JP2003243765A - Nitride semiconductor laser element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitride semiconductor laser element having a p-pad electrode exhibiting good cleavage and adhesive property when a resonant surface is formed by cleaving a ridge-like stripe so as to further improve life characteristic of the laser element for further improving practicality of the element. <P>SOLUTION: This nitride semiconductor laser element has a ridge-like stripe having insulating films 62 on its side faces, and a p-electrode 20 and a p-pad electrode 101 having a larger area than the electrode 20 has both of which are successively formed in an uppermost layer of the stripe. This laser element also has the resonant surface on a cleavage plane 201 formed by cleaving the stripe in the direction perpendicular to the lengthwise direction of the stripe. The p-pad electrode 101 is formed of at least a first thin film layer 31 formed on the whole surface of the p-electrode 20 with the same length as that of the stripe, and a second thin film layer 32 formed on the layer 31 with a length shorter than that of the stripe. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

The present invention relates to a nitride semiconductor (In _a A
The present invention relates to a laser device made of 1 _b Ga _1-ab N, 0 ≦ a, 0 ≦ b, a + b ≦ 1), and particularly to a nitride semiconductor laser device having improved heat dissipation.

[0002]

2. Description of the Related Art In recent years, much research and development has been carried out for practical use of nitride semiconductor laser devices, and various kinds of nitride semiconductor laser devices are known. For example, the inventors of the present invention have disclosed that a practical laser device is Jpn. J. Appl. Phy
s. Vol. 37 (1998) pp. L309-L312, Part 2, No. 3B, 15
In March 1998, n-GaN selectively grown on a sapphire substrate through a partially formed SiO ₂ film.
By laminating a plurality of nitride semiconductor layers to be a laser device structure on a nitride semiconductor substrate made of, removing the sapphire substrate, and forming a resonance plane by cleavage, continuous oscillation at room temperature for 10,000 hours or more Announced a nitride semiconductor laser device that enables FIG. 7 shows a schematic cross-sectional view similar to that of the laser device shown in the JJAP. This Figure 7
As shown in FIG. 2, a ridge-shaped stripe formed by partially etching from the p-side contact layer made of p-GaN to the p-side cladding layer made of a superlattice structure of p-Al _0.14 Ga _0.86 N / GaN is formed. A nitride semiconductor laser device having a p-electrode formed on the upper portion of the stripe and having a resonance surface formed by cleavage. Further, in this laser element, a p pad electrode is formed so as to cover the p electrode.

The p-pad electrode expands the surface area of the p-electrode substantially so that the p-electrode side can be wire-bonded or direct-bonded, and furthermore, the occurrence of defects in the element due to the impact due to the stress during bonding is prevented. is doing. Further, the p-pad electrode dissipates the heat generated in the nitride semiconductor laser device or dissipates it by conducting it to the heat absorbing material. Since the laser element is easily deteriorated by the heat generated during driving, the better the heat dissipation, the more the life characteristics can be improved.

As a laser device having a p-pad electrode formed thereon, for example, the applicant of the present invention has shown in a plan view of FIG.
Disclosed is a laser device in which a p-pad electrode made of Ni and Ni is formed in a size that does not reach a cleavage plane formed by cleaving perpendicularly to the p-electrode. Since the p-pad electrode is thus formed on the p-electrode and the surface area of the p-electrode is substantially widened, in addition to good bonding, heat generated in the laser element is dissipated via the p-pad electrode. . However, in the laser device shown in FIG. 4 of JP-A-10-93186, heat is satisfactorily dissipated through the p-pad electrode at the p-electrode portion having the p-pad electrode on the upper portion. It is difficult to dissipate heat at the portion of the p-electrode near the cleavage plane that does not have the p-pad electrode on the upper portion, and it is not so preferable to further improve the life characteristics.

On the other hand, the applicant of the present invention has filed Japanese Patent Laid-Open No.
As shown in the perspective view of FIG. 2 of Japanese Patent No. 75008, there is disclosed a laser element in which a p-pad electrode made of Au and Ni is formed so as to cover the entire surface of the striped p-electrode. When the p-electrode is entirely covered with the p-pad electrode in this manner, heat can be easily dissipated through the p-pad electrode, as compared with the laser device described in JP-A-10-93186.

[0006]

However, in the laser element described in Japanese Patent Laid-Open No. 1075008, the cleavage of Au forming the p-pad electrode is poor, and when the resonance surface is formed by the cleavage, the p-pad electrode is formed. It is not cleaved satisfactorily, and the p-pad electrode near the cleaved surface is peeled off from the p-electrode or the like and floats, or the cleaved surface of the p-pad electrode in a further floating state is jagged. There are cases. When the p-pad electrode is peeled off so as to float near the cleavage plane, a portion not in contact with the p-electrode is generated, and it becomes difficult to conduct the heat generated in the laser element to the p-pad electrode. If the cleaved surface of the p-pad electrode is notched, in addition to the reduction of heat dissipation, the notched part of the p-pad electrode may be bent at the cleaved surface to cover the resonance surface. In some cases, it may be difficult for the laser light to oscillate.

Therefore, an object of the present invention is to improve the cleavage property when the resonance surface is formed by cleavage in order to further improve the life characteristics in order to further improve the practicality of the laser device.
It is an object of the present invention to provide a nitride semiconductor laser device having a good heat dissipation property, which has a p-pad electrode having a good adhesive property.

[0008]

That is, the object of the present invention is to:
It can be achieved by the following configurations (1) to (5). (1) Resonance consisting of a ridge-shaped stripe having an insulating film on the side surface of the stripe, a p-electrode and a p-pad electrode on the uppermost layer of the stripe, and a cleavage plane in a direction perpendicular to the stripe length direction. In a nitride semiconductor laser device having a plane, the p pad electrode has at least the same length as the stripe length, and includes a first thin film layer containing a metal having good cleavability, and a stripe length on the first thin film layer. And a second thin film layer containing a metal that is formed to have a length shorter than that of the nitride semiconductor laser device. (2) The nitride semiconductor laser device according to claim 1, wherein the first thin film layer has a thickness in the range of 100 to 5000 angstroms. (3) The nitride semiconductor laser element according to claim 1 or 2, wherein at least one end face of the second thin film layer is formed so as not to coincide with the cleavage plane. (4) Between the first thin film layer and the second thin film layer,
4. The nitride semiconductor laser device according to claim 1, further comprising a third thin film layer serving as a barrier layer capable of suppressing diffusion of the second thin film layer. (5) The nitride semiconductor laser device according to claim 4, wherein the third thin film layer has substantially the same size as the second thin film layer. (6) The nitride semiconductor laser device according to claim 4 or 5, wherein the first thin film layer and the third thin film layer are made of the same material.

