JP2008047663A - Semiconductor laser element, manufacturing method thereof, and optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a semiconductor laser element with which work precision of a ridge can be improved and occurrence of a kink can sufficiently be controlled. <P>SOLUTION: The method comprises a process for forming a mask 116 on a surface of a semiconductor layer 101. The mask 116 has a pair of stripe-like openings 115 and 115 along both sides of a region where the ridge is to be formed, and has an etching monitor opening 117 having a size larger than a width size of the stripe-like openings 115 in a region different from a region where the semiconductor laser element is to be formed. The semiconductor layer 101 is dry-etched by using the mask 116 while advance of dry etching is observed through the etching monitor opening 117. Dry etching is stopped at prescribed timing corresponding to advance of dry etching on an etching marker layer 108. Recesses are formed just below the stripe-like openings 115 so as to form the ridge part. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a semiconductor laser device, and more particularly to a method for forming a ridge portion of a semiconductor laser device.

  The present invention also relates to a semiconductor laser device manufactured by such a method of manufacturing a semiconductor laser device.

  The present invention also relates to an optical disc apparatus provided with such a semiconductor laser element.

  One of the major issues in increasing the output of a semiconductor laser device is the occurrence of kink (nonlinearity in the optical output-operating current characteristics of the semiconductor laser device). The kink is a mode other than the basic waveguide mode when the refractive index difference Δn between the inside and outside of the waveguide is large with respect to the width of the waveguide of the semiconductor laser (the width of the ridge formed by processing the clad layer into a stripe shape). This is caused by the generation of a higher-order waveguide mode. Further, as the light output is increased, the refractive index difference Δn increases due to the heat generated in the waveguide, which also causes kinks. In order to suppress kinks, it is necessary to suppress the generation of higher-order waveguide modes in the waveguide, particularly in the horizontal direction. For this purpose, it is effective to narrow the width of the ridge portion. .

  When it is intended to reduce the width of the ridge portion, the ridge portion can be formed narrower by using the dry etching method than by using the wet etching method. This is because, as an advantage of the dry etching method, anisotropic etching can be realized, so that processing controllability of width and shape is improved. On the other hand, however, when the ridge portion is formed using the dry etching method, there is a disadvantage that it is difficult to use the selective etching method that is common in the wet etching method. Therefore, it is difficult to control the etching amount (depth) in the dry etching method compared to the wet etching method. Therefore, when processing the ridge portion by the dry etching method, calculate the etching rate in advance by calculating the conditions, calculate the etching time required to etch only the desired depth, and start etching. In general, etching has been stopped when the time has elapsed.

  When processing the ridge portion, it is required to control the etching with an accuracy of ± 10 nm to several tens of nm, for example, while it is desired to etch at least 1 μm to 2 μm in the depth direction. However, the above-described general method has a problem that the etching amount cannot be sufficiently controlled due to variations in the thickness of the semiconductor layer to be etched and variations in the etching amount of dry etching. As a result, the control of the thickness of the cladding layer beside the ridge waveguide, which is another viewpoint important for suppression of kinks, becomes unstable, and as a result, kinks may occur.

Therefore, for example, in Patent Document 1 (Japanese Patent Laid-Open No. 3-6877) and Patent Document 2 (Japanese Patent No. 2601229), an end point detection layer (cladding) is formed at a depth corresponding to the lower portion of the ridge portion in the cladding layer growth stage. A method has been proposed in which a layer having a composition different from that of the layer is interposed, and the etching amount (depth) control accuracy in processing the ridge portion by dry etching is improved using the end point detection layer.
Japanese Patent Laid-Open No. 3-6877 Japanese Patent Publication No. 2601229

  However, in the proposed method described above, the presence of the end point detection layer sometimes causes a factor to hinder the verticality of the side surface of the final ridge portion. That is, in these proposed methods, as shown in FIGS. 8A and 8B, end point detection having a composition different from that of the clad layer (a layer constituting most of the ridge portion) on the side surface of the ridge portion 920 is performed. There is a problem that the layer 950 is exposed and the end point detection layer 950 partially protrudes (see FIG. 8A) or retracts (see FIG. 8B). This is because the etching characteristics of the end point detection layer 950 are different from the etching characteristics of the cladding layer when the reaction product and damage during the dry etching are removed using a chemical etchant after the processing by the dry etching.

  As described above, when the verticality of the side surface of the ridge portion is hindered, there is a problem that it is impossible to suppress the occurrence of kinks. Furthermore, the insulating film or electrode covering the ridge portion may be disconnected (refers to a phenomenon in which the insulating film or electrode becomes discontinuous due to unevenness on the side surface of the ridge portion).

  Accordingly, a main object of the present invention is to provide a method of manufacturing a semiconductor laser device capable of improving the processing accuracy of the ridge portion and thus sufficiently suppressing the occurrence of kinks.

  A further object of the present invention is to provide a semiconductor laser device capable of sufficiently suppressing the generation of kinks and capable of high output operation by using such a manufacturing method.

  Another object of the present invention is to provide an optical disc apparatus provided with such a semiconductor laser element.

