JP2010098094A - Nitride based semiconductor laser element, and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a nitride based semiconductor laser element, capable of stably suppressing micro-trenches formed when forming a ridge portion. <P>SOLUTION: In this method of manufacturing the nitride based semiconductor laser element, after laminating nitride based semiconductor layers 2-10 on a n-type GaN substrate 1, a projecting ridge portion 11 is formed by dry etching using an ICP etching device. At this time, a mixed gas composed of chlorine gas, argon gas and nitrogen gas is used for an etching gas. This mixed gas is made so that the flow rate of the chlorine gas is not less than 60% and not more than 80%, the flow rate of the argon gas is not less than 5% and not more than 20%, and the flow rate of the nitrogen gas is not less than 5% and not more than 20%, to the flow rate of the total etching gas. In addition, a self-bias voltage impressed on the n-type GaN substrate 1 (a sample to be etched 200) when forming the ridge portion 11 is set so as to become not less than 500 V. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a nitride-based semiconductor laser device and a method for manufacturing the same.

  Nitride-based semiconductors, especially gallium nitride (GaN), have a larger band gap than gallium arsenide-based compound semiconductors, so they are used in blue-violet laser diodes as light sources for high-density optical disks, and even white. The application fields such as light sources, projector light sources, full-color displays, and medical fields are diverse, and the market is expected to expand further in the future.

  However, in the manufacture of electronic devices using nitride semiconductors, etching is difficult because the crystals are chemically very stable. On the other hand, the etching method using wet etching is similar to that of gallium arsenide compound semiconductors. However, it has not been studied enough to be applicable to mass production.

  Under such circumstances, dry etching has become the mainstream in the etching of nitride-based semiconductors.

  In a nitride semiconductor laser device using a nitride semiconductor, after a nitride semiconductor layer is stacked on a substrate, the current path injected into the device is narrowed to increase luminous efficiency and oscillation threshold current. In general, a ridge portion having a convex cross section is provided above the laminated nitride semiconductor layer (laminated structure). This ridge portion is usually processed by dry etching.

However, in the conventional dry etching method, as shown in FIG. 18, when the ridge portion 711 is formed by dry etching, the corner portion 750 of the ridge portion 711 is easily selectively etched as compared with other regions. Then, a notched groove portion (micro-trench) 760 is formed at the corner portion 750 of the ridge portion 711 (the bottom portion of the ridge portion 711) with the etching tip cut into the inside. When the size (depth) d _MT micro trench 760 to be formed is large, a disadvantage that the homogeneity of the etching depth is reduced occurs. This makes it difficult to perform the lateral mode control reliably. Further, since the in-plane uniformity of the etching depth is lowered, the accuracy of the shape of the ridge portion 711 and the etching processing depth is lowered. Therefore, the far radiation pattern (FFP (Far Field Pattern)) of the output light is characteristic. Or the Kink (nonlinearity in the optical output-operating current characteristics of the semiconductor laser element) level is reduced. This causes a problem that the device characteristics are deteriorated.

  Therefore, conventionally, a dry etching method capable of improving the in-plane uniformity of the etching depth in dry etching of a nitride-based semiconductor has been proposed (see, for example, Patent Document 1).

  In the above-mentioned patent document 1, by performing etching in a state in which the sample to be etched is held (heated) at a predetermined temperature, the micro-trench is suppressed, thereby improving the in-plane uniformity. An etching method is disclosed. In this dry etching method, a dry etching apparatus is used in which heating means for heating the sample to be etched is provided in a chamber in which the sample to be etched is disposed.

JP 2003-257939 A

  However, when it is attempted to control the temperature of the sample to be etched in the chamber, it is expected that the temperature of the sample to be etched easily changes depending on the usage status, atmosphere, and usage history of the chamber. There is an inconvenience that it becomes difficult to uniformly control the. For this reason, the conventional dry etching method described in Patent Document 1 has a problem that it is difficult to suppress the micro-trench stably and stably regardless of the usage condition of the chamber.

  The present invention has been made to solve the above-described problems, and one object of the present invention is to provide a nitride-based semiconductor laser device in which deterioration of device characteristics is suppressed and a method for manufacturing the same. It is.

  Another object of the present invention is to provide a method for manufacturing a nitride-based semiconductor laser device capable of stably suppressing a micro-trench generated when a ridge portion is formed.

  In order to achieve the above object, as a result of intensive studies by the inventor of the present application, in the dry etching using nitride-based semiconductor plasma, the composition of the etching gas is changed to maintain (heat) the sample to be etched at a predetermined temperature. It has been found that the effect of suppressing the micro-trench formed at the skirt portion of the ridge portion can be obtained even without this.

  That is, the method for manufacturing a nitride semiconductor laser device according to the first aspect of the present invention includes a stacking step of stacking a nitride semiconductor layer on a substrate, and dry etching using plasma on the nitride semiconductor layer. Thus, a ridge forming step of forming a convex ridge portion in a predetermined region of the nitride-based semiconductor layer is provided. In the ridge formation step, an etching gas composed of a mixed gas containing chlorine, argon and nitrogen is used during dry etching of the nitride-based semiconductor layer.

  In the nitride semiconductor laser device manufacturing method according to the first aspect, as described above, when dry etching using plasma is performed on the nitride semiconductor layer, a mixture containing chlorine, argon, and nitrogen as an etching gas is used. By using gas, it is possible to suppress the micro-trench formed at the skirt portion of the ridge portion. For this reason, since the fall of the in-plane uniformity of the etching depth at the time of formation of a ridge part can be suppressed, the fall of element characteristics can be suppressed.

  In the method for manufacturing a nitride-based semiconductor laser device according to the first aspect, it is not necessary to hold (heat) the sample to be etched (the substrate on which the nitride-based semiconductor layer is laminated) at a predetermined temperature. It is possible to more stably suppress the micro-trench generated during the formation of.

  In the method for manufacturing a nitride-based semiconductor laser device according to the first aspect, preferably, the mixed gas is configured by mixing chlorine gas, argon gas, and nitrogen gas, and chlorine gas with respect to the total etching gas flow rate. The flow rate ratio is 60% to 80%, the flow rate ratio of argon gas is 5% to 20%, and the flow rate ratio of nitrogen gas is 5% to 20%. With this configuration, it is possible to easily suppress the micro-trench generated when the ridge portion is formed.

