Patent Application
20090041929
This invention relates to a film forming apparatus and a film forming method for forming a layer of a predetermined material and, in particular, relates to a film forming apparatus and a film forming method for forming a layer of a predetermined material by evaporating a raw material of the predetermined material.
A method of forming a layer of a predetermined material by evaporating a raw material of a predetermined material is widely used in the manufacture of semiconductor devices, flat panel display devices, and other electronic devices. Description will be restricted hereinbelow to an organic EL display device as one example of those electronic devices. If such an organic EL display device could have a sufficient brightness and a long lifetime, such as several tens of thousands of hours or more, the organic EL display device could implement an ideal flat panel display because the organic EL display device uses organic EL elements of a self-luminosity type and can realize a thin structure due to a reduction of peripheral components, such as backlight elements or devices. Requirements are imposed on the organic EL elements of the organic EL display device in view of characteristics as a display device and are such that lifetimes of the elements are long in spite of a large screen, no variation in luminous brightness appears in the screen and in the element lifetimes, and no defect, such as, typically, a dark spot appears. In order to satisfy such requirements, formation of an organic EL layer is quite important.
As a film forming apparatus for uniformly forming an organic EL layer on a large substrate, use is made of an apparatus described in Patent Document 1 or the like. The film forming apparatus of Patent Document 1 aims to achieve uniformity in film thickness on a large substrate by optimally arranging, in a tree fashion, a piping structure inside an injector disposed in the apparatus.
Currently, an organic EL layer is formed by a vacuum deposition apparatus kept in an atmosphere of 10−6 Torr to 10−7 Torr or less. According to experiments by the present inventors, it has been found out that, in the current vacuum deposition apparatus, an organic EL layer is subjected to extensive contamination by organic compounds in an organic EL layer forming process and, as a result of this, the brightness and lifetime of organic EL light-emitting diodes (OLED) are largely reduced.
Further, in a continuous vacuum deposition apparatus having a load lock chamber, the case where an NPD layer, an Alq3 layer, and an MgAg electrode layer are formed immediately after a glass substrate is transferred into the load lock chamber kept in a vacuum of about 1×10−7 Torr is compared with the case where a substrate is left unchanged in an atmosphere of about 1×10−7 Torr for 30 minutes during forming each layer. In this event, it has been found out that, when samples that are exposed as the latter, to the atmosphere of about 1×10−7 Torr for 30 minutes during forming each layer, the brightness of such samples is reduced to about ⅓ and the lifetime taken until the brightness is degraded to half is reduced to ⅓ or less.
Zealous studies have been conducted about the foregoing lifetime degradation. As a result, the present inventors have found out that organic compounds, which become contamination sources, have high partial pressures in the vacuum state and, simultaneously, mean free paths of molecules of organic compounds become very long and, in consequence, contamination by organic compounds on the surface of a substrate becombe extremely polluted and results in a reduction of the lifetimes of the organic EL elements.
Further, it has been also found out that, in order to reduce variation in luminous brightness in a screen and element lifetime, film properties and film thickness at the time of organic EL element film formation should be uniform, which is quite important. The apparatus described in Patent Document 1 is given as an example of a film forming apparatus for uniformly depositing an organic EL thin film. Although the film thickness of an organic EL element formed by the apparatus of the above-mentioned structure is uniform, dark spots or variation in element lifetime undesirably takes place.
Further, as regards the injector described in Patent Document 1, no disclosure is made about the material and temperature of the injector. This shows that, depending on the conditions, there might raise a problem such that an organic EL material is deposited inside the injector and an organic EL material is decomposed inside the injector and thus decomposed products are deposited on a substrate, and, as a result, such organic EL elements do not act as desirable organic EL elements.
Further, in the conventional film forming method, an evaporated raw material is scattered omindirectionally so as to be deposited on portions other than a substrate and is thus vainly wasted and, further, since evaporation continues for a while even if heating of an evaporating dish is stopped, there is much waste of the raw material during non-film-formation. In order to reduce these wastes, the present inventors have previously proposed a film forming apparatus and a film forming method in that a raw material is conducted by using a carrier gas from a raw material container disposed in a reduced-pressure vessel to the surface of a substrate, in International Publication No. 2005/093120 pamphlet (Patent Document 2).
