Patent Application
20080241587
This invention relates to a film-forming apparatus and a film-forming method for forming a film layer of a predetermined material and, in particular, relates to a film-forming apparatus and a film-forming method for forming a film layer of a predetermined material by evaporating a raw material of the predetermined material.
Methods for forming a film layer of a predetermined material by evaporating a raw material of the predetermined material are widely used in the manufacture of such electronic devices as semiconductor devices, flat panel display devices and others. As one example of such electronic devices, description will be given hereinbelow of an organic EL display device. The organic EL display device with sufficiently high brightness and a lifetime of several tens of thousands of hours or more uses an organic EL element that is a self-luminous element and thus can be formed thin with less peripheral components such as a backlight. Therefore, the organic EL display device is ideal as a flat panel display device. The organic EL element forming such an organic EL display device is required, in terms of characteristics as the display device, such that, while being a large screen, the element lifetime is long, there are no variations in luminous brightness on the screen and in element lifetime, there are no defects typified by dark spots, and so on. Film formation of an organic EL layer is quite important for satisfying those requirements.
As a film-forming apparatus for uniformly forming a film of an organic EL layer on a large substrate, use is comprised of an apparatus described in Patent Document 1 or the like. The film-forming apparatus of Patent Document 1 is intended to ensure uniformity of the film thickness on a large substrate by optimally arranging in a tree fashion the piping structure inside an injector located in the apparatus.
An organic EL layer currently is formed by a vacuum deposition apparatus at 10−6 Torr to 10−7 Torr or less. According to an experiment by the inventors, it has been clarified that, in a current organic EL vacuum deposition apparatus, an organic EL layer is subjected to a large amount of organic contamination in an organic EL layer forming process, so that the brightness and lifetime of an organic EL light emitting diode (OLED) are largely reduced.
A graph of black circles in
As a result of repeating assiduous studies about the foregoing lifetime degradation, the inventors of this invention have found that since, in the vacuum state, the partial pressure of organic compound components serving as a source of contamination increases and simultaneously the mean free path of organic compound molecules increases overwhelmingly, organic compound contamination on the substrate surface becomes quite large to thereby reduce the lifetime of the organic EL element.
Further, it has been ascertained that uniformity in film quality and film thickness at the time of the film formation of the organic EL element is quite important for reducing variations in luminous brightness on the screen and in element lifetime. As a film-forming apparatus for uniformly depositing an organic EL thin film, the apparatus described in Patent Document 1 is cited as an example. However, although the film thickness of an organic EL element formed in the apparatus of such a structure is uniform, dark spots or variation in element lifetime occurs.
Further, according to the injector described in Patent Document 1, there arises a problem that since there is no disclosure about the material and temperature of the injector, the organic EL material is deposited inside the injector and decomposed inside the injector depending on the conditions, thereby causing deposition of the decomposition product on the substrate, so that the organic EL element does not function.
Patent Document 1: Japanese Unexamined Patent Application Publication JP-2004-79904-A2
The conventional film-forming method has a problem that since, basically, the raw material is evaporated from an evaporation dish and adhered to the substrate without directionality (i.e. with non-directionality), the film formation takes time and further it is difficult to form a uniform film. This problem is more serious for film formation on a substrate with an increased area, which is one of the industrial features in recent years. For example, approximately 4 minutes are required for forming a single-color organic EL layer on a glass substrate having a size of 400 mm×500 mm, because, since it is composed of a hole injection layer, a hole transport layer, a light emitting layer, an electron injection layer, and so on, it is necessary to carry out film formation of as many as several organic compound layers. Further, as long as approximately 20 minutes are required for completing formation of a three-color organic EL layer including times for transfer, mask changes, and so on, thereby an increase in cost has been caused.
Further, the conventional film-forming method has a problem that since the evaporated raw material is dispersed without directionality, it is also adhered to portions other than the substrate and hence there is much waste. There is also a problem that since the evaporation continues for some time even after heating of the evaporation dish is stopped, a waste of the raw material occurs during non-film formation. For example, since the organic EL film-forming raw material is expensive, these problems are even more serious.
Therefore, an object of this invention is to provide a film-forming apparatus and a film-forming method that can increase the film-forming rate and enable uniform film formation by directing an evaporated raw material toward a substrate.
Another object of this invention is to provide a film-forming apparatus and a film-forming method that are highly economical with a waste of raw material eliminated.
Another object of this invention is to provide a film-forming apparatus and a film-forming method that can carry out film formation on a large-area substrate at a high rate and highly economically.
Still another object of this invention is to provide a film-forming apparatus and a film-forming method with suppressed organic compound contamination.
