JPH03215388A - Molecular ray epitaxial method and molecular epitaxial device - Google Patents

Abstract

PURPOSE:To make possible to form a graded layer by correctly controlling a composition by varying an angle between the base plate surface and molecular rays and varying a ratio of mixed crystal of an epitaxial film formed on a base plate surface. CONSTITUTION:Molecular rays generated from a molecular rays cells are irradiated to a base plate surface and a crystal is epitaxially grown on the base plate. In said process, an angle between the base plate surface and the molecular rays varies to vary a ratio of mixed crystal of the epitaxial film formed on the base plate surface. For varying the angle between the base plate surface and the molecular rays, an angle displacing device is provided. For instance, a base plate holder 11 is rotated so as to be a desired angle through a driving force-transmitting means 61 by a driving force of a power-generating means 62 controlled with a controlling means 63 to vary an angle between the base plate surface and the molecular rays.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention... The present invention relates to a molecular beam epitaxial method and an apparatus for irradiating a molecular beam onto a substrate to epitaxially grow a crystal containing the constituent elements of the octad molecular beam on the substrate.

[Conventional technology]

A molecular beam epitaxial method is a method of irradiating a substrate with a molecular beam and epitaxially growing a crystal containing the constituent elements of the molecular beam on the substrate. In this method, a substrate and a molecular beam cell for generating molecular beams are provided in a high vacuum container.

Some molecular beam cells are equipped with a crucible and a heater for heating the crucible. A crucible is filled with raw materials for molecular beams, and electricity is applied to a heater to heat and evaporate the raw materials to generate molecular beams. This molecular beam is irradiated onto the substrate to form a desired epitaxial film.

Further, as another method of generating molecular beams, there is also a method of using gas as a raw material for molecular beams. In this method, a source gas whose flow rate is controlled is heated, introduced into a high vacuum container as a molecular beam, and irradiated onto the substrate surface to form a desired epitaxial film.

Related methods and devices of this type include, for example, Japanese Journal of Applied Physics 25.12 (1986), pages L979 to L982.
rnal of Applied physxc
s. 25, 12 (1986) ppL979-982)
, Japanese Journal of Applied Physics 23.2 (1984), pp. 164-167 (
J a p a n e se J o urna
l of Applied physics, 2
3.2 (1984) ppL164-167).

[Problem to be solved by the invention]

The above-mentioned conventional technology has a problem in that the composition of the epitaxial film cannot be accurately controlled in forming a so-called graded layer in which the composition of the epitaxial film is continuously changed as the film grows.

FIG. 1 is an explanatory diagram of a graded layer, and is an example of a case where a Gat x Afl x As layer 64 is epitaxially grown on a GaAs substrate 1. As shown in FIG. Here, X is the mixed crystal ratio of AQ, which is increased linearly with epitaxial growth.

In conventional technology, when forming a graded layer as shown in Fig. 1 using a solid material as a raw material for molecular beams, the temperature of the AQ molecular beam cell is continuously increased to increase the molecular beam intensity of Ga. to relatively and continuously increase the molecular beam intensity of Aff.

However, since the heat capacity of the molecular beam cell is not zero, even if the temperature of the molecular beam cell is set to a desired value, there is a time delay before the temperature actually reaches that value.

Therefore, AΩ controlled by the temperature of the molecular beam cell of AQ
There is also a time delay for the molecular beam intensity to reach a desired value, making it impossible to accurately control the composition of the graded layer.

On the other hand, in the molecular beam epitaxial method that uses a gas material as a raw material for the molecular beam, the molecular beam intensity is controlled by the gas flow rate. Gas flow rate control is performed by a mass flow controller, but with this mass flow controller, even if the flow rate is set to a desired value, there is a time delay in actually reaching that value, or the gas flow rate overshoots. .

Therefore, it is not possible to accurately control the composition of the graded layer.

An object of the present invention is to provide a molecular beam epitaxial method that makes it possible to form a graded layer while accurately controlling the composition, and a molecular beam epitaxial apparatus for the method.

