JP2000174393A - Group iii nitride semiconductor, its manufacture and group iii nitride semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a III nitride semiconductor device having an epitaxial layer which has less through dislocation and does not have cracks and whose thickness is not less than 1 μm on a Si substrate, and to provide a, and the manufacturing method thereof. SOLUTION: In a III nitride semiconductor, masks 3m are locally formed on a semiconductor substrate 1 or a first III nitride semiconductor layer 2b formed of Alx Gay In1-x-yN (0<=x and y and 0<=x+y<=1), and a second III nitride semiconductor layer 4 formed of AlxGayIn1-x-yN (0<=x and y and 0<=x+y<=1) is stacked. The masks are formed by using a material whose surface energy is lower than nitride oxide or silicon nitride.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION A group III nitride semiconductor obtained by epitaxially growing a group III nitride on a substrate, and its selective growth or ELO (epitaxy of lateral over growt).
h) including manufacturing method and including laser diode II
The present invention relates to a group I nitride semiconductor device.

[0002]

2. Description of the Related Art A direct transition and optical energy gap
Al controllable in the range of 1.6 to 6.2 eV_xGa_yI
n_1-xySemiconductor lasers and light emitting diodes using N-based materials
Mode is being prototyped. Al_xGa_yIn_1-xyN-based material
The above-mentioned light-emitting device using a material has a lattice and a coefficient of thermal expansion.
Mainly sapphire substrate and spinel
(MgAl_TwoO_Four) Substrates are widely used. Soshi
And add silicon (Si) and magnesium (Mg)
Control of n-type and p-type by controlling_xGa _y
In_1-xyLight by changing the value of x and y in N
Control of chemical energy gap and double heterogeneity
A laser diode having a (DH) structure has been prototyped. I
However, since an insulating substrate is used, take electrodes on the back of the substrate.
Not attachable, and silicon carbide (SiC) groups
Prototype laser with double heterostructure (DH) using plate
However, there are problems such as the SiC substrate being expensive.
You.

As a countermeasure, the most common and inexpensive Si
Although it is desired to form a DH structure made of a group III nitride such as GaN on a substrate, cracks occur when an epitaxial film having a thickness of 1 μm or more is grown. Si
The following two points can be considered as causes of the breakage of the epitaxial layer made of the group III nitride when the DH structure made of the group III nitride is formed on the substrate.

1) Since the lattice constant of Si is 0.5431 nm, the atomic spacing on the Si (1,1,1) plane is 0.3840 nm (= 5.43 nm).
1 / √2). In contrast, the lattice constant of GaN is 0.
Since it is 3189 nm, the lattice spacing of GaN is smaller than that of GaN, there is about 17% lattice mismatch, and tensile stress is generated in the GaN film heteroepitaxially grown on the Si (1,1,1) plane.

2) The linear expansion coefficient of Si is 2.6 × 10 ^-6 K ^-1
On the other hand, GaN is as large as 5.6 × 10 ⁻⁶ K ^−1, and the shrinkage of GaN when the temperature is lowered is larger. When the temperature is lowered from the growth temperature to room temperature, tensile stress is generated in GaN.

This problem is the same even when a GaN thick film is grown on a sapphire substrate. The sapphire substrate is better than Si in lattice matching with GaN and matching in linear expansion coefficient, but has a tens of μm or more Ga
When an N thick film is formed, cracks occur as in the case of growth on a Si substrate.

However, recently, on a sapphire substrate, Si
ELO (epitaxy of lateral ove) using O ₂ as a mask
A growth-free GaN thick film having a thickness of about 100 μm due to growth has been reported. This is interpreted that the crystal defects are reduced by the ELO growth, so that cracks are hardly formed.

Further, threading dislocations are generated in a GaN epitaxial film directly epitaxially grown on a Si substrate due to a lattice mismatch between the Si substrate and the GaN layer, thereby deteriorating device characteristics.