According to this invention, there is obtained a film-forming apparatus for depositing a film of a predetermined material on a substrate, the film-forming apparatus characterized by comprising a container to be depressurized, a depressurizing means directly or indirectly coupled to the container, first holding means located in the container for holding a raw material used for forming the film of the predetermined material, second holding means located in the container for holding the substrate, evaporation means located in the container for evaporating the raw material, and transport gas-supplying means located in the container for supplying a gas so as to transport the evaporated raw material to the surface of the substrate. In the foregoing apparatus, it is preferable that the evaporation means include means for heating the raw material to a first temperature equal to or higher than a temperature at which the raw material is evaporated and a predetermined portion inside the container be heated to a second temperature exceeding the temperature at which the raw material is evaporated.
Further, in this invention, according to the foregoing film-forming apparatus, there is obtained the film-forming apparatus characterized by further comprising means for maintaining the temperature of the substrate at a third temperature lower than the temperature at which the raw material is evaporated, the film-forming apparatus characterized in that the first temperature and the second temperature are lower than a temperature at which the evaporated raw material is decomposed, or the film-forming apparatus characterized in that the second temperature is higher than the first temperature. It is preferable that the second temperature be higher than the first temperature by 20° C. or more. Further, in the foregoing film-forming apparatus, it is preferable that the third temperature be equal to or lower than the temperature at which the raw material is evaporated, that the predetermined material be an organic EL material and the third temperature be less than 100° C., and that the predetermined portion is a portion adapted to contact the evaporated raw material and excluding the substrate and the second holding means.
In this invention, according to the foregoing film-forming apparatus, there is obtained the film-forming apparatus characterized in that the first holding means is a heat-resistant container for holding the predetermined material or a precursor of the predetermined material, or the film-forming apparatus characterized in that the transport gas-supplying means comprises a gas container placing the first holding means therein and means for introducing the gas into the gas container, and further, the gas container includes a gas ejection portion having a plurality of small holes and located at a portion forming an outlet of the gas so as to face the substrate, so that the gas transports the evaporated raw material to the surface of the substrate through the gas ejection portion. In this case, the predetermined portion includes the gas container. This invention includes other features, respectively, that the transport gas-supplying means includes means for supplying the gas during execution of film formation and stopping supply of the gas during non-execution of film formation, that the evaporation means includes means for evaporating the raw material during the execution of film formation and stopping evaporation of the raw material during the non-execution of film formation, and that the means for heating includes means for heating the raw material to the first temperature during the execution of film formation and heating, during the non-execution of film formation, the raw material to a fourth temperature less than the temperature at which the raw material is evaporated, wherein the difference between the first temperature and the fourth temperature is preferably set to 70° C. to 150° C. It is preferable that the depressurizing means includes means for maintaining the inside of the container at a pressure of 10 mTorr to 0.1 mTorr during the execution of film formation and maintaining the inside of the container at a reduced pressure of 1 Torr or more at least for a certain period during the non-execution of film formation and that the depressurizing means includes means for causing a gas flow in the container to be in a molecular flow region during the execution of film formation and causing a gas flow in the container to be in an intermediate flow region or a viscous flow region at least for a certain period during the non-execution of film formation.
According to this invention, in the foregoing film-forming apparatus, the gas is preferably a xenon (Xe) gas. Alternatively, it is preferable that the gas contain an inert gas as a main component and the inert gas contain at least one of nitrogen (N), Xe, Kr, Ar, Ne, and He, and that the transport gas-supplying means contain means for setting the temperature of the gas to a temperature equal to the first temperature or equal to or higher than the first temperature at least at the stage before transporting the evaporated raw material. It is preferable that the gas container be comprised of a material whose release gas is small in amount or the gas container be comprised of a material whose catalytic effect is small.
The predetermined material or its precursor is preferably exemplified by an organic EL element material and is not particularly limited, but use can be comprised of, for example, 1,1-bis(4-di-paminophenyl)cyclohexane, carbazole or its derivative, triphenylamine or its derivative, quinolinol aluminum complex containing dopant, DPVi biphenyl, silole derivative, cyclopentadien derivative, or an organic EL material for red, blue, or green emission.
In the film-forming apparatus of this invention, the depressurizing means comprises a turbo-molecular pump and a roughing vacuum pump and inert gas-supplying means is preferably provided between the turbo-molecular pump and the roughing vacuum pump in terms of suppressing back diffusion of an exhaust gas to the process chamber. The inert gas preferably contains at least the transport gas component and is more preferably the same gas.
A gasket used in the film-forming apparatus of this invention is preferably comprised of a material whose organic compound release is small in amount, and is exemplified by an organic compound gasket whose release gas is small in amount, an organic compound gasket having been subjected to a step of contacting it with water of 80° C. or more and cleaned, a metal gasket, or the like. The organic compound gasket whose release gas is small in amount is preferably a gasket containing a perfluoroelastomer as a main component. The organic compound gasket is suitable for maintaining air-tightness at a portion with a relatively high attaching/detaching frequency, such as a door for substrate-frequency.