Patent Document 1: Japanese Unexamined Patent Application Publication (JP-A) No. 2004-79904
Patent Document 2: International Publication No. 2005/093120 pamphlet
In the film forming apparatus and the film forming method proposed in Patent Document 2, since it is possible to suppress generation of organic contaminants and material-decomposed/dissociated matters that adversely affect the properties of a film forming material, a high-quality thin film can be deposited. Therefore, when such a film forming apparatus and film forming method are applied to formation of an organic EL device, it is possible to obtain a high-quality organic EL device with a high brightness and a long lifetime.
On the other hand, according to Patent Document 2when a substrate to be subjected to film formation has a large area, it is difficult to uniformly provide the film thickness and so on over the whole area of the substrate. Further, it is difficult to increase the film formation rate to thereby perform film formation efficiently. Further, it is proposed to change the temperature, flow rate, and pressure of gases such as an organic EL raw material and a carrier gas on shifting from the start of film formation to a film forming process and on shifting from the film forming process to stopping of the film formation. However, no proposal has been offered at all about quickly and smoothly switching an atmosphere according to the process, that is, about means for quickly performing a state transition. Therefore, it is difficult to form an organic EL thin film at high rate.
It is an object of this invention to provide a film forming apparatus and a film forming method that can achieve uniform film formation even in the case of a large-area substrate.
Further, it is an object of this invention to provide a film forming apparatus and a film forming method that can increase the film formation rate to thereby perform film formation efficiently.
Further, it is an object of this invention to provide a film forming apparatus and a film forming method that can quickly perform a state transition and, as a result of this, can form a high-quality film at high rate.
It is another object of this invention to provide a film forming apparatus and a film forming method that can continuously deposit a plurality of organic EL raw materials.
It is still another object of this invention to provide a film forming apparatus and a film forming method that can simultaneously form a film made of a plurality of components.
It is another object of this invention to provide a film forming apparatus having a structure in which an ejection vessel for ejecting a raw material gas and a carrier gas onto a substrate and a raw material container are connected by a piping system.
It is an object of this invention to provide a film forming apparatus that can quickly perform a process transition by improving a piping system of the film forming apparatus having the piping system.
According to a first aspect of this invention, there is obtained a film forming apparatus or a film forming method that evaporates a raw material for use in forming a film of a predetermined material and transports the raw material gas, evaporated, using a carrier gas, thereby depositing the film of the predetermined material on a substrate, wherein the carrier gas is caused to flow into evaporation means so as to make a gas phase pressure in the evaporation means equal to that during film formation, at at least one of the time before the film formation and the time of stopping the film formation. The gas that flows in the evaporation means to transport the evaporated raw material is discharged to the outside of the evaporation means. The discharged gas may be sent to, for example, a recovery system or may be sent to another evaporation means separately provided. In this case, there are provided a plurality of raw material containers each forming evaporation means and the raw material gas is transported by the carrier gas from one container to another raw material container during non-film-formation.
During the film formation, the carrier gas and the raw material gas are ejected by an ejection vessel. By this, the pressures and temperatures of the plurality of raw material containers are kept equal during the non-film-formation and the film formation.
A gas pressure control portion having an orifice is provided in a piping system between the evaporation means and the ejection vessel, thereby supplying the carrier gas containing the evaporated raw material to the ejection vessel at a predetermined flow rate and flow velocity. The gas sent from the gas pressure control portion is ejected into the ejection vessel from a plurality of supply ports provided in the ejection vessel. Therefore, it becomes possible to carry out film formation uniformly and at high rate even in the case of a large-area substrate.
Further, according to this invention, by providing the plurality of raw material containers and by selectively setting these raw material containers to an organic EL molecule supply state and quickly and smoothly carrying out a transition between the film formation and the non-film-formation, it is possible to minimize remaining and deposition of molecules of organic compounds and so on. By this, it is possible to form a high-quality, long-lifetime organic EL film.
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Referring to
An organic compound molecule ejection apparatus 151 is disposed in the ejection vessel 15. The organic compound molecule ejection apparatus 151 comprises a plurality of gas dispersion plates (herein, six gas dispersion plates) 152 and a filter 153 made of ceramic, metal, or the like and opposed to the substrate. In this connection, the ejection vessel 15 may also be called a gas ejection portion. The substrate such as the glass substrate is held by a substrate holding portion (not shown) so as to face the organic compound molecule ejection apparatus 151. The substrate is maintained at a temperature lower than a temperature at which the raw material of an organic EL film is evaporated. On the other hand, predetermined portions of the piping system and the ejection vessel 15 are maintained at temperatures higher than the temperature at which the raw material of the organic EL film is evaporated. In this connection, the substrate holding portion, the piping system, and the ejection vessel 15 are provided with temperature controllers (not shown) for controlling them at the predetermined temperatures, respectively.
