JP2016160481A - Deposition cell, thin film preparation apparatus and thin film preparation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a deposition cell, a thin film preparation apparatus and a thin film preparation method, capable of controlling a high molecular flow density to constant in a simple configuration and thereby speeding up a film deposition rate.SOLUTION: There is provided a method for preparing thin film material on a substrate by using a vacuum deposition method, in which a deposition cell 1 as a deposition source is used with at least one discharge port having a structure of a capillary 3 and the inner part of the deposition cell 1 is adjusted to a material vapor pressure that generates a predetermined pressure gradient in the capillary 3. The material vapor pressure that generates the pressure gradient in the capillary 3 is a pressure gradient in which a pressure difference occurs in an incident side 31 and an ejection side 32 in the capillary 3, and the material to be deposited transits from a viscous flow state on the incident side 31 to a molecular flow state on the ejection side 32. Further, in the deposition cell 1, heat conductive material is coated on at least an inner wall 11 of the deposition cell 1 and an inner wall of the capillary 3, and a coating agent which is inactive to the material is applied on the surface of the heat conductive material.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a vapor deposition cell, a thin film manufacturing apparatus, and a thin film manufacturing method as an evaporation source for manufacturing an active layer of an inorganic or organic semiconductor device.

In order to achieve mass production of large-area circuits in flexible devices such as organic electroluminescence (EL) displays using organic semiconductor thin films, RFID (Radio Frequency Identifier) tags, and artificial skin, There is a need to reduce manufacturing costs.
In recent years, technologies for producing single-crystal thin films using wet processes for forming organic semiconductor materials into inks and printing and coating on large-area substrates have been announced, and high carrier mobility has begun to be obtained. Expectations for practical use as a cost process have been gathered. However, the production of a single crystal thin film using this wet process has the following problems.
First, since a method such as printing or coating is used, it is necessary to make an ink and the ink is limited to a material soluble in a solvent. Next, if a functional group that adds solubility to an insoluble material is added, charge transport is hindered by the added functional group. Furthermore, irregularities are likely to occur irregularly due to stress generated when the material is dried. In addition, since the drying / heat treatment performed during film formation takes time, the cycle time becomes long.

On the other hand, the vacuum deposition method is excellent in controllability of film thickness, purity and heterogeneous molecule mixing ratio, and is characterized in that a thin film with good crystallinity can be produced. However, the vacuum deposition method has a problem of high manufacturing cost of a thin film in a large area, and it is difficult to adopt it in a mass production process.
Usually, the vacuum deposition method uses a “crucible” (deposition cell) as a deposition apparatus to evaporate the material to be deposited. Many organic low molecular weight materials are sublimable in vacuum, have low thermal conductivity, and are in a powder state. Therefore, even if the temperature of the deposition cell is controlled to be constant, the entire material does not become a uniform temperature. In addition, depending on the structure and contact state of the individual particles, the evaporated molecules are suddenly released out of the deposition cell, making it difficult to control the high molecular flow density at a constant level. For this reason, since it is necessary to deposit the material under mild conditions in a range where the molecular flow density emitted from the deposition cell can be stably controlled, the film formation rate per area becomes slow.
In addition, the vacuum deposition method requires a large-scale vacuum chamber and a high-performance vacuum pump. In addition to the high cost of introducing these devices, a high vacuum is required in order to suppress residual gas mixing into the thin film. There is a large vacuum pump for evacuation and a long evacuation time.
For these reasons, the vacuum deposition method has a problem that the cycle time is long and the cost per product is high due to the slow deposition rate per area and the waiting time for evacuation. In order to overcome such a problem, a mechanism capable of controlling the deposition rate at a high speed is required.

Under such circumstances, in a vacuum vapor deposition apparatus used for manufacturing an organic EL display, highly accurate vapor deposition is performed by reducing the influence of radiant heat from the evaporation source crucible to the vapor deposition mask and suppressing the expansion of the vapor deposition mask. A vapor deposition apparatus that can perform this is known (see Patent Document 1).
In the case of the vacuum evaporation apparatus disclosed in Patent Document 1, a plurality of protrusions are formed in the crucible longitudinal direction in a state of protruding to the upper part of the crucible facing the deposition target substrate, and the outer shape of the protrusions is a cylindrical shape, It has a truncated cone shape, a truncated pyramid shape, etc., and has a structure protruding from the upper surface of the crucible. And since the radiation blocking body for suppressing the expansion | swelling with the temperature rise of a metal vapor deposition mask is provided in the circumference | surroundings of a projection part, the height of a projection part is the height equivalent to the radiation blocking body upper surface, or Try to be high. The inside of the projecting portion has a shape in which an emission hole for injecting a vapor deposition material evaporated from the inside of the crucible tapers stepwise or continuously from the inside of the crucible toward the vapor deposition substrate. It has a structure that does not hinder the evaporation material evaporated inside from scattering toward the exit side opening of the exit hole.
The vacuum deposition apparatus disclosed in Patent Document 1 is intended to reduce the influence of radiant heat on the deposition mask, and does not control the deposition rate at a high speed.

In addition, an evaporation source and vacuum deposition that can be operated continuously for a long time by forming a metal thin film with a uniform film thickness on a large substrate at high speed to reduce vapor leakage and nozzle temperature drop. An apparatus is known (see Patent Document 2). In the evaporation source and the vacuum evaporation apparatus disclosed in Patent Document 2, a crucible provided with an opening, a heater provided so as to surround the outer wall of the crucible, and the inner wall of the crucible are in contact with the length of the nozzle plate or more. In order to maintain the sealing property between the inner wall of the crucible and the nozzle, a seal part for sealing with the crucible is provided at a part of the nozzle.
In the case of the evaporation source and the vacuum evaporation apparatus disclosed in Patent Document 2, since the inner wall of the crucible is provided so as to be in contact with the length of the nozzle plate or more, it is necessary to provide a structure for supporting the nozzle in the crucible, There is a demerit that the structure of the crucible becomes complicated because it is necessary to select a member for reducing heat dissipation and steam leakage due to a decrease in temperature, to adjust the plate thickness, and to ensure a sealing property. Moreover, in the evaporation source and the vacuum evaporation apparatus disclosed in Patent Document 2, a high molecular flow density cannot be controlled constantly.

