JPH114048A - Nitride semiconductor device and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a laser device possessed of a nitride semiconductor substrate and its resonant plane to be formed by a method wherein the opposed edge faces of an active layer of the nitride semiconductor device are set flush with the cleavage plane of a nitride semiconductor substrate M piane (11-00). SOLUTION: A protective film formed like a stripe vertical to the A plane (112-0) of a sapphire substrate is provided onto the sapphire substrate whose main surface is a C plane (0001). Or, a protective film formed like a stripe vertical to the R plane (11 02) of a sapphire substrate is provided onto the sapphire substrate whose main surface is a A plane (112-0). A nitride semiconductor is grown on the protective film for the formation of a nitride semiconductor substrate. Furthermore, a nitride semiconductor layer which includes an active layer is formed on the nitride semiconductor substrate, the sapphire substrate is removed from the nitride semiconductor substrate, and then the cleavage plane of the M plane (11-00) of the nitride semiconductor substrate is set flush with the edge face of the active layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride semiconductor (In _X Al _Y Ga _{1 -XY} N, 0 ≦ X, 0 ≦ Y, X +
The present invention relates to a nitride semiconductor device comprising Y ≦ 1) and a method for manufacturing the nitride semiconductor device, and more particularly to a nitride semiconductor device using a nitride semiconductor as a substrate and a method for manufacturing the same.

[0002]

2. Description of the Related Art A nitride semiconductor has just recently been put into practical use by the present applicant as a material for a high-brightness blue LED and a pure green high-brightness LED. The present applicant has succeeded in continuous oscillation at room temperature of 406 nm for the first time in the world with a blue laser device using this material. (Nikkei Electronics, 19
This laser device has a multiple quantum well structure of In _x Ga ₁ -xN in the active layer, and the resonance surfaces at both ends of the active layer are formed by etching.
At 0 ° C., continuous oscillation for 27 hours is exhibited at a threshold current density of 3.6 kA / cm ² , a threshold voltage of 5.5 V, and an output of 1.5 mW.

[0003] Sapphire is used as a growth substrate for nitride semiconductors in both current LED devices and laser devices.
As is well known, since sapphire has a lattice mismatch of 13% or more with the nitride semiconductor, the crystal of the nitride semiconductor grown thereon has very many lattice defects. Generally, a semiconductor having many crystal defects is not suitable for a laser device, and it is considered that practical use is difficult. In addition to sapphire, ZnO, G
Devices using substrates such as aAs and Si have also been reported, but even such LEDs have not been realized because nitride semiconductors having good crystallinity are difficult to grow on these substrates.

[0004] Further, a laser device using sapphire as a substrate has a drawback that it is difficult to form the resonance surface of the active layer by cleavage. The present applicant has previously shown a technique of forming a nitride semiconductor cleavage plane by cleaving a wafer in which a nitride semiconductor is stacked on top of sapphire on the M-plane of sapphire. In terms of performance, etc., it was not sufficiently satisfactory for practical use.

On the other hand, attempts have been made to produce a nitride semiconductor substrate which is completely lattice-matched with the nitride semiconductor (for example, Japanese Patent Application Laid-Open No. Sho 61-7621, Japanese Patent Publication No. Sho 61-263).
5, JP-A-51-3779, JP-A-7-165498,
Actually, it is very difficult to obtain a nitride semiconductor substrate, and at present it has not been realized yet.

[0006]

As described above, a nitride semiconductor device using a nitride semiconductor as a substrate is hardly known, for example, how to divide the substrate into chips is not known. . Accordingly, the present invention has been made in view of such circumstances, and it is an object of the present invention to provide a nitride semiconductor device having a nitride semiconductor as a substrate and a novel method for manufacturing the nitride semiconductor device. It is an object of the present invention to provide a laser device having a nitride semiconductor substrate and a method for forming a resonance surface of the laser device.

[0007]

According to the present invention, there is provided a nitride semiconductor device comprising a nitride semiconductor as a substrate, and a nitride semiconductor layer having an element structure including an active layer laminated on the substrate. And the end face of the opposing active layer of the nitride semiconductor device is connected to the nitride semiconductor substrate M surface (1
1-00).

In particular, when the nitride semiconductor layer has a laser element structure, the end face of the active layer of the laser element is a resonance surface of the laser element.

The method for manufacturing a nitride semiconductor device according to the present invention comprises:
On the heterogeneous substrate made of a material different from the nitride semiconductor layer,
A first step of growing a nitride semiconductor to produce a nitride semiconductor substrate; a second step of stacking a nitride semiconductor layer having an element structure including an active layer on the nitride semiconductor substrate; From the nitride semiconductor substrate grown on top,
The method is characterized by including a third step of removing the heterogeneous substrate and a fourth step of cleaving the nitride semiconductor layer including the active layer on the M plane (11-00) of the nitride semiconductor substrate. In the manufacturing method of the present invention, the order of the second step and the third step does not matter. That is, the third step may be performed before or after the second step.

[0010] Preferably, in the first step, a protective film is formed partially on the heterogeneous substrate, and the nitride semiconductor is grown on the protective film. More preferably, a protective film is partially formed on the surface of the nitride semiconductor layer grown on the surface of the heterogeneous substrate in the first step, and the nitride semiconductor is grown up to the upper portion of the protective film. When the protective film is formed, the crystal defects of the nitride semiconductor layer grown on the protective film are reduced, and the crystal defects between the protective films (window portions) are also reduced. The crystallinity of the semiconductor becomes very good. More preferably, the protective film has a stripe shape. When a stripe is formed, the property of anisotropic growth of the nitride semiconductor can be used. The protective film can be formed directly on the surface of the heterogeneous substrate, or after growing a nitride semiconductor layer thinly to several tens of μm or less on the heterogeneous substrate and then forming on the surface of the nitride semiconductor layer. It may be formed on the upper surface of the heterogeneous substrate. It is preferable to form a protective film after growing a nitride semiconductor layer on a heterogeneous substrate since crystal defects occurring on the surface of the nitride semiconductor layer grown on the protective film are further reduced.