[0009]

However, as a mechanism of ELO growth, chemical decomposition is not performed on a material such as SiO ₂ or SiN which has few dangling bonds on the surface. Therefore, this growth method uses MOCVD or MOMBE. It is estimated that the method is effective only for chemical growth methods such as MBE (Electron Beam Epitaxy) or vapor deposition which directly supplies a metal vapor.

An object of the present invention is to prevent cracking even when a thick epitaxial layer having a thickness of 1 μm or more is grown,
Another object of the present invention is to provide a III nitride semiconductor having few threading dislocations on a Si substrate, and to provide a method for manufacturing such a III nitride semiconductor.

[0011]

Means for Solving the Problems To achieve the above object,
Al on the semiconductor substrate or on the semiconductor substrate_xGa
_yIn_1-xyN (where 0 ≦ x, y and 0 ≦ x + y ≦
1) forming a mask on the first group III nitride semiconductor layer
Are locally formed, and Al_xGa _yIn
_1-xyN (however, 0 ≦ x, y and 0 ≦ x + y ≦ 1)
Formed by stacking a second group III nitride semiconductor layer
In the group nitride semiconductor, the mask is silicon oxide or
Is made of a material with lower surface energy than silicon nitride.
And

The material having a low surface energy is at least calcium fluoride (CaF ₂ ), barium fluoride (BaF ₂ ) or strontium fluoride (SrF ₂ ).
Any of the group II fluorides is preferred. Preferably, the semiconductor substrate is a silicon substrate having a surface orientation of (1,1,1), and the mask is a strip having sides parallel to the <1,1,0> direction of the silicon substrate.

On a semiconductor substrate or on a semiconductor substrate
_{l x Ga y In 1-xy} N ( where, 0 ≦ x, y, and 0 ≦
x + y ≦ 1), a mask is locally formed on the first group III nitride semiconductor layer, and Al _x G
a _y In _1-xy N (where 0 ≦ x, y and 0 ≦ x + y
.Ltoreq.1), wherein the second group III nitride semiconductor layer is laminated, and the second group III nitride semiconductor layer is MOCVD, MOMB
It is preferable to perform ELO growth by E, MBE or vapor deposition.

Preferably, the group II fluoride layer is formed by sputtering using a group II fluoride as a target. The group II fluoride layer mask is preferably formed by etching with hydrofluoric acid.

In the above-described group III nitride semiconductor device using a group III nitride semiconductor using a silicon substrate,
The group III nitride semiconductor device is preferably a laser diode. Since the surface energy of the group II fluoride used for the group III nitride semiconductor according to the present invention is lower than that of silicon oxide or silicon nitride, selective growth of the group III nitride semiconductor can be performed excellently as follows. .

Generally, on a material having a low surface energy,
When a substance having a higher surface energy is deposited, aggregation occurs due to a difference in surface energy during the deposition process. This is the same phenomenon that occurs when water is dropped on oil. In the case of growing a group III nitride semiconductor according to the present invention, a group III nitride semiconductor is formed thinly on a Si substrate, and a material (group II fluoride) mask having a small surface energy is locally formed thereon. . By locally forming, an exposed portion of the group III nitride semiconductor is formed on the surface. Thereafter, when a group III nitride semiconductor is formed again,
On materials with low surface energy, the water is just repelled, so it is selectively grown only on the exposed parts.

Since the surface energy of Group II fluoride is lower than that of silicon oxide or silicon nitride, MOCVD or MO
ELO or selective growth can be performed by MBE (molecular metal epitaxy) or MBE (molecular beam epitaxy) or vapor deposition, which cannot be performed selectively using silicon oxide or silicon nitride as a mask, as well as MBE (organic metal molecular beam epitaxy).

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a cross-sectional view perpendicular to the substrate surface of a III nitride semiconductor showing a manufacturing process according to the present invention.
(B) After forming the mask and (c) after forming the III nitride layer.

