JP3670768B2 - Method of manufacturing group III nitride semiconductor laser diode - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a laser diode using a group III nitride semiconductor. In particular, the present invention relates to a method of forming an end face of a laser diode resonator.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, there are known devices in which blue light emitting diodes (LEDs) and blue laser diodes (LDs) are formed by forming respective layers made of a gallium nitride compound semiconductor (AlGaInN) on a sapphire substrate. In order to efficiently reflect and oscillate the light of the laser diode (LD), it is necessary to keep the perpendicularity and parallelism of the resonator end face high. In order to form this resonator end face with high accuracy, it is preferable to cleave. However, in the above element, cleavage is difficult because the substrate and the element layer are formed of different substances. For this reason, an end face is formed by dry etching.
[0003]
[Problems to be solved by the invention]
However, in the case where the end face of the resonator is formed by dry etching as described above, the end face is damaged by ions, and 200-mm unevenness is formed. As a result, there is a problem that the reflectance of light at the end face decreases and the oscillation threshold current increases. In addition, when a reflection film is formed on the end face, since there are irregularities on the end face, the reflection film is not formed as designed, light is scattered at the end face, and the light confinement effect in the active layer is reduced. There is a problem.
[0004]
The present invention has been made in order to solve the above-mentioned problems, and its purpose is to improve the surface specularity of the cavity end face in the laser diode and to improve the light reflectivity at the end face. It is to increase the confinement effect and lower the oscillation threshold current.
[0005]
[Means for Solving the Problems]
In order to achieve the object, a feature of the present invention is that in a method of manufacturing a group III nitride semiconductor laser diode in which a p layer and an n layer made of a group III nitride semiconductor are formed on a substrate, the group III nitride is formed on the substrate. each layer is formed of semiconductor, each layer in order to form an end face of the resonator, and dry etched by reactive ion beam etching (RIBE), reactive ion etching (RIE) or ion beam assisted etching (IBAE), dry The etched end face is further etched by gas cluster ion beam etching. As a result, the unevenness formed on the cavity end face by dry etching is removed by gas cluster ion beam etching, resulting in improved end face specularity, improved light confinement effect, and laser oscillation threshold current. descend. Further, the wafer on which the element is formed is cut into strips in parallel with the end face, the strip-like pieces are erected, and the end face is turned upward to perform the cluster beam etching, so that the end face is The specularity can be further improved.
[0006]
The group III nitride semiconductor is preferably a material represented by Al _X Ga _Y In _1-XY N (0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, 0 ≦ X + Y ≦ 1). A blue short wavelength laser diode can be obtained. In particular, when the semiconductor laser diode is made of a cladding layer made of Al _x1 Ga _{1 -x1} N and an active layer made of In _x2 Ga _{1 -x2} N, the blue laser output can be improved. Further, by using dry ion etching as reactive ion beam etching (RIBE), the end face can be formed efficiently. Further, desirably, the reactive ion beam etching is etching using Cl ₂ gas, thereby enabling etching with a high etching rate. Thereby, the destructive layer generated by the dry etching of the resonator end face can be efficiently removed, and the specularity of the end face can be improved. Gas cluster ion beam etching is performed using an inert gas such as argon (Ar), helium (He), neon (Ne), krypton (Kr), xenon (Xe), radon (Rn), or nitrogen (N ₂ ). By using this, the specularity of the end face is improved.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described based on specific examples. The present invention is not limited to the following examples.