Further, a film-forming apparatus of this invention comprises, at least, a container to be depressurized, a depressurizing means directly or indirectly coupled to the container, film-forming material supply means located inside or outside the container and directly or indirectly coupled to the container for supplying a film-forming material or a film-forming material precursor, and substrate placing means located in the container for placing a substrate to be deposited with the film-forming material, the film-forming apparatus characterized in that the film-forming material supply means has at least evaporation means such as a crucible for evaporating the film-forming material or the film-forming material precursor and the evaporation means is comprised of a material whose release gas is small in amount.
Further, a film-forming apparatus of this invention comprises, at least, a container to be depressurized, a depressurizing means directly or indirectly coupled to the container, film-forming material supply means located inside or outside the container and directly or indirectly coupled to the container for supplying a film-forming material or a film-forming material precursor, and substrate placing means located in the container for placing a substrate to be deposited with the film-forming material, the film-forming apparatus characterized in that the film-forming material supply means has at least evaporation means such as a crucible for evaporating the film-forming material or the film-forming material precursor and the evaporation means is comprised of a material whose catalytic effect is small.
Further, a film-forming apparatus of this invention is a film-forming apparatus coupled to a substrate transfer apparatus and is characterized in that an air having a dew point temperature of −80° C. or less is supplied to a space inside the substrate transfer apparatus. By this, it is possible to reduce the substrate-adsorbed moisture amount and thus suppress contamination of film-forming environment.
Further, a film-forming apparatus of this invention is characterized in that the pressure in a container to be depressurized during film formation and that during non-film formation are in a molecular flow pressure region and an intermediate flow pressure region or a viscous flow pressure region, respectively.
The material whose release gas is small in amount in this invention exhibits the state where when a comparison is made between a generated gas amount of the subject material at a film-forming material evaporation temperature and a generated gas amount of a SUS-316L material, having the same shape as that of the subject material and having the electrolytically polished surface, at such a temperature, the generated gas amount of the former is equal to or less than the generated gas amount of the latter, or the state where the partial pressure, exhibited by a generated gas when a constituent component of a film-forming apparatus is formed by the use of the subject material and located in the film-forming apparatus, is equal to or less than 1/10 of a film-forming pressure. The material conforming to either of them is preferable and the material conforming to both is more preferable.
The material whose catalytic effect is small in this invention exhibits the state where when a comparison is made between a decomposition temperature of a film-forming material or a film-forming material precursor measured when the subject material is brought into contact with the film-forming material or the film-forming material precursor and raised in temperature and a decomposition temperature of the film-forming material or the film-forming material precursor measured when a SUS-316L material having the same shape as that of the subject material and having the electrolytically polished surface is brought into contact with the film-forming material or the film-forming material precursor and raised in temperature, the material composition temperature of the former is equal to or higher than the material decomposition temperature of the latter or the state where when a comparison is made between a decomposition start temperature exhibited by the film-forming material or the film-forming material precursor alone and a decomposition start temperature exhibited when the subject material is brought into contact with the film-forming material or the film-forming material precursor, the difference of the temperature of the latter with respect to the temperature of the former is 20° C. or less. The material conforming to either of them is preferable and the material conforming to both is more preferable.
According to another mode of this invention, there is obtained a film-forming method for depositing a film of a predetermined material on a substrate in a container to be depressurized, the film-forming method characterized by comprising a step of evaporating a raw material used for forming the film of the predetermined material and a step of transporting the evaporated raw material to a surface of the substrate by the use of a gas. In the foregoing film-forming method, it is characterized in that the evaporating step comprises a step of heating the raw material to a first temperature equal to or higher than a temperature at which the raw material is evaporated, and a predetermined portion inside the container is heated to a second temperature exceeding the temperature at which the raw material is evaporated. It is characterized in that the temperature of the substrate is maintained at a third temperature lower than the temperature at which the raw material is evaporated. This invention also includes other features, respectively, that the first temperature and the second temperature are lower than a temperature at which the evaporated raw material is decomposed, that the second temperature is higher than the first temperature, that the second temperature is higher than the first temperature by 20° C. or more, that the third temperature is equal to or lower than the temperature at which the raw material is evaporated, that the predetermined material is an organic EL material and the third temperature is less than 100° C., that the predetermined portion is a portion adapted to contact the evaporated raw material and excluding the substrate, and that the raw material is the predetermined material or a precursor of the predetermined material.
