JP4644955B2 - Nitride semiconductor device fabrication method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a nitride semiconductor device, and more particularly to a method for manufacturing a nitride semiconductor device having a good optical resonance surface.
[0002]
[Prior art]
As one of semiconductor materials capable of lasing light in a short wavelength range from blue to ultraviolet, the composition is shown as In _X Al _Y Ga _1-XY N (0 ≦ X, 0 ≦ Y, X + Y ≦ 1). Gallium nitride compound semiconductors are known.
In particular, a semiconductor laser diode using a gallium nitride compound semiconductor has attracted attention as a light emitting element that emits light in a short wavelength region due to the recent practical application of a light emitting diode made of a gallium nitride compound semiconductor. It has come to be.
[0003]
With the progress of research, semiconductor laser diodes having various structures using gallium nitride compound semiconductors have been proposed.
For example, JP-A-6-283825 discloses a laser diode having a Si-doped n-type AlGaN / Si-doped n-type GaN / Mg-doped p-type AlGaN double heterostructure, and USP 5,146,465 discloses AlGaN. A laser diode is disclosed in which an optical resonant surface is formed of an AlGaN multilayer film using as an active layer.
[0004]
The semiconductor laser element basically has a double heterojunction structure formed by a combination of an active layer / cladding layer of a nitride-based compound semiconductor layer such as InGaN / AlGaN, InGaN / GaN, AlGaN / AlGaN, or the like. .
By using a gallium nitride compound semiconductor containing at least indium (In) and gallium (Ga), for example, InGaN as an active layer, the emission wavelength can be changed in the range of, for example, 370 nm to 460 nm only by InGaN interband emission. it can.
Hereinafter, a semiconductor laser element having a laminated structure of III-V group compound semiconductor layers containing at least Ga and N is referred to as a GaN-based semiconductor laser element.
[0005]
A double heterojunction structure suitable as a semiconductor laser element has an active layer made of non-doped In _X Al _Y Ga _1-XY N (0 ≦ X, 0 ≦ Y, X + Y ≦ 1), which has a different conductivity type than the active layer. It is a double heterojunction structure sandwiched between gallium nitride compound semiconductors with large band gap energy.
For example, a double heterojunction structure in which an active layer is sandwiched between n-type and p-type In _x Al _Y Ga _1-XY N (0 ≦ X, 0 ≦ Y, X + Y ≦ 1) doped with an n-type dopant and a p-type dopant, respectively. is there.
[0006]
Here, the basic structure and manufacturing method of the GaN-based semiconductor laser device will be described with reference to FIG. FIG. 3 is a schematic cross-sectional view showing the basic configuration of the GaN-based semiconductor laser device.
The GaN-based semiconductor laser device 10 is often a mesa stripe-type semiconductor laser device. As shown in FIG. 3, for example, a first cladding layer 14 of an n-type GaN-based compound semiconductor is formed on the C surface of a GaN substrate 12, and A double heterostructure having a laminated structure of an active layer 16 of a GaN-based compound semiconductor and a second cladding layer 18 of a p-type GaN-based compound semiconductor is provided.
[0007]
A striped positive electrode 20 is formed on the second cladding layer 18, and a negative electrode 22 is formed on the back surface of the GaN substrate 12. The negative electrode 22 is formed after the back surface of the GaN substrate 12 is polished and adjusted to a predetermined thickness.
In the present semiconductor laser device 10, by forming the positive electrode 20 with a width of about 1 μm to 20 μm to form a striped optical waveguide, laser oscillation can be caused along the striped optical waveguide.
[0008]
The GaN-based compound semiconductor layer is usually formed by epitaxial growth on the (0001) plane of the underlying GaN-based compound semiconductor or gallium nitride substrate (hereinafter this plane is referred to as the C plane; see FIG. 4). FIG. 4 is a unit cell diagram showing the plane orientation of the GaN-based semiconductor.
In the fabrication of the semiconductor laser device 10 described above, a GaN-based compound semiconductor is oriented on the C surface of the GaN substrate 12 in the C-axis direction, for example, HVPE (hydride vapor phase epitaxy), MOCVD (metal organic vapor phase epitaxy), MBE. It is grown by a vapor phase growth method such as (molecular beam vapor phase growth method) to form a laminated structure.