  In the nitride semiconductor laser device manufacturing method according to the first aspect, the ridge forming step can use an etching apparatus capable of controlling the self-bias voltage applied to the substrate on which the nitride semiconductor layer is formed.

  In this case, the etching apparatus used for the ridge formation step is preferably an inductively coupled plasma apparatus.

  In the case of using the etching apparatus capable of controlling the self-bias voltage, the ridge formation step preferably includes a step of dry etching a predetermined region of the nitride-based semiconductor layer while applying a self-bias voltage of 500 V or more to the substrate. . If comprised in this way, the micro trench produced at the time of formation of a ridge part can be suppressed more easily.

  In the method for manufacturing a nitride-based semiconductor laser device according to the first aspect, preferably, the ridge forming step is performed under a pressure of 0.16 Pa (1.2 mTorr) or more and 0.20 Pa (1.5 mTorr) or less. Including a step of dry etching a predetermined region of the semiconductor layer. If comprised in this way, the micro trench produced at the time of formation of a ridge part can be suppressed further easily.

  In the method for manufacturing a nitride-based semiconductor laser device according to the first aspect described above, the stacking step includes forming a nitride-based semiconductor layer to be stacked on the substrate with at least one of group III elements Ga, In, Al, and B, It is preferable to include a step of forming a compound with N which is a group V element.

  A nitride semiconductor laser element according to a second aspect of the present invention is a nitride semiconductor laser element manufactured by using the method for manufacturing a nitride semiconductor laser element according to the first aspect. With this configuration, it is possible to easily obtain a nitride-based semiconductor laser device in which deterioration of device characteristics is suppressed.

  A nitride semiconductor laser element according to a third aspect of the present invention is formed on at least one of a plurality of nitride semiconductor layers including a light emitting layer and a plurality of nitride semiconductor layers formed on a substrate, And a convex ridge portion extending in a predetermined direction. The convex ridge portion is formed by dry etching using plasma using an etching gas composed of a mixed gas containing chlorine, argon and nitrogen.

  In the nitride-based semiconductor laser device according to the third aspect, as described above, the convex ridge portion is formed by dry etching using plasma using an etching gas composed of a mixed gas containing chlorine, argon, and nitrogen. Therefore, the micro-trench generated in the skirt portion of the ridge portion can be effectively suppressed, so that the in-plane uniformity of the etching depth can be improved. As a result, lateral mode control can be performed reliably, and a decrease in FFP characteristics and a decrease in the Kink level can be suppressed. Therefore, it is possible to obtain a nitride-based semiconductor laser device in which deterioration of device characteristics is suppressed.

  In the nitride-based semiconductor laser device according to the third aspect, preferably, the ridge portion has a chlorine gas of 60% by volume to 80% by volume, an argon gas of 5% by volume to 20% by volume, and 5% by volume. It is formed by dry etching with plasma using a mixed gas composed of nitrogen gas of 20 volume% or less. With this configuration, a nitride semiconductor laser element in which micro-trench generated in the skirt portion of the ridge portion is more effectively suppressed can be obtained.

  In the nitride semiconductor laser element according to the third aspect, preferably, the nitride semiconductor layer is a compound of at least one of group III elements Ga, In, Al, and B and group V element N. The convex ridge portion is in the range of 0.16 Pa (1.2 mTorr) to 0.20 Pa (1.5 mTorr) while applying a self-bias voltage of 500 V or more to the substrate using an inductively coupled plasma apparatus. It is formed by dry etching a part of the nitride-based semiconductor layer under pressure. With this configuration, a nitride semiconductor laser element in which micro-trench generated at the skirt portion of the ridge portion is further effectively suppressed can be obtained.

  As described above, according to the present invention, it is possible to easily obtain a nitride-based semiconductor laser device in which deterioration of device characteristics is suppressed and a manufacturing method thereof.

  Further, according to the present invention, it is possible to easily obtain a method for manufacturing a nitride-based semiconductor laser device capable of stably suppressing the microtrench generated when the ridge portion is formed.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments embodying the present invention will be described in detail with reference to the drawings.

  FIG. 1 is an overall perspective view of a nitride-based semiconductor laser device according to an embodiment of the present invention, and FIG. 2 is a plan view of the nitride-based semiconductor laser device according to an embodiment of the present invention. FIG. 3 is a cross-sectional view of a nitride-based semiconductor laser device according to an embodiment of the present invention, and FIG. 4 is a cross-sectional view illustrating a structure of a light emitting layer of the nitride-based semiconductor laser device according to an embodiment of the present invention. It is. In FIG. 1, illustration of an AR (Anti-Reflection) coating layer and an HR (High-Reflection) coating layer is omitted. First, the structure of a nitride-based semiconductor laser device according to an embodiment of the present invention will be described with reference to FIGS.

  As shown in FIGS. 1 and 2, the nitride-based semiconductor laser device according to one embodiment has a pair of resonator end faces 20 formed by cleavage and facing each other. The pair of resonator end faces 20 includes a light emitting end face 20a from which laser light is emitted and a light reflecting end face 20b opposite to the light emitting end face 20a. The nitride-based semiconductor laser device according to one embodiment has a pair of side end faces 30 that are formed by cleavage and are orthogonal to the resonator end face 20.

In the nitride-based semiconductor laser device according to one embodiment, an n-type GaN layer 2 having a thickness of about 1 μm is formed on an n-type GaN substrate 1 as shown in FIGS. An n-type cladding layer 3 made of n-type Al _0.1 Ga _0.9 N having a thickness of about 0.7 μm is formed on the n-type GaN layer 2. An n-type light guide layer 4 made of n-type GaN having a thickness of about 0.05 μm is formed on the n-type cladding layer 3. A light emitting layer 5 is formed on the n-type light guide layer 4.