In addition, a rare gas is introduced into the chamber, a supersonic molecular beam containing organic molecules of the vapor deposition material is generated, and a molecular beam of the vapor deposition material having high kinetic energy is selectively incident on the substrate by a gap and differential exhaust. Thus, a method for producing a highly crystalline film without raising the temperature of the substrate is known (see Non-Patent Document 1).
In the method of Non-Patent Document 1, there is an advantage that a high molecular flow density can be constantly controlled by a supersonic molecular beam to increase a film forming rate per area, but a large amount of rare gas and an ultrahigh vacuum atmosphere are required. For this reason, there is a problem in the production cost of the film.

JP 2004-214185 A JP 2014-198863 A

S. Iannotta and T. Toccoli, J.A. Polym. Sci. , Part B: Polym. Phys. 41 (2003) 2501

As described above, it is difficult to constantly control the high molecular flow density in the deposition cell in the conventional vacuum deposition method. In order to avoid this problem, when vapor deposition is performed under mild conditions that can be stably controlled, the growth rate is limited to about 1 angstrom / second at a typical distance between the vapor deposition cell and the substrate, and film formation is performed. Incurs a decrease in speed.
In view of such circumstances, an object of the present invention is to provide a deposition cell, a thin film manufacturing apparatus, and a thin film manufacturing method capable of constantly controlling a high molecular flow density and increasing a film forming speed with a simple configuration. .

In order to solve the above-mentioned problems, the thin film production method of the present invention is a method for producing a thin film on a substrate by a vacuum vapor deposition method. In the vapor deposition cell serving as a vapor deposition source, an emission port of at least one capillary structure is provided. It is used, and the inside of the deposition cell is adjusted to a material vapor pressure that generates a predetermined pressure gradient inside the capillary.
By using a capillary structure discharge port in the vapor deposition cell serving as the vapor deposition source, the high molecular flow density can be controlled to be constant and the film formation rate can be increased. It is necessary to adjust the material vapor pressure so that a pressure gradient is generated inside the capillary.
In this specification, the capillary structure is defined as a thin tube (thin tube like hair) structure provided in a part of a casing of a sealed deposition cell. The diameter and length of the capillary structure is sufficiently high due to the pressure difference between the vapor pressure of the vapor deposition material, which is sufficiently increased to the viscous flow region on the entrance side, and the vacuum outside the vapor deposition cell. Conductance that produces as much molecular flux as possible (in the case of a cylindrical capillary with a diameter d and a length l, when the average pressure in the capillary of the raw material molecule with the viscosity coefficient η is p, the conductance is ( (π / 128) · (d ⁴ p / ηl) In the case of the present invention, the pressure difference between both ends of the capillary is large, and the flow is from a viscous flow state to an intermediate flow state to a molecular flow state. It is difficult to determine unless it is based on etc.). Further, in this specification, “capillary structure” may be simply referred to as “capillary”, but “capillary” is used to indicate “capillary structure”.
With the above structure, an equilibrium vapor pressure is achieved in a closed vapor deposition cell at a higher temperature, and a vapor deposition material having a high molecular flow density can be discharged from the discharge port of the capillary structure, so that the film formation rate can be increased. In addition, an abrupt pressure gradient can be formed between the vacuum and the chamber atmosphere.
Note that the material to be vapor-deposited can be any organic or inorganic material as long as it is a sublimable material. The deposition cell has a semi-closed structure and is provided with a capillary structure outlet in the deposition direction.

  Here, the material vapor pressure causing a pressure gradient inside the capillary has a pressure difference between the entrance side and the exit side in the capillary, and the pressure at which the material to be vaporized transitions from the viscous flow state on the entrance side to the molecular flow state on the exit side A gradient is preferred. That is, the gas molecules of the material to be deposited move from the moving state of the viscous flow region on the incident side (the state where the collision frequency of molecules is larger than the frequency of collision of the molecules to the inner wall of the capillary) to the moving state of the molecular flow region on the output side ( The pressure gradient is preferably changed to a state in which the frequency of collision with the inner wall of the capillary is higher than the frequency of collision between the molecules. Inside the capillary, the incident side of the material is inside the evaporation cell, and the emission side of the material is outside the evaporation cell. When the pressure is high, the collision of molecules is dominant in the viscous flow region, and as the pressure decreases, the mean free path of the gas molecules becomes larger, and the collision between the molecule and the wall is greater than the collision between the molecules. It becomes the state of the molecular flow region where the frequency increases.

As described above, when the pressure inside the deposition cell is increased to a pressure at which the material molecules become a viscous flow region, a rapid pressure gradient is generated in the capillary. Under such conditions, the material molecules colliding inside the capillary are accelerated in the direction of the capillary outlet, the average kinetic energy is larger than the thermal equilibrium state, and the material molecules are ejected like a thin beam-like high-speed molecular beam. The high-speed molecular beam in the present invention is a molecular beam emitted from the capillary in the form of a thin beam as a result of having a state in which the average kinetic energy is larger than the thermal equilibrium state in this way. In order to effectively generate such a beam-like high-speed molecular beam, in addition to the above conditions, the pressure distribution inside the capillary is such that the position in the capillary that reaches the molecular flow region is close to the capillary exit side. It is preferable to do so.
High-speed material molecules ejected like a thin beam promote molecular diffusion on the target substrate, and it is not equivalent to improving crystallinity by raising the substrate temperature, but can obtain the same effect Become. Therefore, it is possible to omit the substrate temperature raising process for improving the crystallinity of the thin film formed on the substrate or the structural stability of the amorphous film, further shortening the cycle time of the vacuum deposition method and heating. Two effects of cost reduction of the temperature raising device can be expected.

