JP3216118B2 - Nitride semiconductor device and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an LED (light emitting diode).
Light-emitting elements such as laser diodes (LDs)
Or nitrogen used in light-receiving elements such as solar cells and optical sensors.
Compound semiconductor (In _XAl_YGa_1-XYN, 0 ≦ X, 0 ≦ Y, X
+ Y ≦ 1) and a method for manufacturing the same, particularly
The present invention relates to a nitride semiconductor device having good heat dissipation and a method for manufacturing the same.
I do.

[0002]

2. Description of the Related Art Nitride semiconductors have just recently been put to practical use in full-color LED displays, traffic signals and the like as materials for high-brightness blue LEDs and pure green LEDs. These LEDs have, for example, an n-type nitride semiconductor layer and a p-type nitride semiconductor layer on an insulating substrate made of sapphire, and a single quantum well made of InGaN between the p and n semiconductor layers. It has a double hetero structure in which an active layer of a well structure (SQW: Single-Quantum-Well) is sandwiched. Wavelengths such as blue and green are determined by increasing or decreasing the In composition ratio of the InGaN active layer. Applicants have also recently used this material in pulsed currents at room temperature at 410 ° C.
nm laser oscillation (for example, Jpn.J.Appl.Phy
s.Vol.35 (1996) pp.L217-L220, Appl.Phys.Lett.69 (1
0), 2 Sep. 1996 pp. 1477-1479). Similarly, this laser element also has a double heterostructure in which an active layer having a multi-quantum well (MQW) containing InGaN is sandwiched between p and n semiconductor layers.

Since the characteristics and reliability of a semiconductor element are significantly affected by heat, a semiconductor laser diode (LD) or a light emitting diode (LE) using the semiconductor element is used.
It is very important in practical use to dissipate Joule heat due to a high current density for driving D) and the like, and if the heat is satisfactorily dissipated, the element life will be prolonged. Heat dissipation is LED first
In Japanese Patent Application Laid-Open No. H11-229, the device is mounted on a lead frame made of a metal material having good thermal conductivity to radiate heat. On the other hand, LD
Since high power is loaded compared to the LED, the amount of heat generation is orders of magnitude larger, and in the same method as the LED, the element is rapidly deteriorated by heat. Therefore, the heat dissipation in the LD is mounted on a material having good thermal conductivity such as a diamond heat sink to dissipate the heat.

There are two methods of mounting a nitride semiconductor device such as an LED or an LD on a support such as a heat sink, a submount, a metal post, and a lead frame: face-down and face-up. In face-down, the nitride semiconductor side and the support are mounted so as to face each other, and in face-up, the insulating substrate and the support are mounted so as to face each other. When the nitride semiconductor or the insulating substrate comes into contact with the support, heat is conducted to the support and dissipated. In this case, if the contact is good, the heat dissipation is improved. Further, not only when the insulating substrate is in contact with the support but also when it is not, the heat generated in the nitride semiconductor is dissipated to the outside via the nitride semiconductor and the substrate. That is, when the nitride semiconductor and the insulating substrate are in direct contact with the support, heat is conducted to the support, and when the substrate is not in contact with the support, the surface of each of the nitride semiconductor and the insulating substrate is Dissipates heat from outside.

The nitride semiconductor substrate that dissipates heat in this way is an insulating substrate made of sapphire, spinel, or the like. Therefore, the heat dissipation of the insulating substrate is not so good as compared with the conductive substrate. In order to correct this and efficiently dissipate heat to the outside, it is conceivable to make the substrate thinner or remove the substrate.

[0006]

However, in the process of thinning the substrate, in the process of fabricating the semiconductor laser device, when the substrate is thinned by polishing or the like, the wafer warps due to the lattice constant difference between the nitride semiconductor layer and the substrate. If the thickness of the substrate is thinner than 80 μm due to warpage, the wafer is easily broken. For example, JP-A-5-343742 discloses a method for manufacturing a gallium nitride-based compound semiconductor chip in which a part of a p-type layer is etched to an n-type layer and then the n-type layer is etched or diced to a sapphire substrate. However, this technique is intended to prevent the occurrence of cracks at the cut surface, interface, and chipping when the wafer of the sapphire substrate is cut into chips, and the technique disclosed in this publication reduces the thickness of the substrate to 80 μm. When the thickness is smaller, the wafer tends to be warped. When the wafer is warped by thinning the substrate in this way, when die bonding is performed face up and face down, the insulating substrate and the nitride semiconductor cannot be in good contact with a support such as a heat sink, and heat dissipation is poor. As a result, the threshold value increases, and as a result, the life characteristics deteriorate. Further, since the wafer is broken by the warpage of the substrate, it is not possible to make the substrate thinner and to improve the heat radiation effect.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a thinned substrate without warpage, which prevents warpage that occurs when the substrate of a nitride semiconductor wafer is thinned and cracks at irregular positions of the wafer due to the warpage. It is an object of the present invention to provide a nitride semiconductor device which has good heat dissipation, suppresses a rise in threshold value, and has good life characteristics by manufacturing, and a method for manufacturing the same.

