JP4097343B2 - Manufacturing method of nitride semiconductor laser device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a light emitting element such as an LED (light emitting diode) or LD (laser diode), a light receiving element such as a solar cell or an optical sensor, or a nitride semiconductor (Al _x In _y Ga ₁ ) used in a transistor, an integrated circuit, or the like. _-XY N, _0≤X , _0≤Y , X + Y <1) The present invention relates to a device manufacturing method.
[0002]
BACKGROUND OF THE INVENTION
[Prior art]
We have fabricated a nitride semiconductor laser device including an active layer on a GaN substrate, and have announced the world's first continuous oscillation at room temperature of over 10,000 hours (INCS'97 Proceedings, October 27) -31, 1997, P444-446, and Jpn. J. Appl. Phys. Vol. 36 (1997) pp. L1568-L1571, Part2, No. 12A, 1 December 1997). Furthermore, by removing the sapphire substrate from the laser element and using GaN alone, it has been announced that continuous oscillation of 10,000 hours or more was achieved even at 5 mW output (Jpn. J. Appl. Phys. Vol. 37 (1998). pp. L309-L312, and Appl. Phys. Lett. Vol. 72 (1998) No. 16, 2014-2016).
[0003]
Conventionally, a nitride semiconductor is laminated on a heterogeneous substrate such as sapphire as a method of manufacturing a nitride semiconductor laser device. This is because, when a nitride semiconductor is grown on a substrate, there is no substrate that is lattice-matched with the semiconductor to be grown. Therefore, it is generally on a heterogeneous substrate that is not lattice-matched with a nitride semiconductor such as sapphire, spinel, or silicon carbide. Has grown into.
[0004]
As a method of growing a nitride semiconductor crystal that can greatly reduce crystal defects, the present inventors formed a GaN substrate on a different substrate different from the nitride semiconductor, and formed an element structure on the GaN substrate. Nitride semiconductor laser devices capable of achieving continuous oscillation of about 10,000 hours at a wavelength of about 400 nm and an optical output of 2 mW are disclosed (for example, “Current Status of InGaN-based Multiple Quantum Well Structure Semiconductor Lasers”, 58th JSAP Lecture, Lecture No. 4aZC-2, October 1997, “Present Status of InGaN / AlGaN based Laser Diodes”, The Second International Conference on Nitride Semiconductor-1 (1997) Such as are described in the month.).
[0005]
Since the nitride semiconductor obtained by this method is grown laterally on the protective film, it is generally called lateral overgrowth GaN (LOG, laterally grown GaN).
[0006]
The nitride semiconductor laser device has a crystal growth method in which a conventional crystal defect is extremely present on a sapphire substrate having a C-plane {0001} as a main surface, which is previously provided with an A-plane {112-0} as an orientation flat surface. A large number of GaN layers are grown thinly, and a protective film made of SiO ₂ is formed thereon in a stripe shape, or GaN is selectively etched to form a stripe GaN, from which a halide vapor phase growth method (HVPE) is formed. ), By utilizing the lateral growth of GaN by vapor phase growth method such as metal organic chemical vapor deposition (MOVPE) and growing the GaN layer again, a GaN substrate (thickness 10 μm) with few crystal defects is obtained. Can be formed. The orientation flat surface is precisely called an orientation flat surface, which is a surface obtained by cutting out a disk-shaped wafer to indicate the crystal axis direction.
[0007]
When this GaN substrate is formed, when grown on the sapphire C surface as a property of GaN, the M surface {11-00} of GaN becomes parallel to the A surface of sapphire. When forming GaN on a substrate, first, a protective film or GaN formed in a stripe shape is formed perpendicularly to the A surface with respect to the A surface of sapphire, and further nitrided to form an element structure thereon. When stacking physical semiconductors, the element structure is formed so that the laser resonator direction is perpendicular to the A-plane of sapphire. After forming the element structure in this manner, at least the laser emission surface side is cleaved with the GaN M-plane to obtain a good resonator surface.
[0008]
[Problems to be solved by the invention]
However, this pre-installed orientation flat surface (this is referred to as the first orientation flat surface) is generally a surface provided by using a machine such as a polishing machine, and does not accurately indicate the A surface. There are some that have some errors. Therefore, even if the protective film or GaN and the resonator are formed on the basis of the first orientation flat surface as the A surface, the relationship between the resonator direction and the resonator surface is not perpendicular, and a deviation occurs. A good laser element cannot be obtained.
