Method for forming laser end face

Abstract

To provide a method for forming a smooth laser end face.SOLUTION: A semiconductor laser element 1 includes: a support 31; a metal layer 32 laminated on the support 31; and a semiconductor layer 10 laminated on the metal layer 32. A method for forming a laser end face L in the semiconductor laser element includes: a lower scribe line forming step of forming a linear lower scribe line M1 in parallel to a cleavage plane of the semiconductor laser layer 10 on a lower face of the support 31; an upper scribe line forming step of forming an upper scribe line M2 so as to be along an end of the lower scribe line M1 on a surface of the semiconductor layer 10; and a cleaving step of forming the laser end face L on the semiconductor layer 10 by pressing the semiconductor layer 10 along the upper scribe line M2 from above and cleaving the semiconductor laser element 1.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a method for forming a laser facet. [Background technology]

[0002] Patent Document 1 discloses a nitride semiconductor light-emitting device in which a nitride semiconductor is stacked on a sapphire substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 5-166923 Summary of the Invention [Problem to be solved by the invention]

[0004] The sapphire substrate in Patent Document 1 is insulating. Therefore, electrodes must be formed on the wafer surface to allow current to flow laterally. This often results in nonuniform current distribution in the light-emitting region and high electrical resistance. To address these issues, a vertically conductive device, in which current flows in the stacking direction, is considered. For example, when a vertically conductive structure is adopted for a nitride semiconductor laser device, a p-side electrode formed on the top of an AlGaN-based nitride semiconductor crystal formed on a sapphire substrate is eutectic-bonded to a support made of Si, SiC, or the like using an Au-Sn alloy. When forming the laser facets, if a non-cleavable material is used as the support, the AlGaN crystal will crack in a similar manner to the cracking of the support. Therefore, using a non-cleavable support would prevent the formation of clean cleavage planes for the laser facets. Therefore, a cleavable material, such as Si or SiC, is used as the support. The sapphire substrate is then separated from the AlGaN-based nitride semiconductor crystal using the laser lift-off (LLO) method. The AlGaN-based nitride semiconductor crystal bonded to the support is then cut in the stacking direction and divided into multiple small pieces. The surfaces exposed after the division into the small pieces must be extremely smooth to function as laser reflecting surfaces. Therefore, it is preferable that the surfaces exposed after the division into the small pieces be surfaces formed by cleavage of the crystal (cleavage planes). Therefore, it is necessary to precisely align the orientation of the cleavage planes of the AlGaN-based nitride semiconductor crystal with the orientation of the cleavage planes of the cleavable support. However, aligning the orientation of the cleavable crystal planes of the support and the AlGaN-based nitride semiconductor crystal is extremely difficult. Furthermore, because a non-cleavable Au-Sn alloy formed by eutectic bonding is sandwiched between the AlGaN and the support, misalignment of the crystal planes occurs, preventing linear division and resulting in many steps. As described above, it is difficult to align the cleavage planes of the cleavable support (Si or SiC) and the AlGaN-based nitride semiconductor crystal, and a technology for obtaining smooth laser end faces by cleavage has been desired.

[0005] The present invention has been made in view of the above-mentioned conventional circumstances, and an object to be achieved is to provide a method for forming a smooth laser end face. [Means for solving the problem]

[0006] The method for forming a laser facet of the present invention includes the steps of: A support; a metal layer laminated on the support; a semiconductor layer stacked on the metal layer; A method for forming a laser end facet in a semiconductor laser element having the following features: a lower scribe line forming step of forming a lower scribe line on the lower surface of the support, the lower scribe line being linear and parallel to the cleavage plane of the semiconductor layer; an upper scribe line forming step of forming an upper scribe line on the surface of the semiconductor layer so as to follow at least an end portion of the lower scribe line; and a cleaving step of pressing the semiconductor layer along the upper scribe line to cleave the semiconductor laser element and form laser end faces in the semiconductor layer.

[0007] This method for forming a laser end face makes it possible to obtain a smooth laser end face. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram showing the structure of a semiconductor laser element of Example 1. FIG. [Figure 2] 1A to 1C are schematic diagrams showing the steps of manufacturing the semiconductor laser device of Example 1, illustrating the steps up to bonding a support to an intermediate body. [Figure 3] 2A to 2C are schematic diagrams showing the steps of manufacturing the semiconductor laser device of Example 1, illustrating the steps from peeling off the sapphire substrate to completing the semiconductor laser device. [Figure 4]1A and 1B are schematic diagrams showing the structure of the semiconductor laser element of Example 1, in which (A) is a plan view, (B) is an end view seen from a direction perpendicular to the direction in which the semiconductor layers extend in a strip-like shape, and (C) is an end view seen from the direction in which the semiconductor layers extend in a strip-like shape. [Figure 5] 3A to 3C are schematic diagrams showing steps for forming laser end faces on the semiconductor laser element of Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0009] A preferred embodiment of the present invention will now be described.

