JP5273459B2 - Manufacturing method of semiconductor laser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser capable of suppressing the displacement of the cleavage position and the extension of a small dislocation to an active layer, and to provide a method of manufacturing the same. <P>SOLUTION: A multi steps trench 45 including a trench 45A and a trench 45B formed in at least the trench 45A, is formed on a cleavage line L. The trenches 45A, 45B have strip shapes parallel to the cleavage line L, and are formed on a non-formation region of an upper electrode 32 and between ridge parts 20A formed on a wafer W of surfaces of wafer W. A substrate 10 is cleaved by using the multi steps trench 45 to form a front and a rear edge surfaces S1, S2 along the cleavage line L. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

The present invention relates to a method of manufacturing a semiconductor lasers having a cavity end face formed by cleavage.

  Nitride semiconductors such as GaN, AlGaN, and GaInN have a larger band gap than semiconductors that are already used in semiconductor lasers such as AlGaINAs and AlGaInP. Therefore, the nitride semiconductor laser is a laser that is expected to be widely used in light sources such as high-density optical disk devices, laser beam printers, and full-color displays.

  By the way, GaN used for a nitride semiconductor laser has a lower cleavage property than GaAs used for an infrared to red semiconductor laser. Therefore, in the manufacturing process, about 1 to 2% of defects due to cleavage line deviation occur. Moreover, it is known from observation with a scanning electron microscope (SEM) that a cross-section formed by cleavage has a minute step in the stacking direction. This minute step is considered to be caused by the difference in material hardness between the AlGaN layer used for the cladding layer and the active layer containing In. When such a fine fault occurs in the active layer portion of the cleavage plane, there is a problem that the light emission direction is changed by this fault.

  As a countermeasure against this minute fault, for example, it is conceivable to apply a technique described in Patent Document 1 to form a groove (width about 10 μm) having a depth of about 2 μm parallel to the cleavage line beside the ridge stripe. . This makes it possible to inhibit the fault from extending to the active layer.

Japanese Patent No. 3822976

  By the way, in order to suppress the shift of the cleavage position, for example, it is conceivable to reduce the width of the groove to about 1 μm. Certainly, by narrowing the width of the groove, it is possible to suppress the cleavage position shift and improve the yield. However, if the width of the groove is narrowed too much, the cleavage position is likely to be shifted from the groove, and once it is shifted, the formation of a fine fault on the cleaved cross section is suppressed. Will not be able to. However, if the width of the groove is increased, cleavage will occur in the range of the width of the groove, and the yield cannot be increased.

  As described above, in the conventional method, it is not easy to suppress the cleavage position from shifting and at the same time to prevent the minute fault from extending to the active layer.

The present invention has been made in view of the above problems, its object, at the same time to inhibit the cleavage position is shifted, producing fine fault of possible semiconductor lasers of suppressing extend into the active layer It is to provide a method.

The semiconductor laser of the reference example is provided with a laser structure portion having a pair of cleaved surfaces sandwiching the optical waveguide from the extending direction of the optical waveguide on the semiconductor substrate. The laser structure portion forms a semiconductor layer having an optical waveguide on the semiconductor substrate, and then forms a first groove parallel to the cleavage line on the surface of the semiconductor substrate on the semiconductor layer side, and at least the first layer The second groove is formed inside the groove to form a multistage groove including the first groove and the second groove, and the semiconductor substrate is cleaved using the multistage groove.

The semiconductor laser manufacturing method of the present invention includes the following two steps.
(A) After forming a semiconductor layer having a strip-shaped optical waveguide on a semiconductor substrate, a first groove that is parallel to the cleavage line and reaches the surface of the semiconductor substrate on the semiconductor layer side , A first step of forming a multistage groove including the first groove and the second groove by forming the second groove at least inside the first groove while forming on the surface of the semiconductor substrate on the semiconductor layer side. Step (B) A second step of forming a laser structure portion having a pair of cleavage surfaces that sandwich the optical waveguide from the extending direction of the optical waveguide by cleaving the semiconductor substrate using the multistage groove.