That is, according to the present invention, the p-pad electrode is formed in a shape having the same length as the stripe length so as to cover the entire surface of the p-electrode, and the second thin film layer having a shape shorter than the stripe length. By using a metal that is composed of a thin film layer and that can be satisfactorily cleaved during cleavage for the first thin film layer, and a metal that is difficult to cleave well for the second thin film layer, the cleavage of the p-pad electrode The adhesiveness is good and the p-pad electrode is prevented from being peeled off from the p-electrode or the insulating film at the time of cleavage to improve the adhesiveness. As a result, the heat dissipation from the p-pad electrode is improved and the life characteristics are improved. It is possible to provide an improved nitride semiconductor laser device.

As described above, as the p-pad electrode of the conventional laser element, the p-electrode is not sufficiently covered, or even if it is covered, it is not sufficiently satisfactory in terms of cleavage. Although the p-pad electrode is a part that has received relatively little attention in research into practical use of laser devices,
As a good laser device is realized, it is considered that it cannot be neglected for improving heat dissipation in order to improve practicality.

On the other hand, according to the present invention, as described above, p
The pad electrode is composed of at least a first thin film layer and a second thin film layer having different sizes, and the entire surface of the p electrode is covered with the first thin film layer made of a metal having good cleavage property. The heat is easily conducted and the cleavability is improved,
It is possible to prevent the p-pad electrode from peeling off during cleavage. Further, the present invention, by forming a second thin film layer which is poor in cleavage but is made of a preferable metal at the time of heat dissipation and bonding on the first thin film layer so that its end face does not coincide with the cleavage face, Cleavability at the time of forming the resonance surface by the second thin film layer is not reduced, and heat is satisfactorily dissipated.

In the present invention, the first thin film layer is
If it is one or more of Ni, Ti, Cr, W, Pt, etc.,
It is preferable in terms of cleavability, adhesiveness, and heat dissipation.

In the present invention, the second thin film layer is
It is preferable to use Au in terms of good thermal conductivity and good heat dissipation, and also in terms of adhesion during bonding, relaxation of impact, and the like. The second thin film layer made of Au is inferior in cleavability but has a shape shorter than the stripe length.
The end face of the thin film layer does not coincide with the cleavage plane formed by cleavage, and does not affect the cleavage property of the p-pad electrode.

Further, in the present invention, Pt, W, TiN, Cr and Ni are provided between the first thin film layer and the second thin film layer.
It is preferable to form the third thin film layer containing at least one kind of material such as the above because the third thin film layer serves as a barrier layer and the metal of the second thin film layer can be prevented from diffusing. If the diffusion of the second thin film layer can be prevented as described above, the increase of the resistance and the increase of the threshold value are suppressed, so that the generation of heat inside the laser element is prevented and the life characteristics are improved. preferable.

In the present invention, the first thin film layer is T
When it is made of i, the laser element having a narrow stripe width is preferably used by a method capable of being formed with good reproducibility, and the adhesiveness to the insulating film other than the Si oxide formed on the side surface of the stripe is good, and the cleavage of the p pad electrode is achieved. Peeling at the time can be prevented, which is preferable. The applicant has disclosed in Japanese Patent Application No. 10-126549 that two types of protective films having different etching rates with respect to an etching process are used in order to form a ridge-shaped stripe having a width of 0.5 to 4 μm with good reproducibility. A method of forming an electrode on a stripe and an upper portion of the stripe is proposed. In this method, a Si oxide is used as a protective film having a high etching rate, and a protective film having a low etching rate or not etched (which becomes an insulating film on the side surface of the stripe) other than Si oxide, such as Zr or T, is used.
It is described that it is performed using an oxide such as i or Ta. With this method, a laser element having a narrow stripe width which can be obtained with good reproducibility has a low threshold value and improved life characteristics. However, the p-pad electrode formed from the p-electrode side in the order of Ni / Au has good adhesiveness between Ni and Si oxide when the insulating film formed on the side surface of the stripe is Si oxide. Though there is
If the insulating film is other than Si oxide, the adhesiveness tends to be slightly weakened, and the p-pad electrode may be easily peeled off during direct bonding or wire bonding, or during long-time operation of the laser element. On the contrary,
As described above, by using Ti for the first thin film layer having a specific shape, peeling of the p pad electrode can be favorably prevented even if the insulating film is other than Si oxide, which is preferable.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below with reference to the drawings. In FIG. 1, the p-electrode 20 is formed on the p-side contact layer 13 which is the uppermost layer of the ridge-shaped stripe having the insulating film 62 on its side surface, and the p-electrode 20 is further formed on the p-electrode 20 in order.
3 is a schematic cross-sectional view showing a part of a nitride semiconductor laser device having a p-pad electrode 101 formed by laminating a thin film layer 31 and a second thin film layer 32 of FIG. FIG. 2 is a schematic plan view of the schematic cross-sectional view of FIG. 1 seen from above. The dotted line near the center of FIG. 2 indicates the position of the p-electrode inside the element that does not appear on the surface. The resonance surface of the nitride semiconductor laser device of the present invention is formed on a cleavage plane formed by cleavage in a direction perpendicular to the stripe length direction.

In the present invention, the p-pad electrode 101 is
A barrier composed of at least a first thin film layer 31 and a second thin film layer 32, preferably a barrier capable of suppressing the diffusion of the second thin film layer between the first thin film layer 31 and the second thin film layer 32. A third thin film layer to be a layer is formed. First thin film layer 31
Is formed on the upper portion of the stripe so as to cover the entire surface of the p-electrode 31 with the same length as the stripe and has a larger area than the p-electrode. For example, as shown in FIGS. 1 and 2, the stripe has the same length as the stripe side and p
It is formed so as to cover the electrode 20. Further, the same length as the stripe length means that the first thin film layer 31 is formed on the p-electrode which is continuously formed in a stripe shape, and is cleaved at the same time when the resonance surface is formed. It shows that both end faces of the layer coincide with the cleavage plane.