Further, in the above evaporation cell, it is preferable that at least the inner wall of the evaporation cell and the inner wall of the capillary are coated with a heat conductive material. This is because the inside of the cell is quickly soaked together with the material, and a high molecular flow density can be stably controlled.
The entire deposition cell or the entire capillary may be made of a heat conductive material. Examples of the thermally conductive material include metals, metal oxides, carbon, and composite materials thereof.
Further, when the inner wall of the capillary becomes lower than the temperature of the material vapor, the material aggregates in the capillary and becomes in a closed state. Therefore, in particular, the capillary portion needs to improve heat conduction from the vapor deposition cell heating source. Therefore, it is desirable that the capillary is not formed with a protruding structure as seen in Patent Document 1, but is formed on a thermally conductive material wall in which the length of the capillary is as it is.

When the thermally conductive material coated on the vapor deposition cell is a metal, it is preferable that the surface of the thermally conductive material is coated with a coating agent that is inert to the material. This is to prevent modification such as decomposition of the material by a high-temperature metal. For example, when oxygen-free copper is coated as a thermally conductive material and an organic material is used as a material to be deposited, the surface of oxygen-free copper is an inert film in order to prevent a chemical reaction between the organic material and oxygen-free copper. For example, it is preferable to coat with silicon oxide (SiO ₂ ).

As described above, the capillary structure has a sufficient diameter and length due to the pressure difference between the vapor pressure of the vapor deposition material that has been sufficiently increased to the viscous flow region on the entrance side and the vacuum outside the vapor deposition cell. The size is determined so as to obtain a conductance that generates a molecular flux sufficient to obtain a high film formation rate, but typically has a diameter of 0.1 to 1 mm and a length of 1 to 100 mm. However, it is adjusted so as to satisfy the above conditions depending on the physical properties of the material and the required film forming speed, and is not limited to this range.
Further, the space in the capillary is linear at least at the part where the molecular flow state is achieved. As described above, the vapor deposition cell has a semi-closed structure and is provided with a capillary structure outlet in the vapor deposition direction, but this capillary structure is not affected by the location of the vapor deposition cell due to Pascal's principle. The pressure conditions are the same. Usually, since the substrate is provided on the vapor deposition cell, the capillary structure may be provided at the center of the upper lid of the vapor deposition cell. What is more important than the position where the capillary structure is provided is that the capillary structure is linear. Since the portion in the molecular flow state is linear, many of the gas molecules of the vapor deposition material are emitted in a well-formed beam. If the capillary structure is bent and the portion that is in a molecular flow state is not linear, many of the gas molecules of the vapor deposition material to be released are irregularly scattered by the inner wall of the capillary and are not emitted in the form of a beam. Will occur.

The space shape in the capillary is preferably a cylinder, an elliptical column, a polygonal column, a truncated cone, an elliptical truncated cone, a polygonal truncated cone, or a combination thereof. With these shapes, the space in the capillary is linear in the length direction, and the portion in the molecular flow state is also linear, and a pressure gradient with high directivity is likely to occur.
In the case of a truncated cone, elliptical truncated cone, polygonal truncated cone, etc., the incident side opening area is different from the exit side opening area, and a pressure gradient is likely to occur inside the capillary.At this time, the exit side opening area is larger than the incident side opening area. It is better to enlarge it. However, it should be noted that the directivity of the pressure gradient decreases as the area difference increases.

In the thin film production method of the present invention, the vapor deposition cell may include a plurality of capillary structures having the same shape and the same size, and the plurality of capillaries may be arranged at equal intervals in one or two dimensions.
Although the vapor deposition area of the vapor deposition cell alone is sufficient to produce a fine element, it is necessary to increase the vapor deposition area in order to achieve mass production of large area devices such as large displays. In such a case, the deposition area is increased by scanning the cell or the substrate using an expansion type deposition cell in which capillaries are mounted one-dimensionally or two-dimensionally on the same cell. To do.
Here, for a deposition cell in which capillary structures are arranged one-dimensionally at equal intervals, a thin film is produced by evaporating material on the substrate by scanning the substrate side or roll-to-roll method. To do. On the other hand, for a deposition cell in which capillary structures are two-dimensionally arranged at regular intervals, the substrate can be fixed and deposited depending on the size of the deposition cell and the size of the substrate on which the thin film is formed, or the substrate side A thin film is formed on the substrate by vapor-depositing the material while scanning.
By providing a plurality of capillary structures in a single vapor deposition cell, molecules exceeding the total emitted molecules can be evaporated from the vapor deposition material at a realistic temperature. Further, the structure having a plurality of capillaries in one cell has an advantage that the outgoing molecular flows from all the capillaries become the same as long as the processing accuracy is certain.

  Further, a plurality of vapor deposition cells having the same shape and the same size of the capillary structure may be arranged at equal intervals in one or two dimensions. Then, a thin film is produced by depositing a material on the substrate by a method of scanning the substrate side or a roll-to-roll method.

When the deposition cell has a plurality of capillary structures of the same shape and the same size, and the plurality of capillaries are arranged one-dimensionally or two-dimensionally at equal intervals to form a thin film, the distance between the centers of the capillaries, the substrate, The film thickness distribution of the thin film should be controlled from the distance from the capillary discharge port and the material discharge angle distribution due to the material vapor pressure.
Even when a plurality of vapor deposition cells having the same shape and the same size capillary structure are arranged one-dimensionally or two-dimensionally at equal intervals to produce a thin film, the distance between the centers of the capillaries and the release of the substrate and the capillary The film thickness distribution of the thin film should be controlled from the distance to the outlet and the material discharge angle distribution due to the material vapor pressure.

