JP2009055002A - Optical semiconductor device and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical semiconductor device capable of suppressing a lowering of reliability and suppressing defects created on a surface of a compound semiconductor layer and method of manufacturing the same. <P>SOLUTION: An optical semiconductor device has a compound semiconductor layer 22 that is provided on a substrate 10 and includes a first conductivity type cladding layer 12, activation layer 14 and a second conductivity type cladding layer 16 that is the opposite of the first conductivity type. The method includes the sequential steps of: forming a diffusion source layer 42 on the compound semiconductor layer; forming a first diffusion region 23 in the compound semiconductor layer by carrying out a first heat treatment so that the first diffusion region 23 includes a light emitting facet 38 for emitting light from the activation layer, removing the diffusion source layer; forming an SiN film 46 having a refractive index of 1.9 or higher on the compound semiconductor layer; and turning the first diffusion region 23 into the second diffusion region 24 by carrying out a second heat treatment. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical semiconductor device and a manufacturing method thereof, and more particularly to an optical semiconductor device having a diffusion region in which impurities are diffused so as to include a light emitting end face and a manufacturing method thereof.

  In recent years, for example, in the fields of optical communication and optical storage medium devices, optical semiconductor devices such as laser diodes (LDs) that emit light have been used. In high-power laser diodes, optical damage called COD (Catastrophic Optical Damage) has become a problem, leading to a decrease in reliability. This COD occurs when the light emitting end face from which the laser light is emitted is an absorption region for the laser light.

  As a method for suppressing COD, there is a method in which the band gap of the active layer at the light emitting end face from which the laser light is emitted is made larger than that of the active layer inside the light emitting end face. By this method, absorption of laser light at the light emitting end face can be suppressed, and COD can be suppressed. As a method of increasing the band gap of the active layer on the light emitting end face, a method of forming a diffusion region in which impurities are diffused is often used.

However, in forming a diffusion region in which impurities are diffused, if the impurity concentration in the diffusion region increases, light absorption by free carriers increases, and the problem of COD reoccurs. Patent Document 1 and Patent Document 2 disclose a method in which a diffusion region formed by diffusing impurities is heat-treated again.
JP-A-5-218593 JP 2006-30211 A

  In optical semiconductor devices, reliability tests such as APC (Auto Power Control) and pulse IL measurement for evaluating light output characteristics cause destruction at the light emission end face due to COD, and a decrease in reliability becomes an issue. Yes.

  Further, as in Patent Document 1 and Patent Document 2, the method of heat treating the diffusion region again has a problem that defects occur on the surface of the compound semiconductor layer such as a clad layer and an active layer formed on the substrate.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical semiconductor device capable of suppressing a decrease in reliability and suppressing defects generated on the surface of a compound semiconductor layer, and a method for manufacturing the same.

  The present invention relates to a method of manufacturing an optical semiconductor device comprising a compound semiconductor layer including a first conductivity type cladding layer, an active layer, and a second conductivity type cladding layer opposite to the first conductivity type on a substrate. Forming a diffusion source layer on the compound semiconductor layer and performing a first heat treatment to form a first diffusion region in the compound semiconductor layer so as to include a light emitting end face that emits light from the active layer A step of removing the diffusion source layer, a step of forming a SiN film having a refractive index of 1.9 or more on the compound semiconductor layer, a second heat treatment, and forming the first diffusion region in the first region. And a step of forming two diffusion regions in order. According to the present invention, the second diffusion region having a low impurity concentration and a uniform impurity concentration distribution from the second conductivity type cladding layer to the active layer can be formed in the compound semiconductor layer including the light emitting end face. For this reason, the fall of the reliability of the optical semiconductor device resulting from COD can be suppressed. In addition, by forming a SiN film having a refractive index of 1.9 or more on the compound semiconductor layer before performing the heat treatment on the first diffusion region, defects generated on the surface of the compound semiconductor layer can be suppressed.

  In the above configuration, the temperature of the second heat treatment may be higher than the temperature of the first heat treatment. According to this configuration, it is possible to form a second diffusion region having a low impurity concentration and a uniform impurity concentration distribution from the second conductivity type cladding layer to the active layer.

  In the above configuration, the step of forming the second diffusion region may be a step of forming the second diffusion region so as not to reach the substrate. According to this configuration, leakage current flowing into the second diffusion region can be suppressed. For this reason, the heat_generation | fever in a 2nd diffusion area | region can be suppressed and the fall of the reliability of the optical semiconductor device which arises by heat absorption can be suppressed.

  In the above configuration, the first heat treatment and the second heat treatment may be configured to use rapid thermal annealing or furnace annealing.

  In the above configuration, after the step of forming the second diffusion region, the step of removing the first SiN film, the step of forming a second SiN film having a refractive index of 1.87 or less on the compound semiconductor layer, The third heat treatment is performed, and the step of setting the second diffusion region as the third diffusion region can be sequentially performed. According to this configuration, it is possible to form the third diffusion region having a lower impurity concentration.

  In the above structure, the temperature of the third heat treatment may be lower than the temperature of the second heat treatment. According to this configuration, defects generated on the surface of the compound semiconductor layer can be suppressed.

  In the above-described configuration, the second SiN film may be removed after the step of forming the third diffusion region. According to this configuration, it is possible to suppress a decrease in reliability of the optical semiconductor device.

  The said structure WHEREIN: It can be set as the structure which has the process of removing the surface of the said compound semiconductor layer after the process of removing the said 2nd SiN film | membrane. According to this configuration, it is possible to suppress a decrease in reliability of the optical semiconductor device.

  In the above configuration, the third heat treatment may be configured to use rapid thermal annealing or furnace annealing.

