The n-type AlGaN cladding layer 2 and the n-type GaN guide layer 3 that are n-type semiconductor layers are sequentially formed by using a normal source gas, and then the In _x Ga _1-x N / In _y that is an undoped layer. Ga _1-y N (x>, y ≧ 0) MQW active layer 4 and AlGaN guide layer 5 are epitaxially grown sequentially. 2C, the periphery of the active layer 4 is enlarged, and the active layer 4 is formed by alternately laminating InGaN barrier layers 4a and InGaN well layers 4b.

(P-type semiconductor layer forming step)
Next, a p-type AlGaN cladding layer 6 and a p-type GaN contact layer 7 which are p-type semiconductor layers are sequentially grown on the undoped AlGaN guide layer 5. The growth of the p-type semiconductor layer is performed by doping Mg. At this time, ammonia is used as a nitrogen supply source.

  The growth temperature during the growth by MOCVD is, for example, 750 ° C. during the growth of the active layer 4 and 1000 ° C. for the other layers. Further, the thickness of each layer may be set to a film thickness necessary for obtaining desired characteristics. In addition, other film forming methods such as MBE (Molecular Beam Epitaxy) can be used instead of MOCVD.

(Diffusion source formation process)
Next, as shown in FIG. 3, the solid layer diffusion source 8 is selectively formed on a region in the vicinity of a portion that will later become a resonator end face (hereinafter referred to as “impurity diffusion region”). As a method for selectively forming the solid layer diffusion source 8 on the impurity diffusion region, a resist mask 10 is formed in advance on a region other than the impurity diffusion region (hereinafter referred to as “impurity non-diffusion region”) using photolithography in advance. After the solid layer diffusion source 8 is formed on the surface of the p-type GaN contact layer 7 by vapor deposition or sputtering, the solid layer diffusion source 8 formed in the impurity non-diffusion region can be removed by lift-off.

The film thickness of the solid phase diffusion source 8 may be 50 to 200 nm. As the solid phase diffusion source 8, for example, an oxide such as MgO, ZnO, or SiO ₂ can be used. In order to disorder the active layer 4, it is necessary that an impurity having an amount of 5 × 10 ¹⁸ cm ⁻³ or more pass through the active layer 4 as a concentration of the impurity to be diffused. Further, a protective film such as SiO ₂ , SiN, SiON, or AlN may be formed on the solid phase diffusion source 8 to prevent outward diffusion. This makes it possible to more effectively introduce impurities into the semiconductor layer in the next step.

(Window region forming process)
Next, the substrate 1 on which the solid layer diffusion source 8 is selectively formed on the impurity diffusion region in the diffusion source forming step is heat-treated in an atmosphere containing oxygen, whereby impurity atoms are selected from the solid phase diffusion source 8. In particular, it is diffused into the p-type semiconductor layer and the undoped layer. In addition, it is preferable that the heat processing temperature at this time shall be 800 degreeC or more and less than 1000 degreeC, and it is more desirable to set it as 800 degreeC or more and 900 degrees C or less. The low temperature treatment at a heat treatment temperature of less than 800 ° C. does not promote the diffusion of the impurity element, and the high temperature treatment at 1000 ° C. or more results in a temperature higher than the treatment temperature at the time of epitaxial growth and the crystallinity of the epitaxial growth film deteriorates. It is. By performing the treatment in such a temperature range, the epitaxial growth film can be diffused without adversely affecting the crystallinity. Further, the crystallinity of the impurity diffusion region is maintained.

  The heat treatment time may be set so as to obtain a desired diffusion depth. The necessary diffusion depth passes through the p-type contact layer 7 and the p-type cladding layer 6 and is necessary for the reaction to the active layer 4. Depth. Specifically, a diffusion depth of about 500 nm is sufficient, and the processing time for that is about 10 to 200 minutes. As a result of the disordering of the active layer 4 by the impurities diffused in the active layer 4 in this manner, an optical non-absorbing window structure 14 having a band gap wider than that of the active layer 4 is formed.

FIG. 4 shows the results of SIMS analysis of the diffusion profile of impurity atoms into GaN when heat treatment is performed in an atmosphere containing oxygen. Note that both the vertical axis and the horizontal axis in FIG. 4 are arbitrary scales.
FIG. 4A shows the heat treatment condition dependence of Mg atoms, and it can be seen that Mg atoms do not diffuse at a heat treatment temperature of 700.degree. However, it can be seen that Mg atoms are diffused into GaN by setting the heat treatment temperature to 800 ° C. It can also be seen that by increasing the heat treatment time, the impurity concentration increases and the diffusion depth increases.
FIGS. 4B and 4C are diagrams showing diffusion profiles when Mg, Si, Zn, and O atoms are heat-treated at 850 ° C. in a gas containing oxygen. It can be seen that all atoms are diffused in GaN.

