JP3490229B2 - Method of manufacturing nitride semiconductor laser device - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to a nitride semiconductor (In _X A
TECHNICAL FIELD The present invention relates to a laser element made of 1 _Y Ga _1-XY N, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1) and a manufacturing method thereof, and more particularly to a laser element having a resonance surface formed by etching and a manufacturing method thereof.

[0002]

2. Description of the Related Art Generally, a laser device made of a compound semiconductor needs a resonance surface for resonating the light of the active layer inside the semiconductor layer. Infrared, red, etc. long-wavelength light emitting semiconductor lasers currently in practical use are, for example, GaAlAs and G
It is made of materials such as aAlAsP and GaAlInP, and these materials are grown on a GaAs substrate. Since GaAs has a cleavage property in the material itself, the resonance surface of the long wavelength semiconductor laser is often a cleavage surface utilizing the cleavage property of the GaAs substrate.

On the other hand, nitride semiconductors are often grown on a substrate having no cleavage property, such as sapphire (Al ₂ O ₃ ), so that the substrate is cleaved to form a cleavage plane of the nitride semiconductor. It is difficult to make it a resonance surface. On the other hand, there is also a method of forming a resonance surface of a nitride semiconductor by etching, but if the substrate is divided after the resonance surface is formed by etching, part of the substrate protruding from the resonance surface reflects and transmits the emitted light. Therefore, there is a problem that the beam emitting direction of the emitted laser light is oblique to the horizontal plane of the substrate. When the laser beam becomes oblique, it becomes difficult to couple with the lens.

[0004]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to form a resonance surface on a nitride semiconductor grown on a substrate which is difficult to cleave, and to direct the emission direction of the beam center to the substrate. Is to provide a laser element capable of obtaining a horizontal laser beam and a method for manufacturing the laser element.

[0005]

According to a method of manufacturing a nitride semiconductor laser device of the present invention, an n-type layer having an n-type contact layer, an active layer and a p-type contact layer having an n-type contact layer are formed on a substrate.
First step of growing a nitride semiconductor layer made of a mold layer and then etching the nitride semiconductor layer using a mask until the plane of the n-type contact layer is exposed to form a resonance surface at the etching end face. And a second step of dividing the substrate at the exposed substrate surface between the resonance surfaces, which are formed by etching and are opposed to each other, of the first step and the second step. In between, after removing the mask, a continuous mask is formed on the plane of the n-type contact layer in the direction parallel to the cavity length and the plane of the uppermost p-type contact layer, and the n-type contact on the resonance surface side is formed. Etching again only the layer until the substrate is exposed.

The method for manufacturing a nitride semiconductor laser device according to the present invention is characterized in that, in the first step, an n-electrode forming surface is formed at the same time as a resonance surface.

Further, in the method for manufacturing a nitride semiconductor laser device according to the present invention, in the second step, at the same time when the substrate is divided, at least one of the substrates protruding from the resonance surface formed after the division is
At least one of the protrusion lengths is set to the laser emitted from the resonance surface.
The feature is that the length does not block the light .

Further, in the method for manufacturing a nitride semiconductor laser device according to the present invention, after the second step, a part of the portion including the substrate protruding from the resonance surface is removed so that
It is characterized by having a third step of not blocking the laser light emitted from the laser .

Further, the manufacturing method 5 of the nitride semiconductor laser device of the present invention is characterized in that after the second step or the third step, a dielectric multilayer film is formed on the end surface on the resonance surface side. .

[0010]

1 is a schematic cross-sectional view showing one structure of a laser device of the present invention, showing a view when the device is cut in a direction parallel to the resonance direction of the laser. In FIG. 1, 1 is a substrate, 2 is an n-type layer, 3 is an active layer, 4 is a p-type layer, and as shown in the figure, laser light is formed by etching of nitride semiconductor layers facing each other. It resonates on the resonance plane, and is emitted from the active layer 3 at an angle of θ in each of the A direction and the B direction opposite to the A direction.