Although it is most desirable that the C-plane of the GaN substrate is completely coincident with the (0001) plane, the C-plane having an off angle within about ± 2 ° with respect to the (0001) plane may be used. Good. Also, in place of the GaN substrate, a GaN-based compound semiconductor layer is often epitaxially grown on the C surface of the sapphire substrate.
[0009]
The process up to the above is a wafer process process, and the striped positive electrodes 20 are arranged in parallel on the wafer at a predetermined interval, as shown in FIG. They are arranged in parallel to the A plane (11-20) (direction indicated by a broken line).
When the GaN substrate 12 and the laminated structure thereon are divided into strips with a predetermined width on a plane parallel to the M plane (1-100) plane, the GaN-based compound semiconductor layer on the division plane becomes an optical resonance plane. The striped positive electrode 20 is formed so that the stripe is perpendicular to the dividing surface of the laminated structure of the GaN-based compound semiconductor layers.
[0010]
Next, the GaN substrate 12 and the laminated structure thereon are divided into strips having a predetermined width on the M-plane (1-100) plane of the GaN substrate, and the striped positive electrode 20 is formed as shown in FIG. Bars 24 arranged in the width direction are formed. When dividing into bars, as shown in FIG. 6, a marking line 25 is put on the wafer surface, and the marking is made along the marking line 25 using cleavage. The width W when dividing into strips is the resonator length L of the semiconductor laser element 10.
Next, as shown in FIG. 5C, the bars 24 are divided into planes parallel to the A-plane (1100) plane of the GaN substrate 12 and formed into semiconductor laser chips 26 each having a predetermined width.
In the above description, the fabrication of the GaN-based semiconductor laser element has been described by taking the GaN substrate as an example. However, a sapphire substrate may be used as the substrate. When a sapphire substrate is used as the substrate, the negative electrode 22 is formed not on the back surface of the substrate but on the same side as the positive electrode 20 with respect to the substrate.
[0011]
[Problems to be solved by the invention]
By the way, the optical resonant surface, which is an important component of the semiconductor laser device, needs to be a plane that is orthogonal to the stripe-shaped positive electrode and a smooth surface. If they are not orthogonal and smooth, the laser characteristics of the semiconductor laser element will deteriorate.
However, in the conventional method, the wafer process step is completed, the wafer is turned into a bar to form an optical resonant surface, and then the bar is chipped to form a smooth optical resonant surface orthogonal to the positive electrode. There is a problem that the yield is remarkably lowered.
[0012]
In the above description, a GaN-based semiconductor laser device having a laminated structure of GaN-based compound semiconductor layers formed on a GaN substrate is taken as an example, but this problem is not limited to this, and the problem is formed on a sapphire substrate. This problem is applicable to GaN-based semiconductor laser devices, and further to nitride-based semiconductor devices in general. Furthermore, this problem also applies to a semiconductor laser device having a gain waveguide type mesa stripe structure or a buried hetero type stripe structure.
Therefore, the present invention has been made in view of such circumstances, and an object of the present invention is to provide a nitride-based semiconductor element having good element characteristics on a nitride-based semiconductor substrate or a sapphire substrate with a high yield. It is to provide a method of making.
[0013]
[Means for Solving the Problems]
The present inventor paid attention to the cleaving property of the laminated structure of the GaN substrate and the GaN-based compound semiconductor layer formed thereon in solving the above-described problem.
For example, GaAs-based semiconductor materials used for infrared / red semiconductor laser elements are cubic and have excellent cleavage properties, so that the resonant surface of a semiconductor laser consisting of a cleavage plane of a semiconductor crystal is striped. It becomes a smooth surface orthogonal to the structure.
On the other hand, a sapphire substrate does not have a cleavage property, and a nitride-based semiconductor substrate such as a GaN substrate does not have a cleavage property as excellent as that of a GaAs substrate. Also, the nitride compound semiconductor layer stack structure is inferior in cleavage to the GaAs stack structure.
Due to the above-mentioned problem of cleavage, the present inventor is difficult to obtain a good cleavage plane as an optical resonance surface with a high yield in the conventional method of cleaving at the optical resonance surface to form a bar. From this difference, it was noticed that the optical resonant surface easily deviates in an oblique direction with respect to the stripe structure, and is difficult to become an orthogonal surface.
