Patent Publication Number: US-2009229523-A1

Title: Film depositing apparatus

Description:
The entire contents of a document cited in this specification are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a film depositing apparatus for forming a film on a surface of an elongated substrate in vacuum by CVD and, more particularly, to a film depositing apparatus which, when forming a film continuously on the elongated substrate as it is transported, is capable of forming a film having high uniformity in thickness in the direction of width of the substrate perpendicular to its longitudinal direction. 
     While various types of apparatus are known to be capable of continuous film deposition on an elongated substrate (a web of substrate) in a vacuum-filled chamber by plasma-enhanced CVD, an exemplary system uses a drum electrically connected to the ground and an electrode positioned in a face-to-face relationship with the drum and connected to a radio-frequency power source. 
     In this type of film depositing apparatus, the substrate is wrapped around a specified area of the drum, which is then rotated to thereby transport the substrate in a longitudinal direction as it is in registry with a specified film depositing position, with a radio-frequency voltage being applied between the drum and the electrode to form an electric field while, at the same time, a feed gas for film deposition as well as argon gas and the like are introduced between the drum and the electrode, whereby a film is deposited on the surface of the substrate by plasma-enhanced CVD. This type of film depositing apparatus has already been proposed (see JP 2006-152416 A). 
     JP 2006-152416 A discloses an apparatus for plasma-enhanced CVD that comprises a reaction compartment, gas inlets through which reactive gases are introduced into the reaction compartment, an anode and a cathode electrode that are provided within the reaction compartment to generate plasma discharge between themselves, and a transport mechanism that transports a flexible substrate between the anode and the cathode electrode; the apparatus treats the flexible substrate by plasma-enhanced CVD. 
     The reaction compartment has four gas discharging units for discharging the gas from the inside (see FIG. 1 in JP 2006-152416 A) and each gas discharging unit is equipped with a vacuum pump such as a mechanical booster pump or a rotary pump. 
     The anode electrode has a curved, first discharge surface whereas the cathode electrode has a second discharge surface that is curved along the first discharge surface. The cathode electrode is provided with an electrode-to-electrode distance adjusting mechanism for moving it in a direction parallel to the diameter of the anode electrode, as well as a curvature adjusting mechanism for performing fine adjustment on the curvature of the second discharge surface in accordance with the distance between the anode and cathode electrodes. 
     SUMMARY OF THE INVENTION 
     In the plasma-enhanced CVD apparatus disclosed in JP 2006-152416 A, the reaction compartment is equipped with four gas discharging units for discharging the gas from the inside; however, these units are not provided in symmetrical positions but are located eccentrically with respect to the space between the first discharge surface of the anode electrode and the second discharge surface of the cathode electrode. Thus, in JP 2006-152416 A, when reactive gases are supplied for film deposition, with the flexible substrate being provided between the first discharge surface of the anode electrode and the second discharge surface of the cathode electrode, these reactive gases are discharged in various directions including, for example, the direction of width of the flexible substrate. In this case, the reactive gases flow from the center of the flexible substrate toward either end, where they accumulate to form a film that is thicker at both ends of the flexible substrate to thereby yield an uneven thickness distribution in the direction of its width. Hence, the plasma-enhanced CVD apparatus disclosed in JP 2006-152416 A which does not take into account the direction in which the reactive gases are to be discharged, has the problem that it is incapable of producing films having a uniform thickness distribution. 
     An object, therefore, of the present invention is to solve the aforementioned problem of the prior art by providing a film depositing apparatus which, when forming a film continuously on an elongated substrate as it is transported, is capable of forming a film having high uniformity in thickness in the direction of width of the substrate perpendicular to its longitudinal direction. 
     A film depositing apparatus according to the present invention comprises: a transport means that transports an elongated substrate in a specified transport path; a chamber; an evacuating unit that creates a specified degree of vacuum within the chamber; a rotatable cylindrical drum that is provided within the chamber, that has an axis of rotation in a direction perpendicular to a transport direction of the substrate by the transport means, which is longer than a size of the substrate as measured in the direction perpendicular to the transport direction of the substrate, and around which the substrate transported by the transport means is wrapped in a specified surface region; a film depositing unit comprising a film depositing electrode spaced apart from and in a face-to-face relationship with a surface of the drum, a radio-frequency power source section for applying a radio-frequency voltage to the film depositing electrode, and a feed gas supply section from which a feed gas for forming a film is supplied into a gap between the drum and the film depositing electrode; and a gas-flow regulating means that regulates the feed gas as supplied into the gap between the drum and the film depositing electrode during film formation to be easier to flow in a direction in which the drum rotates than in a direction along which the axis of rotation of the drum extends. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram showing a film depositing apparatus according to a first embodiment of the present invention. 
         FIG. 2  is a schematic side view showing the structure of a film depositing electrode in a film depositing compartment of the film depositing apparatus shown in  FIG. 1 . 
         FIGS. 3A ,  3 B and  4  are a schematic perspective view, a schematic front sectional view and a schematic plan view showing the relative positions of a drum, the film depositing electrode and cover plates in the film depositing compartment shown in  FIG. 1 , respectively. 
         FIG. 5  is schematic front sectional view showing the relative positions of the drum, the film depositing electrode and the cover plates in a film depositing compartment of a film depositing apparatus according to a modification of the first embodiment. 
