JP2007184556A - Semiconductor laser, its fabrication process and evaluation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser which enables failure analysis by observing emitted light without etching a substrate, and also to provide a fabrication process and an evaluation device of a semiconductor laser which enables quality judgment of characteristics under a wafer state. <P>SOLUTION: The surface of a GaN substrate 4 is overlaid sequentially with a first conductivity type GaN buffer layer 5, a first conductivity type AlGaN clad layer 6, a first conductivity type GaN optical guide layer 7, an active layer 8, a second conductivity type AlGaN electron barrier layer 3, a second conductivity type GaN optical guide layer 9, a second conductivity type AlGaN clad layer 10, and a second conductivity type GaN contact layer 11. The second conductivity type clad layer 10 consists of a first conductivity type clad layer 1, and a second conductivity type clad layer 2 forms a ridge portion. A first conductivity type electrode 17 formed on the back side of the GaN substrate 4 is provided with a first opening 18 in a position corresponding a ridge stripe 12 on a GaN substrate 4. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a semiconductor laser, a semiconductor laser manufacturing method, and an evaluation apparatus.

  Conventionally, various semiconductor laser structures, for example, semiconductor laser structures using a GaAs substrate have been proposed (see, for example, Patent Documents 1 and 2). In recent years, blue semiconductor lasers, for example, nitride semiconductor lasers using GaN as a substrate have been developed.

  In these semiconductor lasers, it is necessary to perform a failure analysis in order to identify the cause of the failure that occurs. For example, one of the failure analysis methods performed on GaAs semiconductor lasers is a method called EL analysis. (For example, refer nonpatent literature 1.). The EL analysis is also called an EL method, and is a method of identifying a defective portion by observing EL emission in a semiconductor laser.

  FIGS. 14A and 14B are diagrams showing a process for producing an analysis sample when performing failure analysis of a GaAs semiconductor laser by the EL method. 14A and 14B, 101 is a GaAs substrate, 102 is an n-type cladding layer, 103 is an active layer, 104 is a p-type cladding layer, 105 is a ridge portion, and 106 is a p-type electrode. First, the element of FIG. 14A is embedded in a resin (not shown). Next, the second conductivity type GaAs substrate 101 is polished to the vicinity of the n-type cladding layer 102. Furthermore, using an appropriate etching solution, using the difference in etching rate between the GaAs substrate 101 and the n-type cladding layer 102, only the GaAs substrate 101 is selectively etched and removed. Thereafter, an n-type electrode 107 is formed on the n-type cladding layer 102, whereby the analysis sample shown in FIG. 14B is obtained.

  When a voltage is applied to the n-type electrode 107 and the p-type electrode 106 of this sample, a current flows in a concentrated manner in the ridge portion 105 that is a waveguide. In the active region immediately below the ridge portion 105, electrons and holes are intensively recombined to emit light. In this method, since the GaAs substrate 101 opaque to the EL light is removed, the EL light can be observed from the n-type cladding layer 102 side. Since the light emission is weak or dark in the defective portion, the defective portion can be specified by finding this.

  If the above failure analysis method can be applied to a GaN-based semiconductor laser, the analysis process can be shared, which is advantageous in terms of cost. However, in the GaN-based semiconductor laser, the substrate cannot be removed by wet etching in the analysis sample manufacturing process. This is because there is no appropriate etchant that can selectively etch the GaN substrate with respect to the n-type cladding layer.

  On the other hand, the GaN substrate is a substrate that is transparent to the emitted light. Therefore, a method of applying an EL method to a semiconductor laser having such a substrate without etching the substrate is devised (see Patent Document 3).

  In Patent Document 3, a semiconductor laser that can easily analyze the growth of dislocations and has a transparent InP substrate as well as a GaN substrate is cited as an example. This semiconductor laser has a ridge structure on the main surface side of the substrate and a cathode electrode on the back side of the substrate, and the ridge structure is formed by shifting from the center of the semiconductor laser element to one side. On the other hand, the cathode electrode is formed by shifting in the opposite direction to the ridge structure. In this case, no electrode is formed in the region corresponding to the ridge structure on the back surface side of the substrate, so that the emitted light transmitted through the substrate can be observed.

  However, the method described in Patent Document 3 has the following problems.

  Among reports on defects in semiconductor lasers, there are cases in which dislocations existing at locations away from the ridge portion extend to the light emitting point and eventually lead to fatal defects (see, for example, Non-Patent Document 2). . Non-Patent Document 2 is a report on a GaAs-based semiconductor laser, but this defect can occur similarly in other semiconductor lasers, for example, GaN-based semiconductor lasers. However, when the method of Patent Document 3 is used, such a dislocation may be overlooked.

  The reason is as follows. In Patent Document 3, a region where the cathode electrode is formed and a region where the cathode electrode is not formed are provided with the center of the semiconductor laser element as a boundary. Here, current flows in the active layer on the side where the cathode electrode is formed, and electrons and holes are recombined to emit light. On the other hand, on the side where the cathode electrode is not present, the supplied current is small, and light emission is weak or does not emit light. More specifically, light emission is biased only on the cathode electrode side with the region immediately below the ridge stripe as the center on the active layer. Therefore, a non-light emitting area, that is, a dark area cannot be found on the side where no electrode exists. Therefore, the possibility of the fatal failure described above is overlooked.

  In Patent Document 3, an electrode is formed only on one side of the ridge stripe. As a result, non-uniform stress is generated in the ridge stripe, which may cause a change in optical characteristics such as a far-field image and polarized light. Furthermore, the light emission lifetime may be reduced due to the uneven stress.

  Further, the conventional method has the following problems.

  Conventionally, a semiconductor laser element is roughly mounted on a submount by two types of methods. The first means is called junction down (also referred to as face down), and is a method of mounting the active layer and the substrate so that the active layer and the submount are close to each other. The second means is a system in which the substrate and the submount are mounted close to each other, contrary to the first means.

  In Patent Document 3, failure analysis can be performed without destroying the product at the time of junction-down mounting, whereas the product that performs junction-up (also called face-up) mounting is recombined to junction-down for analysis. There was a need to do. On the other hand, if the inspection can be performed non-destructively, it is desirable because the EL method can be used not only for defect analysis but also for inspection and selection of initial manufacturing variation.

  Further, conventionally, there have been the following problems.

  In a conventional GaN semiconductor laser, a ridge structure is formed on the main surface of a substrate, and a p-type electrode is provided on the ridge structure. On the other hand, the n-type electrode is provided on substantially the entire back surface of the substrate. For this reason, since the light emitted from the active layer is blocked by the n-type electrode, the emitted light could not be observed from the back side of the substrate. Therefore, the GaN-based semiconductor laser element is processed from the wafer state to the bar state, and the quality of the element characteristics is determined by observing the laser beam from the end face. As described above, conventionally, it is not possible to judge whether or not the semiconductor laser device is to be assembled before processing into the bar state, that is, before processing into the bar state, that is, in the wafer state, it is not possible to select the semiconductor laser element to be assembled. It was. Therefore, it is necessary to process all the regions on the wafer into a bar state, and the semiconductor laser elements that are actually defective have also been processed.

JP-A-5-243687 Japanese Unexamined Patent Publication No. 7-30187 JP 2003-179291 A Mitsubishi Electric Corporation “Mitsubishi Semiconductor Reliability Information”, [online], October 14, 2005, Internet <URL: http://www.mitsubishichips.com/Japan/reliability/pdf/4.pdf> IEE Journal of Quantum Electronics, Volume 29, pp 2058-206, FIG. 2, 1993 (IEEE Journal of Quantum Electronics, VOL. 29, pp 2058-206, 1993, FIG. 2)

  The present invention has been made in view of these problems. That is, an object of the present invention is to provide a semiconductor laser having a structure capable of observing emitted light and performing failure analysis without etching a substrate.

  Another object of the present invention is to provide a semiconductor laser having a structure capable of nondestructive failure analysis regardless of whether the semiconductor laser submount mounting method is a junction down type or a junction up type. There is.

  Another object of the present invention is to provide a method of manufacturing a semiconductor laser that performs quality determination in a wafer state.

  Furthermore, another object of the present invention is to provide an evaluation apparatus capable of determining the quality of a semiconductor laser in a wafer state.

  Other objects and advantages of the present invention will become apparent from the following description.

The first invention of the present application is a first conductivity type semiconductor substrate having optical transparency,
A first conductivity type semiconductor layer formed on the surface of the semiconductor substrate;
An active layer formed on the semiconductor layer of the first conductivity type;
A second conductivity type semiconductor layer formed on the active layer;
A ridge formed in the semiconductor layer of the second conductivity type;
A second conductivity type electrode formed on the second conductivity type semiconductor layer;
A first conductivity type electrode formed on the back surface of the semiconductor substrate;
In the semiconductor laser, the first conductivity type electrode has an opening at a position corresponding to the ridge portion of the semiconductor substrate.

The second invention of the present application is a first conductivity type semiconductor substrate having optical transparency,
A first conductivity type semiconductor layer formed on the surface of the semiconductor substrate;
An active layer formed on the semiconductor layer of the first conductivity type;
A second conductivity type semiconductor layer formed on the active layer;
A ridge formed in the semiconductor layer of the second conductivity type;
A second conductivity type electrode formed on the second conductivity type semiconductor layer;
A first conductivity type electrode formed on the back surface of the semiconductor substrate;
The first conductivity type electrode is a semiconductor laser formed on both sides of a region corresponding to the ridge portion and not formed in the region.