Further, in the manufacturing method of the present invention, in the first step, a stripe shape perpendicular to the A-plane (112-0) of the sapphire substrate is formed on the sapphire substrate having the C-plane (0001) as a main surface. Or forming a protective film having a stripe shape perpendicular to the R (11-02) plane of the sapphire substrate on the sapphire substrate having the A-plane (112-0) as a main surface. One step of forming a protective film having a stripe shape perpendicular to the (110) plane of the spinel substrate on the spinel substrate having the (111) plane as a main surface. And a nitride semiconductor is grown on the protective film.

In particular, when a protective film is formed, according to the manufacturing method of the present invention, the active layer performing a predetermined operation is located above the stripe-shaped protective film. It is characterized by being cleaved in a vertical direction.

[0013]

FIG. 1 is a unit cell diagram showing a crystal structure of a nitride semiconductor having a C-axis orientation. The nitride semiconductor has a rhombohedral structure to be precise, but can be approximated by a hexagonal system as shown in this figure. In the device of the present invention, the opposing end faces of the active layer are the resonance faces in the M-plane of the nitride semiconductor.
The M plane is a plane showing the side surface of the hexagonal prism as shown in this figure, and can be represented by six types of plane orientations. However, since all show the same M plane, in this specification, (11- 0
It is assumed that the 0) plane is representative of all M planes.
Similarly, the R-plane is a plane shown in a plane orientation obtained by cutting a hexagonal prism obliquely to the C-axis from one bottom side of the hexagonal column, and each of the six sides of the bottom side can be represented by six types of plane orientations. , All show the same M-plane, so that (1
It is assumed that the 1-02) plane represents the R plane.
Further, as shown in this figure, the A surface indicates a surface obtained by cutting a hexagonal prism perpendicularly to the C axis from two points adjacent to each other in a hexagon, and each vertex of the hexagon has six types of plane orientations. Can be shown, but since they all show the same A side,
In this specification, the (112-0) plane is assumed to represent the A plane.

In the nitride semiconductor device according to the present invention, the nitride semiconductor used as the substrate is In _x Al _Y Ga _{1 -XYN} (0 ≦ X,
Any composition may be used as long as 0 ≦ Y and X + Y ≦ 1), but undoped GaN is preferable. Undoped GaN is easy to grow from a nitride semiconductor having the highest crystallinity to a thick film serving as a substrate, for example, a thick film of 100 μm or more. In addition, GaN such as Si, Ge, S, Se, etc.
An n-type impurity composed of a group element can also be doped.
The n-type impurity controls the conductivity in a preferable range, and
In order to maintain the crystallinity of N, 1 × 10 ¹⁷ / cm ^{3 to} 5
It is desirable to dope in the range of × 10 ²¹ / cm ³ .

Although the plane orientation of the main surface of the nitride semiconductor substrate on which the element structure is laminated is not particularly limited, a nitride semiconductor substrate having a main surface that can be cleaved at the M plane is selected. Is used. The main surface is C
It is also possible to use a nitride semiconductor substrate whose plane orientation is shifted from the plane and the plane A by several degrees.

In a nitride semiconductor device in which a nitride semiconductor layer having an element structure including an active layer is laminated on a nitride semiconductor substrate, a nitride semiconductor layer having good crystallinity is grown to lattice match with the substrate. it can. Conventionally, sapphire, Zn
Although a nitride semiconductor layer is laminated on a heterogeneous substrate such as O, Si, and GaAs, the nitride semiconductor crystal grown on the heterogeneous substrate has a lattice constant mismatch, a difference in thermal expansion coefficient, and the like. There are very many lattice defects, and the orientation of the nitride semiconductor crystal is difficult to be uniform, and it is difficult to obtain a uniform cleavage plane of the nitride semiconductor element by cleavage of the substrate. In the device of the present invention, since a nitride semiconductor layer having an element structure is grown on the nitride semiconductor substrate, the nitride semiconductor layer has very few crystal defects and crystals having a uniform plane orientation. Can grow. Therefore, the nitride semiconductor substrate M
By cleaving the plane, the nitride semiconductor element including the active layer is also cleaved at the same plane on the M plane, so that a cleaved plane close to a mirror plane with uniform orientation can be obtained. Moreover, as shown in FIG. 1, since the M planes have planes parallel to each other, when a laser element having the plane as a resonance plane is manufactured,
A very high reflectivity surface can be obtained.

In the first step of the production method of the present invention,
The heterogeneous substrate may be any substrate as long as it is made of a material different from that of the nitride semiconductor. For example, in addition to the sapphire C surface, sapphire having an R surface and an A surface as main surfaces, and spinel (MgA1 ₂ O ₄ ) may be used. Such an insulating substrate, SiC (6H,
4H, 3C), ZnS, ZnO, GaAs, Si
For example, a substrate material different from a conventionally known nitride semiconductor can be used. A nitride semiconductor layer is grown as a thick film on this heterogeneous substrate to produce a nitride semiconductor substrate. In order to manufacture a nitride semiconductor substrate, it is preferably manufactured by the following method.

That is, a protective film is partially formed on the heterogeneous substrate (not necessarily in contact with it), and a nitride semiconductor is grown on the protective film. Preferably, a protective film is formed partially on the surface of the nitride semiconductor grown on the surface of the heterogeneous substrate, and the nitride semiconductor is grown on the protective film.
As the material of the protective film, a material having a property that the nitride semiconductor does not grow or hardly grows on the surface of the protective film is preferably selected. For example, silicon oxide (SiO _x ), silicon nitride (Si _x N _y ), titanium oxide Oxides such as (TiO _x ) and zirconium oxide (ZrO _x ), nitrides, and multi-layer films thereof, as well as metals having a melting point of 1200 ° C. or more can be used. These protective film materials have the property of withstanding the growth temperature of the nitride semiconductor of 600 ° C. to 1100 ° C. and preventing the nitride semiconductor from growing or hardly growing on the surface thereof. In order to form the protective film material on the surface of the nitride semiconductor, for example, a vapor deposition technique such as vapor deposition, sputtering, or CVD can be used. Further, in order to partially (selectively) form, a photomask having a predetermined shape is manufactured by using a photolithography technique, and the material is vapor-phase-formed through the photomask. A protective film having a predetermined shape can be formed. The shape of the protective film is not particularly limited. For example, the protective film can be formed in a dot, stripe, or checkerboard shape. However, as described later, it is preferable that the protective film be formed in a stripe shape with a specific plane orientation.

