JP2001308462A - Method of manufacturing nitride semiconductor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a GaN semiconductor laser which is reduced in defect, such as the dislocation density, etc., and, at the same time, in driving current and driving voltage. SOLUTION: After an n-type GaN layer is caused to deposit on an n-type SiC substrate, the GaN semiconductor laser is manufactured by working the GaN layer to a ridge-like shape until the formed ridge reaches the substrate and covering at least the side faces of the ridge with TiN/SiNx. Since the stripe-like current injecting area of the laser is provided above a recess section, the laser is not affected by a defect such as the dislocation, etc., and, in addition, the series resistance of the laser can be reduced and anisotropic distortion can be added to an active layer. Consequently, the threshold current of the laser can be reduced, because the optical gain of the laser can be increased. Therefore, the characteristics of the GaN bluish purple semiconductor laser can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a GaN-based semiconductor light emitting device such as a semiconductor laser expected to be applied to the field of optical information processing and the like, and a method of manufacturing the same.

[0002]

2. Description of the Related Art A nitride semiconductor having nitrogen (N) as a group V element is considered to be promising as a material for a short wavelength light emitting device because of its large band gap. Of these gallium nitride-based compound semiconductor (GaN-based semiconductor: Al _x Ga _y In _z
N (0 ≦ x, y, z ≦ 1, x + y + z = 1) has been actively studied, and a blue light emitting diode (LED) and a green L
ED has been put to practical use. In addition, a semiconductor laser having an oscillation wavelength in the 400 nm band has been eagerly desired for increasing the capacity of the optical disk device, and a semiconductor laser using a GaN-based semiconductor as a material has attracted attention and is now reaching a practical level.

FIG. 9 shows GaN in which laser oscillation has been achieved.
1 is a structural sectional view of a semiconductor laser. Sapphire substrate 9
01 on a metalorganic vapor phase epitaxy (MOVPE) method.
aN buffer layer 902, n-GaN layer 903, n-Al
GaN clad layer 904, n-GaN optical guide layer 90
5, Ga _1-x In _x N / Ga _1-y In _y N (0 <y <x <
1) Multiple quantum well (MQW) active layer 906, p
A -GaN light guide layer 907, a p-AlGaN cladding layer 908, and a p-GaN contact layer 909 are grown.
Then, a width of 3 to 10 is formed on the p-GaN contact layer 909.
A ridge stripe having a width of about a micron is formed, and both sides are buried with SiO ₂ 911. On subsequent ridge stripe and SiO ₂ 911, for example, Ni /
Au p-electrode 910 and a part of n-GaN layer 9
For example, Ti /
An n electrode 912 made of Al is formed. In this device, when the n-electrode 912 is grounded and a voltage is applied to the p-electrode 910, carriers are injected into the MQW active layer 906, a gain is generated in the MQW active layer 906, and an oscillation wavelength of 400 n
The laser oscillation in the m band occurs. The oscillation wavelength changes depending on the composition and thickness of the Ga _1-x In _x N / Ga _1-y In _y N thin film which is the material of the MQW active layer 906.

By controlling the width and height of the ridge stripe, the laser is designed to oscillate in the fundamental mode in the horizontal transverse mode. That is, by providing a difference in the light confinement coefficient between the fundamental transverse mode and the higher-order mode (first-order or higher mode), oscillation in the fundamental transverse mode is enabled.

[0005] Sapphire, S
iC, Si, etc. are used, and all substrates are made of GaN.
It is difficult to obtain coherent growth without lattice matching. As a result, there are many dislocations (edge dislocations, screw dislocations, and mixed dislocations). For example, when a sapphire substrate or a SiC substrate is used, dislocations of about 1 × 10 ⁹ cm ⁻² exist. As a result, the threshold current of the semiconductor laser increases and the reliability decreases.

[0006] Selective lateral growth (ELO) has been proposed as a method of reducing dislocation density. This is effective as a method for reducing threading dislocations in a system having a large lattice mismatch.

FIG. 7 schematically shows the distribution of dislocations in a GaN crystal formed by ELO. First, a GaN crystal 702 is deposited on a sapphire substrate 701 by MOVPE or the like. After depositing SiO ₂ 703 by CVD or the like, the SiO ₂ 703 is processed into a stripe shape by photolithography and etching. GaN70
2 as a seed crystal by selective growth
An N layer 704 is deposited. MOVPE or HVPE is used as a growth method. The upper part of the seed crystal is about 1 × 10 ⁹ cm
^Although there is a region 706 having many dislocations at ⁻² , the dislocation density can be reduced to about 1 × 10 ⁷ cm ^{−2 in} the laterally grown portion.

