JP2005020027A - Process for producing gallium nitride based compound semiconductor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an efficient fabrication process in which element characteristics are enhanced by forming a gallium nitride based semiconductor layer free from a crack and a dislocation. <P>SOLUTION: An Al<SB>0.15</SB>Ga<SB>0.85</SB>N layer 2 is formed in stripe-like or lattice-like on a silicon substrate 1. A GaN layer 3 is grown on the exposed region A of the substrate 1 and on the upper region B of the layer 2. GaN is epitaxially grown three-dimensionally (not only in the vertical direction but also in the lateral direction) on the Al<SB>0.15</SB>Ga<SB>0.85</SB>N of the layer 2. Since GaN is grown epitaxially also in the lateral direction, a gallium nitride based semiconductor where dislocation is reduced significantly in the exposed region A of the substrate 1, i.e. the lateral growth direction, can be attained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to the general formula _{Al x Ga y In 1-xy} N (0 ≦ x ≦ 1,0 ≦ y ≦ 1,0 ≦ x + y ≦ 1) The gallium nitride-based compound semiconductor and a manufacturing method thereof. In particular, it relates to a method using lateral epitaxial growth (ELO) on a substrate.

  Gallium nitride compound semiconductors are direct-transition semiconductors whose emission spectrum covers a wide range from ultraviolet to red, and are applied to light-emitting elements such as light-emitting diodes (LEDs) and laser diodes (LDs). The gallium nitride compound semiconductor is usually formed on sapphire.

  However, in the above prior art, when a gallium nitride compound semiconductor is formed on a sapphire substrate, cracks and warpage occur in the semiconductor layer due to a difference in thermal expansion coefficient between sapphire and the gallium nitride compound semiconductor, and dislocation occurs due to a misfoot. For this reason, there is a problem that device characteristics are not good.

  Accordingly, an object of the present invention is to realize an efficient manufacturing method while improving element characteristics by forming a gallium nitride-based semiconductor layer free from cracks and dislocations in view of the above problems.

Means and effects for solving the problems

  In order to solve the above-mentioned problem, the means according to claim 1 is characterized in that the first gallium nitride-based compound semiconductor is formed on the substrate such as stripes or lattices so that the exposed portions of the substrate are scattered. After that, the first gallium nitride compound semiconductor in the island state is grown as a nucleus, but the substrate is not epitaxially grown with the exposed portion of the substrate as a nucleus, and is not chemically bonded to the exposed portion of the substrate. A method for producing a gallium nitride compound semiconductor is characterized in that a second gallium nitride compound semiconductor is grown and formed on the exposed surface of the substrate by lateral growth.

  Here, the lateral direction means the surface direction of the substrate. As a result, the second gallium nitride compound semiconductor does not grow on the exposed portion of the substrate, but grows three-dimensionally on the first gallium nitride compound semiconductor in the plane direction. Then it grows uniformly. As a result, dislocations based on misfit between the substrate and the gallium nitride compound semiconductor grow in the vertical direction and do not grow in the horizontal direction. Therefore, the threading dislocations in the vertical direction of the second gallium nitride compound semiconductor on the exposed portion of the substrate disappear, and the threading dislocations in the vertical direction remain only in the portion above the first gallium nitride compound semiconductor. As a result, the surface density of the threading dislocations in the vertical direction of the second gallium nitride compound semiconductor is extremely reduced. Accordingly, the crystallinity of the second gallium nitride compound semiconductor is improved. Further, since the exposed portion of the substrate and the second gallium nitride compound semiconductor thereabove are not chemically bonded, warpage of the second gallium nitride compound semiconductor is prevented and stress strain is applied to the semiconductor. Entering is suppressed.

  The invention of claim 2 is that the substrate is sapphire, silicon, or silicon carbide, and the crystallinity of the second gallium nitride compound semiconductor obtained on the substrate can be improved.