[0008]

That is, the object of the present invention is to
This can be achieved by the following configurations (1) to (4). (1) A nitride semiconductor comprising a buffer layer having a thickness of at least 0.5 μm and a nitride semiconductor layer having a total thickness of at least 6 μm on an insulating substrate having a thickness of 60 μm or less. Characterized in that a part of the nitride semiconductor element is removed to an insulating substrate. (2) Among the plurality of nitride semiconductor layers having a total film thickness of 6 μm or more, a nitride semiconductor layer containing no n-type impurity and a nitride semiconductor layer containing n-type impurity above the buffer layer Are grown with a total thickness of 6 μm or more. (3) In the method for manufacturing a nitride semiconductor device, a nitride semiconductor having a plurality of nitride semiconductor layers having a total thickness of 6 μm or more is provided on an insulating substrate via a buffer layer having a thickness of 0.5 μm or less. Growing, removing a part of the grown nitride semiconductor to the insulating substrate, and adjusting the thickness of the insulating substrate of the wafer to 60 μm or less after removing a part of the nitride semiconductor to the insulating substrate. The process of
Separating the wafer into chips after adjusting the thickness of the substrate. (4) Of the plurality of nitride semiconductor layers having a total film thickness of 6 μm or more, a nitride semiconductor layer containing no n-type impurity and a nitride semiconductor layer containing n-type impurity above the buffer layer Are grown to a total thickness of 6 μm or more.

Further, an object of the present invention is to provide the following constitutions (5) to (5).
This can be achieved by another preferable mode of (9). (5) The method of manufacturing a nitride semiconductor device according to (3) or (4), wherein the step of separating into chips is a step of scribing a surface of an insulating substrate and then breaking a wafer. Method. (6) The method for manufacturing a nitride semiconductor device according to (5), wherein the breaking is a step of forming a resonance surface of the laser device. (7) The resonance surface is made of a nitride semiconductor.

[0010]

[Outside 1]

(6) The method of manufacturing a nitride semiconductor device according to the item (6), wherein (8) The method according to any one of (1) to (7), wherein the first layer grown in contact with the buffer layer is a nitride semiconductor layer having a thickness of 6 μm or more and containing no impurities. And a method for manufacturing the same. (9) The method according to (1) to (1), wherein after removing a part of the nitride semiconductor to an insulating substrate, an insulating protective film is formed on an end face of the nitride semiconductor and the insulating substrate.
The nitride semiconductor device according to any one of (8) and a method for manufacturing the same.

That is, in the present invention, an n-type impurity containing no impurities (undoped) is contained on an insulating substrate via a thin buffer layer having a thickness of 0.5 μm or less (n-type impurity). And / or a nitride semiconductor layer having a layer structure of a thick film having a total film thickness of 6 μm or more including a plurality of layers such as a (p-type) nitride semiconductor layer containing a p-type impurity. Adjusting the stress caused by the difference between the lattice constant of the nitride semiconductor and the lattice constant of the insulating substrate, and removing a part of the nitride semiconductor on the wafer substrate to the insulating substrate; The stress of the nitride semiconductor continuous on the wafer is divided into individual chips on the wafer. As a result, even if the substrate is thinned, warpage due to the stress of the nitride semiconductor can be prevented, and a very good nitride free of warpage can be prevented. A semiconductor can be obtained.

In the process of thinning a sapphire substrate to which stress is applied, a wafer that is initially substantially horizontal begins to warp due to stress, and the warpage increases, causing the nitride semiconductor to crack at irregular positions. . Therefore, it is difficult to reduce the thickness of the substrate. On the other hand, as a result of various studies, the inventors of the present invention have found that, in the case of a conventionally known nitride semiconductor device and a device, when an insulating substrate of a wafer is polished and thinned, an n-type nitride semiconductor layer is formed on the insulating substrate. Since each chip before being separated above is continuous through the nitride semiconductor, since the stress of the nitride semiconductor exceeds the stress of the insulating substrate as the substrate becomes thinner, warpage may occur. I thought it might be.

Therefore, the present inventors, after laminating a thin buffer layer on a substrate, undoped nitride semiconductor layer (undoped layer), n-type nitride semiconductor layer (n-type layer) and / or p-type nitride semiconductor Before growing a plurality of nitride semiconductor layers including layers (p-type layers) and polishing and thinning the substrate, the nitride semiconductor layer is continuous on the wafer substrate etched to form electrodes. By removing a nitride semiconductor layer (for example, an undoped layer and / or an n-type layer) up to the substrate and making it discontinuous for each wafer chip, stress adjustment and correction are performed to suppress wafer warpage. . As a result, the substrate can be thinned properly without warping the wafer in the process of thinning the substrate, the warpage of the chip after separation is also prevented, and the obtained nitride semiconductor element is suitable for a support such as a heat sink. The heat radiation from the thinned insulating substrate is also improved, and the heat radiation from the thinned insulating substrate is also improved.

