EVAPORATION SOURCE FOR USE IN VAPOR DEPOSITION APPARATUS

There is provided an evaporation source adapted for use in a vapor deposition apparatus in which by heating, in an induction heating method, a crucible filled with a vapor deposition material, the entire crucible including a cap body attains a top-heat state. An evaporation source is provided with: a crucible filled with the vapor deposition material; a cap body to close an upper surface opening of the crucible; and an induction heating coil disposed around the crucible and the cap body. Further, the cap body is provided with a discharge part which allows the passage of the vapor deposition material evaporated or sublimated by heating. The cap body is provided on an external surface thereof with projections each having a corner part.

TECHNICAL FIELD

The present invention relates to an evaporation source for use in a vapor deposition apparatus in which the evaporation source is disposed inside a vacuum chamber for depositing on an object to be deposited (hereinafter also called “to-be-deposited object”), and relates in particular to the evaporation source for heating a vapor deposition material inside a crucible in an induction heating method.

BACKGROUND ART

This kind of evaporation source for use in a vapor deposition apparatus is known, e.g., in patent document 1. The evaporation source is provided with: a crucible filled with a vapor deposition material; a cap body having a discharge nozzle (discharge part) which closes an opening on an upper surface of the crucible and which also allows passage of the vapor deposition material that has been vaporized or sublimated; and an induction heating coil which is disposed around the crucible and the cap body. In this arrangement, when the induction heating coil is charged with an AC current inside the vacuum chamber in a vacuum atmosphere, the crucible and the cap body are heated by Joule heat generated by resistance loss that is caused when induction current (eddy current) flows through the crucible and the cap body. As a consequence, the vapor deposition material inside the crucible is heated by heat conduction from a wall part of the crucible and radiant heat from the cap body.

It is to be noted here that, when the vapor deposition material inside the crucible is heated, the vapor deposition material inside the crucible is not vaporized or sublimated except from an upper layer portion that faces the discharge nozzle. Therefore, at the time of heating the crucible inclusive of the cap body, it is desirable to maintain a temperature gradient with high temperature of the cap body and lower temperature gradient toward the lower end of the crucible (so-called top-heat state) by efficiently heating only the upper layer portion of the vapor deposition material so that the vapor deposition material present in the lower layer portion inside the crucible does not suffer from a heat deterioration (thermal decomposition, thermal denaturation, and the like in case of organic materials) as a result of addition of excessive thermal load to the vapor deposition material. In such a case, in a resistance heating system by utilizing a sheathed heater, and the like, it is easy to attain the top-heat state, but in an induction heating system, a resistance loss will occur depending on a counter area relative to the induction heating coil. Therefore, as a consequence of heating on a priority basis the crucible having a relatively large counter area, if the entire crucible is heated so that the vapor deposition material on the upper layer portion reaches an evaporation temperature or a sublimation temperature, there is a problem in that the lower part of the crucible will attain an excessive heat state (so-called bottom-heat state).

As compared with the resistance heating system, the induction heating system has an advantage in that the responsiveness in heating is better and that heat can be dissipated at a short time after having finished the deposition work. For this reason, development of the induction type of evaporation source that is capable of attaining the top-heat state of the crucible inclusive of the cap body is desired.

PATENT DOCUMENTS

SUMMARY OF THE INVENTION

Problems that the Invention is to Solve

In view of the above-mentioned points, this invention has a problem of providing an evaporation source for use in a vapor deposition apparatus in which, when a crucible filled with a vapor deposition material is heated in the induction heating system, the entire crucible including the cap body becomes a top-heat state.

Means for Solving the Problems

In order to solve the above-mentioned problem, this invention is an evaporation source disposed inside a vacuum chamber, the evaporation source being adapted for use in a vapor deposition apparatus which performs vapor deposition on a to-be-deposited object. The evaporation source comprises: a crucible filled with a vapor deposition material; a cap body for closing an upper surface opening of the crucible; an induction heating coil disposed around the crucible and the cap body; and a discharge part disposed in the cap body in order to allow for passage therethrough of the vapor deposition material that has been evaporated or sublimated by heating, wherein the cap body is provided on an outside surface thereof with projections each having a corner part.

