JP3199594B2 - Method of forming optical resonance surface of nitride semiconductor laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nitride semiconductor (In _XA).
The present invention relates to a method for manufacturing a laser device composed of 1 _Y Ga _{1 -XYN} , 0 ≦ X, 0 ≦ Y, and X + Y ≦ 1), and particularly to a method for forming an optical resonance surface of a nitride semiconductor laser device.

[0002]

2. Description of the Related Art A nitride semiconductor has a band gap of 1.9.
Since it is 5 eV to 6.0 eV and is a direct transition type,
It has been attracting attention as a material for light-emitting elements such as laser diodes (LDs) and light-emitting diodes (LEDs) ranging from ultraviolet to red, and blue LEDs and blue-green LEDs using these materials have just recently been put into practical use. In addition, not only LEDs but also ultraviolet and blue light emitting semiconductor laser devices using nitride semiconductors have been studied.

In general, when manufacturing a laser device, it is necessary to form an optical resonance surface on a semiconductor layer. A conventional semiconductor laser made of a GaAs-based compound semiconductor and oscillating in the infrared region has a cleavage property due to crystal properties, and the cleavage plane is often used as an optical resonance plane of the laser element.

On the other hand, nitride semiconductors do not have cleavage properties due to hexagonal crystal properties. Furthermore, nitride semiconductors are often grown on the surface of a sapphire substrate, and sapphire also has no cleavage due to its crystalline nature. Therefore, conventionally, when manufacturing a laser device using a nitride semiconductor, it was difficult to make the cleavage plane an optical resonance plane.
Laser oscillation did not occur.

[0005]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to form a laser device by forming a cleaved surface from the nitride semiconductor layer grown on a sapphire substrate so as to serve as an optical resonance surface. Is to make it happen.

[0006]

According to the present invention, there is provided a method for forming an optical resonance surface, comprising the steps of: forming a wafer in which at least an n-type layer made of a nitride semiconductor, an active layer, and a p-type layer are sequentially laminated on a sapphire substrate; Forming an optical resonance surface of a nitride semiconductor laser device from
Exposing the mold layer to form a striped nitride semiconductor layer, and etching the p-type layer side of the striped nitride semiconductor layer to a depth not reaching the active layer to form a first split groove. Forming a wafer along the first split groove and the second split groove, and setting the split nitride semiconductor layer surface as an optical resonance surface.

The method of the present invention will be described with reference to the drawings. FIG. 1 is a schematic sectional view showing the structure of a part of a wafer obtained in one step of the method of the present invention, and FIG. 2 is a perspective view showing the shape of the wafer of FIG. FIG. 1 shows a cross section when the perspective view of FIG. 2 is viewed from the direction of the arrow. This wafer basically has a structure in which an n-type layer 2 made of a nitride semiconductor, an active layer 3, and a p-type layer are sequentially stacked on a sapphire substrate 1. Further, as shown in FIG. 2, these nitride semiconductor layers are preliminarily etched in the form of stripes. Thereafter, an optical resonance surface serving as a reflecting mirror is formed on the surface of the nitride semiconductor layer, thereby forming an electrode stripe type laser. An element can be manufactured. A current constriction layer made of an insulator and a positive electrode are formed on the p-type layer along the stripe, and a striped negative electrode is also formed on the n-type layer. Not particularly shown.

The first split groove 10 is formed by etching the p-type layer 4 in a stripe shape to a depth that does not reach the active layer 3. As an etching means for forming the first split groove 10, dry etching is preferably used to control an etching rate, for example, reactive ion etching, ion milling, ion beam assisted etching, focused ion beam etching, etc. Means can be used.