In this case, a flux monitoring capillary having the same shape and size as the capillary structure is preferably provided for each vapor deposition cell.
When a plurality of capillaries are arranged or a plurality of vapor deposition cells are arranged, a flux monitoring capillary is provided separately from the vapor deposition capillaries so that the flux (amount of flow per unit time / unit area) The outgoing molecular velocity can be controlled by the change. For example, in a vapor deposition cell having a plurality of large capillary structures, a monitoring capillary structure (the same shape and size as those for vapor deposition) is provided at a position separated by one, and a crystal resonator is disposed immediately above the emission port. To monitor the molecular flux.

Next, the vapor deposition cell of this invention is demonstrated.
The vapor deposition cell of the present invention is a vapor deposition cell used for producing a thin film on a substrate by a vacuum vapor deposition method. The vapor deposition cell has at least one capillary structure discharge port, and the inside of the capillary has a viscous entrance side. A beam-like molecular beam is emitted when the pressure in the cell is adjusted to a material vapor pressure that generates a pressure gradient that causes a flow state and a molecular flow state on the exit side.
In this vapor deposition cell, at least the inner wall of the vapor deposition cell and the inner wall of the capillary are preferably coated with a heat conductive material. The heat conductive material is preferably a metal, and the surface of the heat conductive material is preferably coated with a coating agent that is inert to the material.
The length of the capillary with respect to the inner diameter is adjusted so that the conductance can be obtained so that the pressure gradient condition is obtained in a state where a target deposition rate is obtained. The space in the capillary is linear at least in the part where the molecular flow state occurs. The space shape in the capillary is a cylinder, an elliptical cylinder, a polygonal cylinder, a truncated cone, an elliptical truncated cone, a polygonal truncated cone, or a combination thereof.

Next, the thin film production apparatus of the present invention will be described.
The thin film production apparatus of the present invention is an apparatus for producing a thin film on a substrate by using a vacuum vapor deposition method. The above-described vapor deposition cell of the present invention includes a plurality of capillary structures having the same shape and the same size. They are arranged one-dimensionally or two-dimensionally at equal intervals. A flux monitoring capillary having the same shape and size as the vapor deposition capillary structure is provided in order to control the flux released from the vapor deposition cell. In order to produce a thin film having a uniform thickness on a large-area substrate, a mechanism for scanning the vapor deposition cell or a combination of a flux monitor and a vapor deposition cell in two orthogonal directions may be provided. Alternatively, for this purpose, it may have a mechanism for scanning a deposition cell or a set of a flux monitor and a deposition cell in one direction and a mechanism for moving the substrate in a direction perpendicular to the mechanism. Good.
Alternatively, the thin film production apparatus of the present invention is an apparatus for producing a thin film on a substrate by a vacuum vapor deposition method, and a plurality of the above-described vapor deposition cells of the present invention are arranged at equal intervals in one or two dimensions. It is a thing. Each vapor deposition cell is provided with a capillary for flux monitoring having the same shape and size as the capillary structure.

According to the present invention, a high molecular flow density is constantly controlled with a simple configuration, and it is possible to stably deposit at a high film formation rate that cannot be achieved by the conventional vacuum deposition method.
Note that the vapor deposition cell can be used as a material evaporation source as a fine particle manufacturing method even in the vicinity of atmospheric pressure, not near vacuum.

Illustration of deposition cell Schematic diagram of film thickness distribution measurement Diagram showing polar coordinates of film thickness distribution Film thickness distribution when changing the deposition rate for each capillary diameter Image of (a) diffused model and (b) model emitting parallel beam The figure which shows the result of having fitted the experimental result using Numerical formula 1. The figure which shows the model of isotropic scattering from the viscous flow area | region in the film-forming speed | rate "high" Ejection image of vapor deposition cell of this example and cell without capillary structure Conceptual diagram of gas molecule injection at three deposition rates of the deposition cell of this example Transition diagram of molecular flow region and viscous flow region in the deposition cell of this example Schematic diagram of the organic thin film transistor fabricated Atomic force microscope (AFM) image of the surface height image of a pentacene thin film prepared by changing the capillary diameter and the deposition rate Diagram of transfer characteristics of organic thin film transistor by capillary diameter and deposition rate change Relationship between mobility and domain size for each capillary diameter and deposition rate Relationship between deposition rate and mobility for each capillary diameter Diagram showing the relationship between parallel beam components and mobility Relationship between deposition rate and domain size (Example 3) AFM image of surface height image of prepared pentacene thin film (Example 3) Relationship diagram of mobility, domain size and film formation rate (Example 3) Relationship diagram between deposition rate and mobility (Example 3) Structural diagram of a deposition cell having a multicapillary structure arranged one-dimensionally (Example 4)

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings. The scope of the present invention is not limited to the following examples and illustrated examples, and many changes and modifications can be made.

FIG. 1 shows a deposition cell. The vapor deposition cell 1 uses ceramics as a cell material, and the cell inner wall 11 is coated with oxygen-free copper. The upper surface of the vapor deposition cell 1 is open, and a semi-closed cell is formed by attaching an upper lid 2. The upper lid 2 is made of oxygen-free copper as a material, and one capillary 3 is formed at the center. The vapor deposition cell 1 is a cylindrical container having an inner diameter of about 10 mm, the capillary 3 provided in the upper lid 2 is a cylindrical hole having an inner diameter d of 1 mm or less, and the length l of the cylinder is about 3 mm.
A vapor deposition material 4 is placed inside the vapor deposition cell 1, and heaters (not shown) are provided on the lower side and the periphery of the vapor deposition cell 1. When the vapor deposition cell 1 is heated with a heater, the vapor deposition material 4 evaporates into gas molecules, and the pressure inside the vapor deposition cell 1 increases. The inside of the capillary 3 in the cell becomes the entrance 31 and the outside of the cell becomes the exit 32, and gas molecules are emitted from the capillary 3.

