JPH0864866A - Manufacture of semiconductor light emitting device - Google Patents

Abstract

PURPOSE: To provide a method for manufacturing a semiconductor light emitting device by which crystal defects and the dislocation caused by mismatching of lattice constants and a difference in a thermal expansion coefficient can be prevented and thereby the number of processes can be decreased. CONSTITUTION: A gallium nitride compound semiconductor layer which includes at least n-type layers 3, 4 and p-type layers 6, 7 and a light emitting section (active layer) 5 is deposited on a substrate 1. After that, an atmosphere is made into an N atmosphere and an ambient temperature is reduced to temperatures at which a GaAs compound semiconductor can be formed by vapor phase epitaxy and the n-type layers of the gallium nitride compound semiconductor layer can be annealed. Then, in the N atmosphere, an Mg-doped GaAs, GaP, InAs, or InP protective film 10 is formed on the surface of the gallium nitride compound semiconductor layer and at the same time, the p-type layers of the gallium nitride compound semiconductor layer are annealed and after that the protective film is removed by etching.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor light emitting device. More specifically, it relates to a method for manufacturing a semiconductor light emitting device using a gallium nitride based compound semiconductor suitable for blue light emission.

Here, a gallium nitride compound semiconductor is a compound of a group III element Ga and a group V element N or
A semiconductor made of a compound in which a part of Ga of the group III element is replaced with another group III element such as Al and In and / or a part of N of the group V element is replaced with another group V element such as P and As. Say.

A semiconductor light emitting device is a light emitting diode (hereinafter referred to as LED) having a double heterojunction such as a pn junction or a pin, a super luminescent diode (SLD) or a semiconductor laser diode (LD).
A semiconductor element that emits light.

[0004]

2. Description of the Related Art Conventionally, blue LEDs have a lower brightness than red and green and are difficult to put into practical use. In recent years, however, gallium nitride compound semiconductors have been used, and a low resistance p-type semiconductor layer doped with Mg has been formed. As a result, the brightness is improved and it is in the limelight.

L of a conventional gallium nitride-based compound semiconductor
The manufacturing method of the ED is performed in the following steps, and a perspective view of the completed gallium nitride based compound semiconductor LED is shown in FIG.

First, a substrate 21 made of sapphire (Al ₂ O ₃ single crystal) or the like is used at a low temperature of 400 to 700 ° C. at a low temperature of 400 to 700 ° C. with a carrier gas H ₂ together with a carrier gas H ₂ by an organometallic compound vapor phase growth method (hereinafter referred to as MOCVD method). Trimethylgallium (hereinafter referred to as TMG) which is a gas, ammonia (NH ₃ ) and SiH ₄ as a dopant are supplied to form a low temperature buffer layer 22 composed of an n-type GaN layer in a thickness of about 0.01 to 0.2 μm. , Then 700-12
The same gas is supplied at a high temperature of 00 ° C, and n-type Ga of the same composition is supplied.
The high temperature buffer layer 23 made of N is formed in a thickness of about 2 to 5 μm.

Then, a raw material gas of trimethylaluminum (hereinafter referred to as TMA) is further added to the above gas, and n
N _- type Al _x Ga _1-x N containing Si as a type dopant
A (0 <x <1) layer is formed, and an n-type cladding layer 24 for forming a double heterojunction is formed to have a thickness of about 0.1 to 0.3 μm.

Next, a material having a bandgap energy smaller than that of the clad layer, for example, trimethylindium (hereinafter, T
MI) is introduced, and Ga _y In _1-y N (0 <y ≦
The active layer 25 composed of 1) is formed to a thickness of about 0.05 to 0.1 μm.

Further, cyclopentadienylmagnesium for Mg or Zn as a p-type impurity (hereinafter, referred to as a p-type impurity by replacing SiH _{4 as an} impurity source gas with the same source gas as the gas used for forming the n-type cladding layer 24). Cp ₂ Mg) or dimethylzinc (hereinafter referred to as DMZn) is added to the reaction tube, and the p-type cladding layer 26 of p-type A
The l _x Ga _1-x N layer is vapor-grown. As a result, the n-type cladding layer 24, the active layer 25, and the p-type cladding layer 26 form a double heterojunction.