In the invention of claim 3, the substrate is silicon, the first gallium nitride compound semiconductor formed in an island state is a gallium nitride compound semiconductor containing aluminum, and the second gallium nitride compound semiconductor is aluminum. The method for producing a gallium nitride compound semiconductor according to claim 1, wherein the gallium nitride compound semiconductor does not contain gallium nitride.
A gallium nitride compound semiconductor containing aluminum is epitaxially grown on silicon, but a gallium nitride compound semiconductor containing no aluminum is not epitaxially grown on silicon. Accordingly, the island-shaped first gallium nitride compound semiconductor is formed on the silicon substrate, and then epitaxially grown on the first gallium nitride compound semiconductor, but not epitaxially grown on the exposed portion of the silicon substrate. The gallium nitride compound semiconductor can be formed. As a result, the second gallium nitride compound semiconductor is epitaxially grown in the lateral direction on the exposed portion of the silicon substrate with the first gallium nitride compound semiconductor as a nucleus, and the gallium nitride compound semiconductor having high crystallinity. Can be obtained.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described based on specific examples.
(First embodiment)
FIG. 1 is a schematic diagram showing a cross-sectional structure of a gallium nitride compound semiconductor according to the first embodiment of the present invention. On the silicon substrate 1, an Al _0.15 Ga _0.85 N layer (first gallium nitride compound semiconductor) 2 having a thickness of about 1000 mm is formed in a stripe shape (FIG. 1B) or a lattice shape (FIG. 1C). Is formed. A GaN layer (second gallium nitride compound semiconductor) 3 having a thickness of about 10 μm is formed in the exposed region A excluding the layer 2 on the silicon substrate 1 and the upper surface region B of the layer 2.

Next, a method for manufacturing this GaN-based compound semiconductor will be described.
This semiconductor was manufactured by sputtering and metal organic vapor phase epitaxy (hereinafter abbreviated as “MOVPE”). The gases used in MOVPE are ammonia (NH ₃ ), carrier gas (H ₂ , N ₂ ), trimethyl gallium (Ga (CH ₃ ) ₃ ) (hereinafter referred to as “TMG”), trimethyl aluminum (Al (CH _{3 3} ) (hereinafter referred to as “TMA”).

First, an n-silicon substrate 1 having a (111) plane, a (100) plane, or a (110) plane as a principal plane cleaned with a hydrofluoric acid solution (HF: H ₂ O = 1: 1) is converted into MOVPE. It is attached to a susceptor placed in the reaction chamber of the apparatus. Next, the substrate 1 was baked at a temperature of 1150 ° C. while flowing H ₂ at normal pressure at a flow rate of 2 liter / min for about 10 minutes in the reaction chamber.

Thereafter, the temperature of the substrate 1 is maintained at 1150 ° C., N ₂ or H ₂ is 10 liter / min, NH ₃ is 10 liter / min, TMG is 1.0 × 10 ⁻⁴ mol / min, trimethylaluminum (Al (CH ₃ ) ₃ ) (hereinafter referred to as “TMA”) is supplied at 1.0 × 10 ⁻⁵ mol / min and silane diluted to 0.86 ppm with H ₂ gas at 20 × 10 ⁻⁸ mol / min. An Al _0.15 Ga _0.85 N layer 2 having a concentration of 1.0 × 10 ¹⁸ / cm ³ was formed.

Next, an SiO ₂ layer was uniformly formed on the layer 2 to a thickness of about 2000 mm by sputtering, a resist was applied, and the SiO ₂ layer was etched into a predetermined shape by photolithography. Next, the Al _0.15 Ga _0.85 N layer 2 was dry etched using the SiO ₂ layer having the predetermined shape as a mask. In this way, a stripe shape (FIG. 1 (b)) or a lattice shape (FIG. 1 (c)) in which the width b of the upper region B of the layer 2 is about 5 μm and the distance a between the exposed regions A of the substrate 1 is about 5 μm. Formed.

Next, the temperature of the substrate 1 is set to 1100 ° C. by the MOVPE method, N ₂ or H ₂ is 20 liter / min, NH ₃ is 10 liter / min, TMG is 1.0 × 10 ⁻⁴ mol / min, and H ₂ gas is 0.86 ppm. Diluted silane was supplied at 20 × 10 ⁻⁸ mol / min to epitaxially grow a GaN layer 3 having a thickness of about 10 μm. At this time, GaN is epitaxially grown on the Al _0.15 Ga _0.85 N layer 2 using the Al _0.15 Ga _0.85 N as a nucleus. However, GaN does not grow epitaxially on the exposed region A of the silicon substrate 1. In the exposed region A of the silicon substrate 1, GaN grows epitaxially in the lateral direction, that is, along the surface direction of the silicon substrate 1 with GaN grown on the Al _0.15 Ga _0.85 N layer 2 as a nucleus. In the GaN layer 3, dislocation occurs in the vertical direction only in the upper region B of the Al _0.15 Ga _0.85 N layer 2, and in the exposed region A of the silicon substrate 1, dislocation does not occur because of lateral epitaxial growth. By making the area of the exposed region A of the silicon substrate 1 larger than the area of the upper region B of the Al _0.15 Ga _0.85 N layer 2, the GaN layer 3 having good crystallinity can be formed over a wide area. . Further, since the silicon substrate 1 and the GaN on the silicon substrate 1 are not chemically bonded, warpage and stress strain of the GaN layer 3 can be greatly reduced.

