JP3319585B2 - Method for manufacturing 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 of manufacturing a laser device comprising 1 _Y Ga _{1 -XYN} , 0 ≦ X, 0 ≦ Y, X + Y ≦ 1), and particularly to a good far field with respect to a laser beam emitted from a resonance surface formed by etching. The present invention relates to a method for manufacturing a nitride semiconductor laser device capable of extracting light having a pattern.

[0002]

2. Description of the Related Art Some nitride semiconductor laser devices have a resonance surface formed in a nitride semiconductor layer including an active layer, and emit a large output coherent light amplified in the active layer from the resonance surface. The present inventors have proposed, as a nitride semiconductor laser device having a resonance surface, a nitride semiconductor laser device capable of continuously oscillating short-wavelength laser light having a wavelength of 410 nm. For example, Appl. Phys. Lett. 69
(1996) 3034, Appl. Phys. Let
t. 69 (1996) 4056, and the like.

The nitride semiconductor laser device proposed by the present inventor can emit laser light of a short wavelength, and is very useful for increasing the density and capacity of an optical memory. The resonance surface of such a nitride semiconductor laser device is formed by etching, cleaving, or polishing the cleaved surface after cleavage. In general, since a nitride semiconductor substrate is made of a material having almost no cleavage such as sapphire or spinel, it is difficult to form a resonance surface by cleavage. In addition, since a resonance surface can be formed by etching regardless of the presence or absence of cleavage, it is relatively easy to form the resonance surface in a state close to a mirror surface as compared with cleavage.

In a conventional nitride semiconductor laser device, for example, as shown in FIG. 2, an n-type nitride semiconductor layer (n-type layer), an active layer, and a p-type nitride semiconductor layer (p-type layer) are formed on a substrate. It is laminated. When exposing an n-type layer (for example, a contact layer) for forming an n-electrode on the laser wafer by etching, a resonance surface is formed at the same time. Also,
Separation of such a nitride semiconductor laser device into chips is performed by using a device such as a dicer or a scriber that divides the wafer by an external force. However, a resonance surface is formed simultaneously with the exposure of the n-type layer. Therefore, the n-type layer exists on the cut surface cut by external force, and cracks are easily generated. In order to prevent the cracks from deteriorating the crystallinity of the nitride semiconductor, lowering the hardness, and shortening the life, the distance from the resonance surface to the cut surface is provided longer as shown in FIG.

[0005]

However, if the distance from the resonance surface to the cut surface is long as shown in FIG. 2, the laser light radiated from the resonance surface is reflected on this portion, and the far-field pattern is formed. It has been found that the single-mode laser beam required for application to higher density and larger capacity of optical memory is not sufficiently satisfactory.

If the distance from the resonance surface to the cut surface is simply shortened in order to improve the far-field pattern, crack prevention when the wafer is cut by an external force becomes insufficient. In order to prevent the nitride semiconductor from cracking when cutting the wafer even when the distance from the resonance surface to the cut surface is shortened, when forming the resonance surface, the n-type layer is not left until the substrate. It is conceivable to cut the wafer after etching and removing the n-type layer on the cut surface. However, if the substrate is etched without forming the n-type layer when forming the resonance surface, the etching depth becomes large, and the resonance surface is not smooth due to the etching conditions, and the far field pattern is easily disturbed.

As described above, if the resonance surface is not sufficiently smooth,
A DVD mode light source that requires a small laser beam diameter for achieving high density and large capacity of an optical memory because a far-field pattern cannot be a sufficiently good single mode, It cannot sufficiently satisfy applications to optical communication fields and the like that require light. When the semiconductor laser device is cut into chips, the substrate is first polished to make the substrate thinner, and then the wafer is cracked using a scriber. However, in the process of polishing the substrate side to reduce the thickness of the substrate, the wafer warps due to the lattice constant difference between the nitride semiconductor layer and the substrate, and the thickness of the substrate is 80 μm.
When the thickness is smaller, the wafer is easily broken. Also, if warping occurs, the scribing process becomes difficult.

