JPH10290051A - Semiconductor device and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a buffer layer from a nitride III-V compound semiconductor and to form the morphology of the surface of the buffer layer into an excellent one. SOLUTION: In this device, a buffer layer 2,which is 5 to 100 nm in thickness, is 10<18> to 10<2-> cm<-3> in carbon concentration and consists of a nitride III-V compound semiconductor, is formed between a substrate 1 and at least one layer of an epitaxially grown layer 3 consisting of a nitride III-V compound semiconductor. Here, this layer 2 is formed by a method wherein firstly, a simple substance containing a group III element as its constituent element is fed to the surface of the substrate 1, then, a compound containing such carbon and nitrogen as dimethyl hydrazine and monomethyl hydrazine as its constituent elements is fed to the surface of the substrate 1 along with a simple substance containing the above group III element as its constituent element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a nitride-based III-V
More specifically, the present invention relates to a semiconductor device including an epitaxially grown layer made of a group III compound semiconductor and a method for manufacturing the same. More specifically, the surface morphology of the epitaxially grown layer is excellent, and a drive current can flow in a direction perpendicular to the substrate. Therefore, the present invention relates to a semiconductor device that can be used also as a laser diode (LD) that emits ultraviolet-blue light and a method of manufacturing the same.

[0002]

2. Description of the Related Art III-V represented by GaAs and GaP
2. Description of the Related Art A semiconductor device having an epitaxially grown layer of a group III compound semiconductor has attracted attention as a light emitting element such as a semiconductor laser or a diode, a light receiving element such as a photodiode or a phototransistor, or an electronic element such as an FET or HBT.

[0003] Then, among these group III-V compound semiconductor, the general _{formula: In x Al y Ga 1-} xy N ( However, 0 ≦ x ≦ 1,0 ≦ y <1) with nitride represented III- Group V compound semiconductors are regarded as important materials for light-emitting and light-receiving elements that can be used in the visible light region to the ultraviolet region. In particular, GaN has attracted attention as a material for blue light-emitting diodes.

[0004] By the way, nitrides represented by GaN II
In order to grow a crystal of an IV group compound semiconductor, all of these materials have a high melting point and the vapor pressure at the melting point is high, so that GaAs, GaP,
Unlike InP, the horizontal Bridgman method or the pulling method cannot be applied. That is, it is difficult to manufacture a bulk crystal of a nitride III-V compound semiconductor, and it is impossible to obtain a single crystal substrate thereof.

Therefore, in crystal growth, a single crystal substrate cannot be used as a substrate for growth, and a substrate of a different material is inevitably used. However, unlike the case of GaAs or InP, in the case of crystal growth of a nitride III-V compound semiconductor, there is no substrate for growth of a material matching the lattice constant and the thermal expansion coefficient.

At present, sapphire (Al ₂ O ₃ ) is mainly used for a substrate used for epitaxial crystal growth of a nitride III-V compound semiconductor, since relatively high quality crystal growth can be realized. Have been. However, the lattice mismatch between the crystal lattice constant of the nitride III-V compound semiconductor and the Al ₂ O ₃ crystal is approximately 1
Since it is 3%, even if the epitaxial growth method is simply applied as it is, a high-quality crystal of a nitride III-V compound semiconductor cannot be obtained.

For these reasons, at present, Al ₂ O ₃
Or on a substrate of alumina, for example, at a temperature of 400 to 600 ° C.
Of amorphous structure with a thickness of about 10 to 50 nm at low temperature
A method of forming a buffer layer of aN or AlN once to take measures to prevent misfit dislocations, and then epitaxially growing a single crystal such as GaN on the buffer layer to form a desired layer structure. Is being done.

However, the above-mentioned buffer layer cannot always completely suppress the misfit dislocation in the epitaxially grown layer sequentially laminated thereon. Therefore, a structure defect is generated on the surface of the epitaxially grown layer to be formed, and the morphology is deteriorated. In addition, the obtained device has a tendency that the light emission luminance and the light emission efficiency are low.

