JPH07201745A - Semiconductor wafer and its manufacture - Google Patents

Abstract

PURPOSE:To notably improve the purity and crystallizability of GaN epitaxial crystal while manufacturing high concentration p type GaN in as grown state by tilting the deposited surface of (0001) surfaced sapphire substrate. CONSTITUTION:Fine oblique (0001) surfaced sapphire single crystal substrate 4 can be formed by mirror polishing the (0001) surface of tilted by several degrees in (21*1*0) direction or (011*0) direction. At this time, numerous steps 6 exist on the fine oblique (0001) surface 5. Accordingly, the step flow mode deposition of GaN epitaxial crystal 2 using the step end as the cardinal point can be easily attained thereby enabling the crystalline defects to be notably diminished.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor wafer in which a nitride thin film crystal of Ga, Al, In or the like is formed on a sapphire crystal substrate and a method for manufacturing the semiconductor wafer.

[0002]

LE based on GaN and related compounds
It is expected that devices such as D, LD and HEMT will be realized.

GaN, AlN and InN are epitaxially grown on the C-face of a sapphire single crystal, that is, on the mirror-polished face of the (0001) face.

Epitaxial growth is mainly carried out by vapor phase growth. In particular, metalorganic vapor phase epitaxy (MO
Although the VPE) method is often used, a chemical vapor phase epitaxy (VPE) method, a molecular beam epitaxy (MBE) method, or a method using photoexcitation or plasma for these methods is also used.

In the MOVPE method, the sapphire single crystal substrate described above is heated to about 1000 ° C. in a hydrogen or nitrogen atmosphere, and a gas of trimethylgallium (TMG) and ammonia (NH ₃ ) is flowed to form an epitaxial thin film of GaN. Growing.

In the case of AlN or InN, trimethylaluminum (TMA) or trimethylindium (TMI) is made to flow instead of TMG for growth.

Conventionally, AlN or Ga is formed on a sapphire substrate.
A thin film of N of about 100 to 1000 A is grown at a low temperature of about 600 ° C. This is heated to about 1000 ° C. and heat-treated, and then GaN is grown at that temperature to obtain G
It has been reported that the quality of the aN layer is improved, and an n-type undoped GaN epitaxial crystal having a carrier concentration of about 4 × 10 ¹⁶ to 2 × 10 ¹⁷ cm ⁻³ has been obtained (known examples 1 and 2). .

Further, zinc (Zn) and magnesium (M
g) added GaN is irradiated with an electron beam (known examples 1 and 3) or annealed in an inert gas (known example 4) to obtain 1 × 10 ^{17 to} 6 × 10 ¹⁸ cm ⁻³ A p-type GaN epitaxial crystal having a carrier concentration has been obtained.

Publicly known example 1: "Electronic material technology for high-intensity blue light emission, edited by Taguchi, P51-58, December 1991 (Science Forum)" Publicly known example 2: S.I. NAKAMURA: J. J. A. P. V
OL30, No10A, 1991, ppL1705-L
1707 Known Example 3: S. NAKAMURA: J. J. A. P. V
OL30, No10A, 1991, ppL1708 to L
1711 Known Example 4: S. NAKAMURA: J. J. A. P. v
ol31, (1992) pp1258-11266 P
art1, No. 5A

[0010]

The GaN crystal grown by the above-mentioned conventional method is still insufficient in purity and crystallinity even if a low temperature growth buffer layer is interposed.

On the other hand, high-concentration n-type GaN (here, high-concentration means a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ or more) epitaxial crystal is easily obtained by Si doping or the like. Although high-concentration p-type GaN epitaxial crystals have been experimentally obtained in part by electron beam irradiation and post-growth heat treatment, until they are easily obtained in the so-called as-grown state without these post-treatments. I have not caught up with.

The inventors of the present invention have not yet studied the growth surface of the substrate, and the quality of the substrate has been improved only by using the non-tilted (0001) plane sapphire substrate to improve the epitaxial growth method and post-process the grown crystal. Focusing on the point that the improvement was made, and from a different viewpoint, the inventors conducted a diligent examination of the growth surface of the substrate. As a result, they found that tilting the growth surface significantly improves the quality.

Therefore, the object of the present invention is to solve the above-mentioned problems of the prior art by tilting the growth surface, to greatly improve the purity and crystallinity, and to enable high-concentration p-type doping. And related compounds (AlN,
It is to provide a semiconductor wafer of InN and a mixed crystal of these and GaN) and a method for manufacturing the same.

