JP2004162108A - Molecular beam source cell for thin film deposition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a molecular beam source cell for thin film deposition which forms a thin film with a uniform thickness even when its molecule ejection ports are arranged near to a solid film-formation surface, thus enhancing film formation efficiency and film thickness uniformity. <P>SOLUTION: The molecular beam source cell for thin film deposition generates molecules for growing a thin film on a solid surface by subliming or vaporizing a film-forming material (a) under heating, and has a plurality of molecule ejection ports 4, 4 for ejecting molecules of the film-forming material toward a film-forming plane 1 for forming the film. These molecule ejection ports 4, 4 are opened so as to mutually face outside obliquely and, concretely, are arranged around a cell head 7 facing the film-forming plane 1. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
According to the present invention, by heating a film-forming material, the film-forming material is sublimated or melted and evaporated to generate molecules of the film-forming material, and the molecules of the film-forming material are emitted toward a solid surface. The present invention relates to a thin film deposition molecular beam source cell used for growing a film by depositing molecules on a solid surface, and a thin film deposition method using the same.
[0002]
[Prior art]
A thin film deposition apparatus called a molecular beam epitaxy apparatus installs a substrate in a vacuum chamber capable of reducing the pressure to a high vacuum, heats the substrate to a required temperature, and moves a molecule such as a Knudsen cell toward a thin film growth surface of the substrate. A source cell is installed. The film-forming material accommodated in the crucible of the molecular beam source cell is heated by a heater to sublimate or melt and evaporate. Then, a film of a film forming material is formed.
[0003]
The molecular beam source cell used in such a thin film deposition apparatus stores a film forming material in a crucible made of, for example, PBN (pyrrolytic boron nitride) having high thermal and chemical stability. Then, the film-forming material is heated by an electric heater provided outside the crucible, thereby sublimating or melting and evaporating the film-forming material to generate film-forming molecules.
[0004]
2. Description of the Related Art In recent years, research and development of organic electroluminescent elements (organic EL elements) have been promoted in fields such as displays and optical communications. This organic EL element is an element in which a light emitting layer is formed of an organic low molecular weight or organic high molecular weight material having EL light emitting ability, and has attracted attention as a self-luminous type element. For example, the basic structure is such that a film of a hole transporting material such as triphenyldiamine (TPD) is formed on a hole injecting electrode, and a fluorescent substance such as an aluminum quinolinol complex (Alq ₃ ) is laminated thereon as a light emitting layer. Further, a metal electrode having a small work function, such as Mg, Li, or Ca, is formed as an electron injection electrode.
[0005]
[Problems to be solved by the invention]
Recently, large screens have become a requirement of the times. Therefore, even in the display using the organic EL as described above, it is required to form an organic EL film on a large-sized substrate. In particular, in a display using an organic EL, it is required to form a uniform organic EL film on a substrate.
[0006]
However, in a conventional vacuum deposition apparatus used for forming an organic EL film, a film-forming material is sublimated or evaporated from one molecular beam source cell to emit molecules toward the surface of the substrate, and the film-forming material is removed. Since this is a method of depositing and growing a film, it is difficult to form a uniform thin film on a large-area substrate.
[0007]
In particular, when the molecular emission port is close to the film deposition surface of the substrate, the film thickness of a part of the substrate deposition surface facing the molecule emission port becomes thicker, and the film thickness decreases rapidly toward the periphery. Such a film thickness distribution is shown. That is, the non-uniformity of the thickness of the thin film increases. On the other hand, if the molecular emission port is separated from the film-forming surface of the substrate, the uniformity of the film thickness is improved, but the molecules are scattered in places other than the film-forming surface of the substrate, so that the film-forming efficiency deteriorates, It is impossible to form a thin film having a required film thickness in a short time with the used material. Organic EL materials are expensive, and low film formation efficiency results in high product costs.
[0008]
SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in a conventional vacuum deposition apparatus using a film thickness gauge, and has as its object to form a thin film having a uniform thickness on a solid film formation surface. More specifically, even when the molecular emission port is close to the solid deposition surface, the thickness of the deposited thin film can be made uniform, thereby achieving both the deposition efficiency and the uniformity of the film thickness. The purpose is to be able to improve.