[0009]
[Means for Solving the Problems]
The present invention has been made in view of the above problems.
In the method for manufacturing a nitride semiconductor laser device of the present invention, a stripe-shaped protective film is parallel to the M plane of the sapphire substrate on a sapphire substrate having the C plane as the main plane and the A plane and the M plane as the orientation flat plane. A nitride semiconductor layer is formed by forming a pattern in a direction and selectively growing GaN thereon, and removing the sapphire substrate and the stripe-shaped protective film from the nitride semiconductor layer to obtain a nitride semiconductor substrate made of only GaN. A first step, a second step of forming at least one second orientation flat surface by cleaving the nitride semiconductor substrate at the M plane, and a nitride semiconductor on the nitride semiconductor substrate. And a third step of forming an element structure so that a resonator direction is perpendicular to the second orientation flat surface, and a fourth step of chipping the nitride semiconductor substrate. This And features.
After the third step, the nitride semiconductor substrate is cleaved in M plane direction of the GaN to form a cavity, then, in the fourth step, the nitride semiconductor substrate is preferably to chip. In the second step, it is preferable to cleave by cutting a part of the nitride semiconductor substrate and applying an external force.
After the third step, it is preferable to include a step of forming an n-electrode on the surface of the nitride semiconductor substrate on the side where the sapphire substrate is removed.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to FIGS.
FIG. 1 is a view of a sapphire substrate showing an embodiment of a manufacturing process of a nitride semiconductor device of the present invention as viewed from the C-plane direction. The sapphire A plane and M plane shown in the figure indicate directions perpendicular to the paper plane. In this case, the A plane is the first orientation flat surface and the M plane is the second orientation flat surface.
[0011]
Examples of the substrate include a sapphire R plane, GaN, SiC (including 6H, 4H), spinel (MgAl ₂ O ₄ ), Si, GaAs, ZnO and the like in addition to the sapphire C plane. In the case of GaN, the orientation plane is formed by cleaving at {11-00} with the {0001} plane as the principal plane, and in the case of SiC by cleaving at {11-00} with the {0001} plane as the principal plane. An orientation flat surface is formed, and in the case of spinel, the orientation surface is formed by cleaving the {111} plane as the main surface and {100} plane, and in the case of Si and GaAs, the {111} surface is the main surface, and {11-0 } The orientation flat surface is formed by cleaving at the surface. Nitride semiconductors can be stacked on these substrates, and a good nitride semiconductor laser element can be formed by forming an element structure using the second orientation flat surface obtained by the respective cleavage as a reference plane. Can be obtained.
[0012]
In the present invention, two second orientation flat surfaces obtained by cleaving may be provided as shown in FIG. By providing two second orientation flat surfaces as shown in FIG. 2, the protective film or GaN and resonator directions can be formed more accurately with respect to the reference surface, and the yield can be improved and a good laser element can be obtained. .
In the present invention, two first orientation flat surfaces formed in advance may be provided as shown in FIG.
[0013]
In the present invention, a method for obtaining the second orientation flat surface by cleaving will be described specifically. In the case of a substrate with strong cleaving ability such as GaN or SiC, a kerf is partially inserted using a device such as a dicer, After that, it can be cleaved neatly by applying a little external force, and the orientation flat surface can be obtained. In addition, in the case of a substrate with a low cleavage property such as sapphire or spinel, scribing or half dicing along the surface to be cleaved makes an overall kerf from end to end, and then an external force is applied to the kerf. Cleavage occurs within the range, and an orientation flat surface can be obtained.
[0014]
In the present invention, the substrate may be an off-angle (tilted) substrate in a step shape. In this case, the resonator direction is formed to be parallel to the direction along the step (step direction). This means that, in the case of a sapphire substrate, a substrate in which the direction along the step (step direction) is parallel to the second orientation flat surface is used. Furthermore, a favorable laser element can be obtained by setting the off angle of the off angle in the range of 0.1 ° to 0.2 °.
Further, in the present invention, the cleavage property is weak, but by cleaving on the M-plane of sapphire having cleavage property, a second orientation flat surface is newly provided, and this is used as a reference surface to form a protective film or GaN in a stripe shape. Then, the direction of the resonator is determined. That is, a stripe-shaped protective film or GaN is formed in parallel to the M-plane of sapphire obtained by cleavage, and the element structure is formed so that the resonator direction is also parallel. A deviation from the emission surface is eliminated, the yield is improved, and a good laser element is obtained.