  The conventional heat treatment in a nitrogen atmosphere or a hydrogen-containing atmosphere is effective in terms of surface protection because nitrogen atom escape from the GaN surface is suppressed, but Ga atoms are removed from the surface. In the case of diffusion based on this, the escape of Ga atoms is difficult to occur, and the diffusion of impurity atoms was not promoted. However, as in the present embodiment, by performing heat treatment in an atmosphere containing oxygen, the reaction between Ga and oxygen is promoted on the surface of the semiconductor laser 100, and Ga atoms escape from the GaN surface. Diffusion of impurity atoms in the solid-layer diffusion source 8 is efficiently promoted from the missing part. As a result, if the heat treatment temperature is 800 ° C. or higher, the impurity atoms can be diffused into the active layer 4 even if the heat treatment is performed at a lower temperature than the heat treatment temperature in a conventional nitrogen atmosphere or hydrogen-containing atmosphere. An optical non-absorbing window region 14 can be formed.

The atmosphere gas containing oxygen includes at least one of O ₂ , O ₃ , CO, CO ₂ , NO, N ₂ O, and NO ₂ , or a mixed gas thereof, or a mixed gas of these gases and an inert gas. It is possible to process using. The oxygen content may be about 20% or more.

(Wafer process)
After completion of the window region forming step, a normal wafer process for manufacturing a semiconductor laser is performed. As shown in FIG. 5, a mask is formed at a predetermined position on the wafer surface in order to form a desired ridge. As a ridge formation method, a resist pattern 10 is formed on the p-type contact layer 7 by using a transfer technique, and a part of the p-type contact layer 7 and the p-type AlGaN cladding layer 6 is formed using the resist pattern 10 as a mask material. Etch. As the etching for forming the ridge, dry etching is used. For dry etching, etching by ICP (Inductively Coupled Plasma), RIE (Reactive Ion Etching), ECR (Electron Cyclotron Resonance), or the like can be used. As an etching gas at this time, a chlorine (Cl) -based gas is used. The etching depth also varies depending on the characteristics of the device, but about 500 nm is required. Further, for ridge etching, similar ridge processing is possible even when a material such as an insulating film is used instead of a resist mask.

Next, as shown in FIG. 6, the insulating film 11 is formed on the side wall 15 a of the ridge 15. As the insulating film, for example, an SiO ₂ film is used. As a method of forming the insulating film 11, a film forming method such as a vapor deposition method, a sputtering method, a CVD method, or the like can be used. The insulating film 11 formed on the ridge upper surface 15b is removed by the back method, and the insulating film 11 is selectively formed only in a region excluding the upper surface 15b of the ridge 15. FIG. 6 shows a lift-off method by self-alignment with a mask used for ridge formation. The film thickness of the insulating film 11 is determined by the optical characteristics of the device, and for example, a film thickness of about 200 nm is required. SiO ₂ is desirable for semiconductor laser fabrication, but any material that can satisfy optical characteristics with SiN or other insulating films may be used.

  Next, as shown in FIG. 7, the p-side electrode 12 is formed on the surface of the p-type contact layer 7, and the back surface n-side electrode 13 of the substrate 1 is formed. As a method for forming the p-side electrode 12, an electrode material is formed by vapor deposition, sputtering, or the like, and selectively formed on the ridge upper surface 15b and the side surface 15a by lift-off. The p-side electrode material may be any material that can achieve ohmic characteristics with the p-type contact layer 7. For example, an electrode structure such as Pd / Ta / Pd is conceivable. In addition, as a pad electrode for connection with the outside, an electrode structure such as Ti / Ta / Ti / Au is conceivable. As the arrangement of the p-side electrode 12 on the surface of the p-type contact layer 7, it is better to arrange it at a position excluding the impurity diffusion region. That is, it is retracted about 2 μm from the impurity diffusion region (formed inward from the resonator end face). For example, if the resonator length is 600 μm, the impurity diffusion region is 20 μm, and the impurity diffusion region recedes by about 2 μm, the electrode width is 600 − ((20 + 2) × 2) = 556 μm. By arranging in this way, the heat injected by the carriers injected from the p-side electrode 12 due to unnecessary recombination due to the impurities in the impurity diffusion region can be reduced, so that the reliability can be further improved. The n-side electrode 13 can be formed, for example, by depositing Ti / Pt / Au in this order and performing Si-containing plasma treatment before forming the electrode to form the low-resistance n-side electrode 13.