[0014]
To explain further, since the sapphire substrate has no cleaving property, and the nitride semiconductor substrate such as the GaN substrate is not as strong as the GaAs substrate, it is not easy to cleave the optical resonant surface even if the substrate is thinned. .
Further, when a guide groove for making it easy to break is inserted, if the groove is formed too deep, there arises a problem that the flatness of the optical resonance surface is deteriorated due to the influence.
Furthermore, since the optical resonant surface is exposed before being formed into a chip, the optical resonant surface is often contaminated or damaged.
[0015]
Therefore, the present inventor first divides the wafer along the A-plane (11-20) plane in order to form a bar so as not to damage the optical resonant surface as much as possible. Then, it was conceived to cleave on the M plane (1-100) plane to make a chip in the manner of folding the bar.
[0016]
In order to achieve the above object, a method for producing a nitride semiconductor device according to the present invention includes a method for producing a nitride semiconductor device having a nitride compound semiconductor layer laminated structure on a nitride semiconductor substrate.
Forming a laminated structure of a nitride-based compound semiconductor layer on the (0001) plane of the substrate;
Processing the upper part of the laminated structure of the nitride-based compound semiconductor layer or forming a stripe-like structure such as a stripe-shaped current injection region in parallel with the A-plane of the substrate on the laminated structure;
Dividing the substrate and the laminated structure into strips having a predetermined width for each stripe structure on the A surface of the substrate, and forming a bar having the stripe structure in the longitudinal direction;
And a step of dividing the bar along the M-plane of the substrate to form a chip having a predetermined length each having a stripe structure.
[0017]
In addition, in the method for manufacturing a nitride-based semiconductor device according to the present invention, a stripe structure such as a stripe-shaped current injection region is formed in a stacked structure while forming a stacked structure of nitride-based compound semiconductor layers on the (0001) plane of the substrate. The present invention can also be applied to a case where a planar structure is embedded and formed parallel to the A surface of the substrate.
Before the step of forming the bar, it is desirable that the back surface of the substrate is polished to adjust the substrate to a predetermined thickness, for example, 200 μm or less, more preferably 100 μm or less.
[0018]
In the method of the present invention, the A plane means the (1120) plane of FIG. 4 (unit cell diagram), and the M plane means the (01-10) plane shown in FIG.
The method of the present invention can be applied without limitation to the structure of the nitride semiconductor device as long as it has a stripe structure, and can be applied to, for example, a semiconductor laser device, an optical amplifier, an optical modulator, a light emitting diode, and the like. Further, the composition of the nitride-based compound semiconductor layer can be applied without restriction.
[0019]
When the wafer is divided into A-bars to form bars, the dividing surface is not an optical resonance surface, so it may be divided using a scriber or dicer, and further, the scriber or dicer blade may be extended to the bottom of the back surface of the substrate. It can also be cut completely.
[0020]
When cleaving on the M surface to form a chip, a method of forming a shallow guide groove and then pressing and breaking using a braking device or a roller may be applied, or a method of breaking without a groove may be applied. Is possible.
In addition, when cleaving from the bar, when guiding grooves are provided on the laminated structure side, guide grooves separated in a dotted line shape may be provided between the stripe structures. If it is a cleavage from a bar, even if it is a guide groove separated in dotted lines, it can be divided by a high yield linearly.
[0021]
In the method of the present invention, a bar structure that is easy to split as much as possible is formed in the laminated structure of a nitride-based compound semiconductor layer having a low cleavage property and a nitride-based semiconductor substrate as much as possible, so that the bar can be stably divided into chips. Can do.
Furthermore, as indicated by the hatched portion in FIG. 4, the M-plane of gallium nitride necessarily has the other M-plane facing each other, so that the light beams facing each other can be obtained by dividing the bar between the two M-planes. The resonant surface can be easily formed.
[0022]
Further, the M-plane of the laminated structure of the nitride-based semiconductor substrate and the nitride-based compound semiconductor layer has the property of being easily broken compared to other plane orientations, for example, the C-plane and the A-plane. The cracked surface (cleavage surface) becomes an optical resonance surface in a state like a mirror surface.