In this invention, there is also obtained a film-forming method characterized by placing the raw material in a heat-resistant container, placing the heat-resistant container in a gas container, and introducing the gas into the gas container, wherein a gas ejection portion having a plurality of small holes is provided at a portion forming an outlet of the gas container so as to face the substrate, thereby causing the gas to reach the surface of the substrate through the gas ejection portion while transporting the evaporated raw material. This invention also includes features of heating the gas container to the second temperature, of supplying the gas during execution of film formation and stopping supply of the gas during non-execution of film formation, of evaporating the raw material during the execution of film formation and stopping evaporation of the raw material during the non-execution of film formation, of heating the raw material to the first temperature during the execution of film formation and heating, during the non-execution of film formation, the raw material to a fourth temperature less than the temperature at which the raw material is evaporated, of setting the difference between the first temperature and the fourth temperature to 70° C. to 150° C., of maintaining the inside of the container at a pressure of 10 mTorr to 0.1 mTorr during the execution of film formation and maintaining the inside of the container at a reduced pressure of 1 Torr or more at least for a certain period during the non-execution of film formation, and of causing a gas flow in the container to be in a molecular flow region during the execution of film formation and causing a gas flow in the container to be in an intermediate flow region or a viscous flow region at least for a certain period during the non-execution of film formation. In the foregoing film-forming method, it is preferable that the gas be a xenon (Xe) gas, that the gas contain an inert gas as a main component, that the inert gas contain at least one of nitrogen (N), Xe, Kr, Ar, Ne, and He, and that the temperature of the gas be set to a temperature equal to the first temperature or equal to or higher than the first temperature at least at the stage before transporting the evaporated raw material.
According to this invention, there are obtained an organic EL device manufacturing method characterized by including a step of forming a film of an organic EL element material by the use of the foregoing film-forming apparatus or film-forming method, and an electronic device manufacturing method characterized by including a step of forming a layer of a predetermined material by the use of the foregoing film-forming apparatus or film-forming method. Further, there are obtained an organic EL device having an organic EL layer formed by the use of the foregoing film-forming method and an electronic device having a layer of a predetermined material formed by the use of the foregoing film-forming method.
According to this invention, since an evaporated film-forming material reaches the surface of a substrate by the flow of a transport gas, the film-forming conditions can be controlled by the flow of the gas and hence a uniform thin film can be deposited on the large-area substrate. That is, by directing the evaporated raw material toward the substrate, it is possible to increase the film-forming rate and achieve uniform film formation. For example, approximately one to two minutes are enough for forming a three-color organic EL layer on a glass substrate having a size of 400 mm×500 mm and hence the film-forming time can be shorted to 1/10 or less as compared with conventional. By directing the evaporated raw material toward the substrate, by raising the temperature of a portion other than the substrate to an evaporation temperature or more to prevent unnecessary adhesion of the evaporated raw material, or by using a heavy gas such as xenon for transport so as to fix the flow of the raw material in a constant direction, the expensive raw material can be selectively adhered only on the substrate, thereby enabling highly economical film formation with a waste of the raw material eliminated. Further, since use is comprised of the method that transfers the evaporated film-forming material on the flow of the transport gas, it is possible to stop ejection of the raw material by stopping the flow of the gas during non-film formation and hence it is possible to prevent generation of waste of the raw material.
The film-forming apparatus of this invention thoroughly eliminates generation of the organic compound contamination substance/material decomposition dissociation substance that adversely affects the properties of the film-forming material, and thus can deposit a high-quality thin film. By using the film-forming apparatus of this invention for forming an organic EL element, it is possible to obtain a high-quality organic EL display device with high brightness and long lifetime.
Hereinbelow, description will be given of facts clarified by the inventors of this invention.
(Contamination from the Atmosphere)
(State of Contamination Under Reduced Pressure)
<Organic compound Adsorption Mechanism under Reduced Pressure≦
Description will be next given of organic compound adsorption behavior onto the surface of a substrate under reduced pressure.
Even in the viscous flow region of 0.8 Torr to 10 Torr, when the pressure decreases so that the partial pressure of organic compound increases and the mean free path increases, the adsorption organic compound amount increases in inverse proportion to the storage pressure.
C(t)=Ce(1−10−t/τ) (1)
where Ce represents a surface equilibrium adsorption amount (molecules/cm2) and τ an adsorption time constant. The results of
Next, description will be given of the temperature/pressure dependence of organic compound amounts evaporated from organic compound adsorbed on the inner surfaces of a chamber, grease, plastics, and O-rings.
On the other hand,
A vapor pressure Pv of organic compound molecules to the gas phase is normally described by the Antonie equation. That is,
Pv=10A×10−B/(C+T(° C.)) (2)
It was possible to clarify the evaporation behavior of eicosane (C20H42) as described above.
[Table 1]
The technique has become obvious that thoroughly suppresses organic compound molecule adsorption onto the substrate surface for ultrahigh-quality process management.
(1) To suppress as low as thoroughly possible the partial pressure of organic compound molecules in a process chamber and a substrate transfer chamber.
(2) To maintain as high as possible the pressure to a process chamber and a substrate transfer chamber within the range where no inconvenience occurs.