[0010] In the upper scribe line forming step of the laser facet forming method of the present invention, the upper scribe line may be formed at a position corresponding to an end of the lower scribe line or in the form of perforations at a predetermined interval along the lower scribe line, which makes it easier to cleave the semiconductor layer linearly.

[0011] In the method for forming a laser facet of the present invention, the support may be made of a material that does not have cleavage properties. In this case, cleavage of the semiconductor layer proceeds along a scribe line on the lower side of the support that is formed parallel to the cleavage plane of the semiconductor layer, thereby making it difficult for the semiconductor layer forming the laser facet to be chipped.

[0012] Next, a first embodiment of the method for forming a laser end face of the present invention will be described with reference to the drawings.

[0013] Example 1 [Configuration of semiconductor laser element] As shown in FIG. 1, the semiconductor laser device 1 of Example 1 includes a support 31, a metal layer 32, an Al2O3 layer 33, a p-side electrode 34, a semiconductor layer 10, a covering layer 50, an n-side electrode 51, an n-side pad electrode 52, and a p-side pad electrode 53.

[0014] The support 31 is formed by sintering fine powder of AlN. That is, the support 31 is a sintered body. The thickness of the support 31 is, for example, 400 μm. The support 31 does not have cleavage properties.

[0015] The metal layer 32 is laminated on the support 31. The metal layer 32 has a gold-tin eutectic layer 32A, a titanium-platinum layer 32B, and a nickel layer 32C. The metal layer 32 does not have cleavage properties. The gold-tin eutectic layer 32A is laminated on the surface of the support 31. The gold-tin eutectic layer 32A is an alloy of Au and Sn and is formed by eutectic bonding.

[0016] The titanium-platinum layer 32B is laminated on the surface of the gold-tin eutectic layer 32A. The titanium-platinum layer 32B is formed by laminating two pairs of Ti and Pt alternately.

[0017] The nickel layer 32C is laminated on the surface of the titanium-platinum layer 32B. The nickel layer 32C is made of Ni. An electrode opening 32D and a pad opening 32E are formed in the nickel layer 32C, penetrating the nickel layer 32C in the film thickness direction. The titanium-platinum layer 32B is formed to protrude into the electrode opening 32D.

[0018] The Al2O3 layer 33 is laminated on the surface of the nickel layer 32C. The Al2O3 layer 33 has an electrode opening 33A and a pad opening 33B formed therein, which penetrate the Al2O3 layer 33 in the thickness direction. The electrode opening 33A is arranged to communicate with the electrode opening 32D of the nickel layer 32C. The pad opening 33B is arranged to communicate with the pad opening 32E of the nickel layer 32C.

[0019] The p-side electrode 34 is laminated on the surface of the titanium-platinum layer 32B facing the electrode opening 33A in the Al2O3 layer 33. The p-side electrode 34 is formed by laminating Ni, Pt, and Au.

[0020] The semiconductor layer 10 is stacked on the metal layer 32. The semiconductor layer 10 includes a p-GaN layer 18, a p-AlGaN layer 17, a cladding layer 16, an electron blocking layer 15, a light emitting layer 14, and an n-AlGaN layer 13. The semiconductor layer 10 is manufactured by crystal growth using MOVPE (metal organic vapor phase epitaxy).

[0021] The p-GaN layer 18 is deposited on the surface of the Al2O3 layer 33, covering the p-side electrode 34 and exposing the pad opening 33B and its periphery. Mg is added to the p-GaN layer 18. The thickness of the p-GaN layer 18 is, for example, 10 nm.

[0022] The p-AlGaN layer 17 is stacked on the surface of the p-GaN layer 18. The p-AlGaN layer 17 is doped with Mg as a p-type impurity. The p-AlGaN layer 17 has an AlN mole fraction of 0 at the interface with the p-GaN layer 18 and an AlN mole fraction of 0.6 at the surface. The p-AlGaN layer 17 has a composition gradient in which the AlN mole fraction varies from 0 to 0.6 in the thickness direction. The thickness of the p-AlGaN layer 17 is, for example, 75 nm.

