JPH05136111A - Pretreatment method for semiconductor substrate and device having the function - Google Patents

Abstract

(57) [Summary] [Object] The present invention aims at forming a natural oxide film existing on a Si substrate into a Si substrate when a semiconductor material is grown on the Si substrate.
An object of the present invention is to provide a pretreatment method that can be removed without damaging the substrate. [Structure] A surface portion of a natural oxide film existing on a Si substrate 8 is removed by ECR hydrogen plasma or Ar plasma, and thereafter, a microwave is incident from a waveguide 4 used in ECR and an electromagnet 9 is excited. After that, the hydrogen oxide was flown and annealed to completely remove the natural oxide film left after the ECR process.
In addition, during this annealing, SiH ₄ , AsH ₃ , Ge may be used together with hydrogen gas or instead of hydrogen gas.
_{H 4, Si 2 H 6,} Si 3 H 8, B 2 H 6, Cl 2, H
One or more reducing gases such as Cl can be used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a pretreatment for removing a natural oxide film existing on a Si substrate when growing a semiconductor material, especially a III-V group compound semiconductor such as GaAs on the Si substrate. Regarding the method.

GaAs is capable of operating at a higher speed than Si and is widely recognized as being useful as a material for a light emitting device. However, it is difficult to obtain a large-diameter substrate and mechanical strength is high. However, due to its high price, it is far behind Si in terms of practical use.

Therefore, attempts have recently been made to grow a GaAs substrate on a low-priced Si substrate which is easy to obtain a large-diameter substrate and is excellent in mechanical strength and to form a light-emitting element or the like on the GaAs growth layer. It has become.

In this case, in order to obtain a light emitting device having good characteristics, it is necessary to grow good GaAs on the Si substrate. For that purpose, it is indispensable to completely remove the natural oxide film unavoidably present on the Si substrate before growing GaAs.

[0005]

2. Description of the Related Art The following two methods have hitherto been attempted as methods for removing a natural oxide film existing on a Si substrate.

First Method Before growing GaAs, Si
The substrate is pre-baked in hydrogen gas at a high temperature of about 1000 ° C. to remove the natural oxide film.

Second Method Before growing GaAs, Si
The substrate is exposed to ECR hydrogen plasma at a relatively low temperature and prebaked to remove the native oxide film.

[0008]

However, each of the above methods has the following problems. That is, in the first method, if the pretreatment is performed at a high temperature, it takes a long time to raise the temperature of the entire reaction chamber to that temperature, and the thermal treatment of the constituent members such as a semiconductor crystal growth apparatus for performing the pretreatment is performed. Since the burden is heavy and it is necessary to frequently replace and repair deteriorated members, the operating rate of the device is reduced, which leads to shortening the life of the device. In addition, the element that has already been created S
When GaAs is grown on the i substrate, the profile of impurities in the Si substrate fluctuates at high temperature, which changes or deteriorates the characteristics.

In the second method, the hydrogen radicals generated in the ECR hydrogen plasma come into direct contact with the Si substrate at the final stage when the natural oxide film disappears.
Causes defects on the substrate surface.

[0010]

In the present invention, Si
The natural oxide film on the substrate is grown on GaAs without burdening the GaAs growth apparatus or the like, or without deteriorating the element characteristics already existing on the Si substrate.
In order to remove the i-substrate surface without causing defects, a step of removing the surface portion of the natural oxide film on the Si substrate by ECR hydrogen plasma, and the natural oxide film left after the step in hydrogen gas The process of removing by annealing was adopted.

[0011]

[Function] To reduce SiO ₂ , which is a natural oxide film, with hydrogen gas, heating at 1000 ° C. or higher is required.
Since hydrogen radicals generated in R hydrogen plasma have a stronger reducing action than hydrogen gas, SiO ₂ can be reduced even at room temperature.

FIG. 2 is an explanatory view of the bonding state of atoms of the natural oxide film on the Si substrate. This figure shows Si on the (100) plane.
In the figure for explaining the cross section in the case where the natural oxide film is formed on the substrate (bulk Si), white circles are Si atoms,
The black circles represent oxygen atoms.

The natural oxide film in such a bonded state is extremely stable, but once the Si--O bond on the surface portion is broken by hydrogen radicals, the remaining natural oxide film remains at a relatively low temperature of 1000 ° C. or lower. , Easily reduced by hydrogen gas.