(3) To shorten as much as possible the residence time of a substrate in a process chamber and a substrate transfer chamber in a depressurized state.
Organic compound contamination sources in the depressurizing chamber relating to item (1) are (a) resin O-rings for use in maintaining hermetic sealing, (b) grease for use in lubricating sliding portions (it is a principle to eliminate sliding portions in the chamber as much as possible), (c) back diffusion of oil from the outlet side of a gas exhaust pump, (d) organic compound adsorption onto the inner surfaces of the chamber from the atmosphere when the inside of the chamber is exposed to the atmosphere, and (e) organic compound adsorption onto the front and back surfaces of a substrate from the atmosphere.
There is no alternative but to use the resin O-ring of item (a) at a portion that is repeatedly opened and closed, like a gate valve provided at a substrate carry-in or carry-out portion. Organic compound released from plastics is in the form of molecules having a relatively small molecular weight.
An organic compound molecule having a small molecular weight is not adsorbed on the surface of the substrate because its adsorption/desorption activation energy is small. Since the organic compound molecule having a molecular weight greater than a certain value (approximately 400 in the case of straight-chain hydrocarbon or phthalate ester and approximately 900 in the case of cyclic siloxane) is not released into the gas phase because its vapor pressure is small, it is not adsorbed on the substrate. Naturally, as the temperature rises, the critical molecular weight of organic compound released into the gas phase shifts to the greater side more and more. Use should be comprised of an O-ring of a resin that contains no low-molecular-weight organic compound that is released into the gas phase and adsorbed on the substrate surface (e.g. DU351 manufactured by Daikin Industries, Ltd.). With respect also to the grease in item (b), use should be comprised of one that contains no low-molecular-weight organic compound that is released into the gas phase.
It is desirable that there be no mechanical sliding portions and the temperature of an O-ring using grease or a grease-using portion be set as low as possible. When using it at high temperature, since the release critical molecular weight shifts to the higher side, taking it into account, organic compound having a molecular weight of 800 or less is not contained in the case of straight-chain hydrocarbon or phthalate ester, organic compound having a molecular weight of 1500 or less is not contained in the case of cyclic siloxane, and so on.
In order to suppress the back diffusion, into the chamber, of organic compound emitted from grease at a pump gear portion in item (c), it is necessary to feed to a purge port a high purity gas such as Ar or N2 which does not adversely affect a process even if it flows backward into the chamber, so that the pressure of the portion where gears and so on using the grease are present never drops to the molecular flow region but is surely controlled in the viscous flow region.
The high-vacuum evacuation turbo-molecular pump 7 (pumping speed S1 (litter/sec)) is coupled to the chamber 6 through the gate valve 1 (butterfly valve or the like) and is coupled to the roughing vacuum pump 9 (pumping speed S2 (litter/min)) through the valve 2. An Ar or N2 gas, which does not affect a process even if it flows backward into the chamber 6, is fed to the purge port 8 of the turbo-molecular pump 7. The roughing vacuum pump 9 is directly coupled to the chamber 6 through the valve 3. The roughing vacuum pump 9 is coupled to the exhaust duct 10 through the valve 4 and an exhaust gas is discharged into the atmosphere from the exhaust duct 10. A N2 gas or a clean dry air containing no moisture or organic compound is fed to the downstream side of the valve 4 so as to prevent the atmospheric components containing moisture and so on from entering the exhaust duct 10 or the roughing vacuum pump 9 while the apparatus is stopped.
During organic film formation, the inside of the chamber is set to a gas pressure from the transition flow region to the molecular flow region where the mean free path of molecules becomes several centimeters or more. As clear from
f
1
+f
2=79Pc S2/60 (3)
during non-film formation, and
f1=79PcS1 (4)
f
1
+f
2=79PBS2/60 (5)
during film formation, where PB represents a pressure on the downstream side of the turbo-molecular pump.
For example, given that S1=12,000 litter/sec and S2=2,400 litter/min in terms of film formation on a large glass substrate, metal substrate, or the like, even if it is set that f1=2,000 cc/min and f2=1,600 cc/min during non-film formation, the chamber pressure Pc during non-film formation only becomes approximately 1 Torr from the foregoing equation (3). If the valve 3 is throttled to set the effective pumping speed of the roughing vacuum pump 9 to 1/10, i.e. 240 litter/min, the chamber pressure Pc becomes approximately 10 Torr.
During film formation, the valve 3 is closed and the valve 1 is opened. Given that the gas flow rates at that time are f1=1,000 cc/min and f2=1,600 cc/min, the chamber pressure Pc is 1.05 mTorr from the foregoing equation (4) and PB on the downstream side of the turbo-molecular pump 7 is 0.82 Torr.