On the other hand, a second split groove 20 is formed on the side of the sapphire substrate 1 where no nitride semiconductor layer is formed. The second split groove 20 may be formed by any method, such as scriber, dicing, etching or the like, as long as it can damage the sapphire substrate at a predetermined position. For example, in FIGS. 1 and 2, the second split groove 20 indicates a scribe line using a scriber. FIG.
FIG. 4 is a schematic cross-sectional view showing a structure of a wafer obtained in one step according to another embodiment of the present invention. In FIG. 3, the second split groove 20 is formed by first cutting the sapphire substrate 1 by a dicer. This shows that after forming a wide groove, the groove is further scribed to form a narrower split groove.

A first split groove 10 and a second split groove 2
Either step may be performed first in order of forming 0. Further, it is very preferable to make the center of the first split groove coincide with the center of the second split groove, since an end face of the split face can be obtained as a parallel face, that is, an optical resonance face parallel to each other.

Next, after forming the first split groove and the second split groove, the wafer is pressed and split at a position along the split groove using, for example, a roller or the like, so that the split nitride semiconductor layer surface Is in a state like a cleavage plane, and an optical resonance surface can be formed.

[0012]

FIG. 4 is a schematic sectional view showing the structure of a wafer when a resonance surface is formed by a method compared with the method of the present invention. When the second split groove 20 is formed only on the sapphire substrate side as shown in FIG. 4 and the wafer is split, as shown by the broken line in FIG. 4, the split nitride semiconductor surface is inclined to be broken or chipped. And so on, and it is difficult to form parallel end faces. Further, as shown by the branched broken line in FIG. 3, the edge of the nitride semiconductor layer is damaged by factors such as impact and stress generated when the wafer is cracked,
Crystallinity deteriorates. However, in the present invention, since the first split groove 10 facing the second split groove 20 is formed on the surface of the p-type layer, the first split groove 10 is formed as shown by a broken line in FIGS. Since it is easy to break straight between the groove 10 and the second split groove 20, even the nitride semiconductor layer having no cleavage has a split surface like a cleavage plane, and optical resonance surfaces parallel to each other are easily formed. Become. Further, the first split groove is formed by etching so as not to reach the active layer. Since the etching causes less damage to the end face of the p-type layer, damage to the active layer in contact with the p-type layer is also reduced at the same time. Accordingly, the end faces of the active layer with less damage can be easily obtained in directions parallel to each other, and function as an optical resonator.

Further, in the method of the present invention, it is desirable to adjust the thickness of the sapphire substrate to 150 μm or less before forming the first split groove or the second split groove. Furthermore, it is desirable to adjust the distance between the bottom of the first split groove and the bottom of the second split groove to 150 μm or less. The distance of the bottom of the split groove is the length of FIG. 3 (a), and the depth of the first split groove 10 and the second split groove 20 is adjusted to substantially adjust the depth of the wafer to be split. It refers to the thickness. This is because, if the thickness of the substrate or the thickness of the substantially cracked wafer is adjusted to 150 μm or less, the wafer is easily broken straight between the split grooves, and the cleavage plane is caused by the resonance of the nitride semiconductor layer. It is because it becomes easy to become a surface. Conversely, as the size becomes larger than 150 μm, the number of wafers that are obliquely cracked increases, and the end face of the nitride semiconductor layer tends to be damaged more.

[0014]

EXAMPLE On a sapphire substrate having a thickness of 350 μm, Ga
200 angstrom buffer layer made of N, Si
5 μm of an n-type contact layer made of doped n-type GaN,
The n-type cladding layer made of Si-doped n-type Al0.3Ga0.7N is 0.1 μm, the second n-type cladding layer made of Si-doped n-type In0.01Ga0.99N is made 500 Å, and non-doped In0.08Ga0.92N. 1 active layer
00 Å, Mg-doped p-type Al0.3Ga0.7
0.1 μm p-type cladding layer made of N, Mg-doped p
A wafer is prepared by sequentially growing a p-type contact layer of type GaN with a thickness of 0.5 μm.

Next, the surface of the p-type contact layer of this wafer is etched from the p-type contact layer side by RIE (Reactive Ion Etching) so that the nitride semiconductor layer has a stripe width of 20 μm. Exposing the contact layer.

