Thin film forming apparatus

Abstract: A thin film forming apparatus which forms a thin film over the film forming surface of a substrate (6) by spraying a mist of a source solution produced by atomization over the film forming surface of the substrate (6) heated at a given temperature. The substrate conveying direction is reversible, or a nozzle (3) for spouting the mist into a film forming chamber (4) and an exhaust duct (5) are connected removably to a hearth (7) forming the bottom wall of the film forming chamber (4) for relocation. The film forming apparatus is capable of forming thin films of different laminate constructions.

Description: The present invention relates to a thin film forming apparatus and, more specifically to a thin film forming apparatus which forms a thin film over the surface of a substrate by spraying an atomized source solution over the surface of the heated substrate as known from EP-A-0 252 440. A conventional thin film forming apparatus of a spraying system sprays a source solution prepared beforehand over the surface of a substrate to form a thin film over the surface of the substrate. The thin film forming apparatus is provided with an atomizer for atomizing a source solution prepared beforehand, a nozzle disposed above the atomizer to spout the atomized source solution into a film forming chamber, and an exhaust duct connected to the film forming chamber. The atomizer comprises a mist box and a sprayer disposed in the mist box. Only a mist of comparatively small droplets of the source solution is spouted through the nozzle into the film forming chamber, and then the mist is exhausted from the film forming chamber through the exhaust duct. Substrates arranged successively in a line are moved at a given speed from a preheating chamber through the film forming chamber to an exit. While being moved through the film forming chamber, the substrates are heated with a heater placed opposite to the backsides of the substrates. The mist of the source solution touches the surfaces of the heated substrates at the same flows through the film forming chamber, a material contained in the solution reacts with oxygen contained in air or the moisture of the source solution to form thin films of an oxide over the surfaces of the substrates. The substrates having the lower surfaces coated with the thin films are delivered from a substrate delivery chamber. Since a proportion of liquid ingredient and gaseous ingredient contained in the mist of the source solution is liable to change while the mist spouted through the nozzle into the film forming chamber flows through the film forming chamber and the exhaust duct, the mists of different states deposit films of different characteristics. That is, the mist of the source solution as spouted into the film forming chamber is a perfect mist, namely, a mist consisting of liquid droplets, and hence a film deposited from such a perfect mist consists of crystals oriented to the plane (200) on a three-dimensional coordinate system, has a comparatively smooth surface, and has a comparatively high electrical resistance because the film contains impurities, such as C1 and F, excessively. On the other hand, most droplets of the mist are vaporized in the vicinity of the exhaust duct and hence a film deposited from such a mist consists of crystals oriented to various planes including the plane (200), has a comparatively coarse surface, and has a comparatively low electrical resistance because the film contains only a small amount of impurities. Although thin films of different characteristics are formed respectively at different positions in the film forming chamber, a thin film having the former characteristics and a thin film having the latter characteristics are formed successively over the surface of the substrate to form a thin film because the substrate is moved in one direction. Some purpose requires a thin film of a construction other than such a layer construction of thin film, however, the conventional thin film forming apparatus is unable to form a thin film meeting such a requirement. Most portion of a thin film formed over the surface of a substrate is formed at a very high film forming rate in the vicinity of the spouting opening of the nozzle, in which the mist is spouted toward the surface of the substrate, and the film forming rate decreases sharply with the distance from the spouting opening of the nozzle. Therefore, the moving speed of the substrate must be comparatively low to form a thin film having a comparatively large thickness. However, reduction in the moving speed of the substrate entails the reduction of the productivity of the thin film forming apparatus. Accordingly, it is an object of the present invention to provide a thin film forming apparatus capable of forming thin films