JP3659056B2 - Manufacturing method of nitride semiconductor laser device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for manufacturing a laser element made of a nitride semiconductor (In _X Al _Y Ga _1-XY N, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1).
[0002]
[Prior art]
In recent years, blue and blue-green laser diodes made of nitride semiconductors have been put into practical use or become practical. Since this nitride semiconductor device has not yet been developed as a substrate that perfectly matches with the nitride semiconductor, a nitride semiconductor layer is forcibly grown on a different substrate such as sapphire having a different lattice constant. Is formed. Therefore, a very large number of crystal defects are generated in a nitride semiconductor crystal grown on a different substrate such as sapphire.
[0003]
Therefore, at present, a conventional gallium nitride layer having a large number of crystal defects is thinly grown on a different substrate, and a protective film such as SiO ₂ is partially formed on the gallium nitride layer, and halide vapor phase growth is performed on the protective film. A gallium nitride substrate with few crystal defects is obtained by growing gallium nitride again by using the lateral growth of gallium nitride by a vapor phase growth method such as HVPE and metal organic vapor phase epitaxy (MOVPE). Growing up. This method is generally called lateral over growth (LOG) because a nitride semiconductor is grown laterally on the protective film.
[0004]
In the above method, although the performance was improved by using a gallium nitride substrate with fewer crystal defects, sapphire, which is the substrate of the nitride semiconductor element, is very hard and has no cleaving property. In the formation of the laser element, it is difficult to make the cleavage surface of the nitride semiconductor a resonance surface by using the cleavage property of the substrate, and it takes time and labor to form the resonance surface.
[0005]
Therefore, conventionally, a method of polishing the sapphire substrate until it becomes thin or a method of completely removing the sapphire substrate has been used.
[0006]
[Problems to be solved by the invention]
However, in order to completely remove the sapphire substrate, it is necessary to grow the underlying layer made of the nitride semiconductor layered on the sapphire substrate considerably thick, which takes a considerable amount of time and is not a very good method in terms of productivity. . Also, in the method of polishing the sapphire substrate until it becomes thin, if the underlying layer made of a nitride semiconductor is laterally grown, the film thickness is somewhat large. Due to the difference in lattice constant between the nitride semiconductor and the nitride semiconductor, stress is generated and the substrate is warped, and subsequent chip formation by scribe becomes very difficult, and it is difficult to obtain a good resonance surface even after chip formation.
[0007]
Therefore, the object of the present invention is to reduce the occurrence of warping, cracking, and chipping of the wafer when the sapphire substrate is thinned by polishing in the nitride semiconductor laser element having laterally grown gallium nitride, It is an object of the present invention to provide a method of manufacturing a nitride semiconductor laser device that can easily form a wafer into a chip and obtain a resonant surface close to a mirror surface.
[0008]
[Means for Solving the Problems]
Accordingly, the present invention provides a method for manufacturing a nitride semiconductor laser device having an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer on a heterogeneous substrate, and at least laterally grown on the heterogeneous substrate. A base layer made of gallium nitride is grown, and the base layer formed on the heterogeneous substrate is grown by sequentially growing the n-type nitride semiconductor layer, the active layer, and the p-type nitride semiconductor layer on the base layer. A step of forming a semiconductor layer with a thickness of 10 μm or more; a step of forming an n-electrode on the surface of the n-type nitride semiconductor layer; and a p-electrode on the surface of the p-type nitride semiconductor layer; lattice form a part to expose the heterogeneous substrate, a step of the step of etching the electrode parallel to stripes, or the electrode and the vertically striped, the polishing from the back surface of the foreign substrate, nitride and the etching A method of manufacturing a semiconductor laser nitride semiconductor laser device of at least the laser emission side of the resonance surface and comprising a surface and a step of forming by cleavage of the semiconductor layer of the element. As a result, the warpage of the substrate can be alleviated and the wafer can be easily made into chips. Further, the exit surface can be a resonance surface close to a mirror surface.
[0009]
The method further comprises a step of scribing the polished surface of the foreign substrate after polishing the foreign substrate. In addition, the width W of the etching is 20 to 650 μm. The heterogeneous substrate may be selected from the group consisting of sapphire, spinel, SiC (including 6H and 4H), GaAs, Si, and ZnO. In addition, the M plane of gallium nitride becomes a cleavage plane by the cleavage.