An active region, that is, a current injection region is formed above the region 705 having a small number of dislocations to improve reliability.

[0009]

However, in this method, a polycrystal is deposited on the selective growth mask SiO ₂ 703, and a region having poor crystallinity is partially formed, which may lower the yield and productivity. Occurs.

In addition, since the p and n electrodes need to be formed on the same plane, there is a disadvantage that the number of steps in laser fabrication increases.

The present invention has been made in view of the above circumstances, and provides a method of manufacturing a highly reliable nitride semiconductor device with a high yield. It is particularly effective in application to a blue-violet semiconductor laser for optical disks.

[0012]

GaN-based semiconductor manufacturing method of the present invention SUMMARY OF] is on a conductive substrate _{Al u Ga v In w N (} u
A + v + w = 1) depositing and forming a ridge by etching the Al _u Ga _v In _w N to reach the substrate into a concave shape, a step of covering at least the side surface of the ridge of a refractory conductive film _{, Al u Ga v in w N} Al the C-plane of a region that is not covered with the conductive film as a seed crystal _x Ga _y I
_{n z N (x + y +} z = 1) and a step of growing crystal.

The method of manufacturing a GaN-based semiconductor of the present invention includes the steps of depositing an _{Al u Ga v In w N (} u + v + w = 1) on a conductive substrate, a substrate Al _u Ga _v In _w N concavely forming an etched ridge to reach a step of coating the side surfaces of the etched bottom surface and a ridge with a high melting point of the conductive film, Al _u Ga _v in _w N region that is not covered with the conductive film C A step of laminating a first cladding layer, an active layer, and a second cladding layer using the surface as a seed crystal, and a step of forming a current confinement structure so that carriers are injected into the active layer above the conductive film. Have.

[0014] GaN-based semiconductor manufacturing method of the present invention, on a conductive substrate _{Al u Ga v In w N (} u + v + w = 1) depositing a, Al _u using the resist as a mask Ga _v an In
_w forming a ridge by etching N in a concave shape to reach the substrate; and depositing a high melting point conductive film;
It has a step of removing the conductive film on the resist and the resist, and a step of further regrown GaN group crystal part exposed on the surface of the Al _u Ga _v In _w N as a seed crystal by a lift-off.

Further, in the method of manufacturing a GaN-based semiconductor according to the present invention, the upper portion of the high melting point conductive film is further covered with an amorphous insulating film.

In addition, electron cyclotron resonance (ECR) plasma, particularly ECR sputtering, is used as a method for depositing a conductive film having a high melting point.

The high melting point conductive film is made of, for example, Ti, Ta, T
iN, TaN, W, such as WSi _x Ti or T
a or W is contained.

The dielectric film is made of SiO ₂ , SiN _x , Al ₂ O ₃ ,
AlN or a compound thereof (for example, SiON or Al
NO) and a multilayer film.

[0019]

Embodiments of the present invention will be described below in detail with reference to the drawings. The production method of the present invention
The nitride semiconductor growth method is not limited to the MOVPE method, but has been proposed for growing a GaN-based semiconductor layer such as a hydride vapor phase epitaxy method (H-VPE method) or a molecular beam epitaxy method (MBE method). The method can be applied to all methods.

The GaN-based semiconductor referred to here is III
A nitride semiconductor containing Ga as a group III element
In addition to a, those containing B, Al, and In are also included.

(Embodiment) FIGS. 1 and 2 (n in FIG. 1)
(Enlarged view in the vicinity of the type GaN 103) is a structural cross-sectional view of a GaN-based semiconductor laser showing an example of the present invention. FIGS. 3 to 5 show a method of manufacturing this laser.

The method of manufacturing the laser shown in FIG. 1 is as follows.

First, on a conductive n-type SiC substrate 101, TMA (trimethylaluminum) and NH
₃ (ammonia) to deposit the high-resistance AlN buffer layer 102. Then change the temperature to 1000 ° C,
TMG (trimethylgallium), NH ₃ and SiH ₄ (monosilane) are supplied to deposit the n-type GaN layer 103 (FIG. 3). At this time, the main surface (surface) of the GaN layer is a C-plane. Next, the resist is processed into a stripe shape by photolithography, and then the GaN layer 103, the AlN buffer layer 102, and a part of the n-type SiC substrate 101 are processed into a recessed shape (concave shape) by dry etching using the resist as a mask. At this time, the width of the recess is about 20 microns, and the width of the ridge (the part with the resist) is about 3 microns.