In the semiconductor laser of the reference example and the semiconductor laser manufacturing method of the present invention, a multistage groove including a first groove and at least a second groove provided inside the first groove is formed in the cleavage line. ing. Thereby, cleavage can be performed with high positional accuracy by the second groove having a width smaller than that of the first groove. Further, even when the cleavage position deviates from the second groove, the cleavage position comes inside the wide first groove. In addition, the first groove can prevent a fine fault that can occur on the cleavage plane during cleavage from extending to the active layer.

According to the semiconductor laser of the reference example and the semiconductor laser manufacturing method of the present invention , the cleavage line includes a multi-stage groove including a first groove and a second groove provided at least inside the first groove. Since it is formed, it is possible to suppress the cleavage position from being shifted, and at the same time, it is possible to suppress the minute fault from extending to the active layer.

Hereinafter, the best mode for carrying out the present invention (hereinafter simply referred to as an embodiment) will be described in detail with reference to the drawings. The description will be given in the following order.

1. Embodiment (there is a second groove only inside the first groove)
2. Modified example (variation of positional relationship between the first groove and the second groove)

[Structure of semiconductor laser 1]
FIG. 1 is a perspective view showing a schematic configuration of a semiconductor laser 1 according to a first embodiment of the present invention. FIG. 1 is a schematic representation, which differs from actual dimensions and shapes.

  In the semiconductor laser 1 of the present embodiment, as will be described in detail later, the band-shaped ridge portion 20A (optical waveguide) is separated from the resonator direction (the extending direction of the ridge portion 20A) by a pair of front end surface S1 and rear end surface S2. It is a so-called edge-emitting semiconductor laser with a sandwiched structure. The semiconductor laser 1 includes, for example, a semiconductor layer 20 (laser structure portion) including a lower cladding layer 21, an active layer 22, an upper cladding layer 23, and a contact layer 24 in this order from the substrate 10 on a substrate 10 (semiconductor substrate). It is equipped with. Note that the semiconductor layer 20 may be further provided with a layer (for example, a buffer layer or a guide layer) other than the above-described layers.

  The substrate 10 is made of a group III-V nitride semiconductor such as GaN, for example. Here, the “III-V nitride semiconductor” means at least one of the group 3B elements in the short period periodic table, and at least N of the group 5B elements in the short period periodic table. Points to things that contain Examples of the III-V nitride semiconductor include gallium nitride compounds containing Ga and N. Examples of the gallium nitride compound include GaN, AlGaN, AlGaInN, and the like. For group III-V nitride semiconductors, an n-type impurity of a group IV or VI element such as Si, Ge, O, or Se, or a group II or group IV element such as Mg, Zn, or C, if necessary. A p-type impurity is doped.

  The semiconductor layer 20 includes, for example, a group III-V nitride semiconductor mainly. The lower cladding layer 21 is made of, for example, AlGaN. The active layer 22 has, for example, a multiple quantum well structure in which well layers and barrier layers respectively formed of GaInN having different composition ratios are alternately stacked. The upper cladding layer 23 is made of, for example, AlGaN. The contact layer 24 is made of, for example, GaN.

  A strip-shaped ridge portion 20 </ b> A is formed on the semiconductor layer 20, specifically, on the upper cladding layer 23 and the contact layer 24. The ridge portion 20A constitutes an optical waveguide together with portions on both sides of the ridge portion 20A in the semiconductor layer 20, and uses the difference in refractive index in the lateral direction (direction perpendicular to the resonator direction). In addition to performing optical confinement in the direction, the current injected into the semiconductor layer 20 is confined. A portion of the active layer 22 immediately below the above-described optical waveguide corresponds to a current injection region, and this current injection region becomes a light emitting region 22A.