[0010]
Furthermore, by forming all of the resonance surfaces by cleaving gallium nitride, it becomes a resonance surface close to a mirror surface, and not only the characteristics as a laser are improved, but also a chip can be obtained effectively and without waste. it can.
[0011]
Further, when cleaving, the total thickness of the semiconductor layer including the n-type nitride semiconductor layer, the active layer, the p-type nitride semiconductor layer, and the heterogeneous substrate is in the range of 140 to 180 μm. By adjusting the thickness of the substrate, good cleaving with reduced occurrence of chipping and the like is achieved. For this reason, since the number of chips destroyed by cleavage can be greatly reduced, the yield is improved.
[0012]
Further, in the present invention, since a part of the nitride semiconductor is etched until the heterogeneous substrate is exposed, when the surface other than the laser emission surface or the resonance surface is cut by scribing, By scribing only the substrate, a chip can be formed without damaging the nitride semiconductor layer.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to FIGS.
[0014]
FIG. 1 is a plan view of a nitride semiconductor wafer showing an embodiment of a manufacturing process of a nitride semiconductor laser device of the present invention. First, as shown by the hatched portion in FIG. 1, an n-type nitride semiconductor, an active layer, and a p-type nitride semiconductor are grown in this order on an underlying layer made of gallium nitride that is laterally grown on a heterogeneous substrate. A portion of the wafer having the p-electrode 22 on the surface and the n-electrode 23 formed on the n-layer surface was etched until the heterogeneous substrate was exposed.
[0015]
The dissimilar substrate is not particularly limited as long as it is a material other than a nitride semiconductor. In addition to sapphire (including A-plane and R-plane), spinel, SiC (including 6H, 4H), GaAs, Si, ZnO Etc. may be used.
[0016]
In the present invention, as shown in FIG. 6, the different substrate may be an off-angle (tilted) substrate on the step. In this case, the resonance surface is formed to be perpendicular to the direction along the step (step difference direction). In the case of a sapphire substrate, if a substrate in which a direction along the step (step direction) is formed perpendicularly to the A surface of sapphire, a nitride semiconductor is stacked on the substrate, and then the resonance surface is cleaved, Further, an element having better characteristics can be obtained.
As a material for the protective film for lateral growth of gallium nitride, a material having a property that the nitride semiconductor does not grow or is difficult to grow on the surface of the protective film is selected. For example, silicon oxide (SiO _x ), silicon nitride ( Oxides such as Si _x N _y ), titanium oxide (TiO _x ) and zirconium oxide (ZrO _x ), nitrides, and multilayer films thereof, and metals having a melting point of 1200 ° C. or higher can be used. These protective film materials can withstand the nitride semiconductor growth temperature of 600 ° C. to 1100 ° C., and the nitride semiconductor does not grow or hardly grow on the surface thereof. In order to form the protective film partially (= selectively), for example, a photomask having a predetermined shape is produced by using a photolithography technique, and the material is formed into a gas phase through the photomask. Thus, a protective film having a predetermined shape can be formed. The shape of the protective film is not particularly limited, and can be formed, for example, in the form of dots, stripes, or a substrate surface, preferably in the form of stripes.
[0017]
When the protective film is formed in a stripe shape, the width of the exposed portion (window) of the protective film is adjusted to 10 μm or less, more preferably 5 μm or less, and most preferably 3 μm or less. When the width is larger than 10 μm, the number of crystal defects grown on the protective film tends to increase. In order to obtain a nitride semiconductor substrate with fewer crystal defects, the ratio W _S / W _W of the width of the window (W _W ) to the width of the protective film (W _S ) should be greater than 1 and 20 or less. Desirably, preferably 10 or less.
[0018]
Etching includes methods such as wet etching and dry etching. Examples of dry etching include reactive ion etching (RIE), reactive ion beam etching (RIBE), and electron cyclotron etching (ECR). Also, the nitride semiconductor can be etched by appropriately selecting an etching gas.
[0019]
The etching width W shown in FIG. 1 is 20 to 650 μm, preferably 50 to 150 μm. If the thickness is smaller than 20 μm, chipping is likely to occur during scribing to damage the nitride semiconductor element. The larger the scribing width, the less the stress caused by the difference in lattice constant between the heterogeneous substrate and the nitride semiconductor substrate, and the less the warpage of the wafer, the easier it becomes to make chips. It gets worse.