FIGS. 2 to 6 are schematic sectional views showing respective structures of the nitride semiconductor wafer in the first step. The operation of the preferred first step will be described below with reference to this drawing. In the drawings, reference numeral 1 denotes a heterogeneous substrate, 2 denotes a nitride semiconductor layer (layer serving as a base layer for forming a protective film), 3 denotes a first nitride semiconductor layer serving as a substrate, and 11 denotes a first protective film. .

In the first step, as shown in FIG. 2, a first protective film 11 is partially formed on the surface of the heterogeneous substrate 1 on which the nitride semiconductor layer 2 has been grown. In addition, heterogeneous substrate 1
A low-temperature growth buffer layer (not shown) may be formed between the nitride semiconductor layer 2 and the nitride semiconductor layer 2 for alleviating lattice mismatch. Forming a buffer layer is preferable because crystal defects can be further reduced. As the nitride semiconductor layer 2 grown on the heterogeneous substrate, undoped (undoped) GaN, GaN doped with an n-type impurity, or GaN doped with Si can be used. The nitride semiconductor layer 2 has a high temperature, specifically 90
It is grown on a heterogeneous substrate at 0 ° C. to 1100 ° C., preferably 1050 ° C., and has a thickness of 1 to 20 μm, preferably 2 to 10 μm.
μm. This range is preferable for obtaining the effects of the present invention. The buffer layer formed between the heterogeneous substrate 1 and the nitride semiconductor layer 2 is made of AlN, GaN, AlGaN,
nGaN or the like is grown at a temperature of not more than 900 ° C. and not less than 200 ° C. with a film thickness of several tens angstroms to several hundred angstroms. This buffer layer is composed of a heterogeneous substrate 1 and a nitride semiconductor layer 2
Although it is formed in order to alleviate the lattice constant irregularity, it may be omitted depending on the nitride semiconductor growth method, the type of the substrate, and the like.

In the present invention, the first protective film 11
May be formed in direct contact with the heterogeneous substrate 1, or may be formed on the heterogeneous substrate 1 by growing a semiconductor layer such as ZnO on the semiconductor layer. When the first protective film 11 is directly formed on the heterogeneous substrate 1, as shown in FIG.
When the protective film 11 is formed directly on the heterogeneous substrate 1, a buffer layer may be formed between the adjacent first protective films 11. The buffer layer used in this case is the same as the buffer layer formed between the heterogeneous substrate 1 and the nitride semiconductor layer 2.

Next, as shown in FIG. 3, the first nitride semiconductor 3 is grown on the first protective film 11 formed on the nitride semiconductor layer 2. Preferably, the first nitride semiconductor 3 is undoped (undoped) GaN or GaN doped with an n-type impurity. When the first protective film 11 is formed on the nitride semiconductor layer 2 thus grown on the heterogeneous substrate 1 and the first nitride semiconductor 3 is grown thereon, the first protective film 11 The first nitride semiconductor 3 is selectively grown on the exposed nitride semiconductor layer 2 without growing the nitride semiconductor 3 thereon. As the growth continues, the first nitride semiconductor 3 covers the first protective film 11 and
As shown in FIG. 4, adjacent first nitride semiconductors 3 are connected to each other.
As shown in (1), it is as if the first nitride semiconductor 3 had grown on the first protective film 11.

The crystal defects (threading dislocations) appearing on the surface of the first nitride semiconductor layer 3 grown in this manner are extremely small as compared with the conventional one. However, the number of crystal defects in the upper portion of the window and the number of crystal defects in the upper portion of the protective film in the initial stage of growth of the first nitride semiconductor 3 are significantly different. In other words, the portion of the first nitride semiconductor 3 grown on the portion (window portion) where the first protective film 11 is not formed on the heterogeneous substrate is formed between the heterogeneous substrate 1 and the nitride semiconductor layer 2. Although crystal defects tend to be easily dislocated from the interface, the portion of the first nitride semiconductor layer 3 grown on the first protective film 11 includes:
There are almost no crystal defects displaced in the vertical direction.

For example, as shown in FIG. 4, crystal defects are schematically shown by a plurality of fine lines extending from the heterogeneous substrate 1 to the surface of the first nitride semiconductor layer 3. Such crystal defects occur very frequently in the nitride semiconductor layer 2 grown on the heterogeneous substrate 1 due to a mismatch in lattice constant between the heterogeneous substrate 1 and the nitride semiconductor layer 2. Most of the crystal defects in the window where the first protective film 11 is not formed are dislocations from the interface between the heterogeneous substrate and the nitride semiconductor layer 2 toward the surface during the growth of the first nitride semiconductor 3. do. However, as shown in FIG. 4, most of the crystal defects generated from the windows are dislocated in the initial growth of the first nitride semiconductor layer 3, but the growth of the first nitride semiconductor layer 3 During the process, the number of crystal defects dislocations in the surface direction on the way tends to decrease drastically, and the number of crystal defects dislocations to the surface of the first nitride semiconductor layer 3 becomes very small. On the other hand, the first nitride semiconductor layer 3 formed on the first protective film 11 is not grown from the substrate, but is formed by connecting the adjacent first nitride semiconductor layers 3 during growth. In addition, the number of crystal defects is very small from the beginning of the growth as compared with that grown from the substrate. As a result,
After the completion of the growth, the surface of the first nitride semiconductor layer 3 (the upper part of the protective film and the upper part of the window) has very few dislocation crystal defects or almost no upper part of the upper part of the protective film according to transmission electron microscope observation. Can not be. By using the first nitride semiconductor layer 3 having very few crystal defects as a growth substrate for a nitride semiconductor having an element structure, a nitride semiconductor element having better crystallinity than before can be realized.