         FIGS. 6A and 6B  are a schematic perspective view and a schematic front sectional view showing the relative positions of the drum, the film depositing electrode plate and end portion members in a film depositing apparatus according to a second embodiment, respectively. 
         FIG. 7  is a schematic front sectional view showing a film depositing compartment of a film depositing apparatus according to a third embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     On the following pages, the film depositing apparatus of the present invention is described in detail with reference to the preferred embodiments shown in the accompanying drawings. 
     First Embodiment 
       FIG. 1  is a schematic diagram showing a film depositing apparatus according to a first embodiment of the present invention.  FIG. 2  is a schematic side view showing the structure of a film depositing electrode in a film depositing compartment of the film depositing apparatus shown in  FIG. 1 . 
       FIG. 3A  is a schematic perspective view showing the relative positions of a drum, the film depositing electrode and cover plates in the film depositing compartment of the film depositing apparatus shown in  FIG. 1 .  FIG. 3B  is a schematic front sectional view showing the relative positions of the drum, the film depositing electrode and the cover plates in the film depositing compartment of the film depositing apparatus shown in  FIG. 1 . 
     The film depositing apparatus generally indicated by  10  in  FIG. 1  is a roll-to-roll type machine that forms a film with a specified function on the surface Zf of a substrate Z or on the surface of an organic layer if it is formed on the surface Zf of the substrate Z; the film depositing apparatus  10  is typically employed to produce functional films such as an optical film or a gas barrier film. 
     The film depositing apparatus  10  is an apparatus for continuously depositing a film on an elongated substrate Z (a web of substrate Z); it comprises basically a feed compartment  12  for feeding the elongated substrate Z, a film depositing compartment (chamber)  14  for forming a film on the elongated substrate Z, a take-up compartment  16  for winding up the elongated substrate Z after the film has been formed on it, an evacuating unit  32 , and a control unit  36 . The control unit  36  controls the actions of the individual elements of the film depositing apparatus  10 . 
     In the film depositing apparatus  10 , the feed compartment  12  and the film depositing compartment  14  are partitioned by a wall  15   a  whereas the film depositing compartment  14  and the take-up compartment  16  are partitioned by a wall  15   b;  a slit of opening  15   c  through which the substrate Z can pass is formed in each of the walls  15   a  and  15   b.    
     In the film depositing apparatus  10 , each of the feed compartment  12 , the film depositing compartment  14  and the take-up compartment  16  is connected to the evacuating unit  32  via a piping system  34 . The evacuating unit  32  creates a specified degree of vacuum in the interiors of the feed compartment  12 , the film depositing compartment  14 , and the take-up compartment  16 . 
     To evacuate the feed compartment  12 , the film depositing compartment  14  and the take-up compartment  16  to maintain a specified degree of vacuum, the evacuating unit  32  has vacuum pumps such as a dry pump and a turbo-molecular pump. Each of the feed compartment  12 , the film depositing compartment  14  and the take-up compartment  16  is equipped with a pressure sensor (not shown) for measuring the internal pressure. 
     Note that the ultimate degree of vacuum that should be created in the feed compartment  12 , the film depositing compartment  14  and the take-up compartment  16  by the evacuating unit  32  is not particularly limited and an adequate degree of vacuum suffices to be maintained in accordance with such factors as the method of film deposition to be performed. The evacuating unit  32  is controlled by the control unit  36 . 
     The feed compartment  12  is a site for feeding the elongated substrate Z, where a substrate roll  20  and a guide roller  21  are provided. 
     The substrate roll  20  is for delivering the elongated substrate Z continuously and it typically has the substrate Z wound around it. 
     The substrate roll  20  is typically connected to a motor (not shown) as a drive source. By means of this motor, the substrate roll  20  is rotated in a direction r in which the substrate Z is rewound; in the embodiment under consideration, the substrate roll  20  is rotated clockwise to deliver the substrate Z continuously in  FIG. 1 . 
     The guide roller  21  is for guiding the substrate Z into the film depositing compartment  14  in a specified transport path. The guide roller  21  is composed of a known guide roller. 
     In the film depositing apparatus  10  of the first embodiment, the guide roller  21  may be a drive roller or a follower roller. Alternatively, the guide roller  21  may be a roller that works as a tension roller that adjusts the tension that develops during the transport of the substrate Z. 
     In the film depositing apparatus of the present invention, the substrate Z is not particularly limited and all kinds of substrates can be employed as long as films can be formed by vapor-phase film deposition techniques. Usable as the substrate Z are various resin films such as a PET film, and various metal sheets such as an aluminum sheet. 
     The take-up compartment  16  is a site where the substrate Z with a film having been formed on the surface Zf in the film depositing compartment  14  is wound up; in this take-up compartment  16 , there are provided a take-up roll  30  and a guide roller  31 . 
     The take-up roll  30  is a device by which the substrate Z on which a film has been deposited is wound up in a roll. 
     The take-up roll  30  is typically connected to a motor (not shown) as a drive source. By means of this motor, the take-up roll  30  is rotated to wind up the substrate Z after the film deposition step. 
     By means of the motor, the take-up roll  30  is rotated in a direction R in which the substrate Z is wound up; in the first embodiment, the take-up roll  30  is rotated clockwise in  FIG. 1 , whereupon the substrate Z after the film deposition step is wound up continuously. 