[0015]
The method for manufacturing a nitride semiconductor device of the present invention is not limited to a nitride semiconductor laser device.
[0016]
【Example】
[Example 1]
FIG. 4 is a schematic cross-sectional view showing the structure of the nitride semiconductor laser device according to one embodiment of the present invention, and specifically shows the structure of the laser device. Hereinafter, Example 1 is demonstrated based on FIG.1 and FIG.4.
As shown in FIG. 1, a sapphire substrate 1 is prepared which has a C plane {0001}, in which an A plane {112-0} is formed as a first orientation flat surface in advance. First, the cleavage of sapphire is used to cleave the sapphire M-plane {11-00} in a direction substantially perpendicular to the A-plane. Using this as the second orientation flat surface, an element structure is formed on the C surface as follows.
[0017]
First, the sapphire substrate 1 is set in a MOCVD reaction vessel, and a layer made of undoped GaN at 500 ° C. is formed as an underlayer at 200 ° C., followed by 2.5 μm of a layer made of undoped GaN at 1050 ° C., A first nitride semiconductor layer having a total film thickness of about 2.5 μm is formed.
[0018]
Next, after growing the first nitride semiconductor layer, a striped photomask is formed on the surface of the first nitride semiconductor layer, and a protective film made of SiO _{2 having a} stripe width of 10 μm and a window portion of 5 μm is formed by a CVD apparatus. Is formed with a film thickness of 0.5 μm. At this time, the stripe direction is formed in parallel to the second orientation flat surface.
[0019]
After forming the stripe-shaped protective film, the wafer is transferred to a reaction vessel, and a second nitride semiconductor layer made of undoped GaN is grown to a thickness of 15 μm at 1050 ° C. using TMG and ammonia as source gases. The nitride semiconductor substrate 2 is obtained as described above.
[0020]
Next, a device structure is formed on the obtained nitride semiconductor substrate 2. First, an n-side contact layer 3 made of GaN or AlGaN, a crack prevention layer made of InGaN (this can be omitted), an n-side cladding layer 4 made of a superlattice of AlGaN and Si-doped GaN, made of GaN n-side light guide layer 5, multi-quantum well structure (MQW) active layer 6 made of InGaN, p-side cap layer 7 made of Mg-doped AlGaN, p-side light guide layer 8 made of Mg-doped GaN, AlGaN and Mg A p-side cladding layer 9 made of a superlattice with doped GaN and a p-side contact layer 10 made of Mg-doped GaN are sequentially stacked.
[0021]
Next, part of the p-side contact layer 10 is dry-etched to expose the n-side contact layer 3. Further, the p-side layer is etched to the p-side cladding layer 9 by RIE to form a ridge, an insulating film 30 such as TiO ₂ as a protective film on the ridge, and a p-electrode 20 and a p-pad electrode 21 on each contact layer, An n electrode 22 and an n pad electrode 23 are formed.
Finally, the wafer is cleaved in the M-plane direction of GaN to form a resonator, and a chip is formed.
[0022]
The laser chip obtained as described above was placed face-up (with the substrate and heat sink facing each other) on the heat sink, each electrode was wire-bonded, and continuous oscillation was attempted at room temperature. At an output of ² kA / cm ² and 20 mW, continuous oscillation with an oscillation wavelength of 405 nm was confirmed, indicating a lifetime of 1000 hours or longer.
[0023]
[Example 2]
In a sapphire substrate 1 having a C plane {0001} as a main surface, in which the A plane {112-0} is formed as a first orientation flat surface in advance, in a direction substantially perpendicular to the A plane using the cleavage of sapphire. As shown in FIG. 2, cleaving is performed at two locations on both sides to expose the M-plane {11-00} of sapphire. Using this as the second orientation flat surface, an element structure is formed on the C surface in the same manner as in the first embodiment.
When the device obtained as described above was tried to continuously oscillate at room temperature, continuous oscillation at an oscillation wavelength of 405 nm was confirmed at an output of a threshold current density of ² kA / cm ² and 20 mW as in Example 1, and 1000 hours. The lifetime was shown above, and the yield could be further increased.