FIG. 2 shows a schematic diagram of film thickness distribution measurement. For the above deposition cell, in order to confirm the release of parallel beam-like gas molecules and to verify the effect, the film thickness for each emission angle with the capillary axis and the film forming speed changed and 0 ° on the injection port axis was set. It was measured. Based on the obtained film thickness distribution, the behavior of vapor deposition molecules under each condition will be described below.
In order to measure the film thickness distribution, a portion directly above the injection port 32 of the vapor deposition cell 1 inside the dome-shaped holder 5 is set to θ = 0 °, and a glass substrate of 19 mm × 13 mm up to θ = 75 ° in 15 ° increments. A total of 6 7 were installed. Moreover, the opening part was provided in the position of 40 degrees and the film thickness sensor 6 was installed.

FIG. 3 shows polar coordinates of the film thickness distribution. The dome-shaped holder 5 shown in FIG. 2 is a spherical surface having a radius of 110 mm with the injection port 32 as the center. Each glass substrate 7 is ultrasonically cleaned in acetone for 10 minutes, and then immersed in acetone heated to 85 ° C. and subjected to UV / O ₃ treatment.
After cleaning the substrate, pentacene was deposited using the deposition cell 1. In this embodiment, three types of capillaries having a length of 3 mm and a diameter of 0.25, 0.50, and 1.00 mm are used. The dome-shaped holder 5 on which the cleaned glass substrate is set is fixed in the vapor deposition chamber, and after evacuation to 2.0 × 10 ⁻⁴ Pa, the vapor deposition cell 1 is heated with an electric heater to increase to a desired film formation rate. After stabilization, the deposition was started. After completion of the vapor deposition, the glass substrate was taken out, the film thickness at the center of each glass substrate was measured with a stylus type step meter, and plotted with polar coordinate display to obtain the film thickness distribution.
In FIG. 3, the film thickness distribution is represented by a relative film thickness with the film thickness at 0 ° as a reference. Further, the range where the filled portion is formed is shown. The broken line indicates a plot of f (θ) = cos θ, which is a diffusion condition from an ideal micro-surface deposition source.

FIG. 4 shows a film thickness distribution diagram when the film formation rate is changed for each capillary diameter.
The exact film formation speed is shown in the upper right of each film thickness distribution chart. Here, for convenience, the deposition rate is divided into three regions of “low”, “mid”, and “high”. For comparison, measurement was performed using a deposition cell (capillary diameter equivalent to 13 mm) having no capillary structure and having an open top. Hereinafter, in order to distinguish from the vapor deposition cell of the present invention, it is referred to as a “conventional cell”.

  In the region where the deposition rate is “low”, the film thickness distribution in the vapor deposition cell is lower than the film thickness distribution of the conventional cell as compared with the film thickness distribution (emission angle distribution) of the conventional cell. It can be seen that the film thickness is greatly reduced on the corner side, and the distribution is narrowed. That is, it can be said that the inside of the crucible is sufficiently a molecular flow region and diffuses according to the size of the exit port.

Next, the correlation between the capillary diameter and the deposition rate will be described. In the column of capillary diameter d = 0.25, when the film formation speed was shifted from “low” to “mid”, the film thickness on the low angle side was remarkably decreased and the distribution became narrower. On the other hand, when the film formation speed shifted from “mid” to “high”, it was confirmed that the film thickness on the low angle side increased again and the film thickness distribution returned to diffuse widely. Even at other capillary diameters, the film thickness distribution in the region where the film formation rate was “mid” was narrow, and it appeared that the film was diffused again in the “high” region.
In addition, when the conventional cell is used, the opening is wide, so the material is depleted by the time the film formation speed reaches “mid” or higher, and the film formation speed is stable because it is not a quasi-closed structure. Since the deposition could not be performed at the deposition rate corresponding to “mid” and “high”, only the result of the deposition rate corresponding to “low” is shown.

FIG. 5 shows (a) a diffusing model (cos ⁿ θ component) and (b) a model (Gauss function component) emitting parallel beams. The film thickness distribution has directivity in the injection direction in which a pressure gradient is generated by collision of molecules in the capillary 3 under the condition that high-speed injection of gas molecules (hereinafter referred to as high-speed molecular beam) occurs. The volume of molecules deposited in each direction as a result of the superposition of the flow of vaporized molecules (I) flying up and the flow of vaporized molecules (II) jumping from the inner wall of the capillary 3 and spreading (II) Determined by. The film thickness distribution obtained by the experiment was fitted with a function representing the effects (I) and (II), and each component was qualitatively evaluated.

First, a Gaussian function is assumed as a component (I) representing a parallel beam having a narrow spread in a direction directly above the deposition cell. Next, the molecular flow distribution that diffuses from the injection port is described by a cos function in the case of an ideal micro-surface deposition source, but in many real systems, it does not become a cos function. Since it is known that the distribution is represented by cos ⁿ θ empirically, a function of cos ⁿ θ is used as the component (II). When the target experimental data is fitted with these functions, the magnitude of each contribution is evaluated. In order to evaluate the magnitude of each contribution, the magnitude of the contribution of the parallel beam component in the emission angle distribution is evaluated by the magnitude of A using the following formula 1. did.

FIG. 6 shows the results of fitting the experimental results using the above Equation 1. In the conventional cell, there is no contribution of the parallel beam component from A = 0, and since n is the smallest in the “low” region, the conventional cell diffuses over a wide range according to the wide aperture diameter of the cell. I understand that. On the other hand, the deposition rate dependency of each capillary diameter of the deposition cell is such that the value of A is sufficient when the deposition rate is “low” at any of d = 0.25, 0.50, and 1.00 mm. small. That is, the contribution of the component (II) is large, and the emission angle distribution is diffused over a wide range.
On the other hand, under the condition where the film formation rate is “mid”, the value of A is large, so that the contribution of the component (I) is large, and it is confirmed that the film is closer to the parallel beam. Such a change indicates that parallel beaming has occurred due to the occurrence of a pressure gradient in the capillary. Also, under this condition, the smaller the capillary diameter d is, the larger A is, and it is confirmed that the smaller the capillary diameter, the larger the emission angle distribution with respect to the change in the deposition rate. did it.