The first thin film layer 31 is not particularly limited as long as it is a metal that can be satisfactorily cleaved at the time of cleavage and can be used as a p-pad electrode. However, the cleaving property and heat conductivity, and further the ohmic property of the p-electrode. A metal that does not reduce Such a first thin film layer 31 of the p-pad electrode 101
Specific examples of the metal used as the material include Ni, Ti, C
r, W, Pt, and the like, and preferably Ni or Ti
And Ti is more preferable. The use of these metals is preferable because the cleaving property is good and the p-pad electrode is less likely to peel off during the cleaving. In particular, when the first thin film layer 31 is composed of Ti, it is preferably used in a method of forming a ridge-shaped stripe having a narrow stripe width described later with good reproducibility, and other than the Si oxide formed on the side surface of the stripe. This is preferable because the adhesiveness with the oxide becomes better and the p-pad electrode 101 is less likely to peel off during cleavage. A laser element having a narrow stripe width is preferable because it has a low threshold value and a small amount of heat is generated, so that the life characteristics are improved. Further, the first thin film layer 31 may be composed of two or more kinds of metals.

Insulating film 6 used in the laser device of the present invention
2 is not particularly limited, but is, for example, SiO ₂ used in FIG. 7 showing a conventional laser device, or a nitride semiconductor laser device having a stripe structure having a stripe width of 0.5 to 4.0 μm described later. Second preferred for forming
Used as a protective film (insulating film) of Ti,
Examples thereof include oxides containing at least one element selected from the group consisting of V, Zr, Nb, Hf, and Ta, BN, SiC, and AlN. Further, Si oxide can be used as the second protective film described later, and in this case, a material that is more easily etched than Si oxide is selected as the material of the first protective film described later.

In the present invention, the thickness of the first thin film layer 31 is not particularly limited, but is 100 to 5000.
Angstrom, preferably 100 to 3000 angstrom, more preferably 500 to 2000 angstrom. When the film thickness of the first thin film layer 31 is in the above range, it is preferable in terms of cleavage, adhesiveness and heat dissipation.
The film thickness of the first thin film layer 31 is at least the film thickness from the p-electrode formed on the upper portion of the stripe, and is formed on the side surface of the stripe or on the plane of the nitride semiconductor layer continuous from the side surface of the stripe. The film thickness of the first thin film layer 31 is not limited to this. The same applies to the film thicknesses of the second and third thin film layers described later.

In the present invention, the second thin film layer 32 has a length shorter than the stripe length and has a size such that the end face of the second thin film layer 32 does not coincide with the cleavage plane. It suffices if it is formed, and for example, as shown in FIGS. 1 and 2, it is formed on the first thin film layer 31 above the p electrode 20 in a size that does not match the cleavage plane 201. The second thin film layer is not particularly limited as long as it has a shape that does not match at least the cleavage plane, and may be formed on the side surface of the stripe, for example. Since the second thin film layer 32 has a shape shorter than the stripe length, at least one end face of the second thin film layer 32 does not coincide with the cleavage plane 201, and preferably both end faces do not coincide with the cleavage plane 201. It is preferable to be formed in a state from the viewpoints of cleavage and heat dissipation. Second thin film layer 3
No. 2 may be inferior in the cleavage property when forming the resonance surface because it is formed in a shape that does not reach the cleavage surface, but in order to easily dissipate the heat conducted from the p-electrode to the outside, Examples of the metal include a metal that has good conductivity and that absorbs impact during bonding and that has good adhesiveness to the wire for wire bonding. Specific examples of the metal forming the second thin film layer 32 include Au and Al, and Au is preferable. The second thin film layer may use two or more kinds of metals.

When the second thin film layer 32 is Au, the thermal conductivity is good, and it is preferable to dissipate the heat generated in the laser element. Further, when the wire for wire bonding is Au wire, the adhesion is good. Become. Further, Au does not have a very good cleavage property, but since it is formed with a length shorter than the stripe length and does not reach the cleavage surface 201, it does not affect the cleavage property when forming the resonance surface. In the present invention,
The thickness of the second thin film layer 32 is not particularly limited, but is 100 to 10000 angstroms, preferably 100 to 9000 angstroms, and more preferably 1000 to 5000 angstroms. When the film thickness of the second thin film layer 32 is in the above range, it is preferable in terms of adhesiveness with a wire, shock absorption, heat dissipation, and the like.

In the present invention, as the third thin film layer,
A material having a high melting point can be used. Specifically, P
At least one kind of material such as t, W, TiN, Cr and Ni can be used, and preferably Pt, W and Ti.
N. When the second thin film layer 32 is Au, the third thin film layer easily diffuses inside the element due to heat, but it is preferable to prevent this and suppress the rise of the threshold value. The third thin film layer may be composed of two or more layers. In the present invention, the thickness of the third thin film layer is not particularly limited, but is 100 to 5000 angstroms,
It is preferably 100 to 3000 angstroms, more preferably 500 to 2000 angstroms. When the film thickness of the third thin film layer is in the above range, it is preferable in terms of barrier performance, adhesiveness and heat dissipation. In addition, the third thin film layer is not particularly limited to the presence or absence of cleavability. When it is made of a material having cleavability, the third thin film layer has a shape that reaches or does not reach the cleavable surface, and does not have cleavability. Is formed to have a size substantially the same as the size of the second thin film layer, and preferably has a shape substantially the same size as the second thin film layer regardless of the cleavage property. Further, the third thin film layer may be formed of the same material as the first thin film layer, and the third thin film layer is further formed on the first thin film layer, so that the second thin film layer The diffusion is more easily prevented.