In order to solve the above problems, a method for manufacturing a semiconductor laser device of the present invention includes:
In a manufacturing method of a semiconductor laser device for forming a waveguide including a striped ridge portion on a semiconductor substrate,
An active layer, a first upper cladding layer, an etching marker layer having a composition different from that of the first upper cladding layer, and a second upper cladding layer having a composition different from that of the etching marker layer are provided on the semiconductor substrate. A step of laminating a semiconductor layer including in order;
Forming a mask on the surface of the semiconductor layer, the mask having a pair of stripe-shaped openings along both sides of a region where the ridge portion is to be formed in the surface of the semiconductor layer, and An etching monitor opening having a size larger than the width of the stripe-shaped opening in a region different from a region where the semiconductor laser element is to be formed;
Dry etching of the semiconductor layer is performed using the mask while observing the progress of the dry etching through the etching monitor opening, and the dry etching is performed at a predetermined timing according to the progress of the dry etching with respect to the etching marker layer. The method includes a step of forming the ridge portion by stopping etching and forming a recess directly below each of the stripe-shaped openings.

  Here, the “predetermined timing according to the progress of the dry etching with respect to the etching marker layer” means, for example, the timing at which the etching marker layer is exposed or disappeared by the progress of the dry etching, or a predetermined time from the timing. Refers to the set timing.

As the mask, for example, a mask using an inorganic material such as SiO ₂ or SiN _x can be used in addition to a resist mask formed using a photolithography method.

  In the method of manufacturing a semiconductor laser device according to the present invention, the ridge portion is formed by dry etching, so that the width of the ridge portion can be made narrower than when the wet etching method is used. Moreover, in the present invention, the dry etching of the semiconductor layer is performed while observing the progress of the dry etching through the etching monitor opening. Since the etching monitor opening has a size larger than the width of the stripe-shaped opening, the progress of the dry etching is easily observed. Then, the dry etching is stopped at a predetermined timing according to the progress of the dry etching with respect to the etching marker layer. Thereby, the ridge portion is formed by forming a recess directly below each of the stripe-shaped openings. Therefore, as compared with a method in which the etching amount is controlled by the elapsed time from the start of the dry etching, in the present invention, the control is performed at the time of forming the concave portion by the dry etching (that is, processing of the ridge portion). The etching time to be shortened, and the etching amount can be accurately controlled in the depth direction. Therefore, according to the present invention, the controllability of the etching depth can be improved while ensuring the perpendicularity of the side surface of the ridge portion, and the processing accuracy of the ridge portion can be improved. As a result, in the semiconductor laser device manufactured according to the present invention, the generation of kinks can be sufficiently suppressed, and a high output operation is possible.

A method of manufacturing a semiconductor laser device according to one embodiment includes:
Prior to the dry etching, including a step of measuring a dry etching rate directly under the etching monitor opening and a dry etching rate directly under the stripe opening,
Based on the difference between the two dry etching rates, as the timing for stopping the dry etching, the etching marker layer disappears immediately below the etching monitor opening, whereas immediately below each stripe opening. The timing is set such that a part of the second upper cladding layer remains in a layered manner on the etching marker layer.

  In the method of manufacturing a semiconductor laser device according to this embodiment, a part of the second upper cladding layer (this is referred to as “second upper cladding lower portion” at the bottom of the recess immediately below the stripe openings after the dry etching. This is called a “layer”). Therefore, the etching marker layer is not exposed when the concave portion is formed by the dry etching (that is, when the ridge portion is processed). As a result, the processing accuracy of the ridge portion can be further improved. Further, since the width dimension of the stripe-shaped opening is for forming the ridge portion of the semiconductor laser element, the dry etching rate immediately below the stripe-shaped opening is caused by the microloading effect in the dry etching step. Is relatively slow with respect to the dry etching rate immediately below the etching monitor opening. Therefore, the two dry etching rates are different from each other. The thickness of the second upper cladding lower layer is accurately controlled by setting the timing for stopping the dry etching based on the difference between the two dry etching rates. Therefore, the processing accuracy of the ridge portion can be further improved.

  In one embodiment of the method of manufacturing a semiconductor laser device, the width dimension of one of the stripe openings is 20 μm or less, and the width dimension of the etching monitor opening is 1 mm or more. .

  In the manufacturing method of the semiconductor laser device according to this embodiment, since the width dimension of one of the stripe-shaped openings is 20 μm or less and the width dimension of the etching monitor opening is 1 mm or more, The microloading effect is reliably exhibited in the etching process. That is, the etching rate immediately below the stripe-shaped opening can be made relatively slower than the etching rate directly below the etching monitor opening. As a result, even if the etching monitor opening and the stripe-shaped opening are simultaneously dry-etched, the etching of the etching monitor opening reaches the etching marker layer first. Therefore, the etching marker layer disappears immediately below the etching monitor opening, while a portion of the second upper cladding layer remains in a layered form on the etching marker layer immediately below each stripe opening. It is easy to set such timing.

  In the method of manufacturing a semiconductor laser device according to one embodiment, the method of observing the progress of the dry etching through the etching monitor opening irradiates light to the semiconductor layer from the outside through the etching monitor opening. It is a method of observing an interference waveform of reflected light reflected by each of the layers included in a semiconductor layer.

  In the method of manufacturing a semiconductor laser device according to this embodiment, only the progress of dry etching in the opening for etching monitoring is performed independently of the progress of etching in the striped opening having a narrower width than the opening for etching monitoring. Is observed. Since the interference waveform of the reflected light reflected by each of the layers included in the semiconductor layer is observed, the progress of the dry etching with respect to the etching marker layer can be easily observed through the etching monitor opening.