  The semiconductor layer 20 is formed with a pair of front end surfaces S1 and rear end surfaces S2 (a pair of cleavage surfaces) that sandwich the ridge portion 20A from the extending direction of the ridge portion 20A. The front end surface S1 and the rear end surface S2 are cleaved surfaces formed by cleavage, for example, and the front end surface S1 and the rear end surface S2 constitute a resonator. The front end surface S1 is a surface for emitting laser light, and a multilayer reflective film (not shown) is formed on the surface of the front end surface S1. On the other hand, the rear end surface S2 is a surface that reflects laser light, and a multilayer reflective film (not shown) is also formed on the surface of the rear end surface S2. The multilayer reflective film on the rear end surface S2 side is a low reflectance film adjusted so that the reflectance of the emission side end surface constituted by the multilayer reflective film and the rear end surface S2 is about 10%, for example. On the other hand, the multilayer reflective film on the rear end surface S2 side is a high reflectance film adjusted so that the reflectance of the reflective side end surface constituted by the multilayer reflective film and the rear end surface S2 is about 95%, for example.

An upper electrode 32 is provided on the upper surface of the ridge portion 20A (the surface of the contact layer 24). The upper electrode 32 is formed by, for example, laminating Ti, Pt, and Au in this order, and is electrically connected to the contact layer 24. On the other hand, a lower electrode 33 is provided on the back surface of the substrate 10. The lower electrode 33 is configured by stacking, for example, an alloy of Au and Ge, Ni, and Au sequentially from the substrate 10 side, and is electrically connected to the substrate 10. Further, an insulating layer 31 is provided on the side surface and the skirt of the ridge portion 20A. The insulating layer 31 is made of, for example, SiO ₂ , SiN, ZrO ₂ or the like.

  Moreover, in the semiconductor laser 1, the multistage notch 30 is provided in each of front end surface S1 and rear end surface S2. The multistage notches 30 are provided on both sides of the ridge portion 20 </ b> A and have a depth reaching the substrate 10. The multistage notch 30 has at least one step in the substrate 10. For example, as illustrated in FIG. 1, the first notch 30 </ b> A reaching the substrate 10 and the first notch 30 </ b> A are provided. And a second notch 30B formed on the bottom surface of the.

  Both the first notch 30A and the second notch 30B have a polygonal shape extending in a direction orthogonal to the resonator direction when viewed from the stacking direction. The end of the first cutout 30A on the ridge 20A side has, for example, a taper shape cut out in a direction intersecting the resonator direction. In the substrate 10, the depth of the first notch 30A is substantially equal to the depth of the second notch 30B, for example. Further, the width of the bottom surface of the first notch 30A is, for example, three times or more the width of the bottom surface of the second notch 30B. Note that the width of the bottom surface of the first notch 30A can be about 10 times the width of the bottom surface of the second notch 30B. Moreover, the multistage notch 30 may have a notch further in the bottom face of the 2nd notch 30B, for example.

[Method of Manufacturing Semiconductor Laser 1]
The semiconductor laser 1 having such a configuration can be manufactured as follows, for example.

  2A and 2B to FIG. 7A and FIG. 7B respectively show the cross-sectional shape and the top surface shape of the element in the manufacturing process. In addition, an example of a cross-sectional configuration in the direction of arrows A-A in each figure (B) is shown in each figure (A). The surface of the substrate 10 is cleaned by, for example, thermal cleaning. Next, the lower clad layer 21, the active layer 22, the upper clad layer 23, and the contact layer 24 are sequentially grown on the cleaned substrate 10 by, for example, the MOCVD method to form the semiconductor layer 20.

  Next, after forming the insulating layer 31 on the semiconductor layer 20 (contact layer 24) by vapor deposition or sputtering, for example, a resist layer 42 having a strip-shaped opening 42A is formed (FIGS. 2A and 2B). ). The opening 42 </ b> A of the resist layer 42 is formed at a location corresponding to the cleavage line L (see FIG. 8), and has a strip shape parallel to the cleavage line L. Further, the opening 42A is formed between the ridge portions 20A formed on the wafer W in the surface of the wafer W (see FIG. 8) and in a region where the upper electrode 32 is not formed.