[0014]

EXAMPLE (First Example) FIG. 1 is an explanatory view of a pretreatment method for a semiconductor substrate of a first example. In this FIG.
1 is an ion generation chamber, 2 is a reaction chamber, 3 is a grid, 4 is a waveguide, 5 is an alumina window, 6 is a sample support, 7 is a heater, 8 is a Si substrate, 9 is an electromagnet, and 10 is a pressure gauge. , 11 is a thermocouple, 12 is a valve, 13 is a flow meter, 14 is a valve,
Reference numeral 15 is a gate valve, 16 is a turbo molecular pump, 17 is a dry pump, 18 is a valve, 19 is a flow meter, and 20 is a valve.

This apparatus is an MOCVD apparatus having a function of generating ECR hydrogen plasma, and its configuration is as shown in the drawing.

That is, the chamber is composed of an ion generating chamber 1 and a reaction chamber 2 which are separated by a grid 3, and a microwave of 2.45 GHz is incident on the ion generating chamber 1 from a waveguide 4 through a window 5 made of alumina. The hydrogen gas is introduced through the valve 12, the flow rate of which is measured by the flow meter 13, the flow rate of which is adjusted by the valve 14, and the hydrogen gas introduced by the interaction with the magnetic field formed by the electromagnet 9. Cyclotron resonance (EC
R) is strongly plasmatized into hydrogen radicals, which are accelerated by an accelerating electric field by the grid 3 and enter the reaction chamber 2.

The reaction chamber 2 is provided with a sample support base 6 which is heated by a heater 7, whose temperature is measured by a thermocouple 11 and whose temperature is controlled, and a pressure gauge 10 constantly monitors the gas pressure. ..

The gas in the reaction chamber 2 is regulated by the gate valve 15 and the turbo molecular pump 16,
It is discharged by the dry pump 17. On the other hand, valve 1
2 is adjusted by adjusting the imbalance between the amount of hydrogen gas introduced from 2 and the amount of hydrogen gas discharged from the gate valve 15.
In order to keep the gas pressure in the chamber constant, the plasma spread and the intensity constant, and to ensure the reproducibility of the process, hydrogen gas for replenishment is introduced from the valve 18 while measuring the flow rate by the flow meter 19. ing.

A method of pretreating a semiconductor substrate of the present invention and a step of growing a semiconductor layer of GaAs or the like on this semiconductor substrate with this apparatus will be described. In the first step, the Si substrate 8 is placed on the sample support base 6 of the above apparatus, exposed to 1 × 10 ⁻³ torr ECR hydrogen plasma, and heated at 800 ° C. for 10 seconds.

By this step, the bond between oxygen atoms and Si atoms on the surface of the natural oxide film on the Si substrate 8 is broken. After that, the incidence of microwaves is stopped and the excitation of the electromagnet is stopped to stop the ECR plasma, and the introduction of hydrogen gas is continued and maintained at 800 ° C. for 1 minute.

By the second step, the natural oxide film on the Si substrate 7 is completely removed, and furthermore, the surface of the Si substrate 8 does not have any defect.

Subsequently, the temperature of the Si substrate 8 is set to 450 ° C.
And keep trimethylgallium (TMG) in this device
And arsine (AsH ₃ ) were introduced at a pressure of 76 torr and MOCVD was performed to form amorphous GaAs on the Si substrate 8.
Of 100 Å, the growth temperature is set to 700 ° C., the pressure of the reaction gas is maintained at 76 torr, and crystalline GaAs is grown to a desired thickness on the amorphous GaAs.

In the above case, if the annealing temperature in the ECR hydrogen plasma is 1000 ° C. or less, there is no problem. However, when the ECR hydrogen plasma is irradiated at around room temperature, the residual gas in the reaction chamber 2 becomes Si substrate. The temperature of the Si substrate 8 is set to 2 ° C. because it may adhere to the upper surface and hinder the removal of the natural oxide film.
It is desirable to keep the temperature above 00 ° C. In the first embodiment described above, B is 1 × 10 ¹⁵ cm as the Si substrate 8.
A (100) plane of a ^-3 doped Si substrate was used.

Although hydrogen gas is used as the annealing gas in the first embodiment, SiH ₄ , AsH may be used together with the hydrogen gas or instead of the hydrogen gas.
₃ , GeH ₄ , Si ₂ H ₆ , Si ₃ H ₈ , B ₂ H ₆ , C
A reducing gas such as l ₂ or HCl can be mixed and used. Since these gases have a strong reducing property, the annealing temperature can be lowered by mixing these gases.