As shown in FIG. 4, the light emitting layer 5 includes an active layer 5a and a GaN layer 5b having a thickness of about 50 nm formed on the active layer 5a. The active layer 5a includes three quantum well layers 5c made of In _0.08 Ga _0.92 N having a thickness of about 4 nm, and four barrier layers 5d made of In _0.03 Ga _0.97 N having a thickness of about 8 nm or about 20 nm. Has a multiple quantum well (MQW) structure in which are alternately stacked.

Also, as shown in FIGS. 1 and 3, a p-type light guide layer 6 made of p-type GaN having a thickness of about 0.1 μm is formed on the light emitting layer 5. A GaN intermediate layer 7 having a thickness of about 0.07 μm is formed on the p-type light guide layer 6. On the GaN intermediate layer 7, an evaporation preventing layer 8 made of p-type Al _0.3 Ga _0.7 N having a thickness of about 30 nm is formed. A p-type cladding layer 9 made of p-type Al _0.1 Ga _0.9 N having a convex portion and a flat portion other than the convex portion is formed on the evaporation prevention layer 8. The p-type cladding layer 9 has a total thickness of convex portions and flat portions of about 0.5 μm and a flat portion thickness of about 60 nm to about 100 nm.

A p-type contact layer 10 made of p-type Al _0.1 Ga _0.9 N having a thickness of about 0.1 μm is formed on the convex portion of the p-type cladding layer 9. The p-type contact layer 10 and the protrusions of the p-type cladding layer 9 form a striped (elongated) ridge portion 11 having a width of about 1.2 μm to about 1.5 μm. The ridge portion 11 is formed by dry etching using an ICP (Inductive Coupled Plasma) etching apparatus (inductively coupled plasma apparatus), which will be described later, as shown in FIG. 2, in a direction perpendicular to the resonator end face 20 ([1-100 ] Direction). The ridge portion 11 is formed in a mesa shape in cross section. The n-type GaN substrate 1 is an example of the “substrate” in the present invention, and includes an n-type GaN layer 2, an n-type cladding layer 3, an n-type light guide layer 4, a light emitting layer 5, a p-type light guide layer 6, The GaN intermediate layer 7, the evaporation preventing layer 8, the p-type cladding layer 9 and the p-type contact layer 10 are each an example of the “nitride-based semiconductor layer” in the present invention.

  In addition, as shown in FIGS. 1 to 3, a p-side ohmic electrode 12 made of Pd having a predetermined thickness is formed in a stripe shape (elongated shape) on the p-type contact layer 10 constituting the ridge portion 11. ing. As shown in FIGS. 1 and 3, a stepped portion 40 is formed at a corner portion (four corners) between the resonator end surface 20 and the side end surface 30 and avoiding the ridge portion 11. The step portion 40 is formed by etching.

In addition, on both sides of the ridge portion 11, a buried layer 13 for current confinement is formed. Specifically, a buried layer 13 made of a dielectric film such as SiO ₂ or TiO ₂ is formed in a portion excluding the p-side ohmic electrode 12 above the ridge portion 11.

  On the upper surface of the buried layer 13, a p-side pad electrode 14 having a larger planar area than the p-side ohmic electrode 12 is formed so as to cover a part of the p-side ohmic electrode 12. As shown in FIGS. 1 to 3, the p-side pad electrode 14 is in direct contact with the p-side ohmic electrode 12 in a portion covering a part of the p-side ohmic electrode 12. The p-side pad electrode 14 has a multilayer structure in which a Mo layer (not shown) and an Au layer (not shown) are sequentially stacked from the buried layer 13 side.

  As shown in FIGS. 1 and 3, an Hf layer (not shown) and an Al layer (not shown) are formed on the back surface of the n-type GaN substrate 1 in order from the back surface side of the n-type GaN substrate 1. An n-side electrode 15 having a multilayer structure that is sequentially laminated is formed. Further, on the n-side electrode 15, a Mo layer (not shown), a Pt layer (not shown), and an Au layer (not shown) are sequentially laminated from the n-side electrode 15 side. A metallized layer 16 is formed.

Further, as shown in FIG. 2, an AR coating layer 17 having a reflectance of 5% to 35% is formed on the light emitting end face 20a. On the other hand, the HR coating layer 18 having a reflectance of 95% is formed on the light reflecting end face 20b. The reflectance of the AR coating layer 17 is adjusted to a desired value by the oscillation output. The AR coating layer 17 is made of, for example, Al ₂ O _3, and the HR coating layer 18 is made of, for example, a multilayer film of SiO ₂ and TiO ₂ . For example, a dielectric film such as SiN, ZrO ₂ , Ta ₂ O ₅ , or MgF ₂ may be used as a material other than the above.

  FIG. 5 is a schematic view showing an example of an ICP etching apparatus for forming a ridge portion of a nitride-based semiconductor laser device according to an embodiment of the present invention. FIG. 6 is a cross-sectional view of a ridge portion of a nitride-based semiconductor laser device formed by using an ICP etching apparatus according to an embodiment of the present invention. Next, an ICP etching apparatus used for forming the ridge portion 11 of the nitride-based semiconductor laser device according to one embodiment of the present invention will be described with reference to FIGS.

  As shown in FIG. 5, an ICP etching apparatus used for forming the ridge portion 11 of the nitride-based semiconductor laser device according to one embodiment of the present invention includes a chamber 100 having an opening at the top, and an opening of the chamber 100. And a lid 110 connected in an airtight manner. A spiral induction coil 120 for generating plasma is provided around the lid 110. A high frequency power source 122 is connected to the induction coil 120 via a matching box (MB) 121.

  In addition, a sample stage (platen) 130 on which a sample 200 to be etched (n-type GaN substrate 1 on which a nitride semiconductor layer is stacked) is placed is provided at the bottom of the chamber 100. It has been. A high frequency power source 133 for applying a self-bias voltage to the sample to be etched 200 (1) is connected to the sample stage 130 via a coupling capacitor 131 and a matching box (MB) 132. As a result, the self-bias voltage applied to the etched sample 200 (1) is controlled.

  Further, the ICP etching apparatus includes a gas controller 140 that adjusts the flow rate of the etching gas and an exhaust device 150. The pressure in the chamber 100 is set to a predetermined value by the gas controller 140 and the exhaust device 150.