  Next, the insulating layer 31 is selectively removed through the opening 42A, for example, by dry etching. As a result, a strip-shaped opening 31A is formed in the insulating layer 31 (FIGS. 3A and 3B). Thereafter, the resist layer 42 is removed.

  Next, the semiconductor layer 20 and the substrate 10 are selectively removed through the opening 31A, for example, by dry etching. As a result, a through hole is formed in a region of the semiconductor layer 20 facing the opening 31A, and a rectangular groove 43 is formed on the surface of the substrate 10 on the semiconductor layer 20 side (see FIGS. B)).

  Next, a resist layer 44 having an opening 44A is formed in a predetermined region including the groove 43 (FIGS. 5A and 5B). When viewed from the stacking direction, the opening 44A has, for example, a strip shape extending in the same direction as the extending direction of the groove 43, and the end of the opening 44A in the extending direction of the opening 44A. However, it has a pointed shape, for example.

  Next, the insulating layer 31 is selectively removed through the openings 44A, for example, by dry etching. Thereby, an opening 31B having the same shape as the opening 44A is formed in a region of the insulating layer 31 facing the opening 44A (FIGS. 6A and 6B). Thereafter, the resist layer 44 is removed.

  Next, the semiconductor layer 20 and the substrate 10 are selectively removed through the openings 31B, for example, by dry etching. Thereby, a through hole is formed in a region of the semiconductor layer 20 facing the opening 31B. In addition, a belt-like groove 45A (first groove) is formed in a region of the substrate 10 facing the opening 31B, and a belt-like groove 45B (second groove) is formed in a region of the substrate 10 corresponding to the groove 43. A groove) is formed (FIGS. 7A and 7B).

  Here, the groove 45A has a polygonal shape extending in a direction orthogonal to the resonator direction when viewed from the stacking direction. An end in the longitudinal direction of the groove 45A has, for example, a pointed shape. In addition, in the case where the end portion in the longitudinal direction of the groove 45A has a pointed shape, the groove 45A can be given a strong cleaving guide property. In the substrate 10, the depth D1 of the groove 45A is, for example, substantially equal to the depth D2 of the groove 45B. The depth D1 of the groove 45A is, for example, about 1 to 2 μm, and the depth D2 of the groove 45B is, for example, about 2 to 2.5 μm. Further, the width W1 of the bottom surface of the groove 45A is, for example, three times or more the width W2 of the bottom surface of the groove 45B. The width W1 of the bottom surface of the groove 45A can be about 10 times the width W2 of the bottom surface of the groove 45B. The width W1 of the bottom surface of the groove 45A is, for example, about 10 μm and has a gentle guide property.

  The groove 45B is formed on the bottom surface of the groove 45A, and a multi-stage groove is formed on the surface of the substrate 10 on the semiconductor layer 20 side by a shallow groove 45A and a deep groove 45B formed at least inside the shallow groove 45A. 45 is formed. For example, as shown in FIG. 8, the grooves 45 </ b> A and 45 </ b> B (multi-stage grooves 45) are formed at locations corresponding to the cleavage line L, and have a strip shape parallel to the cleavage line L. Further, the grooves 45A and 45B (multi-stage grooves 45) are, for example, between the ridge portions 20A formed on the wafer W on the surface of the wafer W as shown in FIG. It is formed in 32 unformed regions.

  FIG. 8 illustrates the case where the groove 45B is formed in the central portion in the short direction of the groove 45A. For example, as shown in FIG. 9, the groove 45B is short of the groove 45A. You may form in the part which remove | deviated from the center of the direction. At this time, for example, as shown in FIG. 9, the groove 45B may be formed on the rear end surface S2 side of the bottom surface of the groove 45A, and although not shown, the front end surface of the bottom surface of the groove 45A. It may be formed on the S1 side.

