Abstract:
A film formation apparatus for plasma CVD and etching methods making use of inductive coupling plasma generators. The apparatus comprises a plurality of plasma generators for inductive coupling methods, one or more film formation gas discharge pipes, and a substrate setting table facing the plurality of plasma generators via a reaction zone. The film formation gas discharge pipes are included in each of two movable members capable of performing reciprocating motions along a substrate surface on the substrate setting table, while intersecting each other. Thereby, a plasma with a relatively high density can be uniformly created over a large area, the film formation gas excited by free radicals in the plasma can uniformly spread over the film formation target, and a film can be formed with a high deposition rate. Consequently, a large-sized substrate with a good quality of thin film can be provided.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to a film formation apparatus, and particularly relates to improved technology of a thin film semiconductor manufacturing apparatus in an inductive coupling method, in which a thin film semiconductor is manufactured using a plasma enhanced chemical vapor deposition (plasma CVD) method or a plasma etching method. 
     (2) Description of the Related Art 
     Recently, flat panel displays (FPDs) have been widely used and it is desirable that their panels are upsized as their uses are increased. Accompanied by such a situation, it is required to efficiently fabricate good quality of electronic devices (thin film semiconductors) such as thin film transistors (TFTs) on the surface of a large-sized substrate in manufacturing processes of FPDs such as liquid crystal displays (LCDs) or organic EL displays (OELDs). 
     Among methods for fabricating thin film semiconductors on the large-sized substrate, there are a plasma CVD method and a plasma etching method. In these methods, a plasma is generated in an enclosed space by exciting an excitable gas containing inert gases and then a film formation gas is added, whereby a chemical reaction (gas reaction) is induced so that a thin film is formed on the surface of the substrate. 
     Here, there are two types of the plasma CVD methods: a capacitive coupling method, and an inductive coupling method. 
     The capacitive coupling method of the plasma CVD methods is configured so that a substrate setting table and an electrode plate are placed so as to face each other, between which a plasma is generated. Gas reactions are excited by tree radicals and the like generated with the plasma, so that a thin film is deposited on the surface of the substrate placed on the substrate setting table. 
     In this capacitive coupling method, a scale of plasma is in proportion to the surface area of the electrode plate. Therefore, this method has an advantage that a thin film can be formed on the relatively large area at one time by increasing the size of the electrode plate. However, since the plasma density is not so high and approximately 10 16  m −3 , a high film formation rate cannot be expected. In addition, the capacitive coupling method is configured so that a plasma spreading over the reaction zone in the apparatus and a substrate are separated from each other by a sheath formed with a self-bias voltage. As such, if positive ions in the plasma are accelerated by the bias voltage and collide with the substrate surface, a uniform film thickness cannot be obtained, which is a serious problem in the method. 
     In contrast, the inductive coupling method of the plasma CVD methods is configured so that, in one example, a workcoil is wound about a cylindrical-shaped tube, a plasma is generated in the cylindrical-shaped tube by a magnetic field produced by electrically charging the workcoil, and a thin film is formed on the substrate surface by exciting gas reactions with the plasma. 
     This inductive coupling method has an advantage that a plasma with a high density (ranging from approximately 10 17  to 10 18  m −3 ) and abundant free radicals can be obtained, so that a film formation rate is higher than the capacitive coupling method and the manufacturability of films is excellent. However, this inductive coupling method is generally not suitable for the film formation in a relatively large area due to structural properties of the film formation apparatus. That is, even when a large-sized coil is employed according to the substrate size, a good quality of plasma is difficult to obtain because of a non-uniform distribution of the magnetic density generated by the large-sized coil. 
     Meanwhile, the plasma etching method is a film formation method, in which a thin film of a desired pattern is formed by allowing radicals generated with plasma to chemically react with a substrate surface to be etched. Here, this plasma may be produced by either the capacitive coupling method or the inductive coupling method as stated above. However, the scale and efficiency of etching considerably depend on the properties of above stated film formation apparatuses, so the current plasma etching method is not regarded as a technique for obtaining a good quality of patterned thin films. 