The method of suppressing the organic compound contamination has been described above. Next, the organic film-forming technique will be described in detail.
Since an organic EL material is raised in temperature so as to be evaporated and formed a film on an opposing glass substrate, metal substrate, or the like, it is quite important not to decompose/dissociate organic EL molecules when the temperature is raised. There are two causes for decomposition/dissociation of the organic EL molecules. One is the decomposition/dissociation due to a catalytic effect exhibited by the surface in contact with the organic EL molecules when the temperature rises to a certain level. The other is the decomposition/dissociation due to oxidative decomposition caused by moisture (H20) or oxygen (O2) adsorbed/occluded to/in the organic EL material. Therefore, before supplying the organic EL material into an evaporation film-forming container, it is necessary to place the organic EL material on a porous carbon heater and raise the temperature from 150° C. to approximately 220° C. to 230° C. by causing a high purity N2 gas (the content of H20 and O2 is 100 ppb or less and preferably 10 ppb or less) to flow through porous carbon, thereby removing the adsorbed/occluded moisture and oxygen.
Next, description will be given of what has been clarified about a material with the least catalytic effect which is optimal for evaporating and gasifying the organic EL material.
Description will be given of the results of Alq3 (C27H18AlN3O3) and NPD (C44H32N2) as typical organic EL materials. The molecular weights, melting points, and glass transition temperatures of Alq3 and NPD are 459.43 and 588.74, none due to sublimation properties and 280° C., and 175° C. and 96° C., respectively.
Evaporation dishes having the surfaces of various measurement samples 22 are inserted into a tube furnace 21 shown in
Table 2 shows temperatures of decomposition/dissociation of Alq3 molecules with different surface materials of the evaporation dishes for evaporating Alq3. Resistance values of various materials in Table 2 are values measured by pushing resistance measurement terminals against various surfaces at a distance of 1 cm therefrom.
[Table 21]
Carbon does not allow Alq3 molecules to be decomposed/dissociated up to 422.5° C., i.e. the highest temperature. Low-resistance SiC, TaN, AlN, BN, TiN, and MgO follow it. The material having as high a decomposition/dissociation start temperature as possible should be used for the evaporation dish and so on.
Next, description will be given with respect to NPD. At first,
Table 3 shows temperatures at which NPD molecules start decomposition/dissociation, with respect to various materials. Like in the case of Alq3 molecules, the decomposition/dissociation start temperature by carbon is the highest, which is 452.8° C. High-resistance SiC, low-resistance SiC, AlN, MgO, Si3N4, and Al2O3 follow it.
[Table 3]
Hereinbelow, Embodiment 1 of this invention will be described with reference to the drawings.
The materials each adapted to evaporate the organic EL material into the gas phase without decomposition/dissociation have been made clear. Description will be next given of an apparatus adapted to form a film of an expensive organic EL material on a glass substrate, plastic substrate, or metal substrate quite efficiently and at a high rate without decomposing/dissociating organic EL molecules.
Referring to
In
Herein, it has been clarified as described before that various organic EL materials are each evaporated in a monomolecular state into the gas phase when heated to approximately 300° C. or more. Further, it has also been clarified that the material which most reluctantly decomposes/dissociates the organic EL molecules is carbon.
Although there are various types where the surface of the substrate 32 such as the glass substrate or the metal substrate faces downward, upward, and sideward, description will be first given of the structure where the substrate is located with the surface thereof facing downward.
The substrate 32 such as the glass substrate, the plastic substrate, or the metal substrate is held in tight contact with the stage 33 by substrate fixing means such as an electrostatic chuck so that the entire surface of the substrate is controlled uniformly and strictly at a temperature near room temperature. The surface temperature of the stage 33 is uniformly and strictly controlled by circulating, over the entire surface of the stage, hydrogen-added cooling water removed of N2 and O2 dissolved from the atmosphere and added with hydrogen (H2) at saturation solubility or less, for example, in an amount of 0.5 to 1.4 ppm. The hydrogen-added water removed of N2 and O2 and added with H2 has an oxidation-reduction potential (ORP) of −400 mV and thus is water shifting to the reduction side by indeed as much as 1V as compared with +600 mV, normally an ORP of water dissolved with N2 and O2 from the atmosphere, thereby not rusting metal or not breeding bacteria. Even if it is used for a long time in a hermetically sealed manner, the water quality is hardly degraded.
In order to control the temperature of the substrate surface at T0 (° C.) near room temperature, the system is configured by keeping constant the cooling water amount flowing in the substrate stage 50, defining beforehand a correlation with a temperature T1 (° C.) at a cooling water outlet by the temperature sensor 55 to be “T0>T1”, discharging a portion of outlet-side cooling water raised in temperature into a return cooling water pipe, and introducing the same amount of cooling water from a cooling water supply pipe on the left side, thereby circulating the cooling water to the substrate stage 50 by the use of a circulation motor.