In FIG. 1, a laser diode 100 has a sapphire substrate 1, and a 500 Å AlN buffer layer 2 is formed on the sapphire substrate 1. Of On the buffer layer 2, in turn, a film thickness of about 2.2 .mu.m, electron concentration ^{2 × 10 18 / cm 3,} Si concentration 4 × 10 ¹⁸ / cm high carrier concentration comprising a silicon-doped GaN of ³ n ⁺ layer 3, N-conducting clad layer 4 made of silicon-doped Al _0.08 Ga _0.92 N with a film thickness of about 1.0 μm, an electron concentration of 2 × 10 ¹⁸ / cm ³ , and an Si concentration of 4 × 10 ¹⁸ / cm ³ . Active layer 5 composed of In _0.08 Ga _0.92 N, p-conductivity composed of Al _0.08 Ga _0.92 N doped with magnesium to a thickness of about 1.0 μm, hole concentration 5 × 10 ¹⁷ / cm ³ , concentration 1 × 10 ²⁰ / cm ³ A mold cladding layer 61, a contact layer 62 made of magnesium-doped GaN having a film thickness of about 0.2 μm, a hole concentration of 7 × 10 ¹⁷ / cm ³ and a magnesium concentration of 2 × 10 ²⁰ / cm ³ are formed. An SiO ₂ layer 9 is formed on the contact layer 62, and an electrode 7 made of Ni that is bonded to the contact layer 62 through a window portion of the SiO ₂ layer 9 is formed. Furthermore, an electrode 8 made of Ni bonded to the layer 3 is formed on the high carrier concentration n ⁺ layer 3.
[0008]
Next, a method for manufacturing the laser diode 100 having this structure will be described. Each layer is sequentially formed on the sapphire substrate 1 of the wafer as shown in FIG. The laser diode 100 was manufactured by vapor phase growth using an organic metal compound vapor phase growth method (hereinafter referred to as “M0VPE”).
The gases used were NH ₃ and carrier gas H ₂ or N ₂ , trimethylgallium (Ga (CH ₃ ) ₃ ) (hereinafter referred to as “TMG”) and trimethylaluminum (Al (CH ₃ ) ₃ ) (hereinafter referred to as “TMA”). ), Trimethylindium (In (CH ₃ ) ₃ ) (hereinafter referred to as “TMI”), silane (SiH ₄ ) and cyclopentadienyl magnesium (Mg (C ₅ H ₅ ) ₂ ) (hereinafter referred to as “CP”). ₂ Mg ”).
[0009]
First, a single-crystal sapphire substrate 1 having a thickness of 100 to 400 μm whose main surface is cleaned by organic cleaning and heat treatment is mounted on a susceptor mounted in a reaction chamber of an M0VPE apparatus. Next, the sapphire substrate 1 was vapor-phase etched at a temperature of 1100 ° C. while flowing H ₂ at normal pressure and a flow rate of 2 liter / min into the reaction chamber.
[0010]
Next, the temperature is lowered to 400 ° C., H ₂ is supplied at 20 liter / min, NH ₃ is supplied at 10 liter / min, and TMA is supplied at 1.8 × 10 ⁻⁵ mol / min, so that the buffer layer 2 of AlN is about 500Å. The thickness was formed. Next, the temperature of the sapphire substrate 1 is maintained at 1150 ° C., H ₂ is 20 liter / min, NH ₃ is 10 liter / min, TMG is 1.7 × 10 ⁻⁴ mol / min, diluted to 0.86 ppm with H ₂ gas. The supplied silane is supplied at 200 ml / min for 30 minutes, and a high carrier concentration n of silicon-doped GaN having a film thickness of about 2.2 μm, an electron concentration of 2 × 10 ¹⁸ / cm ³ , and an Si concentration of 4 × 10 ¹⁸ / cm ^{3 +} Layer 3 was formed.
[0011]
Next, the temperature of the sapphire substrate 1 is maintained at 1100 ° C., N ₂ or H ₂ is 10 liter / min, NH ₃ is 10 liter / min, TMG is 1.12 × 10 ⁻⁴ mol / min, and TMA is 0.47 × 10 ⁻ Silane diluted to ⁴ mol / min and 0.86 ppm with H ₂ gas is supplied at 10 × 10 ⁻⁹ mol / min for 60 minutes, film thickness is about 1 μm, electron concentration is 2 × 10 ¹⁸ / cm ³ , An n-conducting clad layer 4 made of silicon-doped Al _0.08 Ga _0.92 N with a Si concentration of 4 × 10 ¹⁸ / cm ³ was formed.