The third invention of the present application is a first conductivity type semiconductor substrate having light transparency,
A first conductivity type semiconductor layer formed on the surface of the semiconductor substrate;
An active layer formed on the semiconductor layer of the first conductivity type;
A second conductivity type semiconductor layer formed on the active layer;
A ridge formed in the semiconductor layer of the second conductivity type;
A second conductivity type electrode formed on the second conductivity type semiconductor layer;
An electrode of a first conductivity type formed on the back surface of the semiconductor substrate including a position corresponding to the ridge portion of the semiconductor substrate;
The first conductivity type electrode is a semiconductor laser that transmits light emitted from the active layer at the position.

The fourth invention of the present application is a first conductivity type semiconductor substrate;
A first conductivity type semiconductor layer formed on the surface of the semiconductor substrate;
An active layer formed on the semiconductor layer of the first conductivity type;
A second conductivity type semiconductor layer formed on the active layer;
A ridge formed in the semiconductor layer of the second conductivity type;
At least a second conductivity type electrode formed on the upper surface of the ridge portion;
An electrode of a first conductivity type formed on the back surface of the semiconductor substrate including a position corresponding to the ridge portion of the semiconductor substrate;
The second conductivity type electrode may be a semiconductor laser having an opening in a part of the upper surface of the ridge portion.

The fifth invention of the present application includes a semiconductor substrate of a first conductivity type,
A first conductivity type semiconductor layer formed on the surface of the semiconductor substrate;
An active layer formed on the semiconductor layer of the first conductivity type;
A second conductivity type semiconductor layer formed on the active layer;
A ridge formed in the semiconductor layer of the second conductivity type;
At least a second conductivity type electrode formed on the upper surface of the ridge portion;
An electrode of a first conductivity type formed on the back surface of the semiconductor substrate including a position corresponding to the ridge portion of the semiconductor substrate;
The second conductivity type electrode is a semiconductor laser characterized in that light emitted from the active layer is transmitted through the ridge portion.

The sixth invention of the present application includes a step of sequentially forming a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer on the surface of a first conductivity type semiconductor wafer having optical transparency;
Processing the second conductivity type semiconductor layer to form a ridge portion;
Forming a second conductivity type electrode on the second conductivity type semiconductor layer;
Forming a first conductivity type electrode on the back surface of the semiconductor wafer;
Forming openings at all positions corresponding to the ridge portion of the first conductivity type electrode;
For each of a plurality of semiconductor laser elements formed on the semiconductor wafer, a step of applying a voltage via the first conductivity type electrode and the second conductivity type electrode to evaluate characteristics;
And a step of dividing the semiconductor wafer into a plurality of bars after evaluating the characteristics.

The seventh invention of the present application includes a step of sequentially forming a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer on the surface of a first conductivity type semiconductor wafer having optical transparency;
Processing the second conductivity type semiconductor layer to form a ridge portion;
Forming a second conductivity type electrode on the second conductivity type semiconductor layer;
Forming a first conductivity type electrode on the back surface of the semiconductor wafer;
Removing the first conductivity type electrode in all regions corresponding to the ridge portion on the back surface of the semiconductor wafer;
For each of a plurality of semiconductor laser elements formed on the semiconductor wafer, a step of applying a voltage via the first conductivity type electrode and the second conductivity type electrode to evaluate characteristics;
Dividing the semiconductor wafer into a plurality of bars after evaluating the characteristics,
The semiconductor laser manufacturing method is characterized in that the first conductivity type electrode of the semiconductor laser element is formed on both sides of a region corresponding to the ridge portion and is not formed in the region.

The eighth invention of the present application includes a step of sequentially forming a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer on the surface of a first conductivity type semiconductor wafer having optical transparency;
Processing the second conductivity type semiconductor layer to form a ridge portion;
Forming a second conductivity type electrode on the second conductivity type semiconductor layer;
Forming a first conductivity type electrode on the back surface of the semiconductor wafer;
Forming an opening at a position corresponding to a part of the ridge portion in the first conductivity type electrode;
A step of evaluating characteristics of a plurality of semiconductor laser elements formed on the semiconductor wafer having the opening by applying a voltage via the first conductivity type electrode and the second conductivity type electrode. When,
And a step of dividing the semiconductor wafer into a plurality of bars after evaluating the characteristics.

The ninth invention of the present application includes a step of sequentially forming a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer on a surface of a first conductivity type semiconductor wafer having light transmittance;
Processing the second conductivity type semiconductor layer to form a ridge portion;
Forming a second conductivity type electrode on the second conductivity type semiconductor layer;
Forming a first conductivity type electrode on the back surface of the semiconductor wafer;
Removing the first conductivity type electrode in a region corresponding to a part of the ridge portion on the back surface of the semiconductor wafer;
Among the plurality of semiconductor laser elements formed on the semiconductor wafer, the voltage in the region where the first conductivity type electrode is removed is applied via the first conductivity type electrode and the second conductivity type electrode. Applying and evaluating the characteristics;
Dividing the semiconductor wafer into a plurality of bars after evaluating the characteristics,
In the semiconductor laser device in the region where the first conductivity type electrode is removed, the first conductivity type electrode is formed on both sides of the region corresponding to the ridge portion, and is not formed in the region. This is a method of manufacturing a semiconductor laser.

The tenth invention of the present application includes a step of sequentially forming a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer on the surface of a light-transmissive first conductivity type semiconductor wafer;
Processing the second conductivity type semiconductor layer to form a ridge portion;
Forming a second conductivity type electrode on the second conductivity type semiconductor layer;
Forming a first conductivity type electrode having optical transparency on the back surface of the semiconductor wafer;
For each of a plurality of semiconductor laser elements formed on the semiconductor wafer, a step of applying a voltage via the first conductivity type electrode and the second conductivity type electrode to evaluate characteristics;
And a step of dividing the semiconductor wafer into a plurality of bars after evaluating the characteristics.

The eleventh invention of the present application is an evaluation apparatus for evaluating the characteristics of a plurality of semiconductor laser elements formed on a semiconductor wafer,
A first electrode plate having a shape that can contact the first electrode of the semiconductor laser element, and a region that transmits light emitted from the semiconductor laser element;
A second electrode plate having a shape capable of contacting the second electrode of the semiconductor laser element;
A current source or a voltage source connected to the first electrode plate and the second electrode plate;
A light receiving device that receives light emitted from the semiconductor laser element that has passed through the first electrode plate;
An evaluation apparatus comprising: a storage device for recording a semiconductor laser element whose intensity of light received by the light receiving device is a predetermined value or less.

  According to the first invention of this application, since the first conductivity type electrode has the opening at a position corresponding to the ridge portion of the semiconductor substrate, the defect analysis is performed by observing the emitted light without etching the substrate. be able to. In addition, failure analysis can be performed nondestructively for both the junction down type and the junction up type mounting methods.

  According to the second invention of the present application, since the first conductivity type electrodes are formed on both sides of the region corresponding to the ridge portion and are not formed in the region, the emitted light can be emitted without etching the substrate. Failure analysis can be performed by observation. In addition, failure analysis can be performed nondestructively for both the junction down type and the junction up type mounting methods.

  According to the third invention of the present application, the first conductivity type electrode formed on the back surface of the semiconductor substrate including the position corresponding to the ridge portion of the semiconductor substrate transmits the light emitted from the active layer at the position. Failure analysis can be performed by observing the emitted light without etching the substrate. In addition, failure analysis can be performed nondestructively for both the junction down type and the junction up type mounting methods.

  According to the fourth aspect of the present invention, since the second conductivity type electrode has an opening in a part of the upper surface of the ridge portion, the failure analysis can be performed by observing the light emitted from the active layer through the opening. it can. In addition, failure analysis can be performed nondestructively for both the junction down type and the junction up type mounting methods.

  According to the fifth aspect of the present invention, since the second conductivity type electrode transmits the light emitted from the active layer in the ridge portion, the light emitted from the active layer is observed from the opening to perform the failure analysis. Can do. In addition, failure analysis can be performed nondestructively for both the junction down type and the junction up type mounting methods.

  According to the sixth to tenth inventions of the present application, after evaluating the characteristics of the semiconductor laser element, the semiconductor wafer is divided into a plurality of bars. That is, since the quality determination is performed in the wafer state, the semiconductor laser elements to be divided into bars or assembled can be selected in advance.

  According to the eleventh aspect of the present application, the quality of the semiconductor laser element in the wafer state can be determined.

(Embodiment 1)
Hereinafter, the present embodiment will be described in detail with reference to the drawings. In this embodiment, a nitride blue semiconductor laser is taken as an example of the semiconductor laser.

  FIG. 1 is a cross-sectional view of the nitride semiconductor laser according to the first embodiment. First, the components of the present embodiment and the first conductivity type electrode and the first opening that are the characteristic points of the present embodiment will be described.