     The guide roller  31  is similar to the aforementioned guide roller  21  in that the substrate Z being delivered from the film depositing compartment  14  is guided by this roller to the take-up roll  30  in a specified transport path. The guide roller  31  is composed of a known guide roller. Note that like the guide roller  21  in the feed compartment  12 , the guide roller  31  may be a drive roller or a follower roller. Alternatively, the guide roller  31  may be a roller that works as a tension roller. 
     The film depositing compartment  14  functions as a vacuum chamber and it is a site where a film is continuously formed on the surface Zf of the substrate Z by a vapor-phase film deposition technique, typically by plasma-enhanced CVD, as the substrate Z is being transported. 
     The film depositing compartment  14  is typically constructed by using materials such as stainless steel that are commonly employed in a variety of vacuum chambers. 
     In the film depositing compartment  14 , there are provided two guide rollers  24  and  28 , as well as a drum  26  and a film depositing unit  40 . 
     The guide rollers  24  and  28  are spaced apart parallel to each other in a face-to-face relationship; they are also provided in such a way that their longitudinal axes cross at right angles to a direction D in which the substrate Z is transported. 
     The guide roller  24  is a device by which the substrate Z delivered from the guide roller  21  provided in the feed compartment  12  is transported to the drum  26 . The guide roller  24  is rotatable, typically having an axis of rotation in a direction perpendicular to the transport direction D of the substrate Z (this direction is hereinafter referred to as the axial direction), and its length in the axial direction is greater than the length in a width direction W perpendicular to the longitudinal direction of the substrate Z (the latter length is hereinafter referred to as the width of the substrate Z). 
     Note that the substrate roll  20  and the guide rollers  21  and  24  combine to constitute a first transport means in the present invention. 
     The guide roller  28  is a device by which the substrate Z wrapped around the drum  26  is transported to the guide roller  31  provided in the take-up compartment  16 . The guide roller  28  is rotatable, typically having an axis of rotation in the axial direction, and its length in the axial direction is greater than the width of the substrate Z. 
     Note that the guide rollers  28  and  31  as well as the take-up roll  30  combine to constitute a second transport means in the present invention. 
     Except for the features just described above, the guide rollers  24  and  28  have the same structure as the guide roller  21  provided in the feed compartment  12 , so they will not be described in detail. 
     The drum  26  is provided below the space H between the guide rollers  24  and  28 . The drum  26  is so positioned that its longitudinal axis is parallel to those of the guide rollers  24  and  28 . Also note that the drum  26  is electrically connected to the ground. 
     The drum  26  typically assumes a cylindrical shape and has a rotational axis L (see  FIG. 3A ). The drum  26  has end faces  26   a  that are perpendicular to the rotational axis L and which are in a face-to-face relationship with each other in the axial direction A along which the rotational axis L extends (this may be called the direction of the rotational axis). The drum  26  is capable of rotating in the direction of rotation ω about the rotational axis L. Also note that the length of the drum  26  in the axial direction A is greater than the width of the substrate Z. The drum  26 , as it rotates with the substrate Z wrapped around its surface  27  (peripheral surface), transports the substrate Z in the transport direction D while it is kept in registry with a specified film depositing position. 
     It is assumed that the side to the direction of travel parallel to the direction of rotation ω of the drum  26 , namely, the side to which the substrate Z is transported is the downstream side Dd, and the side opposite to this downstream side Dd is the upstream side Du. 
     For temperature adjustment, the drum  26  may be provided in its center with a heater (not shown) for heating the drum  26  and a temperature sensor (also not shown) for measuring the temperature of the drum  26 . In this case, the heater and the temperature sensor are connected to the control unit  36  which adjusts the temperature of the drum  26  such that it is held at a specified temperature. 
     As shown in  FIG. 1 , the film depositing unit  40  is provided below the drum  26  which, with the substrate Z being wrapped around it, rotates so that a film is formed on the surface Zf of the substrate Z as it is transported in the transport direction D. 
     The film depositing unit  40  is a device to form a film, typically by capacitively coupled plasma enhanced CVD (CCP-CVD). The film depositing unit  40  has a film depositing electrode  42 , a radio-frequency power source  44 , and a feed gas supply section  46 . The control unit  36  controls the radio-frequency power source  44  and the feed gas supply section  46  in the film depositing unit  40 . 
     In the film depositing unit  40 , the film depositing electrode  42  is provided in the lower part of the film depositing compartment  14  such that it is spaced by a specified gap S from the surface  27  of the drum  26 . The film depositing electrode  42  is fitted with cover plates (first cover members)  50  in such a way as to cover the end portions γ in the axial direction A of the gap S, that is, the direction of width W of the substrate Z (see  FIGS. 3A and 3B ). 
     As shown in  FIG. 2 , the film depositing electrode  42  has a film depositing electrode plate  60  and a holder  62  that holds the film depositing electrode plate  60 . 
     The film depositing electrode plate  60  may be formed by bending a rectangular member in a curved shape, typically with the same curvature as the surface  27  of the drum  26 . 
     The film depositing electrode plate  60  is disposed along the direction of rotation ω as if to follow the surface  27  of the drum  26 , with its length being parallel to the rotational axis L of the drum  26  and with its surface  60   a  being oriented to the surface  27  of the drum  26 . 
