JPH08186332A - Manufacture of semiconductor element - Google Patents

Abstract

PURPOSE: To provide the manufacturing method, of a semiconductor element, which can form a high-quality p-type layer by increasing the electric activation rate of Mg impurities in a GaN-based compound semiconductor layer and which realizes a high-performance and short-wavelength semiconductor laser or the like. CONSTITUTION: In a method which enables manufacture of a semiconductor element by laminating a compound semiconductor layer on a substrate, Mg doped an AlN cap layer 17 is formed on Mg doped GaN-based compound semiconductor layers 15, 16, a heat treatment is then executed to the GaN-based compound semiconductor layers 15, 16, and the AlN cap layer 17 is then removed.

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 device, and more particularly to a method for manufacturing a semiconductor device with an improved method of adding acceptor impurities.

[0002]

2. Description of the Related Art GaN, which is one of III-V group compound semiconductors containing nitrogen, has a large bandgap of 3.4 eV and is a direct transition type. Therefore, it is expected as a material for a short wavelength light emitting device. There is. It was difficult to grow a low resistance p-type layer with this material, but recently Mg
It is possible to reduce the resistance by irradiating the GaN layer to which is added with an electron beam or heating it in a nitrogen gas atmosphere. It is considered that this decrease in resistance is due to the effect of desorption of hydrogen mixed in the crystal.

However, according to the research conducted by the present inventors, the electrical activation rate of Mg in the GaN layer is still low, and the low resistance p of 1 Ωcm or less necessary for producing a high performance device such as a semiconductor laser is obtained.
For forming the mold layer, Mg is 10 ¹⁹ cm ^-3 or more and 10 ²⁰ c
It was found that it was necessary to add it at a very high concentration of about m ^-3 . With such high-concentration Mg addition, the surface flatness deteriorates as the crystal defects increase, so that it is impossible to realize a high-performance, short-wavelength semiconductor laser or the like.

On the other hand, Al is formed on the GaN layer containing Mg.
A method of forming a low-resistance p-type GaN layer by forming an N layer as a cap layer and then annealing it has been proposed (JP-A-5-183189). However, even in this kind of method, the current situation is that sufficient electrical activation of Mg has not been achieved.

[0005]

As described above, the conventional Ga
When growing an N-based compound semiconductor layer (nitride-based III-V group compound semiconductor layer), it is necessary to add excessive Mg (acceptor impurities) in order to obtain p-type with low resistance. At the same time, there was a problem that the surface flatness deteriorates.

The present invention has been made in consideration of the above circumstances, and an object thereof is to raise the electrical activation rate of acceptor impurities in a nitride-based III-V group compound semiconductor layer to obtain high quality. Another object of the present invention is to provide a method for manufacturing a semiconductor element capable of forming a p-type layer, and realizing a high-performance, short-wavelength semiconductor laser or the like.

[0007]

In order to solve the above problems, the present invention employs the following configurations. That is, the present invention provides a method of manufacturing a semiconductor device by laminating a compound semiconductor layer on a substrate, wherein a nitride-based compound containing an acceptor is used.
Al with an acceptor added on the III-V compound semiconductor layer
After forming the N cap layer, the nitride-based III-V group compound semiconductor layer is heat-treated, and at least a part of the AlN cap layer is removed thereafter. Further, the present invention uses Al ₂ instead of AlN to which an acceptor is added.
It is characterized by using O ₃ as a cap layer.

Here, the following are preferred embodiments of the present invention. (1) The acceptor addition concentration in AlN is 10 ¹⁷ to 10 ²⁰ c
m ^-3 (2) The heat treatment temperature is 700 ° C or higher, preferably 800 ° C or higher and 1200 ° C or lower. (3) The nitride-based III-V compound semiconductor is GaN or AlG
aN and the acceptor impurity is Mg.

[0009]

Function Consider Mg used as an acceptor impurity in a nitride III-V compound semiconductor. If the activation rate of Mg can be increased, the amount of Mg added can be reduced, and a low-defect / low-resistance p-type layer having good surface flatness can be realized.
Therefore, the present inventors investigated the hydrogen concentration in the crystal, which is considered to be deeply related to the decrease in the activation rate of Mg. As a result, it was found that a large amount of hydrogen was mixed in the Mg-doped layer as compared with the undoped layer, and the amount of mixed hydrogen was reduced by the heat treatment.