  As shown in FIG. 1, a first conductivity type GaN buffer layer 5 is formed on the surface of a GaN substrate 4 as a light-transmitting semiconductor substrate, and further, a first conductivity type semiconductor layer is formed thereon. The first conductivity type AlGaN cladding layer 6, the first conductivity type GaN light guide layer 7 as the first light guide layer, the active layer 8, the second conductivity type AlGaN electron barrier layer 3, and the second light guide layer as the second light guide layer. A two-conductivity-type GaN light guide layer 9, a second-conductivity-type AlGaN cladding layer 10 as a second-conductivity-type semiconductor layer, and a second-conductivity-type GaN contact layer 11 are sequentially stacked.

  The second conductivity type cladding layer 10 includes a first second conductivity type cladding layer 1 and a second second conductivity type cladding layer 2. The second second conductivity type cladding layer 2 is formed as a ridge portion (hereinafter referred to as a ridge stripe 12), and an insulating film 14 is formed so as to cover the ridge stripe 12. A second conductivity type electrode 16 is formed on the insulating film 14 and the second conductivity type GaN contact layer 11. In this embodiment, a nitride blue semiconductor laser having an SCH structure in which an active layer is sandwiched between first-conductivity-type and second-conductivity-type light guide layers is taken as an example. It is not limited to this.

  The present embodiment is characterized in that a first opening 18 is provided at a position corresponding to the ridge stripe 12 on the GaN substrate 4 in the first conductivity type electrode 17 formed on the back side of the GaN substrate 4. It is said.

  The position corresponding to the ridge stripe 12 will be described in detail below based on the relationship among the ridge stripe 12, the active layer 8, and the GaN substrate 4.

  First, it is assumed that the ridge stripe 12 is an original image and the image is projected in parallel on the active layer 8. Among the maps, the one having the smallest distance from the original image is defined as the first map. This first mapping points to the area closest to the ridge stripe 12 on the active layer 8. For example, in FIG. 1, the map projected directly below the ridge stripe 12 is the first map.

  Next, the first map is used as an original image, and at least one map projected in parallel on the back surface of the GaN substrate 4 is considered, and this is used as a second map. This second mapping corresponds to the observation region on the back surface of the GaN substrate 4 in the EL method. This second mapping is a position corresponding to the ridge stripe 12 in the present invention.

  In such a semiconductor laser, when a voltage is applied between both electrodes, electrons and holes are injected into the active layer 8 and then recombined to emit EL light. Since the EL light passes through the GaN substrate 4, according to the present embodiment, the EL light can be observed through the first opening 18. Therefore, failure analysis can be performed without removing the GaN substrate 4. The first opening 18 is provided at a position corresponding to the ridge stripe 12 because the current is constricted by the ridge stripe 12 and concentratedly flows immediately below the ridge stripe 12, thereby causing the ridge stripe 12 in the active layer 8 to flow. This is because the EL light concentrates and emits light directly below.

  As described above, in the present embodiment, the first opening 18 is provided in the first conductivity type electrode 17 at a position corresponding to the ridge stripe 12 on the GaN substrate 4. In other words, the first conductivity type electrode 17 exists on both sides of the first opening 18. With such a structure, the injection of electrons is not biased toward one side of the ridge stripe 12. That is, electrons are injected from both sides of the ridge stripe 12 directly below and in the vicinity of the ridge stripe 12. On the other hand, the holes injected from the second conductivity type electrode 16 are narrowed by the ridge stripe 12 and concentrated in the vicinity thereof. Therefore, electrons and holes are distributed on both sides of the ridge stripe 12 and in the vicinity thereof. Therefore, recombination also occurs on both sides of the ridge stripe 12. As a result, EL is emitted immediately below the ridge stripe and in the vicinity of both sides thereof, and failure analysis can be performed not only immediately below the ridge stripe 12 but also in the peripheral regions on both sides thereof.

  Further, since the first conductivity type electrodes 17 are present on both sides of the ridge stripe 12, various physical forces applied to the semiconductor laser are dispersed on both sides of the ridge stripe 12. Thereby, it is possible to prevent the stress from being generated only on one side of the ridge stripe 12. As a result, it is possible to prevent various effects resulting from stress nonuniformity, for example, changes in optical characteristics such as a far-field image and polarized light. Similarly, it is possible to avoid a reduction in the service life such as a load being concentrated on a part of the ridge stripe over a long period due to non-uniform stress, leading to early breakage.

  In the present embodiment, the first conductivity type electrode 17 is formed on both sides of the region corresponding to the ridge stripe 12 on the GaN substrate 4 and may not be formed in the region. The electrode 17 may not have a structure having the first opening 18. This will be described in more detail with reference to FIGS. 3A and 3B described later.

  Next, the structure of each part of the semiconductor laser in FIG. 1 will be described in more detail.

The GaN substrate 4 transmits light having a wavelength of 300 nm to 500 nm corresponding to the emission peak wavelength of the blue semiconductor laser. The first conductivity type GaN buffer layer 5 has a thickness of 10 μm or less (for example, 1 μm), and is doped with, for example, silicon (Si) as the first conductivity type impurity. The first conductivity type GaN buffer layer 5 is formed in order to reduce unevenness on the surface of the GaN substrate and to stack layers to be formed later as flat as possible. The first conductivity type Al _x Ga _1-x N cladding layer 6 has a thickness of 0.5 to 4 μm (for example, 1 μm), doped with, for example, Si as the first conductivity type impurity, and x = 0.05 to 0 .2 (for example, 0.07).

The active layer 8 has, for example, an undoped In _x Ga _1-x N / In _y Ga _1-y N multiple quantum well structure. In this structure, In _x Ga _1-x N as a barrier layer and In _y Ga _1-y N layers as well layers are alternately stacked. The In _x Ga _1-x N layer has a thickness of 7 nm, for example, and x = 0.02. The In _y Ga _1-y N layer has, for example, a thickness of 3.5 nm and y = 0.14. The number of wells is, for example, 3, and either the case where there are well layers at both ends or the case where there are barrier layers may be used.

The second conductivity type AlGaN electron barrier layer 3 has a thickness of 40 nm or less (for example, 10 nm), and in Al _x Ga _1-x N, x = 0.3 or less (for example, 0.18). The second conductivity type GaN light guide layer 9 has a thickness of 50 nm to 200 nm (for example, 100 nm).

The second conductivity type cladding layer 10 includes a first second conductivity type cladding layer 1 and a second second conductivity type cladding layer 2. The first second-conductivity-type cladding layer 1 is made of, for example, Al _x Ga _1-x N with x = 0.05 to 0.2 (for example, 0.07) and has a thickness of 50 nm to 500 nm (for example, 100 nm). is there. For example, Mg is doped as the second conductivity type impurity. The second second conductivity type cladding layer 2 is made of, for example, Al _x Ga _1-x N with x = 0.05 to 0.2 (for example, 0.07) and has a thickness of 200 nm to 4 μm (for example, 400 nm). is there. For example, Mg is doped as the second conductivity type impurity.

  The second conductivity type GaN contact layer 11 has a thickness of 50 nm to 500 nm (for example, 100 nm), and is doped with, for example, Mg as the second conductivity type impurity. On the second conductivity type AlGaN cladding layer 10 and the second conductivity type GaN contact layer 11, for example, a ridge stripe 12 is formed in the (1-100) direction (in the depth direction in FIG. 1). The width is 1 μm to 5 μm (for example, 2.2 μm). The ridge stripe 12 is formed in a low defect region existing between a high transition region having a width of several μm to several tens of μm formed in a stripe shape on the GaN substrate.

Further, an insulating film 14 for surface protection and electrical insulation is formed so as to cover the side surface portion or the lateral bottom surface portion of the ridge stripe 12. This insulating film is, for example, a SiO ₂ film, and the thickness can be, for example, 200 nm.

  A second opening 15 is provided in a portion of the insulating film 14 that corresponds to the upper side of the ridge stripe 12. In the second opening 15, electrical contact is made between the second conductivity type electrode 16 and the second conductivity type contact layer 11. The second conductivity type electrode 16 is formed, for example, by sequentially laminating Pd and Au films.

  As described above, the first conductivity type electrode 17 is formed on the back surface of the GaN substrate 4. The first conductive electrode 17 is formed by sequentially laminating Ti and Au films, for example.

  Next, an example of a manufacturing method of the semiconductor laser according to the present embodiment will be described.

First, the surface of the GaN substrate 4 is cleaned in advance by thermal cleaning or the like. Next, the first conductivity type GaN buffer layer 2 is grown on the GaN substrate 4 by a metal organic chemical vapor deposition (MOCVD) method at a growth temperature of 1000 ° C., for example. Thereafter, the first conductivity type AlGaN clad layer 6 and the undoped InGaN light guide layer 7 are successively grown by the MOCVD method. Both growth temperatures are 1000 ° C. Further, the undoped In _x Ga _1-x N / In _y Ga _1-y N multiple quantum well active layer 8 is grown at 740 ° C. by the MOCVD method.

  Further, the second conductivity type AlGaN electron barrier layer 3, the second conductivity type GaN light guide layer 9, the first second conductivity type AlGaN cladding layer 1, and the second second conductivity type AlGaN cladding layer 2 are similarly formed by MOCVD. And the 2nd conductivity type GaN contact layer 11 is laminated | stacked sequentially. The growth temperature is 1000 ° C., for example.

  After the above crystal growth, a resist is applied to the entire surface of the wafer and lithography is performed. Thereby, a resist pattern having a predetermined shape corresponding to the shape of the mesa portion is formed. Using this resist pattern as a mask, the second conductivity type cladding layer 10 is etched by, for example, RIE to produce the ridge stripe 12 having an optical waveguide structure.

