JP2002114595A - Sample and vapor source for molecular beam epitaxy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sample and a vapor source for molecular beam epitaxy which can vaporize a high melting material at a higher vaporization rate without varying the vaporization amount during the period when the sample is used, and further, to provide a sample and a vapor source for molecular epitaxy which generates a uniform vaporization rate in the sample face. SOLUTION: The vapor source is composed of a crucible filled with a plate type solid sample and a planar heat generator to heat the crucible. The planar heat generator consists of a resistor formed on the bottom face of the crucible. Recesses and projections are formed on the surface in the substrate side of the plate type solid sample.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sample for molecular beam epitaxy and an evaporation source, and more particularly, to a sample form for improving the evaporation amount of a high melting point substance and its evaporation source.

[0002]

2. Description of the Related Art The molecular beam epitaxy method is widely used as a method for growing a crystal thin film of a compound semiconductor such as GaAs, a group IV semiconductor, an oxide superconductor, etc., since a crystal thin film having few impurities and defects can be formed. . For example, AlGa
As / GaAs npn-type HBT (Hetero Bipolar
In the case of manufacturing a transistor, an evaporation source (molecular beam cell) for Ga, As, Al, Si, Be, which is a film constituent element, is installed in a vacuum chamber, and the evaporation source is heated to a predetermined temperature. The vapor flow of the sample filled therein is irradiated onto a GaAs substrate whose temperature is controlled. Thus, n
⁺ -GaAs, n-GaAs, p ⁺ -GaAs, n-AlG
Each film is grown on a GaAs substrate in the order of
Make T. For a substance such as As which is difficult to control the vapor pressure by temperature, arsine (AsH ₃ ) gas may be used instead of solid As, and a thermal decomposition furnace may be used instead of a normal molecular beam cell.

[0003] When a film is grown on a large substrate, the individual evaporation sources are offset from the center axis of the cell with respect to the center axis of the substrate, as described in Japanese Patent Publication No. 3-7638, for example. Are disposed obliquely at a predetermined angle with respect to the substrate. By arranging the evaporation source in this manner and forming the film while rotating the substrate, a thin film having excellent film thickness distribution, composition ratio distribution, and doping distribution can be grown even on a large-area substrate.

FIG. 7 shows an evaporation source of silicon used as an n-type dopant. As shown in FIG. 7, the evaporation source 100 includes a crucible 101 made of PBN (pyrolytic boron nitride) filled with flake-like silicon 107, and a heater 110 provided around the crucible 101.
A thermocouple 106 for crucible temperature measurement is attached. The amount of power supplied to the heater 110 is controlled with high precision so that the crucible temperature is always kept constant, and the amount of silicon evaporated is controlled to a desired value by the crucible temperature. In addition, a reflector 103 made of tantalum or the like for keeping the temperature of the crucible 101 around the heater 110 is arranged.
A cap 104 made of tantalum is attached to the upper part of the crucible.

For example, in the case of forming an n ⁺ -GaAs film, a vapor flow of Ga and As is emitted toward the substrate from an evaporation source of Ga and As, and one evaporation source of silicon is used.
The substrate is heated to a predetermined temperature of 300 ° C. or lower to release silicon vapor in the direction of the substrate. The silicon doping amount is Ga
It is determined by the growth rate of the As film and the evaporation amount of the silicon element. As described above, since the silicon evaporation amount is determined by the crucible temperature, a desired doping amount can be obtained by controlling the crucible temperature. .

[0006]

However, as higher performance of semiconductor devices and larger wafers require higher doping control, the evaporation source having the structure shown in FIG. It has been found that it is difficult to obtain a certain doping amount. For example, when thin film growth is repeated, or before and after sample replacement, the silicon doping amount fluctuates despite the precise control of the crucible temperature, and
It has been found that the doping amount in the substrate surface also varies, and a case where reproducible device characteristics cannot be obtained occurs.

The present inventor has studied the structure of the evaporation source, the form of the evaporation sample, and the like to investigate the cause. The silicon doping amount is correlated with the surface area of the sample surface facing the substrate (that is, the evaporation surface). It has been found that the doping amount changes when the surface area of the evaporation surface changes. That is, the cause of the fluctuation of the doping amount is that the surface area of the sample facing the substrate changes when the film is repeatedly grown using the flake-like sample, and the vibration at the time of opening and closing the shutter disposed above the evaporation source. It is considered that the flakes move to change the state of the evaporation surface, and the area of the evaporation surface naturally changes when a sample is replaced or added.