[0020]
Next, as shown in FIG. 2, the etched wafer is made into chips. II on the laser emission side is cut by cleavage of gallium nitride, and II-II and III-III are cut by scribing. Preferably, it is performed from I-I, but the order of cleavage by cleavage and scribing may be from either. In the II cleavage method, first, a heterogeneous substrate thinly polished from the back surface is scribed along the cleavage plane of gallium nitride. If it has been cut by scribing to a certain extent, it will naturally break at the cleavage plane of gallium nitride, and a resonant surface close to a mirror surface will be obtained. If it does not break naturally, an external force is applied by braking, and a resonance surface close to a mirror surface can be obtained by similar cleavage.
In the present invention, it is preferable to adjust the thickness of the wafer during the cleavage. Specifically, after etching until a part of the heterogeneous substrate is exposed, the thickness of the heterogeneous substrate is adjusted to a total thickness of 140 to 180 μm between the heterogeneous substrate and the semiconductor layer in which the nitride semiconductor is stacked. It is to be. Specifically, the back surface of the heterogeneous substrate on which the nitride semiconductor layer is not laminated is adjusted by polishing or the like so that the total thickness is in the above range. This is because if it is thicker than 180 μm, the cleaving process is inferior and the scribing process becomes complicated, and the chip tends to be cracked or chipped. If it is thinner than 140 μm, the heterogeneous substrate becomes too thin, and the nitride formed on the heterogeneous substrate. The effect of warping by the semiconductor becomes serious, and the rate of chip breakage during polishing, scribing, and cleavage increases. More preferably, by adjusting the thickness in the range of 150 to 160 μm, it is possible to form a resonant surface by more stable cleavage and improve the yield.
[0021]
At this time, the semiconductor layer including the nitride semiconductor formed on the heterogeneous substrate is formed with a film thickness of at least 10 μm, and specifically, at least 10 μm as a nitride semiconductor substrate for forming an element. It is because it forms to the extent.
[0022]
For example, when the dissimilar substrate is sapphire, for example, when the dissimilar substrate is sapphire, a nitride semiconductor layer such as gallium nitride is laminated on sapphire having a C-plane as a main surface, and after polishing the sapphire substrate, the sapphire substrate Scribing along the A side. Since the cleaved gallium nitride M-plane grows almost in parallel with the sapphire A-plane, when the sapphire substrate is scribed along the A-plane, cleavage occurs at the gallium nitride M-plane. Become.
[0023]
In addition, the reflection surface opposite to the laser emission side is cut by scribing only the heterogeneous substrate from which the nitride semiconductor has been removed by etching as in II-II. Similarly to the above, a method of cutting by gallium nitride cleavage may be used. The resonance surface obtained by the former method of cutting only the dissimilar substrate by scribing is formed at the time of etching performed until the dissimilar substrate is exposed, and this also provides a good resonance surface. If the method of cutting by the latter cleavage of gallium nitride is taken, a resonance surface closer to a mirror surface can be obtained, and the characteristics as a laser can be improved.
[0024]
【Example】
[Example 1]
Examples of the present invention will be described below.
[0025]
FIG. 5 shows a structure obtained by an embodiment of the method for manufacturing a nitride semiconductor laser device of the present invention, and the layers are first laminated in this manner. However, the structure of the element is not limited to this, and a nitride semiconductor laser element can be applied even if the layer configuration, chip shape, and the like are different.
[0026]
Using a MOVPE (metal organic vapor phase epitaxy) method, a buffer layer (not shown) made of GaN (gallium nitride) is grown by 200 angstroms on a heterogeneous substrate 1 made of sapphire having a 2 inch φ, C-plane as a main surface, Further, the base layer 2 made of GaN is grown by 4 μm at different temperatures.
[0027]
After the underlayer 2 is grown, a first protective film 20 made of SiO _{2 having a} stripe width of 10 μm and a stripe interval (window portion) of 2 μm is grown to a thickness of 0.5 μm by a CVD apparatus.
[0028]
After forming the first protective film 20, the GaN substrate 3 is grown to a thickness of 15 μm. The laterally grown GaN substrate 3 is obtained by such a method.
