Abstract:
An optical film thickness measuring device, enabling direct measurement of a film thickness of a product in real time accurately without a monitor substrate, includes: a projector, a light receiver, inner beam splitters disposed in a base substrate holder to reflect a measurement beam to a base substrate, an inner optical reflector that totally reflects a measurement beam from the closest inner beam splitter, external beam splitters the measurement beam from the inner beam splitters toward the light receiver, and an outer optical reflector that reflects the measurement beam from the optical reflector toward the light receiver. The measurement beam reflected by the inner beam splitters and the inner optical reflector is passed through the base substrate and then reflected by the external beam splitters and the outer optical reflector to be guided to the light receiver, so that the measurement beam is received by the light receiver.

Description:
TECHNICAL FIELD 
     The present invention relates to an optical film thickness measuring device and a thin film forming apparatus using the optical film thickness measuring device. More specifically, the present invention relates to an optical film thickness measuring device capable of directly measuring a film thickness of a product and measuring a film distribution, and a thin film forming apparatus using the optical film thickness measuring device. 
     DESCRIPTION OF THE RELATED ART 
     In the related art, precision optical filters have been generally used in digital cameras, projectors, DVDs, and the like, and a physical vapor deposition (PVD) method such as sputtering or vacuum evaporation has been used in film-formation of these precision optical filters. Moreover, chemical deposition such as CVD has been known as a technique of forming an optical thin film on a surface of a substrate. 
     In the field of such a thin film forming technique, a carousel-type rotating mechanism is known as an example of a rotating mechanism of a base substrate holding means that holds a substrate (base substrate). In the carousel-type rotating mechanism, a plurality of substrates (base substrates) is held on a peripheral surface of a rotating drum (that is, a base substrate holding means) of which the cross-sectional shape is circular or polygonal, and the rotating drum rotates about a rotating shaft in this state. In this way, in a carousel-type thin film forming apparatus, since the substrates (base substrates) are held on the peripheral surface of the rotating drum, the substrate (base substrate) may not remain at one position during the rotation of the rotating drum, but all substrates (base substrates) rotate about a rotating shaft. 
     Therefore, in order to measure optical properties of thin films such as a film thickness according to an optical method, it is necessary to perform optical measurement on a substrate (base substrate) after temporarily stopping the rotation of the rotating drum. In such a measurement method, there is a problem in that the thin film forming step takes a long period of time since the thin film forming step needs to be stopped whenever the film thickness is measured. 
     In order to solve the above-described problem, a method of optically measuring a film thickness in real time in a state where the rotating drum rotates may be considered. For example, a method of projecting a measurement beam onto a substrate (base substrate) from the outside of the rotating drum and receiving a reflection beam reflected from the substrate (base substrate) can be considered. However, in this method, since the rotating drum is rotating as described above, there is another problem in that it is difficult to measure the film thickness accurately since the angle of light incident on the substrate (base substrate) changes frequently. 
     In order to solve the respective problems described above, a film thickness measuring device that projects and receives light through a rotating shaft of a rotating drum which is a hollow shaft and a thin film forming apparatus including the film thickness measuring device have been developed. The film thickness measuring device includes a rotating drum having a rotating shaft which is a hollow shaft, a total reflection mirror disposed within the rotating shaft, a total reflection mirror disposed on an extension line of the rotating shaft, a light source that emits a measurement beam to the total reflection mirror disposed on the extension line of the rotating shaft via a semi-transparent mirror, and an optical receiver that receives a reflection beam from the total reflection mirror disposed on the extension line of the rotating shaft via the semi-transparent mirror (see, for example, Patent Document 1). 
     According to the film thickness measuring device, the measurement beam from the light source is emitted to the total reflection mirror disposed on the extension line of the rotating shaft via the semi-transparent mirror. The measurement beam emitted to the total reflection mirror within the rotating shaft is reflected to a measurement glass (monitor substrate) held on the rotating drum. On the other hand, the measurement beam emitted to the measurement glass (monitor substrate) is similarly reflected to the total reflection mirror. The reflection beam is emitted to the optical receiver via the semi-transparent mirror. 