On the other hand, in order to perform high-concentration doping without lowering the film growth rate, it is necessary to increase the amount of silicon evaporated. If the heating temperature is increased to increase the amount of evaporation, the crucible material is thermally decomposed, and the crucible material is taken into the film and the desired film quality cannot be obtained.
It cannot be raised above ℃. Therefore, an investigation was made to increase the amount of evaporation using a crucible having a large opening diameter, but a new problem that the dispersion of the doping concentration in the substrate surface becomes large occurred. This is considered to be because the evaporation source having the structure shown in FIG. 7 is heated from the outer peripheral side, so that a temperature distribution occurs in the evaporation surface, and a distribution of the amount of evaporation occurs.

In view of this situation, the present invention solves the above-mentioned problems, and a molecule capable of evaporating a high melting point substance at a higher evaporation rate without fluctuation of the evaporation amount during the use of a sample. It is an object to provide a sample for line epitaxy and an evaporation source. It is a further object of the present invention to provide a molecular beam epitaxy sample and an evaporation source having a uniform evaporation rate in the sample plane.

[0010]

Means for Solving the Problems In order to solve the above object, an evaporation source for molecular beam epitaxy of the present invention comprises a crucible filled with a plate-shaped solid sample and a planar heating element for heating the same. The planar heating element is a resistor formed on the bottom of the crucible.

With this configuration, the distance between the heating element and the evaporation surface facing the substrate side of the sample can be made the same over the entire sample, the sample is uniformly heated from the bottom surface, and the temperature of the sample evaporation surface is reduced. Become uniform. As a result, the evaporation rate over the entire surface of the sample is made uniform, and it becomes possible to grow a thin film in which the doping concentration of, for example, silicon is made more uniform within the substrate surface. Further, since the distance between the heating element and the evaporation surface can be reduced, the heat generated by the heating element can be efficiently transmitted to the sample evaporation surface. As a result, the evaporation rate can be increased even at the same heating temperature, Alternatively, since the heating temperature can be lowered, the thermal decomposition of the crucible can be suppressed.

In addition, since a plate-like sample is used, there is no movement due to vibration unlike a flake-like sample, and the surface state of the evaporation surface is always kept constant, so that a reproducible evaporation rate can be maintained. it can. As a result, a film can be grown with excellent reproducibility of characteristics.

The sample for molecular beam epitaxy of the present invention is a molecular beam epitaxy in which a crucible is heated to evaporate a solid sample filled therein, and a thin film of the solid sample or a thin film containing the solid sample is grown on a substrate. Wherein the solid sample is formed in a plate shape, and irregularities are formed on a surface on a substrate side thereof. By forming irregularities on the sample evaporation surface and increasing the surface area in this way, the amount of evaporation can be further increased.For example, even if a high melting point material such as silicon has a low evaporation rate, silicon can be obtained at a lower temperature. It is possible to grow a film with a high concentration. The thickness of the plate sample is
1 to 5 mm is preferable. In this range, the heat supplied from the heating of the planar heating element is efficiently used for evaporating the sample, the warpage of the substrate is suppressed, and a uniform and high evaporation rate is obtained at a lower heating temperature. Obtainable.

Further, the plate-like sample is preferably divided on a plane perpendicular to the bottom of the crucible, so that the warpage of the plate-like sample caused by heating is suppressed and a thinner sample can be used.

[0015]

FIG. 1 is a schematic sectional view showing an example of an evaporation source for molecular beam epitaxy according to the present invention. The evaporating source 100 of FIG. 1 has a planar heating element 102 formed on the bottom surface, and surrounds a crucible 101 made of pyrolytic boron nitride (PBN) for heating and evaporating a plate-like sample housed therein; Reflector 103 for keeping heat, and reflector 103
And a cap 104 for blocking impurity gas emitted from the inside toward the substrate. 105
Is a current introduction rod for supplying electric power to the sheet heating element 102, and 106 is a thermocouple for measuring the temperature of the crucible.