When the substrate is made of Al ₂ O ₃ , the following problem arises. That is, since the substrate used is electrically insulating, for example, an electrode for driving the device cannot be attached to the back surface of the substrate, and when attaching an electrode, a positive electrode and a negative electrode are formed on the formed epitaxial growth layer. It has to be loaded flat. This means
This means that the number of manufacturing steps is about twice that in the case where GaAs or InP is used as a substrate.

Further, since the cleavage plane of Al ₂ O ₃ does not appear sharply, there is also a problem that it is not a device for an element such that the cleavage plane functions as a resonator as in a semiconductor laser. For these reasons, for a substrate for crystal growth, a study has been made on a material that can replace the above-mentioned Al ₂ O ₃ material, and a Si single crystal has been proposed as one of the materials.

In the case of a semiconductor device manufactured using a Si substrate, the above-mentioned two problems in a device manufactured using an Al ₂ O ₃ material as a substrate are solved, so that there is a possibility as a blue light emitting LD. Is suggested. Also, considering the current level of Si single crystal manufacturing technology, the substrate itself can be made large in area and high in quality, so that the manufacturing cost of the manufactured semiconductor device can be reduced. There is.

As a method for forming an epitaxially grown layer of a nitride III-V compound semiconductor on a Si substrate, the following method is known. For example, the surface of the Si substrate, AlN as in the case of the Al ₂ O ₃ substrate and GaN
Then, an organic metal compound or a simple substance is used as a group III element source, and ammonia or nitrogen plasma is used as a group V element source, and a target epitaxial growth layer is formed on the buffer layer. It is a method of forming.

In this case, AlN functioning as a buffer layer
For layers and GaN layers, the main attention has been paid to controlling the thickness and crystallinity. However, in the case of this method, at present, for example, there is a problem that it is very difficult to control nitrogen plasma, and even if a growth layer having excellent surface morphology is formed, it can be reproduced with good reproducibility on an industrial level. It is difficult to mass produce.

Japanese Patent Application Laid-Open No. 8-56015 discloses that
A method for manufacturing a semiconductor thin film using a Si substrate as a substrate for crystal growth has been proposed. In this method, prior to forming a target epitaxial growth layer, a Si substrate is heat-treated in a heating atmosphere containing hydrogen gas and, for example, methane gas to form a carbonized layer (carbon diffusion layer) directly on the surface of the Si substrate. . Then, the carbonized layer (SiC layer) is made to function as a buffer layer, and a target epitaxial growth layer is formed on the carbonized layer.

In this method, since the lattice constant of the SiC layer constituting the surface layer of the Si substrate is close to, for example, the lattice constant of GaN, the lattice constant of the SiC layer is reduced to the epitaxial growth layer formed on the SiC layer. It is said that the propagation of misfit dislocations is suppressed and the surface morphology of the growth layer is improved.

[0016]

SUMMARY OF THE INVENTION According to the present invention, the surface morphology of a nitride III-V compound semiconductor epitaxial growth layer formed on a substrate for crystal growth is excellent regardless of the material. And therefore
For example, if a Si substrate is used as a substrate, it is possible to provide a novel semiconductor device and a method for manufacturing the same, which can be a blue light emitting LD having good light emitting characteristics by loading a driving electrode on the back surface of the Si substrate. And

[0017]

In order to achieve the above object, according to the present invention, a thickness of 5 nm is provided between a substrate and at least one epitaxially grown layer made of a nitride III-V compound semiconductor. in ~ 100 nm, and the semiconductor device, characterized in that the carbon concentration is 10 ¹⁸ to 10 ²⁰ cm nitride-based ^-3 III-V group compound semiconductor of the buffer layer is formed is provided.

In particular, the substrate is a Si substrate, and the buffer layer is made of Al _1-x Ga _x N (where 0 ≦ x ≦ 1).
Is provided. Further, according to the present invention, in the method for manufacturing a semiconductor device by laminating a buffer layer made of a nitride III-V compound semiconductor and at least one epitaxial growth layer on a surface of a substrate in this order, In forming a layer, first, a simple substance of a group III element is supplied to the surface of the substrate, and then a compound containing carbon and nitrogen as constituent elements together with the simple substance of the group III element is supplied. A method for manufacturing a semiconductor device (hereinafter, referred to as a first manufacturing method) is provided.