Although the number of crystal defects is reduced both in the window on the surface of the first nitride semiconductor layer 3 and in the upper portion of the protective film, the first nitride grown in the upper portion of the window in which the number of crystal defects was large in the initial stage of growth. On the surface of the semiconductor layer 3, crystal defects tend to be slightly larger than those grown on the protective film. This is probably because during the growth of the first nitride semiconductor layer 3 growing in the window portion, the dislocations of many crystal defects stopped, but the crystal defects that continued to be slightly dislocations almost immediately above the window portion. It is considered that dislocation tends to occur easily.

Further, the tendency of dislocation of crystal defects is determined when growing the first nitride semiconductor 3 after forming the protective film.
Molar ratio of nitrogen source gas to group source gas (V / III
Ratio) can be adjusted. First, when the V / III ratio is set to 2000 or less, dislocations of crystal defects do not reach straight to the surface, and the dislocations are likely to bend by 90 ° during growth. In contrast, the V / III ratio was 2000
When it is larger, the crystal defects continue to be dislocated to the surface, but the number tends to increase more than when the V / III ratio is 2000 or less. According to the surface transmission electron microscope observation of the number of crystal defects caused by the difference in the dislocations of the crystal defects, when the V / III ratio is 2000 or less, dislocations are observed only in the upper part of the window and almost no more in the upper part of the protective film. Defects are no longer seen, for example, when the crystal defect concentration at the
^The number is not more than ⁸ / cm ² , preferably not more than 10 ⁷ / cm ² , and is approximately not more than 10 ⁷ / cm ² , preferably not more than 10 ⁶ / cm ² above the protective film. When the V / III ratio is 2
If it is larger than 000, dislocations are observed both over the window and over the protective film, and the number of crystal defects is, for example, 10 ⁸ / cm ^2.
There is a tendency to be above. Preferred values of the V / III ratio are 2000 to 100 and 1500 to 500. When the ratio is in this range, the dislocation of the crystal defect does not easily reach the surface, and a nitride semiconductor having good crystallinity is easily obtained. .

In the present invention, as shown in FIG. 5, the second protective film 12 is formed by forming a portion of the surface of the first nitride semiconductor layer 3 where crystal defects are likely to appear or a crystal appearing on the surface. It is preferable to provide so as to cover the defect. By providing the second protective film 12 in this manner, further dislocations of crystal defects appearing on the surface of the first nitride semiconductor layer 3 can be prevented. It is conceivable that the interrupted crystal defect may relocate to the active layer or the like during operation of the laser element or the like, but this can be preferably prevented. In the present invention, the position where the second protective film 12 is formed is not particularly limited, and the second protective film 12 is formed partially on the surface of the first nitride semiconductor layer 3, preferably on a crystal defect which appears, more preferably. Is the upper part of the window where crystal defects exist in the initial growth of the first nitride semiconductor layer 3. For example, the second protective film 12
As an embodiment of the position where is formed, as shown in FIG. 5, a second protective film 12 is formed above the window of the first nitride semiconductor layer 3. In other words, the lattice defect generated from the interface between the substrate and the nitride semiconductor layer is likely to appear on the surface.
It is desirable to form the protective film 12 and expose the surface of the first nitride semiconductor layer 3 grown on the first protective film 11. By forming the second protective film 12 on the surface of the first nitride semiconductor layer 3 corresponding to the window of the first protective film 11 as described above, when the crystal defects continue to be dislocated from the window. The dislocation of crystal defects can be stopped by the second protective film 12.

In FIG. 5, a flat surface is polished to reduce irregularities on the surface of the first nitride semiconductor layer 3 grown in FIG. A second protective film 12 may be formed on the surface of the semiconductor layer 3. Preferably, the area of the second protective film 12 is the first
Is larger than the area of the window of the protective film 11. Specifically, when the shape of the protective film is formed by dots, stripes, or the like, the surface area of the unit dot and the unit stripe width are made larger than those of the window. This is because, in many cases, crystal defects do not necessarily dislocate perpendicularly from the substrate, but rather displace obliquely or bend halfway. Therefore, it is conceivable that a crystal defect may enter the first nitride semiconductor layer 3 immediately above the first protective film 11, so that the surface area of the second protective film 12 is reduced as shown in FIG. Is preferably larger than the window.

Next, the first protection film 12 on which the second protection film 12 is formed is formed.
Similarly, when the second nitride semiconductor layer 4 is grown on the nitride semiconductor layer 3, the second nitride semiconductor layer 4 does not grow on the second protective film 12 first, Selective growth is performed only on one nitride semiconductor layer 3. First nitride semiconductor layer 3
The second nitride semiconductor layer 4 grown on the first nitride semiconductor layer 3 is made of the same nitride semiconductor and has few crystal defects. Defects are less likely to occur. Since there are few crystal defects on the surface of the first nitride semiconductor layer 3, the number of crystal defects dislocated to the second nitride semiconductor layer 4 is also small, and the second nitride semiconductor layer 3 has better crystallinity than the first nitride semiconductor layer 3. 2 can be grown. Note that, in the first step of the present invention, the first nitride semiconductor layer 3, the second nitride semiconductor layer 4, and any of the nitride semiconductors can be used as the substrate.

In a further preferred embodiment, the shape of the protective film is a stripe. By forming a stripe, anisotropic growth of a nitride semiconductor can be used. That is, the nitride semiconductor tends to grow in a certain direction on a heterogeneous substrate. Therefore, by providing a stripe-shaped protective film perpendicular to the direction in which the nitride semiconductor is easily grown, the nitride semiconductor is nitrided on the protective film. Product semiconductors tend to connect and grow easily. When the area of the protective film is larger than the exposed area (window) of the heterogeneous substrate, a nitride semiconductor with less lattice defects can be easily obtained.