However, depending on the type of gas such as SiH ₄ , the constituent elements thereof may grow on the Si substrate, so it is necessary to pay attention to the mixing amount. and again,
Although hydrogen plasma is used in the above-mentioned first embodiment, an inert Ar plasma having a function of breaking the bonds between Si atoms and oxygen atoms can be used instead of hydrogen plasma.

Further, the first embodiment is an MOCVD apparatus having a function of generating ECR hydrogen plasma, but a CVD apparatus having a function of generating ECR hydrogen plasma is constructed almost in the same manner as described above. You can also
In addition, in the first embodiment, III-V such as GaAs is used.
Although the pretreatment of the Si substrate when growing the group compound semiconductor has been described, the present invention is not limited to this, and can be widely used when growing other materials.

(Second Embodiment) In the first embodiment, an apparatus for pretreating a semiconductor substrate and an MOCVD apparatus for growing a semiconductor material thereon are also used. For example, 65
When growing GaAs at 0-700 ℃, GaAs is S
It adheres not only on the i substrate but also on the wall surface of the device.
When a new Si substrate is annealed at 1000 ° C., GaAs attached to the wall surface or the like, especially As, may evaporate and attach to this new Si substrate, which may have a harmful effect.

For this reason, efforts have been made to reduce the influence of the growth material in the previous step adhered to the wall surface, etc. by setting the annealing temperature to the same level as the growth temperature. In some cases, it may not be possible to approach the growth temperature. In particular, when a single crystal material is grown by the MOCVD method, the natural oxide film on the Si substrate needs to be removed more completely than when an amorphous or polycrystalline material is grown. Is extremely difficult to reduce to.

In such a case, a region for pretreating a semiconductor substrate and a region for growing a material thereon are independently provided, and the regions are connected by a load lock, and a sample such as a Si substrate can be vacuum-transported. ..

[0030]

As described above, when the process of the present invention is performed, the crystal defect density of the outermost surface is 6 × 10 ⁶ cm ^-2, which is 100 × when the GaAs of 3 μm is grown.
GaAs having the same degree of crystallinity as that obtained when preheating in hydrogen gas at 0 ° C. was obtained.

Further, the deterioration of the characteristics due to the fluctuation of the impurity profile of the element previously formed in the Si substrate was not observed.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a pretreatment method for a semiconductor substrate according to a first embodiment.

FIG. 2 is an explanatory diagram of a bonding state of atoms of a natural oxide film on a Si substrate.

[Explanation of symbols]

 1 ion generation chamber 2 reaction chamber 3 grid 4 waveguide 5 alumina window 6 sample support 7 heater 8 Si substrate 9 electromagnet 10 pressure gauge 11 thermocouple 12, 14, 18, 20 valve 13 flow meter 15 gate valve 16 turbo Molecular pump 17 Dry pump 19 Flowmeter

Claims (6)

[Claims] 1. A surface portion of a natural oxide film on a Si substrate is E
A pretreatment method for a semiconductor substrate, comprising: a step of removing by CR hydrogen plasma; and a step of removing a natural oxide film left after this step by annealing in hydrogen gas. 2. The pretreatment method for a semiconductor substrate according to claim 1, wherein the temperature of the Si substrate when exposed to ECR hydrogen plasma is 200 ° C. or higher. 3. The pretreatment method for a semiconductor substrate according to claim 1, wherein Ar plasma is used instead of hydrogen plasma. 4. When annealing, together with hydrogen gas,
Alternatively, instead of hydrogen gas, SiH ₄ , AsH ₃ , Ge
_{H 4, Si 2 H 6,} Si 3 H 8, B 2 H 6, Cl 2, H
The pretreatment method for a semiconductor substrate according to claim 1, wherein one or more reducing gases such as Cl are used. 5. A semiconductor substrate having a function of growing a semiconductor layer and removing a surface portion of a natural oxide film on a Si substrate by ECR hydrogen plasma, and then removing the remaining natural oxide film by annealing in a hydrogen gas. A CVD apparatus having the pretreatment function of 1. 6. Si separately from the region where the semiconductor layer is grown.
After removing the surface portion of the native oxide film on the substrate surface by ECR hydrogen plasma, there is a pretreatment region of the semiconductor substrate for removing the remaining native oxide film by annealing in hydrogen gas. An MOCVD apparatus characterized by being connected.