     In the first embodiment, the film depositing electrode plate  60  is typically disposed in such a way that it aligns with a circle concentric with the surface  27  of the drum  26 . The film depositing electrode plate  60  is set at a specified distance which, in any of its regions, is equal to the distance between the surface  60   a  of the film depositing electrode plate  60  and the surface  27  of the drum  26  as measured on a line that is perpendicular to the surface  60   a  and which passes through the center of rotation O of the drum  26 . 
     In the first embodiment, the film depositing electrode plate  60  is curved to follow the surface  27  of the drum  26  but this is not the sole case of the present invention and a rectangular member may be bended in a similar shape; alternatively, a number of flat rectangular electrode platelets may be arranged along the direction of rotation ω so as to follow the surface  27  of the drum  26 . In this alternative case, electrical conduction is established between the individual electrode platelets, which are arranged in such a way that each electrode platelet is set at a specified distance which is equal to the distance between the surface of each electrode platelet and the surface  27  of the drum  26  as measured on a line that is perpendicular to that surface and which passes through the center of rotation O of the drum  26 . 
     As shown in  FIG. 1 , the film depositing electrode  42  (film depositing electrode plate  60 ) is connected to the radio-frequency power source  44 , which applies a radio-frequency voltage to the film depositing electrode plate  60  in the film depositing electrode  42 . The radio-frequency power source  44  is capable of varying the radio-frequency power (RF power) to be applied. Note that the film depositing electrode  42  and the radio-frequency power source  44  may optionally be connected to each other via a matching box in order to attain impedance matching. 
     The film depositing electrode  42  is of a type that is generally called “a shower head electrode” and the film depositing electrode plate  60  has a plurality of through-holes (not shown) formed at equal spacings in its surface  60   a.  By means of this film depositing electrode  42 , the feed gas G is supplied uniformly into the gap S. 
     The holder  62  is for holding the film depositing electrode plate  60  and, with its interior being hollow (not shown), is connected to the feed gas supply section  46  via a pipe  47 . The hollow portion of the holder  62  communicates with the plurality of through-holes formed in the surface  60   a  of the film depositing electrode plate  60 . 
     As will be described later, the feed gas G supplied from the feed gas supply section  46  flows through the pipe  47 , the hollow portion of the holder  62  and the plurality of through-holes in the film depositing electrode plate  60  to be released from the surface  60   a  of the film depositing electrode plate  60  so that it is supplied uniformly into the gap S. 
     To adjust the temperature of the film depositing electrode plate  60 , the holder  62  may be equipped with a heater (not shown) for heating the film depositing electrode plate  60  and a temperature sensor (also not shown) for measuring the film depositing electrode plate  60 . In this case, the heater and the temperature sensor are connected to the control unit  36  which adjusts the temperature of the film depositing electrode plate  60  such that it is held at a specified temperature. 
     As just described above, the drum  26  and the film depositing electrode plate  60  are each equipped with the heater (not shown) and the temperature sensor (also not shown); this design ensures that the drum  26  has the same temperature as the film depositing electrode plate  60 . 
     The feed gas supply section  46  supplies the film-forming feed gas G into the gap S through the plurality of through-holes formed in the surface  60   a  of the film depositing electrode plate  60  in the film depositing electrode  42 . The gap S between the surface  27  of the drum  26  and the film depositing electrode  42  serves as a space where plasma is to be generated, hence, as a film deposition space. 
     In the embodiment under consideration, if a SiO 2  film is to be formed, the feed gas G is a TEOS gas, with oxygen gas being used as an active species gas. If a silicon nitride film is to be formed, SiH 4  gas, NH 3  gas and N 2  gas (dilution gas) are used. In the first embodiment, even a feed gas containing an active species gas and a dilution gas is simply referred to as a feed gas. 
     The feed gas supply section  46  may be chosen from a variety of gas introducing means that are employed in the CVD apparatus. 
     Also note that the feed gas supply section  46  may supply into the gap S not only the feed gas G but also an inert gas such as argon or nitrogen gas, an active species gas such as oxygen gas, and various other gases that are used in CVD. In this case of introducing more than one species of gas, the respective gases may be mixed together in the same pipe and the mixture be passed through the plurality of holes in the film depositing electrode  42  to be supplied into the gap S; alternatively, the respective gases may be supplied through different pipes and passed through the plurality of holes in the film depositing electrode  42  to be supplied into the gap S. 
     The kinds of the feed gas, the inert gas and the active species gas, as well as the amounts in which they are introduced may be chosen and set as appropriate for various considerations including the kind of the film to be formed and the desired film deposition rate. 
     Note that the radio-frequency power source  44  may be of any known type that is employed in film deposition by plasma-enhanced CVD. The maximum power output and other characteristics of the radio-frequency power source  44  are not particularly limited and may be chosen and set as appropriate for various considerations including the kind of the film to be formed and the desired film deposition rate. 
     The film depositing electrode  42  is in no way limited to such a configuration that a rectangular member is bent in a curved shape and various other electrode configurations may be adopted as long as they are capable of film deposition by CVD; to give one example, it may consist of electrode segments that are arranged in the axial direction of the drum  26 . 