Subsequently, TiN1 is deposited by using the ECR sputtering method.
04 (thickness: 20 nm) and SiN _x 105 (thickness: 20 n)
m) is deposited, and the resist on the ridge stripe and the TiN and SiN _x on the resist are removed by lift-off (FIG. 4).

Using the exposed C-plane of the n-type GaN layer 103 as a seed crystal, the n-type GaN layer 107, n
_-Type Al _0.07 Ga _0.93 N clad layer 108, n-type GaN light guide layer 109, InGaN multiple quantum well (MQW) active layer 110, p-GaN light guide layer 111, p-Al
_0.07 Ga _0.93 N cladding layer 112, p-GaN layer 113
Are sequentially deposited (FIG. 5). At this time, the adjacent ridges do not have to be combined.

Thereafter, the p-GaN layer 113 and the p-Al
_{The 0.07} Ga _0.93 N clad layer 112 is further processed into a ridge stripe shape, and both sides of the ridge are covered with an insulating film 114.
A current injection region is formed. The stripe width is about 2.5 microns. Further, the ridge portion is formed in a region above the air gap 106 where dislocations are small.

The p-GaN layer 11 at the opening of the insulating film 114
The p-electrode 115 is provided on the three surfaces and a part of the insulating film 114. An n-electrode 11 is provided on the back surface of the n-type SiC substrate.
6 are formed.

Thus, the semiconductor laser shown in FIG. 1 is manufactured.

In this device, the n-electrode 116 and the p-electrode 11
5, carriers are injected into the MQW active layer 110, a gain is generated in the active layer, and laser oscillation occurs at a wavelength of 402 nm. The MQW active layer 110 has a thickness of 3
It has a Ga _0.8 In _0.2 N well layer with a thickness of 6 nm and a GaN barrier layer with a thickness of 6 nm.

As shown in FIG. 2, between the n-type GaN layer 103 and the n-type SiC substrate 101, there is a high-resistance AlN buffer layer 102. The AlN layer 102 acts as a barrier for electrons injected from the n-electrode 116, and causes an increase in resistance. However, in the present invention, at least the side walls of the ridge stripe-shaped n-type GaN layer 103, the AlN layer 102, and the n-type SiC substrate 101 are short-circuited by the conductive TiN 104, so that the rise in resistance can be significantly suppressed. Since TiN has a high melting point, it does not decompose when stacking the n-type GaN layer 107 and the multilayer interlayer film thereon. In the present invention, SiN _x 105 is coated on TiN 104 to further suppress evaporation. TiN is n-type S
Since a low-resistance contact resistance is obtained for both the iC and the n-type GaN layer, it is effective for reducing the resistance of the device.

The GaN semiconductor laser of the present invention shown in FIG.
Anisotropic distortion is applied to the ridge stripe in the vertical direction, that is, in the plane, so that the optical gain can be increased and the threshold current can be significantly reduced.

As shown in FIG. 6, the upper portion of the n-type GaN 103 seed crystal has a region 603 having a large number of dislocations of about 1 × 10 ⁹ cm ^−2.
It has been reduced to about ⁶ cm ^-2 .

By forming an active region, that is, a current injection region, above the region 604 having a small number of dislocations, reliability can be improved.

In the present invention, the n-type GaN layer 103, AlN
The layer 102 and the n-type SiC substrate 101 are processed into a ridge shape,
TiN104 / TiN104 /
After forming SiN _x 103, n is formed by MOVPE.
The regrown layer 601 after the type GaN layer 107 is grown.
At that time, polycrystalline GaN 602 may be precipitated as in the conventional case (FIG. 6). However, due to the steps, the polycrystalline GaN 602 does not affect the upper crystal.
As a result, variations in characteristics can be significantly reduced, and the yield can be improved.

When manufacturing a semiconductor laser, it is necessary to form a resonator. The resonator is mainly made by cleavage, but sometimes the substrate may be scratched or cracked. In the conventional method shown in FIG. 7, the substrate and the lowermost GaN layer 7 are formed.
Due to the contact with the semiconductor chip 04, the damage reaches the layer of the semiconductor element, causing a problem that the characteristics are greatly impaired. When the air gap 106 is formed as in the present invention, the damage stops here, so that the influence on the semiconductor element can be significantly reduced.