(Cleaving process)
When the wafer process step is finished, a cleavage plane is formed in the optical non-absorption window region 14 to form a resonator end face. As shown in FIG. 8, the impurity diffusion region 9 including the optical non-absorption window region 14 is formed in the vicinity of both end faces of the resonator, and the optical non-absorption window region 14, that is, the impurity diffusion region 9 is substantially divided into two equal parts. Cleave at the position to make the resonator end face. The width of the optical non-absorption window region 14 in the resonator direction may be about 1 to 20 μm from the resonator end face toward the resonator center. However, this double width is required before cleavage. Thereafter, the semiconductor laser 100 is completed by being separated and assembled into chips.

  As described above, since the reaction between the diffusion source and the semiconductor surface is promoted by using the atmospheric gas containing oxygen during the heat treatment for diffusing the impurity atoms from the solid phase diffusion source into the semiconductor, the conventional atmospheric gas is used. Impurities can be diffused at a lower temperature. As a result, deterioration of the surface of the p-type semiconductor layer due to heat treatment can be suppressed, so that the contact resistance of the p-side electrode can be kept low, and a window structure without light loss can be realized without increasing the operating voltage. It became.

This makes it possible to increase the reliability and output of a semiconductor laser made of a nitride semiconductor. FIG. 9 shows the relationship between the current-light output characteristics of the semiconductor laser having the optical non-absorption window region formed as described above and the current-light output characteristics of the semiconductor laser having no window region. It can be seen that the formation of the optical non-absorption window region makes it possible to obtain a highly reliable semiconductor laser in which no deterioration in characteristics is observed even at higher output. In the present embodiment, an oxide such as MgO, ZnO, or SiO ₂ is used as the solid layer diffusion source 8, but the same effect can be obtained as long as these materials include Mg, Zn, and Si. It is. For example, fluorides and nitrides such as MgF, MgN, ZnN, and ZnF may be used. Further, these stacked structures may be used in a combination that promotes diffusion of impurities.

In the present embodiment, the window region forming step is performed after the p-type contact layer 7 is formed. However, the window region forming step may be performed after the p-type AlGaN cladding layer 6 is formed as shown in FIG. Further, the window region forming step may be performed after a protective film such as AlN is formed on the impurity non-diffusion region other than the impurity diffusion region.
By manufacturing the semiconductor laser 100 in this way, it is possible to suppress the deterioration of the surface of the p-type contact layer 7 and to realize a window structure with no optical loss while keeping the contact resistance of the p-side electrode 12 low. Become.

Embodiment 2. FIG.
FIG. 11 is a cross-sectional view showing a part of the manufacturing process of the nitride semiconductor device in the second embodiment.
The method for manufacturing a nitride semiconductor device according to the second embodiment includes a step of further forming an AlN protective layer 16 on the p-type contact layer 7 after the p-type semiconductor layer forming step shown in the first embodiment. . Other steps are the same as those in the first embodiment.

  FIG. 11 shows a cross-sectional view of the semiconductor laser 100 after the window region forming step in the present embodiment. Here, the AlN protective layer 16 is formed by a crystal growth apparatus, and during growth, ammonia is supplied as a nitrogen supply source so that the growth temperature is 600 ° C. or lower. By forming a film in this way, AlN can be made polycrystalline or amorphous. Alternatively, the film may be taken out from the crystal growth apparatus and formed by another method such as sputtering. The film thickness is 20 nm to 100 nm. The AlN protective film 16 formed outside the impurity non-diffusion region is removed by etching or the like. Then, the solid phase diffusion source 8 is formed in the region from which the AlN protective film 16 has been removed by the same process as the diffusion source forming process described in the first embodiment. The AlN protective film 16 is removed together with the solid phase diffusion source 8 after the window region forming step. The other steps are the same as those shown in the first embodiment. Further, the same effect can be obtained by forming the AlN protective film 16 on the impurity non-diffusion region and then performing vapor phase diffusion using a source gas containing impurities in a crystal growth apparatus or the like.

  According to this embodiment, by performing heat treatment at a low temperature of 800 ° C. to 1000 ° C. in an atmosphere gas containing oxygen, the reaction between the semiconductor surface and the solid phase diffusion source is promoted, and impurities are reduced at a lower temperature than before. Can diffuse. As a result, deterioration of the surface of the p-type semiconductor layer due to heat treatment can be suppressed, so that the contact resistance of the p-side electrode 12 can be suppressed low, and a window structure without light loss can be realized without increasing the operating voltage. It becomes possible.