As a particularly preferred embodiment of the first step, C
A protective film having a stripe shape perpendicular to the A surface (112-0) of the sapphire substrate is formed on the sapphire substrate having the surface (0001) as a main surface. Alternatively, a protective film having a stripe shape perpendicular to the R (11-02) plane of the sapphire substrate is formed on the sapphire substrate having the A-plane (112-0) as a main surface. Or (11
1) A protective film having a stripe shape perpendicular to the (110) plane of the spinel substrate is formed on the spinel substrate whose main surface is the surface. Either step may be used. Then, a nitride semiconductor is grown on the protective film. FIG.
FIG. 3 is a schematic plan view of a main surface side of a heterogeneous substrate. In this figure, the sapphire C plane is the main surface, and the orientation flat (orientation flat) surface is the A surface. As shown in this figure, stripes of the protective film are formed in a direction perpendicular to the A-plane and parallel to each other. As shown in FIG. 7, when a nitride semiconductor is selectively grown on a sapphire C plane,
The nitride semiconductor tends to grow in a direction parallel to the A-plane in the plane, and hardly grows in a direction perpendicular to the A-plane. Therefore, when a stripe is provided in a direction perpendicular to the A plane,
The nitride semiconductors between the stripes are connected and grow easily, and the crystal growth shown in FIGS. 2 to 5 can be easily performed.

Similarly, when a sapphire substrate having the A-plane as the main surface is used, for example, when the orientation flat surface is the R-plane, stripes parallel to each other are formed in the direction perpendicular to the R-plane. Since the nitride semiconductor tends to grow in the stripe width direction, a nitride semiconductor layer with few crystal defects can be grown.

Also with respect to spinel (MgAl ₂ O ₄ ), the growth of the nitride semiconductor is anisotropic, and the growth surface of the nitride semiconductor is (111) and the orientation flat is (11).
When the plane is the 0) plane, the nitride semiconductor tends to grow in a direction parallel to the (110) plane. Therefore (11
When a stripe is formed in a direction perpendicular to the 0) plane, the nitride semiconductor layer and the adjacent nitride semiconductor are connected to each other at the upper portion of the protective film, and a crystal having few crystal defects can be grown.
In the above description, similarly to the case where the second protective film 12 is formed as shown in FIG. 5, it is desirable to form a stripe parallel to the first protective film 11 on the surface of the first nitride semiconductor layer 3. The spinel is cubic and is not shown.

FIG. 8 is a schematic plan view showing a part of FIG. 7 in an enlarged manner. As shown in this figure, on a sapphire substrate having a C-plane as a main surface and an A-plane as an orientation flat surface, the M-plane of the nitride semiconductor substrate grown on the protective film is in a direction parallel to the orientation flat surface. Tend to grow in.
Therefore, when a nitride semiconductor device having an active layer is grown on the nitride semiconductor substrate, if the active layer portion is designed to be located above the protective film, a nitride semiconductor device having good crystallinity will be grown. Can be done. And the fourth
In the step, when the nitride semiconductor substrate is cleaved in a direction perpendicular to the stripe-shaped protective film, the nitride semiconductor device is cleaved on the M plane. A resonance surface can be easily obtained.
FIG. 8 shows sapphire having a C-plane as a main surface, but similarly, sapphire having a A-plane as a main surface,
The same applies to a spinel having a (111) plane as a main surface.

[0035]

【Example】

[Example 1] This example shows MOVPE (metal organic chemical vapor deposition), but the method of the present invention
The method is not limited to the VPE method, and all methods known for growing nitride semiconductors, such as HVPE (halide vapor phase epitaxy) and MBE (molecular beam vapor phase epitaxy), can be applied.

(First Step) A buffer layer (not shown) made of GaN at a temperature of 510 ° C. is formed on a sapphire substrate having a 2-inch φ, C-plane as a main surface and an orientation flat surface as an A-plane at 150 Å. The undoped GaN layer 2 is grown at a temperature of 1050 ° C. to a thickness of 3 μm, and a stripe-shaped photomask is formed thereon.
A protective film made of O ₂ is formed with a thickness of 0.1 μm. The stripe direction is formed in a direction perpendicular to the orientation flat surface as shown in FIG.

After forming the protective film, the substrate was set in a reaction vessel, the temperature was raised to 1050 ° C., and TM was added to the source gas.
G, ammonia, silane gas, and Si is 1 × 10 ¹⁸
/ Cm ³ doped GaN nitride semiconductor layer
It is grown to a thickness of 0 μm. The preferred growth thickness of the nitride semiconductor layer serving as a substrate depends on the thickness and size of the protective film 11 formed earlier, but in order to cover the surface of the protective film 11 and grow up to the upper part of the protective film, It is desirable to grow the protective film 10 times or more, more preferably 50 times or more the thickness of the protective film. The size of the protective film is not particularly limited. For example, when the protective film is formed of a stripe, a preferable stripe width is 0.5 to 100 μm, more preferably a width of about 1 μm to 50 μm. It is desirable that the width be smaller than the stripe width. In other words, when the area of the protective film is larger than that of the window, a nitride semiconductor layer with less crystal defects can be obtained.

After the growth of the nitride semiconductor layer, the wafer is taken out of the reaction vessel, and the surface of the nitride semiconductor layer is wrapped to a mirror surface to obtain a nitride semiconductor substrate made of Si-doped GaN.

(Second Step) Next, the wafer on which the Si-doped GaN substrate has been produced is transferred again to the reaction vessel of the MOCVD apparatus, and a nitride semiconductor layer for forming a laser element structure is grown on the substrate. FIG. 9 is a schematic cross-sectional view showing one structure of the nitride semiconductor device of the present invention, and specifically shows the structure of a laser device. This laser element has a direction parallel to the resonance plane,
That is, a diagram when the element is cut in a direction parallel to the M-plane of the nitride semiconductor substrate is shown. The second and subsequent steps will be described based on FIG.

A wafer having Si-doped GaN as a main surface is set in a reaction vessel of a MOVPE apparatus, and a second GaN film of GaN doped with 1 × 10 ¹⁸ / cm ³ of Si on the GaN substrate 40 at 1050 ° C. The buffer layer 41 is grown by 2 μm. The second buffer layer 41 is a nitride semiconductor single crystal layer grown at a high temperature of 900 ° C. or more, and a buffer layer grown at a low temperature to reduce lattice mismatch between a conventionally grown substrate and the nitride semiconductor. Is distinguished. The second buffer layer 41 may be a strained superlattice layer formed by laminating nitride semiconductors having different thicknesses of 100 angstrom or less, more preferably 70 angstrom or less, and most preferably 50 angstrom or less. preferable. When the strained superlattice layer is used, the crystallinity of the single nitride semiconductor layer is improved, so that a high-power laser element can be realized.