The substrate surface of the Si substrate 1 is {1,1,1},
The cross section is the {1,0,0} plane of the Si substrate. First, the Si substrate
AlN buffer layer 2a next to MBN 10
Then, a base GaN 2b was formed (FIG. 1A). Deposition conditions
Is as follows. Maintain substrate temperature at 600 ℃
Simultaneous irradiation of nitrogen radicals and supply of Al vapor
An AlN buffer layer 2a having a thickness of 20 nm was formed. This and
Nitrogen radicals to prevent nitridation of the Si substrate surface.
Should not be delayed from the start of Al supply. next
Raise the substrate temperature to 800 ℃, nitrogen radicals and Ga vapor
(The vapor pressure is 1 × 10 ^-FourPa) and supply a thickness of 300
A base GaN 2b of nm was formed.

Thereafter, the substrate temperature is lowered to 500 ° C.
A CaF ₂ layer 3 having a thickness of 100 nm was formed by sputtering using F ₂ as a target. And take out the board once,
A pattern was formed by photolithography, and a strip-shaped CaF ₂ mask 3m was formed with a hydrofluoric acid solution. (Figure 1
(B)) Finally, a GaN III nitride layer 4 was formed by MBE. The GaN growth conditions at this time were the same as those of the underlying layer GaN. When the growth was performed to a thickness of about 4 μm, an epitaxial layer (III nitride 4) having a smooth surface without a step at the end of the mask was obtained.

When MBE was directly grown on a Si substrate as in the prior art, the thickness of 1 μm was at the limit where cracks did not occur, and the density of threading dislocation was about 10 ¹⁰ / cm ^2. In the example, no crack was generated even when a 4 μm thick film was grown, and the density of threading dislocations was reduced to about 10 ⁷ / cm ^2, which was about 1/1000 of the conventional value. Example 2 ELO growth was performed under the same conditions as in Example 1, except that the mask material in Example 1 was changed from CaF ₂ to SrF ₂ or BaF _2.
An epitaxial layer having a smooth surface and a small density of threading dislocation was obtained up to about μm. Example 3 The method of epitaxial growth of III nitride in Example 1 was changed from MBE to MOCVD. Like the MBE, a crack-free epitaxial layer could be formed on the Si (1,1,1) plane substrate. Example 4 The epitaxial growth of Example 1 was applied to a prototype laser diode.

FIG. 2 shows a Si substrate and CaF_TwoStrip mask
It is a perspective view which shows the relationship of. CaF _TwoThe strip-shaped mask
The longitudinal direction N of 3 m is flat in the <1 / 2,1 / 2,1> direction of the Si substrate 1.
Of Si that matches the GaN cleavage direction <2,1,1,0>
It is perpendicular to the cleavage direction <1,1,0>. Mask width is 2 μ
m and the mask interval were 10 μm.

A double heterostructure was fabricated by epitaxial growth on the layer grown by ELO in this manner, and a laser having an external constriction structure was fabricated. FIG. 3 is a sectional view of a laser diode manufactured by the method for producing a III nitride according to the present invention. AlN buffer layer 2a and GaN layer 2
The contact layer 4a is made of a 300 nm thick underlayer made of Eb and a 5 μm thick ELO-grown GaN layer.
μm AlGaN n-cladding layer 4b, 50 nm thick G
An active layer 4c of an aInN layer, a p-cladding layer 4d of an AlGaN layer having a thickness of 0.5 μm, and a GaN layer having a thickness of 0.5 μm were sequentially laminated as a p-cap layer 4e. Then, after forming a current blocking layer 5 of SiO _{2 at} a spacing of 5 μm on the p cap layer 4e (the spacing of the current blocking layer is located at the center of the mask spacing), an upper electrode 6a made of Au / Ni is formed. hand,
An external current confinement structure was constructed. Al / T on back side of substrate
A lower electrode 6b made of i was formed.