  In the ICP etching apparatus configured as described above, when a high-frequency large current is passed through the induction coil 120 while introducing an etching gas (mixed gas) into the apparatus, a high voltage and a high-frequency variable magnetic field are simultaneously generated. As a result, inductively coupled plasma is generated in the chamber 100. Ions and radicals are generated by this plasma. Then, by applying high frequency power to the sample 200 to be etched, a self-bias potential is generated between the sample 200 to be etched and the plasma, and the generated ions and radicals are accelerated in the direction of the sample 200 to be etched. Collide with 200. At that time, sputtering by ions and reaction between the ions and radicals and the sample to be etched 200 occur at the same time, and etching can be performed with high accuracy suitable for fine processing.

  Here, in this embodiment, a mixed gas of chlorine gas, argon gas and nitrogen gas is used as the etching gas. The mixed gas has a chlorine gas content of 60% by volume to 80% by volume, an argon gas content of 5% by volume to 20% by volume, and a nitrogen gas content of 5% by volume to 20%. % By volume or less.

  In this embodiment, the high frequency output of the high frequency power source 133 is set so that a self-bias voltage of 500 V or more is applied to the sample 200 to be etched in dry etching using an ICP etching apparatus. Furthermore, the gas pressure in the chamber 100 is set to be 0.16 Pa (1.2 mTorr) or more and 0.20 Pa (1.5 mTorr) or less.

Thereby, in the nitride semiconductor laser device according to the embodiment, as shown in FIG. 6, the micro-trench 60 formed in the skirt portion 50 of the ridge portion 11 is suppressed. Specifically, the size of the micro trench 60 formed (depth) d _MT has been kept below an acceptable (less productive on risk) 30 nm to as a normal device. For example, the size of the micro trench 60 (depth) If d _MT is greater than 30 nm, there is a possibility that is larger than the thickness of the flat portions of the p-type cladding layer 9. In this case, there is a risk that the micro trench 60 reaches the evaporation preventing layer 8 below the flat portion of the p-type cladding layer 9 and the in-plane uniformity of the etching depth is significantly reduced. . The size of the micro trench 60 (depth) d _MT is the depth from the upper surface of the flat portion of the p-type cladding layer 9 to the etched tip (distance).

  7 to 16 are views for explaining a method of manufacturing a nitride-based semiconductor laser device according to one embodiment of the present invention. Next, with reference to FIGS. 1, 4 and 6 to 16, a method for manufacturing a nitride-based semiconductor laser device according to an embodiment of the present invention will be described.

First, an n-type GaN substrate 1 is prepared. Next, as shown in FIG. 7, nitride-based semiconductor layers 2 to 10 are stacked on the prepared n-type GaN substrate 1 using a MOCVD (Metal Organic Chemical Vapor Deposition) method. Specifically, an n-type GaN layer 2 having a thickness of about 1 μm, an n-type cladding layer 3 made of n-type Al _0.1 Ga _0.9 N having a thickness of about 0.7 μm, and about 0 on an n-type GaN substrate 1. An n-type light guide layer 4 and a light-emitting layer 5 made of n-type GaN having a thickness of 0.05 μm are sequentially grown. When the light emitting layer 5 is grown, as shown in FIG. 4, three quantum well layers 5c made of In _0.08 Ga _0.92 N having a thickness of about 4 nm and a thickness of about 8 nm or about 20 nm are formed. After the active layer 5a is formed by alternately growing four barrier layers 5d made of In _0.03 Ga _0.97 N, a GaN layer 5b having a thickness of about 50 nm is grown on the active layer 5a. As a result, an active layer 5a having an MQW structure including three quantum well layers 5c and four barrier layers 5d and a light emitting layer 5 including a GaN layer 5b are formed on the n-type light guide layer 4.

As shown in FIG. 7, a p-type light guide layer 6 made of p-type GaN having a thickness of about 0.1 μm, a GaN intermediate layer 7 having a thickness of about 0.07 μm, and about 30 nm on the light emitting layer 5. An evaporation preventing layer 8 made of p-type Al _0.3 Ga _0.7 N having a thickness of p, a p-type cladding layer 9 made of p-type Al _0.1 Ga _0.9 N having a thickness of about 0.5 μm, and a p having a thickness of about 0.1 μm. A p-type contact layer 10 made of type Al _0.1 Ga _0.9 N is successively grown.

  Subsequently, the p-side ohmic electrode 12 made of Pd having a predetermined thickness is formed on the p-type contact layer 10 by using an electron beam evaporation method or the like. Then, the electrodes are alloyed at a high temperature so that ohmic contact between the p-type contact layer 10 and the p-side ohmic electrode 12 is obtained. Thereafter, as shown in FIG. 8, the p-side ohmic electrode 12 is patterned using a photolithography technique and a wet etching technique.

  Next, as shown in FIG. 9, it is a region that avoids the region where the ridge portion 11 is formed, and becomes a cleavage plane in the process of finally cutting the semiconductor laser element into a bar state (a bar dividing process described later). A groove 40a having a predetermined depth is formed in a portion (intersection portion between the planned cleavage line L1 and the planned cleavage line L2) using a photolithography technique and a dry etching technique.

  Next, as shown in FIG. 10, a striped (elongated) resist 70 having a width of about 1.2 μm to about 1.5 μm and extending in the [1-100] direction on the p-side ohmic electrode 12. Form. Using this resist 70 as a mask, unnecessary portions of the p-side ohmic electrode 12 are removed by dry etching such as reactive ion etching. Then, in order to form the ridge portion 11, dry etching is performed to a depth in the middle of the p-type cladding layer 9 using the resist 70 as a mask.