  In the above structure, the compound semiconductor layer may include Ga and As. According to this configuration, in an optical semiconductor device in which defects are likely to occur on the surface of the compound semiconductor layer, defects generated on the surface of the compound semiconductor layer can be suppressed.

  In the above structure, the diffusion source layer may include Zn.

  The present invention provides a compound semiconductor layer including a first conductivity type cladding layer, an active layer, and a second conductivity type cladding layer opposite to the first conductivity type, which are sequentially provided on a substrate, and the active layer. One of a second diffusion region and a third diffusion region provided in the compound semiconductor layer so as to include a light emitting end face that emits light from the second diffusion region and the third diffusion region. The optical semiconductor device is characterized in that the concentration distribution of impurities contained in any one of the diffusion regions is uniform from the second conductivity type cladding layer to the active layer. According to the present invention, it is possible to suppress a decrease in reliability of an optical semiconductor device due to COD.

  In the above configuration, any one of the second diffusion region and the third diffusion region may not reach the substrate. According to this configuration, it is possible to suppress leakage current flowing into the second diffusion region and the third diffusion region. For this reason, the heat_generation | fever in a 2nd diffusion area | region and a 3rd diffusion area | region can be suppressed, and the fall of the reliability of the optical semiconductor device produced by heat absorption can be suppressed.

  In the above structure, the impurity may be Zn. In the above structure, the compound semiconductor layer may have a ridge portion.

  According to the present invention, the second diffusion region having a low impurity concentration and a uniform impurity concentration distribution from the second conductivity type cladding layer to the active layer can be formed in the compound semiconductor layer including the light emitting end face. For this reason, the fall of the reliability of the optical semiconductor device resulting from COD can be suppressed. In addition, by forming a SiN film having a refractive index of 1.9 or more on the compound semiconductor layer before performing the heat treatment on the first diffusion region, defects generated on the surface of the compound semiconductor layer can be suppressed.

  First, an optical semiconductor device (laser diode) according to Comparative Example 1 manufactured by a conventional manufacturing method will be described. FIG. 1A to FIG. 1E are schematic perspective views showing a method for manufacturing an optical semiconductor device according to Comparative Example 1. FIG. Referring to FIG. 1A, a first conductivity type cladding made of an n-type AlGaInP layer and having a thickness of 2.6 μm is formed on a substrate 10 made of an n-type GaAs substrate by MOCVD (metal organic chemical vapor deposition). The layer 12, the active layer 14 made of AlGaInP / InGaP MQW (multiple quantum well), 20 nm thick, the second conductivity type clad layer 16 made of p-type AlGaInP layer 2.0 μm thick, and the InGaP layer 30 nm thick A p-type contact layer 20 having a thickness of 0.2 μm is grown from the stopper layer 18 and the p-type GaAs layer. Thereby, the compound semiconductor layer 22 is formed on the substrate 10.

  Referring to FIG. 1B, a mask layer (not shown) made of a SiN layer is formed on the p-type contact layer 20 by using, for example, a CVD method. A photoresist (not shown) having an opening in which the first diffusion region 23 is to be formed is formed on the mask layer. The mask layer is removed using the photoresist as a mask. After removing the entire surface of the photoresist, a diffusion source layer (not shown) is formed on the mask layer, and Zn contained in the diffusion source layer is formed of the p-type contact layer 20, the stopper layer 18, the second conductivity type cladding layer 16, and the active layer. Diffusion into the layer 14 and the first conductivity type cladding layer 12 is performed. Thus, the first diffusion region 23 is formed so as to include the light emitting end face 38 that emits light from the active layer 14. Thereafter, after removing the mask layer and the diffusion source layer, a photoresist (not shown) having an opening in the first diffusion region 23 is formed again. The P-type contact layer 20 is removed using the photoresist as a mask. Thereafter, the entire surface of the photoresist is removed.

Referring to FIG. 1C, an SiO ₂ film (not shown) is formed on the stopper layer 18 and the p-type contact layer 20. The photoresist (not shown) having an opening for forming the recess 26 is formed on the SiO ₂ film and the SiO ₂ film is removed with a photoresist as a mask. After entirely removing the photoresist, removing part of the SiO ₂ p-type contact layer 20 so that the film as a mask reaches a second conductivity type cladding layer 16, a stopper layer 18 and the second conductive type cladding layer 16. Thereby, the dent part 26 and the ridge part 28 sandwiched between the dent parts 26 are formed. Thereafter, the entire SiO ₂ film is removed.

  With reference to FIG. 1D, a protective layer 30 made of a SiN layer is formed so as to cover the p-type contact layer 20, the stopper layer 18, and the second conductivity type cladding layer 16. A photoresist (not shown) having an opening on the upper surface of the ridge portion 28 is formed on the protective layer 30. The protective layer 30 is etched using the photoresist as a mask. As a result, the p-type contact layer 20 on the ridge portion 28 is exposed. Thereafter, the entire surface of the photoresist is removed.

  Referring to FIG. 1E, Ti, Mo, and Au are sequentially deposited on the protective layer 30 so as to be in contact with the p-type contact layer 20 exposed on the ridge portion 28 by using an evaporation method. 32 is formed. A low reflection film (not shown) is formed on the end face 34 on the side where the light emitting end face 38 is provided, of both end faces of the compound semiconductor layer 22. A highly reflective film (not shown) is formed on the opposite end face (not shown). Thus, the optical semiconductor device according to Comparative Example 1 is completed.

  Next, the method for forming the first diffusion region 23 described with reference to FIG. FIG. 2A to FIG. 3C are schematic cross-sectional views for explaining in detail the method of forming the first diffusion region 23. Referring to FIG. 2A, a compound semiconductor layer comprising a first conductivity type cladding layer 12, an active layer 14, a second conductivity type cladding layer 16, a stopper layer 18, and a p-type contact layer 20 formed on a substrate 10. On the surface 22, a mask layer 39 made of a SiN layer and having a thickness of 150 nm is formed by using, for example, a CVD method.