FIG. 1 shows the relationship between the heat treatment temperature and the hydrogen concentration when the heat treatment is performed while changing the temperature. The sample is Mg-doped GaN. The hydrogen concentration can be reduced by performing the heat treatment at a temperature of 700 ° C. or higher. In the case of an element such as a semiconductor laser that requires precise control of carrier concentration, it is necessary to suppress the hydrogen concentration to 10% or less of the saturation concentration, and in that case, a treatment at 1000 ° C. or higher is required. However, when the treatment is performed at 800 ° C. or higher, the vaporization of constituent elements such as nitrogen from the surface is rapidly increased and the crystal surface is significantly deteriorated.

In order to prevent surface deterioration due to high temperature treatment, it is important to suppress evaporation of constituent elements such as nitrogen from the surface. According to the research conducted by the present inventors, it has been found that the vaporization of the constituent elements can be suppressed even in a high temperature region where hydrogen can be sufficiently removed by selecting an appropriate method. It is a method of covering the surface with another material (cap layer) and performing heat treatment. In that case, the cap layer has heat resistance, does not contain an element (for example, a donor impurity such as Si or Se) that adversely affects the p-type conversion of the nitride layer due to diffusion, and has good hydrogen permeability. It is important that the lattice constant is close to that of nitride and thermal strain does not enter, and that the film is a dense film that does not pass nitrogen or Ga. Further, since the cap layer is removed after the heat treatment, a material that can be selectively etched with the underlying nitride layer is suitable.

The most important of these conditions is that it does not contain impurities that form a donor level or a deep level, which causes a resistance increase. For this purpose, III-V compound semiconductors are suitable. Among III-V group compound semiconductors, those having a lattice constant close to that of nitride are nitride itself and B.
There is P. However, BP is chemically stable and difficult to etch. Also, GaN is difficult to selectively etch, and InN has no heat resistance.

On the other hand, AlN has excellent heat resistance and can be selectively etched with hydrochloric acid or the like, but it has a problem in terms of hydrogen permeability. However, in our study, III-V
It was found that the hydrogen permeability of the group III nitrides was significantly increased by adding the acceptor. For example, in the case of AlN, sufficient hydrogen permeability can be obtained by adding Mg at 10 ¹⁷ to 10 ²⁰ cm ⁻³ . In particular, by doping the cap layer with the same impurities as the acceptor impurities of the cladding layer, it is possible to prevent an increase in contact resistance due to a decrease in the surface carrier concentration during the heat treatment. Therefore, by using the acceptor-doped AlN for the cap layer, it becomes possible to remove hydrogen while suppressing evaporation of constituent elements such as nitrogen.

Al ₂ O ₃ has a lattice constant different from that of nitride, but it is a material usually used as a substrate for forming a nitride layer, and thermal strain introduced during cooling after heat treatment. Is not a big problem. Moreover, in other respects, all the conditions for the cap layer as described above are satisfied. Further, the Al ₂ O ₃ cap layer is advantageous because it can be easily formed especially by sputtering and can be easily etched by acid or alkali. Therefore, in the present invention, the same effect can be expected even if Al ₂ O ₃ is used as the cap layer.

As described above, in the present invention, heat treatment is performed after depositing AlN or Al ₂ O ₃ to which an acceptor has been added as a heat-resistant cap layer, whereby the heat treatment temperature is increased, and constituent elements such as nitrogen are included. Hydrogen can be removed while suppressing the evaporation of hydrogen. Therefore, the activation rate of Mg is increased, and it is possible to form a p-type nitride layer having a low resistance and a high quality, which has excellent surface flatness without adding excessive Mg. A light emitting device can be realized.

Although Mg has been taken as an example of the acceptor impurity in the above description, a material that functions as an acceptor of a nitride-based III-V group compound semiconductor and whose doping causes hydrogen to be taken into the doped layer. In that case, a similar effect can be expected by providing a cap layer and performing heat treatment.

[0017]

The details of the present invention will be described below with reference to the illustrated embodiments. In FIG. 2, G added with Mg of 5 × 10 ¹⁹ cm ⁻³
Change in resistance value with respect to heat treatment temperature in aN when heat treatment is performed by a method using an acceptor-added AlN cap layer according to the present invention, when an AlN cap layer without an acceptor is used, and when no cap layer is used Indicates.