     As stated above, it cannot be said that a thin film formation apparatus which forms uniform thin films in a relatively large area has been established. 
     The film formation techniques such as the plasma CVD method and the plasma etching method are originally used for a fine patterned circuit in a small size substrate to fabricate LSIs and so on, while film formation techniques have not been yet established for large-sized FPDs. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a film formation apparatus in a plasma CVD method and a plasma etching method making use of an inductive coupling method, by which a good quality of thin film can be formed in a large area and at a relatively high rate, as compared with the conventional film formation apparatus. 
     The above object can be achieved by the film formation apparatus made up of: a plurality of plasma generators; two or more film formation gas discharge means; and a substrate setting means; wherein the plurality of plasma generators are inductive coupling types, the substrate setting means faces the plurality of plasma generators across a reaction zone, and one or more film formation gas discharge means is included in each of two movable members which perform reciprocating motions on axes intersecting each other and parallel to a top surface of a film formation target substrate placed on the substrate setting means. 
     By means of the above structure, a plasma with a relatively high density can be formed in a large area without nonuniformity and a film formation gas excited by free radicals in the plasma can uniformly spread all over the surface of the film formation target on the substrate, so that a film formation process with a high deposition rate can be realized. As a result, a large-sized substrate on which a good quality of thin film is formed can be provided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and the other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings which illustrate a specific embodiment of the invention. 
     In the drawings: 
     FIG. 1 is a partially cutaway view in perspective of the construction of a film formation apparatus of the present invention; 
     FIG. 2 is a horizontal sectional view showing a plasma generation unit of the film formation apparatus of the present invention; 
     FIG. 3 is a vertical sectional view showing the film formation apparatus of the present invention; and 
     FIG. 4 is a horizontal sectional view showing a film formation unit of the film formation apparatus of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     1. The First Embodiment 
     1.1 Construction of the Film Formation Apparatus 
     FIG. 1 is a partially cutaway view in perspective of the construction of a film formation apparatus  1  of the first embodiment of the present invention (hereafter called the “apparatus  1 ”). 
     FIG. 1 orients the apparatus  1  with reference to a Cartesian chamber reference frame having axes X, Y, and Z. As shown in FIG. 1, the apparatus  1  comprises two main structures: (1) a plasma generation unit  10  including an enclosure box consisting of a top plate  11 , a side plate  12 , and a bottom plate  13 , and (2) a film formation unit  20  having a larger enclosure box than the plasma generation unit  10  and placed under the plasma generation unit  10 . 
     The plasma generation unit  10  has a plasma generator  100  and a plurality of workcoils  110   a  to  110   d  built into the enclosure box, while the film formation unit  20  has a substrate setting table  230  and movable units  210  and  220  built into the enclosure box. Their detailed constructions are as follows. 
     1-2. Construction of the Plasma Generation Unit 
     The plasma generation unit  10  comprises a plurality of plasma generators  100  arranged in a 4×4 matrix form in the x and y directions respectively, and a plurality of workcoils  110   a  to  110   d , each of which is arranged so as to be wound about four cylindrical tubes  102  of the plasma generators  100  arranged in the y direction. 
     The plasma generators  100  comprises a plasma excitable gas delivery tube  101  with a diameter of approximately 6.4 mm and a cylindrical quartz tube  102  with a wall thickness of 4 mm and a length of 1 m. The plasma excitable gas delivery tube  101  is arranged so as to penetrate the top plate  11  from the inside of the cylindrical tube  102  and connected to an external inert gas source (not shown), through which a plasma excitable gas (including inert gases, O 2 , and H 2 ) with a predetermined pressure is supplied. A longer axis of the cylindrical tube  102  is set so as to be perpendicular to the top surface of the substrate setting table  230  (i.e., along the z direction), which will be described later. 