Accordingly, an object of the present invention is to provide a single-mode laser beam with a good far-field pattern of the laser beam, and to enable easy polishing and scribing when the element is cut into chips. It is an object of the present invention to provide a method for manufacturing a nitride semiconductor laser device.

[0009]

That is, the object of the present invention can be achieved by the following constitutions (1) and (2). (1) Etching is performed from the p-type layer side of a nitride semiconductor wafer in which an n-type layer, an active layer, and a p-type layer are sequentially stacked on a sapphire substrate to expose the surface of the n-type layer;
A first step of forming a resonance surface on the etched end face, and a groove for separating a laser chip is formed on the surface of the n-type layer exposed in the first step by removing the nitride semiconductor until the sapphire substrate is exposed. A second step, and a third step of removing a corner of the n-type layer plane exposed in the first step above the groove so that the divergence angle of the laser beam becomes 30 ° or more. A method for manufacturing a nitride semiconductor laser device.

(2) In the first step, etching is performed up to the n-type layer under the active layer, and the exposed n-type layer is removed.
The distance between the plane of the mold layer and the lower end surface of the active layer above the plane is W, the distance between the groove end surface formed in the second step and the resonance surface is X, and the distance is removed in the third step. When the thickness of the corner to be formed is Y and the length in the laser beam emission direction is Z, each step is performed so as to satisfy the condition of tan15 ° = W / (X−Z) = Y / Z. The method for manufacturing a nitride semiconductor laser device according to the above (1).

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the drawings. FIG. 1 shows an n-type nitride semiconductor layer (n-type layer) 2 (having a laminated structure such as a contact layer, an optical guide layer and an optical confinement layer), an active layer 3 and a p-type nitride semiconductor layer ( FIG. 3 is a schematic cross-sectional view of a nitride semiconductor on which a p-type layer (a p-type layer) 4 (having a laminated structure of a contact layer, a light guide layer, a light confinement layer, and the like) is laminated (first step). This is masked with a pattern so that it has a predetermined chip size,
The nitride semiconductor 201 is removed by RIE (reactive ion etching) until the substrate 1 is exposed, and a groove is formed (second step). By forming this groove, when the semiconductor laser is chipped, the warpage of the wafer due to the lattice constant difference between the nitride semiconductor and the substrate 1 when the substrate side is polished to reduce the thickness of the substrate 1 can be reduced. Thus, the step of polishing and subsequent cracking of the wafer using a scriber can be facilitated.

FIG. 2 shows a state where the second step is completed. Next, as a third step, the corner 202 of the n-type layer plane exposed in the first step above the groove 201 is removed (third step). Process). The corner 202 to be removed may be cut by a dicer, or may be etched by RIE or the like. If this corner 202 is not removed, the emitted laser is reflected on the n-type layer plane exposed in the first step, and disturbs the far-field pattern.

FIG. 3 is an enlarged view of FIG. By performing this third step, the divergence angle of the emitted laser is set to 30 °.
Adjust as above. Specifically, in the first step, the distance between the exposed plane of the n-type layer and the end face of the active layer above the plane is W, the end face of the groove formed in the second step, Each step is adjusted so that the distance to the surface is X, the thickness of the corner to be removed in the third step is Y, and the length in the laser emission direction is Z.
By setting = W / (X−Z) = Y / Z, the spread angle of the laser can be set to 30 °. When the angle is set to 30 ° or more, the lengths W and Y may be increased. When the divergence angle is 30 °, as shown in FIG. 4, it corresponds to the half-value width 301 of the light intensity distribution of the far field pattern in the direction perpendicular to the active layer, and is 以上 or more of the light intensity showing the maximum value at 0 °. Light can be extracted, which is the most efficient.

In the present invention, the structure, electrodes, etc. of the nitride semiconductor are not particularly limited, and may have any layer structure and shape.

[0015]

[Example 1] The following layer constitution was formed on a sapphire substrate by MOCVD. An n-type contact layer made of n-type GaN and an n-type A
an n-type confinement layer made of lGaN, a light guide layer made of n-type AlGaN, an active layer made of InGaN,
A wafer is prepared in which a light guide layer made of p-type AlGaN, a light confinement layer made of p-type AlGaN, and a p-type contact layer made of p-type GaN are stacked.