Further, in the present invention, the layer grown first in contact with the buffer layer is a nitride semiconductor layer comprising an undoped layer and an n-type layer having a thickness of 6 μm or more, so that warpage can be prevented more favorably. be able to. Furthermore,
In the present invention, when an insulating protective film is formed on the insulating substrate on which a part of the nitride semiconductor is removed and exposed, and on the end face of the nitride semiconductor, an effect of preventing a short circuit at the time of face-down direct bonding is achieved. In addition, it tends to contribute to the effect of preventing the warpage of the wafer together with the above configuration, which is preferable for achieving the object of the present invention.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Insulating substrates used in the present invention include, for example, sapphire having a C-plane as a main surface, R-plane, and A-plane.
Sapphire whose surface is the main surface, spinel (MgA
It is possible to use a conventionally proposed insulating substrate which has a different coefficient of thermal expansion from a nitride semiconductor such as l ₂ O ₄ ) and can grow a nitride semiconductor. When an insulating substrate is used in this manner, the element can be mounted face-up, and heat is directly transmitted to a support such as a heat sink through the substrate, so that the nitride semiconductor layer and the support directly contact each other. On the other hand, when performed in a face-up state, the effect of reducing the thickness of the substrate is remarkably exhibited. Also, in the face-down mode, the thickness of the substrate can be reduced by the configuration of the present invention, so that the heat dissipation from the substrate is improved.

The buffer layer has an effect of alleviating lattice mismatch between the substrate and the nitride semiconductor.
A nitride semiconductor such as 1N or InGaN is formed in a thickness of 10 Å or more and 0.5 μm or less, more preferably 0.2 μm or less.
m, most preferably 0.1 μm or less. Specifically, for example, Al _x Ga ₁ -XN (0 ≦ X
When the buffer layer of <1) is grown, the crystallinity of the nitride semiconductor becomes very good. If the thickness of the buffer layer is larger than 0.5 μm, the crystallinity of the nitride semiconductor layer to be grown next will be deteriorated, and the total thickness of the plurality of nitride semiconductors will be reduced.
Also, it tends to be difficult to grow the nitride semiconductor layer formed first on the buffer layer to a thickness of 6 μm or more. If the thickness of the buffer layer is smaller than 10 angstroms, the effect of the buffer layer is lost and the crystal surface becomes uneven.

The total thickness of a plurality of nitride semiconductor layers such as an undoped layer, an n-type layer and / or a p-type layer on the buffer layer is 6
The thickness may be at least 8 μm, preferably at least 8 μm, particularly preferably at least 10 μm, and preferably at most 100 μm. If the total film thickness is less than 6 μm,
It is difficult to reduce the thickness to 0 μm or less, and if the total film thickness exceeds 100 μm, heat radiation deteriorates, which is not preferable. The undoped layer grown on the buffer layer of the present invention, the nitride semiconductor layer comprising an n-type layer and / or a p-type layer can have various lamination orders and various layer configurations,
The layer configuration and the like are not particularly limited. For example, n-type contact layer, n-type clad layer, guide layer, active layer, guide layer, p
It is possible to adopt a layer configuration formed by combining layers such as a mold cladding layer and a p-type contact layer.

In the present invention, the lamination of the nitride semiconductor layers having a total thickness of 6 μm or more is performed by adjusting the thickness of each layer. Preferably, the thickness of the undoped layer and / or the n-type layer is adjusted. More preferably, after adjusting the film thickness of the undoped layer, the film thickness of the n-type layer is adjusted so that the total film thickness is 6 μm or more.
Since the undoped layer has good crystallinity, after growing the undoped layer, an n-type impurity such as Si or Ge
Growing a nitride semiconductor layer doped with
It is easy to adjust to μm or more. Further, it is preferable to grow a nitride semiconductor layer doped with a p-type impurity on these layers, since a p-type layer can be formed well. Here, it is considered that the p-type cannot be obtained unless the hydrogen contained in the nitride semiconductor layer is separated from the p-type impurity by annealing and partially removed from the semiconductor layer. Therefore, when a nitride semiconductor layer containing a p-type impurity is grown as a thick film, the hydrogen contained therein is less likely to be separated from the nitride semiconductor, and it is difficult to obtain a p-type. For this reason, it is desirable to grow the undoped layer and / or the n-type layer thickly in order to grow the nitride semiconductor as a thick film.

Each of the above nitride semiconductor layers is formed by adjusting the film thickness or the like by an organic vapor deposition method or the like. In the present invention, the n-type layer or the p-type layer refers to n-type layer or n-type layer in the nitride semiconductor layer.
2 shows a layer containing a p-type impurity (n-type dopant) or a p-type impurity (p-type dopant). An undoped layer indicates a layer containing no impurity, and an undoped nitride semiconductor layer may exhibit n-type in some cases.

Further, in the present invention, the nitride semiconductor layer having a thickness of 6 μm or more which is first formed on the buffer layer is
An undoped layer, or an n-type layer doped with Si or Ge,
Or a combination of these, preferably a combination of an undoped layer and an n-type layer. When the undoped layer is grown first, the crystallinity is improved. The thickness of the layer formed first is preferably 6 μm or more, more preferably 7 μm or more and 100 μm or less. When the thickness of the first layer formed on the buffer layer is 6 μm or more, the total thickness of the nitride semiconductor is adjusted to be larger than 6 μm. The composition of the undoped layer and the n-type layer formed first on the buffer layer is preferably such that Al _x Ga ₁ -xN (0 ≦ X <1) is grown, and most preferably, the Al composition ratio (X value ) Grows AlGaN or GaN with 0.5 or less. If the Al composition ratio exceeds 0.5, cracks tend to occur in the nitride semiconductor layer itself, and it tends to be difficult to grow the nitride semiconductor layer to a thickness of 6 μm or more. Further, the nitride semiconductor layer has a property of being n-type even in an undoped state, but the n-type layer formed first on the buffer layer is made of Si, Ge, Sn, S, etc. during the growth of this layer. It is very preferable to form an n-type contact layer for forming an n-electrode by doping with an n-type dopant. When doping with an n-type dopant such as Si, Ge, Sn, or S, the concentration of the n-type dopant is 1 × 10 ¹⁶ cm 1 to 1 × 10 ²¹ cm ³ , preferably 1 × 10 ¹⁶ cm ^3.
× 10 ¹⁷ cm ³ to 1 × 10 ²⁰ cm ³ , more preferably 1 × 10
It is 10 ¹⁸ cm ³ to 1 × 10 ¹⁹ cm ³ .