(Crack Prevention Layer 42) Next, 5 × 1 of Si
A crack preventing layer 42 of In ¹⁸ Ga 0.9 N doped with 0 ¹⁸ / cm ³ is grown to a thickness of 500 Å. The crack prevention layer 42 is made of an n-type nitride semiconductor containing In, preferably InGaN, so that cracks can be prevented from entering the nitride semiconductor layer containing Al. The crack preventing layer is preferably grown to a thickness of 100 Å or more and 0.5 μm or less. If it is thinner than 100 Å, it is difficult to act as a crack prevention as described above.
If it is thicker than m, the crystals themselves tend to turn black. The crack prevention layer 42 can be omitted.

(N-side cladding layer 43) Next, Si was added to 5 ×
A first layer of 10 ¹⁸ / cm ³ doped n-type Al 0.2 Ga 0.8 N, 20 Å;
A superlattice structure having a total film thickness of 0.4 μm is formed by alternately laminating 100 second layers composed of GaN of pe) and 20 angstroms. The n-side cladding layer 43 functions as a carrier confinement layer and a light confinement layer, and is preferably a nitride semiconductor containing Al, preferably a superlattice layer containing AlGaN, and the total thickness of the superlattice layer is 100 Å or more. It is desirable that the growth be made at 2 μm or less, more preferably at 500 Å or more and 1 μm or less. When a superlattice layer is formed, a carrier confinement layer having good crystallinity without cracks can be formed.

(N-side light guide layer 44)
An n-type optical guide layer 44 of n-type GaN doped with × 10 ¹⁸ / cm ³ is grown to a thickness of 0.1 μm. This n-side light guide layer 44 acts as a light guide layer of the active layer,
It is desirable to grow GaN or InGaN, usually 100 Å to 5 μm, more preferably 2 Å.
It is desirable to grow with a film thickness of 00 Å to 1 μm. The n-side light guide layer 44 is usually made of Si, G
e is doped with an n-type impurity such as e to obtain an n-type conductivity type.
In particular, it can be undoped. When a superlattice is used, at least one of the first layer and the second layer may be doped with an n-type impurity or may be undoped.

(Active Layer 45) Next, undoped In0.
A well layer of 2Ga0.8N, 25 angstroms,
An active layer 4 of a multiple quantum well structure (MQW) having a total film thickness of 175 Å formed by alternately laminating barrier layers of undoped In0.05Ga0.95N and 50 Å.
Grow 5.

[0045] (p-side cap layer 46) Next, larger than the band gap energy p-side optical guide layer 47, and larger than the active layer 45, p-type and 1 × 10 ²⁰ / cm ³ doped with Mg AlO. A p-side cap layer 46 of 3Ga0.9N is grown to a thickness of 300 Å. Although the p-side cap layer 46 is p-type, the thickness is small, so that the i-type impurity is doped with n-type impurities to compensate for the carrier.
It may be of a type or undoped, and most preferably a layer doped with a p-type impurity. p-side cap layer 17
Is adjusted to 0.1 μm or less, more preferably 500 Å or less, and most preferably 300 Å or less. This is because if the layer is grown with a thickness greater than 0.1 μm, cracks are easily formed in the p-type cap layer 46, and a nitride semiconductor layer having good crystallinity is difficult to grow. 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. p-side cap layer 46
Although the lower limit of the film thickness is not particularly limited, it is desirable to form the film with a film thickness of 10 Å or more.

(P-side light guide layer 47) Next, the Mg band gap energy is smaller than that of the p-side cap layer 46.
A p-side light guide layer 47 made of p-type GaN doped with 1 × 10 ²⁰ / cm ³ is grown to a thickness of 0.1 μm. This layer functions as a light guide layer of the active layer, and is preferably made of GaN or InGaN, like the n-side light guide layer 44. This layer also functions as a buffer layer when growing the p-side cladding layer 48, and functions as a preferable light guide layer by growing with a film thickness of 100 Å to 5 μm, more preferably 200 Å to 1 μm. . This p-side light guide layer is usually doped with a p-type impurity such as Mg to have a p-type conductivity type, but it is not particularly necessary to dope the impurity. Note that this p
The light guide layer may be a superlattice layer. When a superlattice layer is formed, at least one of the first layer and the second layer may be doped with a p-type impurity or may be undoped.

(P-side cladding layer 48) Next, Mg was added to 1 ×
10 ²⁰ / cm ³ doped with a first layer made of p-type Al0.2Ga0.8N, 20 angstroms, 1 Mg × 10 ²⁰
/ Cm ³ doped second layer of p-type GaN, 20 angstrom alternately laminated to a total film thickness of 0.4 μm
A p-side cladding layer 48 of m superlattice layers is formed.
This layer acts as a carrier confinement layer similarly to the n-side cladding layer 43, and acts as a layer for decreasing the resistivity on the p-type layer side by having a superlattice structure. This p
The thickness of the side cladding layer 48 is not particularly limited, but is not less than 100 Å and not more than 2 μm, and more preferably not more than 5 μm.
It is desirable to grow the film at a thickness of not less than 00 Å and not more than 1 μm.

In the case of a nitride semiconductor device having a double hetero structure having an active layer 45 having a quantum well layer, a thickness 0.1 μm or less in contact with the active layer 45 and having a band gap energy larger than that of the active layer 45. A cap layer 46 made of a nitride semiconductor containing Al is provided, and a p-side light guide layer 47 having a smaller gap energy than the cap layer 46 is provided at a position farther from the active layer than the cap layer 46. It is very difficult to provide a p-side cladding layer 48 made of a superlattice layer containing a nitride semiconductor containing Al having a larger band gap than the p-side light guide layer 47 at a position farther from the active layer than the side light guide layer 47. Preferred. In addition, since the band gap energy of the p-side cap layer 46 is increased, the electrons injected from the n-layer are blocked by the cap layer 46, and the electrons do not overflow the active layer. Become.