  The light applied to the semiconductor layer through the etching monitor opening may be monochromatic light having a specific wavelength or so-called white light having a broad wavelength spectrum. In the case of irradiating white light, the progress of the dry etching can be observed by observing the interference waveform after the reflected light is spectrally converted into monochromatic light.

In the manufacturing method of the semiconductor laser device of one embodiment,
The first upper cladding layer and the second upper cladding layer are each made of AlGaInP,
The etching marker layer is made of GaInP.

  In the manufacturing method of the semiconductor laser device of this embodiment, the refractive index difference of the etching marker layer can be increased with respect to the first upper cladding layer and the second upper cladding layer. As a result, the progress of the dry etching with respect to the etching marker layer can be easily observed by the interference waveform of the reflected light.

  In one embodiment of the method for manufacturing a semiconductor laser device, the wavelength of reflected light for observing the interference waveform is 400 nm or more and 650 nm or less.

  In the method of manufacturing a semiconductor laser device according to this embodiment, when the first upper cladding layer and the second upper cladding layer are each made of AlGaInP and the etching marker layer is made of GaInP, By observing the interference waveform of the reflected light having a wavelength of 650 nm or less, a clear interference waveform that identifies the boundary between the etching marker layer and the first upper cladding layer can be observed. The same applies when a contact layer made of GaAs is provided on the second upper cladding layer. In addition, since the interference waveform is observed for reflected light having a wavelength of 400 nm or more in the etching monitor opening, dirt on the window of a dry etching apparatus for observing the etching state (perform dry etching) This makes it possible to observe the etching state without being affected by the occurrence of deposits on the inside of the window.

In the manufacturing method of the semiconductor laser device of one embodiment,
The semiconductor substrate is made of GaAs,
A lower clad layer made of AlGaInP is provided under the active layer,
The active layer is a quantum well layer formed by alternately laminating AlGaInP and GaInP,
The first upper cladding layer and the second upper cladding layer are each made of AlGaInP,
The distance in the layer thickness direction between the etching marker layer and the active layer is 0.2 μm or more and 0.4 μm or less.

  Here, the “distance between the etching marker layer and the active layer” is defined as the distance from the top of the quantum well layer closest to the etching marker layer to the etching marker layer in the active layer.

  In the semiconductor laser device manufacturing method of this embodiment, a red semiconductor laser device is manufactured by a combination of the substrate, the lower cladding layer, the active layer, and the upper cladding layer. At that time, a waveguide having an appropriate Δn as a red semiconductor laser element is formed. In addition, since the distance in the layer thickness direction between the etching marker layer and the active layer is 0.2 μm or more and 0.4 μm or less, the dry etching is performed, so that the above directly under the etching monitor opening While the etching marker layer disappears, a state in which a part of the second upper cladding layer remains in a layered form on the etching marker layer can be easily realized immediately below each of the stripe-shaped openings.

  In one embodiment of the semiconductor laser device manufacturing method, after the dry etching is stopped, the second upper cladding layer on the etching marker layer disappears immediately below the stripe-shaped opening by using a wet etching method. Etching is selectively performed until the etching is completed.

  In the method of manufacturing a semiconductor laser device according to the present invention, as described above, since the etching accuracy is improved in the step of performing the dry etching, the dry etching is performed immediately below the stripe-shaped opening to the vicinity of the etching marker layer. Can be stopped by advancing. Therefore, in the manufacturing method of the semiconductor laser device of this embodiment, it is possible to shorten the wet etching time until the second upper cladding layer on the etching marker layer disappears immediately below the stripe-shaped opening. Accordingly, the time required for etching the side surface of the ridge portion in the lateral direction (the direction parallel to the surface of the semiconductor substrate) is shortened, and the verticality of the side surface of the ridge portion is caused by the surface orientation of the semiconductor material. It is possible to suppress deviation from the above.

The semiconductor laser device of this invention is
The lower cladding layer, the active layer, the first upper cladding layer, the etching marker layer having a different composition from the first upper cladding layer, and the etching marker layer having a different composition from each other are sequentially stacked on the semiconductor substrate. A semiconductor layer including at least a second upper cladding layer and a contact layer for ohmic contact with the electrode;
A pair of stripe-shaped recesses are formed on the surface of the semiconductor layer at a depth from the surface to the middle of the second upper cladding layer, and the semiconductor substrate includes the semiconductor layer between the pair of stripe-shaped recesses. A waveguide is constituted by a ridge portion having a side surface substantially perpendicular to the surface of the ridge and a ridge terrace portion formed of the semiconductor layer outside the pair of stripe-shaped recesses.

  This semiconductor laser element is manufactured by the method for manufacturing a semiconductor laser element of the above-described invention. In this semiconductor laser element, the generation of kinks can be sufficiently suppressed, and a high output operation is possible.

  An optical disk apparatus according to the present invention is an optical disk apparatus comprising the semiconductor laser element as a light source.

  In this optical disc apparatus, since the semiconductor laser element as the light source can sufficiently suppress the occurrence of kinks, it operates to a higher output than the conventional semiconductor laser element. As a result, the optical disk apparatus of the present invention can read and write at a higher speed than the conventional optical disk apparatus.

  Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

  Hereinafter, a semiconductor laser device, a manufacturing method thereof, and an optical disc apparatus according to the present invention will be described in detail with reference to embodiments shown in the drawings.