When the thickness of the undoped layer or the n-type layer on the buffer layer is 6 μm or more, the substrate is
It is more effective to reduce the thickness to less than m. Although the upper limit is not particularly limited, an undoped layer and an n-type layer having good crystallinity can be usually obtained by growing the film to a thickness of 100 μm or less. If it is grown to a thickness of more than 100 μm, the heat dissipation will be poor. During the growth of the undoped layer and the n-type layer,
Although a nitride semiconductor layer containing an n-type impurity having another composition may be interposed therebetween, it is most preferable to grow the same composition continuously and with a film thickness of 6 μm or more. However, even if an undoped layer or an n-type layer first grown on the buffer layer has a nitride semiconductor layer having another composition different from these or a different impurity-containing nitride semiconductor layer,
Included within the scope of the present invention.

Next, on the undoped layer or n-type layer formed first on the buffer layer, an undoped layer, n
A mold layer and / or a p-type layer is formed. As these layers, various layer configurations can be appropriately selected depending on the configuration of the nitride semiconductor element, and layers having the compositions shown in the undoped layer and the n-type layer can also be used. For example, when an n-type nitride semiconductor layer formed first on a buffer layer is used as a contact layer, an active layer made of InGaN directly, a p-type clad layer made of a p-type nitride semiconductor, a p-type contact layer A wafer may be manufactured by stacking the above elements to form an LED element, or an n-type clad layer, a guide layer, an active layer, a guide layer, a p-type clad layer, a p-type contact layer, and the like may be stacked. A wafer that becomes a laser element may be manufactured. In the present invention, the buffer layer grown on the substrate may be omitted depending on the growth method and the growth apparatus.

In addition, the undoped layer and / or the n-type layer formed first on the buffer layer is 90% or more of the total thickness of the nitride semiconductor layer including a plurality of n-type layers and p-type layers. Is preferable because a nitride semiconductor layer having good crystallinity can be grown. In this case, the n-type layer and p
The total thickness of the nitride semiconductor layer composed of the mold layer and the like is such that the thickness of the undoped layer and / or the n-type layer first grown on the buffer layer is 6 μm or more and the total thickness of the nitride semiconductor layer is Preferably, it is adjusted to be 90% or more.

A total film thickness of 6 μm having the above-mentioned layer structure
Part of the nitride semiconductor is removed up to the insulating substrate before the insulating substrate is thinned. As a method of removing, after forming a ridge, forming a ridge, forming a protective film on the exposed plane of the p-type layer other than the portion to be removed on the uppermost p-type layer, as shown in FIG. Alternatively, the undoped layer is etched to remove a part of the p-type layer. The protective film is provided to prevent the p-type layer from being eroded by etching and to perform pattern etching. After forming SiO ₂ by a plasma CVD method, the protective film is patterned with a photoresist to etch the SiO _2. , An SiO ₂ mask pattern is formed. Then, the p-type layer provided with the protective film is etched to an undoped layer or an n-type layer. The etching method may be either dry or wet. After completion of the etching, the protective film is removed with an acid.

Next, the undoped layer and / or the n-type layer exposed by removing a part of the p-type layer are removed up to the insulating substrate (for example, a sapphire substrate). As a removing method, for example, as shown in FIG. 1, leaving a space for providing an n-type electrode on the surface of the n-type contact layer 3,
The n-type contact layer 3 and the buffer layer 2 are etched or diced to the sapphire substrate 1. In order to minimize stress on the interface between the nitride semiconductor layer and the sapphire substrate 1, etching is preferable. In the case of etching, as described above, it is necessary to form a protective film on a portion other than the etching surface (the electrode forming portions of the p-type layer and the n-type layer).

As described above, the nitride semiconductor layer is laminated on the insulating substrate, the ridge is formed by pattern etching on the p-type layer, and a part of the p-type layer is removed to the undoped layer or the n-type layer. Further, after a part of the undoped layer or the n-type layer is removed to the insulating substrate, the thickness of the insulating substrate of the wafer is adjusted to 60 μm or less, more preferably 50 μm or less. If it is thicker than 60 μm, the heat dissipation is not sufficient,
For example, when a laser device is manufactured, under continuous oscillation,
The element fails within one hour. Although the lower limit varies depending on the thickness of the nitride semiconductor layer to be grown first,
m or more. The thickness of the insulating substrate is 10μ
When the thickness is smaller than m, the physical chip strength at the time of die bonding or wire bonding is not preferable. In order to adjust the thickness of the insulating substrate, there are methods such as polishing and etching. Polishing is performed by lapping using an abrasive as is well known. After lapping, polishing may be performed to make the polished surface mirror-like. As the etching, there are a wet etching method and a dry etching method, and any of them may be used. In wet etching, for example, there is a method using a mixed acid of phosphoric acid and sulfuric acid. The dry etching includes, for example, reactive ion etching (RIE), reactive ion beam etching (RIBE), and electron cyclotron etching (EC).
R), ion beam etching, etc., and any of them can be etched by appropriately selecting an etching gas according to the material of the insulating substrate.