  Referring to FIG. 2B, a photoresist 40 is applied, and an opening 41 is formed at a location where the first diffusion region 23 is to be formed using an exposure technique. Referring to FIG. 2C, the mask layer 39 is etched using the photoresist 40 as a mask. As a result, the opening 41 is also formed in the mask layer 39.

Referring to FIG. 3A, the photoresist 40 is removed. Referring to FIG. 3B, a diffusion source layer 42 made of a mixed layer of ZnO and SiO ₂ and having a thickness of 100 nm is formed on the mask layer 39 so as to cover the opening 41 by using, for example, a sputtering method. . A cap layer 44 made of a SiO ₂ layer and having a thickness of 30 nm is formed on the diffusion source layer 42. Referring to FIG. 3C, the diffusion source layer 42 is heat-treated at 610 ° C. for 9 minutes. Thereby, Zn contained in the diffusion source layer 42 is diffused into the compound semiconductor layer 22, and the first diffusion region 23 is formed. The first diffusion region 23 is formed so as to sufficiently reach the active layer 14. That is, it is formed so as to reach a deep region of the compound semiconductor layer 22. With the above method, the first diffusion region 23 of the optical semiconductor device according to Comparative Example 1 is formed.

FIG. 4 shows the result of evaluating the concentration distribution of Zn contained in the first diffusion region 23 using secondary ion mass spectrometry (SIMS) for the optical semiconductor device according to Comparative Example 1. The horizontal axis in FIG. 4 is the distance from the surface of the compound semiconductor layer 22, and the vertical axis is the Zn concentration. Further, when the Zn concentration becomes 1 × 10 ¹⁸ / cm ³ or more, Zn does not completely enter the lattice position and exists between the lattices. Since this excess Zn easily moves between the lattices during device operation and causes device deterioration, it is desirable to reduce the Zn concentration as much as possible. However, when the Zn concentration is too low, the effect of expanding the band gap by disordering cannot be sufficiently obtained. Accordingly, the target value of the Zn concentration is, for example, about 1 × 10 ¹⁸ / cm ³ . According to FIG. 4, the Zn concentration in the active layer 14 is about 8 × 10 ¹⁸ / cm ³ , which is a higher concentration than the target value. Further, the Zn concentration distribution in the (region D) is large from the upper surface of the second conductivity type cladding layer 16 to the lower surface of the active layer 14, and the standard deviation σ of the region D / the average value of the region D is about 30%.

  In the optical semiconductor device according to Comparative Example 1, as described in FIG. 3C, the first diffusion region 23 is formed in the compound semiconductor layer 22 by performing heat treatment on the diffusion source layer 42. Since the first diffusion region 23 is formed so as to reach the active layer 14 sufficiently, the time for the heat treatment performed on the diffusion source layer 42 becomes long. Therefore, a larger amount of Zn is diffused into the compound semiconductor layer 22, thereby increasing the concentration of Zn contained in the vicinity of the diffusion source layer 42 in the first diffusion region 23 and increasing the concentration of Zn in the active layer 14. It is considered to be a concentration. Further, it is considered that the Zn concentration distribution from the upper surface of the second conductivity type cladding layer 16 to the lower surface of the active layer 14 also increases.

  FIG. 5 shows the result of a reliability test by APC (Auto Power Control) performed on the optical semiconductor device according to Comparative Example 1 having the first diffusion region 23 having such Zn concentration. The horizontal axis in FIG. 5 is the elapsed time, and the vertical axis is the operating current. In addition, the test is performed at an environmental temperature of 75 ° C. with a constant light output of 100 mW. According to FIG. 5, it can be confirmed that a significant increase in operating current occurs after about 60 hours. As shown in FIG. 4, since the Zn concentration in the active layer 14 of the first diffusion region 23 is high, light absorption by the free carriers described above increases, and the vicinity of the light emission end face 38 caused by COD is increased. It is thought to have occurred because of the destruction.

  Next, a pulse IL measurement is performed on some of the optical semiconductor devices according to the comparative example 1 that passed the reliability test by APC for 100 hours. FIG. 6 shows the result of pulse IL measurement. The horizontal axis of FIG. 6 is the injection current, and the vertical axis is the light output. According to FIG. 6, before reaching the specified light output of 300 mW, it can be confirmed that the light output becomes 0 mW near the injection current of 250 mA, and the optical semiconductor device is broken. As shown in FIG. 4, since the Zn concentration distribution in the first diffusion region 23 is large from the upper surface of the second conductivity type cladding layer 16 to the lower surface of the active layer 14, the Zn current distribution due to the operating current of the reliability test by APC Moves from the higher density to the lower density, and the density becomes uniform. As a result, the Zn concentration in the active layer 14 is increased, the light absorption by free carriers is increased, and this is considered to be caused by the destruction near the light emitting end face 38 caused by COD in the pulse IL measurement.

  Thus, the optical semiconductor device according to Comparative Example 1 has a problem with reliability. An example for solving this problem is shown below.

  FIG. 7 is a schematic perspective view of the optical semiconductor device (laser diode) according to the first embodiment. 8A is a schematic cross-sectional view taken along the line AA in FIG. 7, and FIG. 8B is a schematic cross-sectional view taken along the line BB in FIG.