  Furthermore, according to the present embodiment, the AlN protective layer 16 is formed on the p-type contact layer 7 in a region where the solid phase diffusion source 8 is not formed, so that the deterioration of the surface of the semiconductor layer can be prevented. Therefore, high quality active layer quality can be maintained, and high reliability and high output can be achieved without causing deterioration of laser characteristics.

Embodiment 3 FIG.
12 to 15 are cross-sectional views illustrating the manufacturing steps of the nitride semiconductor device according to the third embodiment.
In the first embodiment, the window region forming step is performed after the p-type semiconductor layer forming step. However, in the present embodiment, the window region forming step is performed before the p-type semiconductor layer forming step.

(N-type semiconductor layer forming step, undoped layer forming step)
First, as shown in FIG. 12, the n-type AlGaN is formed on the Ga surface of the first conductivity type n-type GaN substrate 1 whose surface has been previously cleaned by thermal cleaning or the like using, for example, MOCVD, using a normal source gas. The cladding layer 2, the n-type GaN guide layer 3, the undoped In _x Ga _1-x N / In _y Ga _1-y N (x>, y ≧ 0) MQW active layer 4, and the undoped AlGaN guide layer 5 are sequentially formed. Epitaxially grow. The thickness of the undoped AlGaN guide layer 5 is 20 nm. An AlN protective layer similar to that of the second embodiment may be further formed on the undoped AlGaN guide layer 5.

(Solid phase diffusion source formation process)
After the undoped layer forming step, a process for inducing interdiffusion is performed by selectively performing impurity diffusion. As shown in FIG. 13, the solid phase diffusion source 8 is formed only on the portion to be the resonator end face, that is, on the impurity diffusion region 9. In the present embodiment, for example, an MgO film is used as the solid phase diffusion source 8. As a method for selectively forming the MgO film as the solid phase diffusion source 8 on the impurity diffusion region 9 which is a portion serving as the end face, a region other than the vicinity of the resonator end face using photolithography, that is, an impurity non-diffusion region A resist mask 10 is formed thereon, and the MgO film which is the solid phase diffusion source 8 formed in the impurity non-diffusion region other than the cavity end face portion is removed by a lift-off method.

(Window region forming process)
After the solid phase diffusion source forming step, the impurity diffusion region 9 is formed by performing heat treatment for impurity atom diffusion. At this time, the active layer 4 is disordered by the impurities diffused from the MgO film to the active layer 4, so that an optical non-absorption window region 14 having a band gap wider than that of the active layer 4 is formed. The heat treatment is performed in an atmosphere containing oxygen, and the diffusion temperature is preferably 800 ° C. or higher and lower than 1000 ° C., more preferably 800 ° C. or higher and lower than 900 ° C. The heat treatment time is sufficient if the diffusion depth necessary for disordering the active layer 4 is obtained. In this case, it is sufficient that a depth of about 100 nm is obtained, and the treatment time therefor is 2 to 60 minutes. It is preferable to carry out to the extent. Further, in order to obtain the effect of disordering the active layer 4, it is necessary that an impurity having an amount of 5 × 10 ¹⁸ cm ⁻³ or more passes through the active layer 4 as the concentration of the impurity diffused from the solid phase diffusion source 8. There is. As the atmospheric gas containing oxygen, at least one of O ₂ , O ₃ , CO, CO ₂ , NO, N ₂ O, NO ₂ or a mixed gas thereof, or a mixed gas of these gases and an inert gas is used. Can be processed.

(P-type semiconductor layer forming step)
Then, after the window region forming step, the solid phase diffusion source 8 is removed using a hydrofluoric acid-based etching solution. When the AlN protective film is formed, it is removed simultaneously with the solid phase diffusion source 8. Next, heat treatment is performed before growing the p-type semiconductor. As a result, the surface of the undoped layer before growth is made clean, and a p-type semiconductor layer with good crystallinity is grown.

  The p-type semiconductor layer is grown again by MOCVD and doped with Mg. At this time, ammonia is supplied as a nitrogen supply source. Prior to the formation of the p-type semiconductor layer, the shortage of the undoped AlGaN guide layer 5 may be grown in the first regrowth layer, and then the p-type semiconductor layers 6 and 7 may be grown. The growth of the p-type GaN contact layer 7 is performed by doping Mg. At this time, ammonia is supplied as a nitrogen supply source. The growth temperature is 1000 ° C. FIG. 14 shows a cross-sectional shape after the growth of the p-type semiconductor layer.