Next, to form the cap layer 27, a gas similar to that used for the buffer layer 23 is used as an impurity source gas, ie, C.
By supplying p ₂ Mg or DMZn, a p-type GaN layer is grown to about 0.1 to 2 μm.

After that, a protective film such as SiO ₂ or Si ₃ N ₄ is provided on the entire surface of the growth layer of the semiconductor layer, and 400 to 800
The p-type cladding layer 26 and the cap layer 27 are activated by annealing at 20 ° C. for 20 to 60 minutes. The reason why this annealing is performed is as follows. That is, the p-type layer of the gallium nitride based compound semiconductor is doped with Mg or the like as a dopant, but Mg or the like is mixed with H _{2 of} the carrier gas or H of NH ₃ of the reaction gas at the time of doping to change the dopant High resistance without working. Therefore, an annealing process is provided to separate Mg from H and release H to reduce the resistance.

After removing the protective film, a resist is applied and patterned to form an n-side electrode, and a part of each grown semiconductor layer is removed by dry etching to form an n-type GaN layer. A certain buffer layer 23 is exposed. Then, a metal film of Au, Al or the like is formed by sputtering or the like to form both p-side and n-side electrodes 29,
The LED chip is formed by forming 30 and dicing.

Next, in order to make ohmic contact between the electrode metal such as Al and the gallium nitride based compound semiconductor, heat treatment is performed at about 300 ° C. in an H ₂ atmosphere to form an alloy.

[0014]

In the conventional method for manufacturing a semiconductor light emitting device using a gallium nitride-based compound semiconductor, as described above, after providing a protective film such as SiO _{2 on} the surface of the semiconductor layer, annealing is performed. However, since a protective film such as SiO ₂ is formed by a CVD device different from the MOCVD device, the temperature must be temporarily lowered to room temperature after MOCVD, then replaced by the CVD device, and the temperature must be raised to about 300 ° C again. I have to. Moreover, the sapphire substrate and the gallium nitride-based compound semiconductor crystal have large differences in lattice constant and thermal expansion coefficient, and when temperature shocks are repeated at high temperature to return to room temperature, expansion and contraction are repeated, and the buffer in contact with the sapphire substrate is repeated. There is a problem that crystal defects such as cracks and dislocations are generated in the layer, and the crystal defects and dislocations propagate to the light emitting layer side to reduce the luminous efficiency and also reduce the life.

The present invention solves such a problem, suppresses the generation of crystal defects and dislocations due to the mismatch of lattice constants and the difference in thermal expansion coefficient, and can shorten the manufacturing process. The purpose is to provide a manufacturing method.

[0016]

According to the method of manufacturing a semiconductor light emitting device of the present invention, (a) a gallium nitride compound semiconductor layer having at least an n-type layer and a p-type layer on a substrate and forming a light emitting portion is formed. (B) after stacking the gallium nitride based compound semiconductor layer on the gallium nitride-based compound semiconductor layer, a GaAs compound can be vapor-grown at an ambient temperature and a nitrogen gas atmosphere. The temperature is lowered to a temperature at which the p-type layer of gallium nitride based compound semiconductor can be annealed, and (c) GaAs or Ga in which the surface of the gallium nitride based compound semiconductor layer is doped with Mg, respectively.
At least one selected from the group consisting of P, InAs, InP and those in which a part of these Group III elements is replaced with Al is formed as a protective film in the nitrogen atmosphere,
(D) The p-type layer of the gallium nitride based compound semiconductor layer is annealed together with the formation of the protective film, and after the annealing is completed, the temperature is lowered to room temperature and the protective film is removed by etching.

Here, the light emitting portion means a double heterojunction active layer or a portion of a pn junction where electrons and holes are combined to generate light.

Introducing the source gas so as to form a film having a thickness of 0.1 to 2 .mu.m, including the time for forming the protective film and the annealing time, makes it possible to change the atmosphere gas during the annealing. Not only N ₂ but also a Group III or V group material such as Ga exists as a gas, and it is preferable because evaporation of Ga and N from the gallium nitride based compound semiconductor can be suppressed.