     The top outer edge of the cylindrical tube  102  closely contacts with the top plate  11 . A diameter of the bottom edge part  103  of the cylindrical tube  102  is configured so as to be larger (=460 mm) than the other parts of the cylindrical tube  102  (=300 mm). In addition, all of the bottom edge parts  103  are integral with the bottom plate  13  (See FIG. 3 showing a vertical sectional view of the apparatus, which will be described later in detail). 
     FIG. 2 shows a sectional view of the plasma generation unit at an X-Y plane. 
     A workcoil (one of  110   a  to  110   d ) is wound around four plasma generators  100  arranged along the y direction, with a fixed interval (approximately 3 mm in one embodiment) from the surface of each cylindrical tube  102 . This workcoil is wound around the four plasma generators  100  so as to electrically couple with them, and connected to one of plurality of sockets  110   at  to  110   dt  attached to the side plate  12 . A predetermined electric power with a predetermined frequency is externally supplied to the sockets  110   at  to  110   dt.    
     The position of the workcoils  110   a  to  110   d  relative to the cylindrical tubes  102  can be changed as required (i.e., a gap between the cylindrical tubes  102  and workcoils  110   a  to  110   d , and a relative position of the cylindrical tubes  102  to the workcoils  110   a  to  110   d  in the z direction), whereby the scale of plasma generated in the cylindrical tubes  102  (P regions in FIG. 3) and the generation location can be adjusted. 
     As shown in FIG. 3, in the apparatus  1 , the relative position of the workcoils  110   a  to  110   d  is set to be 250 mm above from the bottom edge parts  103  and a distance between the bottom edge parts  103  and the surface of the film formation target placed on the substrate setting table described later is set to be 500 mm. Such a construction prevents unnecessary ions generated with the plasma from doing damage to the surface of the film formation substrate, while enabling selective free radicals such as oxygen radicals which have long lives and are capable of contributing to the film formation to reach to the surface of the film formation target. 
     1-3. Construction of the Film Formation Unit 
     As shown in FIG. 1, the film formation unit  20  has a rectangular enclosure box  21 , in which the movable units  210  and  220  which are movable in the x and y directions respectively, and a substrate setting table  230  are provided. The movable unit  210  ( 220 ) has a unit structure where a movable member  201  ( 202 ) performs a reciprocating motion along a pair of guide shafts  211  and  212  ( 221  and  222 ) whose longitudinal direction is arranged parallel to the y direction (x direction). In a preferred embodiment of the invention, the movable unit  210  is arranged over (upper in the z direction) the movable unit  220  so as to cross each other without interference between them. 
     The rectangular-shaped substrate setting table  230  is placed at the undersurface of the enclosure box  21  and adjusted so that the top face of the substrate setting table  230  becomes horizontal, on which a substrate as a film formation target is placed. The substrate is fixed onto the substrate setting table  230  by means of a well-known method, not shown, (for example, a vacuum chuck method). The substrate setting table  230  has a heater (not shown) built into the enclosure box, whereby a substrate can be heated to 600° C. 
     FIG. 3 is a vertical sectional view of the apparatus  1  along the longitudinal direction of the cylindrical tubes  102 . FIG. 3 does not show sectional views of the movable units  210  and  220  for the sake of convenience. As shown in FIG. 3, a reaction zone is formed in a space between the bottom edge part  103  of the plasma generator  100  and the substrate setting table  230 . 
     FIG. 4 is a sectional view of the film formation unit along the x-y plane. 
     Each end of a pair of guide shafts  211  and  212  ( 221  and  222 ) is supported by and integral with height adjustment units  211   ad   1  and  211   ad   2 ,  212   ad   1  and  212   ad   2  ( 221   ad   1  and  221   ad   2 ,  222   ad   1  and  222   ad   2 ) respectively, whereby the guide shafts  211  and  212  ( 221  and  222 ) can be adjusted in the z direction. More specifically, in one embodiment, the guide shafts  211  and  212  are adjusted so that the movable unit  210  ( 220 ) is situated 200 mm (100 mm) above from the surface of the film formation target on the substrate placed on the substrate setting table  230 . 