     In the first embodiment, the film depositing electrode  42  is of such a configuration that through-holes are formed in the surface  60   a  of the film depositing electrode plate  60 . However, this is not the sole embodiment of the present invention and, as long as the feed gas G can be uniformly supplied to the gap S serving as the film deposition space, slits of opening may be formed in the bent portions of the film depositing electrode plate  60  such that the feed gas G is released through the slits. 
     Also suppose the following on the assumption that the film depositing electrode plate  60  has two end portions  60   b  and  60   c  as shown in  FIG. 2 : the line by which the end portion  60   b  on the upstream side Du in the direction of rotation ω of the drum  26  is connected to the center of rotation O of the drum  26  is written as the first line L 1 ; the line by which the end portion  60   c  on the downstream side Dd in the direction of rotation ω of the drum  26  is connected to the center of rotation O of the drum  26  is written as the second line L 2 ; the angle formed between the first line L 1  and the second line L 2  is written as θ. Since a film is deposited on the surface Zf of the substrate Z over the range of angle θ, the range of angle θ is the film deposition zone  29 . 
     Note that in  FIGS. 3A and 3B , only the film depositing electrode plate  60  is shown as part of the film depositing electrode  42  and the other structural parts are not shown. 
     As shown in  FIGS. 3A and 3B , cover plates  50  do not cover all parts of the gap S defined by the drum  26  and the film depositing electrode plate  60  but they cover the two end portions γ of the gap S in the axial direction A of the drum  26  (i.e., the longitudinal direction of the drum  26 ). As shown in  FIGS. 3A and 3B , the cover plates  50  are provided at the respective end portions  60   d  of the film depositing electrode plate  60  in the axial direction A. 
     The cover plates  50  are each made of a member in plate form having a circular arc shape with a radius corresponding to the curvature of the curved film depositing electrode plate  60 ; they cover the end portions γ of the gap S and partially overlap the end faces  26   a  of the drum  26 . An end face  50   a  of the cover plate  50  which is in a face-to-face relationship with the corresponding end face  26   a  of the drum  26  is spaced by a specified distance s 1  from that end face  26   a  of the drum  26 . The distance s 1  is shorter than the distance d in the gap S. It should be noted here that the cover plates  50  are composed of an insulator such as ceramics including alumina. In the first embodiment, the gap S is left open at the end portions α and β in the direction of rotation ω and communicates with the interior of the film depositing compartment  14 . 
     In the first embodiment, the end portions γ of the gap S are closed with the cover plates  50  and the distance s 1  between each cover plate  50  and the corresponding end face  26   a  of the drum  26  is made shorter than the distance d in the gap S whereas the gap S is left open at the end portions α and β; as a result, a fluid flowing through the gap S in the axial direction A (longitudinal direction) of the drum  26  will experience a greater resistance than when it flows through the end portions α and β of the gap S in the direction of rotation ω of the drum  26  (the transport direction D of the substrate Z) where the gap S is open and presents no resistance. As a result, the fluid flows less smoothly in the axial direction A of the drum  26  than in the longitudinal direction of the substrate Z. Thus, the fluid flows through the gap S more efficiently in the direction of rotation ω of the drum  26  than in the axial direction A (longitudinal direction) of the drum  26 . 
     To put this in terms of conductance which is an index for the ease with which the fluid flows, the first conductance in the direction of rotation ω of the drum  26  is greater than the second conductance in the longitudinal direction of the drum  26  (the direction of width W of the substrate Z). Note that the greater the conductance, the more easily the fluid will flow. 
     Suppose here that during film deposition in the first embodiment, the feed gas G is supplied into the gap S from the feed gas supply section  46 , with a specified degree of vacuum being created within the film depositing compartment  14 ; then, as shown in  FIG. 4 , the pressure difference between the gap S and the film depositing compartment  14  causes the feed gas G to flow through the gap S preferentially along the surface  27  of the drum  26  in the direction of its rotation ω whereas the feed gas G is suppressed from flowing in the axial direction A of the drum  26 . As a result, the feed gas G is preferentially discharged through the end portions α and β of the gap S into the film depositing compartment  14  held at the specified degree of vacuum whereas the feed gas G is inhibited from flowing in the axial direction A of the drum  26  (the direction of width W of the substrate Z). This suppresses any disturbances in the flow of the feed gas G in the direction of width W of the substrate Z and the feed gas G will be discharged uniformly in the direction of width W of the substrate Z. 
     In addition, the first embodiment merely involves the need to position the cover plates  50  in such a way that they close the end portions γ of the gap S and that the distance s 1  to either end face  26   a  of the drum  26  is shorter than the distance d of the gap S; hence, it is at low cost that the feed gas G in the gap S can be discharged uniformly in the direction of width W of the substrate Z while the feed gas G can be supplied uniformly into the gap S in the direction of width W. 
     In the first embodiment, the cover plates  50  are provided at the end portions  60   d  of the film depositing electrode plate  60  in its axial direction A; it should, however, be noted that the structure of the cover plates is by no means limited to this particular case and each of them may be replaced by a cover member  52  (see  FIG. 5 ) which comprises a first part  54  and a second part  56 . The cover member  52  has an L-shaped cross section and is disposed in such a way that it surrounds part of the surface  27  of the drum  26  as well as part of each end face  26   a  of the drum  26 . 
