JP3684106B2 - Deposition equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thin film growth technique such as an electronic device, and particularly to an in-situ observation of a growth surface of a semiconductor or ceramic thin film and a thin film forming apparatus.
[0002]
[Prior art]
A molecular beam epitaxy (MBE) apparatus is widely used for forming an element whose thickness is controlled in units of atomic layers such as a semiconductor device using a superlattice. As a molecular beam source for generating a molecular beam, a plurality of elements are prepared according to a substance to be grown, and a desired material layer is grown by selecting and using a necessary molecular beam source.
[0003]
FIG. 3 shows a conceptual diagram of a conventional molecular beam epitaxy apparatus. A plurality of evaporation sources consisting of a cell 2, a heater 3, and a shutter 4 are arranged in an annular shape in a vacuum chamber evacuated to a high vacuum, and a metal material such as Ga or As stored in the cell 2 is heated by the heater 3. Then, the molecular beam is ejected from the cell 2 in the form of a molecular beam, and this molecular beam is collided on a growth substrate 7 heated by a substrate holder 6 that is installed in a vacuum chamber and includes a heater 5. Epitaxial growth is performed while maintaining the stoichiometric composition ratio by utilizing the difference in coefficient. In addition, epitaxial growth composed of a single element such as Si or Ge is also performed. The shutter 4 mechanically blocks molecular beams from the evaporation source toward the growth target substrate 7 so that the growth can be interrupted, and is attached independently for each evaporation source.
[0004]
Usually, a reflection high energy electron diffraction (RHEED) method is used as a method for evaluating a thin film growth surface. The RHEED is a method in which an electron beam emitted from an electron gun 8 is incident on the growth substrate 7 at a shallow angle of 1 to 2 ° with respect to the growth substrate surface, and a diffraction pattern by the reflected electron beam is projected onto the fluorescent plate 9. In addition to obtaining information on the atomic arrangement of the film, when the intensity change at the diffraction point of the RHEED pattern is measured during thin film growth, vibration corresponding to the growth speed is observed, and this can be used to monitor the growth speed. . This method is disclosed in Japanese Patent No. 2643328 as a “molecular beam crystal growth apparatus”. In recent years, there is also a method of observing a scanned RHEED image using a scanning μ-RHEED microscope.
[0005]
As a method for evaluating the thin film growth surface other than the above, a method of detecting the surface state of the thin film crystal by detecting the intensity change of the reflected light of the laser light incident on the growth crystal surface (disclosed in Japanese Patent Publication No. 7-115990). ), And a method of observing the film formation process with a transmission electron microscope so that the film can be formed directly on the substrate on the sample stage of the transmission electron microscope (disclosed in Japanese Patent Publication No. 7-8755). There is a method of evaluating the surface of a thin film by spectroscopic measurement of luminescence light emitted by beam irradiation (disclosed in Japanese Patent Publication No. 6-280014).
[0006]
[Problems to be solved by the invention]
In order to evaluate the thin film growth surface, it is necessary to observe the form and state in real time. In particular, it is most desirable to obtain a two-dimensional distribution image of a specific physical quantity such as a surface state distribution image or a morphological image in real time, not the overall surface state.
[0007]
Among conventional methods for evaluating a thin film growth surface, a method using RHEED (Japanese Patent No. 2643328), a method using laser light (disclosed in Japanese Patent Publication No. 7-115990), and a method using luminescence light ( Japanese Patent Publication No. 6-280014 discloses only the overall state of the surface although it can be evaluated in real time. Further, in the method using a scanning μ-RHEED microscope or a scanning electron microscope, a surface state distribution image can be obtained, but since it is a scanning type, real-time evaluation is difficult. The only observation method using a transmission electron microscope (disclosed in Japanese Patent Publication No. 7-8755) is to observe the film formation process in real time as an image. However, if this method is applied to a molecular beam epitaxy apparatus, The performance as a molecular beam epitaxy apparatus, such as its size, thickness, and number of evaporation sources, is limited.
[0008]
Accordingly, an object of the present invention is to provide a film forming apparatus having a mechanism capable of observing / evaluating a thin film growth surface in real time without limiting the performance of the film forming apparatus, particularly a molecular beam epitaxy apparatus.