  Referring to FIG. 7, FIG. 8A and FIG. 8B, on the substrate 10 made of an n-type GaAs substrate, the compound semiconductor layer 22 is made of an n-type AlGaInP layer and has a thickness of 2.6 μm. Type cladding layer 12, active layer 14 made of AlGaInP / InGaP MQW (multiple quantum well), thickness 20nm, second conductivity type cladding layer 16 made of p-type AlGaInP layer and thickness 2.0μm, and InGaP layer A stopper layer 18 having a thickness of 30 nm and a p-type contact layer 20 having a thickness of 0.2 μm are sequentially provided. The first conductivity type clad layer 12 and the second conductivity type clad layer 16 may be of the opposite conductivity type, using a p-type GaAs substrate, the first conductivity type clad layer 12 being a p-type clad layer, The two-conductivity-type cladding layer may be an n-type cladding layer.

  With reference to FIGS. 7 and 8A, a p-type contact layer 20, a stopper layer 18, and a depression 26 from which a part of the second conductivity type cladding layer 16 is removed are provided, and a p-type is provided between the depressions 26. A ridge portion 28 including the contact layer 20, the stopper layer 18, and the second conductivity type cladding layer 16 is provided. That is, the compound semiconductor layer 22 has the ridge portion 28. A protective layer 30 made of a SiN layer is provided so as to cover the p-type contact layer 20, the stopper layer 18, and the second conductivity type cladding layer 16. The protective layer 30 on the ridge portion 28 is removed, and a p-side electrode 32 is provided on the protective layer 30 so as to be in contact with the p-type contact layer 20. Referring to FIGS. 7 and 8B, Zn is diffused so as to include a light emitting end face 38 that emits light from the active layer 14 at the end in the BB direction of the compound semiconductor layer 22. A second diffusion region 24 is provided. A low reflection film (not shown) is provided on the end face 34 of the compound semiconductor layer 22 on the side where the light emitting end face 38 is provided, and a high reflection film (not shown) is provided on the end face 36 on the opposite side. ing.

  Referring to FIGS. 7 and 8A, since the active layer 14 is sandwiched between the first conductivity type cladding layer 12 and the second conductivity type cladding layer 16 having a low refractive index, the light propagating through the compound semiconductor layer 22 Is confined in the vicinity of the active layer 14. On the other hand, the equivalent refractive index for light propagating in the vicinity of the active layer 14 under the ridge 28 is larger than the equivalent refractive index for light propagating in the vicinity of the active layer 14 under the depression 26 on both sides of the ridge 28. Therefore, light propagating in the vicinity of the active layer 14 is confined in the vicinity of the active layer 14 below the ridge portion 28. A portion that confines light propagating in the vicinity of the active layer 14 is referred to as a waveguide 48. Referring to FIG. 8B, the light in the waveguide 48 is reflected by the end faces 34 and 36 on both sides of the compound semiconductor layer 22. In this way, the light stimulated and emitted within the waveguide 48 is emitted as output light from the light emitting end face 38 as laser light. Here, the equivalent refractive index is a refractive index felt by propagating light.

  The manufacturing method of the optical semiconductor device according to Example 1 is the same as that of the optical semiconductor device according to Comparative Example 1 except for the method of forming the second diffusion region 24, and FIG. 1 (a) to FIG. 1 (e). The description is omitted here.

  Next, a method for forming the second diffusion region 24 of the optical semiconductor device according to the first embodiment will be described with reference to FIGS. 9A to 9C. Note that the steps up to the step of forming the diffusion source layer 42 and the cap layer 44 are the same as those of the optical semiconductor device according to the comparative example 1, and are not shown in FIG. 2A to FIG.

  Referring to FIG. 9A, a first heat treatment is performed on the diffusion source layer 42 at 610 ° C. for 5 minutes using the mask layer 39 as a mask. Thereby, Zn contained in the diffusion source layer 42 is diffused into the compound semiconductor layer 22, and the first diffusion region 23 is formed. Compared to the method of forming the optical semiconductor device according to Comparative Example 1, the heat treatment time for forming the first diffusion region 23 is short, so that the first diffusion region 23 reaches the active layer 14 slightly. Formed to a depth.

  Referring to FIG. 9B, the mask layer 39, the diffusion source layer 42, and the cap layer 44 are removed. Thereafter, a first SiN film 46 having a refractive index of 1.9 and a thickness of 75 nm is formed on the compound semiconductor layer 22.

  Referring to FIG. 9C, the second heat treatment is performed on the first diffusion region 23 at 630 ° C. for 30 minutes using, for example, rapid thermal annealing (RTA). Thereby, Zn contained in the first diffusion region 23 is diffused into the compound semiconductor layer 22, and the second diffusion region 24 reaching the deep region of the compound semiconductor layer 22 from the first diffusion region 23 is formed. That is, the second diffusion region 24 is formed so as to sufficiently reach the active layer 14. With the above method, the second diffusion region 24 of the optical semiconductor device according to the first embodiment is formed.

FIG. 10 shows the result of evaluating the concentration distribution of Zn contained in the second diffusion region 24 using secondary ion mass spectrometry (SIMS) for the optical semiconductor device according to Example 1. The horizontal axis in FIG. 10 is the distance from the surface of the compound semiconductor layer 22, and the vertical axis is the Zn concentration. According to FIG. 10, the Zn concentration in the active layer 14 is about 2 × 10 ¹⁸ / cm ³ , which is lower than that in Comparative Example 1. Further, from the upper surface of the second conductivity type cladding layer 16 to the lower surface of the active layer 14 (Zone concentration distribution), the standard deviation σ of the region D / average value of the region D is as small as about 6%. I can confirm.