[0023] The cladding layer 16 is laminated on the surface of the p-AlGaN layer 17. The cladding layer 16 is made of AlGaN. The AlN mole fraction of the cladding layer 16 is 0.6 at the interface with the p-AlGaN layer 17, and 0.9 at the surface. The AlN mole fraction of the cladding layer 16 is graded from 0.6 to 0.9 in the thickness direction. The thickness of the cladding layer 16 is, for example, 320 nm.

[0024] The electron blocking layer 15 is laminated on the surface of the cladding layer 16. The electron blocking layer 15 is made of AlGaN. The AlN mole fraction in the electron blocking layer 15 is 0.9. The thickness of the electron blocking layer 15 is, for example, 20 nm.

[0025] The light emitting layer 14 includes a second guide layer 14C, a double quantum well active layer 14B, and a first guide layer 14A. The second guide layer 14C is formed on the surface of the electron blocking layer 15. The second guide layer 14C is made of AlGaN. The AlN mole fraction in the second guide layer 14C is 0.45. The thickness of the second guide layer 14C is, for example, 50 nm.

[0026] The double quantum well active layer 14B is laminated on the surface of the second guide layer 14C. The double quantum well active layer 14B is formed by laminating two pairs of an active layer (with an AlN molar fraction of 0.35) having a thickness of 4 nm and a barrier layer (with an AlN molar fraction of 0.45) having a thickness of 8 nm.

[0027] The first guide layer 14A is stacked on the surface of the double quantum well active layer 14B. The first guide layer 14A is made of AlGaN. The AlN mole fraction in the first guide layer 14A is 0.45. The thickness of the first guide layer 14A is, for example, 50 nm.

[0028] The n-AlGaN layer 13 is stacked on the surface of the first guide layer 14A. The n-AlGaN layer 13 is doped with Si as an n-type impurity. The AlN mole fraction in the n-AlGaN layer 13 is 0.62. The thickness of the n-AlGaN layer 13 is, for example, 2 μm.

[0029] The covering layer 50 is provided so as to cover the exposed surface of the Al2O3 layer 33 and the exposed outer surface of the semiconductor layer 10. The covering layer 50 is made of SiO2. An n-side electrode opening 50A and a pad opening 50B are formed in the covering layer 50 so as to penetrate the covering layer 50 in the film thickness direction. The n-side electrode opening 50A is formed so as to expose the surface of the n-AlGaN layer 13. The pad opening 50B is arranged so as to communicate with the pad opening 33B.

[0030] The n-side electrode 51 is laminated on the surface of the n-AlGaN layer 13 facing the n-side electrode opening 50A. The n-side electrode 51 is formed by laminating Ti, Pt, and Au. In addition, a metal film 51A made of the same material as the n-side electrode 51 is laminated on the surface of the titanium-platinum layer 32B facing the pad opening 32E.

[0031] The n-side pad electrode 52 is laminated on the surface of the n-side electrode 51. The n-side pad electrode 52 is formed by laminating Ti and Au.

[0032] The p-side pad electrode 53 is laminated on the surface of the metal film 51A facing the pad openings 33B and 50B. The p-side pad electrode 53 is formed by laminating Ti and Au. The semiconductor laser device 1 is configured in this manner.

[0033] [Method of manufacturing semiconductor laser element] An example of a manufacturing method for a semiconductor laser device will be described. First, an AlN layer 71 is deposited to a thickness of 1300 nm on a sapphire substrate 70 having a C-plane surface using MOCVD (see FIG. 2A). Next, a SiO2 layer is deposited to a thickness of 420 nm on the surface of the AlN layer 71 using a sputtering device. Then, a resist is applied to the surface of the SiO2 layer to form a resist film, and a fine pattern with a pitch of 1000 nm and a diameter of 500 nm is formed in the resist film using a nanoimprinting device. Next, the exposed SiO2 layer is dry-etched with CF4 gas using an ICP device, and subsequently, the residue of the SiO2 layer is removed using buffered hydrofluoric acid. Next, the surface side of the AlN layer 71 is etched to a depth of 300 nm using Cl2 gas, and the SiO2 layer and resist film used as a mask are removed using buffered hydrofluoric acid. A plurality of protrusions 71A with a pitch of approximately 1000 nm, a diameter of approximately 450 nm, and a height of approximately 300 nm are formed on the surface side of the AlN layer (see FIG. 2B). Then, by MOCVD, a u-AlGaN layer 72 having an AlN mole fraction of 0.68 is deposited to a thickness of 5 μm, an n-AlGaN layer 73 having an AlN mole fraction of 0.5 is deposited to a thickness of 170 nm, and an n-AlGaN layer 13 having an AlN mole fraction of 0.62 is deposited to a thickness of 4 μm, and then each layer of the semiconductor layer 10 from the light emitting layer 14 to the p-GaN layer 18 is deposited on top of them in this order (see Figure 2(C)).