[0009]
[Means for Solving the Problems]
As a method for observing an electron emission image from a flat surface, an emission microscope represented by a photoelectron microscope is known (W. Engel, M. E. Kordesch H. H. Rotermund, S. Kubala and A. et al. von Oertzen Ultramicroscopy, 36 (1991) 148-153.). Emission microscopy is a method of accelerating electrons emitted from a flat sample surface (thermoelectrons, photoelectrons, etc.), forming an image with an electron lens, and observing the surface. Its spatial resolution is the same as that of a scanning electron microscope. However, since the image can be observed in real time, not only the spatial distribution of the emission intensity but also the temporal change can be observed with high temporal resolution (M. mundschau, M.E. Kordesh, B. Rausenberger). , W. Engel, AM Bradshaw and E. Zeitler, Surface Science, 227 (1990) 246-260.). In particular, when the solid surface is irradiated with light that has not been monochromatized, photoelectron emission changes due to a local change in the work function of the surface, so that an enlarged image with a difference in surface state as a contrast can be obtained in real time.
[0010]
In the present invention, the principle of the emission microscope is applied to a film forming apparatus, in particular, a molecular beam epitaxy apparatus, so that a thin film growth surface can be observed / evaluated in real time.
[0011]
That is, the film forming apparatus of the present invention includes a film forming means for forming a film by irradiating a material beam from an evaporation source onto a substrate, and a light source for irradiating light on a film forming surface formed on the substrate. And an electron detection means for detecting photoelectrons emitted from the film formation surface by light emitted from the light source, wherein the electron detection means is emitted from the film formation surface. A lens barrel for imaging the photoelectrons on the imaging plane; means for displaying and recording the electron intensity distribution on the imaging plane; and the lens mirror at the time of irradiation of the material beam and at the time of photoelectron detection. And a means for changing the distance between the tube and the film formation surface .
[0012]
The film forming apparatus of the present invention has the following additional features:
"In the film forming means , the evaporation source is arranged around the lens barrel",
"A plurality of the evaporation sources are arranged, and the plurality of evaporation sources are arranged on a circumference around the lens barrel",
"The evaporation source has a shutter for blocking a molecular beam from the evaporation source toward the film formation surface",
“The film forming apparatus further detects an electron beam irradiating means for irradiating the film forming surface with an electron beam, and electrons irradiated from the electron beam irradiating means reflected on the film forming surface. Having backscattered electron detection means,
"The reflected electron detection means has a visualization means for visualizing a diffraction pattern of the reflected electrons",
“The visualization means is a substrate having a phosphor”;
"The film forming apparatus is a molecular beam epitaxy apparatus"
Is included.
[0013]
According to the film forming apparatus of the present invention, it is possible to observe / evaluate the thin film growth surface in real time without moving the sample (substrate to be grown) at each stage of film forming without impairing the performance as the film forming apparatus. In particular, a two-dimensional image of the thin film growth surface can be observed simultaneously with the periodic structure of the atomic arrangement on the thin film growth surface.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a case where a molecular beam epitaxy apparatus is used as a film forming unit will be described as an example.
[0015]
The means for irradiating the film-forming surface of the growth substrate in the molecular beam epitaxy apparatus is for observing the thin film growth surface on the growth substrate by the principle of an emission microscope. As such light, it is preferable to use ultraviolet rays of a mercury lamp or deuterium lamp which is not monochromatic and has low energy. If monochromatic ultraviolet rays such as resonance lines of He and Ne are used, the energy is high and the spatial resolution of the enlarged image is lowered. On the other hand, in the irradiation with ultraviolet rays that are not monochromatic, the photoelectron emission changes due to the local change in the work function of the surface, so that an enlarged image with the difference in surface state as a contrast can be obtained. When a mercury lamp is used, an ultraviolet irradiation device can be installed outside the vacuum. Therefore, if a mechanism such as a shutter is provided, ultraviolet irradiation can be easily turned on and off.
[0016]
In the molecular beam epitaxy apparatus, it is possible to form a film more uniformly when a suitable gap exists between each evaporation source and the substrate to be grown. On the other hand, at the time of observation / evaluation of the thin film growth surface, an image with a high magnification and resolution can be obtained by narrowing the distance between the lens barrel and the growth substrate and applying a high voltage.
[0017]
Therefore, when a molecular beam epitaxy apparatus is used as the film forming means of the present invention, it is preferable to have a mechanism for changing the relative position of the lens barrel and the growth substrate in the normal direction of the film forming surface. As a result, the distance between each evaporation source and the substrate to be grown can be increased uniformly during film formation, and the magnification and resolution can be increased by applying a voltage while reducing the distance during observation / evaluation. An image can be obtained.
[0018]
【Example】
Examples of the present invention will be described below, but the present invention is not limited to these examples.