In the present invention, the p pad electrode 101 is formed by a sputtering method or the like. In the present invention, the size of the shape of the p-pad electrode is
There is no particular limitation, and it is appropriately adjusted depending on the stripe structure formed on the nitride semiconductor laser device and the size of the p-electrode. As described above, at least the p-pad electrode may have a structure in which the entire surface of the p-electrode is covered with the first thin film layer 31 and the second thin film layer 32 is formed in a size that does not match the cleavage plane. . As one specific embodiment of the size of the p-pad electrode, when the resonator length is 400 μm and the stripe width is 2 μm, for example, the first thin film layer is vertically (stripe direction) 400 μm so as to coincide with the cleavage plane. ,
For example, the width may be 600 μm, and the length may be 350 μm and the width may be 500 μm so that both end surfaces of the second thin film layer do not coincide with the cleavage plane.

The stripe structure of the laser device of the present invention is not particularly limited, and the p pad electrode 101 composed of at least the first thin film layer and the second thin film layer is formed on the p electrode and on the side surface of the stripe. Any structure can be used. A preferable stripe structure is, for example, a stripe structure having a stripe width of 0.5 to 4.0 μm. When the stripe width is in the above range, the threshold value can be lowered, which is preferable. Further, examples of the laser device having a stripe having a narrow stripe width as described above include a laser device having a structure as shown in FIGS. 3 to 5. These laser devices can be formed with good reproducibility even if the stripe width is narrowed.
-126549. ) Is obtained. The method will be described below with reference to FIG. In this method, the first protective film used when forming the waveguide of the stripe and the insulating second protective film formed on the side surface of the stripe are made of different materials so as to have different etching rates by the etching process. By selecting and performing each of the following steps, stripes can be formed with good reproducibility, and an insulating second protective film can be formed at a predetermined position with a uniform film thickness.

FIG. 1 is a schematic sectional view showing a partial structure of a nitride semiconductor wafer in each step for explaining each step of the method for forming a stripe and an electrode of a nitride semiconductor laser device. The cross-sectional view shown in FIG. 1 is
The figure shows a state when cut in a direction perpendicular to the stripe waveguide formed by etching, that is, in a direction parallel to the resonance surface.

First, in the first step, as shown in FIG. 1C, a stripe-shaped first protective film 61 is formed on the p-side contact layer 13 which is the uppermost layer. This first
In the step (1), the first protective film 61 may be made of any material as long as the material has a difference in etching rate from the nitride semiconductor regardless of the insulating property. Further, the first protective film 61
For this reason, it is preferable to form the second protective film 62 by selecting and using a material having an etching rate different from that of the second protective film 62 formed in the third step described later. Examples of the first protective film 61 include Si oxide (including SiO ₂ ), photoresist and the like, and Si oxide is preferable. If the first protective film 61 is a Si oxide, wet etching, dry etching, or the like is used as a method for forming the stripe-shaped waveguide region of the nitride semiconductor laser device in the next second step. Dry etching, which is easy to etch, is preferably used, and the selectivity between the first protective film 61 and the nitride semiconductor, which is important in this dry etching, can be improved. In addition, when the first protective film 61 is selected from the above materials, it has a property that it is more easily dissolved in acid than the second protective film by etching performed using acid in the third step, which is a subsequent step. And has a solubility difference with the second protective film 62,
Particularly, it is preferable to use hydrofluoric acid as the acid used in the third step because it is easily dissolved in hydrofluoric acid. The stripe width (W) of the first protective film is 4 μm to 0.5 μm,
It is preferably adjusted to 3 μm to 1 μm. First protective film 6
The stripe width of 1 corresponds approximately to the stripe width of the waveguide region.

In the first step, as a specific step of forming the first protective film 61, the steps shown in FIGS. 1A and 1B can be mentioned. First, as shown in FIG.
After forming the first protective film 61 on almost the entire surface of the p-side contact layer 13, a stripe-shaped third protective film 63 is formed on the first protective film 61. After that, FIG. 1 (b)
As shown in FIG. 3, after the first protective film 61 is etched with the third protective film 63 attached, the third protective film 63 is removed.
By removing the, the stripe-shaped first protective film 61 as shown in FIG. 1C can be formed. The etching gas, the etching means, or the like is changed with the third protective film 63 attached, and the p-side contact layer 13 is changed.
It can also be etched from the side.

In the first step, as an etching means
For example, like RIE (Reactive Ion Etching)
Dry etching can be used, in which case the
In the first step, the first protective film 61 made of, for example, Si oxide
To etch CF _FourFluorine compound-based
It is desirable to use this gas.

The stripe-shaped first protective film 61 as shown in FIG. 1C can also be formed by the lift-off method. In the lift-off method, a photoresist having stripe-shaped holes is formed on the p-side contact layer 13, a first protective film 61 is formed on the entire surface of the photoresist, and then the photoresist is dissolved and removed. By doing so, only the first protective film 61 in contact with the p-side contact layer 13 is left as shown in FIG. As a method of forming the first protective film 61, it is preferable to form the first protective film 61 by etching as shown in FIGS. 1A and 1B rather than forming the stripe-shaped first protective film 61 by a lift-off method. However, it tends to be easy to obtain a stripe whose edges are almost vertical and whose shape is regular.

Next, in the second step, as shown in FIG. 1D, from the portion of the p-side contact layer 13 on which the first protective film 61 is not formed, the first protective film 61 is not formed. By etching, a stripe-shaped waveguide region corresponding to the shape of the protective film is formed immediately below the first protective film 61. When etching is performed, the structure and characteristics of the laser device differ depending on the position of the etch stop. The etch stop may be stopped at any nitride semiconductor layer as long as it is a layer below the p-side contact layer. In the example shown in FIG. 1, the etch stop is in the middle of the p-side cladding layer 12 below the p-side contact layer 13. When the substrate is etched from the lower end surface of the p-side clad layer in the direction of 0.2 μm in the p-side contact layer, the stripe serves as a ridge to form a refractive index waveguide type laser device. The lower end surface refers to the surface of the clad layer that is the lowest in the thickness direction.If the optical guide layer is below the clad layer as described above, the interface between the guide layer and the clad layer is below. Corresponds to the end face.
When the etch stop is located above the lower end surface, the etching time is shortened and the etching rate is easily controlled, which is convenient in terms of production technology.