After the etching process, the SiO ₂ film 14 having a thickness of 0.2 μm, for example, is again formed on the entire surface of the substrate while leaving the resist pattern used as a mask. As the film forming method, for example, a CVD method, a vacuum deposition method, a sputtering method, or the like is used. Subsequently, a step of removing the resist and simultaneously removing the SiO ₂ film on the ridge stripe, so-called lift-off, is performed. As a result, the second opening 15 is formed on the ridge stripe.

Next, Pt and Au films are sequentially formed over the contact layer 11 and the SiO ₂ film 14 by, for example, vacuum deposition. Thereafter, a resist is applied and lithography is performed to form an electrode pattern. Finally, unnecessary Pt and Au films are removed by wet etching or dry etching to form the second conductivity type electrode 16.

  Subsequently, a first conductivity type electrode 17 is formed on the back side of the GaN substrate 4. First, Ti and Au films are sequentially formed on the back surface of the substrate by vacuum deposition. Subsequently, a resist is applied on the metal film and lithography is performed. Thereafter, an electrode pattern is formed by wet etching or dry etching. At this time, the metal thin film at the position corresponding to the ridge stripe 12 is removed, and electrode layers are formed on both sides of the first opening 18 as shown in FIG. Finally, an alloy process for bringing the electrodes into ohmic contact is performed to form the first conductivity type electrode 17.

  For the purpose of facilitating wire bonding, an Au plating layer as a thick film electrode may be further laminated on the first conductivity type electrode 17. In this case, the process up to the plating process is performed first, and then the resist coating, lithography and etching are sequentially performed. The film thickness of the Au plating layer can be, for example, about 2 μm to 4 μm. In the present embodiment, the first opening 18 is also provided in the Au plating layer.

  After the first conductivity type electrode 17 is formed, the above laminated structure and substrate are processed into a bar shape by cleavage or the like to form both resonator end faces, and end face coating is applied to these resonator end faces. Finally, the bar is formed into chips by cleavage or the like, and the nitride semiconductor laser according to this embodiment is manufactured.

  The semiconductor laser manufactured in this way can be analyzed for defects using the EL method as follows.

  First, soldering is performed with the second conductivity type electrode 16 facing the package. This is a so-called junction-down structure. Thereafter, a current is passed between the second conductivity type electrode 16 and the first conductivity type electrode 17 in the same manner as when the laser is driven. Then, recombination of electrons and holes occurs in the active layer 8, and strong EL emission occurs in a region near the ridge stripe 12. This light emission is observed from the outside and the cause of the failure is analyzed.

  On the other hand, there is a case where so-called junction-up mounting is performed in which soldering is performed with the first conductivity type electrode 17 facing the package. At this time, since there is no metal in the first opening 18, no solder is attached to the first opening 18 even when the first opening 18 is mounted once. Therefore, in this case, if the defective element is recombined to junction down, the EL light can be observed as in the first embodiment.

  FIG. 3A is a perspective view of FIG. 1 viewed from the back side of the GaN substrate 4. As shown in this figure, the first conductivity type electrode 17 is formed continuously along the outer edge of the first opening 18. Here, the shape of the first opening 18 may be a shape including a rectangle, a polygon, a curve, or the like. Further, in FIG. 3A, the first conductivity type electrode 17 has one first opening 18 at a substantially central portion thereof. However, for example, the first conductivity type electrode 17 has a structure having a plurality of openings or a large number of fine openings. It is also possible to provide an opening. However, at this time, the first conductivity type electrode 17 exists on both sides of an arbitrary straight line that equally divides the area of the second mapping.

  Also, the first opening 18 can be made larger than the position corresponding to the ridge stripe 12, that is, larger than the second mapping. Thereby, it is possible to distinguish between a defect existing in the ridge stripe and a defect extending from the outside of the ridge stripe. On the contrary, if the opening 18 is too wide with respect to the position corresponding to the ridge stripe, the current spread will affect the characteristics of the semiconductor laser. Therefore, for example, the width can be the same as the ridge stripe width or the width of the substrate. In this embodiment, the width is twice that of the ridge stripe 12 (for example, 4.4 μm).

  The size of the first opening 18 is determined by how many observation regions are provided for various semiconductor laser elements. Therefore, it is not necessary to provide a large opening depending on the purpose of observation, but conversely, if it is too narrow, it becomes easy to overlook a defective part.

  Furthermore, as described above, in the present embodiment, the first conductivity type electrode 17 may be formed on both sides of the region corresponding to the ridge stripe 12 on the GaN substrate 4 and not formed in the region. The first conductivity type electrode 17 does not necessarily have a structure having the first opening 18.

  FIG. 3B is another example of the first conductivity type electrode in the present embodiment, and corresponds to a perspective view seen from the back side of the GaN substrate 4 in FIG. In FIG. 3B, the first conductivity type electrode 17 is not provided in the region A corresponding to the ridge stripe 12 on the GaN substrate 4. In other words, the first conductivity type electrode 17 is continuously provided in parallel with the ridge stripe 12 and between two opposing sides on the GaN substrate 4. The back surface of the GaN substrate 4 is divided into two locations with the first opening 18 as a boundary, and as a result, the first conductivity type electrodes 17 are formed on both sides of the first opening 18. Even with such a structure, EL light can be observed through the region A. Therefore, failure analysis can be performed without removing the GaN substrate 4.

  In the present embodiment, the first conductivity type electrode 17 is formed in a line-symmetric shape at a position corresponding to the ridge stripe 12 on the GaN substrate 4 to further alleviate the above-described stress non-uniformity. . That is, in FIG. 3B, the shape can be symmetric with the line symmetry axis of the region A as the reference axis. In this case, various physical loads can be received almost uniformly on both sides of the ridge stripe 12. Therefore, it is possible to more effectively prevent the above-described influence on the optical characteristics and the life reduction. Further, by forming the first opening 18 in a shape similar to the above-described mapping, the objectivity with respect to the ridge stripe 12 can be further enhanced, and a greater effect can be obtained.

  In some cases, Au plating or the like is further laminated on the first conductivity type electrode 17 as a thick film electrode. This Au plating has a film thickness of about 2 μm to 4 μm and is provided for the purpose of facilitating wire bonding, for example. At this time, the first opening 18 is provided in the Au plating or the like similarly to the first conductivity type electrode 17.

(Embodiment 2)
The second embodiment is different from the first embodiment in the structure of the first conductivity type electrode on the back side of the GaN substrate 4.

  FIG. 4 is a cross-sectional view of the semiconductor laser in the present embodiment. In this embodiment, a nitride blue semiconductor laser is taken as an example of the semiconductor laser. Moreover, what is shown with the same code | symbol as FIG. 1 is the same as the structure demonstrated in 1st embodiment.

  In FIG. 4, the first conductivity type GaN buffer layer 5 to the second conductivity type electrode 16 are formed on the main surface of the GaN substrate 4 as in the first embodiment. The present embodiment is a nitride-based blue semiconductor laser, which has an SCH structure in which an active layer is sandwiched between first-conductivity-type and second-conductivity-type light guide layers, but the present invention is not necessarily limited thereto. It is not limited.

  In the present embodiment, the first conductivity type light transmission electrode 19 is formed in a region including a position corresponding to the ridge stripe 12 on the back surface of the GaN substrate 4. The first conductivity type light transmitting electrode 19 transmits light having an emission peak wavelength in the blue semiconductor laser of the present embodiment. Since the present embodiment is a blue light emitting laser using a GaN substrate, the first conductivity type light transmissive electrode 19 can have a transmittance of 10% or more with respect to light having a wavelength of 300 nm to 500 nm.

  The first conductive light transmissive electrode 19 may be an electrode made of a transparent electrode material, or may be an electrode having a film thickness that transmits the light. In the former case, the first conductivity type light transmitting electrode 19 can be an electrode made of ITO or ZnO. On the other hand, in the latter case, the first conductivity type light transmissive electrode 19 may have a structure in which, for example, Ti and Au are sequentially laminated, and the total film thickness may be 500 mm (50 nm) or less. Note that the first conductive type light transmissive electrode 19 can be similarly formed by appropriately determining the film thickness when using various conductive materials other than the Ti / Au film.

  According to the above structure, even if the first conductivity type electrode is formed in the region corresponding to the ridge stripe 12, the EL light is transmitted through the electrode, so the EL light is observed from the back side of the GaN substrate 4. be able to. On the other hand, according to the structure in which the first conductive type light transmitting electrode 19 exists including the position corresponding to the ridge stripe 12, injected electrons are not biased and supplied to one side of the ridge stripe 12. That is, electrons are injected from both sides of the ridge stripe 12 directly below and in the vicinity of the ridge stripe 12. Therefore, similarly to the first embodiment, EL light emission observation, that is, failure analysis can be performed on the peripheral regions on both sides of the ridge stripe 12.

  Furthermore, since the first conductive type light transmissive electrode 19 is present including the position corresponding to the ridge stripe 12, the stress becomes non-uniform around the ridge stripe 12 as in the first embodiment. Can also be prevented.

  Next, a method for manufacturing the nitride semiconductor laser according to the present embodiment will be described.