Further, there is provided a method for manufacturing a semiconductor device (hereinafter referred to as a second manufacturing method), wherein carbon is doped when forming the buffer layer.

[0020]

FIG. 1 shows an example of a semiconductor device according to the present invention.
Shown in In the case of the layer structure shown in FIG. 1, a buffer layer 2 to be described later is formed on a substrate 1, and an epitaxial growth layer 3 is further stacked thereon. The epitaxial growth layer is not limited to a single layer as shown in FIG. 1, but may be an arbitrary plurality of layers.

Here, as the substrate, Al ₂
O ₃ may be used, but it is preferable to use a conductive crystal substrate in consideration of flowing a drive current also in the vertical direction of the substrate. Specifically, a Si single crystal substrate, GaAs or Ga
A single crystal substrate made of a group III-V compound semiconductor such as P, 6H-SiC, and the like can be given. Among these, a Si single crystal substrate is preferable because it is available at a low cost and is easy to increase in size.

The buffer layer 2 formed on the substrate 1 is made of a nitride III-V compound semiconductor and has a thickness of 5 to 5.
It is characterized by having a carbon concentration of 100 nm and a carbon concentration of 10 ¹⁸ to 10 ²⁰ cm ^-3 . In particular, as a nitride III-V compound semiconductor, the following formula: Al _{1 -x} Ga _x N (0 ≦ x ≦ 1)
Those having the composition represented by are preferred. Although the reason has not been elucidated yet, if the buffer layer 2 is formed between the substrate 1 and the epitaxial growth layer 3, the propagation of misfit dislocations during the formation of the epitaxial growth layer is suppressed, and the buffer layer 2 is formed. The surface morphology of the epitaxially grown layer becomes good.

When the buffer layer 2 is formed, its thickness is set to 5
When the thickness is smaller than nm, the formed layer is formed in a variegated island-like state, and therefore, there is a problem that the surface of the epitaxial growth layer formed thereon is not flat. In addition, as the thickness of the buffer layer 2 increases, the surface morphology of the epitaxial growth layer formed thereon increases, but on the other hand, when the carbon concentration in the buffer layer is in the range described later, the resistivity increases. When the thickness exceeds 100 nm, it becomes difficult to supply a drive current in a direction perpendicular to the substrate. For this reason, the thickness of the buffer layer 2 is set to 5 to 100 nm.

On the other hand, the buffer layer 2 needs to contain carbon. In that case, the carbon concentration is 10 ¹⁸ cm
^When it is lower than ⁻³ , not only the tendency of the surface morphology of the epitaxial growth layer formed thereon to deteriorate tends to begin to develop, but also when the buffer layer is formed by the first manufacturing method described later, the elemental group III element alone May be attached as droplets to the surface of the buffer layer, making it impossible to form an epitaxially grown layer thereafter.

When the carbon concentration is higher than 10 ²⁰ cm ⁻³ , although the reason is not clear, voids are easily generated between the formed buffer layer and the substrate surface. In particular, when the substrate is a GaAs substrate or a GaP substrate, the above-mentioned voids tend to occur frequently. On the buffer layer 2 described above,
The semiconductor device of the present invention is manufactured by stacking epitaxial growth layers by a known film forming method.

This semiconductor device is manufactured using, for example, a known gas source MBE device. First, the first manufacturing method will be described. The gas source RMBE equipment used is
It consists of two chambers, a sample preparation chamber and a crystal growth chamber, which are connected to each other by a gate valve.Each of these chambers has an exhaust device, and both chambers can be evacuated to a predetermined degree of vacuum. I have.

A substrate holder is provided in the sample preparation chamber, and the substrate set therein can be heated to a predetermined temperature. On the other hand, the crystal growth chamber is provided with a substrate holder for gripping the substrate transferred from the sample preparation chamber,
The temperature of the substrate set here can be controlled.

First, a means for supplying a group III element source is installed in the crystal growth chamber. That is, metal Ga
Supply means, metal Al supply means, metal In supply means, etc., and more specifically, Knudsen cells containing the respective metals. A means for supplying an N source (Group V element) is mounted on the crystal growth layer. That is,
Ammonia supply means, dimethylhydrazine supply means, monomethylhydrazine supply means, etc., from which an N source whose flow rate is precisely controlled by a mass flow controller is irradiated onto a substrate set in a crystal growth chamber. Has become.