  Next, the substrate 10 is cleaved by using the multi-step groove 45 (specifically, by applying a force that warps the substrate 10 to the semiconductor layer 20 side and concentrating the stress on the multi-step groove 45). Then, the front end surface S1 and the rear end surface S2 are formed along the cleavage line L. Subsequently, a multilayer reflective film is formed on the front end face S1 and the rear end face S2. Finally, the bar-shaped substrate 10 is diced. In this way, the semiconductor laser 1 of the present embodiment is manufactured.

[Operation and effect of semiconductor laser 1]
Next, the operation and effect of the semiconductor laser 1 of the present embodiment will be described.

  In the semiconductor laser 1 of the present embodiment, when a predetermined current is supplied to the upper electrode 32 and the lower electrode 33, the current confined by the ridge portion 20A enters the current injection region (light emitting region 22A) of the active layer 22. Injected, light emission is caused by recombination of electrons and holes. This light is reflected by the multilayer reflective film formed on the front end surface S1 and the rear end surface S2, causes laser oscillation at a predetermined wavelength, and is emitted to the outside as a beam from the front end surface S1 side.

  By the way, in the present embodiment, the cleavage line L has a multistage groove 45 including a shallow groove 45A and at least a deep groove 45B formed inside the shallow groove 45A on the surface of the substrate 10 on the semiconductor layer 20 side. Is formed. Thereby, cleavage can be performed with high positional accuracy by the guide effect by the groove 45B narrower than the groove 45A. In addition, since the wide groove 45A has a gentle guide property, even when the cleavage position deviates from the groove 45B, the cleavage position can be surely brought inside the wide groove 45A. Thereby, the yield resulting from cleavage can be improved. Further, the groove 45 </ b> A can prevent a fine fault that can occur on the cleavage plane during cleavage from extending to the active layer 22. As a result, the COD level and the ESD level can be increased. Further, when the groove 45B is formed on the rear end surface S2 side of the bottom surface of the groove 45A, the multistage notch 30 on the front end surface S1 side is more than the multistage notch 30 on the rear end surface S2 side. The notch amount increases. As a result, the amount of strain relaxation in the vicinity of the front end face S1 can be further increased, so that the COD level and ESD level can be further increased.

  As described above, in the present embodiment, it is possible to suppress a minute fault from extending to the active layer 22 and at the same time to prevent the cleavage position from being shifted, so that the COD level and the ESD level can be increased. In addition, the yield resulting from cleavage can be improved.

[Modification]
In the above embodiment, for example, in the dry etching process, the semiconductor layer 20 exposed in the opening 31B is used as a mask for delaying the etching of the substrate 10, and the substrate 10 is selectively etched to thereby form the grooves 45A and 45B. However, it is also possible to form the grooves 45A and 45B all together using other methods. For example, first, as shown in FIGS. 10A and 10B, the resist layer 46 formed on the insulating layer 31 is subjected to multiple exposure and then selectively removed (developed) by dry etching, for example. A multistage opening 46 </ b> A is formed in the resist layer 46. Here, in the multistage opening 46A, there is a portion that is thinner than other portions in addition to the through hole. This thin portion functions as a mask for delaying the etching of the substrate 10 in the next etching process. Next, the insulating layer 31, the semiconductor layer 20, and the substrate 10 are selectively removed through the multistage opening 46A, for example, by dry etching. At this time, since there is a thin portion that functions as a mask for delaying the etching of the substrate 10 in the multistage opening 46A as described above, the groove portion 45B is formed where there is no thin portion, and the groove portion exists where there is a thin portion. 45A is formed. As described above, the grooves 45A and 45B are collectively formed by providing the resist layer 46 with the multi-stage openings 46A and selectively removing the insulating layer 31, the semiconductor layer 20, and the substrate 10 through the multi-stage openings 46A. can do. Further, when this method is used, the number of steps can be reduced as compared with the process described in the above embodiment, and therefore the semiconductor laser 1 can be manufactured at a lower cost than the method described in the above embodiment. Can do.