[0012]
Subsequently, the temperature is maintained at 850 ° C., N ₂ or H ₂ is 20 liter / min, NH ₃ is 10 liter / min, TMG is 1.53 × 10 ⁻⁴ mol / min, and TMI is 0.02 × 10 ^−4. The active layer 5 made of 0.05 μm In _0.08 Ga _0.92 N was formed by supplying 6 mol / min.
[0013]
Subsequently, the temperature is maintained at 1100 ° C., N ₂ or H ₂ is 20 liter / min, NH ₃ is 10 liter / min, TMG is 1.12 × 10 ⁻⁴ mol / min, and TMA is 0.47 × 10 ⁻⁴ mol / min. And CP ₂ Mg is introduced at 2 × 10 ⁻⁴ mol / min for 60 minutes to form a p-conductivity type clad layer 61 made of magnesium (Mg) -doped Al _0.08 Ga _0.92 N with a film thickness of about 1.0 μm. did. The concentration of magnesium in the cladding layer 61 is 1 × 10 ²⁰ / cm ³ . In this state, the clad layer 61 is still an insulator having a resistivity of 10 ⁸ Ωcm or more.
[0014]
Subsequently, the temperature is maintained at 1100 ° C., N ₂ or H ₂ is 20 liter / min, NH ₃ is 10 liter / min, TMG is 1.12 × 10 ⁻⁴ mol / min, and CP ₂ Mg is 4 × 10. ^The contact layer 62 was introduced at a rate of ⁻⁴ mol / min for 4 minutes to form a magnesium (Mg) -doped GaN film having a thickness of about 0.2 μm. The concentration of magnesium in the contact layer 62 is 2 × 10 ²⁰ / cm ³ . In this state, the contact layer 62 is still an insulator having a resistivity of 10 ⁸ Ωcm or more.
[0015]
Next, the electron beam was uniformly irradiated to the contact layer 62 and the clad layer 61 using the electron beam irradiation apparatus. The electron beam irradiation conditions are an acceleration voltage of about 10 KV, a sample current of 1 μA, a beam moving speed of 0.2 mm / sec, a beam diameter of 60 μmφ, and a degree of vacuum of 5.0 × 10 ⁻⁵ Torr. By this electron beam irradiation, the contact layer 62 and the cladding layer 61 become p-conductivity type semiconductors having a hole concentration of 7 × 10 ¹⁷ / cm ³ , 5 × 10 ¹⁷ / cm ³ , and resistivity of 2 Ωcm and 0.8 Ωcm, respectively. . In this way, a wafer having a multilayer structure was obtained.
[0016]
Next, as shown in FIG. 2, a SiO ₂ layer 9 having a thickness of 2000 mm was formed on the contact layer 62 by sputtering, and a photoresist 11 was applied on the SiO ₂ layer 9. Then, as shown in FIG. 3, the photoresist 11 at the electrode formation site A with respect to the high carrier concentration n ⁺ layer 3 was removed on the contact layer 62 by photolithography. Next, the SiO ₂ layer 9 not covered with the photoresist 11 was removed with a hydrofluoric acid etching solution.
[0017]
Next, the contact layer 62, the clad layer 61, the active layer 5 and the clad layer 4 in the region A not covered with the photoresist 11 and the SiO ₂ layer 9 are made BCl at a vacuum degree of 0.04 Torr and a high frequency power of 0.44 W / cm ² . ₃ gases were supplied at a rate of 10 ml / min for dry etching, followed by dry etching with Ar. In this step, as shown in FIG. 4, a hole A for extracting an electrode from the high carrier concentration n ⁺ layer 3 was formed.
[0018]
Next, a photoresist application, a photolithography process, and wet etching are performed on the remaining SiO ₂ layer 9, and as shown in FIG. 5, a window 9 A is formed in the electrode formation portion of the contact layer 62 of the SiO ₂ layer 9. Formed.