Although not shown in FIG. 1, the etch stop may be a nitride semiconductor below the lower end surface of the p-side cladding layer. When the layer closer to the substrate than the lower end surface is used as an etch stop, the threshold value tends to be significantly lowered, which is preferable.

In the second step, wet etching, dry etching or the like is used as the etching means, but dry etching which is easy to etch is preferably used, and dry etching such as RIE (reactive ion etching) is preferably used. Can be used, and in this case, other III-
Cl ₂ and CC which are often used in group V compound semiconductors
A chlorine-based gas such as l ₄ or SiCl ₄ is used. When these gases are used, when Si oxide is used as the first protective film 61, the selection ratio with respect to the Si oxide can be increased. Therefore desirable.

Next, in the third step, as shown in FIG. 1 (e), the second protective film 62 is made of a material different from that of the first protective film 61, and is striped using an insulating material. Side surface of the waveguide, the plane of the nitride semiconductor layer (p-side cladding layer 12 in FIG. 1e) exposed by etching,
And formed on the first protective film 61. Second protective film 62
After forming the first protective film 61 by etching, the second protective film 61 formed on the first protective film 61 is removed by etching.
1F, only the protective film 62 is removed, and the second protective film 62 is continuously formed on the side surface of the stripe and the plane of the p-side cladding layer 12, as shown in FIG. As described above, in order to enable the removal of the first protective film 61 without etching the second protective film 62, as described above, the first protective film 61 and the second protective film 62 are formed. The material of
This is possible by selecting and using those having different etching rates with respect to the etching process performed in the third step. The etching treatment in the third step is not particularly limited, and examples thereof include a method of performing dry etching using hydrofluoric acid.

The material of the second protective film 62 is selected from a material different from that of the first protective film 61, and has an etching rate slower or less likely to be etched than the first protective film 61 in the etching process of the third step. The material is not particularly limited as long as it can form the second protective film 62 on the side surface of the stripe or the like. As a preferable second protective film,
Since Si oxide or a resist material is preferably used as the first protective film 61 as described above, at least a material other than the material of the first protective film 61 is used for the first protective film 61.
A material having a slower etching rate may be used. When the first protective film 61 is a Si oxide, specific examples of the second protective film 62 include, for example, Ti, V, Zr, Nb, Hf,
At least one of oxides containing at least one element selected from the group consisting of Ta, BN, SiC and AlN is used, and more preferably any of Zr oxide, Hf oxide, BN and SiC. One or more materials are used. Further, since the nitride semiconductor is not etched after the second protective film 62 is formed, the second protective film 62 is not considered regarding the etching speed with the nitride semiconductor. Further, Si oxide may be used as the second thin film layer 62, and in this case, a material having a faster etching rate in the third step than the Si oxide is selected for the first protective film 61.

Further, as described above, by forming the second protective film continuously on the first protective film 61, high insulation can be maintained, and a uniform film thickness can be formed on the p-side cladding layer 12. Since it can be formed by, it is possible to prevent the concentration of the current due to the non-uniformity of the film thickness. Further, in the second step, since the etch stop is in the middle of the p-side cladding layer 12, the second protective film 62 is formed on the p-side cladding layer 12 in the third step as shown in FIG. Although it is formed on the flat surface of, when the etch stop is below the p-side cladding layer 12,
The second protective film is formed on the plane of the nitride semiconductor layer that has been etch-stopped.

The second protective film 62 can also be formed by a lift-off method. For example, when the second protective film 62 is one of the specific examples described above and the first protective film 61 is Si oxide, the second protective film 62 is more resistant to hydrofluoric acid than Si oxide. It has etching selectivity such that the etching rate is slow or the etching is difficult. Therefore, as shown in FIG. 1E, the side surface of the stripe waveguide, the plane where the stripe is formed (etch stop layer), and the surface of the first protective film 61 are continuous with the second protective film. After forming the film, only the first protective film 61 is removed by the lift-off method. Then, as shown in FIG. 1F, the second protective film 62 having a uniform thickness with respect to the plane is formed.
Is formed.

Next, in the fourth step, as shown in FIG. 1G, on the second protective film 62 and the p-side contact layer 13, a p-electrode electrically connected to the p-side contact layer is formed. To form. Here, since the second protective film has already been formed by the above process, it is not necessary to perform a fine operation such as forming only the contact layer having a narrow stripe width when forming the p-electrode, and the p-electrode can be formed in a large area. It can be formed and the operability is good.

The other element structure of the laser element of the present invention is not particularly limited, and various known element structures can be used. As a substrate for growing the device structure of the laser device of the present invention, a conventionally known different substrate such as sapphire or spinel, or Si on a different substrate is used.
A nitride semiconductor substrate or the like obtained by forming a protective film made of a material in which a nitride semiconductor such as O ₂ does not grow or does not easily grow and then selectively laterally growing (lateral growth) Can be mentioned. A nitride semiconductor substrate having few crystal defects obtained by lateral growth is preferable. When the device structure is formed on a nitride semiconductor substrate having few crystal defects, the nitride semiconductors forming the device also have few crystal defects, which is preferable for suppressing heat generation in the device.
In addition, it is preferable that the substrate is a nitride semiconductor substrate because it is easy to cleave. The protective film used for the lateral growth has an action different from that of the protective film used for forming the stripe.

The method for growing a nitride semiconductor substrate having few crystal defects obtained by using lateral growth is not particularly limited, and any method may be used. J. A. P.
Vol. 37 (1998) pp. The method according to L309-L312, or a concave-convex portion is formed on the surface of a nitride semiconductor grown on a different substrate different from the nitride semiconductor, and Si is formed on the plane of the convex portion and the concave portion.
After forming the protective film of O ₂ or the like, lateral growth is performed from the nitride semiconductor exposed on the side surface, and the laterally grown nitride semiconductors are connected to each other on the protective film. The nitride semiconductor substrate obtained by the lateral growth may be grown with a different substrate or with the different substrate removed when growing the element structure.

[0041]

[Embodiment 1] FIG. 3 is a schematic cross-sectional view showing the structure of a laser device according to an embodiment of the present invention, showing a view when cut in a direction perpendicular to a stripe waveguide. is there. Hereinafter, Embodiment 1 will be described with reference to this drawing.