     In this way, according to the thin film forming apparatus of the related art, since the measurement beam and the reflection beam are guided through the rotating shaft of the rotating drum which is a hollow shaft, it is possible to measure the film thickness of the measurement glass in real time regardless of the fact that the rotating drum is rotating. 
     However, in the film thickness measuring device, since the emission of the measurement beam to the measurement glass and the reflection of the reflection beam from the measurement glass (monitor substrate) are realized by the single total reflection mirror provided within the rotating shaft, the measurement beam and the reflection beam are introduced from the same end portion of the rotating shaft. Thus, the intensities of the measurement beam and the reflection beam may change due to wobbling, vibration, or the like of the rotating shaft, and an error may occur in the obtained film thickness value. 
     Therefore, the present applicant has already proposed a film thickness measurement technique so that the above problem can be solved. According to the proposed technique, a film thickness measuring device includes a projecting unit that projects a measurement beam toward an inner portion of a base substrate holding means from one side of an axial line of a rotating shaft, a first optical reflection member that is provided inside the base substrate holding means so as to reflect the measurement beam projected from the projecting unit to a base substrate, a second optical reflection member that is provided inside the base substrate holding means so as to reflect a reflection beam reflected from the base substrate to the other side of the axial line of the rotating shaft, a light receiving unit that receives a reflection beam reflected by the second optical reflection member, and a film thickness computing unit that computes a film thickness of a thin film formed on the base substrate based on the reflection beam received by the light receiving unit (Patent Document 2). 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     Patent Document 1: JP 2000-088531 A (Pages 1 to 5, FIGS. 1 and 2) 
     Patent Document 2: JP 2007-211311 A 
     In the technique proposed in Patent Document 2, since the measurement beam and the reflection beam are incident and output from different directions of the axial line of the rotating shaft, it is possible to obtain a high-accuracy film thickness value with small errors. The technique proposed in Patent Document 2 is excellent in that it is possible to obtain a high-accuracy film thickness value with high sensitivity even when measuring the film thickness of a thin film made from a material particularly having low reflectance. 
     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, in the proposed technique, when a plurality of substrates is measured, since a monitor substrate is used, a different substrate (at a phase angle of 120°) disposed at a different position is measured. That is, since the position or space where the monitor substrate (monitor glass) is located is different from that of a product substrate (work substrate) that is subjected to film-formation, the measurement is indirect measurement. Thus, since there is a difference between the monitor substrate (monitor glass) and the product substrate (work substrate) that is subjected to film-formation, the thin film is measured by performing correction using predetermined parameters. 
     In contrast to the indirect measurement, an optical film thickness meter using a direct-view optical monitor is known. However, the optical film thickness meter using a direct-view optical monitor is generally designed for a single product substrate (work substrate), and those designed for various product substrates are not known. 
     As described above, when a large number of optical filters are produced and manufactured according to PVD or the like, in the case of sputtering and evaporation, for example, a product substrate (work substrate) is disposed on a drum or a dome and a film is formed on the product substrate (work substrate). In this case, optical filters having uniform performances can be obtained by repeatedly performing steps of making the film thickness uniform to create a trial film and correcting a correction plate. 
     Since a plurality of channels of optical fibers is used to measure a film distribution, an expensive film thickness meter that includes a plurality of spectrometers is required. Thus, there are problems in that an operation of the film thickness meter is complex, and the cost thereof increases. 
     With the foregoing in view, an object of the present invention is to provide an optical film thickness measuring device capable of directly measuring the film thickness of a product without using a monitor substrate in a thin film forming apparatus that includes a carousel-type rotating mechanism in particular and measuring the film thicknesses of thin films formed on a plurality of substrates disposed in the same line in real time and at a high accuracy. 
     Another object of the present invention is to provide a thin film forming apparatus that uses an optical film thickness measuring device capable of directly measuring a product and controlling the film thickness of the product rather than using a monitor substrate. 
     A further object of the present invention is to provide an optical film thickness measuring device capable of measuring the film thicknesses of products disposed in a plurality of upper and lower stages of a rotating drum using a single optical system and controlling the film thickness, and a thin film forming apparatus using the optical film thickness measuring device. 