In such a structure, the laser stripe direction perpendicular to the cleavage plane of the III nitride layer and the strip-shaped mask 3 m
Since the longitudinal directions are parallel to each other, it is possible to set the stripe so as to be located at a portion without the mask 3m made of CaF ₂ , and it is possible to manufacture a laser diode having a cleavage plane as an optical resonator surface. The current was able to flow from the upper electrode 6a to the lower electrode 6b on the substrate side without being interrupted by the mask 3m.

[0025]

According to the present invention, on a semiconductor substrate, or on a semiconductor substrate _{Al x Ga y In 1- xy N} ( where 0
≦ x, y, and the 0 ≦ x + y ≦ 1) a first group III nitride semiconductor layer made of, locally forming a mask, further _{Al x Ga y In 1-xy} N ( where, 0 ≦ x , Y, and 0
In ≦ x + y ≦ 1) second formed by laminating a Group III nitride Hanshirubeso III group nitride semiconductor formed of a low surface energy than silicon oxide or silicon nitride the mask, CaF _2, BaF ₂ or such as SrF _2,
The second group III nitride semiconductor layer can be laminated by MBE or vapor deposition, which was not possible with a silicon oxide or silicon nitride mask because the material was made of a material. The threading dislocation density in the conductive layer is low, and a thick film of several μm or more can be obtained.

Further, a laser diode having a cleavage plane as an optical resonator plane can be manufactured by using a group III nitride semiconductor layer in which Si is formed on a substrate.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view perpendicular to the substrate surface of a III-nitride semiconductor showing a manufacturing process according to the present invention.
(B) After forming the mask and (c) after forming the III nitride layer.

FIG. 2 is a perspective view showing a relationship between a Si substrate and a strip mask of CaF ₂ .

FIG. 3 is a cross-sectional view of a laser diode manufactured by a method for manufacturing a III nitride according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 silicon substrate 2 base layer 2a buffer layer 2b base GaN layer 3m mask 4III nitride layer 4a contact layer 4b n clad layer 4c active layer 4d p clad layer 4e p cap layer 5 external constriction layer 6a upper electrode 6b lower electrode

Claims (7)

[Claims] 1. A semiconductor device comprising: a semiconductor substrate;
_{l x Ga y In 1-x-} y N ( where, 0 ≦ x, y, and 0 ≦
x + y ≦ 1), a mask is locally formed on the first group III nitride semiconductor layer, and Al _x G
a _y In _1-xy N (where 0 ≦ x, y and 0 ≦ x + y
.Ltoreq.1), wherein the mask is made of a material having a lower surface energy than silicon oxide or silicon nitride. Nitride semiconductor. 2. The material having a low surface energy is at least calcium fluoride (CaF ₂ ), barium fluoride (BaF ₂ ) or strontium fluoride (SrF ₂ ).
The group III nitride semiconductor according to claim 1, wherein the group III nitride is any one of the group II fluorides. 3. The semiconductor substrate has a surface orientation of (1,1,1).
3. The group III nitride semiconductor according to claim 2, wherein the mask has a strip shape having sides parallel to the <1,1,0> direction of the silicon substrate. 4. 4. A semiconductor device comprising: a semiconductor substrate;
_{l x Ga y In 1-x-} y N ( where, 0 ≦ x, y, and 0 ≦
x + y ≦ 1), a mask is locally formed on the first group III nitride semiconductor layer, and Al _x G
a _y In _1-xy N (where 0 ≦ x, y and 0 ≦ x + y
4. The method of manufacturing a group III nitride semiconductor according to claim 1, wherein a second group III nitride semiconductor layer satisfying ≦ 1) is laminated. 5. MO
ELO by CVD, MOMBE, MBE or evaporation
A method for producing a group III nitride semiconductor, which is grown. 5. The group III nitride semiconductor device according to claim 4, wherein said group II fluoride layer is formed by sputtering using a group II fluoride as a target. 6. The method according to claim 5, wherein the mask of the group II fluoride layer is formed by etching with hydrofluoric acid. 7. A group III nitride semiconductor device using a group III nitride semiconductor according to claim 3, wherein said group III nitride semiconductor device is a laser diode. .