  According to the manufacturing method of Comparative Example 1, as shown in FIG. 4, the Zn concentration in the first diffusion region 23 is high, and the Zn concentration distribution from the second conductivity type cladding layer 16 to the active layer 14 is also large. However, according to the manufacturing method of the first embodiment, as shown in FIG. 9A, the first heat treatment is performed on the diffusion source layer 42 to form the first diffusion region 23 having a shallow depth. Then, as shown in FIG. 9B, after removing the diffusion source layer 42 which is a supply source of Zn, as shown in FIG. 9C, a second heat treatment is performed on the first diffusion region 23. Zn contained in the first diffusion region 23 diffuses, and the first diffusion region 23 becomes the second diffusion region 24. Therefore, as shown in FIG. 10, the Zn concentration in the second diffusion region 24 can be lowered, and the Zn concentration distribution from the second conductivity type cladding layer 16 to the active layer 14 can be made uniform. it can. Further, as shown in FIG. 9B, after the first SiN film 46 is formed on the compound semiconductor layer 22, the second heat treatment is performed on the first diffusion region 23, so that Zn contained in the first diffusion region 23 is formed. Can be diffused toward the inside of the compound semiconductor layer 22.

  Next, FIG. 11 shows the result of the APC reliability test for the optical semiconductor device according to Example 1, and FIG. 12 shows the result of the pulse IL measurement. Referring to FIG. 11, in a reliability test by APC for 100 hours, a significant increase in operating current is not confirmed, and it can be confirmed that the device is operating stably. Referring to FIG. 12, it can be confirmed that the light output increases in proportion to the injection current and reaches 300 mW which is the specified output.

According to Example 1, as shown in FIG. 10, the Zn concentration in the active layer 14 is close to the target value (about 1 × 10 ¹⁸ / cm ³ ), and the second conductivity type cladding layer 16 to the active layer 14. The concentration distribution of Zn is uniform. For this reason, destruction near the light emitting end face 38 caused by COD can be suppressed. Therefore, as shown in FIG. 11, the number of optical semiconductor devices in which an abnormality occurs in a reliability test by APC can be reduced. As shown in FIG. 12, an optical semiconductor device having a prescribed output in pulse IL measurement can be reduced. Obtainable. Therefore, according to the optical semiconductor device according to the first embodiment, a decrease in reliability can be suppressed.

  Further, according to the manufacturing method of Example 1, as shown in FIG. 9B, the first SiN film 46 having a refractive index of 1.9 is formed on the compound semiconductor layer 22. Here, the reason why the inventor used the first SiN film 46 having a refractive index of 1.9 will be described below. The inventor forms three types of first SiN films having refractive indexes of 1.8, 1.85, and 1.9 in the step of forming the second diffusion region 24 shown in FIGS. 9A to 9C. An experiment using 46 was conducted. 13 shows the case where the first SiN film 46 having a refractive index of 1.8 is used, FIG. 14A shows the case where the first SiN film 46 having a refractive index of 1.85 is used, and FIG. FIG. 10 is a schematic diagram of an SEM cross-sectional photograph of the optical semiconductor device after the step described with reference to FIG. 9C when the 1.9 first SiN film 46 is used. In the field of optical semiconductors, the refractive index generally used for SiN films is 1.8 to 1.85.

  Referring to FIG. 13, in the case of the first SiN film 46 having a refractive index of 1.8, it can be confirmed that many defects 13 are generated on the surface of the second diffusion region 24 formed in the compound semiconductor layer 22. In the case of the first SiN film 46 having a refractive index of 1.85, as shown in FIG. 14A, the defect 13 on the surface of the second diffusion region 24 is the case of the first SiN film 46 having a refractive index of 1.8. It can be confirmed that it is less than that. In the case of the first SiN film 46 having a refractive index of 1.9, it can be confirmed that the defect 13 hardly occurs on the surface of the second diffusion region 24 as shown in FIG.

  Thus, the reason for the difference in the generation of the defect 13 due to the difference in refractive index will be estimated below. When the refractive index of the SiN film is low, the denseness of the film quality is deteriorated. Therefore, the second heat treatment performed on the first diffusion region 23 described with reference to FIG. 9C causes Ga (gallium), As (arsenic), or the like in the compound semiconductor layer 22 to pass through the first SiN film 46 and be externally transmitted. It is considered that the defects 13 are generated on the surface of the compound semiconductor layer 22 due to evaporation. That is, it is considered that the defect 13 is generated on the surface of the second diffusion region 24. Therefore, when the compound semiconductor layer 22 contains Ga and As such as GaAs, AlGaAs, InGaAs, etc., it is considered that the defects 13 are likely to occur on the surface of the compound semiconductor layer 22.

  Further, as the temperature of the second heat treatment performed on the first diffusion region 23 becomes higher, the defects 13 generated on the surface of the compound semiconductor layer 22 appear more remarkably. When the first diffusion region 23 is formed by performing heat treatment on the diffusion source layer 42 as in the manufacturing method of Comparative Example 1 shown in FIGS. 2A to 3C, the temperature of the heat treatment is high. Since the supply of Zn and Zn becomes excessive, the temperature of the heat treatment is usually suppressed. However, as in the manufacturing method of the first embodiment shown in FIGS. 9A to 9C, the first heat treatment of the diffusion source layer 42 and the second heat treatment of the first diffusion region 23 are performed twice. Thus, when the second diffusion region 24 is formed, the temperature of the second heat treatment of the first diffusion region 23 is preferably higher than the temperature of the first heat treatment of the diffusion source layer 42. For this reason, in the manufacturing method of Example 1, it becomes easy to produce the defect 13 in the compound semiconductor layer 22 surface.

  From these results, the inventor uses the first SiN film 46 having a refractive index of 1.9 or more, and the second heat treatment performed on the first diffusion region 23 shown in FIG. It was possible to suppress the defects 13 generated on the surface. Thereby, suppression of the adhesive fall of the protective layer 30 formed on the compound semiconductor layer 22 and the compound semiconductor layer 22 is suppressed, and the p-side electrode 32 formed on the protective layer 30 so as to be in contact with the p-type contact layer 20. An increase in contact resistance with the p-type contact layer 20 can be suppressed. In particular, when the compound semiconductor layer 22 contains Ga and As, the defect 13 is likely to occur on the surface of the compound semiconductor layer 22, so that the effect of using the first SiN film 46 having a refractive index of 1.9 or more is increased. Further, a SiN film having a refractive index of 1.9 or more may be used for the mask layer 39 shown in FIG. In this case, the defects 13 on the surface of the compound semiconductor layer 22 that may be generated by the first heat treatment performed on the diffusion source layer 42 when forming the first diffusion region 23 can be suppressed.

