JP2005159229A - Manufacturing method of semiconductor laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the manufacturing method of a semiconductor laser having a ridge structure wherein a dry etching is used and the generations of crystal defects and plasma damages are prevented. <P>SOLUTION: In the manufacturing method of a semiconductor laser, there are formed by an MOCVD method successively on an n-type substrate 101 an n-type buffer layer 102, an n-type clad layer 103, an active layer 104, a first p-type clad layer 105, a p-type etching stop layer 106, and a second p-type clad layer 107. Then, the second p-type clad layer 107 is dry-etched until reaching the etching stop layer 106, by using as a mask a stripe-form SiO<SB>2</SB>film 109 formed on the second p-type clad layer 107. Thereafter, deposition substances stuck on the layer 107 by the dry etching are removed therefrom, and only the etching stop layer 106 exposed to the periphery of the ridge of the semiconductor laser is removed selectively by using a sulfuric-acid-based etchant. Further, a thermal cleaning is performed in order to remove the plasma damages of the semiconductor laser. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a semiconductor laser device used as a light source of an optical disc and a method for manufacturing the same.

  With the advent of DVD, the density of optical discs is increasing. As DVD drives, products that support not only reproduction but also recordable / rewritable DVD-RAM, DVD-RW, and the like have been commercialized, and the recording speed has been increased.

  As the optical disc equipment is diversified as described above, the semiconductor laser as the light source is also required to have higher functionality. In particular, high output of a semiconductor laser is strongly desired for recording applications. Although several proposals have been made as means for achieving high output, it is one of the effective means to make the cladding layer above the active layer into a ridge stripe shape having no asymmetry and high perpendicularity.

  By increasing the verticality of the ridge, the kink level that hindered high output can be improved by bringing the current distribution and the light distribution close to each other.

  However, a visible light semiconductor laser having a wavelength in the 650 nm band is generally formed on a substrate having an off-angle whose normal is deviated from the crystal principal axis with respect to the plane orientation of the substrate surface. When the ridge shape is processed using the etching technique, an asymmetric shape reflecting the off-angle of the substrate is obtained, and it is difficult to improve the ridge asymmetry.

  In recent years, a technique for forming a ridge stripe by using a dry etching technique and a wet etching technique together has been proposed (see, for example, Patent Document 1).

  By using this technique, a ridge stripe shape in which the asymmetry of the ridge is improved as compared with the case of processing only by wet etching is obtained.

  In order to obtain a stable shape of the ridge stripe, an etching stop layer made of a material that is less easily etched than the cladding layer is generally provided immediately below the cladding layer. The etching stop layer is preferably made of a material that does not absorb light with respect to the active layer and has a thickness of about several tens of nanometers so as not to affect the laser emission characteristics and current injection into the active layer.

  In order to process the ridge stripe with high accuracy and good reproducibility, it is important to increase the selectivity between the cladding layer and the etching stop layer.

  In order to increase the selectivity, it has been proposed to use a GaInP / AlGaInP multiple quantum well structure instead of the GaInP single-layer etching stop layer as shown in Patent Document 1, thereby suppressing light absorption and selection. (See, for example, Patent Document 2).

  Making the etching stop layer into a multilayer structure in this way has also been proposed for an infrared laser using a GaAs-based material (see, for example, Patent Document 3).

  As another configuration, an example in which an etching stop layer is AlGaAs in an AlGaInP semiconductor laser is also shown (see Patent Document 4).

  Among these, the manufacturing method of the semiconductor laser device in the prior art disclosed in Patent Document 1 will be described with reference to FIG.

As shown in FIG. 3A, an n-type GaAs buffer layer 302, an n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 layer are formed on an n-type GaAs substrate 301 by metal organic vapor phase epitaxy (hereinafter referred to as MOCVD method). P cladding layer 303, GaInP / AlGaInP multiple quantum well structure active layer 304, p-type _{(Al 0.7 Ga 0.3) 0.5 In} 0.5 P first cladding layer 305, p-type Ga _0.5 an In _0.5 P etching stop layer 306, p-type (Al _{A 0.7} Ga _0.3 ) _0.5 In _0.5 P second cladding layer 307 and a p-type Ga _0.5 In _0.5 P intermediate layer 308 are epitaxially grown sequentially. As shown in Patent Document 3, a multilayer film having a GaInP / AlGaInP multiple quantum well structure may be formed as an etching stop layer.