Next, a mask for exposing the n-type layer is formed, and RIE is performed using SiCl ₄ gas and Cl ₂ gas. Next, after removing the mask, a mask having a pattern having a predetermined chip size is applied, and etching is performed by RIE until the sapphire substrate is exposed, thereby forming a groove.

Next, after removing the mask, a p-electrode is formed on the uppermost p-type contact layer, and an n-electrode is formed on the exposed n-type contact layer in a stripe shape parallel to each other. Next, a groove for separating the laser chip is formed on the n-type layer plane exposed by the electrode formation. After forming the groove,
The corner of the n-type layer plane above the groove is cut using a dicer so that the spread angle of the laser is 30 ° or more.

Finally, the substrate was polished to a thickness of 100 μm and scribed to obtain a laser chip. When the laser chip obtained as described above was actually oscillated, a good far-field pattern having a spread angle of 30 ° or more could be obtained. [Example 2] In Example 1, in the step of exposing the n-type layer, a groove is formed so that the distance between the plane of the exposed n-type layer and the end face of the active layer above the plane is 1 μm (W). In the step, the distance between the formed end face of the groove and the resonance surface is 34 μm (X), and in the step of cutting the corner of the n-type layer,
Each step is adjusted so that the thickness of the corner to be removed is 8 μm (Y) and the length in the laser emission direction is 30 μm (Z), and the relationship between these steps is tan15 ° = W / (X−Z) = Y / Z. As a result, the spread angle was 30 °, and a good far-field pattern could be obtained. This divergence angle of 30 ° corresponds to the half width 301 of the light intensity distribution of the far field pattern in the direction perpendicular to the active layer as shown in FIG. The result was the most efficient.

[0019]

According to the present invention, the groove is formed by exposing the substrate after forming the resonance surface, and the corner of the exposed n-type layer plane above the groove is adjusted so that the laser divergence angle is 30 ° or more. By adjusting the depth and cutting, the resonance surface becomes a good smooth surface and the far-field pattern becomes good. In addition, the present invention removes the n-side layer above the cut surface before cutting the substrate to form a groove, so that it is possible to reduce the warpage of the substrate during polishing, thereby facilitating polishing and scribing. it can.

[0020]

[Brief description of the drawings]

[0021]

FIG. 1 is a schematic cross-sectional view of a nitride semiconductor according to an embodiment in a step of a manufacturing method of the present invention.

[0022]

FIG. 2 is a schematic cross-sectional view of a nitride semiconductor according to an embodiment in a step of a manufacturing method of the present invention.

[0023]

FIG. 3 is a schematic cross-sectional view of the nitride semiconductor of one embodiment in a step of the manufacturing method of the present invention, and is an enlarged view of FIG. 2;

[0024]

FIG. 4 is a diagram showing a far field pattern of laser light by the nitride semiconductor laser device of the present invention.

[0025]

[Brief description of reference numerals]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... N-side layer 3 ... Active layer 4 ... P-side layer 301 ... Half width of far field pattern

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-272987 (JP, A) JP-A-7-142763 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 5/00-5/50

Claims (2)

(57) [Claims] 1. A nitride semiconductor wafer having an n-type layer, an active layer, and a p-type layer laminated on a sapphire substrate in order from the p-type layer side to expose a surface of the n-type layer and an etching end face. A first step of forming a resonance surface in
A second step of forming a groove for separating a laser chip on the surface of the n-type layer exposed by the first step by removing the nitride semiconductor until the sapphire substrate is exposed; Removing the corners of the n-type layer plane exposed in the step so that the spread angle of the laser beam becomes 30 ° or more. 2. In the first step, etching is performed up to an n-type layer below the active layer, and a distance between a plane of the exposed n-type layer and a lower end surface of the active layer above the plane is determined. W
When the distance between the groove end face formed in the second step and the resonance surface is X, the thickness of the corner to be removed in the third step is Y, and the length in the laser light emission direction is Z 2. The method for manufacturing a nitride semiconductor laser according to claim 1, wherein each step is performed so as to satisfy a condition of tan15 ° = W / (X−Z) = Y / Z.