[0029]
Next, on the GaN substrate 3, an n-side contact layer 4 made of GaN or AlGaN, a crack prevention layer 5 made of InGaN (this can be omitted), and a superlattice of AlGaN and Si-doped GaN. n-side cladding layer 6, n-side light guide layer 7 made of GaN, multi-quantum well structure (MQW) active layer 8 made of InGaN, p-side cap layer 9 made of Mg-doped AlGaN, p made of Mg-doped GaN A side light guide layer 10, a p-side cladding layer 11 made of a superlattice of AlGaN and Mg-doped GaN, and a p-side contact layer 12 made of Mg-doped GaN are sequentially laminated.
[0030]
Next, a part of the p-side contact layer is etched to expose the n-side contact layer. Further, the p-side layer is etched to the p-side cladding layer by RIE to form a ridge, and a second protective film 21 such as TiO _{2 having} excellent insulating properties on the ridge and a p-electrode 22, n on each contact layer The electrode 23 is formed.
[0031]
Next, a portion necessary as a laser element is masked, and other portions to be removed are etched by RIE until the sapphire substrate is exposed. The etched portion corresponds to the shaded portion in FIG.
[0032]
After the etching is completed, polishing is performed from the side of the sapphire substrate without the nitride semiconductor. At this time, the total thickness of the sapphire substrate and the semiconductor layer including the nitride semiconductor is 150 μm.
[0033]
Next, the laser emission surface side is cut by cleaving gallium nitride. Scribing is performed from the sapphire substrate side in the direction II in FIG. Once it has been scraped to a certain extent, it will naturally break at the cleavage plane of gallium nitride. If it does not break, then apply an external force by braking to obtain a resonant surface close to the mirror surface by cleavage.
[0034]
Subsequently, scribing in the direction of II-II is cut to form a bar-shaped wafer.
[0035]
Next, the bar-shaped wafer is scribed and cut in the direction of III-III to form chips.
[0036]
The laser chip obtained as described above was placed face-up (with the substrate and heat sink facing each other) on the heat sink, each electrode was wire-bonded, and continuous oscillation was attempted at room temperature. At an output of ² kA / cm ² and 20 mW, continuous oscillation with an oscillation wavelength of 405 nm was confirmed, indicating a lifetime of 1000 hours or longer.
[0037]
[Example 2]
After etching a part of the laser element of Example 1 until the sapphire substrate is exposed as shown in FIG. 1 and forming the electrodes, the direction of the resonance surface is the laser emission surface and the reflection surface, both of which are II. As described above, when a laser device was fabricated in the same manner as in Example 1 except that it was cut by cleavage of gallium nitride, the same result as in Example 1 was obtained.
[0038]
[Example 3]
When a part of the laser element of Example 1 is etched until the sapphire substrate is exposed, the etched portion is formed in a stripe shape as indicated by the hatched portion in FIG. Further, when the chip is formed, the direction of the resonance surface is all cut by cleavage of gallium nitride as in II. Other than that, a laser device was fabricated in the same manner as in Example 1, and the same results as in Example 1 were obtained.
[0039]
As shown in FIG. 3, when etching is performed in stripes parallel to the device electrodes, the warpage of the wafer cannot be reduced as much as when etching is performed as shown in FIG. In addition, both the reflection surface opposite to the laser emission side can be cut by cleaving gallium nitride, a good resonance surface can be obtained, and the portion where the wafer is wasted is reduced, thereby improving the yield.
[0040]
[Example 4]
When a part of the laser device of Example 1 is etched until the sapphire substrate is exposed, the etched portion is formed in a stripe shape as indicated by the hatched portion in FIG. When forming a chip, first, the direction of the resonance surface is cut by cleavage of gallium nitride as in II. Other than that, a laser device was fabricated in the same manner as in Example 1, and the same results as in Example 1 were obtained.
[0041]
When etching is performed in a stripe shape perpendicular to the device electrodes as shown in FIG. 4, the wafer warpage cannot be reduced as much as when etching is performed as shown in FIG. 1, but it becomes a resonance surface. Both the laser emission surface and the reflection surface can be cut by cleavage of gallium nitride, and a good resonance surface can be obtained.
[0042]
[Example 5]
A sapphire substrate having a direction along the step (step direction) perpendicular to the A surface of the sapphire substrate as shown in FIG. Specifically, the off angle θ shown in FIG. 6 is not less than 0.10 ° and not more than 0.20 °, preferably 0.15 °, the step difference (height) is about 1 atomic layer, and the terrace width W is about 40. A sapphire substrate having angstrom steps is used.