FIG. 7 shows a model of isotropic scattering from the viscous flow region when the film formation rate is “high”. It can be seen that, under the condition that the film formation rate is “high”, the value of A becomes smaller at all diameters, and a diffused emission angle distribution is obtained. From the result of the film formation rate “high” at the capillary diameter of 1.00 mm where the film formation rate was the fastest, after the contribution of A disappeared, the function of cos ⁿ θ approached n = 1 as the film formation rate increased, and 75 A tendency to diffuse isotropically at angles up to ° was confirmed. Considering that the result n of the conventional cell with the largest aperture diameter is sufficiently large, this is completely different from the form in which molecules diffuse from the inner wall of the capillary, and reflects isotropic scattering from the viscous flow region. It can be said that there is.

  FIG. 8 shows an injection image of a cell that does not have a capillary structure and a vapor deposition cell of this embodiment (three regions of film formation speeds “low”, “mid”, and “high”). FIG. 8A shows an injection image of a vapor deposition cell having a capillary structure, and FIG. 8B shows an injection image of a cell not having a capillary structure. An injection image of a cell not having a capillary structure is similar to an injection image having a deposition rate of “high” in a deposition cell having a capillary structure.

  FIG. 9 summarizes conceptual diagrams of gas molecule injection at three deposition rates of the vapor deposition cell of this example. FIG. 10 shows a transition diagram of the molecular flow region and the viscous flow region in the vapor deposition cell of this example. As shown in FIG. 10, when the pressure increases, the release of gas molecules in the deposition cell changes from the molecular flow region to the viscous flow region. When the film formation rate is “low”, the pressure is low, and thus the molecular flow region is present inside the vapor deposition cell 1, inside the capillary 3, and exiting from the capillary 3 and exiting the vapor deposition cell 1. . In addition, when the film forming speed is “high”, the pressure is high, and therefore, the inside of the vapor deposition cell 1 and the inside of the capillary 3 is in a viscous flow region, and is emitted from the capillary 3 to the outside of the vapor deposition cell 1. After exiting, it changes from a viscous flow region to a molecular flow region. When the film forming speed is “mid”, the inside of the vapor deposition cell 1 is a viscous flow region, and the inside of the capillary 3 is just shifted from the viscous flow region to the molecular flow region, and is emitted from the capillary 3 to the vapor deposition cell 1. After going outside, it is in the molecular flow region.

In Example 1, it was shown that by creating a pressure gradient inside the capillary, parallel beam-like gas molecules having high directivity can be released from the capillary, thereby improving the film formation rate several times that of the conventional method.
In Example 2, a pentacene thin film was formed using the vapor deposition cell of Example 1 under conditions in which the capillary diameter and the film formation speed were changed, and the change in the thin film surface state and the change in the characteristics of the organic thin film transistor (OTFT). Will be described in light of the discharge angle distribution of the capillary.

First, an organic thin film transistor was produced. FIG. 11 shows a structural schematic diagram of the organic thin film transistor fabricated. A highly doped n-type Si wafer with a SiO ₂ thermal oxide film having a thickness of 190 nm (resistivity <0.02 Ωcm) was used as a gate insulating film and a gate electrode / substrate. The surface treatment of the gate insulating film was performed by HMDS (Hexamethyldisilazane) before forming the organic semiconductor layer. By this surface treatment, it is possible to cover the hydroxyl group (silanol group) attached to the substrate surface in the atmosphere to improve the hydrophobicity, and to suppress the adhesion of impurities mainly composed of water before forming the active layer.

  The surface treatment of the gate insulating film by HMDS has the effect of improving the adhesion of deposited molecules, promoting crystal formation, and improving the ON / OFF ratio and mobility when a transistor is manufactured. The surface treatment was performed using an immersion method. The substrate after cleaning was immersed in a HMDS solution diluted to 10% with toluene in a glove bag filled with nitrogen for 2 hours. After the immersion, the substrate was rinsed with toluene, and then ultrasonic cleaning was performed in acetone for 10 minutes in order to completely remove HMDS molecules remaining on the substrate surface.

The cleaned substrate was set in two holders, placed in a vapor deposition chamber, evacuated to a vacuum degree of 2.0 × 10 ⁻⁴ (Pa), and then the vapor deposition cell was heated to 200 ° C. to allow sufficient time. Thereafter, according to each film formation condition, the cell is sequentially heated to the target film formation speed while confirming that the degree of vacuum is not extremely deteriorated, and the vapor deposition speed is sufficiently stabilized. The film was formed with a film thickness. Further, during the film formation, the substrate was rotated at a speed of 15 rpm in order to eliminate the non-uniformity of the film thickness. After forming the film, it was confirmed that the substrate and the vapor deposition cell had cooled sufficiently from the sublimation temperature, and then the substrate was taken out of the vacuum chamber and placed on a metal electrode manufacturing holder and a Ni mask pattern. The substrate was set and Au was vacuum-deposited at 30 nm at 1.0 angstrom / second to form a source-drain electrode pattern. The source-drain electrode has a channel length of 100 μm and a channel width of 5 mm.

  FIG. 12 shows the result of observing an image of the surface height of a pentacene thin film produced by changing the capillary diameter and the film formation rate using an atomic force microscope (AFM). All AFM images are measured by a tapping mode in which the probe and the sample are scanned while being in intermittent contact, and the scan range is 5 μm × 5 μm. The values shown in the upper right of each AFM image indicate the film formation rate and the average crystal domain size (hereinafter simply referred to as domain size) when the pentacene thin film is deposited.

  Under the growth conditions that result in a beam-like emission distribution, there is a concern that thin film growth may be uneven in the substrate, but under the conditions where the capillary diameter becomes 0.25 mm and the film formation speed is “mid”, where the distribution is sharpest. In the grown thin film, pyramidal grains were spread, and it was confirmed that there was no uneven domain size and a uniform film was grown within the range of the image. Further, when looking at the correlation of crystal formation for each film formation rate, the domain size was smaller as the film formation rate increased at any diameter.