  In FIG. 4, the method of stacking the first conductivity type buffer layer 5 to the second conductivity type electrode 16 on the GaN substrate 4 is the same as that described in the first embodiment.

  In the case where a metal thin film is formed as the first conductivity type light transmitting electrode 19 on the back side of the GaN substrate 4, for example, in the case of a structure in which Ti and Au are sequentially laminated, it is manufactured by a vacuum deposition method or the like. Thereafter, an alloy process is performed to make the first conductivity type ohmic contact. On the other hand, when a transparent electrode such as ITO or ZnO is used as the first conductivity type light transmitting electrode 19, it can be produced by, for example, a sputtering method. In this case, since the influence of the film thickness on the light transmittance is small, there is an advantage that the tolerance does not have to be so severe when manufacturing.

  The semiconductor laser manufactured in this way can be analyzed for defects using the EL method as follows.

  In the case of junction down mounting, as in the first embodiment, soldering is performed with the second conductivity type electrode 16 on the package side. Thereafter, a current is passed between the second conductivity type electrode 16 and the light transmission electrode 19 in the same manner as when the laser is driven. At this time, the current is confined in the ridge stripe 12, and recombination of holes and electrons concentrates in the active layer 8, and EL emission is observed.

  As shown in FIG. 5, in the second embodiment, a thick film electrode 20 can be provided to facilitate wire bonding to the n light transmitting electrode 19 side.

  In this case, the thick film electrode 20 is not formed at the position corresponding to the ridge stripe 12 on the light transmission electrode 19, and the first opening 18 is provided as in the first embodiment. For example, as shown in FIG. 6, such a structure can be realized by forming a Ti / Au film having a thickness of 500 mm or less as the light transmission electrode 19 by a vacuum deposition method and forming a gold plating layer as the thick film electrode 20.

  In the present embodiment, the following modifications can be made.

  By making the transmittance of the light transmission electrode 19 with respect to the emission peak wavelength 10% or more, the EL light can be observed more effectively. In the EL method, the above-described light emission distribution is measured, and the presence or absence of an abnormal dark area is confirmed. Here, since the transmittance of the light transmissive electrode 19 is low, if the intensity of the transmitted light becomes too weak, it becomes difficult to measure the light emission distribution described above. In this case, the position of the dark area, that is, the position of the dislocation causing the defect cannot be specified with high accuracy. Although depending on the observation apparatus, it is generally desirable for analysis that at least 10% to 20% of the light emitted from the active layer 8 is obtained.

  In the present embodiment, a nitride blue semiconductor laser has been described. However, the present invention is not necessarily limited to this. If the material, film thickness, etc. of the first conductivity type light transmissive electrode 19 are determined so as to be transmissive to each peak wavelength for various semiconductor lasers using a light transmissive semiconductor substrate, the same applies. The effect of can be obtained. For example, an InP communication laser or the like may have a structure that is transparent to light with a wavelength of 1300 nm to 1550 nm, for example.

(Embodiment 3)
This embodiment is different from the first and second embodiments in that an opening is provided in the upper surface portion of the ridge stripe 12 in the second conductivity type electrode 16.

  FIG. 7 is a cross-sectional view of the semiconductor laser in the present embodiment. In this embodiment, a nitride blue semiconductor laser is taken as an example of the semiconductor laser. Moreover, what is shown with the same code | symbol as FIG. 1 is the same as the structure demonstrated in 1st embodiment.

  In FIG. 7, as in the first embodiment, the first conductive type GaN buffer layer 5 to the second conductive type electrode 16 are formed on the main surface of the GaN substrate 4.

  A first conductivity type electrode 17 is provided on the back surface of the GaN substrate 4 so as to include a position corresponding to the ridge stripe 12. In the present embodiment, it is formed on the entire back surface of the GaN substrate 4.

  This embodiment is characterized in that an opening is provided in a part of the upper surface of the ridge stripe 12 in the second conductivity type electrode 16 and the second conductivity type GaN contact layer 11 is exposed to the outside. However, it is assumed that the second conductivity type GaN contact layer 11 and the second conductivity type electrode 16 always overlap in a part of the region and are electrically connected.

  With the above structure, junction-up mounting can be performed, and EL light can be observed through the first opening 15. In this case, like the second opening 18 in the first embodiment, the first opening 15 serves as an observation window. Therefore, it is not necessary to re-mount a product once mounted at junction-up again at junction-down for failure analysis.

  Also in this structure, as in the first embodiment, since the first conductivity type light transmitting electrode 19 exists including the position corresponding to the ridge stripe 12, the injected electrons are biased to one side of the ridge stripe 12. Not supplied. Therefore, as described above, EL light emission observation, that is, failure analysis can be performed not only immediately below the ridge stripe 12 but also in the peripheral regions on both sides thereof.

  Further, as in the first embodiment, since the first conductivity type light transmission electrode 19 exists including the position corresponding to the ridge stripe 12, the stress does not become uneven around the ridge stripe 12.

  Next, the manufacturing method of the present embodiment will be described.

  First, in accordance with the manufacturing method of the first embodiment, the first conductivity type buffer layer 5 to the second conductivity type electrode 16 are laminated on the GaN substrate 4. Thereafter, a part of the second conductivity type electrode 16 is removed by etching or the like, and at least a part of the upper surface of the ridge stripe 12 is exposed. Etching means can be appropriately selected from wet etching and dry etching.

(Embodiment 4)
The present embodiment is different from the first and second embodiments in that a second conductivity type light transmission electrode is provided as the second conductivity type electrode.

  FIG. 8 is a cross-sectional view of the semiconductor laser in the present embodiment. In this embodiment, a nitride blue semiconductor laser is taken as an example of the semiconductor laser. Moreover, what is shown with the same code | symbol as FIG. 1 is the same as the structure demonstrated in 1st embodiment.

  In FIG. 8, as in the first embodiment, the first conductivity type GaN buffer layer 5, the first conductivity type cladding layer 6, the first conductivity type GaN light guide layer 7, the active layer 8, on the main surface of the GaN substrate 4; A second conductivity type AlGaN electron barrier layer 3, a second conductivity type GaN light guide layer 9 as a second electrode side guide layer, a second conductivity type AlGaN cladding layer 10, and a second conductivity type GaN contact layer 11 are sequentially stacked. Has been. Further, a ridge stripe 12, an insulating film 14, and a second opening 15 are provided.

  Here, on the second opening 15, a second conductivity type light transmitting electrode 21 is formed. The second conductivity type electrode 21 is formed on the entire top surface of the ridge stripe 12.

  A first conductivity type electrode 17 is provided on the back surface of the GaN substrate 4 so as to include a position corresponding to the ridge stripe 12. In the present embodiment, it is formed on the entire back surface of the GaN substrate 4.

  With the above structure, junction-up mounting can be performed, and EL light can be observed through the second conductivity type light transmitting electrode 21 as in the second embodiment. In this case, the second conductivity type light transmissive electrode 21 transmits EL light emission. That is, it has the same effect as the first conductivity type light transmitting electrode in the second embodiment. Therefore, it is possible to analyze non-destructively a product mounted by junction-up.

  Also in this structure, as in the first embodiment, since the first conductivity type light transmitting electrode 19 exists including the position corresponding to the ridge stripe 12, the injected electrons are biased and supplied to one side of the ridge stripe 12. It will not be done. Therefore, as described above, EL light emission observation, that is, failure analysis can be performed not only immediately below the ridge stripe 12 but also in the peripheral regions on both sides thereof.

  Further, as in the first embodiment, since the first conductivity type light transmission electrode 19 exists including the position corresponding to the ridge stripe 12, the stress does not become uneven around the ridge stripe 12.

  An example of the manufacturing method of Embodiment 4 is as follows.

  First, in accordance with the manufacturing method of the first embodiment, the first conductive type buffer layer 5 to the second opening 15 are formed on the GaN substrate 4. Thereafter, the second conductivity type light transmissive electrode 21 is formed by sequentially laminating, for example, Pd and Au films using a vacuum deposition method, a sputtering method, or the like. At this time, by appropriately adjusting the film thickness, a structure having transparency to EL light can be obtained as in the case of the first conductivity type light transmitting electrode 19 in the second embodiment.

  Furthermore, in order to facilitate the observation of the EL light, the light transmittance of the second conductive light transmissive electrode 21 with respect to the EL light can be 10% or more.

  Moreover, as the second conductivity type light transmitting electrode 21, ITO, ZnO, SnO, or the like as a transparent electrode can be used. When these transparent electrodes are used, there is an advantage that the tolerance of the film thickness does not have to be tightened during the production.

(Embodiment 5)
In the first to fourth embodiments, the semiconductor laser that can analyze defects by observing the light emitted from the active layer without etching the substrate has been described. As described in the above embodiment, this semiconductor laser is evaluated for a semiconductor laser element in which each semiconductor layer or electrode is formed on a semiconductor wafer, then cleaved to form a bar, and further formed into chips. be able to. However, the present invention is not limited to this method, and the characteristics of the semiconductor laser element can be evaluated at a stage before cleaving, that is, in a wafer state. According to the latter method, it is possible to determine whether or not an element in which a defect has occurred is assembled before being formed into chips, so the range in which many defective products are generated on the wafer is divided into bars. Therefore, it is possible to simplify the process. Therefore, in the present embodiment, a method for manufacturing a semiconductor laser using the latter method and an evaluation apparatus for evaluating the characteristics of the semiconductor laser element will be described.