According to this invention, when an AC current is charged through the induction heating coil inside the vacuum chamber in a vacuum atmosphere, an induction current (eddy current) flows through the crucible and the cap body. At this time, since projections each having a corner part on an outside surface of the cap body are provided, resistance loss will be augmented at the corner parts (edge parts) of the projections. In other words, the calorific value improves when the magnetic flux density to work on the cap body and the quality of material of the cap body are supposed to be equal to a case, for comparison purpose, in which projections are not provided. As a result, it becomes possible to cause the cap body to generate heat on a priority basis so that the entire crucible inclusive of the cap body can be made into the top-heat state. By the way, in this invention, when the “corner parts” of the projections are referred to, it should be understood to include not only the case in which the projections have square profiles but also the case in which the projections are rounded to such a degree as to be able to increase the resistance losses (e.g., having a profile of ellipse).

In this invention, preferably the cap body comprises: a cover plate part provided with the discharge part; and a peripheral wall part vertically disposed from an outer edge of the cover plate part downward such that: a lower end of the peripheral wall part is detachably fitted onto an upper end of the crucible and that; an outside surface of the peripheral wall part is provided with a plurality of the above-mentioned projections in a manner to be vertically or circumferentially extended. According to this arrangement, the outside surface of the peripheral wall part has a shape of repeating projections so that the length for the eddy current to flow therethrough becomes longer, thereby still further augmenting the resistance loss. The calorific value of the cap body can further be augmented so that the entire crucible including the cap body can surely be made to be the top-heat state.

By the way, in order to attain the top-heat state of the crucible inclusive of the cap body in case the cap body is not provided with projections, it may be considered to set smaller the winding pitch of the induction heating coil that is positioned around the cap body than the winding pitch of the induction heating coil that is positioned around the crucible, thereby creating magnetic flux densities into coarse one and dense one. However, the counter area of the cap body that lies opposite to the induction heating coil is still smaller in this arrangement. It is therefore still far from attaining the top-heat state. On the other hand, according to this invention, the winding pitch of the induction heating coil that is positioned around the cap body is set smaller than the winding pitch of the induction heating coil that is positioned around the crucible. In this arrangement, the eddy current to flow through the crucible becomes smaller, and therefore the crucible is restrained from getting heated and, consequently, the entire crucible inclusive of the cap body can surely be made to the top-heat state.

MODES FOR CARRYING OUT THE INVENTION

With reference to the drawings, a to-be-deposited object is defined as a glass substrate (hereinafter referred to as “substrate Sw”) of a predetermined thickness having a rectangular profile. A description will now be made of an evaporation source DS adapted for use in a vapor deposition apparatus with reference to an example in which a predetermined thin film is formed on one surface of the substrate Sw by vapor deposition. In the following descriptions, the terms showing the directions such as “upper”, “lower”, and the like are described on the basis ofFIG.1.

With reference toFIG.1, reference character Dm is a vapor deposition apparatus provided with evaporation sources DS1according to a first embodiment of this invention. The vapor deposition apparatus Dm is provided with a vacuum chamber1to which, although not explained by particularly illustrating, is connected a vacuum pump through an exhaust pipe. It is thus so arranged that the vacuum chamber1can be maintained inside thereof at a predetermined pressure (vacuum degree). Further, at an upper part of the vacuum chamber1there is provided a substrate transfer apparatus2. The substrate transfer apparatus2has a carrier21for holding the substrate Sw in a state in which the lower surface of the substrate serving as a film-forming surface is left open. It is thus so arranged that by means of a driving apparatus (not illustrated), the carrier21and further the substrate Sw can be moved at a predetermined velocity in one direction inside the vacuum chamber1. As the substrate transfer apparatus2there can be used as known one and, therefore, no further description thereof will be made. On a bottom surface of the vacuum chamber1there are arranged a plurality of the evaporation sources DS1of the first embodiment at a distance from each other in the moving direction of the substrate Sw.

With reference also toFIG.2, each of the evaporation sources DS1has the same construction and is provided with a storing container3of a bottomed cylindrical shape, the storing container being disposed on the bottom surface of the vacuum chamber1in a posture in which the opening3afaces upward. A crucible4is stored inside the storing container3and, at the same time, an induction heating coil6is disposed between the storing container3and the crucible4.