Further, the crystal growth chamber is provided with a supply means of metal Mg containing metal Mg in a Knudsen cell and a supply means of metal Si containing metal Si in a Knudsen cell, and the epitaxial growth formed is formed. The layer is doped with these metals so that the conductivity of the epitaxially grown layer can be controlled. The crystal growth chamber is equipped with a radiation thermometer and a color thermometer so that the substrate temperature can be measured and controlled. In addition, a movable ionization vacuum gauge is installed and the surface of the substrate can be measured. The irradiation density of the group III element to be irradiated is measured and controlled.

First, after a cleaning process is performed on a substrate, the substrate is held in a substrate holder in a sample preparation chamber, the chamber is evacuated to a predetermined vacuum degree, and the substrate is heated to obtain a substrate. To remove moisture and the like adhering to the surface. Next, the substrate is transferred to the crystal growth chamber, held in the substrate holder, heated and held at a predetermined temperature, and the operation for forming a buffer layer on the surface is started. The operation is performed on the Si substrate by G
The case where the buffer layer is formed with aN will be described.

First, the surface of the Si substrate is irradiated with metal Ga to form a metal Ga layer having a thickness of about one atomic layer on the surface of the substrate. Then, while irradiating the metal Ga, dimethylhydrazine and / or monomethylhydrazine are simultaneously supplied. The dimethylhydrazine and monomethylhydrazine are (CH ₃ ) ₂ NN
As it is shown by _{H 2, CH 3 NH · NH} 2, a compound as constituent elements carbon and nitrogen. That is, G to be formed
For the aN buffer layer, it is both a N source and a carbon source.

Therefore, by the above series of operations,
Dimethyl hydrazine and monomethyl hydrazine are thermally decomposed and the nitrogen element nitrides the metal Ga, and at the same time the carbon element of the methyl group is dispersed in the nitride, and the GaN containing carbon is deposited on the Si substrate. A layer will be formed. Here, dimethylhydrazine and monomethylhydrazine are illustrated as materials that are both a nitrogen source and a carbon source.However, in the case of the present invention, the above materials are not limited thereto, and nitrogen and carbon are used as constituent elements. Any compound may be used as long as it is a compound that can form a nitride with metal Ga by thermal decomposition. In addition to those described above, for example, phenylhydrazine, tertiary butylamine, aniline and the like can also be used.

In the first manufacturing method, it is an essential requirement that the Si substrate is irradiated with metal Ga first, and then the metal Ga and dimethylhydrazine and / or monomethylhydrazine are simultaneously supplied. In this operation, for example, when dimethylhydrazine or monomethylhydrazine is first irradiated on the Si substrate, or when metal Ga and dimethylhydrazine and / or monomethylhydrazine are supplied simultaneously, the surface layer of the Si substrate is nitrided and converted to SiNx. This is because the crystallinity of the epitaxial growth layer formed thereon is deteriorated.

In this operation, if the temperature of the Si substrate is too low, the thermal decomposition of dimethylhydrazine or monomethylhydrazine does not proceed (because the surface becomes excessively Ga), which causes inconveniences such as formation of Ga droplets on the substrate surface. If the temperature is too high, on the other hand, if the epitaxial growth with good morphology is difficult to occur on the buffer layer, it will be difficult.
It is preferable to control the temperature within a range of 50 ° C.

The irradiation amount of dimethylhydrazine or monomethylhydrazine affects the carbon concentration of the GaN buffer layer to be formed. This carbon concentration is 10 ¹⁸ to 10 ²⁰ cm ^-3
, The irradiation amount of these N (C) sources is set to 2 to
It may be set in the range of 100 sccm. Considering the load on the apparatus and the problem of reproducibility of the formed buffer layer, the irradiation amount of dimethylhydrazine and / or monomethylhydrazine is preferably 20 to 50 sccm.

By performing the above operation for a predetermined time, a GaN layer having a thickness of 5 to 100 nm is formed on the Si substrate. In the case of forming a buffer layer made of Al _1-x Ga _x N (0 ≦ x ≦ 1), in the above-described operation, first, a monolayer of metal Al or metal Ga is formed on a Si substrate. do it.