Next, as shown in FIG. 3B, a dielectric film such as a SiO ₂ film 309 or a resist is deposited and processed into a stripe shape by using a photolithography technique or an etching technique, and then a dry etching technique is used. The p-type Ga _0.5 In _0.5 P intermediate layer 308 and the p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P second cladding layer 307 are partially etched.

Next, the p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P second cladding layer 307 is etched using a wet etching technique until reaching the etching stop layer 306, thereby forming a ridge stripe.

  As shown in FIG. 3C, an n-type AlInP current blocking layer 310 and a p-type GaAs contact layer 311 are grown sequentially. Next, electrodes (not shown) are formed on the front surface and the back surface of the substrate to manufacture a semiconductor laser device.

In the above manufacturing method, if the etching stop layer is exposed after the formation of the ridge stripe, the hetero barrier relaxation due to the sharpness of the interface between the etching stop layer and the current blocking layer occurs during the subsequent growth of the current blocking layer, resulting in a current confinement loss. For example, Japanese Patent Application Laid-Open No. H10-228867 discloses a manufacturing method in which the etching stop layer is removed by dry etching using a chlorine system as a countermeasure (see Patent Document 3).
JP 2003-69154 A JP-A-7-162089 Japanese Patent Laid-Open No. 7-142808 JP-A-4-27184 JP 2002-190646 A

  However, if the etching stop layer, the active layer material, and the p-type second cladding layer material to be ridge-stripe processed are the same P-based material, especially when the ridge-shaped processing is all performed by dry etching, the etching stop layer is selected. It is difficult to ensure the property, and there is a high possibility that the etching will proceed through the etching stop layer, which may be a major factor in yield reduction.

  Therefore, in the above prior art, the ridge stripe processing is first performed by dry etching and then by wet etching. However, if wet etching is performed, the processing shape depends on the crystal plane orientation. On the substrate having corners, the film epitaxially grown on the substrate has the same crystal orientation, and there is a problem that the vertical shape of the ridge obtained by dry etching is broken. As described above, this is a factor that hinders high output.

  In addition, when wet etching is performed later, the selectivity of the etching stop layer can be made relatively high. However, the etching stop layer is still missing in part of the wafer due to variations in the etching depth of the dry etching. This can cause the problem of yield loss.

  Further, as disclosed in Patent Document 2, it is possible to further ensure selectivity by making the etching stop layer a GaInP / AlGaInP multiple quantum well structure, but in this case, the outermost surface after etching is the same as the cladding layer. A GaInP layer is formed in consideration of the selection ratio.

  Then, when an AlInP current blocking layer is formed thereon, a current blocking loss due to a hetero barrier occurs between the etching stop layers. As a countermeasure against this, it is conceivable to remove the etching stop layer by dry etching using a chlorine-based gas as described in Patent Document 3, but the etching of the etching stop layer is stopped with good controllability on the surface of the AlGaInP cladding layer immediately below. That is quite difficult. This is because the Al composition of the cladding layer is as low as about 30%. Further, this etching may cause plasma damage due to the use of a chlorine-based gas or damage the ridge shape already formed.

Also, as disclosed in Patent Document 5, there is a method of increasing the Al composition and improving the etching selectivity as the Al _0.4 Ga _0.6 As layer, but in this case also, the buried growth is performed without removing the plasma damage. Therefore, the crystallinity is deteriorated due to the influence of the interface state, and it is difficult to obtain good device characteristics.

  In order to solve the above-mentioned conventional problems, the present invention stops etching with high selectivity in the etching stop layer regardless of whether the dry etching technique or the wet technique is used. By making the shape possible, not only can the current distribution and light distribution not be biased and the output can be increased, but also by using an etching stop layer with high selectivity, the etching stop layer can be easily removed by wet etching. In order to further eliminate plasma damage by heat treatment, the loss of the etching stop layer and the current block loss due to the steep interface during the subsequent growth of the current block layer can be suppressed. The purpose is to provide.