     Among guide shafts  211  and  212  ( 221  and  222 ), the surface of the guide shaft  212  ( 222 ) is externally threaded, so that the guide shaft  212  ( 222 ) is rotatively driven by a servomotor  210 M ( 220 M) attached to one side of the guide shaft  212  ( 222 ). The externally threaded guide shaft  212  ( 222 ) is engaged with a pipe unit  216  ( 226 ) (described later) whose internal surface is threaded corresponding to the external threaded portion of the guide shaft  212  ( 222 ). Thereby, when the servomotor  210 M ( 220 M) is activated, the movable member  201  ( 202 ) can precisely perform a reciprocating motion in the y (x) direction along a pair of guide shafts  211  and  212  ( 221  and  222 ). 
     The movable member  201  ( 202 ) comprises a pair of pipe units  215  and  216  ( 225  and  226 ) through which the guide shafts are passed, a film formation gas discharge pipe  217  ( 227 ) arranged so as to be perpendicular to the pair of guide shafts  211  and  212  ( 221  and  222 ) and fixed to the pair of pipe units  215  and  216  ( 225  and  226 ), a film formation lamp  218  ( 228 ), an exhaust tube  219  ( 229 ), and so on. These film formation gas discharge pipe  217  ( 227 ), film formation lamp  218  ( 228 ), and exhaust tube  219  ( 229 ) are arranged from the enclosure box  21  in this order as shown in FIG.  4 . 
     The film formation gas discharge pipe  217  ( 227 ) is a hollow glass pipe and a plurality of fine openings with a diameter of 0.2 mm are provided in a line along the longitudinal axis with an interval of 5 mm on the surface of the film formation gas discharge pipe  217  ( 227 ). Thereby, a film formation gas is jetted through the openings into the reaction zone  250  from the pipe. The fine openings are configured so that a film formation gas is jetted at an incident angle of 45 degrees to the top surface of the substrate setting table  230 . This incident angle is adjustable to the other degrees. The film formation gas is supplied to the film formation gas discharge pipe  217  ( 227 ) through a valve  210 VA ( 220 VA) attached to the enclosure box  21  from the outside, via flexible hoses connected to both ends of the film formation gas discharge pipe  217  ( 227 ). 
     Here, the fine openings with the other, sizes may be arranged in the other arranged manners. In addition, a plurality of film formation gas discharge pipes may be provided in place of the film formation gas discharge pipe  217  ( 227 ). 
     The exhaust tube  219  ( 229 ) is a hollow glass pipe having almost the same construction as the film formation gas discharge pipe  217  ( 227 ) and serves for exhausting a film formation gas after the film formation reaction (exhaust gas) to the outside of the enclosure box  21 . The exhaust gas is sucked through the fine openings of the exhaust tube  219  ( 229 ) and exhausted to the outside of the enclosure box  21  through a valve  210 VB ( 220 VB) attached to the outside surface of the enclosure box  21 , via flexible hoses  213  ( 223 ) connected to both ends of the exhaust tube  219  ( 229 ). 
     Here, the driving force for discharging/exhausting gases to/from the film formation gas discharge pipe  217  ( 227 )/exhaust tube  219  ( 220 ) are supplied by a compressor (not shown) so that gases flow with predetermined flow rates. 
     The film formation lamp  218  ( 228 ) radiates light for accelerating a film formation reaction to the substrate setting table  230  (in a preferred embodiment, light whose peak wave-length is 147 nm is employed as an example). Although a xenon lamp is used in this embodiment, the other lamps with desired peak wave-length or a plurality of lamps may be used. 
     Exhaust holes (conductance valves)  241  to  244  are provided at four corners of the internal undersurface of the enclosure box  21 , through which the gas within the enclosure box  21  is exhausted. A turbo-molecular pump (not shown) is connected to the exhaust holes  241  to  244 , whereby the flow rate of the exhaust gas and the air pressure in the enclosure box  21  can be adjusted. 
