JP4890362B2 - Manufacturing method of semiconductor laser device - Google Patents

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.

  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. If the verticality of the side surface of the ridge portion is inhibited in this way, there is a problem that after all, the occurrence of kinks cannot be suppressed. 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).

  Moreover, since the above-mentioned end point detection layer is disposed inside the clad layer, it must be configured as a thin film with little optical influence. For this reason, the detection itself of the end point detection layer is unstable, and in practice, it is difficult to improve the etching control accuracy.

Accordingly, an 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 by improving the controllability of the etching depth and thus sufficiently suppressing the occurrence of kinks.

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,
On the semiconductor substrate, a buffer layer, a first lower cladding layer having a different composition from the buffer layer, an etching stopper layer, a second lower cladding layer having a different composition from the etching stopper layer, an active layer, A laminating step of laminating a semiconductor layer including at least an upper clad layer having a single composition ;
Forming a first photomask having a first etching monitor opening in a monitor region different from a region where the semiconductor laser element is to be formed on the semiconductor substrate;
Performing a wet etching of the semiconductor layer with an etchant using the first photomask, and exposing the etching stop layer in the monitor region ,
The composition of the etching stop layer is set such that the etching rate for the etching stop layer by the etchant is slower than the etching rate for the second lower cladding layer,
After removing the first photomask, the semiconductor layer has a pair of stripe-shaped openings along both sides of the region where the ridge portion is to be formed on the surface of the semiconductor layer, and a second etching monitor opening in the monitor region Forming a second photomask having a portion;
Using the second photomask, dry etching of the semiconductor layer is performed while observing the progress of the dry etching through the second etching monitor opening, and the first lower cladding layer disappears in the monitor region. The dry etching is stopped at a predetermined timing according to the above, and a recess having a depth that stops in the middle of the upper cladding layer is formed immediately below each stripe-shaped opening , so that the above-mentioned of the upper cladding layer A second etching step is included in which the ridge portion is formed by a portion left between the recesses .

Here, “the etching rate for the etching stop layer is slow” includes the case where the etching rate for the etching stop layer is substantially zero (negligible).

The “predetermined timing according to the disappearance of the first lower cladding layer” is set, for example, at the timing when the first lower cladding layer disappears due to the progress of the dry etching, or shifted from the timing by a predetermined time. Refers to the timing.

As each of the photomasks, 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, in the second etching step, the semiconductor layer is dry etched while observing the progress of the dry etching through the second etching monitor opening. By setting the dimensions of the first etching monitor opening and the second etching monitor opening to a dimension sufficient for the observation, the progress of the dry etching can be easily observed. For example, the progress of the dry etching is easily observed by a method of irradiating light to the second etching monitor opening from the outside and observing the interference waveform of the reflected light. Then, the dry etching is stopped at a predetermined timing according to the disappearance of the first lower cladding layer in the monitor region. As a result, a recess having a depth that stops in the middle of the upper cladding layer is formed immediately below each stripe-shaped opening, so that the portion of the upper cladding layer left between the recesses can form the ridge. Forming part. Therefore, in the present invention, the etching amount can be accurately controlled in the depth direction as compared with the method in which the etching amount is controlled by the elapsed time from the start of the dry etching. 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.

Further, in this method of manufacturing a semiconductor laser device, when the etching stop layer is exposed in the first etching step, an etching solution having a slower etching rate for the etching stop layer than the etching rate for the second lower cladding layer. Therefore, the first etching step can be completed in a state where the etching stopper layer is exposed and substantially not etched.

In one embodiment of the method for manufacturing a semiconductor laser device, in the stacking step, the total thickness of the etching stop layer and the first lower cladding layer is set to a height of the ridge portion to be formed. It is set so that it may become substantially the same.

  According to the method for manufacturing a semiconductor laser device of this embodiment, in order to form the ridge portion, the dry etching is performed at the timing when the first lower cladding layer disappears in the second etching step due to the progress of the dry etching. Etching may be stopped. Thereby, the processing accuracy of the ridge portion can be further improved.

  In one embodiment of the method of manufacturing a semiconductor laser device, the method of observing the progress of the dry etching through the second etching monitor opening in the second etching step is the same as that described above through the second etching monitor opening. It is a method of irradiating a semiconductor layer with light and observing an interference waveform of reflected light reflected by the layer on the semiconductor substrate.

  In the method of manufacturing a semiconductor laser device according to this embodiment, in the second etching step, the monitor region is independent of the progress of etching in the stripe-shaped opening narrower than the second etching monitor opening. Only the progress of dry etching is observed. Since the interference waveform of the reflected light reflected by the layer on the semiconductor substrate is observed, the progress of the dry etching can be easily observed through the second 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 one embodiment of the method of manufacturing a semiconductor laser device, the second lower cladding layer is made of AlGaInP, and the etching stop layer is made of GaInP.