  In the following description, “n−” and “p−” represent n-type and p-type, respectively. Further, throughout this specification, “upper” means a direction away from the substrate, and “lower” means a direction closer to the substrate. Crystal growth proceeds from “down” to “up”.

[First embodiment]
FIG. 1 shows the structure of a semiconductor laser device manufactured by the manufacturing method of one embodiment of the present invention.

This semiconductor laser device is a red semiconductor laser device having a wavelength of emitted light of 650 nm. The n-GaAs buffer layer 102 and n- (Al _0.7 Ga ₀ ) are sequentially stacked on the n-GaAs substrate 101. _.3 ) _0.5 In _0.5 P lower cladding layer 103, (Al _0.545 Ga _0.455 ) _0.5 In _0.5 P lower guide layer 104, multiple strain quantum well active layer 105, (Al _{0 .545} Ga _0.455 ) _0.5 In _0.5 P upper guide layer 106, p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P first upper cladding layer 107, Ga _{0. 63} In _0.37 P etching marker layer 108, p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P second upper cladding layer 109, p-Ga _0.51 In _0.49 P intermediate Layer 110, and p ⁺ A GaAs contact layer 111 is provided.

  Of the semiconductor layer stacked on the substrate 101, a pair of stripe-shaped recesses 128, 128 having a depth extending from the surface of the contact layer 111 to the middle of the second upper cladding layer 109 are formed by etching. A waveguide 130 is formed by the ridge portion 120 formed of a semiconductor layer between the pair of stripe-shaped recesses 128 and 128 and the ridge terrace portions 121 and 121 formed of a semiconductor layer outside the pair of stripe-shaped recesses 128 and 128. ing.

  Of the second upper clad layer 109, the portion that forms the striped ridge portion 120 and the ridge terrace portion 121 together with the contact layer 111 and the intermediate layer 110 is referred to as a “second upper clad upper layer 109 a”. A portion corresponding to a portion below the bottom surface is referred to as a “second upper clad lower layer 109b”. In the present embodiment, the thickness of the second upper cladding lower layer 109b is 0.05 μm. Further, the width dimension of each stripe-shaped recess 128, that is, the horizontal interval between the ridge 120 and the ridge terrace 121 is 10 μm.

An insulating layer 112 made of SiO ₂ is formed so as to cover the inner surfaces of the pair of stripe-shaped recesses 128, 128 and the upper surface of the ridge terrace 121. A p-side electrode 113 is formed so as to cover the upper surface of the p ⁺ -GaAs contact layer 111 forming the insulating layer 112 and the ridge portion 120. An n-side electrode 114 is formed on the surface (back surface) opposite to the side on which the semiconductor layer is laminated of the n-GaAs substrate 101. The p-side electrode 113 and the n-side electrode 114 are in ohmic contact with the upper surface of the contact layer 111 forming the ridge portion 120 and the rear surface of the substrate 101, respectively.

  Next, a method for manufacturing the semiconductor laser device of FIG. 1 will be described with reference to FIGS.

First, as shown in FIG. 2, an n-GaAs buffer layer 102 (layer thickness: 500 nm), n- (Al _0.7 Ga ₀ ) is formed on the (100) plane of a 3-inch diameter n-GaAs substrate (wafer) 101. _.3 ) _0.5 In _0.5 P lower cladding layer 103 (layer thickness: 2.8 μm), (Al _0.545 Ga _0.455 ) _0.5 In _0.5 P lower guide layer 104 (layer thickness: 35 nm), multiple strain quantum well active layer 105, (Al _0.545 Ga _0.455 ) _0.5 In _0.5 P upper guide layer 106 (layer thickness: 35 nm), p- (Al _0.7 Ga _{0. 3} ) _0.5 In _0.5 P first upper cladding layer 107 (layer thickness: 240 nm), Ga _0.63 In _0.37 P etching marker layer 108 (layer thickness: 13 nm), p- (Al _0.7 Ga _{0.3) 0.5} In _0.5 P second upper click MOCVD of a lad layer 109 (layer thickness: 1.2 μm), a p-Ga _0.51 In _0.49 P intermediate layer 110 (layer thickness: 35 nm), and a p ⁺ -GaAs contact layer 111 (layer thickness: 500 nm) sequentially. Crystal growth is performed by (metal organic vapor phase epitaxy).

The multi-strain quantum well active layer 105 includes a Ga _0.445 In _0.555 P quantum well layer (layer thickness: 5 nm, 4 layers) and (Al _0.545 Ga _0.455 ) _0.5 In _0.5 P. Barrier layers (layer thicknesses from the substrate side: 20 nm, 6.3 nm × 3 layers, 20 nm) are alternately stacked. Note that the structure of the multi-strain quantum well active layer 105 is not directly related to the essence of the present invention, so the detailed cross-sectional structure of the multi-strain quantum well active layer 105 is not shown.

  Next, as shown in FIG. 3, photolithography is performed to form a resist mask 116 on the surface of the substrate 101 in this state. The upper half of FIG. 3 shows the entire substrate 101 as viewed obliquely from above, and the lower half of FIG. 3 schematically shows a cross section near the center of the substrate 101.

  As can be seen from FIG. 3, the resist mask 116 has stripe-shaped openings 115 in the regions where the respective stripe-shaped recesses 128 are to be formed in the regions where the respective semiconductor laser elements are to be formed on the surface of the substrate 101. An etching monitor opening 117 having a size larger than the width of the stripe-shaped opening 115 is provided in a region (substantially central portion of the substrate 101) different from the region where the semiconductor laser element is to be formed.