Here, in the present embodiment, the formation of the ridge portion 11 by dry etching is performed by the above-described ICP etching apparatus. At this time, an etching gas used for dry etching is a mixed gas of chlorine gas, argon gas, and nitrogen gas. The mixed gas has a chlorine gas flow ratio of 60% to 80%, an argon gas flow ratio of 5% to 20%, and a nitrogen gas flow ratio of 5% to the total etching gas flow. More than 20%. When the ratio of chlorine gas is so high as to exceed this range, protrusion-like roughness and residues are likely to occur on the surface to be etched (etching surface). On the other hand, when the ratio of chlorine gas is lower than this range, the etching rate is reduced. Further, by mixing argon gas, the occurrence of protrusion-like roughness on the surface to be etched is further suppressed, and by mixing nitrogen gas, the depth (size) d _{MT of the} microtrenches 60 (see FIG. 6). Is suppressed (reduced).

  Further, the self-bias voltage applied to the n-type GaN substrate 1 (the sample to be etched 200) when the ridge portion 11 is formed is set to be 500 V or more. The self-bias voltage is more preferably set to be 600 V or higher, and further preferably set to be 700 V or higher.

  The ridge 11 is formed by dry etching under a pressure of 0.16 Pa (1.2 mTorr) or more and 0.20 Pa (1.5 mTorr) or less. Specifically, the gas pressure in the chamber of the ICP etching apparatus is set to be 0.16 Pa (1.2 mTorr) or more and 0.20 Pa (1.5 mTorr) or less. Thereby, the surface roughness of the etching surface is suppressed, and the perpendicularity of the etching profile can be improved.

  Further, in the dry etching by the ICP etching apparatus, the etching depth is controlled so that the p-type cladding layer 9 having a thickness of about 60 nm to about 100 nm is left on the evaporation prevention layer 8.

  As a result, as shown in FIGS. 10 and 11, a striped (elongated) ridge is formed by the convex portion of the p-type cladding layer 9 and the p-type contact layer 10 and extends in the [1-100] direction. Part 11 is formed. The groove 40a described above is formed in the step portion 40 (see FIG. 1) of the nitride-based semiconductor laser element by cleaving in a later step.

Subsequently, as shown in FIG. 12, the p-side ohmic electrode 12 on the ridge portion 11 is removed by forming a dielectric film such as SiO ₂ or TiO ₂ by using an electron beam evaporation method, a sputtering method, or the like. A buried layer 13 for current confinement is formed in the portion.

  Next, as shown in FIGS. 13 and 14, an Mo layer (not shown) and an Au layer (not shown) are sequentially formed from the substrate (wafer) side by using an electron beam evaporation method, a sputtering method, or the like. Thus, the p-side pad electrode 14 having a multilayer structure is formed on the buried layer 13. The p-side pad electrode 14 is formed in a substantially rectangular shape when seen in a plan view, and a plurality of p-side pad electrodes 14 are formed in a matrix.

  Next, in order to make it easy to divide the substrate (wafer), the back surface of the n-type GaN substrate 1 is ground or polished to reduce the thickness of the n-type GaN substrate 1 to about 100 μm. Then, the surface is adjusted by dry etching or the like on the ground or polished surface.

  Thereafter, as shown in FIG. 15, an Hf layer (not shown) and an Al layer (not shown) are formed on the back surface of the n-type GaN substrate 1 from the back surface side of the n-type GaN substrate 1 using a vacuum deposition method or the like. ) Are sequentially formed to form the n-side electrode 15 having a multilayer structure. Then, a Mo layer (not shown), a Pt layer (not shown) and an Au layer (not shown) are sequentially formed on the n-side electrode 15 from the n-side electrode 15 side, thereby forming a metallized structure having a multilayer structure. Layer 16 is formed. Note that before the n-side electrode 15 is formed, dry etching or wet etching may be performed for the purpose of adjusting electrical characteristics on the n-side.

  Subsequently, as shown in FIG. 16, the substrate (wafer) is separated by cleavage to form the resonator end face 20. The cleavage of the substrate (wafer) is performed along the planned cleavage line L1 shown in FIGS. 9 and 14 by using a scribing / breaking method or a laser scribing method. As a result, the substrate (wafer) is separated at the position of the planned cleavage line L1, and the resonator end face 20 is formed along the direction ([11-20] direction) orthogonal to the direction in which the ridge portion 11 extends. At this time, a smooth resonator end face 20 is obtained by forming the groove 40a.

  Further, due to the separation of the substrate (wafer), the resonator end face 20 to be the light emitting end face 20a of one element (chip) and the resonator end face 20 to be the light reflecting end face 20b of the other adjacent element (chip). And are formed simultaneously. It is cut out into a bar state by the above-described element isolation step (bar dividing step).

Then, a coating is applied to the end face of the bar (resonator end face 20) using a technique such as vapor deposition or sputtering. Specifically, the AR coating layer 17 made of Al ₂ O ₃ is formed on the light emitting end face 20a. Further, the HR coating layer 18 made of a multilayer film of SiO ₂ and TiO ₂ is formed on the light reflecting end face 20b.

  Finally, the bars are separated along the planned cleavage line L2 along the [1-100] direction, so that individual chips (elements) are separated. Thus, the nitride-based semiconductor laser device according to the embodiment of the present invention shown in FIG. 1 is manufactured.

  Next, experiments conducted for confirming the effects of the nitride-based semiconductor laser device according to the present embodiment and the manufacturing method thereof will be described. In this experiment, in order to confirm the effect of the etching gas composition on the micro-trench, the depth (size) of the micro-trench generated at the bottom of the ridge when the ridge is formed by changing the composition of the etching gas evaluated.

  Moreover, the sample which used the mixed gas of chlorine gas, nitrogen gas, and argon gas as etching gas was made into the Example, and the other sample was made into Comparative Examples 1-3. In Comparative Example 1, chlorine gas was used as the etching gas, and in Comparative Example 2, a mixed gas of chlorine gas and argon gas was used as the etching gas. In Comparative Example 3, a mixed gas of chlorine gas and nitrogen pixel was used as an etching gas.

  In the embodiment, the flow rate ratio of chlorine gas to the total etching gas flow rate is 67% (flow rate: 20 ml / min (0 ° C., 1 atm)), and the flow rate ratio of nitrogen gas is 20% (flow rate: 6 ml / min (0 ° C.). 1 atm)), and the flow rate ratio of argon gas was 13% (flow rate: 4 ml / min (0 ° C., 1 atm)).