In this regard, in the BCF (Burton, Cabrera, Frank) model, which is a standard model of vapor phase growth, (a) incident and evaporation of vapor deposition molecules, (b) Considering a substrate with no impurities and unevenness, considering the three stages of surface diffusion, (c) crystal nucleus generation and growth, the deposited molecules are facets that are flat crystal planes on the atomic scale, and vicinal surfaces. The layer is grown as described above, and the generation of crystal nuclei is also due to the formation of uniform nuclei derived from thermal fluctuations.
When the finally grown crystals collide with each other and cover the deposition range of the substrate, more grains exist per unit area. Along with this, the size of each crystal grain and domain is reduced. Therefore, the domain size decreases as the deposition rate increases.

FIG. 13 shows changes in the transfer characteristics of the OTFT due to changes in capillary diameter and film formation rate. In the region where the film formation rate is “high”, even if a pentacene thin film is formed at a rate of 30 times or more and about 42 times the maximum at the rate of conventional vacuum deposition, it operates as an OTFT. The mobility was also relatively high at 0.174 cm ² / Vs. In this device having an active layer thickness of 30 nm, the time required for forming the active layer was very fast, about 10 seconds.

  Next, the correlation between the mobility for each capillary diameter and the deposition rate will be described. FIG. 14 shows the relationship between the mobility and domain size for each capillary diameter and the deposition rate. As shown in FIG. 14, at d = 1.00 mm and 0.50 mm where the capillary diameter is large, both mobility and domain size decrease as the film formation rate is increased, and the tendency is that the capillary diameter is small. 0.50 mm was smaller. Moreover, although the mobility is generally low at d = 0.25 mm where the capillary diameter is the smallest, the mobility is hardly decreased and the film formation rate is “mid”, although the domain size is decreased. Increased slightly.

  FIG. 15 shows the relationship between the film forming speed and the mobility for each capillary diameter. Since the mobility is not inversely proportional to the deposition rate only when the capillary diameter is 0.25 mm, it is presumed that the carrier transport barrier height decreases with the domain size. Also, only when the capillary diameter is 0.25 mm, the mobility is maximized despite the decrease in the domain size in the state of the high-speed molecular beam, and the carrier mobility inside the domain increases with the improvement in crystal orientation. It is estimated that it has improved.

  FIG. 16 shows the relationship between parallel beam components and mobility. As shown in FIG. 16, when the parallel beam component A in the film thickness distribution measurement is compared with the mobility of the OTFT created under the conditions, the film formation rate “low” (0.25) is reduced as the capillary diameter is reduced. , 0.50, and 1.00 are on the upper side of the graph) and the film formation speed “mid” (parallel beam state) is small, and the overall change is small. From this result, the vapor deposition molecules injected with a pressure gradient by the vapor deposition cell of this example reached the target substrate with higher kinetic energy than that deposited by the conventional cell, thereby raising the substrate temperature. It can be said that there is a possibility that a crystal having higher crystallinity can be produced.

In Example 2 described above, the substrate is placed in a vapor deposition chamber, and in order to eliminate film thickness non-uniformity during film formation, the vapor deposition cell is heated while rotating the substrate at a speed of 15 rpm, thereby sufficiently stabilizing the vapor deposition rate. Then, a film having a thickness of about 30 nm was formed in a range of 10 mm in diameter.
In Example 3, the rotation of the substrate is stopped, and the film that is intermittently applied to the substrate by the rotation is formed to form a film, and the distance between the deposition cell and the substrate is reduced to reduce the flux. The film was deposited and deposited under high directivity conditions. That is, the film was formed under conditions that would increase the high-speed molecular beam effect. And the organic thin-film transistor of the same size as Example 2 was produced, and the characteristic comparison was performed. The result of film formation under the same conditions as the film formation rate “mid” in Example 2 using a vapor deposition cell having a capillary diameter d of 0.25 mm is shown.

  Usually, when the deposition rate is low and the substrate temperature is high, the domain grows greatly. Conversely, when the deposition rate is high and the substrate temperature is low, the domain tends to hardly grow. However, in FIG. 17, there is no difference in the substrate temperature, and the film formation rate is substantially high (when compared with Example 2, even if the same film formation condition “mid” is used, the deposition cell and the substrate As the distance between the two approaches, the film size becomes 5.71 angstroms / second, which is high), but the domain size does not decrease. That is, when focusing on the diameter d of 0.25 mm where the tendency to parallel beam formation was large and the deposition was performed under a condition with a large incident flux, the domain size did not decrease. Here, the fact that the domain size does not decrease can be said to be an effect close to the heating of the substrate.

  FIG. 18 shows an AFM image of the surface height image of the produced pentacene thin film. FIG. 19 shows the relationship between mobility and domain size and the deposition rate, and FIG. 20 shows the relationship between deposition rate and mobility. When a thin film transistor was formed using a film-formed film, the mobility was significantly improved as compared with a substrate having substantially the same domain size as compared with Example 2. This tends to be different from the effect of heating the substrate in which the mobility is improved by increasing the domain size.

Example 4 describes a deposition cell in which a plurality of capillary structures having the same shape and the same size are arranged one-dimensionally at equal intervals. The vapor deposition cell of Example 3 is intended to be applied industrially to a large area device.
FIG. 21 shows a structural diagram of a vapor deposition cell having a multi-capillary structure arranged one-dimensionally. In FIG. 17, (1) is the upper surface of the vapor deposition cell, (2) is the long side cross section of the vapor deposition cell, and (3) is the short side cross section of the vapor deposition cell. A plurality of cylindrical capillaries 3 having the same shape and the same size are provided on the upper surface of one vapor deposition cell 41. The capillaries 3 are designed at equal intervals in consideration of the emission angle distribution under the film forming conditions. Under such conditions, it is guaranteed that the discharge angle distribution of each capillary is the same. Therefore, by installing the capillary 3m for flux monitoring at a point away from the deposition range, a single flux monitor is provided. With this, the amount of film formation can be observed.