  In the resist mask 116, the width dimension of the portion 116a covering the region where the ridge portion 120 is to be formed is 1.2 μm, and the width dimension of the portion 116b covering the region where the ridge terrace portion 121 is to be formed is set to 178.8 μm. Has been. The distance between these two portions 116a and 116b is set to 10 μm in accordance with the width dimension of the stripe-shaped recess 128.

  The etching monitor opening 117 is provided for observing the progress of dry etching in the next process through the etching monitor opening 117. The size of the etching monitor opening 117 is set to 2 mm square larger than the width of the stripe-shaped opening so that the progress of dry etching can be easily observed.

  Next, as shown in FIG. 4, dry etching of the semiconductor layer stacked on the substrate 101 is performed using the resist mask 116 while observing the progress of the dry etching through the etching monitor opening 117.

In order to perform this dry etching, an ICP (inductively coupled plasma) dry etching apparatus is used, the etching gas is Cl ₂ , and the gas pressure is 0.01 Torr.

  Of the semiconductor layers stacked on the substrate 101, what is actually dry-etched is a region immediately below each stripe-shaped opening 115 and a region immediately below the etching monitor opening 117. In the semiconductor layer, a region immediately below the etching monitor opening 117 is referred to as a “monitor region 118”.

  As a method of observing the progress of dry etching through the etching monitor opening 117, the monitor region 118 is irradiated with visible light VL from the outside through the etching monitor opening 117 and is included in the semiconductor layer of the monitor region 118. A method of observing the interference waveform of the reflected light VL ′ reflected by each layer is adopted.

  At this time, the width dimension of the monitor region 118 is 2 mm, whereas the width of each stripe-shaped opening 115 is sufficiently small as 10 μm. Therefore, the stripe-shaped opening narrower than the monitor region 118 due to the microloading effect. The etching rate is slow immediately below the portion 115. Therefore, if the formation position and etching time of the etching marker layer in the semiconductor layer are appropriately set, the etching marker layer 108 disappears in the monitor region 118, while the etching marker layer 108 is directly below each stripe-shaped opening 115. In addition, it is possible to realize a state in which a part 109b of the second upper cladding layer 109 remains in a layered state.

  That is, first, the etching rate immediately below the stripe-shaped opening 115 and the etching rate in the monitor region 118 are measured. In the case of the configuration and dry etching conditions of this embodiment, the etching rate immediately below the stripe-shaped opening 115 was 90% of the etching rate of the monitor region 118 (etching monitor opening 117).

  As described above, the etching marker layer 108 (layer thickness: 13 nm) is formed between the first upper cladding layer 107 (layer thickness: 240 nm) and the second upper cladding layer 109 (layer thickness: 1.2 μm). In other words, it is set at a position corresponding to about 20% from the bottom with respect to the total thickness of the upper cladding layers 107 and 108.

  Then, the dry etching is stopped at a predetermined timing according to the progress of the dry etching with respect to the etching marker layer 108, and a stripe shape having a pattern corresponding to the shape of the opening 115 is provided immediately below each stripe opening 115. A recess 128 is formed. As a result, the etching marker layer 108 disappears in the monitor region 118, while a portion 109 b of the second upper cladding layer 109 remains in a layered state immediately below each stripe-shaped opening 115. it can.

  In the present embodiment, dry etching is stopped at the timing when the etching marker layer 108 disappears in the monitor region 118 and the first upper cladding layer 107 is further etched by 100 nm. At that time, the etching stopped at 71.8 nm above the etching marker layer 108 just below the stripe-shaped opening 115.

  Thereafter, a part of the surface side of the second upper cladding layer 109 is wet-etched using buffered HF (hydrofluoric acid), thereby removing the reaction product and the damaged layer by dry etching.

  As a result, in the monitor region 118, etching proceeds to the middle of the first upper cladding layer 107 beyond the etching marker layer 108, while a stripe-shaped recess 128 is formed immediately below each stripe-shaped opening 115. Is done. The ridge 120 between the pair of stripe openings 115 and 115 and the ridge terrace 121 outside the pair of stripe openings 115 and 115 constitute a waveguide. The thickness of the second upper cladding lower layer 109b remaining immediately below each stripe-shaped recess 128 is 0.05 μm.

Subsequently, as shown in FIG. 5, a SiO ₂ film having a thickness of 150 nm is formed thereon using plasma CVD, and the SiO ₂ film is formed on the contact layer 111 on the ridge portion 120 by photolithography and etching. The insulating film 112 is processed so as to be exposed. Further, a metal thin film is deposited in this order on Ti, Pt, and Au to form a p-side electrode 113 that is in ohmic contact with the upper surface of the contact layer 111.

After the formation of the p-side electrode 113, as shown in FIG. 1, the substrate 101 is ground from the back surface side to a desired thickness (here, about 110 μm) by a lapping method. Then, by using resistance heating vapor deposition from the back side, AuGe alloy (alloy of Au 88% and Ge 12%), Ni, and Au are stacked as an n-side electrode material, and heated at 390 ° C. for 1 minute in an N ₂ atmosphere. Then, the n-side electrode material is alloyed. In this way, the n-side electrode 114 is formed on the back surface of the substrate 101.