     If the cover member  52  is to be provided, the length of the film depositing electrode plate  60  in its axial direction A is made generally the same as the width of the substrate Z and positioned in a face-to-face relationship with the region  27   a  of the drum  26  around which the substrate Z is wrapped. 
     The first part  54  of the cover member  52  is a member in plate form that is curved with the same curvature as the film depositing electrode plate  60  and which is positioned in a face-to-face relationship with the region  27   b  of the drum  26  around which the substrate Z is not wrapped. The first part  54  of the cover member  52  is connected to the corresponding end portion  60   d  of the film depositing electrode plate  60  such that it is made integral with the film depositing electrode  60 . The distance between the surface  54   a  of the first part  54  and the surface  27  of the drum  26  is the same as the distance d between the surface  60   a  of the film depositing electrode plate  60  and the surface  27  of the drum  26 . 
     The second part  56  of the cover member  52  is connected to the first part  54  but spaced from the corresponding end face  26   a  of the drum  26  in its axial direction A. The second part  56  is constructed in the same way as the cover plate  50  in the first embodiment and is made of a member in plate form having a circular arc shape with a radius corresponding to the curvature of the film depositing electrode plate  60 . 
     The second part  56  is such that the distance between the end face  26   a  of the drum  26  and the corresponding face  56   a  of the second part  56  is s 1  and shorter than the distance d in the gap S, as in the case of the cover plate  50  in the first embodiment. Note further that the first part  54  and the second part  56  of the cover member  52  are also made of an insulator such as ceramics including alumina. 
     The above-described modifications of the first embodiment are also capable of attaining the same effects as the first embodiment but, in addition, since the film depositing electrode plate  60  does not extend as far as the region  27   b  of the drum  26  around which the substrate Z is not wrapped, the reaction product can be suppressed from accumulating in that region  27   b.    
     We next describe how the film depositing apparatus  10  according to the first embodiment works. 
     In the specified path starting from the feed compartment  12  and passing through the film depositing compartment  14  to reach the take-up compartment  16 , the elongated substrate Z is transported through the film depositing apparatus  10  from the feed compartment  12  down to the take-up compartment  16  while a film is formed on the substrate Z in the film depositing compartment  14 . 
     In the film depositing apparatus  10 , the elongated substrate Z that has been wound around the substrate roll  20  is unwound and transported into the film depositing compartment  14  via the guide roller  21 . In the film depositing compartment  14 , the substrate Z passes over the guide roller  24 , the drum  26  and the guide roller  28  to be transported into the take-up compartment  16 . In the take-up compartment  16 , the elongated substrate Z passes over the guide roller  31  to be wound up by the take-up roll  30 . After passing the elongated substrate Z through this transport path, a specified degree of vacuum is maintained in the interiors of the feed compartment  12 , the film depositing compartment  14  and the take-up compartment  16  by means of the evacuating unit  32 ; then, in the film depositing unit  40 , a radio-frequency voltage is applied from the radio-frequency power source  44  to the film depositing electrode  42  while, at the same time, the feed gas G to form a film is uniformly supplied from the feed gas supply section  46  through the pipe  47  and the holder  62  so that it is released into the gap S through the plurality of through-holes formed in the surface  60   a  of the film depositing electrode plate  60 . 
     When electromagnetic waves are radiated around the film depositing electrode  42 , a plasma localized in the neighborhood of the film depositing electrode  42  is generated in the gap S (film deposition space), whereupon the feed gas is excited and dissociated to yield a reaction product that serves to form a film. This reaction product accumulates to form a film of specified thickness on the surface Zf of the substrate Z within the range of the film depositing electrode  42 , namely, in the film deposition zone  29  defined by the range of angle θ about the center of rotation O of the drum  26 . 
     On this occasion, in the gap S between the drum  26  and the film depositing electrode  42  (the film depositing electrode plate  60 ), the pressure difference between the gap S and the film depositing compartment  14  causes the feed gas G to flow preferentially along the surface  27  of the drum  26  in the direction of its rotation ω (see  FIG. 4 ) whereas the feed gas G is inhibited from flowing in the axial direction A of the drum  26 . As a result, the feed gas G in the gap S is discharged uniformly in the direction of width W of the substrate Z while the feed gas G is supplied uniformly into the gap S in the direction of width W. Consequently, the reaction product formed by the feed gas G is supplied uniformly in the direction of width W of the substrate Z so that it accumulates on the surface Zf of the substrate Z uniformly in the direction of width W of the substrate Z. As a result, a uniform film having a small thickness distribution in the direction of width W is formed in a specified thickness. 
     Then, the substrate roll  20  around which the elongated substrate Z has been wound is rotated clockwise incrementally by means of the motor, whereupon the elongated substrate Z is delivered continuously and with the substrate Z being held on the drum  26  in the position where the plasma is being generated, the drum  26  is rotated at a specified speed to ensure that the film depositing unit  40  allows a layer to be formed continuously in a specified thickness on the surface Zf of the elongated substrate Z, particularly in such a way that it is uniform with a small thickness distribution in the direction of width W of the substrate Z. The substrate Z having the specified layer formed on its surface Zf passes over the guide rollers  28  and  31  so that the functional film, or the elongated substrate Z with the deposited layer, is wound up by the take-up roll  30 . 