Therefore, by combining bar formation by cutting A-plane, which is hard to break, and chip formation by cleavage of M-plane, the mechanical cutting load is concentrated on A-plane and the damage to M-plane that becomes the optical resonance surface is reduced. I can.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described specifically and in detail with reference to the attached drawings.
Embodiment Example This embodiment example is an example of an embodiment of a method for manufacturing a nitride-based semiconductor device according to the present invention. FIG. 1 shows an example of a nitride-based semiconductor device manufactured by the method of this embodiment. FIG. 2 is a cross-sectional view showing a configuration, and FIG. 2 is a plan view showing a longitudinal arrangement of stripe-like positive electrodes on a substrate (wafer).
As the substrate, for example, an n-type GaN substrate 30 having a substrate thickness of 350 μm in which the C surface is the main surface and the M surface and the A surface are orientation flat is used.
[0024]
First, on the main surface (C surface) of the GaN substrate 30, using a MOCVD method, a GaN buffer layer 31 having a thickness of 300 mm, an n-type GaN underlayer 32 having a thickness of 4 μm, and a thickness of 1. 3 μm Si-doped n-type AlGaN cladding layer 33, 500 μm thick active layer 34 made of n-type InGaN layer, 0.6 μm thick Mg-doped p-type AlGaN cladding layer 35, and 0.1 μm thick Mg A p-type contact layer 36 made of a doped p-type GaN layer is epitaxially grown to form a stacked structure.
[0025]
Next, a multilayer metal film (not shown) for forming a positive electrode is deposited on the uppermost p-type contact layer 36 by a sputtering method or the like, and subsequently, as shown in FIG. A mask having a predetermined stripe shape extending in a direction parallel to the plane, that is, the plane A (direction indicated by a solid line) is formed on the multilayer metal film, and the multilayer metal film is etched to form 2 μm on the p-type contact layer 36 A positive electrode 37 having a stripe shape with a width is formed.
Next, the substrate surface (back surface) of the GaN substrate 30 on the side where the GaN-based compound semiconductor layer is not formed is polished to adjust the substrate thickness to 80 μm. After polishing, the negative electrode 38 is formed on the back surface.
The negative electrode 38 may be formed on the entire back surface of the substrate 30 or may be formed avoiding a region where a guide groove for dividing the wafer is formed.
[0026]
After forming the negative electrode 38, the wafer is set on a scriber, and the back surface of the GaN substrate 30 is scribed in a direction parallel to the A-plane along the dividing line shown by the solid line in FIG. As shown, a bar 39 is formed.
Next, the bar 39 is scribed in a direction parallel to the M-plane orthogonal to the A-plane (direction indicated by a dotted line) or pressed by a braking blade and divided to obtain a GaN-based semiconductor having the stacked structure shown in FIG. A laser element / chip 40 is formed.
[0027]
When the resonator length is 200 μm or more and 1000 μm or less, the width of the bar 39 is, for example, 300 μm. Next, the bar 39 is divided into chips 40 having a resonator length of 700 μm.
This chip 40 has the structure of a GaN-based semiconductor laser device as shown in FIG. 1, and the M-plane (1-100) plane orthogonal to the A-plane is the optical resonance surface of the GaN-based semiconductor laser device. Yes.
[0028]
A GaN-based semiconductor laser device sample having the stacked structure shown in FIG. 1 is manufactured according to the manufacturing method of this embodiment described above, the chip 40 is provided on the heat sink, and the positive electrode 37 and the negative electrode 38 are wire-bonded to the connection terminals. Later, when laser oscillation was attempted at room temperature, laser oscillation with an oscillation wavelength of 400 nm was confirmed at a threshold current density of 15 kA / cm ² , and it was found that the laser had good laser characteristics.
[0029]
In the present embodiment example, the production of a GaN-based semiconductor laser device using a GaN substrate has been described as an example. However, the method of the present invention can also be applied when a sapphire substrate is used instead of a GaN substrate.
In that case, the method of the present invention can be applied by forming a negative electrode in a stripe shape in the same direction on the same side as the positive electrode 37 with respect to the substrate.