(Underlayer 2) 1 inch φ, a heterogeneous substrate 1 made of sapphire having a C plane as a main surface is set in a MOVPE reaction vessel, and the temperature is set to 500 ° C., and trimethylgallium (TMG) and ammonia (NH) are added. ₃ ) with GaN
A buffer layer of 100 Å is grown to a film thickness of 200 Å. After the growth of the buffer layer, the temperature is set to 1050 ° C. and the underlayer 2 also made of GaN is grown to a film thickness of 4 μm. This underlayer acts as an underlayer for partially forming a protective film on the surface and then performing selective growth of the nitride semiconductor substrate.

(Protective film 3) After growth of the underlayer, the wafer is taken out of the reaction container, a stripe-shaped photomask is formed on the surface of this underlayer, and a stripe width of 10 μm and a stripe interval (window portion) of 2 μm are measured by a PVD apparatus. SiO
_A protective film 3 made of ₂ is formed.

(Nitride Semiconductor Substrate 4) After forming the protective film, the wafer is set again in the MOVPE reaction vessel, the temperature is raised to 1050 ° C., and the nitride semiconductor substrate 4 made of undoped GaN is used by using TMG and ammonia. Grow with a film thickness of 20 μm. Since this nitride semiconductor substrate is laterally grown on the protective film 3, the number of crystal defects is 10 5 / cm ² or less, which is two or more digits smaller than that of the base layer 2.

(N-side contact layer 5) Next, using ammonia and TMG, and silane gas as an impurity gas, Si was 3 × 10 ¹⁸ / at 1050 ° C. on the nitride semiconductor substrate 1.
cm ³ -doped n-side contact layer 5 made of GaN
Grow with a film thickness of μm.

(Crack prevention layer 6) Next, TMG, TM
Using I (trimethylindium) and ammonia at a temperature of 800 ° C., a crack prevention layer 6 of In _0.06 Ga _0.94 N is grown to a thickness of 0.15 μm. The crack prevention layer can be omitted.

(N-side cladding layer 7) Subsequently, 1050 ° C.
Using TMA (trimethylaluminum), TMG, and ammonia, a layer of undoped Al _0.16 Ga _0.84 N is grown to a thickness of 25 Å, and then TM
Stop A, flow silane gas, and add Si at 1 × 10 ¹⁹ / cm
^A layer of ^3- doped n-type GaN is grown to a thickness of 25 Å. These layers are alternately laminated to form a superlattice layer, and the superlattice has a total film thickness of 1.2 μm.
The side cladding layer 7 is grown.

(N-side light guide layer 8) Subsequently, the silane gas is stopped, and the n-side light guide layer 8 made of undoped GaN is grown to a thickness of 0.1 μm at 1050 ° C. The n-side light guide layer 8 may be doped with an n-type impurity.

(Active layer 9) Next, the temperature is set to 800 ° C., and the barrier layer made of Si-doped In _0.05 Ga _0.95 N is set to 1
Then, a well layer made of undoped In _0.2 Ga _0.8 N is grown at the same temperature.
It is grown to a film thickness of 0 angstrom. A barrier layer and a well layer are alternately laminated twice, and finally, the barrier layer ends, and the total quantum film thickness is 380 angstroms.
W) active layer is grown.

(P-side cap layer 10) Next, the temperature is adjusted to 10
Raise to 50 ℃, TMG, TMA, ammonia, Cp ₂ M
g (cyclopentadienylmagnesium), which has a bandgap energy larger than that of the p-side optical guide layer 11 and is Mg-doped 1 × 10 ²⁰ / cm ³ p-type Al _0.3 Ga
_A p-side cap layer 7 made of _0.7 N is grown to a film thickness of 300 angstrom.

(P-side light guide layer 11) Subsequently, Cp ₂ M
g and TMA are stopped, and at 1050 ° C., a p-side optical guide layer 11 made of undoped GaN having a bandgap energy smaller than that of the p-side cap layer 10 is grown to a film thickness of 0.1 μm.

(P-side clad layer 12) Subsequently, 1050
A layer of undoped Al _0.16 Ga _0.84 N was grown at 25 ° C. to a thickness of 25 Å, followed by Cp 2 Mg,
The TMA is stopped, and a layer made of undoped GaN is grown to a film thickness of 25 Å to grow a p-side cladding layer 12 made of a superlattice layer having a total film thickness of 0.6 μm.

(P-side contact layer 13) Finally, 105
Mg was added to the p-side cladding layer 9 at 0 ° C. in an amount of 1 × 10 ²⁰ /
cm ³ -doped p-type GaN p-side contact layer 1
3 is grown to a film thickness of 150 Å.

The wafer on which the nitride semiconductor has been grown as described above is taken out of the reaction vessel, and a protective film made of SiO ₂ is formed on the surface of the p-side contact layer which is the uppermost layer.
Etching is performed with SiCl ₄ gas using RIE (reactive ion etching) to expose the surface of the n-side contact layer 5 on which the n-electrode is to be formed, as shown in FIG. Thus, SiO ₂ is optimal as a protective film for deeply etching a nitride semiconductor.

Next, as shown in FIG. 6A, a first protective film 61 made of Si oxide (mainly SiO ₂ ) is formed on almost the entire surface of the uppermost p-side contact layer 13 by a PVD device. Is formed to a film thickness of 0.5 μm, a mask having a predetermined shape is applied on the first protective film 61, and a third protective film 63 made of photoresist is formed with a stripe width of 2 μm.
m and the thickness is 1 μm.

Next, as shown in FIG. 6B, after the third protective film 63 is formed, CF ₄ gas is used by a RIE (reactive ion etching) device, and the third protective film 63 is used as a mask. The first protective film is etched into stripes. After that, by processing with an etching solution to remove only the photoresist, the first protective film 61 having a stripe width of 2 μm can be formed on the p-side contact layer 13 as shown in FIG. 6C.

Further, as shown in FIG. 6D, after the stripe-shaped first protective film 61 is formed, S is again formed by RIE.
The p-side contact layer 13 and the p-side cladding layer 12 are etched using iCl ₄ gas to form a stripe-shaped waveguide region (ridge stripe in this case). When forming a stripe, it is very preferable that the cross-sectional shape of the stripe is a forward mesa shape as shown in FIG.