The planar heating element 102 is composed of a resistor that generates heat when energized. As shown in the bottom view of the crucible of FIG. 2, a resistor 108 such as pyrolytic graphite (PG) uniformly heats the entire bottom of the crucible. Is formed in a predetermined shape as follows,
A current introduction unit 109 is provided at both ends. As shown in the enlarged view of FIG. 3, for example, the current introducing portion 109 is connected to a current introducing rod 105 by a molybdenum screw 112 via a tantalum washer 113 and a carbon washer 114.
And the crucible 101 is heated by applying a current to the PG resistor 108 from the outside. Here, the shape of the resistor may be any shape as long as it can uniformly heat the entire crucible, and the position of the current introducing unit 109 is not limited. It is preferable that the resistors other than the bottom of the crucible be formed wide so that a temperature distribution does not occur as a whole due to a rise in temperature at that portion.

The crucible 101 and the sheet heating element 10 of the present invention
2 can be produced, for example, by the method shown in FIG.
First, a carbon base 115 having a projection corresponding to a crucible shape is prepared (a), and a thermal CVD is formed on this base.
The pyrolytic boron nitride (PBN) layer 101 is removed by a 0.
5 to 2 mm (b), followed by pyrolytic graphite (PG)
A layer 108 is formed to a thickness of about 50 μm (c). Next, the PG layer is processed into a desired shape by machining or the like (d), and the PBN protective film 111 is formed again by the thermal CVD method (e). After that, the PBN at the current introducing portion is removed, and the carbon base 115 is removed. Since the carbon substrate and the PBN have significantly different coefficients of thermal expansion, the carbon substrate can be easily removed by returning to room temperature. The crucible is completed by washing the inner surface of the crucible as necessary.

The reflector 103 is processed into a shape surrounding the crucible, and has a structure in which a plurality of the crucibles are stacked at predetermined intervals to reflect the heat from the crucible and keep the temperature. Keep constant. Note that tantalum or molybdenum is used as the material.

The evaporation source is constituted as shown in FIG.
1 is filled with a plate-shaped evaporating material 107, and an electric power is supplied from an external power supply (not shown) to a resistor 108 via a current introducing line 105 to heat the crucible 101. At this time, the thermocouple 10
The amount of current supplied to the resistor 108 is controlled based on the temperature measured by 6 and the crucible is always maintained at a constant temperature. As described above, since the resistor 108 is formed directly on the bottom of the crucible, heat generated by energization is efficiently transmitted to the sample evaporation surface, and a higher evaporation rate can be obtained at the same heating temperature. Conversely, a lower heating temperature is required to obtain the same amount of evaporation, so that the thermal decomposition of PBN can be suppressed and the crucible life can be extended. In addition, since the entire evaporation surface of the sample is uniformly heated, the sample is uniformly evaporated from the entire surface. As a result, even with a high melting point material such as silicon, a uniform and higher evaporation rate can be obtained. Further, since the evaporation source of the present invention has a configuration in which the distribution of the evaporation rate does not occur in the evaporation surface even if the crucible opening area (sample area) is increased, the crucible area can be further increased if necessary. A large amount of evaporation can be obtained.

In the present invention, the opening diameter of the crucible 101
The depth may be appropriately selected according to the thickness of the plate-shaped sample or the like. For example, in the case of a crucible for silicon doping, the depth is 5 to 5.
A depth of about 10 mm is preferably used. The opening diameter may be any size as long as the sample can be accommodated, and an opening diameter that is generally about 1 to 2 mm larger than the sample diameter is selected.

Next, the sample for molecular beam epitaxy of the present invention will be described. In the present invention, a sample having irregularities formed on the surface on the evaporation surface side is preferably used. By forming the irregularities, the evaporation area is increased, and the amount of evaporation can be increased. Here, the concavo-convex shape may be any shape. For example, as shown in FIG.
(A) a semi-column, (b) a hemisphere, (c) a quadrangular prism (cube),
(D) grooves, (e) triangular prisms and the like are illustrated,
For example, the shape or the like may be determined so as to have a desired surface area in accordance with the required dope amount or the like. Therefore, the size and pitch of the uneven shape are not particularly limited, but it is preferable that the surface shape (surface area) hardly changes over the period of use of the sample, and it is usually about several μm to several mm. Is 100 μm to 1 mm. The thickness of the sample is not particularly limited, but is preferably about 1 to 5 mm in consideration of heat transfer efficiency and substrate warpage.