[0019]
Next, Ni is uniformly vapor-deposited on the entire upper surface of the wafer, and after applying a photoresist, a photolithography process, and an etching process, as shown in FIG. 6, with respect to the high carrier concentration n ⁺ layer 3 and the contact layer 62 Electrodes 8 and 7 were formed.
[0020]
Next, dry etching for forming the resonator end face was performed as follows. A photoresist is uniformly applied to the entire upper surface of the wafer, and the SiO ₂ layer 9 is left by the width of the length of the resonator (in the y-axis direction) by photolithography. Further, at the center of the SiO ₂ layer 9, y Striped window portions having a length in the axial direction and a width in the x-axis direction were removed. Then, a resist mask 12 covered along the x axis with the width of the length of the resonator was formed as shown in FIG.
[0021]
Next, Cl ₂ gas is supplied at a rate of vacuum of 1 mTorr and high frequency power of 300 W at a rate of 5 ml / min, and reactive ion beam etching (until the sapphire substrate 1 is exposed to the portion of the window not covered with the resist mask 12). RIBE) was dry etched.
[0022]
After that, the wafer 10 shown in FIG. 8A processed as described above is scribed along the length direction (y-axis) of the laser resonator (direction perpendicular to the end face S of the resonator) to scribe grooves 15. It is formed and then dicing grayed in the x-axis direction parallel to the end surface of the resonator, as shown in FIG. 8 (b), to give the respective strips 14.
[0023]
After that, as shown in FIG. 8C, each strip 14 is arranged so that the end face S of the resonator is on the upper side, and a gas cluster ion beam using Ar gas is applied to the end face S so that the end face S Was etched. Thereafter, the vertical direction of each strip 14 was reversed, the lower end face was turned up, and similarly, the end face was etched by applying a gas cluster ion beam using Ar gas to the end face. The etching conditions are a cluster size of 3000, an acceleration energy of 20 keV, and an ion dose of 1 × 10 ¹⁶ IONS / cm ² . By this etching with a gas cluster ion beam, the unevenness of 200 mm on the end surface S etched by RIBE could be reduced to 20 mm or less.
[0024]
Next, in order to protect the resonator end surface S, SiO ₂ was deposited on the resonator end surface S by sputtering. Each strip 14 was pressed with a roller and separated into each element chip using a scribe groove already formed along the y-axis direction. In this way, as shown in FIG. 7, the resonator end face S having high perpendicularity to the substrate 1 and high parallelism between the end faces, high surface flatness and high specularity was obtained. As a result, the reflectance of light at the resonator end surface S is increased, the light confinement effect is high, and the threshold current can be reduced. The laser diode 100 thus obtained had a drive current of 1000 mA, a light emission output of 10 mW, and an oscillation peak wavelength of 380 nm.
[0025]
A protective film of SiO ₂ is formed on the resonator end face S. A multi-layer formed of silicon oxide such as SiO ₂ , silicon nitride such as Si ₃ N ₄ , and other dielectrics such as TiO ₂ is formed on the end face S. It may be formed. The reflectivity at the end face S can be further improved by optimally designing the thickness of each of the multiple layers.
The above gas cluster ion beam etching used Ar gas, but helium (He), neon (Ne), krypton (Kr), xenon (Xe), radon (Rn), nitrogen (N ₂ ), etc. gas may be performed by CO _2.
In addition to Cl ₂ , BCl ₃ , SiCl ₄ , and CCl ₄ can also be used as the reactive gas for RIBE. In addition to RIBE, dry ion etching may be reactive ion etching (RIE) or ion beam assisted etching (IBAE).