The number (layout pitch) of temperature control cooling water pipes C1, C2, to Cn of the substrate stage 50 and the inner diameter thereof are determined in the following manner. That is, the number layout pitch) is determined so that the difference in temperature of the substrate surface is within ±1° C. and preferably within ±0.3° C. This temperature variation on the substrate surface is directly reflected on thickness variation of an organic film formed. For example, when the substrate temperature is 30° C., the temperature difference of ±0.3° C. corresponds to a temperature variation of 1%. The inner diameter of the cooling water pipe is set to a narrow inner diameter in a region where the cooling water forms slightly turbulent flow and not laminar flow so that the cooling water flowing inside the pipe efficiently carries out heat exchange with respect to the wall surface of the pipe. If the inner diameter is too narrow so that the cooling water forms excessively strong turbulent flow, although the heat exchange efficiency increases, the pressure drop for forcing the cooling water to flow becomes too large. Therefore, the load of a cooling water circulation pump becomes too large and hence the power consumption of the entire system becomes excessive. As a result, the Reynolds number of the cooling water flowing in the cooling water pipe is desirably set in the range of 1000 to 7000. In order to reduce the pressure drop and shorten a time in which the cooling water flows through the stage, the cooling water pipes C1, C2, to Cn are arranged in parallel. Unless the same amount of the cooling water flows in all the cooling water pipes, the temperature of the substrate surface is not maintained uniform.
The inner diameter of the cooling water pipe should be controlled quite accurately. The inner diameter should be controlled with an accuracy within ±1%. The size of a large-area substrate subjected to organic film formation is 1 m, 2 m, . . . , or 5 m or more. Therefore, the substrate stage becomes quite large. It is not easy to accurately control the inner diameter of a long narrow pipe. Even in that case, the cooling water amount flowing in all the cooling water pipes should be the same. Assuming that the flow rate is constant, a pressure drop Pd of cooling water in a region of slightly turbulent flow depends on an inner diameter D and a length L of a cooling water pipe as follows.
Pd∝L/Dα
In a turbulent flow region,
Pd∝L/Dβ
Therefore, inner diameter variations are respectively raised to the a powers and the β powers, thereby leading to changes in pressure drop so as to be directly reflected on changes in flow rate. Herein, α=2 and β=approximately 1.25. In order to solve this problem, at an inlet portion or an outlet portion of each cooling water pipe 59, a narrow pipe portion having an inner diameter d2 smaller than an inner diameter d1 of the cooling water pipe having a length L1 may be provided by a very short length L2 as shown in
The inner diameter of this narrow pipe portion with the short length L2 is finished to an accuracy within ±0.3%. A total pressure drop Pt of this pipe is the sum of a pressure drop Pt1 at the cooling water pipe portion and a pressure drop Pt2 at the narrow pipe portion.
Pt∝L1/D1α+L2/D2β
By setting the narrow pipe portion pressure drop L2/D2β to be greater than the cooling water pipe portion pressure drop L1/D1α, pressure drop variation is determined only by the narrow pipe portion inner diameter accuracy, so that in all the cooling water pipes the cooling water amount for each pipe can be the same. The inner diameter of a narrow pipe having a very short length can be controlled, for example, at approximately ±0.1%.
Next, an organic film-forming method will be described. In
The evaporated organic compound molecules are confined inside the organic compound molecule ejection apparatus 35 (
The ejected gas contains evaporated organic compound molecules so that the organic compound molecules are adsorbed on the substrate surface controlled at a temperature near room temperature. When the substrate has a large area, a gas having a mass greater than Ar with mass number 40 is desirable for accurately forming a gas flow pattern. Kr with mass number 80, Xe with mass number 131, or particularly krypton Kr is preferable. Naturally, it may also be a mixed gas of Ar and Kr or Ar and Xe. The organic compound molecule ejection gas is heated to the same temperature as that of the evaporation dish 36 by a heater before flowing into the organic compound molecule ejection apparatus 35. This is for preventing occurrence of change in temperature of the evaporation dish 36. The pressure inside the chamber 31 during organic film formation is set to a transition flow region of approximately several mTorr to 0.1 mTorr or less. This is the range where the mean free path of gas molecules is several mm to several tens of centimeters.
At the stage where an organic film having a predetermined thickness is formed on the substrate surface, the organic compound molecule ejection gas is stopped and the temperature of the evaporation dish is dropped to the temperature of the non-film formation state. When the film formation is finished, the valves 11 and 12 are closed, the valve 15 is opened, and the valve 20 is opened to introduce the gas such as Ar or N2, thereby setting the pressure inside the chamber to approximately 1 to 10 Torr. In order to achieve the pressure balance between the inside of the organic compound molecule ejection apparatus and the inside of the chamber, it is effective to feed a small amount of gas inside the organic compound molecule ejection apparatus.