Next, after the thickness of the insulating substrate is reduced to 60 μm or less, the wafer is separated into chips. For example, scribing and dicing can be used to separate the chips into chips. Preferably, the substrate is broken by scribing to separate chips. Moreover, by scribing the substrate surface on which the nitride semiconductor is not grown, chips can be separated at accurate positions. On the other hand, in dicing, cracks tend to be formed in the cut surface, and when a laser element is manufactured, it is difficult to obtain a smooth surface that becomes a resonance surface by dicing.

Further, in the present invention, when manufacturing a laser device, if the substrate is thinned and the substrate side is scribed and broken, a resonance surface of the laser device can be formed on the broken surface. Many insulating substrates on which nitride semiconductors can be grown have no cleavage properties, such as sapphire. However, even with a nitride semiconductor grown on a non-cleavable substrate, the nitride semiconductor is cleaved depending on the plane orientation of the grown nitride semiconductor by making the substrate as thin as possible, and the cleavage plane is It can be a resonance surface.

Further, the cleavage plane is desirably the M plane of the nitride semiconductor layer. When the nitride semiconductor is approximated by a hexagonal columnar hexagonal system, the M-plane is a quadrangular plane corresponding to the side surface thereof, and can be represented by six types of plane orientations. (Hatched portions in FIG. 2) indicate all plane orientations. When cleaved on the M-plane of the nitride semiconductor, a very good yield and a cleaved surface close to a mirror surface can be obtained. FIG. 2 shows the plane orientation of the M plane.

[0031]

FIG. 1 is a schematic sectional view of a laser device according to one embodiment of the present invention, and the manufacturing method of the present invention will be described in detail with reference to this drawing. The general formula In _x Al _Y Ga _{1 -XY} N (0 ≦ X, 0 ≦ Y, X + Y ≦
1) It simply indicates the composition of the nitride semiconductor, and even if different layers are represented by the same general formula, X
Values, Y values, etc. do not indicate the same value.

[Example 1] 1) Sapphire (C surface) having a thickness of 300 μm and 2 inches φ
2) 200 angstrom buffer layer 2 made of GaN 3) contact layer 3 made of Si-doped n-type GaN 6
μm 4) 500 angstrom of crack preventing layer 4 made of Si-doped n-type In0.1Ga0.9N 5) 0.5 μm 6) of n-type cladding layer 5 made of Si-doped n-type Al0.2Ga0.8N 6) made of Si-doped GaN 0.2 μm of light guide layer 6
m 7) 25 well layers of undoped In0.2Ga0.8N
The active layer 7 (total thickness of the active layer: 250 Å) in which barrier layers made of undoped In0.01Ga0.95N are stacked in three pairs of 50 Å and finally a well layer is stacked.
8) 300 .ANG. Of p-type cap layer 8 made of Mg-doped p-type Al0.1 Ga0.9 N, and 9) 0.2 .mu.m of optical guide layer 9 made of Mg-doped GaN.
m 10) A p-type cladding layer 10 made of Mg-doped p-type Al0.2Ga0.8N is deposited to a thickness of 0.5 μm. (Total thickness of nitride semiconductor layer 7.7
25 μm, including buffer layer)

1) As described above, in addition to the sapphire C plane, sapphire having an R plane or an A plane as a main surface, or an insulating substrate such as spinel (MgA1 ₂ O ₄ ) is used as the substrate 1. Can be.

2) The buffer layer 2 is also made of Al as described above.
N, GaN, AlGaN or the like can be grown at a temperature of 900 ° C. or less, and can be grown with a film thickness of 10 Å to 0.5 μm or less, more preferably 20 Å to 0.2 μm or less.

3) The n-type contact layer 3 corresponds to an n-type nitride semiconductor layer grown next to the buffer layer. This n-type contact layer is composed of In _x Al _Y Ga _{1 -XYN} (0 ≦ X, 0
.Ltoreq.Y, X + Y.ltoreq.1), more preferably, AlYGa1-YN having a Y value of 0.5 or less. Above all, by using GaN doped with Si or Ge, an n-type having a high carrier concentration can be obtained. A layer is obtained and a favorable ohmic contact with the n-electrode is obtained. This layer is grown to a thickness of 6 μm or more as described above, more preferably 7 μm.
It is desirable that the film be grown to a thickness of, for example, 20 μm or less.

4) By growing the crack preventing layer 4 from an n-type nitride semiconductor containing In, preferably InGaN, an n-type clad layer containing Al to be grown next can be grown as a thick film. , Very preferred.
In the case of LD, it is necessary to grow a layer to be a light confinement layer, preferably with a thickness of 0.1 μm or more. Conventionally, a thick AlGaN layer is directly formed on a GaN or AlGaN layer.
Was grown, cracks were formed in AlGaN grown later, making it difficult to fabricate the device. However, this crack prevention layer prevents cracks from entering into the n-type clad layer containing Al to be grown next. be able to. The crack prevention layer is preferably grown to a thickness of 100 Å or more and 0.5 μm or less. When the thickness is less than 100 Å, it is difficult to function as a crack prevention as described above, and when the thickness is more than 0.5 μm, the crystal itself tends to turn black. In addition, this crack prevention layer is formed by a growth method,
Depending on the conditions of the growth apparatus and the like, it can be omitted, but L
When producing D, it is desirable to grow it. This crack preventing layer may be grown in the n-type contact layer.