  On the other hand, in Comparative Example 1, since chlorine gas is used as an etching gas, the flow rate ratio of chlorine gas to the total etching gas flow rate is 100% (flow rate: 20 ml / min (0 ° C., 1 atm)). In Comparative Example 2, the flow rate ratio of chlorine gas to the total etching gas flow rate is 83% (flow rate: 20 ml / min (0 ° C., 1 atm)), and the flow rate ratio of argon gas is 17% (flow rate: 4 ml / min (0 And 1 atm)). In Comparative Example 3, the flow rate ratio of chlorine gas to the total etching gas flow rate is 77% (flow rate: 20 ml / min (0 ° C., 1 atm)), and the flow rate ratio of nitrogen gas is 23% (flow rate: 6 ml / min (0 ° C., 1 atm)).

  The etching depth for forming the ridge portion was 550 nm in both the example and the comparative example. In both the examples and comparative examples, the high frequency output on the coil side was 150 W, and the high frequency output on the sample stage (platen) side was 275 W. Thereby, the self-bias voltage was set to be about 750V.

  Other conditions were the same in the examples and comparative examples. Note that the ICP etching apparatus described above was used as the dry etching apparatus.

The results are shown in Table 1. Incidentally, the trench ratio in Table 1 is expressed in the ratio of trench depth d _MT% for etch depth (550 nm). Further, the trench depth is the depth (distance) from the upper surface of the flat portion of the p-type cladding layer 9 to the etching tip of the micro-trench as shown in FIG.

上記表１に示すように、実施例と比較例１〜３とを比べた結果、マイクロトレンチのトレンチ深さｄ_MTは、実施例の方が比較例１〜３よりも小さくなることが確認された。具体的には、塩素ガスをエッチングガスとして使用した比較例１ではトレンチ深さｄ_MTが２２．６ｎｍであり、塩素ガスとアルゴンガスとの混合ガスをエッチングガスとして使用した比較例２ではトレンチ深さｄ_MTが２１．５ｎｍであり、塩素ガスと窒素ガスとの混合ガスをエッチングガスとして使用した比較例３ではトレンチ深さｄ_MTが１７．１ｎｍであった。これに対し、塩素ガス、窒素ガスおよびアルゴンガスの混合ガスをエッチングガスとして使用した実施例ではトレンチ深さｄ_MTが７．２ｎｍであった。これより、実施例では、比較例に比べてトレンチ深さｄ_MTが６０％〜７０％程度小さくなることが判明した。

As shown in Table 1, the results compared with Comparative Examples 1-3 and Examples, the trench depth d _MT micro trenches, it was confirmed that towards the Example is smaller than Comparative Examples 1 to 3 It was. Specifically, in Comparative Example 1 using chlorine gas as an etching gas, the trench depth d _MT is 22.6 nm, and in Comparative Example 2 using a mixed gas of chlorine gas and argon gas as the etching gas, the trench depth is set. is d _MT is 21.5 nm, a mixed gas of chlorine gas and nitrogen gas in Comparative example 3, the trench depth d _MT was used as the etching gas was 17.1Nm. On the other hand, in an example using a mixed gas of chlorine gas, nitrogen gas and argon gas as an etching gas, the trench depth d _MT was 7.2 nm. From this, in the embodiment, the trench depth d _MT was found to be about 60% to 70% smaller than the comparative example.

  Further, in Comparative Example 1 and Comparative Example 3 in which the etching gas does not contain argon gas, a lot of protrusion-like roughness and residues are generated on the etching surface, whereas in the example and comparative example 2 in which the etching gas contains argon gas. In addition, almost no protruding roughness or residue was observed. From this, it was confirmed that by mixing argon gas at a flow rate ratio of 5% or more and 20% or less, protrusion-like roughness or residue on the etching surface is suppressed.

Further, as a result of comparing the example in which the etching gas contains nitrogen gas and the comparative example 2 in which the etching gas does not contain nitrogen gas, the example in which the nitrogen gas is contained does not contain the nitrogen gas. D _MT is getting smaller. From this, it was confirmed that the micro trench was suppressed by mixing nitrogen gas at a flow rate ratio of 5% or more and 20% or less.

  In addition, when the flow rate ratio of chlorine gas is high enough to exceed 80%, it has been confirmed that protrusion-like roughness and residue are likely to be generated on the surface to be etched (etching surface). On the other hand, when the ratio of chlorine gas was lower than 60%, the etching rate was reduced.

  From the above, it was confirmed that by using a mixed gas of chlorine gas, nitrogen gas and argon gas as the etching gas, the surface roughness is small and the microtrench is suppressed (improved).

Subsequently, in order to confirm the influence of the self-bias voltage on the micro-trench, a sample in which the ridge portion is formed by changing the self-bias voltage is manufactured, and the trench depth d of the micro-trench generated at the skirt portion of the ridge portion is produced. _MT was compared.

  As the etching gas, a mixed gas of chlorine gas, nitrogen gas and argon gas was used as in the above example. Similarly to the above embodiment, the chlorine gas flow rate is 20 ml / min (0 ° C., 1 atm), the nitrogen gas flow rate is 6 ml / min (0 ° C., 1 atm), and the argon gas flow rate is 4 ml / min. It was set to min (0 degreeC, 1 atm).

  An ICP etching apparatus was used as the dry etching apparatus, and the pressure in the chamber during dry etching was set to 0.16 Pa (1.2 mTorr). In addition, the self-bias voltage was changed in the range of about 450 V to about 800 V by setting the high frequency output on the coil side to 150 W and the high frequency output on the sample stage (platen) side to 125 W to 300 W.

FIG. 17 is a graph showing the relationship between the trench depth of the microtrench and the self-bias voltage. The vertical axis of FIG. 17 shows the trench depth d _MT micro trenches occurring in the foot of the ridge portion, the horizontal axis of FIG. 17 shows the value of self-bias voltage during dry etching . From the results shown in FIG. 17, with an increase in the self-bias voltage, it reads tend trench depth d _MT micro trench is reduced. Further, by the self-bias voltage than 500V, it is confirmed can be suppressed in the micro trench trench depth d _MT below production on less risky 30 nm. Note that since microtrench tends to be suppressed as the self-bias voltage increases, the self-bias voltage is more preferably 600 V or more, and even more preferably 700 V or more.