After etching, an SiO ₂ film serving as a current confinement layer is formed on the entire surface of the stripe-shaped p-type contact layer, and then a positive electrode is formed on the entire surface of the current confinement layer and the p-type contact layer. A striped negative electrode is formed on the n-type contact layer.

Next, after forming a mask on the surface of the positive electrode, a first split groove having a shape as shown in FIG. 2 is formed by RIE. However, the first split groove has a width of 5 μm and a depth up to the middle of the p-type contact layer.

After forming the first split groove, the sapphire substrate is
Polish to a thickness of 00 μm. After polishing, the sapphire substrate side is scribed to form a second split groove. However, the second split groove scribes the sapphire substrate at the center of the width of the first split groove. On the other hand, a scribe line perpendicular to the second split groove is formed on the sapphire substrate side in a direction parallel to the electrodes.

The wafer formed as described above is pressed with a roller, and the nitride semiconductor layer surface obtained by splitting the wafer at a position where the first split groove and the second split groove coincide with each other is used as an optical resonator. And an electrode stripe type laser chip having a chip width of 400 μm.

Next, after masking the cleaved nitride semiconductor layer surface, SiO ₂ and ZrO ₂ are formed on the cleaved surface by a sputtering device.
A dielectric multilayer film is formed. This dielectric multilayer film has an effect of reflecting the wavelength of the active layer by 90% or more.

After the laser chip thus obtained was set on a heat sink, laser oscillation was attempted at the temperature of liquid nitrogen.
% Or more, oscillation at an oscillation wavelength of 420 nm was confirmed at a threshold current density of 1.3 kA / cm ² .

Example 2 In Example 1, when polishing the substrate, the thickness of the substrate was set to 1
When a laser device was obtained in the same manner except that the thickness was set to 50 μm, laser oscillation was confirmed in 60% or more of the laser devices obtained from the wafer.

[0023]

As described above, according to the method of the present invention, a resonator can be formed by cleavage even in a nitride semiconductor layer laminated on a sapphire substrate which has not been cleaved, so that a laser device can be realized. It became. Furthermore, when a reflecting mirror made of a dielectric multilayer film is formed on the surface of the resonator, light can be effectively confined. in this way,
Since a short-wavelength laser can be realized by the method of the present invention, the nitride semiconductor laser element as a light source for writing and reading has a great industrial value.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a partial structure of a wafer obtained by one step of the method of the present invention.

FIG. 2 is a perspective view showing a partial shape of the wafer of FIG. 1;

FIG. 3 is a schematic sectional view showing a partial structure of a wafer obtained by one step of another method of the present invention.

FIG. 4 is a schematic sectional view showing a partial structure of a wafer obtained by one step of a method compared with the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Sapphire substrate 2 ... N-type nitride semiconductor layer 3 ... Active layer 4 ... P-type nitride semiconductor layer 10 ... First split groove 20 ...・ Second split groove

Claims (3)

(57) [Claims] 1. A method for forming an optical resonance surface of a nitride semiconductor laser device from a wafer in which at least an n-type layer made of a nitride semiconductor, an active layer, and a p-type layer are sequentially stacked on a sapphire substrate. A step of etching the p-type layer to expose the n-type layer to form a stripe-shaped nitride semiconductor layer, and the p-type layer side of the stripe-shaped nitride semiconductor layer does not reach the active layer. Forming a first split groove by etching at a depth, forming a second split groove on the sapphire substrate side facing the stacked nitride semiconductor layer surface, and the first split groove, and Splitting the wafer along the second split groove and setting the split nitride semiconductor layer surface as an optical resonance surface. 2. The method according to claim 1, wherein the sapphire substrate is polished before the first split groove or the second split groove is formed, and the thickness of the substrate is adjusted to 150 μm or less. The forming method as described above. 3. The method according to claim 1, wherein the distance between the bottom of the first split groove and the bottom of the second split groove is adjusted to 150 μm or less.