respectively having different constructions. To achieve the object of the invention, the present invention provides a thin film forming apparatus with the features of claim 1. Subject matter of subclaims 2 to 7 are preferred embodiments of the invention. The thin film forming apparatus in accordance with the present invention is capable of changing the relation between the respective positions of the nozzle and the exhaust duct, and the substrate conveying direction by reversing the substrate conveying direction, changing the respective positions of the nozzle and the exhaust duct in the film forming chamber, or selectively using one of the two exhaust ducts to form a thin film of a desired construction consisting of component thin films respectively having different characteristics. Employment of a plurality of nozzles facilitates forming a thin film having a comparatively large thickness. Fig. 1 is a fragmentary longitudinal sectional view of a thin film forming apparatus in a first embodiment according to the present invention; Fig. 2 is a fragmentary longitudinal sectional view of a thin film forming apparatus in a second embodiment according to the present invention; Fig. 3 is a fragmentary longitudinal sectional view of a thin film forming apparatus in a third embodiment according to the present invention; Fig. 4 is a fragmentary longitudinal sectional view of a thin film forming apparatus in a fourth embodiment according to the present invention. Preferred embodiments of the present invention will be described hereinafter with reference to the accompanying drawings. The thin film forming apparatus comprises at least one atomizer 1, 1' for producing a mist of a source solution by atomization, at least one nozzle 3, 3' placed upright on top of the atomizer 1 and having a spouting opening into a film forming chamber 4, 4', and two exhaust ducts 5, 5' connected to the film forming chamber 4. The mist of the source solution is spouted through the at least one nozzle 3, 3' into the film forming chamber 4, 4'. The mist spouted into the film forming chamber 4, 4' flows through the film forming chamber 4, 4' and is discharged through one of the two exhaust ducts 5, 5' from the film forming chamber 4, 4'. The film forming chamber 4 is a tunnel-shaped space having a bottom surface defined by a hearth 7, and side surfaces defined by side walls 18. Supporting ribs for supporting a substrate 6 at its opposite sides project inward respectively from the opposite inner surfaces of the side walls 18. The lower surface of the substrate 6 supported on the supporting ribs define the ceiling of the film forming chamber 4. Practically, a plurality of substrates 6 are arranged successively in a line and are moved at a given speed. A soaking plate 8 is disposed over the substrates 6 so as to extend from the preheating chamber 12 through the film forming chamber to the substrate delivery chamber 13. A heating element 9 is disposed over the soaking plate 8 to heat the substrates 6 at a given temperature. Referring to Fig. 1, a thin film forming apparatus in the first embodiment according to the present invention is provided with one nozzle 3 connected to a hearth 7 by a connecting member 15, and two exhaust ducts 5 and 5' connected to the hearth 7 by connecting members 16 and 16' at positions respectively on the opposite sides of the nozzle 3. Valves 17 and 17' are provided respectively in the exhaust ducts 5 and 5' to open or close the exhaust ducts 5 and 5'. When the valve 17' is closed to exhaust the mist through the exhaust duct 5, the mist spouted through the nozzle 3 flows through a right-hand film forming chamber 4 in a direction indicated by arrows. When the valve 17 is closed to exhaust the mist through the exhaust duct 5', the mist flows through a left-hand film forming chamber 4' in the reverse direction. In this case, the exhaust duct 5' may be used as an intake duct for supplying the carrier gas. Referring to Fig. 2, a thin film forming apparatus in a second embodinent according to the present invention is provided with two nozzles 3 and 3' connected to a hearth 7 respectively by connecting members 15 and 15', a partition member 10 mounted on a connecting member 14 and disposed between the nozzles 3 and 3', and two exhaust ducts 5 and 5' disposed respectively on the outside of the nozzles 3' and 3. Valves 17 and 17' are provided respectively in the exhaust ducts 5 and 5' to open or close the same. Mists spouted respectively into film forming chambers 4 and 4' flow in opposite directions. Both the film forming chambers 4 and 4', or either the film forming chamber 4 or 4' may be used. Referring to Fig. 3, a thin film forming apparatus in a third embodiment according to the present invention is provided with two nozzles 3 and 3' connected to a hearth 7 by connecting