[0019]
( Reference example )
A reference example will be described with reference to FIG.
[0020]
Reference numeral 1 denotes a high-vacuum chamber, which is evacuated by a vacuum pump from an exhaust unit 22 and has a plurality of evaporation sources including a combination of a cell 2, a heater 3, and a shutter 4, a substrate holder 6, a substrate 7 to be grown, an electron gun 8, and a fluorescent plate 9. The lens barrel 10 is maintained at a vacuum degree of 1.3 × 10 ^{−7 to} 1.3 × 10 ⁻⁹ Pa, and the quadrupole mass analyzer 21 can analyze the gas components in the high vacuum chamber 1. It can be done.
[0021]
The substrate 7 to be grown is held by a substrate holder 6, and a heater 5 for heating the substrate 7 to be grown to a predetermined temperature is provided in the substrate holder 6. In addition, the substrate holder 6 can perform coarse and fine movements in three axial directions, continuous rotation operation, and tilt operation by a manipulator (not shown). The periphery of the substrate holder 6 is covered with a liquid nitrogen shroud (not shown) to protect the substrate from impurities.
[0022]
A lens barrel 10 is installed to face the holding surface of the growth substrate 7 on the substrate holder 6, and a plurality of evaporation sources are arranged on the circumference centering on the lens barrel at the tip of the lens barrel 10. Each evaporation source is provided with a heater 3 for heating the cell 2 to a set temperature, and the evaporation port is provided with a shutter 4 for opening and closing the evaporation port to control the release of evaporated molecules. The heater 3 and the shutter 4 are controlled by a control device (not shown) connected outside the vacuum. Each evaporation source is covered with a liquid nitrogen shroud (not shown) in order to suppress emission gas generated from the periphery of the cell by being heated to a high temperature by a heater.
[0023]
An RHEED electron gun 8 and a fluorescent plate 9 are provided at predetermined diagonal positions in the high vacuum chamber 1 at a predetermined minute angle with respect to the surface of the substrate 7 to be grown on the substrate holder 6. A high-energy electron beam of about 10 keV emitted from the substrate hits the surface of the growth substrate 7 on the substrate holder 6, and the electron beam reflected by the surface hits the fluorescent plate 9 to obtain a diffraction pattern. The diffraction pattern is observed / recorded via the viewport 18. Usually, when the intensity of the diffraction spot of the diffraction pattern is measured, vibration corresponding to the growth rate is observed, and this can be used to monitor the growth rate.
[0024]
An objective lens 11, an intermediate lens 12, a projection lens 13, an objective aperture 14, a multichannel plate 15, and a fluorescent plate 16 are disposed in a lens barrel 10 that is placed on the substrate holder 6 so as to face the holding surface of the growth substrate 7. Is provided. Further, an ultraviolet irradiation device 20 for irradiating the surface of the growth substrate 7 with ultraviolet rays is installed at a position where the growth substrate 7 is desired.
[0025]
When observing the growth surface of the thin film on the substrate 7 to be grown, ultraviolet rays of a mercury lamp or a deuterium lamp which are not monochromatic and have low energy are used.
[0026]
The photoelectrons emitted from the thin film growth surface on the growth substrate 7 by the ultraviolet irradiation are accelerated from several keV to several tens keV by the acceleration voltage applied between the growth substrate 7 and the lens barrel 10, and the objective lens 11. Electrons that have passed through the objective aperture 14 disposed on the rear focal plane are magnified by the intermediate lens 12 and the projection lens 13 and imaged on the multichannel plate 15. At this time, the objective lens 11 mainly functions for focus adjustment, and the intermediate lens 12 mainly functions for magnification setting. The electrons amplified by the multichannel plate 15 display an image on the fluorescent plate 16, and this image is observed / recorded via the view port 17.
[0027]
Next, the actual growth of the epitaxial film in the molecular beam epitaxy apparatus of this reference example configured as described above will be described.
[0028]
A GaAs substrate is attached to the substrate holder 6 as the substrate 7 to be grown, Ga is sealed in one of the vapor deposition source cells 2, and As is sealed in the other cell. After confirming that the inside of the chamber 1 is maintained in a high vacuum state by the exhaust system, the substrate holder 6 and each cell 2 are set to predetermined set temperatures (for example, the substrate holder 6 is 590 ° C., the Ga evaporation source cell is 970 ° C., The As evaporation source cell is heated to 290 ° C. First, the shutter of the As evaporation source cell is opened, and then the shutter of the Ga evaporation source cell is opened, whereby Ga molecules and As molecules are emitted toward the GaAs substrate surface, and a GaAs epitaxial film is formed on the GaAs substrate surface. Be filmed. At this time, when the vibration of the RHEED diffraction pattern (change in the intensity of the diffraction point) was measured, attenuation of the amplitude was observed. It was also possible to observe the photoelectron image by irradiating the GaAs epitaxial film with ultraviolet light from a deuterium lamp and applying a voltage of 5 kV to the lens barrel.