On the other hand, the two organic EL raw material containers 11 and 12 are each provided with an evaporating dish and a heater for evaporating an organic EL material. The illustrated two organic EL raw material containers 11 and 12 hold the same organic EL raw material, each thus having a function as a raw material holding portion and each further having a function as an evaporator for evaporating the organic EL material in the container 11, 12. What is shown as “Orifice” in the figure is a gas pressure control portion having an orifice and a valve for adjusting/controlling a gas pressure.
Further, the illustrated piping system comprises a carrier gas piping system for introducing a carrier gas such as xenon (Xe), argon (Ar), or krypton (Kr) into the ejection vessel 15 and an organic EL molecular gas piping system connecting the organic EL raw material containers 11 and 12 and the ejection vessel 15 to each other. The organic EL raw material containers 11 and 12 are also each provided with piping for introducing and exhausting the carrier gas.
The illustrated carrier gas piping system comprises first piping for feeding the carrier gas to the upper and lower two gas dispersion plates 152 of the ejection vessel 15 and second piping for feeding the gas to the four gas dispersion plates 152 disposed at the center of the ejection vessel 15. Herein, the first piping is connected to the two gas dispersion plates 152 through a valve V1, a mass flow controller (MFC 1), and an orifice 2, while, the second piping is connected to the four gas dispersion plates 152 through a valve V2, an MFC 2, a valve V17, and an orifice 1.
On the other hand, upstream of the organic EL raw material container 11, the piping for introducing the carrier gas is provided and this piping has two valves V3 and V5 and an MFC 3 provided between these two valves V3 and V5, while, the piping having a valve V6 is provided as piping for exhausting the carrier gas.
Further, downstream of the organic EL raw material container 11, there is provided a piping system connected to the orifice 1 through valves V9, V16, and V14 and there is further provided a piping system connected to the orifice 1 through valves V10 and V13. These valves, the orifice 1, and the MFC 3 constitute first gas supply means reaching the ejection vessel 15 from the organic EL raw material container 11.
Likewise, upstream of the organic EL raw material container 12, the piping for introducing the carrier gas is provided and this piping has two valves V4 and V7 and an MFC 4 provided between these two valves V3 and V5, while, the piping having a valve V8 is provided as piping for exhausting the carrier gas.
Further, downstream of the organic EL raw material container 12, there is provided a piping system connected to the orifice 1 through valves V11, V15, and V13 and there is further provided a piping system connected to the orifice 1 through valves V12 and V14. These constitute second gas supply means for connecting between the ejection vessel 15 and the organic EL raw material container 12.
In the illustrated piping system, the piping systems (V9, V16, V14 and V11, V15, V13) reach the orifice 1 from the organic EL raw material containers 11 and 12, respectively, and have lengths equal to each other and, further, the lengths of the piping from the orifice 1 to the respective four gas dispersion plates 152 each forming a supply port are also equal to each other. In other words, by providing 2n (n is a positive integer) supply ports that serve to supply an organic EL molecular gas, the lengths of the piping reaching these supply ports from the orifice 1, respectively, can be made equal to each other. That is, the piping systems reaching the supply ports from the organic EL raw material containers 11 and 12, respectively, are arranged symmetrical to each other and, as a result of this, have lengths equal to each other. This also applies to the piping system connected to the orifice 1 from the organic EL raw material container 11 through the valves V10 and V13 and the piping system connected to the orifice 1 from the organic EL raw material container 12 through the valves V12 and V14.
The gas supply system constituted by the foregoing piping system is maintained at a pressure approximate to an atmospheric pressure, while, the inside of the ejection vessel 15 is maintained at a pressure of 1 Torr to several tens of Torr. For maintaining a pressure differential therebetween, the orifices 1 and 2 are provided in the illustrated example. The flow rates of the carrier gas are determined by the MFCs 1 to 4 and, further, since the number of the gas supply ports in the organic EL molecule ejection vessel 15 is set to 2n, the lengths of the piping from the pressure adjusting orifice 1 to the respective gas supply ports can be made equal to each other. In any event, by providing the foregoing piping system, it is possible to cause the gas to simultaneously reach the respective gas supply ports at the same pressure.