400 ° C. when no cap layer is used
The effect of reducing the resistance value is recognized at the above heat treatment temperatures, and the resistance value further decreases as the treatment temperature increases. 700 ° C
The lowest resistance value can be obtained in the range
The resistance increases again by the heat treatment at 00 ° C. or higher. Further, when the undoped AlN cap layer is used, the resistance value monotonously decreases as the processing temperature rises, but becomes saturated at 800 ° C. or higher. On the other hand, in the method according to the present invention, 7
The resistance remarkably decreases as the processing temperature rises even at a processing temperature of 00 ° C. or higher, and at 800 ° C. or higher, the resistance reducing effect does not change significantly, but monotonously decreases with the processing temperature range up to 1000 ° C. or higher.

That is, if the cap layer is not used, 700
At a treatment temperature of ℃ or more, the hydrogen removing effect improves with temperature, but crystal defects increase because vaporization of constituent elements such as nitrogen becomes intense at the same time. Therefore, it is considered that the resistance value reducing effect is hindered, and that the resistance value is increased at 900 ° C. or higher despite the increase of the processing temperature. By using the AlN cap layer, desorption of the constituent elements from the surface can be suppressed. However, when no acceptor is added, the hydrogen permeability is poor and the resistance value is saturated. On the other hand, in the method according to the present invention, the desorption of the constituent elements from the surface cannot be ignored without the cap layer, and there is no increase in defects due to the desorption of the constituent elements even at a temperature of 700 ° C. or higher.
In addition, since hydrogen can be effectively removed due to its high hydrogen permeability, a crystal having a lower resistance than the conventional one was obtained. This effect is particularly remarkable at the processing temperature of 800 ° C. or higher. However, if the temperature exceeds 1200 ° C, the crystal quality of GaN may be impaired.

Further, here, AlN by adding an acceptor
The effect of improving the hydrogen permeability of is remarkable at 10 ¹⁷ cm ⁻³ or more, but it is difficult to add acceptors in an amount of more than 10 ²⁰ cm ^{−3 in} terms of manufacturing. Therefore, in the present invention, the preferable amount of acceptor added to the AlN cap layer is 10 ¹⁷ to 10 ²⁰ cm ⁻³ .

FIG. 3 shows the relationship between the Mg concentration and the resistance value in the GaN layer when heat-treated at 800 ° C. for 30 minutes in an Ar atmosphere. In the conventional method that does not use a cap layer,
No decrease in resistance was observed unless Mg was added in an amount of more than 10 ¹⁹ cm ^-3 which causes clouding. On the other hand, in the method according to the present invention using the acceptor-doped AlN cap layer, the electrical activation rate of Mg can be improved, so that a resistance value is obtained even at a Mg concentration of 10 ¹⁹ cm ⁻³ or less at which a flat film can be obtained. Could be reduced. These effects are
The same was true for mixed crystals of 1N and InN.

FIG. 4 is a sectional view of the device structure of a semiconductor laser produced by the method of the embodiment of the present invention. On the c-plane of the sapphire substrate 10, a first buffer layer 11 of AlN (10 nm), a second buffer layer 12 of GaN (1.0 μm), S
i-doped n-type AlGaN (1.0 μm) cladding layer 1
3, GaN (0.5 μm) active layer 14, Mg-doped p
Type AlGaN (1.0 μm) cladding layer 15 and Mg-doped p-type GaN (0.5 μm) contact layer 16 are sequentially formed. Although not shown in the drawing, electrodes are provided on the side surface of the n-type cladding layer 13 and the upper surface of the p-type contact layer 16, respectively.

FIG. 5 is a schematic configuration diagram showing a growth apparatus used in the method of the embodiment of the present invention. Reference numeral 21 in the drawing is a reaction tube made of quartz, and a raw material mixed gas is introduced into the reaction tube 21 from a gas introduction port 22. The gas in the reaction tube 21 is exhausted from the gas exhaust port 23.
A susceptor 24 made of carbon is arranged in the reaction tube 21, and the sample substrate 20 is placed on the susceptor 24. The susceptor 24 is induction heated by the high frequency coil 25. The concentration of the substrate 20 is measured by the illustrated thermocouple 26 and controlled by another device (not shown).