5) The n-type cladding layer 5 functions as a carrier confinement layer and a light confinement layer, and it is desirable to grow a nitride semiconductor containing Al, preferably AlGaN, and more than 100 Å and less than 2 μm, more preferably By growing the layer with a thickness of 500 Å or more and 1 μm or less, a carrier confinement layer having good crystallinity can be formed.

6) The light guide layer 6 functions as a light guide layer of an active layer, and is preferably used to grow GaN or InGaN, and is usually grown to a thickness of 100 Å to 5 μm, more preferably 200 Å to 1 μm. It is desirable. In the first embodiment, Si is doped, but the light guide layer may be undoped.

7) The active layer 7 includes a well layer made of a nitride semiconductor containing In and having a thickness of 70 Å or less, and a barrier layer made of a nitride semiconductor having a larger band gap energy than the well layer having a thickness of 150 Å or less. , A laser is likely to oscillate.

8) The cap layer 8 is doped with a p-type impurity. However, since the cap layer 8 is thin, the cap layer 8 may be an i-type doped with an n-type impurity and compensated for carriers.
Type or undoped. The thickness of the cap layer is 0.1μ
m, more preferably not more than 500 angstroms, most preferably not more than 300 angstroms. This is because if the layer is grown with a thickness greater than 0.1 μm, cracks are easily formed in the cap layer, and it is difficult to grow a nitride semiconductor layer having good crystallinity. In addition, carriers cannot pass through the energy barrier due to the tunnel effect. When the composition ratio of Al is larger and the thickness of AlGaN is smaller, the LD element is more likely to oscillate. For example, if the Y value is 0.
In the case of two or more Al _Y Ga ₁ -YN, it is desirable to adjust the thickness to 500 Å or less. Although the lower limit of the film thickness of the cap layer 8 is not particularly limited, it is desirable to form the cap layer 8 with a film thickness of 10 Å or more.

9) The light guide layer 9 is preferably made of GaN or InGaN as in the case of the light guide layer 6). This layer also functions as a buffer layer when growing the p-type cladding layer, and is preferably 100 Å to 5 μm, more preferably 200 Å to 5 Å.
By growing with a film thickness of 1 μm, it functions as a preferable light guide layer. This light guide layer may be undoped.

10) Like the n-type cladding layer, the p-type cladding layer 10 functions as a carrier confinement layer and a light confinement layer, and is a nitride semiconductor containing Al, preferably A
It is desirable to grow lGaN, and it is possible to form a carrier confinement layer with good crystallinity by growing it at 100 Å or more and 2 μm or less, more preferably 500 Å or more and 1 μm or less. Further, as described above, it is preferable to form this layer as a nitride semiconductor layer containing Al because a contact resistance difference between the p-type contact layer and the p-electrode can be generated.

In the case of an active layer having a quantum structure having a well layer made of InGaN as in this embodiment, a p-type cap layer containing Al having a thickness of 0.1 μm or less is provided in contact with the active layer. A light guide layer having a smaller gap energy than the p-type cap layer is provided at a position farther from the active layer than the mold cap layer, and a band is provided at a position farther from the active layer than the light guide layer and the band is smaller than the light guide layer. It is very preferable to provide a p-type cladding layer made of a nitride semiconductor containing Al having a large gap. In addition, since the thickness of the p-type cap layer is set to be as thin as 0.1 μm or less, it does not act as a carrier barrier, and holes injected from the p-layer pass through the p-type cap layer by a tunnel effect. And recombine efficiently in the active layer,
The output of D is improved. That is, the injected carrier is
Since the band gap energy of the p-type cap layer is large, even if the temperature of the semiconductor element rises or the injected current density increases, carriers do not overflow the active layer and are blocked by the p-type cap layer. Carriers are stored in the active layer, and light can be emitted efficiently. Therefore, even if the temperature of the semiconductor element rises, the luminous efficiency is hardly reduced, so that an LD with a low threshold current can be realized.

11) The p-type contact layer 11 is made of p-type I
n _X Al _Y Ga _{1 -XYN} (0 ≦ X, 0 ≦ Y, X + Y ≦ 1), preferably GaN doped with Mg
Then, the most preferable ohmic contact with the p electrode 20 can be obtained.

After the nitride semiconductor layer including the active layer 7 is laminated on the substrate 1 with the above configuration, the wafer is annealed in a nitrogen atmosphere in a reaction vessel to reduce the amount of hydrogen contained in the p-type layer. The portion is removed to further reduce the resistance of the p-type layer.

Next, a mask having a predetermined shape is formed on the surface of the uppermost p-type contact layer, and the uppermost p-type contact layer 11 is formed by an RIE (reactive ion etching) apparatus as shown in FIG. And the p-type cladding layer 10 are mesa-etched to form a ridge shape having a stripe width of 4 μm.