[0029]
( Example)
In this embodiment, as shown in FIG. 2, a structure having a function of changing the distance between the lens barrel 10 including the evaporation source and the growth substrate 7 in the normal direction of the film formation surface will be described. .
[0030]
When a film is formed, it is possible to form a film uniformly if there is an appropriate space between each evaporation source and the substrate to be grown. Therefore, as shown in FIG. 2A, the distance between the lens barrel 10 and the growth substrate 7 is kept away at the time of film formation. In addition, there are molecules for film formation between each evaporation source during deposition and the substrate to be grown. If a high voltage is applied between the lens barrel and the substrate to be grown in this state, there is a risk of discharge. There is. Therefore, RHEED vibration is used as a film formation monitor.
[0031]
On the other hand, at the time of observation, an image with a high magnification and resolution can be obtained by applying a high voltage while narrowing the distance between the lens barrel and the substrate to be grown. Accordingly, when observing the surface at each stage of film formation, as shown in FIG. 2B, the distance between the lens barrel 10 and the growth substrate 7 is made closer, and a voltage of 15 kV or more is applied to the lens barrel. To do.
[0032]
In FIG. 2B of the present embodiment, the lens barrel 10 including the evaporation source is brought close to the growth substrate 7, but the growth substrate 7 may be made closer to the lens barrel 10.
[0033]
【The invention's effect】
According to the film forming apparatus of the present invention, the thin film growth surface can be observed / evaluated in real time without impairing the performance as the film forming apparatus. In particular, a two-dimensional image of the thin film growth surface can be observed simultaneously with the periodic structure of the atomic arrangement on the thin film growth surface.
[Brief description of the drawings]
FIG. 1 is a schematic view of a molecular beam epitaxy apparatus for explaining a reference example .
FIG. 2 is a schematic view of a molecular beam epitaxy apparatus for explaining an embodiment in the present invention.
FIG. 3 is a schematic view of a conventional molecular beam epitaxy apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 High vacuum chamber 2 Cell 3 Heater 4 Shutter 5 Heating heater 6 Substrate holder 7 Growth substrate 8 Electron gun 9 Fluorescent plate 10 Lens barrel 11 Objective lens 12 Intermediate lens 13 Projection lens 14 Objective aperture 15 Multichannel plate 16 Fluorescent plates 17 and 18 , 19 Viewport 20 UV irradiation device 21 Quadrupole mass spectrometer 22 Exhaust system

Claims (8)

A film forming means for forming a film by irradiating a material beam from an evaporation source onto a substrate, a light source for irradiating light on a film forming surface formed on the substrate, and light irradiated from the light source , An electron detection means for detecting photoelectrons emitted from the film formation surface, wherein the electron detection means forms an image of the photoelectrons emitted from the film formation surface on the imaging surface And a means for displaying and / or recording the electron intensity distribution on the imaging surface, and changing the distance between the lens barrel and the film formation surface when the material beam is irradiated and when photoelectrons are detected. film forming apparatus characterized in that it comprises a means for. 2. The film forming apparatus according to claim 1 , wherein the evaporation source includes the evaporation source disposed around the lens barrel.   The film forming apparatus according to claim 2, wherein a plurality of the evaporation sources are arranged, and the plurality of evaporation sources are arranged on a circumference centered on the lens barrel.   The film forming apparatus according to claim 2, wherein the evaporation source has a shutter for blocking a molecular beam from the evaporation source toward the film formation surface.   The film forming apparatus further includes an electron beam irradiating unit that irradiates the film forming surface with an electron beam, and a reflection that detects electrons reflected from the film forming surface by electrons irradiated from the electron beam irradiating unit. The film forming apparatus according to claim 1, further comprising an electron detection unit.   6. The film forming apparatus according to claim 5, wherein the reflected electron detection means includes a visualization means for visualizing a diffraction pattern of the reflected electrons.   The film forming apparatus according to claim 6, wherein the visualization unit is a substrate having a phosphor.   The film forming apparatus according to claim 1, wherein the film forming apparatus is a molecular beam epitaxy apparatus.

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