[Means to solve the problem]

The molecular beam epitaxial method, which enables the formation of graded layers with precisely controlled composition, is achieved by changing the angle between the molecular beam and the substrate. Furthermore, a molecular beam epitaxial device that enables the formation of a graded layer with a precisely controlled composition can be achieved by providing an angle displacement device that can change the angle formed between the substrate surface and the molecular beam.

An example of the angular displacement device includes a substrate holder rotation means, a power generation means for driving the substrate holder rotation means, a driving force transmission means for transmitting the driving force of the power generation means to the substrate holder rotation means, and a power generation means. A device having a control means for controlling the above-mentioned information is conceivable.

Furthermore, if a stepping motor, for example, is used as the power generating means, the angle between the substrate surface and the molecular beam can be changed continuously.

Furthermore, an angular displacement device that integrates a substrate holder and a substrate holder rotation means is also conceivable.

[Effect]

The operation of the above means will be explained below using drawings. In FIG. 2, the direction 4 of the first molecular beam 2 and the normal 6 of the substrate 1 are shown.
Let the angle formed by the direction be OL. Further, the angle formed by the direction 5 of the second molecular beam 3 and the normal line 6 of the substrate 1 is 02.

In this case, the number J1 of constituent elements of the first molecular beam deposited on the substrate 1 per unit time and unit area is expressed as follows.

J1=SIC1cos (θ1) Here, St and Ct are the fixation rate of the constituent elements of the first molecular beam onto the substrate and the intensity of the first molecular beam, respectively.

Further, the number J2 of constituent elements of the second molecular beam deposited on the substrate 1 per unit time and unit area is expressed as follows.

J engineering=SaCz cos(θ2) where. Sz-Cz are the fixation rate of the constituent elements of the second molecular beam onto the substrate and the intensity of the second molecular beam, respectively. Therefore, when the substrate 1 is irradiated with the first and second molecular beams simultaneously, the mixed crystal ratio Xe of the constituent elements of the first molecular beam on the substrate 1 is expressed by the following equation. As an example, SL=Sl
．． Considering the case of cL=c, it becomes. That is, by continuously changing the angle between the substrate surface and the molecular beam, the mixed crystal ratio can be controlled almost continuously.

In order to change the angle formed between the substrate surface and the molecular beam, an angle displacement device is provided in the vacuum container.

For example, by rotating the substrate holder 11 at a desired angle using the rotational force of the power generation means 62 controlled by the control means 63 via the driving force transmission means 61, the angle between the substrate surface and the molecular beam can be adjusted. It is possible to change the angle at which the

〔Example〕

Examples of the present invention will be described below. Note that the present invention is not limited to the following examples.

FIG. 3 is a conceptual diagram showing a first embodiment of the molecular beam epitaxial method of the present invention, in which Ga. −
3 is an example of a method for forming an xAQxAs layer.

A GaAs substrate 1 and a molecular beam cell are provided in the high vacuum container 9. The gas in the high vacuum container 9 is exhausted by the vacuum pump 7 via the gate valve 8. Furthermore, a liquid nitrogen shroud 10 is provided in the high vacuum container 9, and the degree of vacuum in the high vacuum container 9 is increased by flowing liquid nitrogen into this.

14, 15, 16, 17.18 are Ga molecular beam cell 1
00 components, which are a shirt reflector, a thermocouple, a heater, and a crucible, respectively.

19,20,21,22,2]t, molecule for AQ? cell 2
00 components, respectively: Schutter reflector, thermocouple, heater, and crucible.

24, 25, 26, 27.28 are As molecular beam cell 3
00 components, respectively: shutter, reflector, thermocouple, heater, and crucible. The angle between the Ga molecular line and the AQ molecular line is 30°. AQ
The angle formed by the molecular beam of As and the molecular beam of As is 30°. θ
■, θ2 are the normal direction of the surface of the GaAs substrate 1 and G
These are the angle formed by the molecular beam of a, and the angle formed between the normal direction of the surface of the GaAs substrate 1 and the molecular beam of An.