In the present invention, the case where GaN is used as the seed crystal has been described.
For example, AlGaN or InGaN may be used.

In the present invention, ECR sputtering is used for depositing a conductive film and a dielectric film. In the case of TiN, solid Ti is used as a raw material, N ₂ is used as a reactive gas, and A is used as a plasma gas.
Use r. In the case of SiN _x , solid S
i, N ₂ is used as a reactive gas, and Ar is used as a plasma gas. By using ECR sputtering for depositing these films, a high-quality film can be obtained at a low temperature.

Further, as a highly conductive film with a melting point in the present invention has been described with reference to TiN, Ti, Ta, TaN and W, a high melting point such as WSi _x, n-type GaN or n-type SiC
Any material may be used as long as it has a low contact resistance to the substrate.

In the present invention, SiN _x is used as the dielectric film.
Is used, but other dielectric films or amorphous insulating films such as SiO ₂ , SiON, Al ₂ O ₃ , AlNO,
TiO ₂ , ZrO ₂ , Nb ₂ O ₅ , amorphous Si, or a multilayer film of these may be used.

These films can be obtained relatively easily by using ECR sputtering. Although the case where sapphire is used for the substrate has been described, the effect of the present invention is great even if another substrate, for example, ZnO, GaN, or the like is used.

In this embodiment, the case where the n-type GaN layer 103 serving as a seed crystal is formed by two-stage growth via a buffer layer has been described. You may.

In this embodiment, a lift-off process is used for forming the ridge of the seed crystal. However, another method may be used as long as a ridge stripe can be formed.

[0043]

As described above, according to the present invention, a method of manufacturing GaN-based semiconductor of the present invention, Al on a conductive substrate _u Ga _v an In
depositing a _{w N (u + v + w} = 1), Al u Ga v In
forming a ridge by etching the _w N to reach the substrate into a concave shape, a step of covering at least the side surface of the ridge of a refractory conductive film is coated with a conductive film of Al _u Ga _v In _w N Al _x
And a step of growing a Ga _y In _z N (x + y + z = 1) crystal, whereby a high-quality Al _x Ga _y In _z N crystal can be produced with a high yield.

[0044] Further, the method of manufacturing GaN-based semiconductor device of the present invention, on a conductive substrate _{Al u Ga v In w N (} u + v + w
= 1) depositing a, Al _u Ga _v In _w a step N by etching to reach the substrate concavely to form a ridge, the step of coating the side surfaces of the etched bottom surface and a ridge with a high melting point of the conductive film When, Al _u Ga _v in _w N conductive film in the first cladding layer C surface area which is not covered as a seed crystal, the active layer, and laminating a second cladding layer, the conductive film Forming a current confinement structure so that carriers are injected into the upper active layer, whereby the reliability can be increased by reducing the dislocation density, and the series resistance and drive voltage can be reduced. Further, since anisotropic strain can be applied to the active layer, the optical gain can be increased, and the threshold current and the drive current can be significantly reduced. Characteristics It is possible to above.

Also, a method for manufacturing a GaN-based semiconductor according to the present invention
Is the Al on the conductive substrate_uGa_vIn _wN (u + v + w =
1) a step of depositing, and using a resist as a mask Al_u
Ga_vIn _wEtch N until it reaches the substrate in a concave shape
Step of forming ridge and depositing high melting point conductive film
Process and lift-off by resist and on resist
Removing the conductive film of Al_uGa_vIn_wTable of N
The part exposed on the surface is used as a seed crystal to further add a GaN-based crystal.
A GaN-based crystal of good quality
Can be manufactured with high yield.

Further, in the method of manufacturing a GaN-based semiconductor according to the present invention, the upper portion of the high-melting-point conductive film is further covered with an amorphous insulating film, so that a low-resistance device can be manufactured with good reproducibility.

Further, TiN or S
Not only iN _x but also other films such as SiO ₂ , SiO
N, Al ₂ O ₃ , AlNO, TiO ₂ , ZrO ₂ , Nb
₂ O ₅ , amorphous Si, Ti, Ta, TaN, W, W
Good quality films such as Si _x can be obtained relatively easily at low temperatures.

[Brief description of the drawings]

FIG. 1 is a sectional view of an element of a GaN-based semiconductor laser showing an embodiment of the present invention.