     Means for Solving the Problems 
     According to an optical film thickness measuring device of the present invention, the above objects are solved by an optical film thickness measuring device for an optical thin film forming apparatus including a rotating base substrate holding means, comprising: a projecting unit that projects a measurement beam from one side of an axial line of a rotating shaft of the rotating base substrate holding means toward the inside of the base substrate holding means, a light receiving unit that receives the measurement beam from the projecting unit, a plurality of inner beam splitters that is provided inside the base substrate holding means so as to reflect the measurement beam projected from the projecting unit to a base substrate, an inner optical reflection member that is provided inside the base substrate holding means so as to totally reflect a measurement beam from the closest inner beam splitter among the plurality of inner beam splitters, a plurality of external beam splitters that is provided outside the base substrate holding means so as to reflect the measurement beam from the plurality of inner beam splitters toward the light receiving unit, and an outer optical reflection member that is provided outside the base substrate holding means so as to reflect the measurement beam from inner the optical reflection member toward the light receiving unit; in which the measurement beam reflected by the plurality of inner beam splitters and the inner optical reflection member is passed through the base substrate and then reflected by the plurality of external beam splitters and the outer optical reflection member so as to be guided to the light receiving unit, so that the measurement beam is received by the light receiving unit. 
     With the configuration, it is possible to directly measure the film thickness of a product without using a monitor substrate and to measure the film thicknesses of thin films formed on a plurality of substrates disposed in the same line in real time and at a high accuracy. Moreover, since a single optical system is used, and a movable optical component is not used, it is possible to have a high reliability and improve maintenance properties. 
     In this case, it is preferable for the axial line of the rotating shaft of the base substrate holding means to be positioned within a hollow rotating shaft that forms the center of the base substrate holding means, for the inner beam splitter and the inner optical reflection member to be disposed within the rotating shaft, and for the rotating shaft to be configured such that a wall surface of the rotating shaft allows the reflected measurement beam to pass therethrough. In this case, the measurement beams reflected by the inner beam splitter and the inner optical reflection member have substantially the same intensity. 
     In this way, when measurement beams having the same intensity are emitted to the respective base substrates (substrates) which are products, it is possible to obtain the same measurement sensitivity (accuracy). 
     Moreover, it is preferable for the optical film thickness measuring device to further include a film thickness computing unit that computes a film thickness of a thin film formed on the base substrate based on the measurement beam received by the light receiving unit. 
     Further, it is preferable for the plurality of external beam splitters and the outer optical reflection member to be covered with a hollow housing, and for a portion of the housing to which the measurement beam is incident to be configured such that the portion allows the measurement beam to pass therethrough. 
     With this configuration, it is possible to prevent contamination of the external beam splitter and the outer optical reflection member and to further improve maintenance properties. 
     Still further, it is preferable for a shutter device to be provided between the plurality of external beam splitters and the outer optical reflection member. 
     By using the shutter device in this manner, it is possible to block the optical path, and to exclude a base substrate (substrate) from a measurement target when the base substrate (substrate) as a measurement target is not set. 
     Moreover, it is preferable for the projecting unit and the light receiving unit to be provided in the same direction or at the same planar position of the optical thin film forming apparatus. 
     As above, when the projecting unit and the light receiving unit are provided in the same direction of the optical thin film forming apparatus or at the same planar position (for example, on the upper surface of the substrate holding means), since the projecting unit and the light receiving unit are in the same direction or at the same planar position, it is easy to provide the projecting unit and the light receiving unit. Thus the attachment properties and the maintenance properties of the optical film thickness measuring device are improved. In particular, since the projecting unit and the light receiving unit are positioned on the upper surface, various operations such as attachment or maintenance are made easier than when the projecting unit and the light receiving unit are disposed on the lower surface. 
     Moreover, the projecting unit and the light receiving unit may be provided in the opposite directions or at the opposite planar positions of the optical thin film forming apparatus. 
     By configuring in this way, since the projecting unit and the light receiving unit can be provided on the opposite sides as in the device according to the related art, it is not necessary to change the layout of the device according to the related art. 
     According to a thin film forming apparatus of the present invention, the above objects are solved by a rotating thin film forming apparatus forming a thin film, using the optical film thickness measuring device according to any one of claims  1  to  8  including: a base substrate holding means capable of rotating about an axial line of a rotating shaft in a state where a base substrate disposed in a vacuum chamber is held, a film raw material supply means that supplies a film raw material for forming the thin film to the vacuum chamber, and a film-formation process area in which the thin film is formed on the base substrate. 