     1-4. Effects of the Preferred Embodiment in the Invention 
     Since the inductive coupling method is adopted in the preferred embodiment of the present invention, a plasma with a relatively high density (ranging from approximately 10 17  to 10 18  m −3 ) can be produced, whereby abundant free radicals can be obtained. By means of these abundant free radicals, the film formation gases can chemically react with a higher rate when compared with the capacitive coupling method, so that an excellent film manufacturability can be achieved. 
     The present invention is to achieve the above stated object. That is, in the conventional film formation apparatuses, when the workcoil increases in size according to the substrate size, there is a problem of non-uniformity of the distribution of magnetic field generated by the workcoil (a doughnut-shaped plasma generates). However, the present invention can avoid the problem. 
     In addition, using the apparatus in the invention, an excellent plasma can be produced to a large-sized film formation target. Thus, when the plasma etching method applies to the apparatus of the invention, an effective etching operation can be conducted. 
     In order to achieve the above object, firstly a plurality of plasma generators  100  (4×4 in the x and y directions respectively, 16 pieces in total) in the inductive coupling method are provided, whereby a plasma with a more uniform distribution can be obtained with plasma generators  100 . As a result, a plasma with high density can be produced when compared with the capacitive coupling method. 
     Secondly, since a film formation gas discharge means moves all over the surface of the film formation target, a film formation condition with reduced non-uniformity and a film formation process with a high deposition rate can be realized. 
     Thirdly, a distance between the plasma generators  100  and the substrate, and a relative position of the cylindrical tubes  102  of the plasma generators  100  to the workcoils are adjustable, so that free radicals generated with the plasma which have long lives can selectively contribute to the film formation reaction. Such a construction prevents unnecessary ions generated with the plasma from doing damage to the surface of the film formation substrate, so that an excellent film whose surface does not have an unevenness can be formed. Therefore, the apparatus  1  of the present invention can realize the film surface whose level of evenness is within 10%. 
     2. Embodiments 
     The following describes confirmed effects of the apparatus  1  according to the above stated embodiments. 
     2-1. Embodiment 1 (Plasma CVD Method) 
     Experimental conditions for the embodiment 1 are as follows: 
     Film formation area in the substrate: 550 mm×670 mm 
     Plasma excitable gas: mixed gas of Ar and O 2 , mixture ratio (by volume) 3:1, Ar gas flow rate: 30 sccm O 2  gas flow rate: 10 sccm internal pressure: 150 mTorr 
     RF current: frequency: 100 MHz, RF power: 600 W 
     Film formation gas: SiH 4 , flow rate: 5 sccm 
     Film formation lamp: not operated 
     Exhaust gas flow rate is adjusted according to the film formation rate and generating conditions of particles. 
     Moving speed of the movable members: 100 mm/sec 
     According to the above experimental conditions, when the apparatus  1  is activated, air filled in the apparatus is exhausted through the exhaust holes  241  to  244  at first. Then, the plasma excitable gas is introduced into the apparatus through the plasma excitable gas delivery tube  101  and the RF power is applied to the workcoils. As a result, a plasma in an H mode is generated vertically in the area with 80 mm length from the region in the vicinity of the workcoils along the z direction. 
     Here, the distance between the plasma and the substrate is set so that unnecessary ions do not damage the film formation surface, by adjusting a relative position of workcoils to the cylindrical tubes  102  in the z directions Thus, O 2  radicals having relatively long lives can reach from the plasma to the substrate setting table with a higher priority than the other kinds of radicals. The substrate setting table heats a substrate so that the temperature of the substrate surface is kept to 400° C. by the operation of the internal heater. 