     Described above is the way in which the elongated substrate Z having the layer formed continuously in a specified thickness on the surface Zf, particularly in such a way that it is uniform with a small thickness distribution in the direction of width W of the substrate Z, namely, the functional film, can be produced by the film depositing apparatus  10  according to the first embodiment. The function of the functional film produced depends on the properties or the type of the layer formed on the substrate Z. 
     Second Embodiment 
     We next describe a second embodiment of the present invention. 
       FIG. 6A  is a schematic perspective view showing the relative positions of the drum, the film depositing electrode plate and end portion members in the film depositing apparatus according to the second embodiment of the present invention. 
       FIG. 6B  is a schematic front sectional view showing the relative positions of the drum, the film depositing electrode plate and the end portion members in the film depositing apparatus according to the second embodiment of the present invention. 
     In the following description of the second embodiment, those structural elements which are identical to those of the film depositing apparatus according to the first embodiment which is shown in  FIGS. 1 to 4  and those which are identical to the elements of the modification of the first embodiment which is shown in  FIG. 5  are identified by like numerals or symbols and will not be described in detail. 
     Also note that in  FIGS. 6A and 6B , only the drum, film depositing electrode plate and end portion members are illustrated and the illustration of the other elements is omitted. Those structural elements which are not illustrated in  FIGS. 6A and 6B  are identical to their counterparts in the film depositing apparatus according to the first embodiment. 
     The film depositing apparatus according to the second embodiment only differs from the film depositing apparatus  10  according to the first embodiment (see  FIG. 1 ) in that the dimension of the film depositing electrode plate  60  in the longitudinal direction is shorter and that the end portion members (second cover members)  58  are provided in place of the cover plates  50 ; the other structural elements are identical to their counterparts in the film depositing apparatus  10  according to the first embodiment and will not be described in detail. 
     In the second embodiment, the length of the film depositing electrode plate  60  in the axial direction A (longitudinal direction) is generally the same as the length of the region  27   a  of the drum  26  around which the substrate Z is wrapped and it is positioned in a face-to-face relationship with this region  27   a.  A gap S is defined between the film depositing electrode plate  60  and the drum  26  to serve as a film deposition space; that part of the gap S which is in the neighborhood of each end portion  60   a  of the film depositing electrode plate  60  is an end portion γ in the axial direction A (longitudinal direction) of the drum  26 . 
     Each of the end portion members  58  is in a face-to-face relationship with the region  27   b  of the drum  26  around which the substrate Z is not wrapped and it is provided in such a way that it substantially closes the corresponding end portion γ of the gap S and that it is integral with the corresponding end portion  60   d  of the film depositing electrode plate  60 . The distance between the face  58   a  of each end portion member  58  that is in a face-to-face relationship with the drum  26  and the surface  27  of the region  27   b  of the drum  26  is s 2 . The distance s 2  is shorter than the distance d between the drum  26  and the film depositing electrode  42 . In other words, each of the end portion members  58  is positioned in such a way that the gap between its face  58   a  and the surface  27  of the drum  26  is narrower than the gap S between the drum  26  and the film depositing electrode  42 . 
     The end portion members  58  are typically made of an insulator such as ceramics including alumina. 
     In the second embodiment, either end portion γ of the gap S (film deposition space) communicates with a narrower gap. Thus, when a fluid flowing through the gap S wants to go to the outside through the end portion γ, the end portion member  58  presents resistance to the passage of the fluid by constricting the gap S. As a result, the fluid will find it more difficult to flow through either end portion γ of the gap S in the axial direction A of the drum  26  than when it flows through the end portions α and β of the gap S where the gap S is open to the interior of the film depositing compartment  14 . In other words, the feed gas G flows through the gap S more efficiently in the direction of rotation ω of the drum  26  than in its axial direction A. In the second as well as the first embodiment, the gap S (film deposition space) is such that the first conductance in the direction of rotation ω of the drum  26  is greater than the second conductance in the longitudinal direction of the drum  26  (the direction of width W of the substrate Z). 
     Thus, in the second as well as the first embodiment, the pressure difference between the gap S into which the feed gas G has been supplied for film deposition and the film depositing compartment  14  causes the feed gas G to flow through the gap S preferentially along the surface  27  of the drum  26  in the direction of its rotation ω whereas the feed gas G is suppressed from flowing through in the axial direction A of the gap S, to thereby yield the same effect as in the first embodiment. 
     What should also be mentioned about the second embodiment is that each of the end portion members  58  is provided n a face-to-face relationship with the region  27   b  of the drum  26  around which the substrate Z is not wrapped and the film depositing electrode plate  60  does not extend as far as this region  27   b;  hence, the reaction product is suppressed from accumulating in the region  27   b  of the drum  26  around which the substrate Z is not wrapped. 
     Third Embodiment 
     We next describe a third embodiment of the present invention. 
       FIG. 7  is a schematic front sectional view showing the film depositing compartment of a film depositing apparatus according to the third embodiment of the present invention. 
     Note that in  FIG. 7 , the system configuration is illustrated in a simplified form and that only the drum, film depositing electrode plate and the radio-frequency power source are illustrated, with the illustration of the other elements being omitted. Those structural elements which are not illustrated in  FIG. 7  are identical to their counterparts in the film depositing apparatus according to the first embodiment. 