In the above embodiment, the width “a” of the exposed region A of the silicon substrate 1 formed in a stripe shape or a lattice shape is about 5 μm. However, if the width “a” of the exposed region A exceeds 10 μm, the lateral growth is long. Time is required, and if the width a of the exposed region A of the silicon substrate 1 is less than 1 μm, it becomes difficult to form a good GaN film. Therefore, the range of 1 to 10 μm is desirable. The width b of the upper region B of the Al _0.15 Ga _0.85 N layer 2 is 5 μm. However, if the width b of the upper region B of the Al _0.15 Ga _0.85 N layer 2 exceeds 10 μm, the probability of dislocation generation increases. If the width b of the region B is less than 1 μm, nucleation for lateral growth cannot be performed well, and therefore lateral epitaxial growth with good crystallinity becomes difficult. Therefore, the range of 1 to 10 μm is desirable. Further, from the viewpoint of the crystallinity of the layer 3, the ratio a / b of the width a of the exposed region A of the silicon substrate 1 to the width b of the upper region B of the Al _0.15 Ga _0.85 N layer 2 is preferably 1 to 10.

In the above embodiment, a silicon substrate is used, but other conductive substrates, sapphire substrates, silicon carbide, and the like can be used. In the case of using a conductive substrate, electrodes can be formed on the back surface of the substrate and the uppermost layer of the element layer formed on the substrate so that a current can flow perpendicularly to the substrate surface. Current supply efficiency is improved.
In this example, the composition of the layer 2 was Al _0.15 Ga _0.85 N, but the general formula Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1,0 ≦ y ≦ 1,0 ≦ x A gallium nitride compound semiconductor of + y ≦ 1) can be used. In order to perform epitaxial growth on the silicon substrate 1, Al _x Ga _1-x N (0 <x ≦ 1) (including AlN) is desirable. The layer 3 uses general formula _{Al x Ga y In 1-xy} N (0 ≦ x ≦ 1,0 ≦ y ≦ 1,0 ≦ x + y ≦ 1) The gallium nitride-based compound semiconductor of any composition ratio The composition ratio may be the same as that of the layer 2 or may be a different composition ratio. However, it is necessary to set the composition ratio so as not to epitaxially grow with respect to the substrate.
In this embodiment, the thickness of the layer 2 is about 1000 mm. However, if the layer 2 is thick, cracks increase. If the layer 2 is thin, the layer 3 does not grow using the layer 2 as a nucleus. Therefore, the thickness of the layer 2 is desirably 500 mm to 2000 mm.

(Second embodiment)
In the first embodiment described above, only one Al _0.15 Ga _0.85 N layer 2 is provided as the first gallium nitride compound semiconductor. The present embodiment is characterized in that the first gallium nitride compound semiconductor is formed of two layers of an Al _0.15 Ga _0.85 N layer 21 and a GaN layer 22 thereon.

FIG. 2 is a schematic diagram showing a cross-sectional structure of a gallium nitride compound semiconductor according to the second embodiment of the present invention. An Al _0.15 Ga _0.85 N layer 21 having a thickness of about 1000 mm is formed on the silicon substrate 1, and a GaN layer 22 having a thickness of about 1000 mm is formed on the layer 21. The layer 21 and the layer 22 constitute a first gallium nitride compound semiconductor. These layers 21 and 22 are formed in a stripe shape or a lattice shape as in the first embodiment. A GaN layer 3 having a thickness of about 10 μm is formed on the layer 22 and the exposed region A of the silicon substrate 1.