[0009]
[Means for Solving the Problems]
In the present invention, in order to achieve the above object, not only one but also a plurality of molecule discharge ports 4, 4,... Are provided in one molecular beam source cell, and these molecule discharge ports 4, 4,. , And the molecules are radially emitted toward the film formation surface 1 from the molecule release ports 4, 4,... Toward the film formation surface 1.
[0010]
That is, the molecular beam source cell for depositing a thin film according to the present invention generates a molecule for growing a thin film on a solid surface by heating the film forming material a and sublimating or evaporating the film forming material a. A plurality of molecule outlets 4, 4,... For releasing molecules of the material forming the thin film are provided toward the thin film forming surface 1, and these molecule outlets 4, 4,. It was made.
More specifically, a plurality of molecular emission ports 4, 4,... Are arranged around the center of the cell head 7 facing the thin film deposition surface 1.
[0011]
As described above, the molecules of the thin-film material are emitted from the molecular emission port of the molecular beam source cell toward the film-forming surface of the substrate, and when the film is formed, the film in the portion of the film-forming surface facing the molecule emission port and the front surface is formed. The thickness is large, and the film thickness becomes thinner toward the periphery. This tendency becomes more remarkable as the distance between the film-forming surface of the substrate and the molecular emission port of the molecular beam source cell is shorter.
[0012]
On the other hand, in the above-described molecular beam source cell for forming a thin film according to the present invention, a plurality of molecule discharge ports 4 for releasing molecules of a material forming the thin film toward the film-forming surface 1 of the thin film are provided. Are open obliquely outwardly from each other, so that the amount of molecules to be deposited on the film-forming surface 1 of the substrate is such that the amount of molecules deposited on the film-forming surface 1 is opposite to the molecular discharge port on the film-forming surface. It does not shift to the central part of and spreads around it. As a result, a thin film having a uniform thickness can be formed as a whole over a wide range of the deposition surface 1. In other words, even when the molecular emission ports 4, 4,... Are close to the film formation surface 1 of the substrate, a thin film having a uniform thickness is easily formed.
[0013]
In particular, as described above, the plurality of molecule discharge ports 4, 4,... Are arranged around the center of the cell head 7 facing the thin film deposition surface 1, and these molecule discharge ports 4, 4,. The amount of molecules deposited on the film-forming surface 1 of the substrate is not biased to a position facing the center of the cell head 7 on the film-forming surface 1 and is dispersed around the film-forming surface 1. A high thin film can be formed.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described specifically and in detail with reference to the drawings.
FIG. 1 is a longitudinal sectional side view showing an embodiment of a molecular beam source cell for depositing a thin film according to the present invention, and FIG. 2 is a plan view thereof. This embodiment is an example in which the film deposition surface 1 of the substrate is directed horizontally downward, and the cell head 7 of the molecular beam source cell is vertically directed upward so as to face the film deposition surface 1.
[0015]
The molecular beam source cell has a crucible 5 in which a film forming material a is stored. The film-forming material a housed in the crucible 5 is heated by the heating unit 3 provided near the opening of the crucible 5, whereby the film-forming material a sublimates or evaporates to generate its molecules.
[0016]
The opening side of the crucible 5 communicates with the buffer chamber 6. The buffer chamber 6 is a small room for temporarily retaining molecules of the film forming material evaporated from the film forming material a stored in the crucible 5. A heating unit 2 is provided on the upper opening side of the buffer chamber 6 for heating molecules of the evaporated film-forming material a and keeping the molecules in a molecular state.
[0017]
A cell head 7 covers the opening of the buffer chamber 6. This cell head 7 has a cap shape, and has four molecule emission ports 4, 4,... The number of the molecular emission ports 4, 4,... Can be appropriately changed depending on the material for forming the film, the area of the film forming surface 1 of the substrate on which the film is formed, and the like. It is good to provide on the same circumference at equal intervals. Further, in the embodiment shown in FIGS. 1 and 2, the molecular emission ports 4 are provided on one circumference around the center of the cell head 7. May be provided on the concentric circles.