     Also note that in the following description of the third embodiment, those structural elements which are identical to those of the film depositing apparatus according to the first embodiment which is shown in  FIGS. 1 to 4  and those which are identical to the elements of the modification of the first embodiment which is shown in  FIG. 5  are identified by like numerals or symbols and will not be described in detail. 
     The film depositing apparatus according to the third embodiment differs from the film depositing apparatus  10  according to the first embodiment (see  FIG. 1 ) in that there are provided no cover plates  50  and they are also different in the size of the film depositing compartment  14 ; the other structural elements are identical to their counterparts in the film depositing apparatus  10  according to the first embodiment and will not be described in detail. 
     In the third embodiment, the length of the film depositing electrode plate  60  in the axial direction A is generally the same as the length of the drum  26  and each end face  26   a  of the drum  26  is flush with the corresponding end portion  60   d  of the film depositing electrode plate  60 . A gap S is defined between the film depositing electrode plate  60  and the drum  26  to serve as a film deposition space. The distance in the gap S is d. 
     The film depositing compartment  14  according to the third embodiment is such that its inner surface  14   a  in a face-to-face relationship with the corresponding end face  26   a  of the drum  26  is spaced from the end face  26   a  of the drum  26  by a distance of g. The distance g between the end face  26   a  of the drum  26  and the inner surface  14   a  of the film depositing compartment  14  is shorter than the distance d in the gap S between the film depositing electrode  42  (the film depositing electrode plate  60 ) and the drum  26 . In other words, the gap between the end face  26   a  of the drum  26  and the inner surface  14   a  of the film depositing compartment  14  is narrower than the gap S between the film depositing electrode  42  (the film depositing electrode plate  60 ) and the drum  26 . Note that the end portions α and β of the gap S are open to the interior of the film depositing compartment  14 . 
     In the third embodiment, the distance g between either end face  26   a  of the drum  26  and the inner surface  14   a  of the film depositing compartment  14  is made shorter than the distance d of the gap S between the film depositing electrode  42  (the film depositing electrode plate  60 ) and the drum  26 . Thus, when a fluid flowing through the gap S wants to leave it through the end portion γ, the small distance g between either end face  26   a  of the drum  26  and the inner surface  14   a  of the film depositing compartment  14  poses a resistance to the passage of the fluid. As a result, the fluid will find it more difficult to flow through either end portion γ of the gap S in the axial direction A of the drum  26  than when it flows through the end portions α and β of the gap S where the gap S is open to the interior of the film depositing compartment  14 . In other words, the feed gas G flows through the gap S more efficiently in the direction of rotation ω of the drum  26  than in its axial direction A. In the third as well as the first embodiment, the gap S (film deposition space) is such that the first conductance in the direction of rotation ω of the drum  26  is greater than the conductance of the flow through either end portion γ of the gap S in the axial direction A of the drum  26  into the film depositing compartment  14 . 
     Thus, in the third as well as the first embodiment, the fluid can be caused to flow more smoothly in the direction of rotation ω (circumferential direction) of the drum  26  than in its axial direction A. Hence, as in the first embodiment, the pressure difference between the gap S into which the feed gas G has been supplied for film deposition and the film depositing compartment  14  causes the feed gas G to flow through the gap S preferentially along the surface  27  of the drum  26  in the direction of its rotation ω whereas the feed gas G is suppressed from flowing through in the axial direction A of the gap S, to thereby yield the same effect as in the first embodiment. 
     A further advantage of the third embodiment is that no extra structural members are required to control the direction in which the fluid can flow through the gap S more efficiently than in other directions and that therefore the production cost can be reduced. 
     In each of the foregoing embodiments of the present invention, the layer to be deposited is not particularly limited and as long as the CVD process is applicable, layers having the required functions that depend on the functional films to be produced can appropriately be formed. The thickness of the layer to be deposited is not particularly limited, either, and the required thickness may be determined as appropriate for the performance required by the functional film to be produced. 
     It should also be noted that the number of layers to be deposited is not limited to one but may be two or more. If a multi-layer film is to be formed, the individual layers may be the same or different from each other. 
     In each of the foregoing embodiments of the present invention, if a gas barrier film (water vapor barrier film) is to be produced as the functional film, the layer to be deposited on the substrate is an inorganic film such as a silicon nitride film, an aluminum oxide film, or a silicon oxide film. 
     If protective films for a variety of devices or apparatuses including display devices such as organic EL displays and liquid-crystal displays are to be produced as the functional film, the layer to be deposited on the substrate is an inorganic film such as a silicon oxide film. 
     Further in addition, if the functional film produced is any of an anti-light reflective film, a light reflective film, and various other optical films for use in filters, the layer to be deposited on the substrate is a film having the desired optical characteristics or a film comprising materials that exhibit the desired optical characteristics. 
     The functional film thus produced by the film depositing apparatus according to any one of the foregoing embodiments of the present invention is characterized in that the layer formed on the substrate has superior uniformity in thickness and, hence, uniform thickness, particularly in the direction of width of the substrate, so the functional film, if it is a gas barrier film, features good enough gas barrier property. 
     While the film depositing apparatus of the present invention has been described above in detail, the present invention is by no means limited to the foregoing embodiments and it should be understood that various improvements and modifications are possible without departing from the scope and spirit of the present invention.