  From the above, it was confirmed that the microtrenches can be suppressed (improved) by setting the self-bias voltage during dry etching to 500 V or higher.

  Note that the chlorine gas contained in the etching gas easily causes surface roughness of the etching surface. When the pressure in the chamber is higher than 0.20 Pa (1.5 mTorr) (the gas pressure increases), the surface roughness becomes significant. . For this reason, it is preferable to set the internal pressure of the ICP etching apparatus to 0.20 Pa (1.5 mTorr) or less. On the other hand, since discharge becomes difficult if the pressure in the chamber is too low, the pressure in the chamber of the ICP etching apparatus is preferably set to be 0.16 Pa (1.2 mTorr) or more.

  In the present embodiment, as described above, when the ridge portion 11 is formed by dry etching using plasma, a mixed gas containing chlorine, argon, and nitrogen is used as an etching gas to form the ridge portion 50 of the ridge portion 11. The micro-trench 60 to be performed can be suppressed. For this reason, since it is possible to suppress a decrease in in-plane uniformity of the etching depth when the ridge portion 11 is formed, the transverse mode control can be reliably performed. In addition, it is possible to suppress a decrease in the FFP characteristic of the output light and to suppress a decrease in the Kink level. Thereby, the deterioration of element characteristics can be suppressed.

  Further, in the configuration of the present embodiment described above, since the micro trench 60 is suppressed, the influence of the micro trench 60 on the total etching amount can be reduced. Thereby, the fall of manufacturing yield can also be suppressed.

  Further, in this embodiment, since it is not necessary to hold (heat) the sample 200 to be etched at a predetermined temperature, the micro-trench 60 generated when the ridge portion 11 is formed can be more stably suppressed.

  In the present embodiment, the mixed gas used as the etching gas has a flow rate ratio of chlorine gas with respect to the total etching gas flow rate of 60% to 80%, a flow rate ratio of argon gas of 5% to 20%, and nitrogen gas. By setting the gas flow rate ratio to 5% or more and 20% or less, it is possible to easily suppress the micro-trench 60 generated when the ridge portion 11 is formed. Further, by configuring the mixed gas in this way, it is possible to easily suppress the occurrence of surface roughness of the etching surface.

  Further, in the present embodiment, by performing dry etching while applying a self-bias voltage of 500 V or more to the sample 200 to be etched, the micro-trench 60 generated when the ridge portion 11 is formed can be more easily suppressed.

  Further, in the present embodiment, the micro-trench generated when the ridge portion 11 is formed more easily by setting the pressure in the chamber 100 to 0.16 Pa (1.2 mTorr) or more and 0.20 Pa (1.5 mTorr) or less. 60 can be suppressed, and the occurrence of surface roughness of the etched surface can be more easily suppressed, so that deterioration of element characteristics can be easily suppressed.

  In the present embodiment, a nitride-based semiconductor laser device in which deterioration of device characteristics is suppressed can be easily obtained by forming a nitride-based semiconductor laser device using the above manufacturing method.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and further includes all modifications within the meaning and scope equivalent to the scope of claims for patent.

  For example, in the above-described embodiment, an example in which an n-type GaN substrate is used is shown. However, the present invention is not limited to this, and a substrate made of InGaN, AlGaN, AlGaInN, or the like, or an insulating substrate such as a sapphire substrate. May be used. In addition, as for each layer of the nitride-based semiconductor layer that is crystal-grown on the substrate, the thickness, composition, and the like can be appropriately combined with or changed to those suitable for desired characteristics. For example, the semiconductor layers may be added or deleted, or the order of the semiconductor layers may be partially changed. Further, the conductivity type may be changed for some semiconductor layers. That is, it can be freely changed as long as the basic characteristics as a nitride semiconductor laser element are obtained.

  In the above embodiment, an example in which dry etching is performed using an ICP etching apparatus has been described. However, the present invention is not limited to this, and any etching apparatus capable of controlling the self-bias voltage applied to a sample to be etched can be used. The present invention can be applied to apparatuses other than the ICP etching apparatus. Examples of apparatuses other than the ICP etching apparatus include an ECR plasma etching apparatus, a parallel plate type dry etching apparatus, a magnetron etching apparatus, and a helicon wave plasma etching apparatus.

  Moreover, although the example which comprised the p side ohmic electrode from Pd was shown in the said embodiment, this invention is not restricted to this, As long as it is a material with a large work function, a p side ohmic electrode is comprised with materials other than Pd. May be. For example, the p-side ohmic electrode may be made of Ni, Pt, Au, or the like.

  Moreover, although the example which formed the resonator end surface by cleavage was shown in the said embodiment, this invention is not limited to this, A resonator end surface (light emission end surface, light reflection end surface) is used using methods other than cleavage. It may be formed. For example, the resonator end face may be formed using a technique such as dry etching.

  Moreover, although the example which formed the ridge part in the cross-sectional mesa shape was shown in the said embodiment, this invention is not limited to this, You may form a ridge part in cross-sectional shapes other than a mesa shape.

  In the above embodiment, the case where the ridge portion is formed to extend in the [1-100] direction and the end face of the resonator is formed in the direction along the [11-20] direction has been described. However, the present invention is not limited thereto, and these directions may be crystallographically equivalent directions. That is, the ridge portion may be formed so as to extend in the direction represented by <1-100>, and the resonator end surface may be formed along the direction represented by <11-20>.

  In the above embodiment, an example is shown in which each nitride-based semiconductor layer is crystal-grown using the MOCVD method. However, the present invention is not limited to this, and each nitride-based semiconductor layer is formed using a method other than the MOCVD method. The crystal may be grown. As a method other than the MOCVD method, for example, the HVPE method (Hydride Vapor Phase Epitaxy), the MBE method (Molecular Beam Epitaxy), and the like are conceivable.