[0018]
In FIG. 1, a dashed line indicated by a symbol o is the center line of the molecular beam source cell, and the center line o passes through the center of the cell head 7, and the center of the cell head 7 faces the film-forming surface 1 of the substrate in this direction. ing. That is, the center axis o intersects the center of the film-forming surface 1 of the substrate at right angles to the same surface 1.
[0019]
The directions of the plurality of molecular emission ports 4, 4,... Are all inclined at an angle θ equal to the radiation direction about the central axis o. The inclination angle θ of the molecular emission ports 4, 4,... With respect to the central axis o is 30 ° in FIG. 1, which is the material to be formed, the distance between the molecule emission ports 4, 4,. An optimum value is appropriately selected depending on the material to be formed, the area of the film formation surface 1 of the substrate on which the film is formed, and the like. Further, a case where a plurality of molecular emission ports 4, 4,... Are respectively provided on a plurality of concentric circles having different diameters around the center of the cell head 7 may be used. The angle of inclination θ with respect to the central axis o may be different between the molecular emission ports 4, 4,... On the inner circumference and the molecular emission ports 4, 4,. Preferably, the inclination angle θ of the molecular emission ports 4, 4,... On the inner circumference is small, and the inclination angle θ of the molecular emission ports 4, 4,.
[0020]
Further, in the embodiment shown in FIGS. 1 and 2, a molecular emission port 8 is provided in the direction of the center axis o at the center position of the cell head 7 through which the center axis o passes. The molecule outlet 8 is a secondary molecule outlet 8 having a smaller diameter than the molecule outlets 4 provided around the molecule outlet. Of course, such a secondary molecular emission port 8 may not be provided.
[0021]
In such a molecular beam source cell for depositing a thin film, a part of molecules generated by being heated by the heating unit 3 and evaporating or sublimating from the film forming material in the crucible 5 is firstly transferred to the buffer chamber 6 as a small room. enter. Further, these molecules are released from the buffer chamber 6 through the molecule release ports 4, 4,... And are deposited on the film formation surface of the substrate 1.
[0022]
At this time, the plurality of molecule discharge ports 4, 4,... Are arranged around the center of the cell head 7 facing the thin film deposition surface 1, and these molecule discharge ports 4, 4,. Therefore, the amount of molecules deposited on the film-forming surface 1 of the substrate does not shift to the center position of the film-forming surface 1 facing the center of the cell head 7 but is dispersed around the center. Therefore, a thin film having high uniformity in film thickness can be formed.
[0023]
Note that, for example, when the angle θ of the direction of the molecular emission ports 4, 4,... With respect to the central axis o of the molecular beam source cell is large, the position of the film formation surface 1 of the substrate facing the center of the cell head 7, that is, FIG. In this case, the film thickness of the thin film at the position where the central axis o intersects the film-forming surface 1 may be rather thinner than the film thickness around the thin film. In this case, as described above, the thickness distribution can be improved by providing a secondary molecule emission port 8 different from the molecule emission ports 4, 4,... At the center of the cell head 7. .. May be provided at the center of the cell head 7, or a plurality of secondary molecule outlets 8 may be provided around the center of the cell head 7. Also in this case, a plurality of secondary molecular emission ports 8, 8,... May be opened on a plurality of concentric circles having different diameters around the center of the cell head 7. Are provided on a plurality of concentric circles having different diameters around the center of the cell head 7, respectively, and the inclination angle θ of the molecular discharge ports 4, 4,. It is also effective to increase the inclination angle θ of the molecular emission ports 4, 4,... On the outer circumference.
[0024]
FIG. 3 shows an embodiment of horizontal deposition in which the film deposition surface 1 of the substrate is oriented vertically and the molecular beam source cell is oriented horizontally instead of the vertical evaporation method shown in FIGS. That is, this embodiment is an example in which the film deposition surface 1 of the substrate is oriented vertically and horizontally, and the cell head 7 of the molecular beam source cell is horizontally oriented so as to face this. Other configurations are the same as those of the embodiment shown in FIGS. 1 and 2, and the same parts are denoted by the same reference numerals.