(P-side contact layer 49) Finally, a p-side contact layer 49 made of p-type GaN doped with Mg at 2 × 10 ²⁰ / cm ³ is grown to a thickness of 150 Å. The p-side contact layer has a thickness of 500 Å or less, more preferably 400 Å or less.
Adjust the film thickness to 0 Å or more. As described above, when the nitride semiconductor layer having the element structure was grown by lamination, the plane orientation of the nitride semiconductor element portion was changed to the GaN substrate 4
The plane orientation coincided with zero.

After completion of the reaction, the wafer is annealed in a nitrogen atmosphere at 700 ° C.
The resistance of the mold layer is further reduced. After annealing, the wafer is taken out of the reaction vessel, and as shown in FIG. 9, the uppermost p-type contact layer 20 and the p-type clad layer 19 are etched by a RIE apparatus to form a ridge shape having a stripe width of 4 μm. Ni / Au on the entire surface of the ridge
A p electrode 51 is formed. The ridge formation position is Ga
When forming an N substrate, a ridge on a stripe is formed at a position corresponding to a position directly above a stripe-shaped protective film formed on a sapphire substrate and parallel to the stripe-shaped protective film.

Next, as shown in FIG. 9, the surface of the p-side cladding layer 48 and the contact layer 49 excluding the p-electrode 51
_An insulating film 50 made of ₂ is formed, and a p pad electrode 52 electrically connected to the p electrode 51 via the insulating film 50 is formed.

(Third Step) After the formation of the p-electrode, the sapphire substrate 1, the buffer layer, the GaN layer 2, and the protective film of the wafer are polished and removed to expose the surface of the Si-doped GaN substrate 40. An n-electrode 53 made of Ti / Al is formed with a thickness of 0.5 μm on the entire surface of the substrate, and Au / Sn is formed thereon for metallization with a heat sink.
And forming a thin film.

(Fourth Step) Next, the substrate is cleaved at a position perpendicular to the stripe ridge from the n-electrode side 53, that is, at the M plane of the GaN substrate 40, and a resonance plane is formed on the end face M plane of the active layer. Make it.

Finally, a dielectric multilayer film made of SiO ₂ and TiO ₂ is formed on the resonance surface, and the bar is cut in a direction parallel to the p-electrode to form a laser chip. The laser chip was placed face up (with the GaN substrate and the heat sink facing each other) on the heat sink, and the p-pad electrode 52 was wire-bonded to perform laser oscillation at room temperature. At room temperature, the threshold current density was 2.1 kA. At / cm ² and a threshold voltage of 4.2 V, continuous oscillation of an oscillation wavelength of 405 nm was confirmed, and a life of 500 hours or more was shown.

[Embodiment 2] The surface A is a principal surface of a heterogeneous substrate.
Sapphire having an R plane as an orientation flat surface is used. The protective film is made of Si ₃ N ₄ and has a stripe shape perpendicular to the R plane as in the first embodiment. The stripe width is 12 μm, the stripe interval (window) is 4 μm, and the film thickness is 0.1 μm. On this protective film, C-axis oriented undoped GaN
A nitride semiconductor substrate was grown to a thickness of 120 μm, and a C-axis-oriented nitride semiconductor laser device structure was grown on this GaN substrate in the same manner as in Example 1 to produce a laser device in the same manner. However, a laser device having substantially the same characteristics as the laser device of Example 1 was obtained.

Example 3 A nitride semiconductor substrate is obtained by HVPE (hydride vapor phase epitaxy). First, (11
1) The plane is the main plane, and the orientation flat is the (110) plane.
A 1 inch φ spinel (MgAl ₂ O ₄ ) substrate is prepared. On the surface of the spinel substrate, as in Example 1,
A photomask is formed, and a protective film 11 made of SiO ₂ is formed.
Are formed in a stripe shape perpendicular to the orientation flat surface. The stripe width is 12 μm and the stripe interval is 6
μm.

In the HVPE apparatus, a quartz boat containing Ga metal is installed inside a reaction vessel tube made of quartz.
Further, the above-mentioned substrate 1 inclined at an angle is set at a position away from the quartz boat. Note that a halogen gas supply pipe is provided at a position in the reaction vessel close to the Ga metal, and an N source supply pipe is provided at a position close to the substrate separately from the space between the supply of the halogen gas. A nitrogen carrier gas and mainly HCl gas are introduced from a halogen gas pipe. At this time, the Ga metal boat was heated to 900 ° C., and the spinel substrate side was heated to 900 ° C.
Heated to 050 ° C. Then, HCl gas and Ga are reacted to generate GaCl _3, and ammonia gas is mainly supplied similarly to the nitrogen carrier gas from the N source supply pipe close to the spinel substrate side, and further, silane gas is supplied together with the halogen gas. Then, growth is performed at a growth rate of 50 μm / hr for 3 hours to grow GaN doped with Si having a thickness of 150 μm at 1 × 10 ¹⁸ / cm ³ .

Thereafter, a nitride semiconductor layer having a laser element structure was stacked on a GaN substrate in the same manner as in Example 1 by using the MOVPE method to obtain a nitride semiconductor laser element. A laser device having substantially the same characteristics as the device was obtained.

Fourth Embodiment A laser device is obtained in the same manner as in the first embodiment except that the order of the second step and the third step is reversed. In other words, after forming a nitride semiconductor substrate on a sapphire substrate via a protective film, the sapphire substrate,
The protective film is polished and removed, leaving only the Si-doped GaN substrate. On this GaN substrate, a nitride semiconductor layer having a laser element structure is grown in the same manner as in the first embodiment. Since the sapphire substrate and the protective film are removed at the position where the ridge stripe is formed, a mark serving as a starting point is put on the GaN substrate side before the nitride semiconductor element is grown. This laser element also exhibited almost the same characteristics as in the first embodiment.

Example 5 150 μm obtained in Example 1
On the surface of a Si-doped GaN substrate having a stripe width of 10 μm and a stripe interval of 6 μm,
A second protective film made of i ₃ N ₄ is formed with a thickness of 0.1 μm. As shown in FIG. 6, the position of the second protective film is shifted from the position of the first protective film 11 formed earlier.
The mask is aligned so that the 10 μm stripe of the second protective film is located at the position of the 6 μm window of the first protective film 11, and a stripe parallel to the first protective film 11 is formed. .