  The manufacturing method of the semiconductor laser in the present embodiment includes the following steps.

  First, a first conductive type semiconductor layer, an active layer, and a second conductive type semiconductor layer are sequentially formed on the surface of a light-transmitting first conductive type semiconductor wafer. Next, after processing a part of the second conductivity type semiconductor layer to form a ridge portion, a second conductivity type electrode is formed on the second conductivity type semiconductor layer. Next, after forming a first conductivity type electrode on the back surface of the semiconductor wafer, an opening is formed at a position corresponding to the ridge portion of the first conductivity type electrode.

  Specifically, the above steps can be performed in the same manner as in the first embodiment.

For example, a first conductivity type GaN buffer layer is grown on a GaN wafer as a semiconductor wafer by metal organic chemical vapor deposition (MOCVD). Thereafter, the first conductivity type AlGaN cladding layer and the undoped InGaN optical guide layer are successively grown by MOCVD. The growth temperature can be 1000 ° C. for all. Further, an undoped In _x Ga _1-x N / In _y Ga _1-y N multiple quantum well active layer is grown at 740 ° C. by the same MOCVD method.

  Next, a second conductivity type AlGaN electron barrier layer, a second conductivity type GaN light guide layer, a second conductivity type AlGaN cladding layer, a second conductivity type AlGaN cladding layer, and a second conductivity type GaN contact layer are sequentially stacked by MOCVD. To do. The growth temperature can be 1000 ° C. for all.

  After the above crystal growth is completed, a resist is applied on the entire GaN wafer to form a resist pattern corresponding to the shape of the mesa portion. Using this resist pattern as a mask, the second conductivity type AlGaN cladding layer and the second conductivity type GaN contact layer are etched by RIE, for example, to form a ridge portion which is an optical waveguide.

After the etching step, an SiO ₂ film is formed on the entire surface of the GaN wafer by the CVD method, the vacuum evaporation method, the sputtering method, or the like while leaving the resist pattern used as a mask. Subsequently, the SiO ₂ film on the ridge stripe is removed simultaneously with the removal of the resist pattern by lift-off.

Next, a Pt film and an Au film are sequentially formed on the second conductivity type GaN contact layer and the SiO ₂ film by a vacuum deposition method or the like. Thereafter, a resist is applied and lithography is performed to form an electrode pattern. Finally, unnecessary Pt film and Au film are removed by wet etching or dry etching. Thereby, a second conductivity type electrode can be formed on the second conductivity type GaN contact layer.

  Next, a first conductivity type electrode is formed on the back surface of the GaN wafer. For example, a Ti film and an Au film are sequentially formed on the back surface of the GaN wafer by vacuum deposition. Subsequently, a resist is applied thereon and lithography is performed. Thereafter, an electrode pattern is formed by wet etching or dry etching. At this time, the Ti film and Au film at the position corresponding to the ridge portion are removed, and an opening is formed in the first conductivity type electrode. Thereby, a structure in which the first conductivity type electrodes are provided on both sides of the opening, that is, a structure similar to that of FIG. 1 of the first embodiment is obtained.

  Through the above steps, a plurality of semiconductor laser elements are formed on the semiconductor wafer. This is shown in FIG.

  FIG. 9 is a schematic plan view of the semiconductor wafer as viewed from the side of the first conductivity type electrode. In the figure, 141 is a semiconductor wafer, 142 is a first conductivity type electrode, 143 is an opening, and 146 is a semiconductor laser element. In this figure, the outer shape of the region in which the semiconductor laser element is provided is rectangular, but the present invention is not limited to this and may have other shapes.

  In the present embodiment, electrical characteristics and optical characteristics are evaluated for each of the semiconductor laser elements in the state of FIG. Specifically, it can be performed using the evaluation apparatus shown in FIG.

  In FIG. 10, the evaluation apparatus 201 includes a first electrode plate 202, a second electrode plate 203, and a voltage source 204 connected to them. Here, the first electrode plate 202 has a shape capable of contacting the first conductivity type electrode of the semiconductor laser element, and the second electrode plate 203 is the second conductivity type electrode of the semiconductor laser element. It has a shape that can be touched. However, the first electrode in the present invention corresponds to the first conductivity type electrode, and the second electrode in the present invention corresponds to the second conductivity type electrode. In the present embodiment, a current source may be used instead of the voltage source 204.

  The first electrode plate 202 includes a region that transmits light emitted from the semiconductor laser element. For example, the first electrode plate 202 can be a sapphire substrate on the surface of which a thin film containing at least one metal element and having a transmittance of more than 10% at a wavelength of 395 nm to 410 nm is formed. Specifically, a sapphire substrate on which a thin film of indium tin oxide (ITO) is formed can be given.

  When performing the evaluation, as shown in FIG. 10, first, the first electrode plate 202 is brought into contact with the first conductivity type electrode of the semiconductor laser element (not shown) formed on the semiconductor wafer 205, The second electrode plate 203 is brought into contact with the second conductivity type electrode of the semiconductor laser element. Next, when a voltage is supplied from the voltage source 204, a voltage is simultaneously applied to the entire semiconductor laser element via the first electrode plate 202 and the second electrode plate 203. Then, light emission occurs in the active layer of each semiconductor laser element, and the emitted light is observed through the opening provided in the first conductivity type electrode and the first electrode plate 202. By receiving this emitted light by the light receiving device 206, the optical characteristics of each semiconductor laser element can be evaluated.

  The light receiving device 206 includes an optical microscope (not shown) for observing the light emitting region and the spatial uniformity of light emission on the semiconductor wafer 205, and a light receiving element having sensitivity in the wavelength range of light emitted from the semiconductor laser element. (Not shown). As the light receiving element, for example, a CCD having sensitivity at a wavelength of 395 nm to 410 nm can be used. Moreover, it is preferable that the light receiving element further includes a spectroscope that splits the emitted light.

  In the present embodiment, the intensity of the light of each semiconductor laser element received by the light receiving device 206 is sent to the storage device 207, and the semiconductor laser element having an intensity equal to or less than a predetermined value is stored in the storage device 207. However, a semiconductor laser element having an intensity equal to or less than a predetermined value may be selected in advance by a light receiving device, and only data relating to the selected semiconductor laser element may be sent to the storage device 207. It should be noted that the semiconductor laser element having an intensity of a predetermined value or less includes a semiconductor laser element that does not emit light at all. In this way, by extracting data from the storage device 207, it is possible to grasp the location where a defect has occurred on the semiconductor wafer 205. Therefore, it is not necessary to apply a process of dividing the wafer into bars or assembling chips at this location.

  Further, in the present embodiment, as shown in FIG. 10, by providing an ammeter 208 and a voltmeter 209, the electrical characteristics of the semiconductor laser element can be measured. Then, by sending the measured data to the storage device 207 and causing the storage device 207 to store semiconductor laser elements having a value equal to or less than a predetermined value, defects occur on the semiconductor wafer 205 as in the case of optical characteristics. You can see where it is. Therefore, it is not necessary to apply a process of dividing the wafer into bars or assembling chips at this location.

  As described above, according to the manufacturing method of the semiconductor device of the present embodiment, the characteristics of the semiconductor laser element can be evaluated in the wafer state. Further, according to the evaluation apparatus of the present embodiment, it is possible to determine whether the characteristics of the semiconductor laser element in the wafer state are good or bad.

  Note that the present invention is not limited to the present embodiment, and various modifications can be made without departing from the spirit of the present invention.

  For example, in the above embodiment, the openings are provided at all positions corresponding to the ridge portion of the first conductivity type electrode, but the first conductivity type electrode is opened at a position corresponding to a part of the ridge portion. A part may be provided. For example, as shown in FIG. 11, one opening 113 can be provided for each predetermined unit area of the first conductivity type electrode 112. The semiconductor wafer 111 is provided with a plurality of semiconductor laser elements 116. By providing the opening 113 as described above, the semiconductor laser element 116 may or may not have the opening 113. Will be mixed. In this case, the semiconductor laser element 116 can be evaluated as follows.

  First, as described in FIG. 10, the first electrode plate and the second electrode plate of the evaluation apparatus are brought into contact with the first conductivity type electrode and the second conductivity type electrode of the semiconductor laser element, respectively. Next, a voltage is supplied from a voltage source, and a voltage is simultaneously applied to the entire semiconductor laser element via the first electrode plate and the second electrode plate. At this time, the voltage may be applied only to the entire semiconductor laser element having the opening.

  In a semiconductor laser element to which a voltage is applied, light emission occurs in the active layer. The emitted light is observed through an opening provided in the first conductivity type electrode and the first electrode plate. Therefore, the optical characteristics of the semiconductor laser element can be evaluated by receiving the emitted light with the light receiving device.