[0026]
In the above embodiment, the active layer 5 is composed of In _0.08 Ga _0.92 N, and the cladding layers 4 and 61 are composed of Al _0.08 Ga _0.92 N. However, the general formula Al _X Ga _Y In _1-XY N (0 ≦ X ≦ 1, Binary, ternary, and quaternary group III nitride semiconductors represented by 0 ≦ Y ≦ 1, 0 ≦ X + Y ≦ 1) can be used. At this time, the composition ratio of the active layer and the clad layer may be selected so that the band gap of the active layer becomes narrower than the band gap of the clad layer and the lattice constant is matched when forming a double heterojunction. . In addition, when an arbitrary quaternary group III nitride semiconductor is used, the band gap and the lattice constant can be independently changed, so that a double heterojunction in which the lattice constants in the respective layers are matched is possible. Although it is desirable to form a double heterojunction, the present invention is not limited to a double heterojunction, and may be a single heterojunction, a homojunction or the like. A structure may be adopted.
[0027]
In the above embodiment, the mask for the etching process when forming the electrode 8 has etching resistance against dry etching, such as metal, resist, etc. in addition to SiO ₂ , and is selective to the underlying GaN-based semiconductor. Any material that can be etched or stripped can be used. Furthermore, although the Makusu of Enchingu process for forming a resonator end face with photoresists, and other, has etching resistance to dry etching of SiO ₂ or the like, to the underlying electrodes 7 and 8, selectively Any material that can be etched or stripped can be used.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a configuration of a light emitting diode according to a specific embodiment of the present invention.
FIG. 2 is a cross-sectional view showing a manufacturing process of the laser diode of the embodiment.
FIG. 3 is a cross-sectional view showing a manufacturing process of the laser diode of the embodiment.
FIG. 4 is a cross-sectional view showing a manufacturing process of the laser diode of the embodiment.
FIG. 5 is a cross-sectional view showing a manufacturing process of the laser diode of the embodiment.
FIG. 6 is a perspective sectional view showing the manufacturing process of the laser diode of the same example.
FIG. 7 is a perspective sectional view showing the structure of the laser diode of the same example.
FIG. 8 is an explanatory diagram showing a wafer cutting method and a cluster beam etching method.
[Explanation of symbols]
100 ... Laser diode 1 ... Sapphire substrate 2 ... Buffer layer 3 ... High carrier concentration n ⁺ layer 4 ... Clad layer (n layer)
5 ... Active layer 61 ... Clad layer (p layer)
62 ... contactor layer 7,8 ... metal electrode 9 ... SiO ₂ layer 12 ... photoresist S ... cavity facet 14 ... strips 15 ... scribe groove

Claims (6)

In a method of manufacturing a group III nitride semiconductor laser diode in which a p layer and an n layer made of a group III nitride semiconductor are formed on a substrate,
Forming each layer of a Group 3 nitride semiconductor on the substrate;
It said layers to form an end face of the resonator, and dry etched by reactive ion beam etching (RIBE), reactive ion etching (RIE) or ion beam assisted etching (IBAE),
The dry etched end face is further etched by gas cluster ion beam etching ,
The gas cluster ion beam etching is performed in a state where the wafer on which the element is formed is cut into strips in parallel with the end face, the strip-like pieces are erected, and the end face is faced upward. about
A method for producing a group III nitride semiconductor laser diode. The group III nitride semiconductor is Al _X Ga _Y In _1-XY N (0≤X≤1, 0≤Y≤1, 0≤X + Y≤1). A method for producing a Group III nitride semiconductor laser diode.   2. The method of manufacturing a group III nitride semiconductor laser diode according to claim 1, wherein the dry etching is reactive ion beam etching (RIBE). _{2. The} method of manufacturing a group III nitride semiconductor laser diode according to claim 1, wherein the reactive ion beam etching is etching using Cl2 gas. 2. The group III nitride semiconductor laser diode according to claim 1, wherein the semiconductor laser diode has a cladding layer made of Al _x1 Ga _1-x1 N and an active layer made of In _x2 Ga _1-x2 N. 3. Production method. The gas cluster ion beam etching uses an inert gas such as argon (Ar), helium (He), neon (Ne), krypton (Kr), xenon (Xe), radon (Rn), nitrogen (N ₂ ), etc. The method for producing a group III nitride semiconductor laser diode according to claim 1, wherein the method is performed.

Images