FIG. 2 is a sectional view of a GaN-based semiconductor laser according to an embodiment of the present invention;

FIG. 3 is a structural sectional view showing a method of manufacturing a GaN-based semiconductor laser according to an embodiment of the present invention in the order of steps;

FIG. 4 is a structural sectional view showing a method of manufacturing a GaN-based semiconductor laser according to an embodiment of the present invention in the order of steps;

FIG. 5 is a structural cross-sectional view showing a method of manufacturing a GaN-based semiconductor laser according to an embodiment of the present invention in the order of steps;

FIG. 6 is a diagram for illustrating the effect of the present invention, showing a state in which a GaN single crystal grows in the second growth.

FIG. 7 is a cross-sectional view of a device of a conventional GaN-based quantum well semiconductor laser.

[Explanation of symbols]

Reference Signs List 101 n-type SiC substrate 102 AlN buffer layer 103 n-type GaN layer 104 TiN film 105 SiN _x film 106 air gap 107 n-type GaN layer 108 n-Al _0.07 Ga _0.93 N cladding layer 109 n-GaN optical guiding layer 110 MQW active layer 111 p-GaN optical guide layer 112 p-Al _0.07 Ga _0.93 N cladding layer 113 p-GaN layer 114 insulating film 115 p electrode 116 n electrode 601 regrowth layer 602 polycrystal 603 region with many dislocations 604 region with reduced dislocation 701 Sapphire substrate 702 GaN layer 703 SiO ₂ 704 GaN layer 705 n-GaN layer 706 n-AlGaN cladding layer 707 n-GaN light guide layer 708 Active layer 709 p-GaN light guide layer 710 p-AlGaN cladding layer 711 p-GaN Contact layer 712 p electrode 713 SiO ₂ 714 n electrode

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Ryoko Miyanaga 1006 Kadoma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. 72) Inventor Yuzaburo Ban 1006 Kazuma Kadoma, Osaka Prefecture F-term (reference) 5F041 AA40 CA04 CA05 CA34 CA40 CA74 FF16 5F073 AA13 AA45 AA55 AA74 CA07 CB04 CB07 DA05 DA24 DA35 EA29

Claims (8)

[Claims] To 1. A conductive substrate _{Al u Ga v In w N (} u +
v depositing a + w = 1), forming a ridge by etching the Al _u Ga _v In _w N to reach the substrate into a concave shape, a step of covering at least the side surface of the ridge of a refractory conductive film , Al _u Ga _v in _w Al the C-plane of a region that is not covered with the conductive film of N as a seed crystal _x Ga _y I
_{n z N (x + y +} z = 1) A process for fabrication of a nitride semiconductor device and a step of growing a crystal. To 2. A conductive substrate _{Al u Ga v In w N (} u +
v depositing a _{+ w = 1), Al u} Ga v In a step of the _w N is etched to reach the substrate concavely to form the ridge to cover the side surfaces of the etched bottom surface and a ridge with a high melting point of the conductive film a step, a step of laminating Al _u Ga _v in _w N first cladding layer C surface area that is not covered with the conductive film as a seed crystal, the active layer, a second clad layer, conductive Forming a current confinement structure such that carriers are injected into the active layer above the conductive film. To 3. A conductive substrate _{Al u Ga v In w N (} u +
v depositing a + w = 1), a step of etching the Al _u Ga _v In _w N to reach the substrate concavely to form a ridge a resist as a mask, depositing a high melting point of the conductive film, removing the conductive film on the resist and the resist by a lift-off, Al _u Ga _v in
_{w The} part exposed on the surface of N is used as a seed crystal and
Regrowing a base crystal. 4. The method for manufacturing a nitride semiconductor device according to claim 1, wherein an upper portion of the high melting point conductive film is further covered with an amorphous insulating film. 5. The method for manufacturing a nitride-based semiconductor device according to claim 1, wherein electron cyclotron resonance (ECR) plasma is used as a method for depositing a conductive film having a high melting point. 6. The method for manufacturing a nitride-based semiconductor device according to claim 5, wherein ECR sputtering is used as a method for depositing the conductive film. 7. The method for manufacturing a nitride semiconductor device according to claim 1, wherein the conductive film contains Ti, Ta, or W. 8. The dielectric film is made of SiN _x , SiO ₂ , SiON,
Al ₂ O _3, a method of manufacturing a nitride-based semiconductor device according to claim 1, any three of which contain AlNO.