After the formation of the ridge, a mask is formed on the exposed plane of the p-type layer, and the plane of the n-type contact layer 3 is exposed symmetrically with respect to the stripe-shaped ridge as shown in FIG. . As described above, the n-electrode 22 should be formed.
By providing the mold contact layer 3 symmetrically with respect to the ridge stripe, the current from the n-layer also uniformly affects the active layer, and the threshold value decreases.

After exposing the plane of the n-type contact layer 3, the n-type contact layer 3 and the buffer layer 2 are further etched to the sapphire substrate, leaving a space for providing the n-type electrode 22 on the surface of the n-type contact layer 3. I do. By doing so, the n-type layer is divided on a wafer basis for each chip, so that the stress of the n-type layer can be corrected, and the wafer is prevented from warping in the step of thinning the substrate.

Next, the p-type contact layer 1 at the top of the ridge
First, an ohmic p-electrode 20 made of Ni and Au is formed on almost the entire surface. On the other hand, an ohmic n-electrode 22 made of Ti and Al is formed on almost the entire surface of the striped n-type contact layer. It should be noted that the almost entire surface refers to an area of 80% or more. As described above, the threshold value is lowered by forming the n-electrode on the entire surface and symmetrically with respect to the ridge.

Next, after forming the electrodes, an insulating film 30 made of SiO ₂ was formed over the exposed insulating substrate 1, the nitride semiconductor layer on the electrode side, and the entire surface of the p-electrode 20 and the n-electrode 22. Thereafter, an opening is formed by etching in the insulating film 30 corresponding to the upper portion where the p-electrode 20 and the n-electrode 22 are formed. Next, as shown in FIG. 1, a p-pad electrode 21 and an n-pad electrode 23 electrically connected to the p-electrode 20 and the n-electrode 22 via the insulating film 30 are formed. The p-pad electrode 21 has the effect of increasing the substantial surface area of the p-electrode 20 to enable wire bonding on the p-electrode side. The n-pad electrode 23 also reduces peeling of the n-electrode,
This has the effect of increasing the current that can be injected from the n-electrode.

As described above, the wafer on which both electrodes are formed is transferred to a polishing apparatus, and the sapphire substrate 1 on which the nitride semiconductor is not formed is wrapped using a diamond polishing agent. Is set to 20 μm. After lapping, the substrate surface is mirror-finished by polishing with a finer abrasive at 1 μm.

After polishing the substrate, the polished surface side of the sapphire substrate corresponding to the direction perpendicular to the stripe-shaped electrodes is scribed and then cleaved in a bar shape to form a resonator on the cleaved surface.
Note that the cleavage plane is the M plane of the nitride semiconductor surface grown on the sapphire substrate. In addition, the resonator can be manufactured by etching the end face by dry etching means such as RIE. In addition, the cleavage plane can be formed by mirror polishing. However, as in the present embodiment, it is most desirable that the cleavage plane be the M plane of the nitride semiconductor and the resonance plane be the resonance plane.

After the cleavage, a dielectric multilayer film made of SiO ₂ and TiO ₂ was formed on the resonator surface, and finally the bar was cut in a direction parallel to the p-electrode to form a laser chip. Due to this cutting, the effective yield of elements that can be taken out as an effective laser element from one wafer was 90% or more. Next, the chip was placed face-up (in a state where the substrate and the heat sink faced each other), and the electrodes were wire-bonded, and laser oscillation was attempted at room temperature. A threshold current density of 3.5 kA / cm ² was obtained. , Oscillation wavelength 40
A continuous oscillation of 5 nm was confirmed, and a continuous oscillation of about 6 days was confirmed.

Example 2 The n-type contact layer 3 was 7 μm
A laser device was fabricated in the same manner as in Example 1 except that the laser device was grown at a film thickness of 3.5 A / cm.
^{In 2} , the continuous oscillation of the oscillation wavelength of 405 nm was confirmed, and the continuous oscillation of 6 days was also confirmed. The substantial yield of the laser device was 90% or more.

Example 3 A laser device was fabricated in the same manner as in Example 1 except that the sapphire substrate was polished to 40 μm, and the threshold current density was 3.7 kA / cm ² .
Continuous oscillation at an oscillation wavelength of 405 nm was confirmed, and continuous oscillation for 5 days was confirmed. The actual yield of the laser element was also 90% or more.

Example 4 1) Sapphire (C-plane) with a thickness of 300 μm and 2 inches φ
2) 200 angstrom buffer layer 2 made of GaN 3) 6 μm layer made of undoped GaN 4) 2 μm first n-type layer made of Si-doped n-type GaN
m5) 500 angstrom of a crack prevention layer made of Si-doped n-type In0.1Ga0.9N 4 ') Si-doped n-type GaN also on the crack prevention layer
A second n-type layer made of 2 μm is grown. (Total thickness of nitride semiconductor layer: 11.725 μm, including buffer layer)

Next, an n-type cladding layer 5 is directly grown on the second n-type layer, and thereafter, a layer above the n-type cladding layer 5 is grown in the same manner as in the first embodiment to nitride. A semiconductor wafer is manufactured and annealed in the same manner.
The mold layer is further reduced in resistance.

After the annealing, the p-type cladding layer 10 and the p-type cladding layer 10 are mesa-etched to form a ridge shape having a stripe width of 4 μm, and then etching is performed until the surface of the second n-type layer is exposed. In the case of the fourth embodiment, the second n-type layer corresponds to the contact layer.