  In the configuration in which the opening is provided at a position corresponding to a part of the ridge portion in the first conductivity type electrode, the semiconductor laser element having the opening and the semiconductor laser element having no opening are mixed. Here, in the semiconductor laser element in which no opening is provided, the emitted light generated in the active layer cannot be observed. Therefore, when this configuration is evaluated, the distribution of defects on the semiconductor wafer can be grasped, but the defects of individual semiconductor laser elements cannot be grasped. However, many defects occur with a distribution. That is, there are many semiconductor laser elements having similar defects around the defective semiconductor laser element. For example, such distribution is seen in the case of defects due to the non-uniformity of the etchant in the etching process. Therefore, even in the configuration in which the opening is provided in a part of the first conductivity type electrode, it is possible to grasp to some extent the location where the defect has occurred on the semiconductor wafer. It is possible to select in advance semiconductor laser elements to be divided into two or assembled. If one opening is provided for each predetermined unit area of the first conductivity type electrode, the openings can be uniformly distributed on the semiconductor wafer, so that it is easy to grasp the defective portion.

  Further, in the above embodiment, the opening is provided in the first conductivity type electrode. However, as shown in FIG. 3B of the first embodiment, on both sides of the region corresponding to the ridge portion on the back surface of the semiconductor wafer. A structure may be adopted in which a first conductivity type electrode is provided and the first conductivity type electrode is not provided in this region. This structure is obtained by forming the first conductivity type electrode on the back surface of the semiconductor wafer and then removing the electrode in the region corresponding to the ridge portion. Also in this case, since the emitted light can be observed through the region where the first conductivity type electrode is not provided, the semiconductor laser element can be evaluated in the same manner as described above. An example is shown in FIG. In this figure, 121 is a semiconductor wafer, 122 is a first conductivity type electrode, and 126 is a semiconductor laser element. The region 123 is a portion where the first conductivity type electrode 122 is not provided.

  The region where the first conductivity type electrode is not provided may be a region corresponding to a part of the ridge portion on the back surface of the semiconductor wafer. For example, as shown in FIG. 13, for each predetermined unit area of the first conductivity type electrode 132, a region where the electrode is removed can be provided. The semiconductor wafer 131 is provided with a plurality of semiconductor laser elements 136. By removing the first conductivity type electrode 132 as described above, the semiconductor laser element 136 has a region corresponding to the ridge portion. Those in which the first conductivity type electrode 132 is not formed and those in which the electrode 132 is formed are mixed.

  The structure shown in FIG. 13 is obtained by forming the first conductivity type electrode on the back surface of the semiconductor wafer and then removing the electrode in the region corresponding to a part of the ridge portion. In this case, the emitted light of the semiconductor laser element in the region where the first conductivity type electrode is not removed cannot be observed. Therefore, although the distribution of defects on the semiconductor wafer is obtained by the evaluation, semiconductor laser elements to be divided into bars or assembled should be selected in advance as in the structure of FIG. Is enough. In addition, if one region from which the first conductivity type electrode is removed is provided for each predetermined unit area of the first conductivity type electrode, this region can be uniformly distributed on the semiconductor wafer. It becomes easy to grasp the defective part.

  Further, in the present embodiment, the first conductivity type electrode may be an electrode having optical transparency. Specifically, a structure similar to that described in Embodiment 2 can be employed. According to this structure, the emitted light of the semiconductor laser element can be observed without providing the opening. The first conductivity type electrode may be, for example, an electrode made of a transparent electrode material or an electrode having a film thickness that allows light to pass through. Note that light may be transmitted through a part of the first conductivity type electrode. In this case, since the emitted light from the semiconductor laser element having an electrode through which light does not pass cannot be observed, the result obtained by the evaluation is a distribution of defects on the semiconductor wafer, but it is divided into bars or assembled It is sufficient to select in advance the semiconductor laser elements to be performed.

  The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

  For example, in the first and second embodiments, the nitride semiconductor laser using GaN as a substrate has been described. However, even when a material other than GaN is used, the structure of the present invention can be used as long as the semiconductor laser structure has a transparent substrate. By using the same effect, the same effect can be obtained.

  In Embodiments 3 and 4, the effects of the present invention can be obtained regardless of the type of substrate.

  In addition, the effect of the present invention can be obtained even when the back surface of the GaN substrate is inclined or uneven, has a curved surface portion, or has a ridge stripe shape different from the embodiment. The same applies to a structure having a plurality of ridge stripes such as a monolithic structure.

2 is a cross-sectional view of the semiconductor laser in the first embodiment. FIG. 2 is an example of a cross-sectional view of the semiconductor laser in the first embodiment. FIG. (A) is an example of the perspective view of the semiconductor laser in Embodiment 1, (b) is another example. FIG. 4 is an example of a cross-sectional view of a semiconductor laser in a second embodiment. FIG. 12 is another example of a cross-sectional view of the semiconductor laser in the second embodiment. FIG. 4 is an example of a cross-sectional view of a semiconductor laser in a second embodiment. FIG. 6 is a cross-sectional view of a semiconductor laser according to a third embodiment. FIG. 6 is a cross-sectional view of a semiconductor laser in a fourth embodiment. In Embodiment 5, it is an example of the top view of the semiconductor laser element formed on the semiconductor wafer. FIG. 10 is a configuration diagram of an evaluation device in a fifth embodiment. In Embodiment 5, it is another example of the top view of the semiconductor laser element formed on the semiconductor wafer. In Embodiment 5, it is another example of the top view of the semiconductor laser element formed on the semiconductor wafer. In Embodiment 5, it is another example of the top view of the semiconductor laser element formed on the semiconductor wafer. (A) And (b) is a figure which shows the defect analysis method in a GaAs type semiconductor laser.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st 2nd conductivity type clad layer 2 2nd 2nd conductivity type clad layer 3 2nd conductivity type AlGaN electron barrier layer 4 GaN substrate 5 1st conductivity type GaN buffer layer 6 1st conductivity type AlGaN clad layer 7 1st One conductivity type GaN light guide layer 8 Active layer 9 Second conductivity type GaN light guide layer 10 Second conductivity type AlGaN cladding layer 11 Second conductivity type GaN contact layer 12 Ridge stripe 14 Insulating film 15 Second opening 16 Second conductivity Type electrode 17 First conductive type electrode 18 First opening 19 First conductive type light transmitting electrode 20 Thick film electrode 21 Second conductive type light transmitting electrodes 141, 111, 121, 131, 205 Semiconductor wafers 142, 112, 122, 132 First-conductivity-type electrodes 143, 113 Openings 146, 116, 126, 136 Semiconductor laser device 201 Evaluation device 202 First electrode plate 203 Second Electrode plates 204 voltage source 206 receiving device 207 storage device 208 ammeter 209 voltmeter

Claims (32)