After the formation of the second protective film, the wafer is returned to the reaction vessel again, and a second nitride semiconductor made of GaN doped with 1 × 10 ¹⁸ / cm ^{3 of} Si using TMG, ammonia and silane gas as source gases. After the layer was grown to a thickness of 150 μm, it was taken out of the reaction vessel and the surface was mirror-polished.
This time, the second nitride semiconductor layer is used as a substrate.

After the second step, a nitride semiconductor layer having a structure of the laser device is laminated in the same manner as in the first embodiment to manufacture a laser device. However, when forming the ridge stripe, the stripe position of the ridge stripe is formed in the nitride semiconductor layer immediately above the second protective film formed later. This laser device has a threshold current density of 2.0 kA / cm ² , a threshold voltage of 4.0 V and an oscillation wavelength of 4 at room temperature.
A continuous oscillation of 05 nm was confirmed, indicating a life of 1000 hours or more.

[0063]

According to the present invention, despite the fact that nitride semiconductors are currently evaluated as ideal semiconductors, since nitride semiconductor substrates do not exist, nitride semiconductor devices with many lattice defects grown on heterogeneous substrates are used. Has been put to practical use. Therefore, when a device such as a laser device in which crystal defects immediately affect the life is realized, the device life is extended in several tens of hours. However, according to the growth method of the present invention, a nitride semiconductor substrate that could not be grown conventionally can be obtained. Therefore, when a nitride semiconductor layer serving as an element structure is stacked on the nitride semiconductor substrate, very large lattice defects are generated. A small number of nitride semiconductor devices can be realized. In addition, since the nitride semiconductor substrate is cleaved in a specific plane orientation, the cleavage surface of the nitride semiconductor element grown on the substrate becomes mirror-like, and if that surface is used as a resonance surface, a resonance with a high reflectivity is obtained. Surface can be made. As described above, by using the method of the present invention, a laser element which cannot be realized conventionally can be almost brought to a practical level. In addition, the present invention can be applied not only to laser devices, but also to any electronic devices using nitride semiconductors such as LED devices, light receiving devices, solar cells, transistors, etc. using a nitride semiconductor substrate, and has a great industrial value. is there.

[Brief description of the drawings]

FIG. 1 is a unit cell diagram showing a crystal structure of a nitride semiconductor with a C-axis orientation.

FIG. 2 is a schematic cross-sectional view showing each structure of a nitride semiconductor wafer in a first step.

FIG. 3 is a schematic cross-sectional view showing each structure of a nitride semiconductor wafer in a first step.

FIG. 4 is a schematic cross-sectional view showing each structure of a nitride semiconductor wafer in a first step.

FIG. 5 is a schematic cross-sectional view showing each structure of a nitride semiconductor wafer in a first step.

FIG. 6 is a schematic cross-sectional view showing each structure of a nitride semiconductor wafer in a first step.

FIG. 7 is a schematic plan view illustrating a preferred first step on the main surface side of the heterogeneous substrate.

FIG. 8 is a schematic plan view showing a part of FIG. 7 in an enlarged manner.

FIG. 9 is a schematic cross-sectional view showing one structure of a nitride semiconductor device of the present invention.

[Explanation of symbols]

 1 ··· Different substrate 2 ··· Buffer layer 3 ··· First nitride semiconductor layer 4 serving as substrate 4 ··· Second nitride semiconductor layer 11 serving as substrate 11 ··· 1st protective film 12... 2nd protective film

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor: Adult Iwasa, 491-100, Kaminakacho Oka, Anan City, Tokushima Prefecture Inside Nichia Kagaku Kogyo Co., Ltd. Aka Chemical Industry Co., Ltd.

Claims (8)

[Claims] 1. A nitride semiconductor device comprising a nitride semiconductor as a substrate, and a nitride semiconductor layer having an element structure including an active layer laminated on the substrate, wherein the nitride semiconductor device has an opposing active layer. A nitride semiconductor element, wherein a layer end face is coincident with a cleavage plane of the nitride semiconductor substrate M plane (11-00). 2. The nitride semiconductor device according to claim 1, wherein the end surface of the active layer is a resonance surface of a laser device. 3. A first step of growing a nitride semiconductor on a heterogeneous substrate made of a material different from that of the nitride semiconductor layer to produce a nitride semiconductor substrate, and including an active layer on the nitride semiconductor substrate. A second step of laminating a nitride semiconductor layer having an element structure, a third step of removing the heterogeneous substrate from the nitride semiconductor substrate grown on the heterogeneous substrate, and an M surface (11) of the nitride semiconductor substrate. -00), a fourth step of cleaving the nitride semiconductor layer including the active layer in (-00). 4. The nitride semiconductor according to claim 3, wherein in the first step, a protective film is formed partially on the heterogeneous substrate, and the nitride semiconductor is grown up to the upper part of the protective film. Device manufacturing method. 5. The nitride according to claim 4, wherein the protective film is partially formed on the surface of the nitride semiconductor layer grown on the surface of the heterogeneous substrate in the first step. A method for manufacturing a semiconductor device. 6. The method according to claim 4, wherein the protective film has a stripe shape. 7. In the first step, a protective film having a stripe shape perpendicular to the A-plane (112-0) of the sapphire substrate is formed on the sapphire substrate having the C-plane (0001) as a main surface. Process, or A side (112-
Forming a protective film having a stripe shape perpendicular to the R (11-02) plane of the sapphire substrate above the sapphire substrate having the main surface of (0), or a spinel substrate having the (111) plane as the main surface On top of that spinel substrate (1
10. A method according to claim 3, further comprising the step of forming one of the steps of forming a protective film having a stripe shape perpendicular to the plane, wherein a nitride semiconductor is grown on the protective film. 7. The method for manufacturing a nitride semiconductor device according to any one of 6. 8. The method according to claim 6, wherein the active layer is located above the stripe-shaped protective film, and is cleaved in a direction perpendicular to the stripe in the fourth step. A method for manufacturing a nitride semiconductor device according to the above.