  For simplicity, the mixed crystal ratio in the composition of each layer is omitted, but the mixed crystal ratio of the elements described is not zero (the same applies hereinafter).

In the method of manufacturing a semiconductor laser device according to this embodiment, the first etching step can be completed in a state where the etching stop layer is exposed and hardly etched. Therefore, in the second etching step, the time from the start of dry etching of the etching stop layer to the disappearance of the first lower cladding layer becomes constant. As a result, the processing accuracy of the ridge portion can be further improved.

  In one embodiment of the method for manufacturing a semiconductor laser device, the first lower cladding layer is made of AlGaInP, and the buffer layer is made of GaAs.

  In the manufacturing method of the semiconductor laser device of this embodiment, the difference (refractive index difference) between the refractive index of the first lower cladding layer and the refractive index of the buffer layer can be increased. Therefore, in the second etching step, the interference waveform of the reflected light can be more easily observed through the second etching monitor opening, and the progress of the dry etching can be more easily observed.

  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 the embodiment, in the second etching step, the reflected waveform having a wavelength of 650 nm or less is observed in the second etching monitor opening to observe the interference waveform. A clear interference waveform that identifies the boundary between the lower cladding layer and the buffer layer can be observed. Further, since the interference waveform is observed for the reflected light having a wavelength of 400 nm or more in the second etching monitor opening, dirt (dry etching) on the window of the dry etching apparatus for observing the etching state is observed. This makes it possible to observe the etching state without being affected by the occurrence of deposits on the inside of the window.

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

Hereinafter, a method for manufacturing a semiconductor laser device of 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 first lower cladding layer 103, n-Ga _0.51 In _0.49 P etching stop layer 104, n- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P second lower cladding layer 105, (Al _0.545 Ga _0.455 ) _0.5 In _0.5 P lower guide layer 106, multiple strain quantum well active layer 107, (Al _0.545 Ga _{0. 455} ) _0.5 In _0.5 P upper guide layer 108, p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P 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 from the surface of the contact layer 111 to the middle of the 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 upper clad layer 109, a 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 an “upper clad upper layer 109 a” and is below the bottom surface of the striped recess 128. The portion corresponding to is called “upper clad lower layer 109b”. In the present embodiment, the thickness of the upper clad lower layer 109b is 0.303 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 stacked 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 first lower cladding layer 103 (layer thickness: 1.65 μm), n-Ga _0.51 In _0.49 P etching stop layer 104 (layer thickness: 13 nm), n − (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P second lower cladding layer 105 (layer thickness: 1.137 μm), (Al _0.545 Ga _0.455 ) _0.5 In _0.5 P lower guide layer 106 (layer thickness: 35 nm), multiple strain quantum well active layer 107, (Al _0.545 Ga _0.455 ) _0.5 In _0.5 P upper guide layer 108 (layer thickness: 35 nm), p _{- (Al 0.7 Ga 0.3) 0.5} In 0.5 Upper cladding layer 109 _{(thickness: 1.453μm), p-Ga 0.51} In 0.49 P intermediate layer 110 (thickness: ^35nm), p + -GaAs contact layer 111 (thickness: 500 nm) sequentially, Crystal growth is performed by MOCVD (metal organic chemical vapor deposition method), and the layers are stacked.

In this stacking step, the total thickness of the etching stop layer 104 and the first lower cladding layer 103 is substantially equal to the height of the ridge 120 to be formed (optically optimal height). Are set to be the same.

The multi-strain quantum well active layer 107 includes Ga _0.445 In _0.555 P quantum well layers (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. Since the structure of the multi-strain quantum well active layer 107 is not directly related to the essence of the present invention, the detailed cross-sectional structure of the multi-strain quantum well active layer 107 is not shown.

  Next, as shown in FIG. 3, photolithography is performed to form a resist mask 119 as a first photomask 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 (also in FIG. 4 described later). The same.)

  As can be seen from FIG. 3, the resist mask 119 is formed on a monitor region (substantially central portion of the substrate 101) different from the region where the semiconductor laser element is to be formed on the surface of the substrate 101 (including the semiconductor layer). A first etching monitor opening 117 is provided. The dimension of the first etching monitor opening 117 is set to a dimension sufficient for observing the progress of dry etching in the second etching process described later, in this example, 2 mm square.