[0024]
[Example 3]
In the sapphire substrate 1 whose principal surface is the C plane {0001}, in which the A plane {112-0} is formed as the first orientation flat surface in advance, the off angle is further stepped, and the off angle is 0.13 °. A substrate in which the direction along the step (step difference direction) is formed perpendicular to the A plane is used. First, the cleavage of sapphire is used to cleave the sapphire M-plane {11-00} in a direction substantially perpendicular to the A-plane. Using this as the second orientation flat surface, an element structure is formed on the C surface in the same manner as in the first embodiment.
The laser element obtained as described above exhibited almost the same characteristics as in Example 1.
[0025]
[Example 4]
As shown in FIG. 1, a sapphire substrate 1 is prepared which has a C-plane with the A-plane formed in advance as a first orientation flat surface. First, the cleavage of sapphire is used to cleave the sapphire in the direction substantially perpendicular to the A plane to expose the M plane of sapphire. Using this as the second orientation flat surface, an element structure is formed on the C surface as follows.
First, the sapphire substrate 1 is set in a MOCVD reaction vessel, and a layer made of undoped GaN at 500 ° C. is formed as an underlayer at 200 ° C., followed by 2.5 μm of a layer made of undoped GaN at 1050 ° C., A nitride semiconductor layer having a total film thickness of about 2.5 μm is formed.
[0026]
Next, after a nitride semiconductor layer is grown, a striped photomask is formed on the surface of the nitride semiconductor layer, and a protective film made of SiO _{2 having a} stripe width of 10 μm and a window portion of 5 μm is formed by a CVD apparatus with a thickness of 0.5 μm. Form with thickness. At this time, the stripe direction is formed in parallel to the second orientation flat surface.
Subsequently, a portion of the GaN on which the SiO ₂ film is not formed is etched by the RIE until the sapphire substrate is exposed to form irregularities, thereby forming the GaN in a stripe shape, and finally the SiO ₂ on the upper portion of the convex portion is formed. Remove.
[0027]
After forming the striped GaN, the wafer is transferred to a reaction vessel, and at 1050 ° C., a second nitride semiconductor layer made of undoped GaN is grown to a thickness of 15 μm using TMG and ammonia as source gases. The nitride semiconductor substrate 2 is obtained as described above.
Other than that, a laser device was fabricated in the same manner as in Example 1, and showed almost the same characteristics as in Example 1.
[0028]
[Example 5 ]
As shown in FIG. 1, a sapphire substrate 1 is prepared which has a C-plane with the A-plane formed in advance as a first orientation flat surface. First, the cleavage of sapphire is used to cleave the sapphire in the direction substantially perpendicular to the A plane to expose the M plane of sapphire. Using this as the second orientation flat surface, an element structure is formed on the C surface as follows.
[0029]
First, the sapphire substrate 1 is set in a MOCVD reaction vessel, and a layer made of undoped GaN at 500 ° C. is formed as an underlayer at 200 ° C., followed by 2.5 μm of a layer made of undoped GaN at 1050 ° C., A first nitride semiconductor layer having a total film thickness of about 2.5 μm is formed.
On the sapphire substrate 1 fabricated as described above, the n-side contact layer 3, the n-side cladding layer 4, the n-side light guide layer 5, the active layer 6 having a multiple quantum well structure, the p-side cap layer 7, and the p-side light guide. Layer 8, p-side cladding layer 9 and p-side contact layer 10 are laminated.
[0030]
Next, when the p-electrode 20 and the p-pad electrode 21 are formed on the p-side contact layer 10 and the n-electrode 22 and the n-pad electrode 23 are formed on the n-side contact layer 3 exposed by etching, both electrodes are made of sapphire. It is formed in a bar shape parallel to the second orientation flat surface so as to be parallel to the M surface.
Finally, the wafer is cleaved in the M-plane direction of GaN to form a resonator, and a chip is formed.
[0031]
Although the laser device obtained as described above is slightly inferior to Example 1, continuous oscillation at an oscillation wavelength of 405 nm is confirmed at room temperature at a threshold current density of ² kA / cm ² and an output of 20 mW, and a lifetime of 1000 hours or more. showed that.
[0032]
[Example 6 ]
FIG. 5 is a schematic cross-sectional view showing the structure of the nitride semiconductor laser device according to one embodiment of the present invention, and specifically shows the structure of the laser device. Hereinafter, Example 6 is demonstrated based on FIG.1 and FIG.5.