[0043]
Except that a stripe-shaped first protective film 20 made of SiO ₂ after growth of the underlayer 2 is formed on the sapphire substrate perpendicularly to the direction along the step (step direction), the same as in Example 1. When a laser element was manufactured by laminating, a result almost the same as or better than that of Example 1 was obtained.
[0044]
【The invention's effect】
As described above, the present invention provides a method for manufacturing a nitride semiconductor laser device having gallium nitride laterally grown on a different substrate and growing a nitride semiconductor layer on the gallium nitride, and a part of the nitride semiconductor layer. Is etched until the heterogeneous substrate is exposed, so that the warpage of the substrate can be alleviated and the wafer can be easily formed into chips.
[0045]
Further, by forming at least the laser emission side of the etched nitride semiconductor laser element as a resonance surface by cleavage of gallium nitride, the laser emission surface can be made a resonance surface close to a mirror surface.
[Brief description of the drawings]
FIG. 1 is a plan view of a nitride semiconductor wafer showing an embodiment of a manufacturing process of a nitride semiconductor laser device of the present invention.
FIG. 2 is a plan view of a nitride semiconductor wafer showing an embodiment of a manufacturing process of the nitride semiconductor laser device of the present invention.
FIG. 3 is a plan view of a nitride semiconductor wafer showing an embodiment of another manufacturing process of the nitride semiconductor laser device of the present invention.
FIG. 4 is a plan view of a nitride semiconductor wafer showing an embodiment of another manufacturing process of the nitride semiconductor laser device of the present invention.
FIG. 5 is a schematic cross-sectional view showing an embodiment of a nitride semiconductor laser device obtained by the method for manufacturing a nitride semiconductor laser device of the present invention.
FIG. 6 is a schematic cross-sectional view showing an enlarged part of a substrate used in another manufacturing process of the nitride semiconductor laser device of the present invention.
[Brief description of symbols]
DESCRIPTION OF SYMBOLS 1 ... Dissimilar substrate 2 ... GaN base layer 2 ... GaN substrate 3 ... N side contact layer 4 ... Crack prevention layer 5 ... N side clad layer 6 ... N side light guide Layer 7 ... Active layer 8 ... p-side cap layer 9 ... p-side light guide layer 10 ... p-side cladding layer 11 ... p-side contact layer 20 ... first protective film 21 ... Second protective film 22 ... p electrode 23 ... n electrode

Claims (6)

In a method of manufacturing a nitride semiconductor laser device having an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer on a different substrate,
A base layer made of at least laterally grown gallium nitride is grown on the heterogeneous substrate, and the n-type nitride semiconductor layer, the active layer, and the p-type nitride semiconductor layer are grown on the heterogeneous substrate in this order to form the base layer on the heterogeneous substrate. A step of setting the thickness of the semiconductor layer including the base layer to be formed to 10 μm or more;
Forming an n-electrode on the n-type nitride semiconductor layer surface and a p-electrode on the p-type nitride semiconductor layer surface;
Etching a portion of the nitride semiconductor layer in a lattice shape until a heterogeneous substrate is exposed, a stripe shape parallel to the electrode, or a stripe shape perpendicular to the electrode ;
Polishing from the back surface of the heterogeneous substrate;
And a step of forming at least a laser emission side of the etched surface of the nitride semiconductor laser element by cleaving the semiconductor layer.   2. The method of manufacturing a nitride semiconductor laser device according to claim 1, further comprising a step of scribing a polished surface of the different substrate after polishing the different substrate.   The heterogeneous substrate has a first main surface and a second main surface, and includes the n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer on the first main surface. A semiconductor layer is formed, and at the time of the cleavage, the thickness of the heterogeneous substrate is adjusted so that the sum of the thickness of the heterogeneous substrate and the thickness of the semiconductor layer is in a range of 140 to 180 μm. The method for manufacturing a nitride semiconductor laser device according to claim 1, wherein:   2. The method of manufacturing a nitride semiconductor laser device according to claim 1, wherein a width W of the etching is 20 to 650 [mu] m.   2. The method of manufacturing a nitride semiconductor laser device according to claim 1, wherein the different substrate is selected from the group consisting of sapphire, spinel, SiC (including 6H and 4H), GaAs, Si, and ZnO.   2. The method for manufacturing a nitride semiconductor laser device according to claim 1, wherein the M-plane of gallium nitride becomes a cleavage plane by the cleavage.

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