In the laser element of the present invention, the portion including the substrate protruding from the resonance surface in the A direction is removed. That is, the laser light emitted at the angle of θ is prevented from being blocked by the end portion of the substrate 1 protruding from the resonance surface. On the other hand, the laser light emitted from the resonance surface in the B direction is partially blocked by the end portion of the substrate 1. However, in the laser element of the present invention, the laser light emitted from any one of the resonance surfaces. However, it suffices that the portion protruding from the resonance plane is not blocked. This is because the laser light emitted from one of the actual laser elements is used as a writing and reading light source, but a detector (photodetector) for controlling the laser light is installed in the direction from which the other laser light is emitted. It Therefore, the detector need only read the signal such as the intensity of the laser beam, and the center of the beam does not need to be horizontal with respect to the substrate. However, it is desirable that the two directions of laser light emitted from the resonance surface are not blocked by the portion including the substrate protruding from the resonance surface. Therefore, the claims of the present application include one in which one of the laser beams is not blocked as shown in FIG.

FIG. 2 is also a schematic sectional view showing another structure related to the laser device of the present invention, and the same reference numerals as those in FIG. 1 indicate the same members. The difference between this laser device and the laser device of FIG. 1 is that in the etching of the resonance surface, first, the substrate 1 is not etched as in FIG. 1 but stopped in the middle of the n-type layer 2 (specifically, Specifically, the etching for exposing the n-type contact layer on which the n-electrode is to be formed and the etching for forming the resonance surface are simultaneously performed.) Second, not only the A direction but also the B direction. That is, the laser beam is prevented from being blocked by the end portion of the substrate 1 by removing the portion projecting from the resonance surface at.

As shown in FIG. 2, when the resonance surface is formed by etching, if the etching is stopped in the middle of the n-type layer 2, the etching to the n-type contact layer where the n electrode is to be formed and the resonance surface are formed. There is an advantage that the etching for forming the can be performed at the same time. However, when the substrate is divided, if the n-type layer remains on the resonance surface side, a shock during division may cause cracks from the n-type layer on the resonance surface side. It is desirable to carry out until the substrate is reached as shown in FIG.

FIG. 3 is also a perspective view showing another structure of the laser device of the present invention, which is a partially enlarged view of the laser device near the resonance surface. The difference between this figure and the laser device of FIGS. 1 and 2 is that, even if most of the portion projecting from the cavity surface is not removed, a portion of the substrate 1 is partially removed by etching to remove the laser beam from the cavity surface. This is where the emitted laser light is not blocked by a part of the substrate. Also in this figure, the etching on the resonance surface side is performed until the substrate is reached.

As shown in these figures, the laser device of the present invention is a laser device having a resonance surface formed by etching so that laser light emitted from the resonance surface is not blocked by a portion protruding from the resonance surface side. Therefore, a laser element whose beam center is horizontal to the substrate can be realized. Whether or not the laser light is blocked can be determined by observing the far-field pattern of the laser light. Specifically, if the far field pattern is substantially vertically symmetrical with respect to the horizontal direction of the substrate, it can be determined that the laser light is not blocked by the substrate. The length of the protrusion is 20 μm or less from the resonance surface, and more preferably 10 μm.
It is set to be not more than μm, most preferably not more than 5 μm. This also applies to the first and second aspects of the production method of the present invention described below.

Next, a method for manufacturing a laser device according to the present invention will be described with reference to the drawings. FIG. 4 is a schematic cross-sectional view illustrating the first aspect of the present invention, showing the structure of the wafer in the first step. This figure shows the structure when a wafer having a resonance surface formed by etching is cut in a direction parallel to the resonance direction of laser light. The same reference numerals as those in FIGS. 1 to 3 denote the same members.

In the first step of the present invention, after the nitride semiconductor layer is grown on the substrate, the nitride semiconductor layer is etched to form a resonance surface on the etching end face. The etching end surface should be substantially perpendicular to the substrate.
The end faces that are etched perpendicularly to each other with the active layer in between serve as resonance surfaces. As the etching means, for example, dry etching means such as reactive ion etching (RIE), reactive ion beam etching (RIBE), and ion milling can be preferably used. These dry etching means can be selected by appropriately selecting an etching gas, By controlling the etching rate, it is possible to fabricate resonance planes whose etching end faces are smooth and are substantially parallel to each other. When the resonance surface is formed in the first step as described above, the surface of the n-type layer 2 continuous with the resonance surface is exposed, and the resonance surface of one laser element and the resonance surface of the other laser element face each other. It becomes the structure. That is, by etching, a resonance surface and a resonance surface facing each other can be formed continuously.