At this time, the temperature range for forming the buffer layer becomes wider as the Al composition ratio increases. And
In the case of AlN, the range is 550 to 850 ° C. However, in the case of Al _1-x Ga _x N (0 ≦ x ≦ 1) composition,
As the content of Al increases and the thickness of the layer increases, the buffer layer formed has a problem that cracks are easily formed.

Therefore, Al _1-x Ga _x N (0 ≦ x ≦ 1)
When the buffer layer is formed, it is necessary to control the thickness of the layer according to the Ga mole fraction x. That is, x>
In the case of the composition of 0.8, the upper limit of the thickness is set to 100 nm, and in the case of the composition of x = 0.8 (Al _0.2 Ga _0.8 N), the upper limit of the thickness is 50 nm, and the composition of x = 0 ( In the case of (AlN), the upper limit of the thickness is set to 10 nm. And
In the case of a composition of 0 <x <0.8, the thickness of the buffer layer corresponds to the upper limit of the thickness when x = 0 (10 nm) and the thickness when x = 0.8, corresponding to the value of x. The value obtained by comparing and distributing the upper limit value (50 nm) may be set as the upper limit value.

On the buffer layer thus formed, II
A predetermined group III element is supplied from the supply means of the group I element source, and an N source is supplied from the supply means of the N source to form an epitaxial growth layer having a predetermined composition. At this time, the conductivity of the epitaxial growth layer to be formed is controlled by doping the metal Mg or the metal Si. Next, a second manufacturing method will be described.

In the case of the apparatus used in this manufacturing method, the crystal growth chamber of the above-mentioned gas source MBE apparatus is further provided with a carbon source supply means. Specifically, a supply means such as propane or butane is mounted. These flow rates are controlled by a mass flow controller. Also,
In order to efficiently incorporate carbon from the carbon source into the buffer layer, a heating mechanism is attached to the supply means.

Then, the buffer layer is formed as follows. Forming a monolayer of metal Ga, metal Al, etc. on a Si substrate first is the same as in the first manufacturing method. Next, the monolayer is irradiated together with the N source from the N source supply means and the carbon source from the carbon source supply means. At this time, the N source need not be a compound containing carbon and nitrogen as constituent elements. Specifically, ammonia can be used. Of course, the above-mentioned dimethylhydrazine, monomethylhydrazine or the like can be used as the N source.

By this operation, a nitride-based compound semiconductor such as GaN contained in a state doped with carbon by the thermal decomposition of a carbon source is grown to a predetermined thickness on the Si substrate. A buffer layer is formed.

[0043]

【Example】

Example 1 A single n-type Si substrate having a plane orientation of (111) was prepared. The substrate was ultrasonically cleaned with acetone, and then boiled with nitric acid for 1 minute and immersed in hydrofluoric acid for 1 minute for 5 cycles.
After repeated removal of the natural oxide film on the surface by repeating the process, the sample was immediately introduced into the sample preparation chamber of the gas source MBE apparatus and set on the substrate holder.

The sample preparation chamber was evacuated to a vacuum of 1 × 10 ⁻⁶ Pa, and the substrate was heated to 300 ° C. to remove water molecules adsorbed on the surface. Then, the substrate was transported to the crystal growth chamber and set in a substrate holder, and the substrate was heated at 1000 ° C. for 30 minutes while the degree of vacuum in the chamber was set at 1 × 10 ⁻⁷ Pa to perform thermal cleaning.

Then, a buffer layer made of GaN was formed on the Si single crystal substrate as follows. First, the substrate temperature was lowered to 650 ° C. and maintained for 10 minutes to stabilize the temperature. While maintaining this state, the substrate surface was irradiated with metallic Ga for 3 seconds. The irradiation conditions at that time were set so that the pressure value of the Ga molecular beam by a movable ionization vacuum gauge provided at the substrate position showed 3.0 × 10 ⁻⁵ Pa. Under this condition, a Ga layer having a thickness of about one layer is formed on the substrate.