  The wafer obtained through the above steps is divided into a plurality of bars having a desired resonator length (here, 1500 μm), and then end coating is performed on the bars, and the bars are further formed into chips (1500 μm × 200 μm). To divide. After the divided chip is mounted on the submount, the submount is die-bonded to the stem, and wire bonding is further performed to complete the semiconductor laser device.

  Thus, in this method of manufacturing a semiconductor laser device, dry etching is stopped at a predetermined timing according to the progress of dry etching on the etching marker layer 108. Therefore, the etching time to be controlled is shorter than when the etching amount is controlled by the elapsed time from the start of etching of the contact layer 111. As a result, the accuracy of the thickness of the remaining second cladding lower layer 109b is greatly improved. As a result, in the manufactured semiconductor laser device, the generation of kinks can be sufficiently suppressed, and a high output operation is possible.

  Furthermore, according to the manufacturing method of the semiconductor laser device of this embodiment, the etching marker layer 108 disappears in the monitor region 118, but the dry etching cannot reach the etching marker layer 108 immediately below the stripe-shaped opening 115. Accordingly, the cross section of the etching marker layer 108 is not exposed on the side surface of the ridge portion 120. As a result, even if the reaction product and the damage layer removal step are performed after the dry etching step, the side etching or etching of the etching marker layer portion due to the difference in material between the etching marker layer and the cladding layer as shown in FIG. The problem of the bulging is basically eliminated, and the verticality of the side surface of the ridge portion 120 can be maintained.

  Here, as the timing for stopping the dry etching, the etching marker layer 108 disappears in the monitor region 118, but the second upper cladding layer is formed on the etching marker layer 108 immediately below the stripe-shaped opening 115. The timing is set such that a part 109b of 109 remains in a layered state. More specifically, the thickness of the second upper clad lower layer 109b after dry etching is determined by removing the thickness of the second upper clad lower layer 109b to be finally formed, reaction products and damage after dry etching by wet etching. It may be set in consideration of the reduced thickness of the second upper clad lower layer 109b.

As a result, the verticality of the side surface of the ridge 120 and the controllability of the etching depth can be achieved at a high level, and the generation level of the kink is improved as compared with the conventional semiconductor laser element. Semiconductor laser elements can be manufactured. Further, since the verticality of the side surface of the ridge portion 120 is improved, the ridge portion 120 can be satisfactorily covered with the SiO ₂ insulating film 112, and disconnection of the insulating film 112 and the electrode 113 formed thereon can be suppressed. It was like that.

  In the present embodiment, the monitor area 118 (etching monitor opening 117) is a square of 2 mm × 2 mm, but of course, the present invention is not limited to this, and a rectangle, a polygon, a circle, or the like is arbitrarily selected. It is possible. However, in view of the fact that the semiconductor laser element has a striped ridge waveguide, by forming an elongated rectangle parallel to the stripe-shaped opening 115, the most useless area that cannot be formed on the wafer is the most. Can be reduced.

  In addition, light to be irradiated for observing the progress of etching is actually collected by using an optical system such as a lens so that a spot having a diameter of about several tens to several hundreds of μm is formed on the sample to be etched. If there is no flat opening that is at least as large as the spot diameter, the observed interference waveform will be disturbed (noise will be added).

  As shown in this embodiment, when AlGaInP is used as the material of the upper cladding layers 107 and 109, GaInP is appropriate as the material of the etching marker layer 108. By using GaInP for AlGaInP, the difference in refractive index between these material layers can be increased. As a result, the progress of dry etching on the etching marker layer 108 can be easily observed by the interference waveform of the reflected light VL ′.

  For the combination of the upper cladding layers 107 and 109 and the etching marker layer 108 described above, the wavelength of the light VL applied to the monitor region 118 is preferably 400 nm or more and 650 nm or less.

  The light VL applied to the monitor region 118 may be monochromatic light having a specific wavelength as described above, or may be so-called white light having a broad wavelength spectrum. In the case of irradiating white light, the progress of the dry etching can be easily observed by observing the interference waveform after spectrally converting the reflected light into any single color light of 400 nm or more and 650 nm or less. Can do. By doing so, not only a light source that emits only a specific wavelength (for example, a laser or an LED), but also a so-called incandescent lamp such as a halogen lamp or a mercury lamp that is a light source that emits light containing various wavelength components, or a fluorescent lamp Can also be used as an irradiation light source.

  Here, for a reflected light having a wavelength of 650 nm or less, a clear interference waveform for observing the boundary between the etching marker layer 108 and the first upper cladding layer 107 is observed by observing the interference waveform. Will be able to. In addition, by using reflected light having a wavelength of 400 nm or more, the influence of dirt on the window portion of the dry etching apparatus for observing the etching state (attachment is generated inside the window by performing dry etching). The etching state can be observed without receiving. When the etching state is observed using reflected light having a wavelength of less than 400 nm, if the window portion becomes dirty, the detected signal intensity is immediately reduced, which is not preferable.

  The etching marker layer 108 is preferably formed at a distance of 0.2 μm or more and 0.4 μm or less from the active layer 106.

  By forming the etching marker layer 108 at this distance, when the waveguide 130 having an appropriate refractive index difference Δn as a red semiconductor laser element is formed, the etching marker layer 108 disappears in the monitor region 118. A state in which a part 109b of the second upper cladding layer 109 remains in a layer form on the etching marker layer 108 can be easily realized immediately below the stripe-shaped opening 115. Therefore, the etching marker layer 108 is not exposed on the side surface of the ridge portion 120, and the verticality of the side surface of the ridge portion 120 is improved.