     According to the thin film forming apparatus of the present invention, it is possible to provide an apparatus that uses the properties of the optical film thickness measuring device. 
     As described above, according to the optical film thickness measuring device and the thin film forming apparatus of the present invention, since a plurality of beam splitters and total reflection mirrors are arranged along the axial line of the rotating shaft of the base substrate holding means, it is possible to directly measure the film thicknesses of a plurality of base substrates (substrates) to be products which are arranged along the axial line of the rotating shaft of the base substrate holding means. Therefore, by measuring the plurality of base substrates, it is possible to measure the film thicknesses of the base substrates (substrates) which are the actual products and to directly control the film thickness of the product itself rather than a monitor substrate. 
     Effects of the Invention 
     According to the present invention, it is possible to directly measure the film thickness of a product without using a monitor substrate and to measure the film thicknesses of thin films formed on a plurality of substrates disposed in the same line in real time and at a high accuracy. 
     Moreover, fulfilling the performance required for the optical film thickness meter, when a thin film is formed, it is possible to directly measure a base substrate (product substrate) loaded on the rotating base substrate holding means. It is possible to provide an optical film thickness measuring device capable of measuring the film thicknesses of the products located at a plurality of upper and lower stages of the rotating drum with the same sensitivity (accuracy) and controlling a film thickness by using one optical system, and a thin film forming apparatus using the optical film thickness measuring device. In particular, since a movable optical component is not used, it is possible to obtain high reliability, improve maintenance properties, and to reduce a cost associated with maintenance. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional explanatory top view of an optical film thickness measuring device and a thin film forming apparatus according to an embodiment of the present invention. 
         FIG. 2  is a cross-sectional explanatory view of the thin film forming apparatus of  FIG. 1  along arrows A-A. 
         FIG. 3  is a partial cross-sectional perspective top view of a rotating drum of  FIG. 2 . 
         FIG. 4  is a similar partial cross-sectional perspective view to  FIG. 3 , illustrating a third embodiment. 
         FIG. 5  is a similar cross-sectional explanatory view to  FIG. 2 , illustrating another example of the third embodiment. 
         FIG. 6  is a partial cross-sectional perspective top view of a rotating drum of  FIG. 5 . 
         FIG. 7  is a similar cross-sectional explanatory view to  FIG. 2 , illustrating another example of a fifth embodiment. 
         FIG. 8  is an explanatory view illustrating an arrangement example of a projection lens. 
         FIG. 9  is an explanatory view of a mirror unit. 
         FIG. 10  is an explanatory view of the mirror unit. 
         FIG. 11  is a block diagram illustrating a functional configuration of an optical film thickness measuring device and a thin film forming apparatus according to each embodiment of the present invention. 
         FIG. 12  is a similar cross-sectional explanatory view to  FIG. 2 , illustrating another embodiment. 
         FIG. 13  is an explanatory view of a basic configuration of an optical film thickness measuring device, in which a projecting unit and a light receiving unit are arranged in the same direction. 
         FIG. 14  is an explanatory view of a basic configuration of an optical film thickness measuring device, in which a projecting unit and a light receiving unit are arranged in the opposite directions. 
         FIG. 15  is an explanatory view illustrating methods of calculating optical output in  FIGS. 13 and 14 , and comparison of relative optical output. 
         FIG. 16  is a view illustrating the output from a base substrate (substrate) in a first embodiment. 
         FIG. 17  is a view illustrating the output from a base substrate (substrate) in a second embodiment. 
         FIG. 18  is a view illustrating the output from a base substrate (substrate) in a third embodiment. 
         FIG. 19  is a view illustrating the output from a base substrate (substrate) in a fourth embodiment. 