[0034] Next, an Al2O3 layer 33, a p-side electrode 34, and the nickel layer 32C and titanium-platinum layer 32B of the metal layer 32 are laminated to form an intermediate body M (see FIG. 2(D)). Then, the gold-tin eutectic layer 32A of the metal layer 32 is used to bond the titanium-platinum layer 32B to the support body 31 on which Ti / Pt / Au has been vapor-deposited (see FIG. 2(E)). In this way, the intermediate body is bonded to the support body 31.

[0035] Next, the back surface of the sapphire substrate 70 (i.e., the surface opposite to the surface on which the semiconductor layer 10 is stacked) is mirror-polished, and the sapphire substrate 70 is peeled off from the semiconductor layer 10 using a laser lift-off (LLO) method. After that, the AlN layer 71, the u-AlGaN layer 72, and the n-AlGaN layer 73 are polished by CMP to expose the n-AlGaN layer 13 of the semiconductor layer 10, and the exposed surface is smoothed (see FIG. 3(A)). Note that FIG. 3 is shown upside down compared to FIG. 2. Next, dry etching is performed so that the semiconductor layer 10 remains in a strip-like form on the surface of the support 31. At this time, the Al2O3 layer 33 is exposed in the area excluding the strip-shaped semiconductor layer 10 (see FIG. 3(B)).

[0036] Then, a covering layer 50 is formed of SiO2 so as to cover the strip-shaped semiconductor layer 10 and the exposed Al2O3 layer 33 (see FIG. 3(C)). The covering layer 50 is formed by sputtering. An n-side electrode opening 50A is formed in the covering layer 50 covering the surface of the semiconductor layer 10, and an n-side electrode 51 and an n-side pad electrode 52 are laminated so as to cover the n-side electrode opening 50A. Furthermore, pad openings 50B, 33B, and 32E are formed in the region where the Al2O3 layer 33 is exposed, excluding the strip-shaped semiconductor layer 10, and a metal film 51A and a p-side pad electrode 53 are laminated so as to cover the pad openings 50B, 33B, and 32E (see FIG. 3(D)). In this way, the semiconductor laser device 1 is completed.

[0037] As shown in FIG. 4, the semiconductor laser device 1 has strip-shaped semiconductor layers 10 arranged in parallel ridges along the surface of the support 31. To generate laser light from the semiconductor laser device 1 formed in this manner, a pair of parallel laser end faces L (see FIG. 1) must be formed on the semiconductor laser device 1. The pair of laser end faces L must be parallel to each other, perpendicular to the stacking direction of the semiconductor layers 10, and smooth. Specifically, the pair of exposed side faces of the light-emitting layer 14 must be smooth, while the pair of exposed side faces of the metal layer 32 and the support 31 do not need to be smooth. To form such laser end faces L, the semiconductor laser device 1 shown in FIG. 4 is cleaved along a straight line C.

[0038] [Example of laser end face formation method] Next, an example of a method for forming the laser end face L will be described. First, a lower scribe line forming step is performed. Specifically, a linear lower scribe line M1 is formed on the lower plate surface (lower surface) of the support 31 along the straight line C (see FIG. 4) (see FIG. 5(A)). Here, the scribe line is a scribe line that is drawn so as to be parallel to the cleavage plane of the semiconductor layer 10. The scribe line can be formed using, for example, a laser scriber. The lower scribe line M1 is formed continuously and linearly from one end to the other end on the lower plate surface (lower surface) of the support 31. The depth of the lower scribe line M1 from the lower plate surface of the support 31 is approximately 93 μm to 95 μm.

[0039] Next, an upper scribe line forming step is performed. Specifically, an upper scribe line M2 is formed on the surface of the semiconductor layer 10 along the straight line C (see FIG. 4) (see FIG. 5(B)). For example, the upper scribe line M2 is formed on the surface of the semiconductor layer 10 located at both ends of the straight line C in FIG. 4(A). When the semiconductor laser element 1 is viewed from above, the upper scribe line M2 is formed so as to overlap along both ends of the lower scribe line M1. The depth of the upper scribe line M2 from the surface of the n-side pad electrode 52 is approximately 80 μm to 90 μm.