[0019]

According to the method of manufacturing the semiconductor light emitting device of the present invention, the MO
After stacking the gallium arsenide-based compound semiconductor layer in the CVD process, immediately in a nitrogen gas atmosphere, the temperature is lowered to about 700 ° C., and a gallium arsenide-based compound semiconductor layer doped with Mg is formed as a protective film. However, since annealing is performed, compounds of group III and V elements such as Ga and As are coated on the surface of the gallium nitride based compound semiconductor layer, and in addition to N ₂ , elements of group III and group V are used as organic compounds. Since it exists in the atmosphere, it functions as an effective mask, and Ga or N is removed from the gallium nitride compound semiconductor layer.
Annealing can be performed without letting go of the above. Therefore, a CVD process for forming a protective film after MOCVD is not required, and the heat treatment process only needs to be performed once by MOCVD.
As a result, there is no repeated temperature change and no thermal shock is applied, so that crystal defects and dislocations are less likely to occur, and the luminous efficiency is improved and the reliability is also improved.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a semiconductor light emitting device of the present invention will be described below with reference to the accompanying drawings.

1 to 2 are process cross-sectional explanatory views of an embodiment of a method for manufacturing a semiconductor light emitting device according to the present invention.

First, as shown in FIG. 1A, a low-temperature buffer layer 2 made of a gallium nitride-based compound semiconductor layer such as n-type GaN is formed on a substrate 1 made of sapphire or the like by MOCVD to 400 to 700. ℃, the high temperature buffer layer 3 at 700 ~ 1200 ℃ 0.01
The growth is about 0.2 μm and about 2 to 5 μm. After that, the n-type cladding layer 4, the non-doped or n-type or p-type active layer 5, the p-type cladding layer 6, and the cap layer 7 are sequentially laminated. The clad layers 4 and 6 are usually 0.1 to 0.3 μ
m, and the active layer 5 is formed to a thickness of about 0.05 to 0.1 μm. The film formation of these gallium nitride based compound semiconductor layers is performed by introducing the same source gas as described in the prior art and reacting to grow.

In order to form the above-mentioned cladding layer 4 into an n type, Si, Ge and Sn are replaced with SiH ₄ , GeH ₄ and SnH.
The gas such as ₄ is mixed into the reaction gas and the cladding layer 6
In order to form p-type, Mg and Zn are replaced by Cp ₂ Mg and D
It is mixed in the raw material gas as an organometallic gas of MZn. The cap layer 7 is for ohmic contact with the electrode metal, is made of p-type GaN, etc., and is formed to a thickness of 0.2 μm or more.

After stacking the gallium nitride-based compound semiconductor layer, the atmosphere is set to G and the ambient temperature is set to G.
The temperature at which the aAs compound can be vapor-grown and the p-type layer of the gallium nitride based compound semiconductor layer can be annealed is lowered to about 550 to 800 ° C.
The nitrogen gas atmosphere is used here to prevent N in the GaN layer from escaping to the outside. Further, since Ga may escape, for example, GaAs, GaP, InA
s, InP, or a protective film 1 made of these compounds in which some or all of the group III elements are replaced by Al
0 is deposited to a thickness of about 0.1 to 2 μm by the MOCVD method (see FIG. 1B). When the protective film 10 is formed, the p-type layer of the gallium nitride based compound semiconductor layer is annealed,
H combined with the dopant Mg is separated and released to the outside to reduce the resistance of the p-type layer. After forming the protective film 10, the annealing may be continued at the same temperature under N ₂ atmosphere, but the film forming time of the protective film 10 is the same as the annealing time of 30 to 30.
If the flow rate of the reaction gas is adjusted so that a protective film having a thickness of about 0.1 to 2 μm is formed in about 60 minutes, the organic gas of the group III and group V elements is added to the atmosphere gas during the annealing. Since it is present, it becomes difficult for elements of any composition to escape from the gallium nitride based compound semiconductor layer, which is preferable.

After that, when the annealing is completed, the temperature is lowered to room temperature and the protective film 10 is removed by wet etching. The etching conditions differ depending on the material of the protective film. For example, in the case of GaAs and GaP layers, the etching solution is a mixed solution of sulfuric acid and hydrogen peroxide solution, a mixed solution of nitric acid and hydrochloric acid, and the etching temperature is 10-5
The temperature is 0 ° C. for about 1 to 10 minutes. In the case of the InAs and InP layers, the etching solution is a mixed solution of sulfuric acid and hydrogen peroxide solution, a mixed solution of hydrochloric acid and hydrogen peroxide solution, and the temperature during etching is 10 to 50 ° C. for 1 to 10 minutes. Is.