  In order to achieve the above object, a method of manufacturing a semiconductor laser device according to the present invention includes a first conductive type cladding layer, an active layer, a second conductive type first cladding layer, and a first conductive layer on a semiconductor substrate. Forming an etching stop layer having an Al content higher than that of the first conductivity type cladding layer and a second conductivity type second cladding layer in this order; and forming the second conductivity type second cladding layer of the laser resonator Etching into a longitudinally extending ridge shape; removing an etching stop layer outside the second conductivity type second cladding layer etched into the ridge shape; and the second conductivity type first cladding. Chemically treating the surface of the layer and the side surface of the ridge-shaped second conductivity type second cladding layer; and heat treating the semiconductor substrate formed up to the second conductivity type second cladding layer; Wherein it comprises the steps of forming a first conductivity type current blocking layer on a semiconductor substrate, and forming a second conductivity type contact layer on the first conductivity type current blocking layer.

  The etching stop layer preferably has an Al content higher than that of the second conductivity type second cladding layer.

  The etching stop layer is preferably a material that does not absorb light emitted from the active layer.

  The etching stop layer is preferably made of a material system different from that of the second conductivity type cladding layer.

  The etching stop layer preferably has a thickness of 1 nm to 20 nm.

  In the step of etching the second conductivity type second cladding layer into a ridge shape, the second conductivity type second cladding layer is etched using dry etching, and the selectivity to the etching stop layer is 3 or more. It is preferable.

  In the step of removing the etching stop layer, it is preferable that the etching stop layer is removed using wet etching, and the selectivity with respect to the first cladding layer of the second conductivity type is 60 or more.

  In the step of removing the etching stop layer, it is preferable that the etching stop layer is removed by wet etching, and the side etching of the etching stop layer is within 0.2 μm.

  The surface treatment is preferably performed by etching the surface of the second conductivity type first cladding layer and the side surface of the ridge-shaped second conductivity type second cladding layer in a range of 0.5 nm to 4 nm.

  The heat treatment step of the semiconductor substrate is preferably performed at a temperature of 600 ° C. or higher and within 20 minutes using a crystal growth apparatus or a heat treatment furnace.

  As described above, by using AlGaAs, which is a material system different from the second conductivity type AlGaInP second cladding layer processed into a ridge shape as an etching stop layer, a highly perpendicular ridge stripe can be formed using dry etching. By making this possible and greatly improving the symmetry between the current distribution and the light distribution, the kink level can be dramatically improved.

  Further, after the ridge formation, the etching stop layer is selectively removed by wet etching, and then the smoothness is improved by surface treatment of the ridge side surface and the second conductivity type AlGaInP first cladding layer, and the crystal of the damaged layer is recovered by annealing. As a result, a good current blocking layer can be formed without causing a current block loss even in subsequent crystal growth, and device characteristics with high oscillation efficiency can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing each step of the manufacturing method in the present embodiment.

First, as shown in FIG. 1A, an n-type GaAs buffer layer 102, an n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer 103, a GaInP-based material are formed on an n-type GaAs substrate 101 by MOCVD. active layer 104, p-type _{(Al 0.7 Ga 0.3) 0.5 In} 0.5 P first cladding layer 105, p-type Al _0.45 Ga _0.55 As etching stop layer 106, and p-type _{(Al 0.7 Ga 0.3) 0.5 In} 0.5 P second cladding A layer 107 and a p-type Ga _0.5 In _0.5 P intermediate layer 108 are sequentially formed.

  Note that the n-type GaAs substrate 101 used in the present embodiment is an off-substrate whose substrate main axis is inclined from the surface by several degrees to several tens of degrees.

  Further, the active layer 104 of the GaInP-based material may be an active layer having a GaInP / AlGaInP multiple quantum well structure as in the conventional example.

Next, as shown in FIG. 1B, an SiO ₂ film 109 is formed on the p-type second cladding layer 107, and then processed into stripes by photolithography and dry etching techniques. Using the striped SiO ₂ film 109 as a mask, the second cladding layer 107 is dry-etched up to the Al _0.45 Ga _0.55 As etching stop layer 106.