[0040] Next, a cleavage step is performed. Specifically, a pressing piece P of a tabletop breaker is used to press the semiconductor layer 10 from above along the upper scribe line M2 (see FIG. 5(C)). This causes the semiconductor laser element 1 to be cleaved along a straight line C (see FIG. 5(D)). That is, the lower scribe line M1 is a straight line parallel to the cleavage plane of the semiconductor layer 10. By cleaving the semiconductor laser element 1 in this manner, a laser end facet L is formed on the semiconductor laser element 1. The laser end facet L is the cleavage plane of the semiconductor layer 10. Then, in the semiconductor laser element 1, a lower scribe line M1 (lower scribe line forming process) and an upper scribe line M2 (upper scribe line forming process) are formed at a position different from the position where the laser end face L was previously formed, so as to be parallel to the previously formed laser end face L, and by performing the cleavage process again at this position, it is possible to obtain a semiconductor laser element 1 with a pair of laser end faces L formed (see Figure 1).

[0041] Next, the effects of the above embodiment will be described.

[0042] The method for forming a laser end face of the present invention is a method for forming a laser end face L in a semiconductor laser device 1 having a support 31, a metal layer 32 stacked on the support 31, and a semiconductor layer 10 stacked on the metal layer 32. This method for forming the laser end face L includes a lower scribe line forming step of forming a lower scribe line M1 in a straight line parallel to the cleavage plane of the semiconductor layer 10 on the lower surface of the support 31, an upper scribe line forming step of forming an upper scribe line M2 on the surface of the semiconductor layer 10 so as to follow an end of the lower scribe line M1, and a cleaving step of pressing the semiconductor layer 10 from above along the upper scribe line M2 to cleave the semiconductor laser device 1 and form the laser end face L in the semiconductor layer 10. This configuration makes it possible to obtain a smooth laser end face L.

[0043] The support 31 is made of a material that does not have cleavage properties. A lower scribe line M1 is formed on the back surface of the support 31 parallel to the cleavage plane of the semiconductor layer 10 (AlGaN-based nitride semiconductor crystal), and cleavage of the semiconductor layer 10 proceeds along this lower scribe line M1. This makes it easier to cleave the support 31 together with the semiconductor layer 10, making it less likely that the semiconductor layer 10, on which the laser facet L is formed, will be chipped.

[0044] The present invention is not limited to the first embodiment described above with reference to the drawings, and the following embodiments are also included within the technical scope of the present invention. (1) Unlike the above embodiment, in the upper scribe line forming step, the upper scribe line may be formed at a position corresponding to the end of the lower scribe line or in the form of perforations at a predetermined interval along the lower scribe line. This configuration makes it easier to cleave the semiconductor layer in a linear fashion. (2) In the above embodiment, sintered AlN, which does not have cleavage properties, is used, but cleavable SiC, Si, etc. may also be used as the support. (3) In the above embodiment, the crystals are grown by stacking using the MOVPE method, but this is not limiting and other methods such as MOCVD, MBE, sputtering, and LPEE may also be used to grow the crystals by stacking. (4) Unlike the above embodiment, a semiconductor other than a nitride semiconductor may be used as the semiconductor layer. [Explanation of symbols]

[0045] 1: Semiconductor laser element 10: Semiconductor layer 31:Support 32: Metal layer L: Laser end face M1: Lower scribe line M2: Upper scribe line

Claims

1. A support; a metal layer laminated on the support; a semiconductor layer stacked on the metal layer; A method for forming a laser end facet in a semiconductor laser element having the following features: a lower scribe line forming step of forming a lower scribe line on the lower surface of the support, the lower scribe line being linear and parallel to the cleavage plane of the semiconductor layer; an upper scribe line forming step of forming an upper scribe line on the surface of the semiconductor layer so as to follow at least an end portion of the lower scribe line; a cleaving step of pressing the semiconductor layer along the upper scribe line to cleave the semiconductor laser element, thereby forming laser facets in the semiconductor layer.

2. 2. The method for forming a laser facet according to claim 1, wherein in the upper scribe line forming step, the upper scribe line is formed at a position corresponding to an end of the lower scribe line or in the form of perforations at a predetermined interval along the lower scribe line.

3. 3. The method for forming a laser facet according to claim 1, wherein the support is made of a material that does not have cleavage properties.

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