Further, the sample may be divided by a plane perpendicular to the crucible surface. By dividing, the warpage of the substrate is suppressed, and the in-plane uniformity of the evaporation rate is further improved. In addition, a thinner sample can be used, and the heat transfer efficiency can be further improved. The number of divisions is preferably 3 to 4.

For forming the irregularities on the surface of the sample, for example, machining, laser processing, etching and the like can be used. For example, in the case of silicon, plate-like silicon is cut out from a bulk crystal, and its surface is subjected to a process such as lapping, polishing, etching, or the like to make its surface smooth and uniform in thickness. In the case of the present invention, irregularities are formed by using abrasive grains such as alumina or carbon random having a coarse particle size during lapping (machining). Alternatively, after performing a lapping or polishing treatment, a mask for obtaining a desired shape may be applied at the time of etching, and etching may be performed using a mixed acid including nitric acid, hydrofluoric acid, and glacial acetic acid. Further, it is also possible to form various shapes by using anisotropic etching.

Next, a method for growing an n ⁺ GaAs film using the evaporation source of FIG. 1 for silicon doping will be described. The GaAs substrate was heated to 550 ° C. and irradiated with a Ga vapor stream from a Ga evaporation source whose temperature was controlled to 1000 ° C., and arsine (AsH ₃ ) was placed in a 850 ° C. pyrolysis furnace.
0 sccm is introduced, and a vapor stream of As generated by decomposition is irradiated. At the same time, the planar heating element of the silicon evaporation source is energized and heated to 1300 ° C., and the generated Si vapor is irradiated on the substrate. In this way, the n-type GaAs single crystal is reduced to about 1 μm
Per hour.

The crucible has an inner diameter of 51.5 mm and a depth of 1.
When a 0 mm crucible is used and a 1 mm thick, 2 inch diameter flat silicon substrate is used as a silicon evaporation sample, the Si doping amount is 4 × 10 ¹⁸ / cm ³ , whereas the groove shown in FIG. 0.5mm height, 0.25m width
The doping amount in the case of using a silicon substrate having irregularities (m, pitch 0.5 mm) is increased to 1 × 10 ¹⁹ / cm ^3. By forming irregularities on the evaporation surface of the sample, the doping amount or the evaporation amount is increased. It is possible to do.

For example, in the case of n ⁺ -GaAs of HBT,
Since a doping amount of about 1 × 10 ¹⁹ / cm ³ is required, when a flat sample is used, it is necessary to attach two or three silicon evaporation sources or to reduce the film growth rate. By using a sample, a desired doping amount can be obtained with one evaporation source, so that the molecular beam epitaxy apparatus can be reduced in size and cost.

Although the above description has been given mainly of the silicon sample and its evaporation source, the present invention is not limited to silicon, but is applied to an evaporation sample in which a solid is sublimated and its vapor is irradiated on a substrate, and the evaporation source is applied. It can be used not only for doping but also for thin film growth. Further, the crucible material is not limited to PBN, and for example, a metal crucible such as tantalum can be used. However, in this case, an insulation layer such as PBN is formed on the bottom of the crucible, and a current-heating resistor is formed thereon. Also, the crucible material is not limited to PBN, and for example, a metal crucible such as tantalum can also be used. However, in this case, P
An insulating layer such as BN is formed, and a heating resistor for electric current is formed thereon.

On the other hand, the sample of the present invention (that is, a plate-like sample having an uneven surface formed on the surface) is not only an evaporation source having the structure shown in FIG. 1 but also a planar heating element below the crucible as shown in FIG. Is disposed separately from the crucible, and an evaporation source configured to heat from the bottom of the crucible can also be suitably used. Here, the planar heating element of FIG. 6A can be manufactured by forming a PBN layer, a PG resistor pattern, and a PBN protective film on a carbon substrate, similarly to the manufacturing method shown in FIG. . Tantalum washer 113, carbon washer 1
14 and the molybdenum screw 112 using the current introduction unit 1
The crucible 101 is connected and fixed to the surface heating element 05, and the crucible 101 is used by placing the crucible on the planar heating element. 6 (b) is an example in which a tungsten wire 116 is used as a resistor. In this case, the tungsten wire is formed by a molybdenum block 117 and a molybdenum screw 112 having cuts. It is fixed to the current introduction rod 105.