Next, in the second step, the substrate is divided between the resonance surfaces which are successively formed by etching and which face each other and face each other. For example, the substrate is divided at the position shown by the alternate long and short dash line in FIG. To divide the substrate, conventionally used substrate cutting means such as scribing or dicing is used. For example, in the case of a sapphire substrate, to divide the substrate by scribing, the thickness of the substrate should be 150 μm before scribing.
The substrate can be accurately cut from the scribe line by polishing to a thickness of m or less, more preferably 100 μm or less to make the substrate thinner.

Next, in the third step, part or all of the portion including the substrate protruding from the resonance surface is removed. In FIG. 4, the portion including the substrate protruding from the resonance surface refers to the protruding n-type layer 2 and the substrate 1. In the third step, when laser light having an emission angle θ is emitted from the resonance surface,
The downward light is reflected and transmitted by the etching plane (substrate plane or n-type layer plane) so as not to be blocked.
Specifically, the portion projecting from the resonance surface is removed so that the laser beam does not strike the etching plane.
As a concrete means for this purpose, any one means selected from lapping, cutting or etching is desirable. The lapping is performed by using a fine powder such as diamond, SiC, or alumina for the protrusion from the resonance surface to shorten the entire length of the protrusion. Lapping is convenient because it can smooth the divided surface. It is also possible to cut the protruding portion by dicing. A laser element as shown in FIGS. 1 and 2, for example, can be produced by means such as lapping and cutting. Further, etching may be used to remove only an unnecessary portion where the laser beam is emitted and comes into contact with the substrate side, as shown in FIG.

FIG. 5 is a schematic sectional view for explaining the second embodiment of the manufacturing method of the present invention. This figure also shows the structure when a wafer having a resonance surface produced by etching is cut in a direction parallel to the resonance direction of laser light. The same reference numerals as those in FIGS. 1 to 4 denote the same members.

In the second aspect of the present invention, similarly to the first aspect, in the first step, the nitride semiconductor layer is etched from the wafer in which the nitride semiconductor layer is laminated on the substrate 1, A resonance surface is formed on the etching end surface. further,
The feature of the second aspect lies in the following second step. Between the resonance surface and the resonance surface, which are continuously formed by etching, the substrate 1 is divided at a position shown by a chain line in FIG. The portion including the above substrate does not block the laser light emitted from the resonance surface. When the second step is performed, it is not necessary to perform lapping, cutting, etching or the like on the portion protruding toward the resonance surface side after the division as in the first aspect, and the third step is unnecessary. This is because, as shown in FIG. 5, the substrate is divided at a position very close to one of the continuous resonance surfaces. Thus, when the substrate is divided at a position very close to one of the resonance surfaces, one resonance surface side having the active layer has a portion protruding from the resonance surface to block the laser light. As described above, even if the laser beam on the side where the detector is installed is blocked, there is no practical problem.

Furthermore, the first aspect of the manufacturing method of the present invention,
In the second aspect, it is desirable to etch the nitride semiconductor on the resonance surface side until the substrate is exposed, between the first step and the first step and the second step. This is because if there is an n-type layer between the facing resonance surfaces and the resonance surface, if a crack is generated in the n-type layer at the end of the division surface due to the impact during division, the crack is generated. It may propagate to the body, for example the n-type layer below the active layer. However, when the substrate is also etched, only the substrate is broken, and the n-type layer can be prevented from being damaged.