Next, a method of manufacturing the semiconductor laser having the structure shown in FIG. 4 using the growth apparatus shown in FIG. 5 will be briefly described. First, the substrate 10 is heated to 1100 ° C. in hydrogen to clean the surface. Then, after lowering the substrate temperature to 450 to 900 ° C., the H ₂ gas is switched to NH ₃ gas or an organic compound containing N, for example, (CH ₃ ) ₂ N ₂ H ₂ , and depending on the layer to be grown. Growth is performed by introducing an organometallic compound. When the AlN buffer layer 11 is formed, an organometallic Al compound such as Al (CH ₃ ) ₃ or Al
(C ₂ H ₅ ) ₃ is introduced to grow the AlN first buffer layer 11. GaN second buffer layer 12, active layer 1
4. When forming the contact layer 16, an organometallic Ga compound such as Ga (CH ₃ ) ₃ or Ga (C ₂ H ₅ ) is used.
Introduce ₃ to grow. AlGaN cladding layer 13,
When forming 15, the organic metal Al compound and the organic metal G
Growth is performed by introducing both of the a compound.

In addition, In may be added in order to narrow the band gap of the GaN active layer 14, in which case an organometallic In compound such as In (CH ₃ ) ₃ or In (C
₂ H ₅ ) ₃ is introduced and In is added.

At the time of doping, a doping raw material is also introduced at the same time. As a raw material for n-type doping when forming the cladding layer 13, Si hydride such as SiH ₄ or organometallic Si compound such as Si (CH ₃ ) ₄ is used. Organometallic Mg is used as a p-type doping raw material when the cladding layer 15 and the contact layer 16 are formed.
Compounds such as Cp ₂ Mg or organometallic Zn compounds,
For example, Zn (CH ₃ ) ₂ or the like is used.

Here, in this example, in order to increase the activation rate of the p-type dopant Mg in the Mg-doped p-type AlGaN cladding layer 15 and the p-type GaN contact layer 16, as shown in FIG. After forming a Mg-doped AlN cap layer 17 (10 to 1000 nm) on 16 and cooling to room temperature, 800 to 1200 ° C. in a gas containing no hydrogen such as Ar, He, and nitrogen or in a vacuum.
Heat treatment. Then, etching is performed at a temperature of 70 to 200 ° C. with an acid containing hydrochloric acid, phosphoric acid, sulfuric acid or an alkaline etching solution containing NaOH, KOH, etc.
The cap layer 17 is removed. The heat treatment may be performed in a vacuum, but it is more effective to perform the heat treatment in a gas containing no hydrogen because evaporation of constituent elements is hindered. Also here
The film thickness of the AlN cap layer 17 is set to 10 to 1000 nm, because if the film thickness is thin, the vaporization prevention of constituent elements such as nitrogen may be insufficient, and if the film thickness is large, hydrogen permeability decreases. Because there is a tendency.

More specifically, 1 × NH ₃ is used as a raw material.
10 ^-3 mol / min, Ga (CH ₃ ) ₃ at 1 × 10 ^-5 mol / mi
n, Al (CH ₃ ) ₃ was introduced at 1 × 10 ^-6 mol / min and A
The lGaN cladding layer 15 is grown. In the case of the GaN contact layer 16, the supply of Al is stopped, and in the case of the AlN cap layer 17, the supply of Ga is stopped. Substrate temperature is 10
50 ° C, pressure 75 Torr, total flow rate of source gas is 1 l / min,
The amount of Mg added to the p-type AlGaN cladding layer 15, the p-type GaN contact layer 16 and the AlN cap layer 17 is 5 ×.
It was set to 10 ¹⁸ cm ^-3 . The doping raw materials in the clad layers 13 and 15 are SiH ₄ as n-type and C as p-type.
Use p ₂ Mg. The heat treatment after forming the AlN cap layer 17 was performed at 1000 ° C. for 30 minutes in Ar in the growth apparatus of FIG. The cap layer 17 was removed by etching with phosphoric acid (85%) at 120 ° C. for 15 minutes.