  In the present invention, the microloading effect is used to provide the above-described difference in etching rate between the etching monitor opening 117 and the stripe-shaped opening 115 where the ridge waveguide is formed. This microloading effect becomes more prominent as the size of the region to be etched differs. However, if the width of the etching monitor opening 117 is 1 mm or more and the width of the stripe-shaped opening 115 is 20 μm or less. A sufficient etching rate difference can be produced between the openings. In this embodiment, the width of the etching monitor opening is 2 mm, and the width of the ridge waveguide forming stripe-shaped opening is 10 μm.

  The effect can also be increased by increasing the gas pressure during dry etching. That is, in order to change the difference in the etching rate (etching rate), the ratio of the width of the etching monitor opening 117 and the width of the stripe-shaped opening 115 may be changed, or the gas pressure condition may be changed.

  In addition to using the microloading effect, the etching marker layer 108 disappears in the monitor region 118 by using a technique such as etching away a certain amount of the semiconductor layer in the monitor region 118 first. On the other hand, a state in which a part 109b of the second upper cladding layer 109 remains in a layer form on the etching marker layer 108 can be realized immediately below each stripe-shaped opening 115.

[Second Embodiment]
FIG. 6 shows the structure of a semiconductor laser device manufactured by a modification of the above manufacturing method.

  This semiconductor laser device is different from the semiconductor laser device of FIG. 1 in that there is no second upper clad lower layer 109b, and the insulating film 112 is in contact with the etching marker layer 108 at the bottom of each stripe-shaped recess 128. Is different.

  When manufacturing this semiconductor laser device, after the dry etching is stopped, the etching is performed immediately below each stripe-shaped opening 115 by a wet etching method, which also serves to remove reaction products and damage by the dry etching. Etching is selectively performed until the second upper cladding layer 109 on the marker layer 108 disappears.

  As described above, since the etching accuracy is improved in the dry etching process, the dry etching can be advanced and stopped immediately below the stripe-shaped opening 115 to the immediate vicinity of the etching marker layer 108. Therefore, in the manufacturing method of this modified example, the wet etching time until the second upper cladding layer 109 on the etching marker layer 108 disappears immediately below the stripe-shaped opening 115 can be shortened. Therefore, the time for which the side surface of the ridge portion 120 is etched in the lateral direction is shortened, and the deviation from the perpendicularity of the side surface of the ridge portion 120 that occurs due to the plane orientation of the semiconductor material can be suppressed. It becomes possible.

  Therefore, the control of the etching depth can be increased to the level of the growth accuracy of the semiconductor layer by epitaxial growth, while the influence of isotropic etching which is a weak point of wet etching can be largely eliminated.

  As a result, even if this modification is used, the manufactured semiconductor laser element can sufficiently suppress the occurrence of kinks and can perform a high output operation.

[Third embodiment]
FIG. 7 shows an example of the structure of the optical disc apparatus 200 according to the present invention. The optical disc apparatus 200 is used for writing data on the optical disc 201 and reproducing the written data.

  The optical disc apparatus 200 includes a semiconductor laser element 202 that oscillates in a wavelength band of 650 nm shown in FIG. 1, a collimator lens 203, a beam splitter 204, a λ / 4 polarizing plate 205, an objective lens 206 for laser light irradiation, A light receiving element objective lens 207, a signal detecting light receiving element 208, and a signal light reproducing circuit 209 are provided.

  In this optical disc apparatus, at the time of writing, the signal light L emitted from the semiconductor laser element 202 is converted into parallel light by the collimator lens 203, transmitted through the beam splitter 204, and the polarization state is adjusted by the λ / 4 polarizing plate 205. Thereafter, the light is condensed by the objective lens 206 and irradiated onto the optical disc 201. At the time of reading, the optical disc 201 is irradiated with a laser beam not carrying a data signal along the same path as at the time of writing. This laser beam is reflected on the surface of the optical disc 201 on which data is recorded, passes through the laser beam irradiation objective lens 206, the λ / 4 polarizing plate 205, and then is reflected by the beam splitter 204 to change the angle by 90 °. The light is condensed by the light receiving element objective lens 207 and is incident on the signal detecting light receiving element 208. The recorded data signal is converted into an electric signal by the intensity of the laser beam incident in the signal detection light-receiving element 208, and is reproduced by the signal light reproducing circuit 209 to the original signal.

  In the optical disk device of the second embodiment, since the semiconductor laser element 202 that can suppress the generation of kinks up to a higher output is used, higher-speed writing is possible as compared with the conventional optical disk device.

  Here, an example in which the semiconductor laser element 202 that oscillates at a wavelength of 650 nm is applied to a recording / reproducing optical disc apparatus has been described. However, another wavelength band (for example, a 780 nm band) manufactured by applying the manufacturing method of the first embodiment. Needless to say, the present invention can also be applied to an optical disc apparatus provided with the semiconductor laser element (1).