Thereafter, a laser device was manufactured and oscillated in the same manner as in Example 1, and the threshold current density was also 3.2.
At kA / cm ² , continuous oscillation at an oscillation wavelength of 405 nm was confirmed, and continuous oscillation for 7 days was also confirmed. The actual yield of the laser element was also 90% or more.

Example 5 A laser device was fabricated in the same manner as in Example 4 except that the sapphire substrate was polished to 50 μm. The laser device was also manufactured at the same threshold current density of 3.3 kA / cm ² .
Continuous oscillation at an oscillation wavelength of 405 nm was confirmed, and continuous oscillation for 6 days was confirmed. The actual yield of the laser element was also 90% or more.

Comparative Example 1 A laser device was manufactured in the same manner as in Example 1 except that the thickness of the n-type contact layer was changed to 4 μm. The substrate could be polished only up to 80 μm. With the above polishing, the wafer was broken at an irregular position. Since it is difficult to form a resonance surface by cleavage on a wafer polished to 80 μm,
When a laser element was formed by etching by RIE, continuous oscillation was performed at a threshold current density of 4.5 kA / cm ² , but the element was cut off in only 60 minutes.

Comparative Example 2 A laser device was manufactured in the same manner as in Example 1 except that the thickness of the n-type contact layer was changed to 3 μm. The substrate could be polished only up to 100 μm. With the above polishing, the wafer was broken at an irregular position. Since it is difficult to form the resonance surface by cleavage on a wafer polished to 100 μm, the wafer was formed by etching by RIE to form a laser device. As a result, continuous oscillation was performed at a threshold current density of 5.0 kA / cm ² . However, the element was cut off in a very short time.

Comparative Example 3 In Example 1, the substrate was
A laser device was fabricated in the same manner except that the surface was polished to 0 μm and the resonance surface was formed by RIE, and continuous oscillation was performed at a threshold current density of 4.3 kA / cm ² , but the device was cut off in 3 hours. I have.

[Comparative Example 4] In Example 1, the n-type contact layer 3 and the buffer layer 2 were not removed to the substrate 1,
A laser device was fabricated in the same manner except that the n-type nitride semiconductor layer was continuous on the insulating substrate of the wafer as described above. The substrate such as a heat sink cannot be sufficiently contacted with the substrate by bonding, resulting in poor heat dissipation.
Continuous oscillation occurred at a threshold current density of 4.0 kA / cm ² ,
The element has run out in time.

[0065]

Industrial Applicability The present invention prevents warpage that occurs when a substrate of a nitride semiconductor wafer is thinned, and prevents cracks at irregular positions of the wafer due to the warpage, improves heat dissipation, and raises the threshold. And a method of manufacturing the nitride semiconductor device having improved lifetime characteristics. Particularly, in the case of a laser element, the continuous oscillation time can be made longer. Further, since the substrate is thin, the cleavage plane of the nitride semiconductor can be easily set as a resonance plane. Although the present invention has been described with respect to a laser device, it goes without saying that the present invention can be applied to other devices using a nitride semiconductor device, such as an LED and a light receiving device.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing the structure of a laser device according to one embodiment of the present invention.

FIG. 2 is a unit cell diagram schematically showing a crystal structure of a nitride semiconductor.

FIG. 3 is a schematic sectional view showing the structure of a laser device used in Comparative Example 4 of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Sapphire substrate 2 ... Buffer layer 3 ... N-type contact layer 4 ... Crack prevention layer 5 ... N-type cladding layer 6 ... N-type light guide layer 7 ... Active layer 8 ... p-type cap layer 9 ... p-type light guide layer 10 ... p-type cladding layer 11 ... p-type contact layer 20 ... p electrode 21 ... p pad electrode 22 ... n electrode 23 ... n pad electrode 30 ... insulating film

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 33/00 H01S 5/00-5/50

Claims (4)

(57) [Claims] 1. A buffer layer having a thickness of at least 0.5 μm and a total thickness of at least 0.5 μm on an insulating substrate having a thickness of 60 μm or less.
A nitride semiconductor device comprising: a nitride semiconductor including a nitride semiconductor layer having a thickness of not less than μm; and removing a part of the nitride semiconductor to an insulating substrate. 2. A nitride semiconductor layer containing no n-type impurity and a nitride containing an n-type impurity above the buffer layer among the plurality of nitride semiconductor layers having a total film thickness of 6 μm or more. 2. The nitride semiconductor device according to claim 1, wherein the semiconductor layer is grown with a total thickness of 6 μm or more. 3. A method for manufacturing a nitride semiconductor device, comprising:
Growing a nitride semiconductor having a plurality of nitride semiconductor layers having a total thickness of 6 μm or more on an insulating substrate via a buffer layer having a thickness of 0.5 μm or less; Removing the part to the insulating substrate, adjusting the thickness of the insulating substrate of the wafer to 60 μm or less after removing a part of the nitride semiconductor to the insulating substrate, and removing the wafer after adjusting the thickness of the substrate. And a step of separating into chips. 4. A nitride semiconductor layer containing no n-type impurity and a nitride containing an n-type impurity above the buffer layer among the plurality of nitride semiconductor layers having a total film thickness of 6 μm or more. 4. The method for manufacturing a nitride semiconductor device according to claim 3, wherein the semiconductor layer is grown to a total thickness of 6 μm or more.