[0029]

As is clear from the above description, the amount of evaporation of a sample can be increased by using a plate-like sample as the evaporation sample and forming an uneven shape on the surface thereof.
For example, a GaAs film doped with high concentration Si can be grown at a high speed. Further, since the heating is performed from below the crucible, the temperature distribution in the sample surface is made uniform, and a uniform evaporation amount can be obtained. Therefore, even for a large-sized substrate, uniform and high-concentration doping can be performed in the substrate. In addition, since the evaporation source of the present invention does not cause variation in the evaporation amount even if the crucible opening diameter and the sample area are increased, the doping at a higher concentration can be performed by increasing the sample area as necessary. . Conversely, by increasing the amount of evaporation in this manner, the heating temperature can be reduced, and the life of the crucible can be extended.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing one configuration example of a deposition source for molecular beam epitaxy.

FIG. 2 is a schematic bottom view showing a resistor of a sheet heating element.

FIG. 3 is a schematic diagram illustrating a method of connecting a resistor current introduction unit and a current introduction rod.

FIG. 4 is a schematic view illustrating a method for producing an evaporation source according to the present invention.

FIG. 5 is a schematic diagram showing a surface shape of a sample for molecular beam epitaxy of the present invention.

FIG. 6 is a schematic diagram showing another configuration example of an evaporation source in which the sample of the present invention is suitably used.

FIG. 7 is a schematic sectional view showing a conventional evaporation source for molecular beam epitaxy.

[Explanation of symbols]

 Reference Signs List 100 evaporation source, 101 crucible, 102 sheet heating element, 104 cap, 105 current introduction rod, 106 thermocouple, 107 evaporation sample, 108 resistor, 109 current introduction section, 110 heater 111 PBN protective film, 112 molybdenum screw, 113 tantalum washer, 114 carbon washer, 115 carbon base, 116 tungsten wire, 117 wire fixing block.

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[Procedure amendment]

[Submission Date] October 16, 2000 (2000.10.
16)

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0024

[Correction method] Change

[Correction contents]

Next, a method for growing an n ⁺ -GaAs film using the evaporation source of FIG. 1 for silicon doping will be described. The GaAs substrate was heated to 550 ° C. and irradiated with a Ga vapor stream from a Ga evaporation source whose temperature was controlled to 1000 ° C., and arsine (AsH ₃ ) was placed in a 850 ° C. pyrolysis furnace.
0 sccm is introduced, and a vapor stream of As generated by decomposition is irradiated. At the same time, the planar heating element of the silicon evaporation source is energized and heated to 1300 ° C., and the generated Si vapor is irradiated on the substrate. In this way, the n-type GaAs single crystal is reduced to about 1 μm
Per hour.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction contents]

For example, in the case of n ⁺ -GaAs of HBT,
Since a doping amount of about 1 × 10 ¹⁹ / cm ³ is required, when a flat sample is used, it is necessary to attach two or three silicon evaporation sources or reduce the film growth rate. Since a desired doping amount can be obtained with one evaporation source, the size and cost of the molecular beam epitaxy apparatus can be reduced.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0027

[Correction method] Change

[Correction contents]

Although the above description has been given mainly of the silicon sample and its evaporation source, the present invention is not limited to silicon, but is applied to an evaporation sample in which a solid is sublimated and its vapor is irradiated on a substrate, and the evaporation source is applied. It can be used not only for doping but also for thin film growth. Further, the crucible material is not limited to PBN, and for example, a metal crucible such as tantalum can be used. However, in this case, an insulation layer such as PBN is formed on the bottom of the crucible, and a current-heating resistor is formed thereon.

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Claims (4)

[Claims] In a molecular beam epitaxy for heating a crucible to evaporate a solid sample filled therein and growing a thin film of the solid sample or a thin film containing the solid sample on a substrate, the solid sample is formed into a plate shape. A sample for molecular beam epitaxy, characterized in that irregularities are formed on the substrate side surface. 2. The sample for molecular beam epitaxy according to claim 1, wherein the solid sample is divided by a plane perpendicular to the bottom of the crucible. 3. The sample for molecular beam epitaxy according to claim 1, wherein the solid sample is silicon having a thickness of 1 to 5 mm. 4. A molecule comprising a crucible filled with a plate-shaped solid sample and a planar heating element for heating the crucible, wherein the planar heating element is a resistor formed on a bottom surface of the crucible. Evaporation source for line epitaxy.