[0030]
【The invention's effect】
As described above, according to the method of the present invention, a stripe-shaped structure such as a stripe-shaped current injection region is formed in parallel to the A-plane of the substrate, and then the strip-shaped structure is formed in a strip-like shape for each stripe-shaped structure on the A-plane of the substrate. By dividing, forming a bar having a stripe-shaped structure in the longitudinal direction, and further dividing the bar on the M-plane of the substrate to form chips each having a predetermined length having a stripe-shaped structure, Compared with the method, it is possible to manufacture a nitride-based semiconductor element having a high yield, a flat optical resonance surface, and good element characteristics.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing a configuration of a GaN-based semiconductor laser device manufactured by a method of an embodiment.
FIGS. 2A to 2C are diagrams for explaining steps of forming a bar and a chip when a GaN-based semiconductor laser device is manufactured by the method of the embodiment.
FIG. 3 is a perspective view showing a typical configuration of a GaN-based semiconductor laser device.
FIG. 4 is a unit cell diagram showing the surface orientation of GaN.
FIGS. 5 (a) to 5 (c) are diagrams illustrating a process of forming a bar and a chip when a GaN-based semiconductor laser device is manufactured by a conventional method, respectively.
FIG. 6 is a schematic cross-sectional view showing a state where a marking line is provided.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... GaN-type semiconductor laser element, 12 ... GaN board | substrate, 14 ... 1st clad layer, 16 ... Active layer, 18 ... 2nd clad layer, 20 ... Positive electrode, 22 ... Negative electrode , 24... Bar, 26... Chip, 30... GaN substrate, 31... N-type GaN buffer layer, 32... N-type GaN underlayer, 33. …… p-type cladding layer, 36 …… p-type contact layer, 37 …… positive electrode, 38 …… negative electrode, 39 …… bar, 40 …… chip.

Claims (7)

Forming a stacked structure of nitride compound semiconductor layers on a (0001) surface of a nitride semiconductor substrate ;
Processing the upper part of the laminated structure of the nitride-based compound semiconductor layer, or forming a stripe-shaped structure such as a stripe-shaped current injection region in parallel with the A surface of the nitride-based semiconductor substrate on the laminated structure;
In A plane of the nitride-based semiconductor substrate a nitride-based semiconductor substrate and a laminated structure for each stripe structure is divided into strip of a predetermined width, and forming a bar having a stripe-like structure in the longitudinal direction,
In the M plane of the nitride semiconductor substrate by dividing the bar by cleavage, respectively, to form a predetermined length of the chip having a stripe-shaped structure, that have a step of forming a cleavage plane of M surface the method for manufacturing a nitride compound-based semiconductor device. While forming a nitride-based compound semiconductor layer stacked structure on the (0001) surface of the nitride-based semiconductor substrate , a stripe-shaped structure such as a stripe-shaped current injection region is formed on the A-plane of the nitride-based semiconductor substrate. A step of embedding in parallel;
In A plane of the nitride-based semiconductor substrate a nitride-based semiconductor substrate and a laminated structure for each stripe structure is divided into strip of a predetermined width, and forming a bar having a stripe-like structure in the longitudinal direction,
In the M plane of the nitride semiconductor substrate by dividing the bar by cleavage, that together form a predetermined length of the chip having a stripe-shaped structure, respectively, have a step of forming a cleavage plane of M surface nitrogen Method for producing a compound semiconductor device. Before the step of forming the bars, the production of nitride-based semiconductor device according to 請 Motomeko 1 or 2 TO ADJUST by polishing the rear surface of the nitride semiconductor substrate in the nitride semiconductor substrate having a predetermined thickness Method. As the nitride-based semiconductor substrate using the gallium nitride substrate, according to any one of the 請 Motomeko 1 that form a laminated structure of a GaN-based compound semiconductor layer as a multilayer structure of a nitride-based compound semiconductor layer 3 Of manufacturing a nitride semiconductor device. The method for manufacturing a nitride-based semiconductor device according to 請 Motomeko 4 that use sapphire substrate instead of the GaN substrate. In the step of forming the bar, cutting the wafer, diced or scribed to a method for manufacturing a nitride semiconductor device as set forth 請 Motomeko 1 you bar into any one of the five. In the step of forming the chip, a method for manufacturing a nitride semiconductor device according to any one of the 請 Motomeko 1 you divide the bar by braking device 6.

Images