[0014]

The present invention uses, as a substrate for epitaxially growing GaN or the like, a so-called slightly inclined surface substrate obtained by mirror-polishing a (0001) surface of a sapphire single crystal substrate with a predetermined crystal axis tilted. There is. By epitaxially growing GaN or the like on this slightly inclined (0001) plane, a high-quality epitaxial crystal of high-concentration p-type GaN and related compounds is realized.

That is, the semiconductor wafer of the present invention is (0
001) plane in <21 * 1 * 0> direction or <011 *
On the slightly inclined (0001) plane of the sapphire crystal substrate having a mirror surface slightly inclined in the 0> direction, gallium nitride (Ga
N), aluminum nitride (AlN), indium nitride (InN), or a mixed crystal of p-type, n-type, or i-type thin film in a single-layer or multi-layer structure.

The semiconductor wafer of the present invention is (000
1) Face in <21 * 1 * 0> direction or <011 * 0>
On the sapphire (0001) plane of the sapphire crystal substrate having a mirror surface slightly inclined in the direction, a GaN buffer layer and a p-type Ga
A N-type layer and an n-type GaN layer are sequentially laminated to form a blue light emitting diode wafer.

Further, in the method for manufacturing a semiconductor wafer of the present invention, the (0001) plane of the sapphire single crystal substrate is mirror-polished with a slight inclination, and a single layer or a multi-layered epitaxial layer of the wafer is grown thereon. It is the one.

Further, according to the method of manufacturing a semiconductor wafer of the present invention, a buffer layer is grown on a sapphire crystal substrate, a p-type GaN layer and an n-type GaN layer are grown thereon, and a pn-structure GaN epitaxial crystal is grown. In a method of manufacturing a semiconductor wafer having a phase growth step, a (0001) plane is formed on a sapphire crystal substrate in a <21 * 1 * 0> direction or in a <21 * 1 * 0> direction.
This is a sapphire crystal substrate having a mirror surface of a surface slightly inclined in the 011 * 0> direction.

In these semiconductor wafers and the semiconductor wafer manufacturing method, it is preferable that the slight inclination angle is 2 ° to 10 °.

It is something.

[0021]

In the conventional GaN epitaxial crystal grown on the (0001) plane sapphire substrate, there are many vacancies from which nitrogen is removed and other crystal defects, which are undoped GaN.
It is considered that this is one of the reasons why the purity is poor and that p-type GaN cannot be easily obtained.

It is considered that these crystal defects occur during the epitaxial growth of crystals. That is, in the GaN / sapphire crystal, since the so-called heteroepitaxial growth in which the sapphire substrate and the GaN crystal have considerably different physical properties such as lattice constants, as shown in FIG. 3, the (0001) plane sapphire single crystal substrate 1 has a (0001) plane. It is considered that the GaN epitaxial crystal 2 that grows in No. 3 easily undergoes island-shaped three-dimensional growth, which easily causes the above defects.

On the other hand, GaAs on the GaAs substrate
In homoepitaxial growth, such as epitaxial growth, on the same type of substrate, the epitaxial growth mode is two-dimensional growth, so crystal defects are greatly reduced.

By the way, the above-mentioned low temperature grown AlN buffer and low temperature grown GaN buffer are considered to have the effect of promoting this two-dimensional growth, but they are still insufficient. In order to realize the two-dimensional growth, it is effective to set the growth mode to the step flow mode.

At this point, as shown in FIG. 1, when the slightly inclined (0001) plane sapphire single crystal substrate 4 of the present invention is used, many steps 6 are present in the slightly inclined (0001) plane 5, so that Step flow mode growth of the GaN epitaxial crystal 2 based on the step edge is easily realized.

Therefore, good quality Ga due to two-dimensional growth is obtained.
Crystals of N and related compounds can be obtained. Further, a high-concentration p-type GaN epitaxial crystal can be easily obtained in an as-grown state without post-treatment such as electron beam irradiation or heat treatment after growth, while the concentration of the n-type GaN epitaxial crystal can be further increased.

[0027]

EXAMPLES Examples of the semiconductor wafer of the present invention in which a nitride thin film crystal of Al, Ga or the like is vapor-phase formed on a sapphire single crystal substrate on a slightly inclined surface will be described below.