As a result, Mg which is a dopant for the p-type layer
The junction between H and H is cut, activation is achieved, and a laminated film of a gallium nitride-based compound semiconductor including at least an n-type layer and a p-type layer is obtained in which the resistance of the p-type layer is reduced.

Next, in order to form the n-side electrode, a resist is applied and patterned, and as shown in FIG. 1C, the gallium nitride based compound semiconductor layer is formed from the opened portion of the resist film 11. A part is removed by dry etching to expose the high temperature buffer layer 3 which is an n-type GaN layer. Then, a metal film of Au, Al or the like is formed by sputtering or the like, the p-side electrode 8 electrically connected to the p-type layer on the surface of the laminated compound semiconductor layer, and the n-type on the exposed surface of the high temperature buffer layer 3. An n-side electrode 9 electrically connected to the layer is formed (see FIG. 1D). Next, LED chips are formed by dicing each chip.

Although the above-mentioned embodiment is a double hetero-coupled LED, the present invention is similarly applied to a normal pn-junction LED, a laser diode of various structures, and the like which use a gallium nitride based compound semiconductor. it can. Further, the gallium nitride based compound semiconductor is not limited to the material having the above-mentioned composition, and is generally Al _p Ga _q In.
_1-pq N (0 <p ≦ 1, 0 <q ≦ 1, 0 <p + q ≦ 1)
For example, the composition may be changed by selecting p and q so that the ratio of each composition is selected so that the bandgap energy of the active layer becomes smaller than the bandgap energy of the clad layer. In addition, the Al
_The present invention can be similarly applied to a material obtained by substituting a part or all of N of _p Ga _q In _{1 -pq} N with As and / or P or the like.

[0029]

According to the method for manufacturing a semiconductor light emitting device of the present invention, the step of annealing the p-type compound semiconductor layer and the step of forming the protective film on the surface of the laminated gallium nitride compound semiconductor layer are performed simultaneously. Since it is carried out, the elements of the gallium nitride based compound semiconductor do not escape during the annealing, and it is not necessary to return to room temperature once to form the protective film after forming by MOCVD. In addition, it is possible to prevent crystal defects and dislocations caused by repeated temperature changes. As a result, it is possible to obtain a semiconductor light emitting device having good light emitting characteristics, high reliability, and low cost.

[Brief description of drawings]

FIG. 1 is a process sectional view showing an example of a method for manufacturing a semiconductor light emitting device of the present invention.

FIG. 2 is a perspective view showing an example of a conventional semiconductor light emitting device.

[Explanation of symbols]

 1 substrate 2 low temperature buffer layer 3 high temperature buffer layer 4 n-type clad layer 5 active layer 6 p-type clad layer 7 cap layer 10 protective film

Claims (2)

[Claims] 1. A method comprising: (a) laminating a gallium nitride compound semiconductor layer having at least an n-type layer and a p-type layer on a substrate and forming a light emitting portion by a metal organic chemical vapor deposition method;
(B) A p-type layer of the gallium nitride-based compound semiconductor layer, which is capable of vapor-depositing a GaAs compound at a surrounding temperature while stacking the gallium nitride-based compound semiconductor layer in a nitrogen gas atmosphere. To a temperature at which GaN can be annealed, and (c) GaAs, GaP, InAs, InP and p-type dopants each having a p-type dopant doped on the surface of the gallium nitride-based compound semiconductor layer, and part of these Group III elements are Al. And at least one selected from the group consisting of those substituted with a protective film in the nitrogen atmosphere, and (d) the protective film and the p-type layer of the gallium nitride-based compound semiconductor layer. Is annealed, and after the annealing is completed, the temperature is lowered to room temperature and the protective film is removed by etching. 2. The method for manufacturing a semiconductor light emitting device according to claim 1, wherein the source gas is introduced so that the time for forming the protective film and the annealing time are combined to form a film having a thickness of 0.1 to 2 μm.