The crucible4has a bottomed cylindrical shape and is disposed on the lower surface of the storing container3. The crucible4is detachably provided with a cap body5in such a manner as to close an opening on an upper surface (also called “an upper surface opening”)4aof the crucible4. The cap body5is provided with: a cover plate part51having opened therein a plurality of openings51a(discharge parts51a); and a peripheral wall part52which is vertically disposed from an outer edge of the cover plate part51downward. The lower end of the peripheral wall part52has formed therein a recessed part52awhich recesses upward. By fitting an upper end of the crucible4into the recessed part52a, the cap body5is arranged to be detachably fitted into the crucible4(see the portion enclosed by a chained line inFIG.2). In this case, although not illustrated in particular, projected parts are disposed on an upper end of the crucible4at a circumferential distance from one another so that each of the projected parts comes into point contact with the recessed part52aof the cap body5. The crucible4and the cap body5are made of electrically conductive material such as carbon, graphite, titanium, stainless steel (SUS), boron nitride (BN) and the like, or a material by processing a metallic film or a graphite film on the surface of ceramic material such as boron nitride and the like.

In addition, inFIG.2, the portion enclosed by a dashed line is an enlargement of the peripheral wall part52of the cap body5. On the outer surface of the peripheral wall part52of the cap body5, there are vertically formed a plurality of projections52bat an equal distance from one another, thereby repeating the recessions and projections. Each of the projections52bis formed by machining in the form of countersinking the peripheral wall part52so as to have a profile of rectangle in cross section over an entire continuous length of the circumferencial surface. In this case, the number of the projections52b, the height h from the outer surface of the peripheral wall part52of the projections52b, and the width w in the vertical direction of the projections52bare appropriately set depending on the temperature of heating the vapor deposition material Vm, the area of the peripheral wall part52, the distance between the peripheral wall52and the induction heating coil6(so as to keep the induction heating coil6out of contact with the peripheral wall52), or taking into consideration the ease of workability and the like. For example, the height h shall be set above 100 μm, and the width w shall be set within a range of 0.1 to 10 mm.

Inside the crucible4there is stored an inner crucible part41. The inner crucible part41is made of a material with heat resistance and relatively small heat conductivity such as ceramics, titanium, and stainless steel. Inside the inner crucible part41the vapor deposition material Vm is filled. As the evaporation material Vm an organic material is appropriately selected depending on the thin film to be deposited on the substrate Sw, and the material in the form of granules or tablets is utilized. In this embodiment, a description is made of an example in which the inner crucible part41is filled with the vapor deposition material Vm, but without providing the inner crucible part41inside the crucible4, the crucible4may be filled with the vapor deposition material Vm.

The induction heating coil6is wound at a predetermined winding pitch so as to cover the entire circumference of the crucible4and the cap body5is electrically connected to an AC power supply (not illustrated). In this arrangement, when the induction heating coil6is charged with AC current by the AC power supply inside the vacuum chamber1in a vacuum atmosphere, the crucible4and the cap body5get heated by the Jule heat that is generated by the resistance loss when the induction current (eddy current) flows through the crucible4and the cap body5. In this embodiment, the winding pitch of the induction heating coil6is so arranged that the winding pitch Ph1of the induction heating coil6positioned around the cap body5is smaller than the winding pitch Ph2of the induction heating coil positioned around the crucible4.

According to the above arrangement, in case a predetermined organic film is deposited on a lower surface of the substrate Sw by the above-mentioned vapor deposition apparatus Dm, once the induction heating coil6is charged with the AC power supply inside the vacuum chamber1in the vacuum atmosphere, the induction current (eddy current) flows through the crucible4and the cap body5. At this time, as a result of having provided the outside surface of the cap body5with projections52beach having a corner part, resistance loss will be augmented at the corner part (edge part) of each of the projections52b. The calorific value improves when the magnetic flux density to work on the cap body5and the quality of material of the cap body5are supposed to be equal to a case, for comparison purpose, in which projections52bare not provided. As a result, it is possible to cause the cap body5to generate heat on a priority basis so as to make the entire crucible inclusive of the cap body5into the top-heat state.

Further, according to this invention, by providing the outside surface of the peripheral wall part52of the cap body5with a plurality of circumferentially extending projections52b, the distance in which the eddy current flows becomes longer, resulting in further augmentation in the resistance loss. It is thus possible to further augment the calorific value of the cap body5to surely attain the top-heat state of the entire crucible inclusive of the cap body5. Furthermore, as a result of setting smaller the winding pitch Ph1of the induction heating coil6that is positioned around the cap body5than the winding pitch ph2of the induction heating coil6that is positioned around the crucible4, the crucible4is restrained from getting heated. As a consequence, the entire crucible inclusive of the cap body5can surely be made into the top-heat state.