<Example 1> A sapphire single crystal substrate mirror-polished with a (0001) plane tilted in the <21 * 1 * 0> direction by 2 ° was set on a graphite susceptor in a reaction furnace of a MOVPE apparatus to obtain high purity. The inside of the furnace was purged by sufficiently flowing hydrogen.

Next, the substrate was heated to 1000 ° C. or higher by heating the susceptor while flowing hydrogen gas into the furnace, and held for 10 minutes or longer. After that, the substrate temperature is set to 600 ° C. and TMA
And NH ₃ were flown into the furnace to grow a so-called low temperature grown AlN buffer layer with a thickness of 50 nm.

Then, the supply of TMA to the furnace was stopped, the substrate was heated to 1030 ° C. with hydrogen and NH ₃ flowing, and then TMG was flown into the furnace to grow GaN to a thickness of 5 μm. When the electrical characteristics of this undoped GaN epitaxial crystal were measured by the Hall effect method, it was found to be n-type and the carrier concentration was about 5 × 10 ¹⁵ cm ^−3, showing a significant improvement in purity as compared with the conventional one.

During the growth, hydrogen, NH ₃ , TMG, T
MA flow rate is 10 l / min, 5 l / min, 3
cc / min and 0.8 cc / min.

<Embodiment 2> The (0001) plane is oriented in the <21 * 1 * 0> direction by 5 ° and 10 °.
When the same epitaxial growth as in Example 1 was evaluated using a tilted sapphire substrate, an undoped GaN crystal with a similar carrier concentration was obtained. The carrier concentration tended to decrease as the tilt angle increased.

<Embodiment 3> The (0001) plane is oriented in the <011 * 0> direction by 2 °, 5 ° 10
When the same epitaxial growth as in Example 1 was performed using a sapphire substrate tilted at an angle of 0, the same results as in Examples 1 and 2 were obtained.

Example 4 A GaN buffer layer was used instead of the AlN buffer layer used in Example 1 at 600 ° C. for 20 nm.
An undoped GaN crystal was grown under the same conditions as in Example 1 except for the growth. The carrier concentration of the undoped GaN epitaxial crystal was about 1 × 10 ¹⁵ cm ^{−3 in} n-type, and a crystal of higher purity than that of Example 1 was obtained.

<Embodiment 5> This embodiment is an LE shown in FIG.
It is an example of a pn junction GaN epitaxial crystal wafer for D. MOVPE was performed on GaN epitaxial crystals 7, 8 and 9 having a pn structure by using a slightly inclined (0001) plane sapphire single crystal substrate 4 having a plane obtained by tilting the (0001) plane by 2 ° in the <21 * 1 * 0> direction. Grew up by law.

In the same manner as in Example 1, the substrate 4 was heated at 1050 ° C. while flowing hydrogen gas to clean the surface. Next, the substrate temperature was lowered to 500 ° C. and hydrogen, TMG and NH ₃ were flown to grow the low temperature growth GaN buffer layer 7 to 25 nm. Next, while flowing hydrogen and NH ₃ , the substrate temperature is adjusted to 1030
The temperature was raised to ℃ and hydrogen, TMG, NH ₃ and biscyclopentadiethyl magnesium (CP ₂ Mg) were flown to grow the p-type GaN layer 8 to 2 μm.

Subsequently, hydrogen, TMG, NH ₃ and disilane (Si ₂ H ₆ ) were flown to grow the n-type GaN layer 9 to a thickness of 2 μm. Then, cool the crystal while flowing NH ₃ and hydrogen 60
When the temperature reached 0 ° C. to 800 ° C., the flow of hydrogen and NH ₃ was stopped, and instead, high-purity N ₂ gas was flowed to cool to room temperature.

Here, hydrogen, NH ₃ , TMG, CP ₂ M
The flow rate of g, Si ₂ H ₆ , and N ₂ is 20 l / mi.
n, 5 l / min, 1 cc / min, 2 cc / min,
1 × 10 ⁻⁴ cc / min and 20 l / min.

The carrier concentration of the grown crystal is n-type GaN.
Layer 9 is Si-doped with disilane, 5 × 10 ¹⁹ cm ⁻³ , p
The type GaN layer 8 was 1 × 10 ¹⁹ cm ⁻³ in the as-grown state, and both p-type GaN layer and n-type GaN layer having a much higher carrier concentration exceeding 1 × 10 ¹⁸ cm ⁻³ were obtained.