[0023]

EXAMPLES Example 1 (First Mode) On a 2-inch φ sapphire substrate, an n-type contact layer made of n-type GaN, an n-type optical confinement layer made of n-type AlGaN, and an n-type An optical guide layer made of AlGaN,
A laser wafer is prepared in which an active layer made of InGaN, an optical guide layer made of p-type AlGaN, a p-type optical confinement layer made of p-type AlGaN, and a p-type contact layer made of p-type GaN are stacked. In addition to sapphire, a substrate proposed for growing a nitride semiconductor such as SiC, spinel, ZnO, MgO, or Si can be used as the substrate, and the substrate is not particularly limited. Further, the laminated structure of the nitride semiconductor is merely an example for laser oscillation, and is not limited to this structure.

(First Step) Next, a mask having a mask shape as shown in FIG. 6 is formed on the uppermost layer of the nitride semiconductor of this wafer. In addition,
In FIG. 6, the horizontal length of the mask shown by the hatched portion corresponds to the cavity length of the laser element. After mask formation, SiC
RIE (reactive ion etching) is performed using l ₄ gas and Cl ₂ gas to expose the n-type contact layer on which an electrode is to be formed and to form a resonance surface in a portion corresponding to the vertical direction of the mask. By this etching, the n-type contact layer on which the electrode is to be formed is exposed, and at the same time, the resonance surface is formed on the surface of the nitride semiconductor layer which is in the vertical direction of the mask. After removing the mask, an n-electrode is formed on the exposed n-type contact layer and a p-electrode is formed on the uppermost p-type contact layer in stripes parallel to each other.

(Second Step) After the electrodes have been formed, the substrate is lapped (polished) to a thickness of 80 μm, and as shown by the alternate long and short dash line in FIG. After scribing from, the wafer is crushed to form bar-shaped laser chips.

Further, a dielectric multilayer film made of SiO ₂ and TiO ₂ is formed on the resonance surface side of the bar-shaped laser chip using a plasma CVD apparatus to form a reflecting mirror.

(Third Step) After forming the reflecting mirror, the protruding substrate and the n-type contact layer on the resonance surface side of the bar-shaped laser chip are lapped and removed to a length of 5 μm. In the lapping, the lapping surface is stopped at a position where it does not touch the surface of the nitride semiconductor dielectric multilayer film formed previously. Perform the same operation on the other resonance surface side of the same bar-shaped laser chip,
The parts on both sides protruding from the resonance surface are removed.

As described above, the bar-shaped laser chip, which has been polished to remove the protruding portion, is divided by scribing at a position parallel to the n-electrode to obtain a rectangular laser chip. FIG. 2 is a schematic cross-sectional view showing the structure of this laser chip.

When the laser chip obtained as described above was placed on a heat sink in a face-up state and was actually oscillated, the far-field pattern of the laser light emitted from the resonance surface was above and below the horizontal direction of the substrate. It was symmetric and had no interference due to the reflection of the laser light, and it was shown that the laser light was not blocked by the substrate and the beam center was horizontal to the substrate.

[Embodiment 2] (Second Mode) Similar to Embodiment 1, steps up to the first step are performed to expose the surface of the n-type contact layer and the resonance surface of the laser element at the same time.

After removing the mask, a continuous mask is formed on the plane of the n-type contact layer in the direction parallel to the cavity length and the plane of the uppermost p-type contact layer, and RIE is performed again to the resonance plane side. Only a certain n-type contact layer is etched until the substrate surface is exposed. After etching, the mask is removed, and the uppermost p-type contact layer is formed as in Example 1.
An electrode parallel to the n-type contact layer is formed.

(Second Step) After the electrodes are formed, the substrate is lapped in the same manner as in Example 1 and then, as shown by the alternate long and short dash line in FIG. After scribing from the sapphire substrate side, the wafer is pressed to produce bar-shaped laser chips.

After that, a laser element was manufactured in the same manner as in Example 1. As with the laser element in Example 1, the far-field pattern of the laser light emitted from the resonance surface was vertically symmetrical with respect to the horizontal direction of the substrate. It was shown that interference due to reflection of laser light did not appear, the laser light was not blocked by the substrate, and the beam center was horizontal to the substrate.