1 is an overall perspective view of a nitride-based semiconductor laser device according to an embodiment of the present invention. 1 is a plan view of a nitride-based semiconductor laser device according to an embodiment of the present invention. 1 is a cross-sectional view of a nitride-based semiconductor laser device according to an embodiment of the present invention. It is sectional drawing which showed the structure of the light emitting layer of the nitride-type semiconductor laser element by one Embodiment of this invention. It is the schematic diagram which showed an example of the ICP etching apparatus for forming the ridge part of the nitride-type semiconductor laser element by one Embodiment of this invention. It is sectional drawing of the ridge part of the nitride type semiconductor laser element by one Embodiment of this invention formed using the ICP etching apparatus. It is sectional drawing for demonstrating the manufacturing method of the nitride type semiconductor laser element by one Embodiment of this invention. It is sectional drawing for demonstrating the manufacturing method of the nitride type semiconductor laser element by one Embodiment of this invention. It is a top view for demonstrating the manufacturing method of the nitride type semiconductor laser element by one Embodiment of this invention. It is sectional drawing for demonstrating the manufacturing method of the nitride type semiconductor laser element by one Embodiment of this invention. It is a perspective view for demonstrating the manufacturing method of the nitride type semiconductor laser element by one Embodiment of this invention. It is sectional drawing for demonstrating the manufacturing method of the nitride type semiconductor laser element by one Embodiment of this invention. It is sectional drawing for demonstrating the manufacturing method of the nitride type semiconductor laser element by one Embodiment of this invention. It is a top view for demonstrating the manufacturing method of the nitride type semiconductor laser element by one Embodiment of this invention. It is sectional drawing for demonstrating the manufacturing method of the nitride type semiconductor laser element by one Embodiment of this invention. It is a top view for demonstrating the manufacturing method of the nitride type semiconductor laser element by one Embodiment of this invention. It is the graph which showed the relationship between the trench depth of a micro trench, and a self-bias voltage. It is sectional drawing which showed an example of the ridge part of the nitride type semiconductor laser element formed by the conventional dry etching.

Explanation of symbols

1 n-type GaN substrate (substrate)
2 n-type GaN layer (nitride semiconductor layer)
3 n-type cladding layer (nitride semiconductor layer)
4 n-type light guide layer (nitride-based semiconductor layer)
5 Light emitting layer (nitride semiconductor layer)
5a Active layer (nitride semiconductor layer)
5b GaN layer (nitride-based semiconductor layer)
6 p-type light guide layer (nitride semiconductor layer)
7 GaN intermediate layer (nitride semiconductor layer)
8 Evaporation prevention layer (nitride semiconductor layer)
9 p-type cladding layer (nitride semiconductor layer)
10 p-type contact layer (nitride semiconductor layer)
11 Ridge part 12 p-side ohmic electrode 13 buried layer 14 p-side pad electrode 15 n-side electrode 16 metallized layer 17 AR coating layer 18 HR coating layer 20 resonator end face 30 side end face 40 step part 50 skirt part 60 microtrench

Claims (11)

A stacking step of stacking a nitride-based semiconductor layer on the substrate;
A ridge forming step of forming a convex ridge portion in a predetermined region of the nitride-based semiconductor layer by performing dry etching with plasma on the nitride-based semiconductor layer;
The method of manufacturing a nitride semiconductor laser device, wherein the ridge forming step uses an etching gas composed of a mixed gas containing chlorine, argon and nitrogen during dry etching of the nitride semiconductor layer The mixed gas is constituted by mixing chlorine gas, argon gas and nitrogen gas,
The flow rate ratio of the chlorine gas to the total etching gas flow rate is 60% to 80%, the flow rate ratio of the argon gas is 5% to 20%, and the flow rate ratio of the nitrogen gas is 5% to 20%. The method for manufacturing a nitride-based semiconductor laser device according to claim 1, wherein: The ridge forming step includes
3. The method according to claim 1, further comprising a step of etching the nitride-based semiconductor layer using an etching apparatus capable of controlling a self-bias voltage applied to the substrate on which the nitride-based semiconductor layer is formed. The manufacturing method of the nitride-type semiconductor laser element of description.   4. The method for manufacturing a nitride semiconductor laser element according to claim 3, wherein the etching apparatus used in the ridge formation step is an inductively coupled plasma apparatus. The ridge forming step includes
5. The nitride-based semiconductor laser device according to claim 3, further comprising a step of dry-etching a predetermined region of the nitride-based semiconductor layer while applying a self-bias voltage of 500 V or more to the substrate. Production method.   The ridge forming step includes a step of dry-etching a predetermined region of the nitride-based semiconductor layer under a pressure of 0.16 Pa or more and 0.20 Pa or less. The method for producing a nitride-based semiconductor laser device according to the item. The laminating step includes
The method includes forming a nitride-based semiconductor layer stacked on the substrate from a compound of at least one of group III elements Ga, In, Al, and B and group V element N. A method for manufacturing a nitride-based semiconductor laser device according to any one of claims 1 to 6.   A nitride-based semiconductor laser device manufactured using the manufacturing method according to claim 1. A plurality of nitride-based semiconductor layers formed on a substrate and including a light-emitting layer;
A convex ridge formed on at least one of the plurality of nitride-based semiconductor layers and extending in a predetermined direction;
The nitride semiconductor laser element, wherein the convex ridge portion is formed by dry etching using plasma using an etching gas comprising a mixed gas containing chlorine, argon and nitrogen.   The ridge portion uses the mixed gas composed of 60% by volume to 80% by volume of chlorine gas, 5% by volume to 20% by volume of argon gas, and 5% by volume to 20% by volume of nitrogen gas. The nitride-based semiconductor laser device according to claim 9, wherein the nitride-based semiconductor laser device is formed by dry etching using plasma. The nitride-based semiconductor layer is composed of a compound of at least one of group III elements Ga, In, Al, and B and group V element N,
The convex ridge portion is formed on the nitride-based semiconductor layer under a pressure of 0.16 Pa or more and 0.20 Pa or less while applying a self-bias voltage of 500 V or more to the substrate using an inductively coupled plasma apparatus. The nitride-based semiconductor laser device according to claim 9, wherein the nitride-based semiconductor laser device is formed by dry etching the portion.

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