members 15 and 15' respectively at positions near exhaust ducts 5' and 5 provided respectively with valves 17' and 17. The mist of the source solution is spouted through the nozzle 3' while the valve 17 is closed to make the mist flow through a film forming chamber 4 in a direction indicated by arrows and is exhausted through the exhaust duct 5'. The mist is spouted through the nozzle 3 while the valve 17' is closed to make the mist flow through the film forming chamber 4 in the reverse direction. Referring to Fig. 4, a thin film forming apparatus in a fourth embodiment according to the present invention is provided with two exhaust ducts 5 and 5' connected to a hearth 7 by connecting members 16 and 16', partition members 10 connected to the hearth 7 by connecting members 14, mist guides 11 disposed between the exhaust ducts 5 and 5', and two nozzles 3 and 3' connected to the hearth 7 by connecting members 15 an 15' respectively on the outside of the exhaust ducts 5 and 5'. Valves 17 and 17' are provided respectively in the exhaust ducts 5 and 5' to open or close the same. The mists spouted in film forming chambers 4 and 4' flow through the film forming chambers 4 and 4' in opposite directions. Both the film forming chambers 4 and 4' or either the film forming chamber 4 or 4' may be used. The mist guides 11 and the nozzle 3' may be omitted when only the film forming chamber 4' is used. The thin film forming apparatus shown in Figs. 1 to 4 employ connecting members 14, 15, 15', 16 and 16' to connect removably the nozzles 3 and 3' and the exhaust ducts 5 and 5' to change the arrangement of the nozzles 3 and 3' and the exhaust ducts 5 and 5'. However, the means for changing the respective positions of the nozzles 3 and 3' and the exhaust ducts 5 and 5' are not necessarily essential, because the flowing direction of the mist in the film forming chambers 4 and 4' can be changed by properly operating the exhaust ducts 5 and 5'. As is apparent from the foregoing description, according to the present invention, the relation between the direction of flow of the mist in the film forming chamber and the substrate conveying direction can be changed to form thin films of various laminate constructions and different characteristics meeting diversified purposes. The thin film forming apparatus provided with a plurality of nozzles is able to form a thin film of a comparatively large thickness without reducing the productivity of the thin film forming apparatus.

Claims: A thin film forming apparatus comprising: an atomizer (1) for atomizing a source solution for forming a thin film; a film forming chamber (4); at least one nozzle (3) connected to the film forming chamber (4) at a position near one end of the film forming chamber (4) to spout a mist of the source solution produced by the atomiser (1) into the film forming chamber (4); at least one exhaust duct (5) connected to the film forming chamber (4) at a position near the other end of the film forming chamber (4) to exhaust the mist from the film forming chamber (4); substrate feed means for feeding substrates (6) into the film forming chamber (4) so that the film forming surfaces of the substrates (6) define the ceiling of the film forming chamber (4); and heating means (9) for heating the substrates (6); characterized by two exhaust ducts (5, 5') each being provided with a valve (17, 17'). A thin film forming apparatus according to claim 1, characterized in that the two exhaust ducts (5, 5') are provided at positions on opposite sides of the at least one nozzle (3). A thin film forming apparatus according to claim 2, characterized in that two nozzles (3, 3') are provided. A thin film forming apparatus according to claim 3, characterized in that a partition member (10) is disposed between the nozzles (3, 3'). A thin film forming apparatus according to claim 1, characterized in that the two exhaust ducts (5, 5') are provided between two nozzles (3, 3'). A thin film forming apparatus according to claim 5, characterized in that mist guides (11) are disposed between the exhaust ducts (5, 5'). A thin film forming apparatus according to one of the preceding claims, characterized in that at least one nozzle (3) and at least one exhaust duct (5) are removably connected to a hearth (7) forming the bottom wall of the film forming chamber (4) for relocation.

Inventors: IIDA HIDEYO C O TAIYO YUDEN CO, IMAI MIZUHO C O TAIYO YUDEN CO, SEKIGUCHI MIKIO C O TAIYO YUDE, SHIBA NOBUYASU C O TAIYO YUDEN, IIDA, HIDEYO, C/O TAIYO YUDEN CO. LTD., IMAI, MIZUHO, C/O TAIYO YUDEN CO. LTD., SEKIGUCHI, MIKIO, C/O TAIYO YUDEN CO. LTD., SHIBA, NOBUYASU, C/O TAIYO YUDEN CO. LTD.
Applicants: TAIYO YUDEN KK, TAIYO YUDEN CO., LTD.
Application year: 1990
Main classification: B05B13
IPC codes: H01L31, C23C16, H01B5, C23C18, H01B13, H01L21, C03C17