Next, a wet etching process as a first etching process is performed using this resist mask 119, and n- (Al _0.7 Ga _0.3 ) _0.5 In is formed from the GaAs contact layer 111 shown in FIG. _{The portion up to 0.5} P second lower cladding layer 105 is removed, and the etching stopper layer 104 is exposed in the first etching monitor opening 117.

Specifically, in this wet etching process, the GaAs contact layer 111 is first removed by etching with a mixed aqueous solution of sulfuric acid and hydrogen peroxide. Next, using a mixed aqueous solution of sulfuric acid and saturated bromine water, p-Ga _0.51 In _0.49 P intermediate layer 110 and p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P The middle of the upper cladding layer 109 is removed by etching. Subsequently, using phosphoric acid, the remainder of the p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P upper cladding layer 109 and (Al _0.545 Ga _0.455 ) _0.5 In _{The 0.5} P upper guide layer 108 is removed by etching. Further, using the same mixed aqueous solution of sulfuric acid and saturated bromine water as described above, the multiple strain quantum well active layer 107 and the (Al _0.545 Ga _0.455 ) _0.5 In _0.5 P lower guide layer 106 are used. Then, the n- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P second lower cladding layer 105 is etched and removed halfway. Finally, the remaining n- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P second lower cladding layer 105 is removed by etching using phosphoric acid similar to that described above. As a result, the n-Ga _0.51 In _0.49 P etching stop layer 104 is exposed in the first etching monitor opening 117. Thereafter, the resist mask 119 is removed.

Thus, when exposing the etch stop layer 104 of the lower layer of the second lower cladding layer 105 is etched, the etching rate is slow etching solution to the etch stop layer 104 as compared with the etching rate of the second lower cladding layer 105 Is used. Accordingly, the first etching process can be completed in a state where the etching stopper layer 104 is exposed and substantially not etched.

  Next, as shown in FIG. 4, photolithography is performed to form a resist mask 116 as a second photomask on the surface of the substrate 101 in this state.

  As can be seen from FIG. 4, this 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. In addition, a second etching monitor opening 118 is provided in a monitor region (a region corresponding to the first etching monitor opening 117 in FIG. 3) provided in a substantially central portion of the substrate 101.

  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 second etching monitor opening 118 is provided for observing the progress of dry etching in the next process through the second etching monitor opening 118. The size of the second etching monitor opening 118 is a 2 mm square larger than the width of the stripe-shaped opening 115, similarly to the size of the first etching monitor opening 117, so that the progress of dry etching can be easily observed. Is set to

  Next, as shown in FIG. 5, as a second etching step, dry etching of the semiconductor layer stacked on the substrate 101 using the resist mask 116 is progressed through the second etching monitor opening 118. Observe while observing.

In order to perform this dry etching, an ICP (inductively coupled plasma) dry etching apparatus is used, the etching gas is a mixed gas of Ar and SiCl ₄ , and the gas pressure is 1.6 mTorr.

  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 second etching monitor opening 118. In the semiconductor layer, a region immediately below the second etching monitor opening 118 is referred to as a “monitor region 118M”.

  As a method of observing the progress of dry etching through the second etching monitor opening 118, visible light VL is irradiated to the monitor region 118M from the outside through the second etching monitor opening 118, and the semiconductor in the monitor region 118M is used. A method of observing the interference waveform of the reflected light VL ′ reflected by each layer 104, 103, 102 included in the layer is adopted.

When dry etching progresses and the first lower cladding layer 103 disappears in the monitor region 118M, the above-described interference waveform changes accordingly. As described above, in the stacking step, the total thickness of the etching stopper layer 104 and the first lower cladding layer 103 is set to the height of the ridge 120 to be formed (optically optimal). The height is set to be substantially the same. Corresponding to the setting, in the second etching step, the dry etching is stopped at the same timing when the interference waveform is changed, that is, at the same timing when the first lower cladding layer 103 disappears.

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

  As a result, etching finally proceeds to the surface of the buffer layer 102 in the monitor region 118M, while a stripe-shaped recess 128 is formed immediately below each stripe-shaped opening 115. A waveguide 130 is configured by 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. The thickness of the upper clad lower layer 109b remaining immediately below each stripe-shaped recess 128 is 0.325 μm.