After forming the ridge stripe, the wafer is PVd.
Then, as shown in FIG. 6E, the _second protective film 62 made of Zr oxide (mainly ZrO ₂ ) is formed on the first protective film 61 and exposed by etching.
It is continuously formed on the side clad layer 12 to have a film thickness of 0.5 μm.

Next, the wafer is dipped in hydrofluoric acid, and the wafer shown in FIG.
As shown in (f), the first protective film 61 is removed by the lift-off method.

Next, as shown in FIG. 6G, the surface of the p-side contact layer exposed by removing the first protective film 61 on the p-side contact layer 13 is made of Ni / Au.
The electrode 20 is formed. However, the p-electrode 20 has a stripe width of 100 μm, and as shown in FIG.
Formed over the protective film 62.

Next, the entire surface of the p-electrode 20 is continuously contacted with T
The first thin film layer 31 made of i is formed with a film thickness of 1000 angstroms, and the first thin film layer 31 is further formed on the side surface of the stripe as shown in FIG. On the continuously formed first thin film layer 31, a size that does not correspond to a cleavage plane when a resonance surface is formed by cleavage in a later step, that is, avoid an upper portion of a portion that becomes the cleavage plane, and intermittently Then, a second thin film layer 32 made of Au is formed to a thickness of 8000 angstroms, and a p pad electrode 101 made up of the first thin film layer 31 and the second thin film layer 32 is formed.

After the p-pad electrode is formed, the surface of the n-side contact layer 5 exposed first is an n-layer made of Ti / Al.
The electrode 21 is formed in a direction parallel to the stripe, and an n pad electrode made of Ti / Pt / Au is formed thereon.

As described above, the n electrode, the p electrode, and the p electrode
After polishing the sapphire substrate of the wafer on which the pad electrode was formed to 70 μm, the substrate was cleaved in a bar shape in the direction perpendicular to the striped electrodes, and the cleavage plane (11-0
A resonator is formed on the 0 plane, the plane corresponding to the side surface of the hexagonal columnar crystal = M plane). A dielectric multilayer film made of SiO ₂ and TiO ₂ is formed on the resonator surface, and finally, in a direction parallel to the p-electrode,
The bar is cut to obtain a laser device as shown in FIG. The resonator length is preferably 300 to 500 μm.

This laser element is set on a heat sink,
When each electrode was wire-bonded and a laser oscillation was tried at room temperature, an oscillation wavelength of 400 to 420n
m and a threshold current density of 2.9 kA / cm ² , room temperature continuous oscillation was exhibited. Further, peeling or floating of the p-pad electrode 101 when cleaving the wafer is significantly reduced as compared with the conventional case, and the cleavage can be performed satisfactorily, and the heat generated during the operation of the laser element is satisfactorily transmitted through the pad electrode. Can be dissipated in a short period of time, the rise in threshold value can be suppressed, and the life characteristics can be improved.

[Second Embodiment] In the first embodiment, the second thin film layer 32 is provided between the first thin film layer 31 and the second thin film layer 32.
A laser device was obtained in the same manner except that a third thin film layer made of Pt was formed in the same shape as in. The cleavability is as good as in Example 1, and the third thin film layer made of Pt serves as a barrier layer to prevent the diffusion of the second thin film layer made of Au and prevent the threshold value from rising. A laser device having slightly better characteristics than Example 1 was obtained.

[Embodiment 3] FIG. 4 is a schematic sectional view showing the structure of a laser device according to another embodiment of the present invention. Embodiment 3 will be described below with reference to this drawing.

(Nitride Semiconductor Substrate 40) In Example 1, after forming the stripe-shaped protective film 3 on the surface of the underlayer 2,
The wafer is set again in the MOVPE reaction vessel, the temperature is set to 1050 ° C., and undoped GaN is grown to a thickness of 5 μm using TMG and ammonia. afterwards,
The wafer is transferred to an HVPE (hydride vapor phase epitaxy) apparatus, and Ga metal, HCl gas, and ammonia are used as raw materials, and a nitride semiconductor substrate 40 made of undoped GaN is grown to a film thickness of 200 μm. MO like this
When a nitride semiconductor is grown on the protective film 3 by the VPE method and then a GaN thick film of 100 μm or more is grown by the HVPE method, the crystal defects are reduced by one digit or more as compared with the first embodiment. After the growth of the nitride semiconductor substrate 40, the wafer is taken out of the reaction container, and the sapphire substrate 1, the buffer layer 2, the protective film 3, and the undoped GaN layer are removed by polishing to obtain the nitride semiconductor substrate 40 alone.

Thereafter, in the same manner as in Example 1, the n-side contact layers 5 to 5 are formed on the nitride semiconductor substrate 40 on the side opposite to the polishing side.
The layers up to the p-side contact layer 13 are laminated.

After the growth of the p-side contact layer 13, the stripe-shaped first protective film 61 is formed in the same manner as in Example 1, and then, in the second step, the etching stop is performed on the surface of the n-side contact layer 5. To do. After that, similarly to the example, the second protective film 62 containing ZrO ₂ as a main component is formed on the side surface of the stripe waveguide and the surface of the n-side contact layer 5, and then an electrode is formed on each contact layer. Then, the p-pad electrode 10 is formed on the formed p-electrode in the same manner as in the first embodiment.
1 to form a laser device having a structure as shown in FIG. When the resonance surface is formed, the cleavage surface of the nitride semiconductor substrate is the same M surface as in the first embodiment. Cleavability is as good as in Example 1, and the obtained laser device is in Example 1.
The threshold current density was reduced to 1.8 kA / cm ² and the life was improved three times or more.

[Embodiment 4] FIG. 5 is a schematic sectional view showing the structure of a laser device according to another embodiment of the present invention. Embodiment 4 will be described below with reference to FIG.