[Embodiment 3] In the same manner as in Embodiment 2, after the n-type contact layer on the resonance surface side is removed and the substrate is exposed in the first step, the laser light is emitted from the active layer. A mask having a predetermined shape is formed except for the plane of the corresponding substrate.

Next, RIE is performed to remove the substrate on which the mask is not formed. A wafer having a shape in which holes are formed between the resonance surfaces in this way is scribed between the resonance surfaces in the same manner as in Example 1 to form bar-shaped chips. Split into. FIG. 3 is a perspective view showing the shape near the resonance surface after division.

After the reflecting mirror was formed on the resonance surface side of the obtained bar-shaped chip as described above, it was divided into rectangular chips at a position parallel to the n-electrode in the same manner as in Example 1. To produce a laser device. As with the laser elements of Examples 1 and 2, this laser element also had a far-field symmetry in the far-field pattern of the laser light emitted from the resonance surface, indicating that the laser light was not blocked by the substrate.

[0037]

In the laser device having the portion protruding from the resonance surface, a part of the laser light emitted from the active layer is reflected and transmitted by the etching plane remaining after the substrate is divided, and is blocked. When a part of the laser light emitted from the resonance surface side is reflected by the remaining substrate, nitride semiconductor, etc., the output is reduced and the beam is emitted obliquely and is vertically symmetrical with respect to the horizontal direction of the substrate. Far field pattern cannot be obtained. Particularly in the case of a semiconductor laser, a lens is provided in front of the resonance surface from which the laser light is emitted for the purpose of focusing the laser light. If there is another member that blocks the laser light on the side of the emitted light, for example, the light may not be collected well. However, according to the laser device of the present invention, since the laser light is emitted horizontally, the above-mentioned problems can be solved and the laser light can be easily condensed.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing one structure of a laser device of the present invention.

FIG. 2 is a schematic cross-sectional view showing another structure according to the laser device of the present invention.

FIG. 3 is a perspective view showing a structure in the vicinity of a resonance surface of the laser device of the present invention.

FIG. 4 is a schematic cross-sectional view showing the structure of a wafer obtained in one step of the manufacturing method of the present invention.

FIG. 5 is a schematic cross-sectional view showing the structure of a wafer obtained in one step of the manufacturing method of the present invention.

FIG. 6 is a partial plan view showing the shape of a mask formed on the surface of the uppermost nitride semiconductor.

[Explanation of symbols]

1 ... substrate 2 ... N-type layer 3 ... Active layer 4 ... P-type layer

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-63-19891 (JP, A) JP-A-4-255285 (JP, A) JP-A-8-228025 (JP, A) JP-A-7- 249830 (JP, A) JP 63-318183 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 5/00-5/50

Claims (4)

(57) [Claims] 1. A nitride semiconductor layer comprising an n-type layer having an n-type contact layer, an active layer and a p-type layer having a p-type contact layer is grown on a substrate, and then the nitride semiconductor layer is formed. Between the resonance surface and the resonance surface, which are formed by etching until the flat surface of the n-type contact layer is exposed to form a resonance surface at the etching end surface, and which are continuously formed by etching. And a second step of dividing the substrate at the exposed surface of the substrate, the n-type being parallel to the cavity length after the mask is removed between the first step and the second step. A step of forming a continuous mask on the plane of the contact layer and the plane of the uppermost p-type contact layer, and etching again only the n-type contact layer on the resonance surface side until the substrate is exposed. Nitride semiconductor laser device Production method. 2. In the second step, at the same time when the substrate is divided, at least one of the substrates protruding from the resonance surface formed after the division is
At least one of the protrusion lengths is set to the laser emitted from the resonance surface.
2. The method for manufacturing a nitride semiconductor laser device according to claim 1 , wherein the length is set so as not to block the light . 3. After the second step, by removing a part of the portion including the substrate protruding from the resonance surface, the resonance surface is removed.
2. The method for manufacturing a nitride semiconductor laser device according to claim 1, further comprising a third step of not blocking the laser light emitted from the laser diode . 4. The nitride semiconductor laser device according to claim 1, wherein a dielectric multilayer film is formed on the end surface on the side of the resonance surface after the second step or the third step. Manufacturing method.