Subsequently, as shown in FIG. 6, 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 face coating is performed on the cleavage surface of the bars, and the bars are further formed into chips (1500 μm × 200 μm). 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, the total thickness of the etching stop layer 104 and the first lower cladding layer 103 is set to the height of the ridge portion 120 to be formed in the stacking step. In response to the setting, the first lower cladding layer 103 disappeared in the monitor region 118M in accordance with the setting. The dry etching is stopped at the same timing. As a result, the ridge 120 is formed by forming the stripe-shaped recess 128 immediately below each stripe-shaped opening 115. Therefore, compared with the method in which the etching amount is controlled by the elapsed time from the start of the dry etching, this manufacturing method can control the etching amount with respect to the depth direction with high accuracy. Therefore, in this manufacturing method, the controllability of the etching depth can be improved while ensuring the perpendicularity of the side surface of the ridge portion 120, and the processing accuracy of the ridge portion 120 can be improved. As a result, in the manufactured semiconductor laser element, the generation of kinks can be sufficiently suppressed, and a high output operation is possible.

Further, in the present embodiment, the reflected light VL ′ caused by the first lower cladding layer 103 and the buffer layer 102 that are thinned in the monitor region 118M immediately before the dry etching is stopped in the second etching step. The interference waveform disappears with the disappearance of the first lower cladding layer 103. Therefore, it is easy to detect the end point of etching. Furthermore, in the present embodiment, the first lower cladding layer 103 is made of n- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P, and the buffer layer 102 is made of GaAs. Therefore, the difference (refractive index difference) between the refractive index of the first lower cladding layer 103 and the refractive index of the buffer layer 102 can be increased. Therefore, in the second etching step, the interference waveform of the reflected light VL ′ can be more easily observed through the second etching monitor opening 118, and the progress of the dry etching can be more easily observed. As a result, the processing accuracy of the height of the ridge portion 120 (in other words, the layer thickness of the second cladding layer lower layer 190b) is greatly improved. As a result, in the manufactured semiconductor laser element, generation of kinks can be further suppressed.

In the present embodiment, the semiconductor layers provided for observing the interference waveform of the reflected light VL ′ are substantially only the etching stopper layer 104 and the first lower cladding layer 103, and the etching stopper layer 104 is Since the layer thickness is thin, the first lower cladding layer 103 having almost a single composition occupies it. Therefore, the influence of the variation in the thickness of each semiconductor layer in the stacking step can be reduced, and the variation in the etching amount in the second etching step can be suppressed. As a result, the processing accuracy of the height of the ridge portion 120 is greatly improved. As a result, in the manufactured semiconductor laser element, generation of kinks can be further suppressed.

  Furthermore, according to the manufacturing method of the semiconductor laser device of the present embodiment, other semiconductor layers (cladding layers) having etching characteristics such as a conventional end point detection layer (see FIG. 8) are formed in the semiconductor layer constituting the ridge portion 120. Layer) is not included. Therefore, after processing by the above dry etching, when the reaction product and damage at the time of dry etching are removed using a chemical etchant, the etching characteristics of the end point detection layer impair the verticality of the side surface of the ridge portion 120. Does not occur fundamentally. Therefore, it becomes possible to maintain the verticality of the side surface of the ridge portion 120.

In the above description, the total thickness of the etching stop layer 104 and the first lower cladding layer 103 is set to be substantially the same as the height of the ridge 120 to be formed. did. More preferably, after processing by the above dry etching, it is set in consideration of a reduction in the thickness of the upper clad lower layer 109b when the reaction product and damage during dry etching are removed using a chemical etchant. That is, the height is set to be the same as the height of the ridge 120 to be finally formed after removing the damage.

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 region 118M (the dimensions of the first and second etching monitor openings 117 and 118) is a square of 2 mm × 2 mm. However, of course, the present invention is not limited to this. It is possible to select arbitrarily such as a polygon and a circle. 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).

  For the combination of the material of the first lower cladding layer 103 and the material of the buffer layer 102 described above, the wavelength of the light VL irradiated to the monitor region 118M is preferably 400 nm or more and 650 nm or less.

  Here, for the reflected light having a wavelength of 650 nm or less, by observing the interference waveform, a clear interference waveform for identifying the boundary between the first lower cladding layer 103 and the buffer layer 102 can be observed. It becomes like this. 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 light VL applied to the monitor region 118M may be monochromatic light having a specific wavelength as described above, or may be so-called white light having a broad wavelength spectrum. When irradiating white light, the reflected light VL ′ is spectrally converted into any single color light of 400 nm or more and 650 nm or less, and then the progress of the dry etching is easily observed by observing the interference waveform. 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.