In this case, etching using inductively coupled plasma or reactive ion plasma is effective for maintaining the vertical shape with good controllability. As an etching gas at the time of ridge stripe processing, a gas in which SiCl ₄ , O ₂ gas or the like is mixed with SF ₆ at an appropriate ratio was used.

  Thereafter, as shown in FIG. 1C, the deposit deposited by dry etching is removed, and only the etching stop layer 106 exposed around the ridge is selectively removed using a sulfuric acid-based etchant.

Next, as shown in FIG. 1 (d), the substrate 101 on which each of the above layers is formed is subjected to a surface treatment using a sulfuric acid-based etchant and then placed in the MOCVD reactor again, and the SiO ₂ film 109 is masked. As described above, the n-type AlInP current blocking layer 110 is selectively grown. At that time, thermal cleaning is performed (not shown) in order to remove damage formed by dry etching.

Thereafter, the SiO ₂ film 109 is removed from the MOCVD reactor (not shown), and is again placed in the MOCVD reactor to grow the p-type GaAs contact layer 111. Note that the thermal cleaning for removing the plasma damage layer is not limited to the MOCVD furnace, and the same effect can be obtained by using a heat treatment furnace.

  As described above, by using an AlGaAs material as the etching stop layer 106, a ridge stripe can be formed only by dry etching, and a highly perpendicular shape can be obtained.

  Further, by using different materials for the etching stop layer and the cladding layer, only the etching stop layer can be easily wet-etched.

Note that when the Al content of the etching stop layer 106 is low, it is difficult to suppress light absorption and to ensure selectivity by dry etching. Therefore, the composition of the etching stop layer is Al _x Ga _1-x As (x ≧ 0. 4) is desirable.

  In particular, when the Al content is higher than that of the p-type second cladding layer 107, it is easy to keep the selectivity high.

  This is because if the Al content is low, the energy gap of the etching stop layer 106 becomes smaller than the energy of the emission wavelength, and light absorption may occur, resulting in a decrease in output and thermal runaway.

  FIG. 2 shows the relationship between the Al content in the AlGaAs material and the absorption wavelength. In this embodiment, since the active layer 104 made of a GaInP-based material having an emission wavelength in the 650 nm band is used, it is necessary to determine the composition so that light emission having a shorter wavelength than that wavelength can be obtained.

Even if the composition is determined as described above, the p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P second cladding layer 107 and the AlGaAs etching stop layer 106 have different material systems and different Al compositions. It is possible to ensure an etching selectivity of 3 or more during etching.

  The thickness of the etching stop layer 106 is 1 nm or more and 20 nm or less. This is to suppress the side etching of the etching stop layer 106 toward the inside of the ridge in the process of removing the etching stop layer 106, and to suppress the influence on the horizontal divergence angle due to this. It is. By setting the film thickness in this way, the side etching of the etching stop layer 106 can be within 0.2 μm at the bottom of the ridge.

  In the step of removing the etching stop layer 106 shown in FIG. 1C, since an As-based material is used, high selectivity can be maintained with respect to the clad layer that is a P-based material, and the selectivity is 60. The above is also possible. As a result, the etching stop layer can be easily removed with high accuracy.

  For example, etching can be performed with high selectivity by appropriately mixing hydrogen peroxide with sulfuric acid.

  Further, as the above-described surface treatment, a p-type second processed into a ridge shape and a surface of the p-type first cladding layer 105 by performing treatment using a sulfuric acid-based etchant having an etching rate of several nm / min. The side surface of the clad layer 107 was etched by about 0.5 nm to 4 nm, which corresponds to several atomic layers.

  As a result, even when a metamorphic layer is formed at the interface between the p-type first cladding layer 105 and the etching stop layer 106, or when a polymer layer or the like is formed on the side surface of the p-type second cladding layer 107, these are removed. The n-type current blocking layer 110 having good crystallinity can be obtained in a subsequent process by removing and improving the surface smoothness.

  In addition, in order to remove the plasma damage layer generated by dry etching, the n-type current blocking layer 110 is grown, and the crystallinity is restored by annealing at about 700 ° C. for about 2 minutes in a hydrogen or nitrogen atmosphere. After removing the damage, the n-type current blocking layer 110 was grown.