  According to the manufacturing method of Example 1, as shown in FIG. 9A, when the first diffusion region 23 is formed, the diffusion heat source layer 42 is subjected to the first heat treatment at 610 ° C. for 5 minutes. As shown in (c), when the second diffusion region 24 is formed, a second heat treatment is performed on the first diffusion region 23 at 630 ° C. for 30 minutes. As described above, by setting the temperature of the second heat treatment performed when forming the second diffusion region 24 higher than the temperature of the first heat treatment performed when forming the first diffusion region 23, Zn can be diffused into the compound semiconductor layer 22, and the second diffusion region 24 having a low concentration of Zn and a small concentration distribution can be formed. In particular, the temperature of the second heat treatment performed on the first diffusion region 23 when forming the second diffusion region 24 is preferably 630 ° C. to 850 ° C.

  Further, as shown in FIG. 9C, the case where rapid thermal annealing (RTA) is used for the second heat treatment performed on the first diffusion region 23 when forming the second diffusion region 24 is shown as an example. It is not limited to this. Other methods such as furnace annealing can also be used. In addition, when the first diffusion region 23 shown in FIG. 9A is formed, rapid thermal annealing, furnace annealing, or the like can also be used for the first heat treatment performed on the diffusion source layer 42.

  Furthermore, although the case where the diffusion source layer 42 contains Zn and the second diffusion region 24 is formed by diffusing Zn is shown as an example, the present invention is not limited thereto. The diffusion source layer 42 may contain other impurities as long as the destruction near the light emitting end face 38 due to COD can be suppressed.

  Example 2 is an example in which the third diffusion region is formed by performing the third heat treatment on the second diffusion region 24 following the step of forming the second diffusion region 24 by the second heat treatment. The structure of the optical semiconductor device according to the second embodiment is the same as that of the first embodiment except that the third diffusion region 25 is provided instead of the second diffusion region 24, and FIGS. Since it is shown in FIG.8 (b), description is abbreviate | omitted. The manufacturing method is the same as that of Example 1 except that a third heat treatment is performed on the second diffusion region 24 to form the third diffusion region 25, and FIGS. 1 (a) to 1 (e) and FIG. This is shown in FIGS. 9A to 9C.

  Next, a process of forming the third diffusion region 25 by performing the third heat treatment on the second diffusion region 24 will be described with reference to FIGS. First, the second diffusion region 24 is formed using the manufacturing method shown in FIGS. 9A to 9C. Thereafter, referring to FIG. 15A, the first SiN film 46 is removed.

  Referring to FIG. 15B, a second SiN film 47 having a refractive index of 1.85 and a thickness of 150 nm is newly formed on the compound semiconductor layer 22. The refractive index of the second SiN film 47 is preferably 1.87 or less. The reason for using a SiN film having a refractive index of 1.87 or less is as follows. As described with reference to FIGS. 13 and 14, since the SiN film having a low refractive index has poor film quality, the substance diffused by the heat treatment is taken into the SiN film. This is to make use of this property to incorporate Zn diffused by the heat treatment into the second SiN film 47 using the second SiN film 47 having a relatively low film quality and a refractive index of 1.87 or less. .

  Referring to FIG. 15C, the third diffusion region 25 is formed by performing a third heat treatment at 600 ° C. for 30 minutes, for example, using rapid thermal annealing (RTA). Here, the refractive index of the second SiN film 47 is 1.85, which is lower than that of the first SiN film 46 (refractive index 1.9) used in forming the second diffusion region 24. For this reason, as described with reference to FIGS. 13 and 14, the number of defects 13 increases in the third heat treatment. However, the generation of the defect 13 is suppressed by setting the temperature of the third heat treatment to be lower than the temperature of the second heat treatment. Therefore, a preferable temperature in the third heat treatment is 550 ° C to 600 ° C. Further, as described above, the SiN film having a low refractive index has poor density, and the diffused material is easily taken in. Therefore, Zn contained in the second diffusion region 24 is diffused by the third heat treatment and taken into the second SiN film 47. For the third heat treatment, furnace annealing or the like can be used in addition to rapid thermal annealing.

  FIG. 16 shows the results of evaluating the concentration distribution of Zn contained in the second diffusion region 24 using secondary ion mass spectrometry (SIMS) for the semiconductor device according to Example 2. The horizontal axis of FIG. 16 is the distance from the surface of the compound semiconductor layer 22, and the vertical axis is the concentration of Zn. The solid line graph in FIG. 16 shows the concentration profile of the third diffusion region 25 of Example 2, and the broken line graph shows the concentration profile of the second diffusion region 24 of Example 1. As shown in FIG. 16, according to Example 2, the concentration of Zn in the active layer 14 can be further reduced as compared with Example 1. This is presumably because Zn contained in the second diffusion region 24 was taken into the second SiN film 47 by the third heat treatment.

  As shown in FIG. 15C, after the third heat treatment is performed, Zn is diffused into the second SiN film 47 and the surface of the p-type contact layer 20, and the second SiN film 47 and the p-type contact layer 20 are formed. The Zn concentration with the surface is high. Zn diffused in the second SiN film 47 and the surface of the p-type contact layer 20 moves again in the internal direction of the compound semiconductor layer 22 in a high temperature and high electric field state where the optical semiconductor device operates. For this reason, the reliability of the optical semiconductor device is lowered. Therefore, as shown in FIG. 17, it is preferable to perform the third heat treatment to form the third diffusion region 25, then remove the second SiN film 47, and then remove the surface portion of the p-type contact layer 20. The surface portion of the p-type contact layer 20 may be removed by, for example, about 50 nm using a wet etching method. Alternatively, only the second SiN film 47 may be removed without removing both the second SiN film 47 and the surface of the p-type contact layer 20.