In Example 4, the nitride semiconductor substrate 40
At the time of manufacturing, the silane gas is added to the raw material in the HVPE apparatus to grow the nitride semiconductor substrate 50 of GaN doped with Si of 1 × 10 ¹⁸ / cm ³ to a film thickness of 200 μm. The Si concentration is 1 × 10 ¹⁷ / cm ^{3 to} 5 × 10 ¹⁹ / c.
A range of m ³ is desirable. Nitride semiconductor substrate 50
After the growth, the sapphire substrate 1, the buffer layer 2, the protective film 3, and the undoped GaN layer are polished and removed in the same manner as in Example 1 to form the nitride semiconductor substrate 50 alone.

Then, the crack prevention layer 6 to the p-side contact layer 13 are grown on the nitride semiconductor substrate 50 in the same manner as in the first embodiment. After the growth of the p-side contact layer 13 and the formation of the stripe-shaped first protective film 61 in the same manner as in Example 1, in the second step, the etching stop is performed on the surface of the n-side cladding layer 7 shown in FIG. And After that, in the same manner as in the example, the second protective film 62 containing ZrO2 as a main component is formed on the side surface of the stripe waveguide and the surface of the n-side cladding layer 7, and then the second protective film is interposed. To form the p-electrode 20. On the formed p electrode 21, a first thin film layer 31 made of Ti is formed to have a film thickness of 1000 angstroms so as to have the same length as the stripe length, and the same shape as that of the second thin film layer 32 is formed from Pt. FIG. 5 shows a p-pad electrode 101 formed by sequentially laminating a third thin film layer having a thickness of 1000 angstroms and a second thin film layer 32 made of Au with a shape shorter than the stripe length having a thickness of 8000 angstroms. To form. Although not shown, the third thin film layer is formed in the same shape as the second thin film layer. On the other hand, the n-electrode 21 is formed on almost the entire rear surface of the nitride semiconductor substrate. After electrode formation
Cleavage at the M-plane of the nitride semiconductor substrate to form a resonance plane,
When a laser device having a structure as shown in FIG. 5 was obtained, a laser device was obtained which had good cleaving properties and substantially the same characteristics as in Example 3.

[Embodiment 5] The p-pad electrode shown in FIG.
N with the same length as the stripe to cover the entire surface of the p-electrode
The first thin film layer made of i has a film thickness of 1000 angstroms, and the second thin film layer made of Au has a film thickness of 8000 angstroms and has a shape shorter than the stripe length so that the end face of the second thin film layer does not coincide with the cleavage plane. A laser element is manufactured in the same manner as in FIG. 7 except that the laser elements are formed in order. As a result, the cleavage property when forming the resonance surface is good, the peeling of the p-pad electrode can be prevented, and the heat dissipation property is good.

[0074]

According to the present invention, the p-pad electrode is formed by laminating the first thin film layer and the second thin film layer in a specific shape, so that the resonance surface is formed by cleavage even when the entire surface of the p electrode is covered. In this case, the cleavage property of the p-pad electrode is improved, and the p-pad electrode can be prevented from peeling off from the p-electrode, the insulating film, etc., whereby the heat generated in the laser element is radiated well through the p-pad electrode. Therefore, it is possible to obtain a laser device having improved life characteristics. Further, the present invention provides better cleavage by specifying the composition of the first thin film layer of the p-pad electrode. Furthermore, according to the present invention, by using Ti for the first thin film layer of the p-pad electrode, an insulating film other than Si oxide is formed on the side surface of the narrow stripe that enables the threshold value to be lowered. In this laser device as well, the cleavage property is good, and the adhesion property with the insulating film is better, and peeling or floating of the p-pad electrode can be prevented, which is preferable.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a part of a nitride semiconductor laser device according to an embodiment of the present invention.

FIG. 2 is a schematic plan view showing a part of the nitride semiconductor laser device according to the embodiment shown in FIG.

FIG. 3 is a schematic cross-sectional view of a nitride semiconductor laser device according to one embodiment of the present invention.

FIG. 4 is a schematic cross-sectional view of a nitride semiconductor laser device according to an embodiment of the present invention.

FIG. 5 is a schematic cross-sectional view of a nitride semiconductor laser device according to one embodiment of the present invention.

FIG. 6 is a schematic cross-sectional view showing a partial structure of a wafer obtained in each step for explaining each step of the method of the present invention.

FIG. 7 is a schematic cross-sectional view showing the structure of a conventional laser device.

[Explanation of symbols]

1 ... Heterogeneous substrate 2 ... Underlayer 3 ... Protective film for growing nitride semiconductor substrate 4, 40, 50 ... Nitride semiconductor substrate 5 ... n-side contact layer 6 ... Crack prevention layer 7 ... n-side clad layer 8 ... n-side light guide layer 9 ... Active layer 10 ... p-side cap layer 11 ... p-side light guide layer 12 ... p-side clad layer 13 ... p-side contact layer 61 ... First protective film 62 ... Second protective film 63 ... Third protective film 20 ... p electrode 21 ... n electrode 31 ... First thin film layer 32 ... second thin film layer 101 ... Pad electrode

Claims (6)

[Claims] 1. A ridge-shaped stripe having an insulating film on a side surface of the stripe, a p-electrode and a p-pad electrode on the uppermost layer of the stripe, and further from a cleavage plane in a direction perpendicular to the stripe length direction. In the nitride semiconductor laser device having the following resonance surface, the p-pad electrode has at least the same length as the stripe length, and includes a first thin-film layer containing a metal having good cleavability,
A nitride semiconductor laser device comprising at least a second thin film layer containing a metal formed on the first thin film layer with a length shorter than a stripe length. 2. The first thin film layer is 100-5000.
The nitride semiconductor laser device according to claim 1, wherein the range is angstrom. 3. The nitride semiconductor laser device according to claim 1, wherein the second thin film layer is formed so that at least one end face thereof does not coincide with the cleavage plane. 4. The third thin film layer serving as a barrier layer capable of suppressing the diffusion of the second thin film layer between the first thin film layer and the second thin film layer. The nitride semiconductor laser device according to claim 1. 5. The nitride semiconductor laser device according to claim 4, wherein the third thin film layer has substantially the same size as the second thin film layer. 6. The nitride semiconductor laser device according to claim 4, wherein the first thin film layer and the third thin film layer are made of the same material.