  In the above embodiment, the groove 45B is formed in the bottom surface of the groove 45A shorter than the length in the longitudinal direction of the groove 45A. For example, as shown in FIG. It may be formed with the same length as the length in the longitudinal direction. In the above embodiment, the groove 45B is formed only in the bottom surface of the groove 45A. For example, as shown in FIG. 11B, the groove 45B may be formed so as to protrude from the bottom surface of the groove 45A. Good. Further, for example, as shown in FIG. 11C, the groove 45A may be formed only at the end of the groove 45B.

  Although the present invention has been described with reference to the embodiment and its modifications, the present invention is not limited to the above-described embodiment and the like, and various modifications can be made.

  For example, in the above-described embodiment and the like, the case where the semiconductor laser 1 includes only one ridge portion 20A has been described, but a plurality of semiconductor lasers 1 may be provided.

  In the above-described embodiments and the like, the present invention has been described by taking a gallium nitride based semiconductor laser as an example. The present invention can also be applied to group III semiconductor lasers. The present invention is also applicable to semiconductor lasers whose oscillation wavelength is not always in the visible range, such as AlGaAs, InGaAs, InP, and GaInAsNP.

1 is a perspective view of a semiconductor laser according to an embodiment of the present invention. FIG. 6 is a cross-sectional view and a top view for explaining an example of a manufacturing method of the semiconductor laser of FIG. FIG. 3 is a cross-sectional view and a top view for explaining a process following FIG. 2. FIG. 4 is a cross-sectional view and a top view for explaining a process following FIG. 3. FIG. 5 is a cross-sectional view and a top view for explaining a process following FIG. 4. FIG. 6 is a cross-sectional view and a top view for explaining a process following FIG. 5. FIG. 7 is a cross-sectional view and a top view for explaining a step following FIG. 6. FIG. 8 is a top view illustrating an example of an overall configuration of an upper surface in the step of FIG. 7. FIG. 8 is a top view illustrating another example of the overall configuration of the upper surface in the step of FIG. 7. FIG. 10 is a top view for explaining another example of the method for manufacturing the semiconductor laser of FIG. 1. FIG. 10 is a top view for explaining another example of the method for manufacturing the semiconductor laser of FIG. 1.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 10 ... Board | substrate, 20 ... Semiconductor layer, 20A ... Ridge part, 21 ... Lower clad layer, 22 ... Active layer, 22A ... Light-emitting region, 23 ... Upper guide layer, 24 ... Contact layer, 30 ... Multi-stage cutting Notch, 30A ... first notch, 30B ... second notch, 31 ... insulating layer, 32 ... upper electrode, 33 ... lower electrode, 45 ... multi-step groove, 45A, 45B ... groove, S1 ... front end surface, S2 ... rear end face.

Claims (2)

After forming a semiconductor layer having a strip-shaped optical waveguide on the semiconductor substrate, a first groove that is parallel to the cleavage line and reaches the surface on the semiconductor layer side of the semiconductor substrate is formed in the semiconductor substrate. Of these, the first groove is formed on the surface on the semiconductor layer side, and at least a second groove is formed inside the first groove, thereby forming a multistage groove including the first groove and the second groove. And the process of
A second step of forming a laser structure having a pair of cleaved surfaces sandwiching the optical waveguide from an extending direction of the optical waveguide by cleaving the semiconductor substrate using the multistage groove. Manufacturing method. In the first step, a resist layer having a multistage opening formed by multiple exposure and development is disposed, and then the semiconductor substrate is etched through the multistage opening, whereby the first groove and the second groove are formed. The method for manufacturing a semiconductor laser according to claim 1 , wherein the grooves are formed in a lump.

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