Then, while continuing the irradiation of the metal Ga,
At the same time, dimethylhydrazine was irradiated at a rate of 20 sccm for 10 minutes. A GaN layer having a thickness of 50 nm was formed. Then, the N source was switched to ammonia and the substrate temperature was set to 850.
The temperature was raised to ° C. and maintained for 10 minutes to stabilize the temperature. While maintaining this state, an epitaxial growth layer was formed on the GaN layer to manufacture a light emitting device.

That is, first, Ga and Si were simultaneously irradiated while irradiating ammonia, and the carrier concentration was 2 × 10
A Si-doped n-type GaN layer having a thickness of ¹⁸ cm ^-3 and a thickness of 2 μm is formed as a cladding layer, and Ga, In and M are further formed thereon.
g and Si to irradiate with n-type carrier concentration of 1 × 10 ¹⁷
In _0.1 Ga _0.9 N having a cm ⁻³ and a thickness of 0.1 μm was formed as an active layer. Furthermore, ammonia, Ga, Mg
Irradiation, the carrier concentration is 1 × 10
A GaN cladding layer of ¹⁸ cm ^-3 was formed.

When the surface of the uppermost layer of the obtained device was observed with a Nomarski microscope, it was found to be a mirror surface having no tissue defect. In the manufactured device, the carbon concentration of the Si-doped n-type GaN layer (buffer layer) was measured by secondary ion mass spectrometry (SIMS). As a result, the carbon concentration in the buffer layer was 1 × 10 ¹⁹ cm ⁻³ .

When a p-type Si single crystal substrate was used as the substrate, the manufactured device had excellent surface morphology as in Example 1. Examples 2 to 5, Comparative Examples 1 to 3 Example 1 except that the type of N source and the irradiation amount of the N source were changed as shown in Table 1 when forming the buffer layer.
A light emitting device was manufactured in the same manner as described above.

Table 1 shows the surface states of these light emitting devices and the carbon concentration in the buffer layer. The irradiation amount of the N source in Table 1 is indicated by a pressure value measured by a movable ionization vacuum gauge disposed near the substrate.

[0051]

[Table 1]

As is clear from Table 1, when the carbon concentration is 10
¹⁸ to 10 ²⁰ cm ^-3 and apparatus of forming a buffer layer is (Example 2
5) are excellent in surface morphology.

[0053]

As is clear from the above description, in the semiconductor device of the present invention, no tissue defect is generated in the epitaxial growth layer made of a nitride III-V nitride compound semiconductor such as GaN, Excellent morphology. Since the substrate may be made of a conductive material such as a Si substrate, for example, an electrode for driving the device can be loaded on the back surface.
Useful as D.

Further, in the case of the present invention, since a Si substrate can be used as the substrate, a large apparatus as a whole can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of the apparatus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Carbon-containing buffer layer 3 Epitaxial growth layer

Claims (6)

[Claims] 1. A method according to claim 1, wherein the substrate has a thickness of 5 to 100 nm and a carbon concentration of 10 ¹⁸ to 10 between the substrate and at least one epitaxially grown layer made of a nitride III-V compound semiconductor.
A semiconductor device comprising a buffer layer of a nitride III-V compound semiconductor of 10 ²⁰ cm ^-3 formed thereon. 2. The semiconductor device according to claim 1, wherein said substrate is a Si substrate. 3. A nitride III-V for forming said buffer layer.
A group compound semiconductor is represented by the following formula: Al _1-x Ga _x N (where x
Represents a number satisfying 0 ≦ x ≦ 1). 4. A method of manufacturing a semiconductor device by laminating a buffer layer made of a nitride III-V compound semiconductor and at least one epitaxial growth layer on a surface of a substrate in this order, wherein the buffer layer is When forming, first, a simple substance of a group III element is supplied to the surface of the substrate, and then a compound having carbon and nitrogen as constituent elements is supplied together with the simple substance of the group III element. Semiconductor device manufacturing method. 5. The method according to claim 4, wherein the compound containing carbon and nitrogen as constituent elements is dimethylhydrazine and / or monomethylhydrazine. 6. A method of manufacturing a semiconductor device by laminating a buffer layer made of a nitride III-V compound semiconductor and at least one epitaxial growth layer on a surface of a substrate in this order, wherein the buffer layer is A method for manufacturing a semiconductor device, comprising doping carbon when forming.