<Example 6> The growth and evaluation of Example 5 are described below.
The same results as in Example 5 were obtained when the substrate was tilted 5 ° and 10 ° in the 21 * 1 * 0> direction and the substrate was tilted 2 °, 5 ° and 10 ° in the <011 * 0> direction. I got the result.

<Other Embodiments> Incidentally, a slight inclination (0001)
As a crystal that can be grown on a plane sapphire single crystal substrate,
In addition to AlN and GaN, there are InN, a mixed crystal of these, and a multilayer structure epitaxial crystal containing these.

The epitaxial growth method uses MOVP.
Other than E, other vapor phase growth methods such as MBE and plasma CVD can be used.

Further, in place of the sapphire substrate, Ga using silicon carbide (SiC) or a silicon substrate is used.
Even in the epitaxial growth of N and related compounds, the growth on the slightly inclined surface of the present invention is possible, and the quality of the epitaxial crystal can be improved.

[0044]

【The invention's effect】

(1) According to the semiconductor wafer of the first aspect, it is possible to realize a high-quality GaN and related compound epitaxial crystal with few crystal defects.

(2) According to the semiconductor wafer of the second aspect, a blue light emitting diode with higher brightness can be manufactured.

(3) According to the semiconductor wafer manufacturing method of the third aspect, a high-quality semiconductor epitaxial layer with few crystal defects can be formed on the sapphire substrate.

(4) According to the method of manufacturing a semiconductor wafer of claim 4, p-type Ga having a high concentration in an as-grown state is obtained.
N can be easily realized.

(5) According to the invention described in claim 5, since the fine tilt angle is defined to be an optimum value, a high-quality GaN and related compound epitaxial crystal with fewer crystal defects can be realized.

[Brief description of drawings]

FIG. 1 is a schematic substrate growth cross-sectional view showing a two-dimensional growth mode (step flow mode) of a GaN epitaxial crystal on a slightly inclined (0001) plane sapphire substrate for explaining an embodiment of a semiconductor wafer of the present invention.

FIG. 2 is a cross-sectional view of an example of a pn junction GaN epitaxial crystal wafer for LEDs for explaining an example of a semiconductor wafer of the present invention.

FIG. 3 shows Ga on a conventional (0001) plane sapphire substrate.
FIG. 3 is a schematic diagram of a substrate growth cross section showing a three-dimensional growth mode of an N epitaxial crystal.

[Explanation of symbols]

 2 GaN epitaxial crystal 4 Slightly (0001) plane Sapphire single crystal substrate 5 Slightly (0001) plane 6 Step 7 Low temperature growth GaN buffer layer 8 p-type GaN layer 9 n-type GaN layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shoji Kuma 3550, Kidayomachi, Tsuchiura City, Ibaraki Prefecture Hitachi Cable Ltd. Advanced Research Center

Claims (5)

[Claims] 1. A mirror surface having a (0001) plane slightly inclined in the <21 * 1 * 0> (hereinafter, 1 * means 1 with a bar above) or <011 * 0> direction. Gallium nitride (GaN), aluminum nitride (AlN), indium nitride (InN), or a mixed crystal of p-type and n-type on the sapphire crystal substrate on the slightly inclined (0001) plane.
Type or i-type thin film single or multi-layered semiconductor wafer is laminated. 2. A sapphire crystal substrate having a mirror surface in which the (0001) plane is slightly tilted in the <21 * 1 * 0> direction or the <011 * 0> direction is provided with GaN.
A semiconductor wafer in which a buffer layer, a p-type GaN layer, and an n-type GaN layer are stacked. 3. A method for manufacturing a semiconductor wafer, which comprises mirror-polishing a (0001) plane of a sapphire crystal substrate while slightly tilting it, and growing an epitaxial layer having a semiconductor single layer or a multi-layer structure thereon. 4. A buffer layer is grown on a sapphire crystal substrate, and a p-type GaN layer and an n-type GaN layer are grown thereon to form a p-type GaN layer.
A method of manufacturing a semiconductor wafer having a step of vapor-phase growing an n-structure GaN epitaxial crystal, wherein a (0001) plane is <21 * on the sapphire crystal substrate.
A method of manufacturing a semiconductor wafer, which uses a sapphire crystal substrate having a mirror surface of a surface slightly inclined in the 1 * 0> direction or the <011 * 0> direction. 5. The semiconductor wafer according to claim 1 or 2, or the semiconductor wafer manufacturing method according to claim 3 or 4, wherein the fine tilt angle is in the range of 2 ° to 10 °.