In the gallium nitride compound semiconductor of the second embodiment, the layer 21 and the layer 22 are uniformly formed on the silicon substrate 1 in the first embodiment, and then the SiO ₂ layer having a predetermined pattern is used as a mask. As shown in FIG. 1B or 1C, the layer 22 is formed into a stripe shape or a lattice shape by dry etching. Subsequent formation of the GaN layer 3 is the same as in the first embodiment.

  The growth process of the GaN layer 3 having a thickness of about 10 μm is as follows. GaN grows in a direction perpendicular to the surface with GaN in the upper region B of the GaN layer 22 as a nucleus. In the exposed region A of the silicon substrate 1, GaN grows epitaxially in the lateral direction with GaN grown on the exposed region B of the layer 22 as a nucleus. Thus, in this embodiment, GaN epitaxially grows in the vertical and horizontal directions with GaN as the nucleus, so that GaN having higher crystallinity than that in the first embodiment can be obtained.

In the present embodiment has the GaN and a layer 22 and the layer 3, typically a layer 22 and the layer 3 having the same composition ratio formula _{Al x Ga y In 1-xy} N (0 ≦ x ≦ 1,0 ≦ A gallium nitride compound semiconductor of y ≦ 1,0 ≦ x + y ≦ 1) may be used. However, the layer 3 needs to have a composition ratio that does not grow epitaxially with respect to the substrate. When silicon is used for the substrate, a gallium nitride compound semiconductor that does not contain Al is preferably used. Of course, the composition ratio between the layer 22 and the layer 3 may be changed.

In all the above embodiments, the dislocation-free GaN substrate can be obtained by removing the silicon substrate 1 or the portion C from the silicon substrate 1 to the layer 2 or the layer 22 by polishing or etching. In all the above embodiments, GaN is used for the layer 3, but InGaN having an arbitrary composition ratio may be used. Further, a semiconductor layer of another material may be formed on the layer 3. In particular, by further growing a gallium nitride-based compound semiconductor, an element having good characteristics such as a light emitting diode and a laser can be obtained.
In all the embodiments described above, an AlGaN buffer layer or an AlGaInN buffer layer having an arbitrary composition ratio may be provided between the substrate 1 and the layer 2 or the layer 22. This buffer layer has a crystal structure such as an amorphous form formed at a temperature lower than the single crystal growth temperature of the layers 2 and 22 or an amorphous structure in which microcrystals are mixed.

As the element layer, a light emitting diode or laser having a quantum structure such as SQW or MQW can be formed.
In all the above examples, the MOVPE method was performed in a normal pressure atmosphere, but may be performed under reduced pressure growth. Moreover, you may carry out by the combination of a normal pressure and pressure reduction.
The GaN-based compound semiconductor obtained in the present invention can be used for a light emitting device such as an LED or LD, and can also be used for a light receiving device and an electronic device.

Industrial application fields

  The present invention can provide a semiconductor with improved device characteristics.

1 is a schematic cross-sectional view showing the structure of a gallium nitride compound semiconductor according to a first specific example of the present invention. The typical sectional view showing the structure of the gallium nitride compound semiconductor concerning the concrete 2nd example of the present invention.

Explanation of symbols

1 Silicon substrate 2 Al _0.15 Ga _0.85 N layer (first gallium nitride compound semiconductor)
3 GaN layer (second gallium nitride compound semiconductor)
21 Al _0.15 Ga _0.85 N layer (first gallium nitride compound semiconductor)
22 GaN layer (first gallium nitride compound semiconductor)

Claims (3)

A first gallium nitride compound semiconductor is formed in an island state such as a stripe shape or a lattice shape on the substrate so that the exposed portions of the substrate are scattered, and then the first gallium nitride system in the island state is formed. Growing a compound semiconductor as a nucleus, growing a second gallium nitride compound semiconductor that is not epitaxially grown using the exposed portion of the substrate as a nucleus and is not chemically bonded to the exposed portion of the substrate, and the substrate A method for producing a gallium nitride-based compound semiconductor, comprising forming the exposed surface by lateral growth. The gallium nitride compound semiconductor manufacturing method according to claim 1, wherein the substrate is sapphire, silicon, or silicon carbide. The substrate is silicon, the first gallium nitride compound semiconductor formed in the island state is a gallium nitride compound semiconductor containing aluminum, and the second gallium nitride compound semiconductor does not contain aluminum. 2. The method for producing a gallium nitride compound semiconductor according to claim 1, wherein the gallium nitride compound semiconductor is a gallium nitride compound semiconductor.