In a general substrate transfer system, a substrate is transferred while its surface to be formed with an element thereon faces upward. A complicated system is required for rotating downward, as shown in
As described before, even in the case of a single-color organic EL layer, it is necessary to form a plurality of film layers. In order to successively form the plurality of film layers, a plurality of organic compound ejection apparatuses as shown in
When organic compound molecules having a certain weight, i.e. a molecular weight of several hundreds to approximately 1000, are contained in a heavy base gas such as Xe or Kr and irradiated onto a substrate, the gas flow accurately reaches the substrate surface, which is thus more preferable. The organic compound molecules, which are solidified near room temperature, are adsorbed on the substrate surface and only the Xe gas or Kr gas is discharged to the outside by the exhaust pumps. Xe and Kr are highly expensive gases as compared with Ar and N2 that are normally used industrially. It is desirable that a Xe or Kr recovery circulation system be provided subsequently to the roughing vacuum pump.
In order to achieve the Xe gas or Kr gas recovery efficiency of 99.99% or more or 99.9% or more, the flow rate of the purge gas to the turbo-molecular pump 77 and the roughing vacuum pump 78 should be set equal to or less than that of the Xe gas or the Kr gas. Naturally, it should be necessary to prevent incorporation of evaporated components from grease used for bearings and so on of the pumps.
Further,
In each of them, the adsorption cylinder is provided therein with an adsorbent for adsorbing impurities such as noble gas components or nitrogen and Xe or Kr is separated/purified by changing the pressure inside the adsorption cylinder to repeat adsorption/desorption.
The lifetime and luminous properties of an organic EL element can be improved by removing organic compound contamination of an organic EL thin film. On the other hand, when transferring a glass substrate to a film-forming apparatus after cleaning, if use is comprised of a transfer apparatus that does not cause organic contamination on the substrate surface, the lifetime and luminous properties can be further improved. For such transfer of the glass substrate, it is most desirable to transfer the substrate, facing upward or downward, by gas levitation transfer with a clean dry air using porous ceramics as shown in
Since the substrate is levitated/transferred in a clean dry air atmosphere containing no moisture or no organic compound, not only ultrahigh-quality film formation is enabled because moisture or organic compound are not adsorbed at all on the outermost surface of the substrate, but also static electricity is not carried at all in gas levitation transfer using porous ceramics and, therefore, a problem such as dielectric breakdown or disconnection in an element or at element peripheral portions can be reduced, thereby enabling an improvement in production yield and a reduction in production cost.
A film-forming apparatus in Embodiment 4 of this invention will be described with reference to
Among them, in the film-forming apparatus in this embodiment, the gaskets 122 provided between the substrate introduction door 121 and the substrate introduction chamber 123 and between a deposition source chamber and a shutter mechanism are comprised of perfluoroelastomer and the other gaskets are comprised of Cu. By this configuration, it is possible to minimize the number of gaskets containing the organic compound and, further, even the gaskets containing the organic compound use the material whose organic compound release is very little, and therefore, it is possible to suppress incorporation of impurities, released from the gaskets, into an organic compound thin film formed on the substrate. Further, the deposition source container is comprised of Al2O3 and its inner surfaces are made substantially flat by polishing, and therefore, there is almost no catalysis so that it is possible to suppress thermal decomposition of the deposition material inside the deposition source container.
As a result of forming an organic EL layer by the use of this deposition apparatus and measuring the properties of an organic EL element, the brightness at the same current was improved by 30% as compared with the case of using conventional ones (general fluororubber gaskets and a general deposition source container) and the luminance half-decay lifetime became twice, i.e. 10000 hours. Since the organic compound release from the gaskets is suppressed and the decomposition of the deposition material in the deposition source container is suppressed, the incorporation of the impurities into the organic EL layer is suppressed. Therefore, it was possible to improve the brightness and the lifetime.
According to this invention, since an evaporated film-forming material reaches the surface of a substrate by the flow of a transport gas, the film-forming conditions can be controlled by the flow of the gas and hence a uniform thin film can be deposited on the large-area substrate. The film-forming apparatus of this invention thoroughly eliminates generation of the organic compound contamination substance/material decomposition dissociation substance that adversely affects the properties of the film-forming material, and thus can deposit a high-quality thin film. By using the film-forming apparatus and the film-forming method of this invention for forming an organic EL element, it is possible to obtain a high-quality organic EL display device with high brightness and long lifetime. The film-forming apparatus and the film-forming method of this invention are effectively applicable not only to the organic EL field but also to all the other fields where raw materials are evaporated to form films with respect to flat panel display devices, semiconductor devices, and other general electronic devices.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-097112 | Mar 2004 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP05/05928 | 3/29/2005 | WO | 00 | 11/7/2006 |