As shown in FIG. 1, a sapphire substrate 1 is prepared which has a C plane {0001}, in which an A plane {112-0} is formed as a first orientation flat surface in advance. First, the cleavage of sapphire is used to cleave the sapphire M-plane {11-00} in a direction substantially perpendicular to the A-plane. Using this as the second orientation flat surface, an element structure is formed on the C surface in the same manner as in the first embodiment.
[0033]
Until the protective film made of SiO ₂ and the second nitride semiconductor are grown, the next nitride semiconductor substrate obtained from the sapphire side is used as the underlayer made of undoped GaN or the first layer, as in Example 1. Polishing is performed until the nitride semiconductor layer is exposed to obtain a nitride semiconductor substrate 2 made of only GaN. The nitride semiconductor substrate 2 is cleaved at the M plane to form a second orientation flat surface.
[0034]
Next, an element structure is formed on the nitride semiconductor substrate 2. In the case of GaN, since the M-plane of GaN corresponds to the second orientation flat surface, the resonator direction of the element is set with respect to the second orientation flat surface. To form vertically.
Finally, the p-electrode 20 is formed on the p-side contact layer, and the n-electrode 22 is formed on the nitride semiconductor surface obtained by polishing to form a chip.
[0035]
The laser device obtained as described above was confirmed to exhibit continuous oscillation at an oscillation wavelength of 405 nm at a threshold current density of ² kA / cm ² and an output of 20 mW at room temperature, which was almost the same as in Example 1, and had a lifetime of 1000 hours or longer. showed that.
[0036]
【The invention's effect】
As described above, according to the present invention, an element structure is obtained in a method for manufacturing a nitride semiconductor device in which a nitride semiconductor is epitaxially grown using a vapor phase growth method on a substrate plane on which a first orientation flat surface is provided in advance. Before laminating the nitride semiconductor, the substrate is cleaved to form at least one second orientation flat surface, thereby eliminating the deviation between the cavity direction and the laser emission surface, and improving the yield. As a result, a good laser element can be obtained.
[Brief description of the drawings]
FIG. 1 is a view of a sapphire substrate showing an embodiment of a manufacturing process of the present invention as viewed from the direction of a C-plane.
FIG. 2 is a view of a sapphire substrate showing another embodiment of the manufacturing process of the present invention as seen from the direction of the C-plane.
FIG. 3 is a view of a sapphire substrate showing another embodiment of the manufacturing process of the present invention as viewed from the direction of the C-plane.
FIG. 4 is a schematic cross-sectional view showing the structure of a nitride semiconductor laser device according to an embodiment of the present invention.
FIG. 5 is a schematic cross-sectional view showing the structure of a nitride semiconductor laser device according to another embodiment of the present invention.

Claims (4)

A stripe-shaped protective film is formed in a direction parallel to the M surface of the sapphire substrate on the sapphire substrate with the C surface as the main surface and the A surface and the M surface as the orientation flat surfaces, and GaN is selectively grown thereon. by forming a nitride semiconductor layer, a first step of the nitride semiconductor substrate of only GaN and the sapphire substrate is removed and a stripe-shaped protective layer from the nitride semiconductor layer,
A second step of forming at least one second orientation flat surface by cleaving the nitride semiconductor substrate at the M plane;
A third step of laminating a nitride semiconductor on the nitride semiconductor substrate and forming an element structure so that a resonator direction is perpendicular to the second orientation flat surface;
And a fourth step of forming the nitride semiconductor substrate into a chip. A method for manufacturing a nitride semiconductor laser device, comprising: After the third step, by cleaving the nitride semiconductor substrate at the M-plane direction of the GaN to form a cavity, then, in the fourth step, and characterized in that chips of the nitride semiconductor substrate The method for manufacturing a nitride semiconductor laser device according to claim 1. In the second step, put kerf in a part of the nitride semiconductor substrate, the manufacturing method of the nitride semiconductor laser device according to claim 1 or 2, characterized in that the cleavage by applying an external force . After the third step, according to any one of claims 1 to 3, further comprising a step of forming an n-electrode on the surface on which the removal of the sapphire substrate of the nitride semiconductor substrate A method for manufacturing a nitride semiconductor laser device.

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