A first conductivity type semiconductor substrate having optical transparency;
A first conductivity type semiconductor layer formed on the surface of the semiconductor substrate;
An active layer formed on the semiconductor layer of the first conductivity type;
A second conductivity type semiconductor layer formed on the active layer;
A ridge formed in the semiconductor layer of the second conductivity type;
A second conductivity type electrode formed on the second conductivity type semiconductor layer;
Comprising a first conductivity type electrode formed on the back surface of the semiconductor substrate;
The semiconductor laser according to claim 1, wherein the first conductivity type electrode has an opening at a position corresponding to the ridge portion of the semiconductor substrate. A first conductivity type semiconductor substrate having optical transparency;
A first conductivity type semiconductor layer formed on the surface of the semiconductor substrate;
An active layer formed on the semiconductor layer of the first conductivity type;
A second conductivity type semiconductor layer formed on the active layer;
A ridge formed in the semiconductor layer of the second conductivity type;
A second conductivity type electrode formed on the second conductivity type semiconductor layer;
Comprising a first conductivity type electrode formed on the back surface of the semiconductor substrate;
The semiconductor laser according to claim 1, wherein the first conductivity type electrode is formed on both sides of a region corresponding to the ridge portion and is not formed in the region.   The semiconductor laser according to claim 1, wherein the semiconductor substrate is a GaN substrate. A first conductivity type semiconductor substrate having optical transparency;
A first conductivity type semiconductor layer formed on the surface of the semiconductor substrate;
An active layer formed on the semiconductor layer of the first conductivity type;
A second conductivity type semiconductor layer formed on the active layer;
A ridge formed in the semiconductor layer of the second conductivity type;
A second conductivity type electrode formed on the second conductivity type semiconductor layer;
A first conductivity type electrode formed on the back surface of the semiconductor substrate including a position corresponding to the ridge portion of the semiconductor substrate;
The semiconductor electrode according to claim 1, wherein the first conductivity type electrode transmits light emitted from the active layer at the position.   The semiconductor laser according to claim 4, wherein the first conductivity type electrode at the position is made of a transparent electrode material.   The semiconductor laser according to claim 4, wherein the first conductivity type electrode at the position has a thickness through which the light is transmitted.   The semiconductor laser according to claim 4, wherein the semiconductor substrate is a GaN substrate.   The semiconductor laser according to claim 7, wherein the first conductivity type electrode has a transmittance of 10% or more with respect to light having a dominant wavelength of 300 nm to 500 nm. A first conductivity type semiconductor substrate;
A first conductivity type semiconductor layer formed on the surface of the semiconductor substrate;
An active layer formed on the semiconductor layer of the first conductivity type;
A second conductivity type semiconductor layer formed on the active layer;
A ridge formed in the semiconductor layer of the second conductivity type;
At least a second conductivity type electrode formed on the upper surface of the ridge portion;
A first conductivity type electrode formed on the back surface of the semiconductor substrate including a position corresponding to the ridge portion of the semiconductor substrate;
The semiconductor laser according to claim 2, wherein the second conductivity type electrode has an opening in a part of the upper surface of the ridge portion.   The semiconductor laser according to claim 9, wherein the semiconductor substrate is a GaN substrate. A first conductivity type semiconductor substrate;
A first conductivity type semiconductor layer formed on the surface of the semiconductor substrate;
An active layer formed on the semiconductor layer of the first conductivity type;
A second conductivity type semiconductor layer formed on the active layer;
A ridge formed in the semiconductor layer of the second conductivity type;
At least a second conductivity type electrode formed on the upper surface of the ridge portion;
A first conductivity type electrode formed on the back surface of the semiconductor substrate including a position corresponding to the ridge portion of the semiconductor substrate;
The second conductivity type electrode transmits light emitted from the active layer in the ridge portion.   The semiconductor laser according to claim 11, wherein the second conductivity type electrode on the upper surface of the ridge portion is made of a transparent electrode material.   The semiconductor laser according to claim 11, wherein the second conductivity type electrode on the upper surface of the ridge portion has a thickness through which the light is transmitted.   The semiconductor laser according to claim 11, wherein the semiconductor substrate is a GaN substrate.   The semiconductor laser according to claim 14, wherein the second conductivity type electrode has a transmittance of 10% or more with respect to light having a dominant wavelength of 300 nm to 500 nm. Forming a first conductive type semiconductor layer, an active layer and a second conductive type semiconductor layer in order on the surface of the first conductive type semiconductor wafer having optical transparency;
Processing the second conductivity type semiconductor layer to form a ridge portion;
Forming a second conductivity type electrode on the second conductivity type semiconductor layer;
Forming a first conductivity type electrode on the back surface of the semiconductor wafer;
Forming openings at all positions corresponding to the ridge portion of the first conductivity type electrode;
For each of a plurality of semiconductor laser elements formed on the semiconductor wafer, a step of applying a voltage via the first conductivity type electrode and the second conductivity type electrode to evaluate characteristics;
And a step of dividing the semiconductor wafer into a plurality of bars after evaluating the characteristics.   The step of evaluating the characteristics includes contacting a first electrode plate having a light-transmitting region with the first conductivity type electrode and a second electrode plate with the second conductivity type electrode. A voltage is simultaneously applied to the whole of the plurality of semiconductor laser elements through the first electrode plate and the second electrode plate, and the light emitted from the active layer is transmitted to the opening and the first electrode plate. The method of manufacturing a semiconductor laser according to claim 16, comprising a step of observing through the semiconductor laser. Forming a first conductive type semiconductor layer, an active layer and a second conductive type semiconductor layer in order on the surface of the first conductive type semiconductor wafer having optical transparency;
Processing the second conductivity type semiconductor layer to form a ridge portion;
Forming a second conductivity type electrode on the second conductivity type semiconductor layer;
Forming a first conductivity type electrode on the back surface of the semiconductor wafer;
Removing the first conductivity type electrode in all regions corresponding to the ridge portion on the back surface of the semiconductor wafer;
For each of a plurality of semiconductor laser elements formed on the semiconductor wafer, a step of applying a voltage via the first conductivity type electrode and the second conductivity type electrode to evaluate characteristics;
Dividing the semiconductor wafer into a plurality of bars after evaluating the characteristics,
The method of manufacturing a semiconductor laser, wherein the first conductivity type electrode of the semiconductor laser element is formed on both sides of a region corresponding to the ridge portion and is not formed in the region.   The step of evaluating the characteristics includes contacting a first electrode plate having a light-transmitting region with the first conductivity type electrode and a second electrode plate with the second conductivity type electrode. A voltage is simultaneously applied to the whole of the plurality of semiconductor laser elements via the first electrode plate and the second electrode plate, and the light emitted from the active layer is applied to the ridge portion on the back surface of the semiconductor wafer. The method for manufacturing a semiconductor laser according to claim 18, comprising a step of observing through a corresponding region and the first electrode plate. Forming a first conductive type semiconductor layer, an active layer and a second conductive type semiconductor layer in order on the surface of the first conductive type semiconductor wafer having optical transparency;
Processing the second conductivity type semiconductor layer to form a ridge portion;
Forming a second conductivity type electrode on the second conductivity type semiconductor layer;
Forming a first conductivity type electrode on the back surface of the semiconductor wafer;
Forming an opening at a position corresponding to a part of the ridge portion in the first conductivity type electrode;
A step of evaluating characteristics of a plurality of semiconductor laser elements formed on the semiconductor wafer having the opening by applying a voltage via the first conductivity type electrode and the second conductivity type electrode. When,
And a step of dividing the semiconductor wafer into a plurality of bars after evaluating the characteristics.   21. The method of manufacturing a semiconductor laser according to claim 20, wherein the opening is provided for each predetermined unit area of the first conductivity type electrode.   The step of evaluating the characteristics includes contacting a first electrode plate having a light-transmitting region with the first conductivity type electrode and a second electrode plate with the second conductivity type electrode. The voltage is applied simultaneously to the entire semiconductor laser element formed on the wafer or the entire semiconductor laser element having the opening in the first electrode plate and the second electrode plate. 22. The method of manufacturing a semiconductor laser according to claim 20, further comprising a step of observing light emitted from the active layer through the opening and the first electrode plate. Forming a first conductive type semiconductor layer, an active layer and a second conductive type semiconductor layer in order on the surface of the first conductive type semiconductor wafer having optical transparency;
Processing the second conductivity type semiconductor layer to form a ridge portion;
Forming a second conductivity type electrode on the second conductivity type semiconductor layer;
Forming a first conductivity type electrode on the back surface of the semiconductor wafer;
Removing the first conductivity type electrode in a region corresponding to a part of the ridge portion on the back surface of the semiconductor wafer;
Among the plurality of semiconductor laser elements formed on the semiconductor wafer, the voltage in the region where the first conductivity type electrode is removed is applied via the first conductivity type electrode and the second conductivity type electrode. Applying and evaluating the characteristics;
Dividing the semiconductor wafer into a plurality of bars after evaluating the characteristics,
In the semiconductor laser device in the region where the first conductivity type electrode is removed, the first conductivity type electrode is formed on both sides of the region corresponding to the ridge portion, and is not formed in the region. A method for producing a semiconductor laser, comprising:   24. The method of manufacturing a semiconductor laser according to claim 23, wherein the region for removing the first conductivity type electrode is provided for each predetermined unit area of the first conductivity type electrode.   The step of evaluating the characteristics includes contacting a first electrode plate having a light-transmitting region with the first conductivity type electrode and a second electrode plate with the second conductivity type electrode. The semiconductor laser element formed on the semiconductor wafer via the first electrode plate and the second electrode plate, or a region in which the first conductivity type electrode is removed. 25. The method of manufacturing a semiconductor laser according to claim 24, further comprising the step of applying a voltage simultaneously to the entire semiconductor laser element and observing light emitted from the active layer through the region and the first electrode plate. Forming a first conductive type semiconductor layer, an active layer and a second conductive type semiconductor layer in order on the surface of the first conductive type semiconductor wafer having optical transparency;
Processing the second conductivity type semiconductor layer to form a ridge portion;
Forming a second conductivity type electrode on the second conductivity type semiconductor layer;
Forming a first conductivity type electrode having optical transparency on the back surface of the semiconductor wafer;
For each of a plurality of semiconductor laser elements formed on the semiconductor wafer, a step of applying a voltage via the first conductivity type electrode and the second conductivity type electrode to evaluate characteristics;
And a step of dividing the semiconductor wafer into a plurality of bars after evaluating the characteristics.   The step of evaluating the characteristics includes contacting a first electrode plate having a light-transmitting region with the first conductivity type electrode and a second electrode plate with the second conductivity type electrode. A voltage is simultaneously applied to the whole of the plurality of semiconductor laser elements through the first electrode plate and the second electrode plate, and light emitted from the active layer is transmitted to the first conductive type electrode and the first electrode plate. 27. The method of manufacturing a semiconductor laser according to claim 26, comprising a step of observing through one electrode plate. An evaluation apparatus for evaluating the characteristics of a plurality of semiconductor laser elements formed on a semiconductor wafer,
A first electrode plate having a shape that can contact the first electrode of the semiconductor laser element, and a region that transmits light emitted from the semiconductor laser element;
A second electrode plate having a shape capable of contacting the second electrode of the semiconductor laser element;
A current source or a voltage source connected to the first electrode plate and the second electrode plate;
A light receiving device that receives light emitted from the semiconductor laser element that has passed through the first electrode plate;
An evaluation apparatus comprising: a storage device for recording a semiconductor laser element in which the intensity of light received by the light receiving device is a predetermined value or less. A measuring device for measuring electrical characteristics of the semiconductor laser element;
The evaluation apparatus according to claim 28, wherein the storage device further includes a function of recording a semiconductor laser element whose value measured by the measurement device is equal to or less than a predetermined value.   The evaluation according to claim 28 or 29, wherein the first electrode plate is a sapphire substrate including at least one kind of metal element, and a thin film having a transmittance of more than 10% at a wavelength of 395 nm to 410 nm formed on a surface thereof. apparatus.   The evaluation apparatus according to claim 30, wherein the thin film is a thin film of indium tin oxide (ITO).   32. The evaluation apparatus according to claim 28, wherein the light receiving device includes a CCD having sensitivity at a wavelength of 395 nm to 410 nm.

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