12 is a heater for heating the substrate, and 13 is a thermocouple for measuring the temperature of the substrate. With these, the GaAs substrate 1 is
Maintain at 0°C.

Ga molecular beam cell, AQ molecular beam cell. The temperatures of the As molecular beam cell were 900°C, 1000°C, and 250''C, respectively.

In this state, when GatxAΩxAsfi is epitaxially grown while changing the angle between the GaAs substrate 1 and the molecular beam, the AQ mixed crystal ratio X changes continuously with respect to θ2 as shown in FIG. 4.

In other words, the normal direction of the surface of the GaAs substrate 1 and the AC
The AQ mixed crystal ratio decreases continuously as the angle formed by the molecular lines increases.

FIG. 5 is a conceptual diagram showing a second embodiment of the molecular beam epitaxial method of the present invention.
3 is an example of a method for forming an ai xA Q x As layer.

A high vacuum container 9 is equipped with a GaAs substrate 1 and a molecular beam cell. The gas in the high vacuum container is exhausted by the vacuum pump 7 via the gate valve 8. In addition, a liquid nitrogen shroud 1o is provided in the high vacuum container 9,
By flowing liquid nitrogen through this, the degree of vacuum inside the high vacuum container 9 is increased.

Reference numerals 14, 15, 16, 17, and 30 are components of the triethyl gallium molecular beam cell 101, which are a Schutter reflector, a thermocouple, a heater, and a nozzle, respectively.

Reference numerals 19, 20, 21, 22, and 31 are components of the trimethylaluminum molecular beam cell 201, which are a shutter, a reflector, a thermocouple, a heater, and a nozzle, respectively.

24, 25, 26, 27, and 32 are components of the arsine molecular beam cell 301, which are a shutter reflector, a thermocouple, a heater, and a nozzle, respectively.

The angle between the triethylgallium molecular beam and the trimethylaluminum molecular beam is 30''}-The angle between the trimethylaluminum molecular beam and the arsine molecular beam is 30@.
θ1 and θ2 are the angle between the normal direction of the surface of the GaAs substrate 1 and the triethylgallium molecular beam, and the angle between the normal direction of the surface of the GaAs substrate 1 and the trimethylaluminum molecular beam, respectively.

12 is a heater for heating the substrate, and 13 is a thermocouple for measuring the temperature of the substrate. With these, the GaAs substrate 1 is
Hold at 0 0'C.

The temperatures of the molecular beam cell for triethylgallium, the molecular beam cell for trimethylaluminum, and the molecular beam cell for arsine are 100°C, 100°C, and 900°C, respectively. By setting the flow rate of trimethyl gallium to lee/mid, the flow rate of trimethyl aluminum to 0.4 cc/o+in, and the flow rate of arsine to 10 cc/min, the angle formed between the GaAs substrate 1 and the molecular beam is not changed. When grown epitaxially, the Aff mixed crystal ratio X is θ
2, it changes as shown in FIG. That is, Ga
As the angle between the normal direction of the surface of the As substrate 1 and the trimethylaluminum molecular beam becomes larger, the AQ mixture ratio decreases continuously.

7 and 8 show a first embodiment of the molecular beam epitaxial apparatus of the present invention. Ga on GaAs substrate
．． 1. This is an example in which an AfixAs layer is epitaxially grown.

A GaAs substrate 1 and a molecular beam cell are provided in a high vacuum container 9, and the gas in the high vacuum container 9 is exhausted by a vacuum pump 7 via a gate valve 8. Furthermore, there is a liquid nitrogen shroud in the high vacuum container 9, and by flowing liquid nitrogen into this, the degree of vacuum in the high vacuum container 9 is increased.

14, 15, 16, 17, 18 are Ga molecular beam cells 10
0 components, respectively: shutter, reflector, thermocouple, heater, and crucible.