  In the second embodiment, as in the first embodiment, good results can be obtained with respect to the reliability test by APC and the pulse IL measurement, and a decrease in reliability can be suppressed.

  Example 3 is an example in which the conditions of the first heat treatment and the conditions of the second heat treatment are different from those of Example 1. The structure of the optical semiconductor device according to the third embodiment is the same as that of the first embodiment, and the description thereof is omitted because it is illustrated in FIGS. 7, 8A, and 8B. In the manufacturing method, when the first diffusion region 23 is formed, the temperature of the first heat treatment performed on the diffusion source layer 42 is 610 ° C. and the time is 2 minutes, and the second diffusion region 24 is formed. In this case, except that the temperature of the second heat treatment performed on the first diffusion region 23 is 630 ° C. and the time is 5 minutes, FIGS. 1A to 1E and FIGS. This is the same as the optical semiconductor device according to Example 1 shown in c).

FIG. 18 shows the result of evaluating the concentration distribution of Zn contained in the second diffusion region 24 using secondary ion mass spectrometry (SIMS) for the optical semiconductor device according to Example 3. The horizontal axis in FIG. 18 is the distance from the surface of the compound semiconductor layer 22, and the vertical axis is the concentration of Zn. According to FIG. 18, the concentration of Zn in the active layer 14 is about 1 × 10 ¹⁸ / cm ³ . Further, from the upper surface of the second conductivity type cladding layer 16 to the lower surface of the active layer 14, the Zn concentration distribution (region D) has a small value of about 9% of the standard deviation σ of the region D / the average value of the region D. I can confirm.

  Next, FIG. 19 shows the result of the APC reliability test for the optical semiconductor device according to Example 3, and FIG. 20 shows the result of the pulse IL measurement. Referring to FIG. 19, in a reliability test using APC for 100 hours, a significant increase in operating current is not confirmed, and it can be confirmed that the device is operating stably. Referring to FIG. 20, it can be confirmed that the light output increases in proportion to the injection current and reaches 300 mW which is the specified output. Thus, also in the optical semiconductor device according to the third embodiment, it is possible to suppress a decrease in reliability.

According to the third embodiment, the temperature of the first heat treatment performed on the diffusion source layer 42 when the first diffusion region 23 is formed is 610 ° C. and the time is 2 minutes, and the second diffusion region 24 is formed when the second diffusion region 24 is formed. The temperature of the second heat treatment performed on one diffusion region 23 is 630 ° C. and the time is 5 minutes. Therefore, as shown in FIG. 18, the region where the Zn concentration is 1 × 10 ¹⁸ / cm ³ does not reach the substrate 10. That is, the second diffusion region 24 does not reach the substrate 10.

  Here, FIG. 21 shows the I of the first example in which the second diffusion region 24 reaches the substrate 10 (see FIG. 10) and the third example in which the second diffusion region 24 does not reach the substrate 10. -V characteristics are shown. Referring to FIG. 21, it can be confirmed that the current in Example 3 is suppressed from around 1.0 V to around 2.2 V compared to Example 1. This is because when the second diffusion region 24 does not reach the substrate 10, a leak current flowing from the p-side electrode 32 into the substrate 10 through the second diffusion region 24 can be suppressed. When the current flowing through the second diffusion region 24 is suppressed, heat generation in the second diffusion region 24 can be suppressed. That is, it is possible to suppress breakage in the vicinity of the light emitting end face 38 caused by heat absorption. As a result, the optical semiconductor device according to the third embodiment can be more reliable than the optical semiconductor device according to the first embodiment. Therefore, the second diffusion region 24 is preferably formed so as not to reach the substrate 10. Note that the third diffusion region 25 formed in Example 2 is also preferably formed so as not to reach the substrate 10 for the same reason.

In the first to third embodiments, as shown in FIGS. 10, 16 and 18, the concentration of Zn in the active layer 14 is approximately 2 × ¹⁰ 18 / cm ³ and about 1 × ¹⁰ 18 / cm ³ Showed the case. However, the present invention is not limited to these cases, and even when the Zn concentration in the active layer 14 is in the range of 1 × 10 ¹⁸ / cm ³ to 5 × 10 ¹⁸ / cm ³ , the same as in the first to third embodiments. Therefore, it is possible to suppress a decrease in the reliability of the optical semiconductor device. In particular, it is preferable that the concentration of Zn in the active layer 14 is in the range of 0.5 × 10 ¹⁸ / cm ³ to 5 × 10 ¹⁸ / cm ³ .