The semiconductor laser thus manufactured is composed of a p-type GaN compound semiconductor layer (AlGaN cladding layer 15,
Since the activation rate of Mg in the GaN contact layer 16) can be increased, a p-type GaN-based compound semiconductor layer having a low resistance can be formed without excessively adding Mg. Therefore, a high-quality p-type GaN-based compound semiconductor layer can be grown, and the performance and the life of the short wavelength semiconductor laser can be improved.

Next, a semiconductor laser was manufactured in exactly the same manner except that an Al ₂ O ₃ cap layer was formed instead of the Mg-doped AlN cap layer. More specifically, an Al ₂ O ₃ cap layer is formed by sputtering, cooled to room temperature, heat-treated in Ar at 1000 ° C. for 30 minutes, and etched with hydrochloric acid (85%) at 70 ° C. for 15 minutes. And the Al ₂ O ₃ cap layer was removed. Also in this case, the activation rate of Mg of the obtained p-type GaN-based compound semiconductor layer was increased, and the p-type GaN-based compound semiconductor layer of low resistance and high quality could be grown without excessive addition of Mg.

The present invention is not limited to the above embodiment. In the examples, GaN or AlGaN is used for the low-resistance p-type compound semiconductor layer, but the present invention is not limited to these GaN-based compound semiconductors, and any nitride-based III-V group compound semiconductor can be applied. Is. Further, the film thickness of the cap layer, the doping amount of the acceptor, and the heat treatment temperature after forming the cap layer can be appropriately changed according to the specifications. Further, the present invention can be applied not only to the semiconductor laser but also to the manufacture of a light emitting diode and further to the manufacture of various semiconductor elements having a p-type nitride III-V group compound semiconductor layer. In addition, various modifications can be made without departing from the scope of the present invention.

[0032]

As described in detail above, according to the present invention, on the nitride-based III-V group compound semiconductor layer to which the acceptor is added,
By performing heat treatment after forming the acceptor-added AlN or Al ₂ O ₃ cap layer, the heat treatment temperature can be raised, and hydrogen can be removed while suppressing evaporation of constituent elements such as nitrogen. A high-quality p-type layer can be formed by increasing the electrical activation rate of acceptor impurities in the system III-V group compound semiconductor layer, which contributes to the realization of a high-performance short-wavelength semiconductor laser and the like. It will be possible.

[Brief description of drawings]

1 is a diagram for explaining the operation of the present invention, GaN
FIG. 6 is a characteristic diagram showing the relationship between the heat treatment temperature and the hydrogen concentration of.

FIG. 2 is a characteristic diagram showing a relationship between a heat treatment temperature and a resistance value of GaN containing Mg.

FIG. 3 is a characteristic diagram showing the relationship between the Mg concentration and the resistance value when heat-treated in an Ar atmosphere.

FIG. 4 is a cross-sectional view of an element structure showing a semiconductor laser produced by a method according to an embodiment of the present invention.

FIG. 5 is a schematic configuration diagram showing a crystal growth apparatus used in an example method of the present invention.

FIG. 6 is a schematic diagram showing a procedure for forming a Mg-doped AlN cap layer and performing heat treatment.

[Explanation of symbols]

 10 ... Sapphire substrate 11 ... AlN first buffer layer 12 ... GaN second buffer layer 13 ... Si-doped n-type AlGaN cladding layer 14 ... GaN active layer 15 ... Mg-doped p-type AlGaN cladding layer 16 ... Mg-doped p-type GaN contact layer 17 ... Mg-doped AlN cap layer 20 ... Sample substrate 21 ... Quartz reaction tube 22 ... Gas inlet 23 ... Gas exhaust port 24 ... Susceptor 25 ... High frequency coil 26 ... Thermocouple

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[Procedure amendment]

[Submission date] February 2, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 2

[Correction method] Change

[Correction content]

Claims (2)

[Claims] 1. A step of forming an AlN cap layer containing an acceptor on a nitride group III-V group compound semiconductor layer containing an acceptor, and a step of heat-treating the nitride group III-V group compound semiconductor layer. And a step of removing at least a part of the AlN cap layer, the method of manufacturing a semiconductor device. 2. A step of forming an acceptor-added Al ₂ O ₃ cap layer on an acceptor-doped nitride-based III-V group compound semiconductor layer, and a heat treatment on the nitride-based III-V-group compound semiconductor layer. And a step of removing at least a part of the Al ₂ O ₃ cap layer, a method of manufacturing a semiconductor device.