  This suppresses the generation of crystal defects in combination with the previously performed surface treatment and allows good crystal growth. Further, the generation of interface states can be suppressed, and the device characteristics can also be improved.

  In addition, although the effect of this invention can be exhibited if annealing is performed at 600 ° C. or more, in order to suppress the influence on the device characteristics due to the diffusion of Zn which is a p-type dopant, it is within 20 minutes when performed at 700 ° C. Is desirable.

  The same effect can be obtained even if short-time annealing by RTP (Rapid Thermal Process) is used.

  The method for manufacturing a semiconductor laser device according to the present invention is useful as a method for manufacturing a semiconductor laser device with high output and high reliability, because the ridge shape is improved and the crystallinity of the current blocking layer is not impaired.

Manufacturing process explanatory diagram of a semiconductor laser device in an embodiment of the present invention The figure which showed Al content rate and absorption edge wavelength of the etching stop layer in embodiment of this invention Manufacturing process explanatory diagram of a semiconductor laser device in the prior art

Explanation of symbols

101, 301 n-type GaAs substrate 102, 302 n-type GaAs buffer layer 103, 303 n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer 104 GaInP-based active layer 105, 305 p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P first cladding layer 106 p-type Al _0.45 Ga _0.55 As etching stop layer 107, 307 p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P second cladding layer 108, 308 p-type Ga _0.5 In _0.5 P intermediate layer 109, 309 SiO ₂ film 110, 310 n-type AlInP current blocking layer 111, 311 p-type GaAs contact layer 304 GaInP / AlGaInP multiple quantum well structure active layer 306 p-type Ga _0.5 In _0.5 P etching stop layer

Claims (10)

On the semiconductor substrate, a first conductivity type cladding layer, an active layer, a second conductivity type first cladding layer, an etching stop layer having an Al content higher than that of the first conductivity type cladding layer, and a second Forming a conductive second cladding layer in this order;
Etching the second conductivity type second cladding layer into a ridge shape extending in the longitudinal direction of the laser resonator;
Removing an etching stop layer outside the second conductivity type second cladding layer etched into the ridge shape;
Chemically treating the surface of the second conductivity type first cladding layer and the side surface of the ridge-shaped second conductivity type second cladding layer;
Heat-treating the semiconductor substrate formed up to the second conductivity type second cladding layer;
Forming a first conductivity type current blocking layer on the semiconductor substrate;
Forming a second conductivity type contact layer on the first conductivity type current blocking layer. 2. The method of manufacturing a semiconductor laser device according to claim 1, wherein the etching stop layer has an Al content higher than that of the second conductivity type second cladding layer. 3. The method of manufacturing a semiconductor laser device according to claim 1, wherein the etching stop layer is a material that does not absorb light emitted from the active layer. 4. The method of manufacturing a semiconductor laser device according to claim 1, wherein the etching stop layer is made of a material system different from that of the second conductivity type cladding layer. 5. The method of manufacturing a semiconductor laser device according to claim 1, wherein the etching stop layer has a thickness of 1 nm to 20 nm. In the step of etching the second conductivity type second cladding layer into a ridge shape,
6. The semiconductor laser device according to claim 1, wherein the second cladding layer of the second conductivity type is etched by dry etching, and a selection ratio with respect to the etching stop layer is 3 or more. Manufacturing method. In the step of removing the etching stop layer,
7. The method of manufacturing a semiconductor laser device according to claim 6, wherein the etching stop layer is removed by wet etching, and the selection ratio to the first conductivity type first cladding layer is 60 or more. In the step of removing the etching stop layer,
8. The method of manufacturing a semiconductor laser device according to claim 7, wherein the etching stop layer is removed by wet etching, and side etching of the etching stop layer is within 0.2 [mu] m. The surface treatment is performed by etching the surface of the first conductivity type first cladding layer and the side surface of the ridge-shaped second conductivity type second cladding layer in a range of 0.5 nm to 4 nm. Item 9. A method for manufacturing a semiconductor laser device according to Item 7 or 8. 10. The method of manufacturing a semiconductor laser device according to claim 1, wherein the heat treatment step of the semiconductor substrate is performed at a temperature of 600 ° C. or more and within 20 minutes using a crystal growth apparatus or a heat treatment furnace.

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