In order to confirm the above-mentioned effects, the following evaluation was made using the above-mentioned vapor deposition source DS1. In other words, by using the crucible4and the cap body5which are made of titanium, there were provided, over the entire circumference, a plurality of projections52bhaving a height h of 100 μm from the external surface of the peripheral wall part52and a vertical width w of 2.0 mm, and an evaluation was made of the resistance loss of the crucible4and the cap body5. At this time, the winding pitch Ph1of the induction heating coil6that was positioned around the cap body5was set at 10 mm, and the winding pitch Ph2of the induction heating coil6that was positioned around the crucible4was set at 30 mm, and the coil6was charged with electricity of 20 A at a frequency of 200 kHz. As a comparative experiment, by using a sample having no projections on the peripheral wall of the cap body5, the resistance losses of the crucible4and the cap body5were evaluated.

In the comparative experiment, the resistance loss of the crucible4was 8.4 W/m3, and the resistance loss of the cap body5was 4.2 W/m3. The resistance loss of the cap body5was smaller than the resistance loss of the crucible4. On the other hand, in the experiment of this invention, the resistance loss of the crucible4was 3.2 W/m3, and the resistance loss of the cap body5was 8.6 W/m3. The resistance loss of the cap body5was thus larger than the resistance loss of the crucible4. It has thus been confirmed that the top-heat state has been attained.

Descriptions have so far been made of the embodiments of this invention. As long as the technical concept of this invention is not deviated, various modifications can be made. In the above-mentioned evaporation source DS1according to the above-mentioned first embodiment, a description was made of an example in which projections52bhaving disposed, on an outside surface of the peripheral wall part52, a plurality of cross-sectional shape elongated vertically (longitudinal direction of the crucible4). The position in which the projections52bare disposed need not be limited to the above-mentioned example, but the projections may be disposed, e.g., on an outside surface of the lid plate part51. In addition, the shape of the projections can augment the resistance loss at the time of flowing of the induction current (eddy current) and, at the same time, as long as the projections have a predetermined length, the shape of the projections need not be limited to the above. It may be so arranged that the shape of the projections52bhas a cross section of a rounded profile to such a degree as can increase the resistance loss.

In other words, as shown inFIGS.3(a) and3(b), bearing the same reference numerals with reference to the same members or elements, the evaporation source relating to a modified example may be that the sectional shape of the projections may be oblong rounded to such a degree as to augment the resistance loss (projection52cinFIG.3(a)) or substantially pentagonal in section having chamfered surface (projection52dinFIG.3(b)). In these shapes of the corner parts, the outside surface of the peripheral wall part52became a shape to repeat the projection/recession. As a result, the resistance loss will be augmented by enlarging the distance in which the eddy current flows, thereby increasing the calorific value of the cap body5.

In the evaporation source DS1according to the above-mentioned first embodiment, a description was made of an example in which a plurality of projections52bextend in the circumferential direction of the peripheral wall part25, but the pattern of the projections is not limited thereto. With reference toFIG.4in which the same reference numerals have been assigned to the same members or elements, in the evaporation source DS2according to a second embodiment, a plurality of projections are provided in a pattern in which each of the projections52eextends in the vertical direction of the peripheral wall part52. It is to be noted that the portion enclosed by a chained line inFIG.4is an enlarged view showing the peripheral wall part52of the cap body5as seen from an upper side. Further, it is also considered to provide a lattice-shaped pattern in which each of the circumferentially extended projections52band each of the vertically extended projections52ecross each other, or a spirally shaped pattern around a generating line of the peripheral part52.

Furthermore, in the above-mentioned first embodiment, a description was made of an example in which the winding pitch Ph1, at a position around the cap body5, of the induction heating coil6was set smaller than the winding pitch Ph2, at a position around the crucible4, of the induction heating coil6. Without being limited to the above, the winding pitch of the induction heating coil may be set equally in relation to the one positioned around the cap body5and the one positioned around the crucible4.

EXPLANATION OF MARKS

Dm vapor deposition apparatusDS1, DS2vapor deposition sourceSw substrate (to-be-deposited object)Vm vapor deposition material1vacuum chamber4crucible4aupper surface opening5cap body51lid plate part51adischarge part52peripheral wall part52b-52eprojections6induction heating coilPh1winding pitch of induction heating coil positioned around a cap bodyPh2winding pitch of induction heating coil positioned around a crucible