  In addition, when the dry etching conditions and the like are different from those of the present embodiment, an etching rate may be different due to the microloading effect between the monitor region 118M and the inside of the stripe-shaped opening 115 where the ridge waveguide is formed. This microloading effect is basically a phenomenon in which the etching rate increases as the area to be etched increases, and as the area to be etched decreases, the etching rate varies depending on the size of the area to be etched. It is. When this microloading effect is observed, the difference in etching rate is taken into consideration, and when the first lower cladding layer 103 disappears in the monitor region 118M, the stripe-shaped recess is formed immediately below the stripe-shaped opening 115. The layer thickness of the first lower cladding layer 103 may be adjusted in the stacking step so that the depth of 128 becomes a desired depth and, as a result, the height of the ridge portion 120 becomes a desired height. This layer thickness can be adjusted at a position away from the multi-strain quantum well active layer 107. Therefore, adjustment can be performed without optically affecting the semiconductor laser element to be manufactured. Further, when the microloading effect is positively utilized, if the width of the second etching monitor opening 118 is 1 mm or more and the width of the stripe-like opening 115 is 20 μm or less, each opening Thus, a sufficient difference in etching rate can be generated.

[Second Embodiment]
FIG. 7 shows an example of the structure of an optical disc apparatus 200 provided with the semiconductor laser element of FIG. 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 this optical disc apparatus 200 , since the semiconductor laser element 202 that can suppress the occurrence of kinks to a higher output is used, higher-speed writing is possible as compared with the conventional optical disc apparatus.

  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).

  Note that the present invention is not limited to the illustrated examples described above, and various changes can be made without departing from the spirit of the present invention, such as the oscillation wavelength of the semiconductor laser element and the polarity of the electrodes. It is.

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 wet etching is formed. 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 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.

101 n-GaAs substrate 102 n-GaAs buffer layer 103 n-AlGaInP first lower cladding layer 104 n-GaInP etching stop layer 105 n-AlGaInP second lower cladding layer 107 multiple strain quantum well active layer 109 p-AlGaInP upper cladding layer 111 p ⁺ -GaAs contact layer 112 insulating layer 113 p-side electrode 114 n-side electrode 115 striped opening 116, 119 resist mask 117 first etching monitor opening 118 second etching monitor opening 118M monitor region 120 ridge part 121 Ridge Terrace

Claims (6)

In a manufacturing method of a semiconductor laser device for forming a waveguide including a striped ridge portion on a semiconductor substrate,
On the semiconductor substrate, a buffer layer, a first lower cladding layer having a different composition from the buffer layer, an etching stopper layer, a second lower cladding layer having a different composition from the etching stopper layer, an active layer, A laminating step of laminating a semiconductor layer including at least an upper clad layer having a single composition ;
Forming a first photomask having a first etching monitor opening in a monitor region different from a region where the semiconductor laser element is to be formed on the semiconductor substrate;
Performing a wet etching of the semiconductor layer with an etchant using the first photomask, and exposing the etching stop layer in the monitor region ,
The composition of the etching stop layer is set such that the etching rate for the etching stop layer by the etchant is slower than the etching rate for the second lower cladding layer,
After removing the first photomask, the semiconductor layer has a pair of stripe-shaped openings along both sides of the region where the ridge portion is to be formed on the surface of the semiconductor layer, and a second etching monitor opening in the monitor region Forming a second photomask having a portion;
Using the second photomask, dry etching of the semiconductor layer is performed while observing the progress of the dry etching through the second etching monitor opening, and the first lower cladding layer disappears in the monitor region. The dry etching is stopped at a predetermined timing according to the above, and a recess having a depth that stops in the middle of the upper cladding layer is formed immediately below each stripe-shaped opening , so that the above-mentioned of the upper cladding layer A method of manufacturing a semiconductor laser device, comprising a second etching step of forming the ridge portion by a portion left between the recesses . In the manufacturing method of the semiconductor laser device according to claim 1,
In the laminating step, the total thickness of the etching stopper layer and the first lower cladding layer is set to be substantially the same as the height of the ridge portion to be formed. A method of manufacturing a semiconductor laser device. In the manufacturing method of the semiconductor laser device according to claim 1,
The method of observing the progress of the dry etching through the second etching monitor opening in the second etching step includes irradiating the semiconductor layer with light from the outside through the second etching monitor opening, and A method of manufacturing a semiconductor laser device, comprising: a method of observing an interference waveform of reflected light reflected by an upper layer. In the manufacturing method of the semiconductor laser device according to claim 1,
The method of manufacturing a semiconductor laser device, wherein the second lower cladding layer is made of AlGaInP, and the etching stop layer is made of GaInP. In the manufacturing method of the semiconductor laser device according to claim 1,
A method of manufacturing a semiconductor laser device, wherein the first lower cladding layer is made of AlGaInP and the buffer layer is made of GaAs. In the manufacturing method of the semiconductor laser device according to claim 3 ,
A method of manufacturing a semiconductor laser device, wherein the wavelength of reflected light for observing the interference waveform is 400 nm or more and 650 nm or less.

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