[0025]
FIG. 4 shows an embodiment of the present invention, in which the thin film deposition molecular beam source cell shown in FIG. 1 and the conventional thin film deposition molecular beam source cell are used to emit molecules of the organic EL material, respectively. Is a film thickness distribution of a thin film when a thin film is formed by depositing the film on a film forming surface of a substrate. It is shown as a percentage of the maximum film thickness. The solid line is an example of the present invention, and the broken line is a comparative example.
[0026]
As shown in FIG. 5, a 30 cc crucible was used in each of the example and the comparative example. Four molecule emission ports are provided on the circumference at 90 ° intervals. The molecular emission port is inclined at an angle θ = 30 ° equal to the radiation direction about the center axis of the molecular beam source cell passing through the center of the cell head. There is no central molecular outlet 8 as shown in FIGS. On the other hand, the molecular beam source cell used in the comparative example has a molecular emission port having the same diameter as the molecular emission port of the molecular beam source cell used in the above example at the center of the cell head. The molecular emission port faces the center axis direction of the molecular beam source cell passing through the center of the cell head, and faces the film forming surface of the substrate. In the example, the distance from the molecular emission port of the molecular beam source cell to the film formation surface of the substrate was 200 mm, and in the comparative example, it was 180 mm.
[0027]
As is clear from the results of the film thickness distribution shown in FIG. 4, in the example, the film thickness of the thin film is the largest at the center of the film forming surface of the substrate that intersects with the central axis of the molecular beam source cell, and is located 70 to 80 mm away therefrom. However, a film thickness of 90 to 97% of the maximum film thickness was obtained. On the other hand, in the comparative example, the film thickness of the thin film is the same at the center of the film forming surface of the substrate, but at a position 70 to 80 mm away therefrom, it is extremely 65% of the maximum film thickness value. It has become thin.
[0028]
【The invention's effect】
As described above, in the molecular beam source cell for forming a thin film according to the present invention, a thin film having a uniform thickness as a whole can be formed over a wide range of the film forming surface 1. That is, even if the molecular emission ports 4, 4,... Are close to the film-forming surface 1 of the substrate, it becomes easier to form a thin film having a uniform thickness, so that the film-forming efficiency can be improved. Thereby, it is possible to improve both the film forming efficiency and the film thickness uniformity.
[Brief description of the drawings]
FIG. 1 is a partially broken side view showing one embodiment of a molecular beam source cell for depositing a thin film according to the present invention.
FIG. 2 is a plan view showing an embodiment of the molecular beam source cell for depositing a thin film.
FIG. 3 is a partially broken side view showing another embodiment of the molecular beam source cell for depositing a thin film according to the present invention.
FIG. 4 shows a film forming surface of a substrate using a molecular beam source cell for depositing a thin film according to an embodiment of the present invention and a conventional molecular beam source cell for depositing a thin film, and radiating molecules of the organic EL material from them. 4 is a graph showing a film thickness distribution of a thin film when deposited on a thin film to form a thin film.
FIG. 5 shows a method of using the molecular beam source cell for depositing a thin film and the conventional molecular beam source cell for depositing a thin film according to the above-described embodiment, and irradiating molecules of the organic EL material from them to deposit them on the film forming surface of the substrate. FIG. 4 is an explanatory diagram showing a state in which the operation is performed.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Deposition surface of substrate 2 Heating unit 3 Heating unit 4 Molecular discharge port 5 Crucible 7 Cell head

Claims (2)

By heating the film-forming material (a), the film-forming material (a) is sublimated or evaporated to generate molecules for growing a thin film on a solid surface. A plurality of molecule outlets (4), (4)... For releasing molecules of the material forming the thin film toward the film forming surface (1) are provided, and these molecule outlets (4), (4). A molecular beam source cell for depositing a thin film, characterized by being opened outward. 2. The deposition molecule according to claim 1, wherein the plurality of molecule outlets are arranged around the center of the cell head facing the thin film deposition surface. 3. Source cell.

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