As described above, in the case of the vapor deposition cells of Example 2 and Example 3, it was possible to stably deposit at a high film formation rate that could not be achieved by the conventional cell. We succeeded in depositing pentacene molecules at a deposition rate of 26.5 angstroms / second, which is 25 times faster than the conventional rate, and confirmed the operation of the field effect transistor fabricated using the deposited thin film. In spite of the fact that the substrate temperature was not raised, a practical carrier mobility of about 0.2 cm ² / Vs could be confirmed. Also, under this production condition, for example, the time required for forming the active layer of the organic transistor was only 7 seconds.
Such a film formation rate is a value when an apparatus having a long distance between the conventional cell and the substrate is used as it is. As in Example 3, a scanning deposition cell having a large number of capillaries is used on the substrate. In the case where they are arranged close to each other, it may be possible to increase the film forming speed by several tens of times.
Further, at such a high film formation rate, the molecular beam density incident on the substrate per unit time becomes high, so that the ratio of taking in the residual gas in the film formation chamber into the film is relatively small. Therefore, it is possible to form a film having an equivalent amount of impurities with an apparatus having a degree of vacuum that is about two orders of magnitude lower than the conventional one, and an effect of reducing the apparatus cost can be expected.

  The present invention is useful for production of large area organic semiconductor devices such as organic EL displays, organic transistor circuits, and organic solar cells.

DESCRIPTION OF SYMBOLS 1,41 Evaporation cell 2 Upper cover 3 Capillary 4 Evaporation material 5 Dome holder 6 Film thickness sensor 7 Glass substrate 11 Cell inner wall 12 Heater 31 Incident port 32 Ejection port

Claims (20)

In a method for producing a thin film on a substrate by a vacuum deposition method,
An evaporation cell serving as an evaporation source uses at least one capillary structure outlet,
A method for producing a thin film, characterized in that the inside of the vapor deposition cell is adjusted to a material vapor pressure that generates a pressure gradient inside the capillary. The material vapor pressure that creates a pressure gradient inside the capillary is:
There is a pressure difference between the entrance side and the exit side in the capillary,
The thin film manufacturing method according to claim 1, wherein the material to be deposited is a pressure gradient that makes a transition from the viscous flow state on the incident side to the molecular flow state on the emission side.   The thin film production method according to claim 1 or 2, wherein in the vapor deposition cell, at least an inner wall of the vapor deposition cell and an inner wall of the capillary are coated with a heat conductive material. The thermally conductive material is a metal;
The thin film manufacturing method according to claim 3, wherein the surface of the thermally conductive material is coated with a coating agent that is inert to the material.   The method for producing a thin film according to claim 1, wherein the length of the capillary with respect to the inner diameter is twice or more.   6. The method for producing a thin film according to claim 1, wherein the space in the capillary has a linear shape at least in a molecular flow state.   The spatial shape in the capillary is a cylinder, an elliptical column, a polygonal column, a truncated cone, an elliptical truncated cone, a polygonal truncated cone, or a combination thereof. A thin film manufacturing method according to claim 1.   The vapor deposition cell includes a plurality of the capillary structures having the same shape and the same size, and the plurality of capillaries are arranged at equal intervals one-dimensionally or two-dimensionally. The thin film production method according to any one of the above.   The thin film production according to any one of claims 1 to 7, wherein the plurality of vapor deposition cells having the same shape and the same size of the capillary structure are arranged one-dimensionally or two-dimensionally at equal intervals. Method.   The film thickness distribution of the thin film is controlled from the distance between the centers of the capillaries, the distance between the substrate and the discharge port of the capillary, and the discharge angle distribution of the material by the material vapor pressure. The thin film production method according to 8 or 9.   The thin film manufacturing method according to claim 8 or 9, wherein a flux monitoring capillary having the same shape and the same size as the capillary structure is provided for each vapor deposition cell. In a deposition cell used to produce a thin film on a substrate by vacuum deposition of material,
The deposition cell comprises at least one capillary structure outlet;
A beam-like molecular beam is emitted when the pressure inside the cell is adjusted to a material vapor pressure in which a pressure gradient is generated so that the entrance side is in a viscous flow state and the exit side is in a molecular flow state inside the capillary. Deposition cell.   The vapor deposition cell according to claim 12, wherein in the vapor deposition cell, at least an inner wall of the vapor deposition cell and an inner wall of the capillary are coated with a heat conductive material. The thermally conductive material is a metal;
The deposition cell according to claim 13, wherein the surface of the thermally conductive material is coated with a coating agent that is inert to the material.   The evaporation cell according to any one of claims 12 to 14, wherein a length of the capillary with respect to an inner diameter is twice or more.   The vapor deposition cell according to any one of claims 12 to 15, wherein the space in the capillary has a linear shape at least in a molecular flow state.   The space shape in the capillary is a cylinder, an elliptical cylinder, a polygonal cylinder, a truncated cone, an elliptical truncated cone, a polygonal truncated cone, or a combination thereof. A vapor deposition cell according to any one of the above. In an apparatus for producing a thin film on a substrate by a vacuum deposition method,
The vapor deposition cell according to any one of claims 12 to 17, comprising a plurality of the capillary structures having the same shape and the same size, wherein the plurality of capillaries are arranged one-dimensionally or two-dimensionally at equal intervals. Thin film manufacturing equipment. In an apparatus for producing a thin film on a substrate by a vacuum deposition method,
A thin film production apparatus, wherein a plurality of vapor deposition cells according to any one of claims 12 to 17 are arranged one-dimensionally or two-dimensionally at equal intervals. 20. The thin film production apparatus according to claim 18, wherein a flux monitoring capillary having the same shape and the same size as the capillary structure is provided for each vapor deposition cell.