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

FIG. 1A to FIG. 1E are schematic perspective views showing a method for manufacturing an optical semiconductor device according to Comparative Example 1. 2A to 2C are schematic cross-sectional views (No. 1) showing a method of forming the first diffusion region in the optical semiconductor device according to Comparative Example 1. FIG. FIGS. 3A to 3C are schematic cross-sectional views (No. 2) showing a method of forming the first diffusion region in the optical semiconductor device according to Comparative Example 1. FIGS. FIG. 4 shows the results of evaluating the Zn concentration distribution in the first diffusion region of the optical semiconductor device according to Comparative Example 1 using secondary ion mass spectrometry (SIMS). FIG. 5 shows the result of a reliability test by APC for the optical semiconductor device according to Comparative Example 1. FIG. 6 shows the result of pulse IL measurement for the optical semiconductor device according to Comparative Example 1. FIG. 7 is a schematic perspective view of the optical semiconductor device according to the first embodiment. 8A is a schematic cross-sectional view taken along the line AA in FIG. 7, and FIG. 8B is a schematic cross-sectional view taken along the line BB in FIG. FIG. 9A to FIG. 9C are schematic cross-sectional views illustrating a method for forming the second diffusion region in the optical semiconductor device according to the first embodiment. FIG. 10 shows the results of evaluating the Zn concentration distribution in the second diffusion region of the optical semiconductor device according to Example 1 using secondary ion mass spectrometry (SIMS). FIG. 11 shows the results of a reliability test by APC for the optical semiconductor device according to Example 1. FIG. 12 shows the results of pulse IL measurement for the optical semiconductor device according to Example 1. FIG. 13 is a schematic diagram of an SEM cross-sectional photograph of the optical semiconductor device when the refractive index of the first SiN film 46 is 1.8. 14A is a schematic diagram of a SEM cross-sectional photograph of the optical semiconductor device when the refractive index of the first SiN film 46 is 1.85, and FIG. 9 is a schematic diagram of an SEM cross-sectional photograph of an optical semiconductor device in the case of 9. FIG. FIG. 15A to FIG. 15C are schematic cross-sectional views illustrating a method of forming the third diffusion region in the optical semiconductor device according to the second embodiment. FIG. 16 shows the results of evaluating the Zn concentration distribution in the third diffusion region of the optical semiconductor device according to Example 2 using secondary ion mass spectrometry (SIMS). FIG. 17 is a schematic cross-sectional view showing a step of removing the surfaces of the second SiN film and the compound semiconductor layer. FIG. 18 shows the results of evaluating the Zn concentration distribution in the second diffusion region of the optical semiconductor device according to Example 3 using secondary ion mass spectrometry (SIMS). FIG. 19 shows the result of the APC reliability test for the optical semiconductor device according to Example 3. FIG. 20 shows the results of pulse IL measurement for the optical semiconductor device according to Example 3. FIG. 21 shows the results of IV measurement for the optical semiconductor device according to Example 1 and the optical semiconductor device according to Example 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Substrate 12 1st conductivity type clad layer 13 Defect 14 Active layer 16 2nd conductivity type clad layer 18 Stopper layer 20 p-type contact layer 22 Compound semiconductor layer 23 1st diffusion region 24 2nd diffusion region 25 3rd diffusion region 26 Depression Part 28 ridge part 30 protective layer 32 p-side electrode 34 end face 36 end face 38 light emitting end face 39 mask layer 40 photoresist 41 opening 42 diffusion source layer 44 cap layer 46 first SiN film 47 second SiN film 48 waveguide

Claims (15)

In a method for manufacturing an optical semiconductor device comprising a compound semiconductor layer including a first conductivity type cladding layer, an active layer, and a second conductivity type cladding layer opposite to the first conductivity type on a substrate.
Forming a diffusion source layer on the compound semiconductor layer;
Performing a first heat treatment and forming a first diffusion region in the compound semiconductor layer so as to include a light emitting end face that emits light from the active layer;
Removing the diffusion source layer;
Forming a first SiN film having a refractive index of 1.9 or more on the compound semiconductor layer;
Performing a second heat treatment to make the first diffusion region a second diffusion region;
Are sequentially executed. A method for manufacturing an optical semiconductor device, comprising:   2. The method of manufacturing an optical semiconductor device according to claim 1, wherein the temperature of the second heat treatment is higher than the temperature of the first heat treatment.   3. The method of manufacturing an optical semiconductor device according to claim 1, wherein the step of forming the second diffusion region is a step of forming the second diffusion region so as not to reach the substrate.   4. The method of manufacturing an optical semiconductor device according to claim 1, wherein the first heat treatment and the second heat treatment use rapid thermal annealing or furnace annealing. 5. After the step of forming the second diffusion region, removing the first SiN film;
Forming a second SiN film having a refractive index of 1.87 or less on the compound semiconductor layer;
Performing a third heat treatment to make the second diffusion region a third diffusion region;
5. The method of manufacturing an optical semiconductor device according to claim 1, wherein the optical semiconductor device is sequentially executed.   6. The method of manufacturing an optical semiconductor device according to claim 5, wherein the temperature of the third heat treatment is lower than the temperature of the second heat treatment.   7. The method of manufacturing an optical semiconductor device according to claim 5, further comprising a step of removing the second SiN film after the step of forming the third diffusion region.   8. The method of manufacturing an optical semiconductor device according to claim 7, further comprising a step of removing a surface of the compound semiconductor layer after the step of removing the second SiN film.   9. The method of manufacturing an optical semiconductor device according to claim 5, wherein the third heat treatment uses rapid thermal annealing or furnace annealing.   The method for manufacturing an optical semiconductor device according to claim 1, wherein the compound semiconductor layer contains Ga and As.   The method of manufacturing an optical semiconductor device according to claim 1, wherein the diffusion source layer contains Zn. A compound semiconductor layer including a first conductivity type clad layer, an active layer, and a second conductivity type clad layer which is a conductivity type opposite to the first conductivity type, sequentially provided on the substrate;
Including any one of a second diffusion region and a third diffusion region provided in the compound semiconductor layer so as to include a light emission end face that emits light from the active layer,
An optical semiconductor device, wherein a concentration distribution of impurities contained in any one of the second diffusion region and the third diffusion region is uniform from the second conductivity type cladding layer to the active layer.   13. The optical semiconductor device according to claim 12, wherein any one of the second diffusion region and the third diffusion region does not reach the substrate.   The optical semiconductor device according to claim 12, wherein the impurity is Zn.   The optical semiconductor device according to claim 12, wherein the compound semiconductor layer has a ridge portion.

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