  The subsequent steps and all the growth temperatures are the same as those in the first embodiment. FIG. 15 shows a cross-sectional view of the semiconductor laser according to the present embodiment manufactured through the above steps. Since the window region is formed during the epitaxial growth, the impurity diffusion region 9 is only in the vicinity of the active layer 4.

  According to the present embodiment, as a result of performing the window region forming step before the p-type semiconductor layer forming step, the p-side electrode 12 having no deterioration can be formed on the surface of the p-type contact layer 7. The contact resistance between the p-type contact region 7 and the p-type contact region 7 can be kept low, and a window region without light loss can be formed without increasing the operating voltage. Further, since the diffusion of the p-type dopant into the active layer due to the high-temperature heat treatment in the window region forming step can be avoided, the laser characteristics are not deteriorated.

  Furthermore, according to the present embodiment, the diffusion distance of impurity atoms can be shortened, so that the heat treatment time can be shortened. As a result, a window structure with no optical loss can be realized without causing an increase in operating voltage, and crystal deterioration near the active layer due to high-temperature heat treatment in the window region forming process can be avoided, resulting in deterioration of laser characteristics. Therefore, it is easy to achieve high reliability and high output.

  In the first to third embodiments, GaN emitting blue-violet laser light having a wavelength of 405 nm has been described as an example of a nitride semiconductor. However, the present invention is not limited to this material, and blue (wavelength: 436 nm). ) And a nitride semiconductor such as GaN that emits laser light having a wavelength of about 400 to 490 nm.

  1 n-type GaN substrate, 2 n-type AlGaN cladding layer, 3 n-type GaN guide layer, 4 InGaN / InGaN-MQW active layer, 4a InGaN barrier layer, 4b InGaN well layer, 5 AlGaN guide layer, 6 p-type AlGaN cladding layer 7 p-type GaN contact layer, 8 solid phase diffusion source, 9 impurity diffusion region, 10 resist, 11 insulating film, 12 p-side electrode, 13 n-side electrode, 14 optical non-absorbing window region, 15 ridge, 16 AlN protection Film, 100 semiconductor laser.

Claims (6)

A first conductive type semiconductor layer forming step of stacking a first conductive type nitride semiconductor layer on a substrate;
Forming an active layer and a guide layer made of a nitride semiconductor on the nitride semiconductor layer of the first conductivity type;
A second conductive type semiconductor layer forming step of stacking a second conductive type nitride semiconductor layer on the guide layer;
A diffusion source forming step of selectively forming a solid phase diffusion source in a predetermined region on the second conductivity type nitride semiconductor layer;
A window region forming step of forming an optical non-absorption window region by diffusing impurity atoms from the solid phase diffusion source to a region including the active layer by performing a heat treatment in an atmosphere containing oxygen;
A method of manufacturing a nitride semiconductor device, comprising: a cleaving step of forming a cleaved surface to be an end face of a laser resonator in the optical non-absorption window region. A protective film forming step of forming a protective film on a region of the second conductivity type nitride semiconductor layer where the solid layer diffusion source is not formed;
The method for manufacturing a nitride semiconductor device according to claim 1, wherein the window region forming step is performed after the protective film forming step. A first conductive type semiconductor layer forming step of stacking a first conductive type nitride semiconductor layer on a substrate;
Forming an active layer and a guide layer made of a nitride semiconductor on the nitride semiconductor layer of the first conductivity type;
A diffusion source forming step of selectively forming a solid phase diffusion source in a predetermined region on the guide layer;
A window region forming step of forming an optical non-absorption window region by diffusing impurity atoms from the solid phase diffusion source to a region including the active layer by performing a heat treatment in an atmosphere containing oxygen;
A second conductive type semiconductor layer forming step of stacking a second conductive type nitride semiconductor layer on the guide layer;
A method of manufacturing a nitride semiconductor device, comprising: a cleaving step of forming a cleaved surface to be an end face of a laser resonator in the optical non-absorption window region. A protective film forming step of forming a protective film on the guide layer and in a region where the solid layer diffusion source is not formed;
The method for manufacturing a nitride semiconductor device according to claim 3, wherein the window region forming step is performed after the protective film forming step.   5. The method of manufacturing a nitride semiconductor device according to claim 1, wherein the heat treatment in the window region forming step is performed at a temperature of 800 ° C. or higher and lower than 1000 ° C. 6.   The said solid layer diffusion source contains 1 or 2 or more atoms selected from the group which consists of Mg, Zn, Si, and O as an impurity, The any one of Claim 1 thru | or 5 characterized by the above-mentioned. Of manufacturing a nitride semiconductor device.

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