It is a figure which shows the cross-section of the semiconductor laser element produced by the manufacturing method of one Embodiment of this invention. FIG. 4 is a process diagram for explaining the manufacturing method of the semiconductor laser element of FIG. 1 and shows a state after crystal growth. FIG. 2 is a process diagram for explaining a method of manufacturing the semiconductor laser device of FIG. 1 and shows a state in which a resist mask for dry etching is formed. FIG. 8 is a process diagram for describing the manufacturing method of the semiconductor laser element of FIG. 1 and shows a state after the dry etching process. FIG. 8 is a process diagram for describing the manufacturing method of the semiconductor laser element of FIG. 1, and shows a state after the p-side electrode formation process. It is a figure which shows the cross-section of the semiconductor laser element produced by the modification of the said manufacturing method. It is a figure which shows the structure of the optical disk apparatus provided with the semiconductor laser element of FIG. It is a figure explaining the problem of the conventional method which performed dry etching using the end point detection layer, and formed the ridge part.

Explanation of symbols

101 n-GaAs substrate 105 multiple strain quantum well active layer 107 p-AlGaInP first upper cladding layer 108 GaInP etching marker layer 109 p-AlGaInP second upper cladding layer 109a second upper cladding upper layer 109b second upper cladding lower layer 111 p ⁺ -GaAs contact layer 112 insulating layer 113 p-side electrode 114 n-side electrode 115 striped opening 116 resist mask 117 etching monitor opening 118 monitor region 120 ridge portion 121 ridge terrace portion

Claims (10)

In a manufacturing method of a semiconductor laser device for forming a waveguide including a striped ridge portion on a semiconductor substrate,
An active layer, a first upper cladding layer, an etching marker layer having a composition different from that of the first upper cladding layer, and a second upper cladding layer having a composition different from that of the etching marker layer are provided on the semiconductor substrate. A step of laminating a semiconductor layer including in order;
Forming a mask on the surface of the semiconductor layer, the mask having a pair of stripe-shaped openings along both sides of a region where the ridge portion is to be formed in the surface of the semiconductor layer, and An etching monitor opening having a size larger than the width of the stripe-shaped opening in a region different from a region where the semiconductor laser element is to be formed;
Dry etching of the semiconductor layer is performed using the mask while observing the progress of the dry etching through the etching monitor opening, and the dry etching is performed at a predetermined timing according to the progress of the dry etching with respect to the etching marker layer. A method of manufacturing a semiconductor laser device, comprising: a step of stopping etching and forming the ridge portion by forming a recess directly below each of the stripe-shaped openings. In the manufacturing method of the semiconductor laser device according to claim 1,
Prior to the dry etching, including a step of measuring a dry etching rate directly under the etching monitor opening and a dry etching rate directly under the stripe opening,
Based on the difference between the two dry etching rates, as the timing for stopping the dry etching, the etching marker layer disappears immediately below the etching monitor opening, whereas immediately below each stripe opening. A method of manufacturing a semiconductor laser device, comprising setting a timing such that a part of the second upper cladding layer remains in a layered state on the etching marker layer. In the manufacturing method of the semiconductor laser device according to claim 1,
A method of manufacturing a semiconductor laser device, wherein a width dimension of one of the stripe openings is 20 μm or less, and a width dimension of the etching monitor opening is 1 mm or more. In the manufacturing method of the semiconductor laser device according to claim 1,
In the method of observing the progress of the dry etching through the etching monitor opening, the semiconductor layer is irradiated with light from the outside through the etching monitor opening and reflected by the respective layers included in the semiconductor layer. A method of manufacturing a semiconductor laser device, which is a method of observing an interference waveform of reflected light. In the manufacturing method of the semiconductor laser device according to claim 4,
The first upper cladding layer and the second upper cladding layer are each made of AlGaInP,
A method of manufacturing a semiconductor laser device, wherein the etching marker layer is made of GaInP. In the manufacturing method of the semiconductor laser device according to claim 5,
A method of manufacturing a semiconductor laser device, wherein a wavelength of light for observing the interference waveform is 400 nm or more and 650 nm or less. In the manufacturing method of the semiconductor laser device according to claim 1,
The semiconductor substrate is made of GaAs,
A lower clad layer made of AlGaInP is provided under the active layer,
The active layer is a quantum well layer formed by alternately laminating AlGaInP and GaInP,
The first upper cladding layer and the second upper cladding layer are each made of AlGaInP,
A method of manufacturing a semiconductor laser device, wherein a distance in a layer thickness direction between the etching marker layer and the active layer is 0.2 μm or more and 0.4 μm or less. In the manufacturing method of the semiconductor laser device according to claim 1,
After the dry etching is stopped, using a wet etching method, etching is selectively performed until the second upper cladding layer on the etching marker layer disappears immediately below the stripe-shaped opening. A method for manufacturing a semiconductor laser device. The lower cladding layer, the active layer, the first upper cladding layer, the etching marker layer having a different composition from the first upper cladding layer, and the etching marker layer having a different composition from each other are sequentially stacked on the semiconductor substrate. A semiconductor layer including at least a second upper cladding layer and a contact layer for ohmic contact with the electrode;
A pair of stripe-shaped recesses are formed on the surface of the semiconductor layer at a depth from the surface to the middle of the second upper cladding layer, and the semiconductor substrate includes the semiconductor layer between the pair of stripe-shaped recesses. A semiconductor laser characterized in that a waveguide is constituted by a ridge portion having a side surface substantially perpendicular to the surface of the semiconductor substrate and a ridge terrace portion formed of the semiconductor layer outside the pair of stripe-shaped recesses. element. An optical disc apparatus comprising the semiconductor laser element according to claim 9 as a light source.

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