     In the above state, SiH 4  gas as a film formation gas filled in the film formation gas discharge pipe  217  ( 227 ) is jetted into the reaction zone  250  through the fine openings. Then, SiH 4  molecules included in the film formation gas are decomposed by the O 2  radicals generated with the plasma into SiO 2 , and these SiO 2  molecules are deposited onto the surface of the film formation target in the substrate. The exhaust gas after the film formation reaction is sucked through the fine openings of the exhaust tube  219  ( 229 ) and exhausted through a valve  210 VB ( 220 VB) attached to the enclosure box  21  to the outside, via flexible hoses  213  ( 223 ) connected to both ends of the exhaust tube  219  ( 229 ). 
     In this state, when movable members  201  and  202  perform a reciprocating motion 10 times, perpendicularly intersecting each other, an SiO 2  film whose average film thickness is 750 Å and with reduced damages is formed on the surface of the film formation target in the substrate. In this SiO 2  film, the difference between the maximum and minimum values of the film thickness is within ±5%. It takes approximately 15 min to deposit the film on the large-sized substrate (550 mm×670 mm). Actually, an OH density contained in the SiO 2  film can be reduced to 50 ppb or less by this method, so that large-sized substrates for FPDs such as current-driven type organic EL devices, on which high-reliability pixel transistors are fabricated, can be formed. 
     As stated above, a film with an adequate film thickness can be speedily formed on the large-sized substrate by means of the embodiment 1. 
     2-2. Embodiment 2 (Plasma CVD Method) 
     Experimental conditions for the embodiment 2 are as follows: 
     Film formation area in the substrate: 550 mm×670 mm 
     Plasma excitable gas: mixed gas of Ar and H 2 , mixture ratio: 1:3, Ar gas flow rate: 10 sccm H 2  gas flow rate: 30 sccm internal pressure: 50 mTorr 
     Film formation lamp: light exposure using a Xe lump with a peak wave-length of 147 nm 
     RF current: frequency: 70 MHz, RF power: 1 kW 
     Film formation gas: SiH 4 , flow rate: 5 sccm 
     Exhaust gas flow rate is adjusted according to the film formation rate. 
     Moving speed of the movable members: 100 mm/sec 
     According to the above stated experimental conditions, when movable members  201  and  202  perform a reciprocating motion 15 times, perpendicularly intersecting each other, SiH 4  molecules included in the film formation gas are decomposed by the Ar and H 2  radicals generated with the plasma, so that a polycrystalline Si film whose average film thickness is 100 nm is formed on the surface of the film formation target in the substrate. In this polycrystalline Si film, the particle diameter of crystals is 0.7 μm on average and the difference between the maximum and minimum values of the film thickness is within ±10%. Here, the particle diameter of the polycrystalline Si can be increased to 1 μm. 
     In this embodiment 2, almost the same effects as in the embodiment 1 can be obtained. 
     2-3. Embodiment 3 (Plasma Etching Method) 
     Experimental conditions for the embodiment 3 are as follows: 
     Etched target film: SiO 2  film 
     Film formation area in the substrate: 550 mm×670 mm 
     Plasma excitable gas: CF 4  (flow rate: 10 sccm internal pressure: 10 mTorr) 
     Film formation lamp: not operated 
     RF current: frequency: 70 MHz, RF power: 400 W 
     Film formation gas: not used 
     Exhaust gas flow rate is adjusted according to the film formation rate. 
     Movable units are not moved. 
     According to the above stated experimental conditions, CF 4  molecules are decomposed in the plasma and a lot of F radicals are generated, so that the SiO 2  film can be etched with an excellent rate. Since ions generated with the plasma do not collide against the target in this etching process, the target can be etched excellently in the relatively large area. 
     3. Others 
     The film formation apparatus of the present invention may be used when organic LEDs and the like are fabricated. More specifically, a transparent electrode (ITO) film is formed on the surface of the substrate, and the surface of this film is processed using O 2  radicals by the film formation apparatus according to the invention. 
     Alternatively, the film formation apparatus according to the invention may be incorporated into a well-known multi-chamber system. 
     Although the present invention has been fully described by way of examples with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Therefore, unless such changes and modifications depart from the scope of the present invention, they should be construed as being included therein.