19, 20, 21, 22, 23 are AQ molecular beam cells 20
0 components, respectively, which are a shutter, a reflector, a thermocouple, a heater, and a crucible. 24, 25, 26, 27, 28 are molecular beam cells 30 for As
0 components, respectively: shutter, reflector, thermocouple, heater, and crucible.

The angle formed by the Ga molecular beam and the AQ molecular beam is 30°, and the angle formed by the AΩ molecular beam and the As molecular beam is 30°. 11, 12, and 13 are board holder heaters, respectively.
This is a thermocouple, and while measuring the temperature of the substrate 1 with the thermocouple 13, the power input to the heater for heating the substrate is adjusted to bring the substrate temperature to the desired temperature. 6o is a substrate holder rotator for rotating the substrate holder 11 and changing the angle formed between the substrate 1 and the molecular beam.

62 is a power generator placed outside the high vacuum container 9;
The substrate holder rotator is operated via the driving force transmission shaft 61.

63 is a control device that controls the power generation means 62;
This makes the angle between the substrate 1 and the molecular beam a desired value.

9 and 10 show a second embodiment of the molecular beam epitaxial apparatus of the present invention. G on GaAs substrate
This is an example in which a L-1A Q x As layer is epitaxially grown.

A G a As substrate 1 and a molecular beam cell are provided in a high vacuum container 9 , and the gas in the high vacuum container 9 is exhausted by a vacuum pump 7 via a gate valve 8 . Furthermore, there is a liquid nitrogen shroud 10 in the high vacuum container 9, and the degree of vacuum in the high vacuum container 9 is increased by flowing liquid nitrogen into this.

Reference numerals 14, 15, 16, 17, and 30 are the constituent elements of the triethyl gallium molecular beam cell 101, which are a shutter, a reflector, a thermocouple, a heater, and a nozzle. Reference numerals 19, 20, 21, 22, and 31 are components of the molecular beam cell 201 for trimethylaluminum, which are a Schutter reflector, a thermocouple, a heater, and a nozzle, respectively.

24, 25, 26, 27, and 32 are the components of the arsine molecular beam cell 301, which are a shutter, a reflector, a thermocouple, a heater, and a nozzle, respectively. 34 is a cylinder filled with triethyl gallium,
The generated triethyl gallium gas is then restricted in flow rate by a mass flow controller 33 and guided to a molecular beam cell for triethyl gallium. The cylinder 34 and the mass flow controller 33 are provided inside the oven 35 and maintained at a constant temperature.

A cylinder 37 is filled with trimethylaluminum, and the trimethylaluminum gas generated therefrom is guided to a molecular beam cell for trimethylaluminum with its flow rate restricted by a mass flow controller 36. cylinder 3
7. A mass flow controller 36 is provided within the oven 38 and maintained at a constant temperature.

Reference numeral 40 denotes a cylinder filled with arsine, and the flow rate of arsine gas generated from the cylinder is controlled by a mass flow controller 39 and guided to a molecular beam cell for arsine.

The angle between the triethylgallium molecular beam and the trimethylaluminum molecular beam is 30'. The angle between the trimethylaluminum molecular line and the arsine molecular line is 30'.

Reference numerals 11, 2, and 13 denote a substrate holder, a heater, and a thermocouple, and while measuring the temperature of the substrate 1 with the thermocouple 13, the power input to the heater for heating the substrate is adjusted to bring the substrate temperature to a desired temperature.

60 is a substrate holder rotator for rotating the substrate holder 11 and changing the angle formed between the substrate 1 and the molecular beam.

62 is a power generator placed outside the high vacuum container 9;
The substrate holder rotator is operated via the driving force transmission shaft 62.

Reference numeral 63 denotes a control device for controlling the power generating means 62, thereby adjusting the angle between the substrate 1 and the molecular beam to a desired value.

〔Effect of the invention〕

According to the present invention, the mixed crystal ratio can be controlled to change continuously by changing the angle formed between the substrate surface and the molecular beam.