In the example shown in
For example, in the case where the organic EL raw material is Alq3, the temperature T1 is about 270° C., the temperature of the ejection vessel 15 is about 300° C., and the temperature of the piping system is maintained at 270° C. to 300° C., while, the temperature (T2) of the raw material container 12 which is not supplying the raw material is maintained at 100 to 220° C.
Hereinbelow, referring also to
Referring to
Referring to
In this mode 2, the carrier gas (flow rate f1) that was fed through the valve V2, the MFC 2, V17, and the orifice 1 is stopped. On the other hand, in order to keep the pressure in the ejection vessel 15 and the pressure in a chamber constant, it is preferable that the carrier gas flow rate from the raw material container 11 serving to supply organic EL molecules to the ejection vessel 15 be, in principle, set equal to the foregoing flow rate f1. That is, the carrier gas flow rate in the path of V10, V13, and the orifice 1 is preferably equal to the flow rate f1 of the carrier gas that was fed in the path of V2, the MFC 2, V17, and the orifice 1 in the mode 1.
Referring to
In the mode III, since V13 is put into the open state while V15 is put into the closed state, the carrier gas containing organic EL molecules flows from the raw material container 11 side to the raw material container 12 at the flow rate f1 in the mode II. On the other hand, since the valves V2 and V17 are set to the open state, the carrier gas flows into the ejection vessel 15 through the orifice 1 at the flow rate f1 equal to that in the mode 1. By this carrier gas, organic EL molecules in the piping from the valve V13, which was in the open state in the mode 11, and the valve V14 to the ejection vessel 15 and organic EL molecules in the piping from the valve V17 to the ejection vessel 15 are blown off. Therefore, the expelling of the organic EL molecules is extremely fast at the time of stopping the film formation. The valves V13 and V15 operate as a control portion for discharging the gas containing the organic EL molecules.
As described above, the film forming apparatus according to this invention operates with the operation sequence of the modes I to III. The foregoing operation sequence has been described in the case of supplying organic EL molecules from the raw material container 11, while, in the case of feeding organic EL molecules from the raw material container 12, the operation exactly symmetric to the foregoing operation is carried out to thereby perform the same processing. In this case, since the piping system shown in
In the illustrated example, at the time of switching to the non-film-forming state, the carrier gas containing organic EL molecules is caused to flow from the one (at the temperature where the raw material is evaporated) of the raw material containers to the other (at the temperature where the raw material is not evaporated) thereof and used for separating and discharging moisture and so on of the raw material in the other and then is exhausted to an exhaust system (gas recovery system or the like), but it may be directly exhausted to the exterior (gas recovery system or the like).
Referring to
All the ejection vessels have exactly the same structure, the same piping system is connected to each of them, and the flow rates of carriers are set equal to each other. It is preferable that the temperatures of the respective ejection vessels be set according to individual properties of organic EL molecules. Further, the ejection vessels are preferably made of stainless, and an ejection portion of each ejection vessel is in the form of a stainless filter and is welded to the body. All the inner surfaces of the ejection vessels may be treated with Al2O3.
Referring to
Since the piping systems of the material containers 11a to 11c are respectively controlled in the manner as described with reference to
When a temperature TO of the ejection vessel 15 is set to 300° C., the temperatures T1′ to T3′ of the material containers 11a to 11c are set to, for example, 200° C., 210° C., and 270° C. and the temperatures of the piping systems between the respective material containers 11a to 11c and the ejection vessel 15 are set to values between T0 and T1′, between T0 and T2′, and between T0 and T3′, respectively. This makes it possible to prevent adsorption of organic EL molecules on the surfaces of the piping systems. It is preferable to select a filter so that the gas pressure in the ejection vessel 15 takes a value where the raw material gases are sufficiently mixed in the viscous flow region (e.g. a pressure of several Torr to several tens of Torr).
This invention is applicable to organic EL film formation to thereby obtain a high-quality organic EL device. Further, this invention is not only applicable to the film formation for organic EL, but also applicable to film formation for various display devices and so on that are each required to have a high quality and a long lifetime.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-110760 | Apr 2005 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2006/306276 | 3/28/2006 | WO | 00 | 11/15/2007 |