Furthermore, since the angle between the substrate surface and the molecular beam can be changed accurately, it is possible to form a graded layer whose composition is precisely controlled.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of a graded layer, Fig. 2 is a principle diagram for explaining the present invention, Fig. 3 is a conceptual diagram showing the first embodiment of the molecular beam epitaxial method of the present invention, and Fig. 4 is a diagram showing the dependence of the mixed crystal ratio on the molecular beam incident angle, FIG. 5 is a conceptual diagram showing the second embodiment of the molecular beam epitaxial method of the present invention, and FIG. 6 is a diagram showing the molecular beam incident angle dependence of the mixed crystal ratio FIG. 7 is a conceptual diagram showing the first embodiment of the molecular beam epitaxial apparatus of the present invention, FIG. 8 is a conceptual diagram of the apparatus of FIG. 7 viewed from the direction of arrow A, and FIG. 9 10 is a conceptual diagram showing a second embodiment of the molecular beam epitaxial apparatus of the present invention, and FIG. 10 is a conceptual diagram of the apparatus shown in FIG. 9 viewed from the direction of arrow B. 1... Ga As substrate, 2... First molecular beam,
3... Second molecular beam, 4... Direction of first molecular beam,
5... Direction of second molecular beam, 6... Normal direction of substrate, 7... Vacuum pump, 8... Gate valve, 9...
・High vacuum container, 10...liquid nitrogen shroud, 11・
...Substrate holder 12...Heater 13...Thermocouple, 14, 19.24...Shutter 15.20.
25...Reflector, 16,21,26...Thermocouple, 17,22.27...Heater 18,23,2
8... Crucible, 29... Normal direction of substrate, 30,3
1.32... Nozzle, 33, 36, 39... Mass flow controller 34... Triethyl gallium cylinder,
35, 38... Oven, 37. Triethyl aluminum cylinder, 40... Arsine cylinder, 41'' Vacuum pump, 42, 43, 44, 45, 46, 47, 48
,49,50,51,52,53,54,55,56,
57, 58.59... Valve, 60... Substrate holder rotator, 61... Driving force transmission shaft, 62... Power generator, 6 3... Control equipment, 6 4-G a. −
, A Q x As epitaxial layer, 100...Ga
Molecular beam cell for triethyl gallium, 101... Molecular beam cell for triethyl gallium, 200... Molecular beam cell for AQ, 201...
Molecular beam cell for triethylaluminum, 300...A
Molecular beam cell for s, 301... Molecular beam cell for arsine. 1st Figure 1 Funerary membrane thickness 3rd Figure 200 M portion yILtre No. Cow diagram θ2 (Kasu No. 5 Figure Pigeon θ2 (匍鵠'i' round revolution δ En A Tensho box 200MM Labor J spear 9t) No. 9 What Torino + 1 and that L Mini U 4 Bogoto

Claims (1)

[Claims] 1. In the molecular beam epitaxial method in which a molecular beam generated from a molecular beam cell is irradiated onto the substrate surface to epitaxially grow crystals on the substrate, the angle between the substrate surface and the molecular beam is changed to grow the substrate surface. A molecular beam epitaxial method characterized by changing the mixed crystallinity of an epitaxial film formed. 2. A molecular beam cell that generates a molecular beam and a substrate holder that holds a substrate are provided in a vacuum container, and the molecular beam generated from the molecular beam cell is irradiated onto the substrate surface to epitaxially grow crystals on the substrate. A molecular beam epitaxial apparatus comprising an angle displacement device so as to change the angle formed between the substrate surface and the molecular beam. 3. As an angular displacement device, a substrate holder rotation means, a power generation means for driving the substrate holder rotation means, a driving force transmission means for transmitting the driving force of the power generation means to the substrate holder rotation means, and a power generation means are controlled. a control means for
The molecular beam epitaxial apparatus according to claim 2, further comprising: a molecular beam epitaxial apparatus. 4. The molecular beam epitaxial apparatus according to claim 3, wherein a stepping motor is used as the power generating means.