     
    
    
     REFERENCE NUMERALS 
       1 : thin film forming apparatus 
       10 : processing chamber 
       11 : vacuum chamber 
       11   a : thin film forming chamber 
       11   b : load lock chamber 
       11   c ,  11   d : door 
       13 : rotating drum (base substrate holding means) 
       13   a : rotating shaft 
       13   b ,  17   a : gear 
       13   c : opening 
       14 : partition wall 
       15 : vacuum pump 
       16   a ,  16   b : pipe 
       17 : rotating drum driving motor 
       20 : sputtering means 
       22   a ,  22   b : target 
       24   a : AC power supply 
       30 : sputtering gas supply means 
       31 ,  33 : mass flow controller 
       32 : sputtering gas cylinder 
       34 : reactive gas cylinder 
       35 : pipe 
       35   a ,  35   b : correction plate driving motor 
       36   a ,  36   b ,  36   c : film thickness correction plate 
       40 : plasma generation means 
       41 : case member 
       42 : dielectric plate 
       43 : antenna 
       44 : matching box 
       45 : high-frequency power supply 
       50 : reactive gas supply means 
       51 : oxygen gas cylinder 
       52 ,  54 : mass flow controller 
       53 : argon gas cylinder 
       55 : pipe 
       60 : optical film thickness measuring device 
       61 : light source 
       61   a : light-emitting element 
       61   b : filter 
       62 : projection optical fiber 
       63 : projection head 
       64 : projecting-side focusing lens 
       65   a : first beam splitter 
       65   b : second beam splitter 
       65   c : first total reflection mirror 
       66   a : third beam splitter 
       66   b : fourth beam splitter 
       66   c : second total reflection mirror 
       66   k : total reflection mirror 
       66   l ,  66   m : beam splitter 
       67 : receiving-side optical fiber 
       68 : receiving-side focusing lens 
       69 : reception head 
       71 : spectroscopic measurement device 
       71   a : light-receiving element 
       71   b : light-dispersing element 
       80 : film thickness computing unit 
       81 : CPU 
       82 : memory 
       83 : hard disk 
       84 : I/O port 
       83   a : film thickness correlation data 
       83   b : film thickness computation program 
       90 : film thickness controller 
       91 : film thickness control signal generation unit 
       100   a ,  100   b ,  100   c : optical path switching shutter 
       101 : driving unit 
       102   a ,  102   b ,  102   c : shielding plate 
       160 : cylindrical member 
       165   a  to  165   d : beam splitter (BS 1  to BS 4 ) 
       166   a  to  166   d : beam splitter (BS 5  to BS 8 ) 
       165   e ,  166   e : total reflection mirror 
     V: valve 
     S: base substrate (substrate) 
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. Members, arrangements, and the like described below are not limited to the present invention, but may naturally be modified in various manners according to the spirit of the present invention. 
       FIGS. 1 to 19  relates to embodiments of the present invention, in which  FIG. 1  is a cross-sectional explanatory top view of an optical film thickness measuring device and a thin film forming apparatus;  FIG. 2  is a cross-sectional explanatory view of the thin film forming apparatus of  FIG. 1  along arrows A-A;  FIG. 3  is a partial cross-sectional perspective top view of a rotating drum of  FIG. 2 ;  FIG. 4  is a similar partial cross-sectional perspective view to  FIG. 3 , illustrating a third embodiment;  FIG. 5  is a similar cross-sectional explanatory view to  FIG. 2 , illustrating another example of the third embodiment;  FIG. 6  is a partial cross-sectional perspective top view of a rotating drum of  FIG. 5 ;  FIG. 7  is a similar cross-sectional explanatory view to  FIG. 2 , illustrating another example of a fifth embodiment;  FIG. 8  is an explanatory view illustrating an arrangement example of a projection lens;  FIGS. 9 and 10  are explanatory views of a mirror unit;  FIG. 11  is a block diagram illustrating a functional configuration of an optical film thickness measuring device and a thin film forming apparatus according to each embodiment;  FIG. 12  is a similar cross-sectional explanatory view to  FIG. 2 , illustrating another embodiment;  FIG. 13  is an explanatory view of a basic configuration of an optical film thickness measuring device, in which a projecting unit and a light receiving unit are arranged in the same direction;  FIG. 14  is an explanatory view of a basic configuration of an optical film thickness measuring device, in which a projecting unit and a light receiving unit are arranged in the opposite directions;  FIG. 15  is an explanatory view illustrating methods of calculating optical output in  FIGS. 13 and 14 , and comparison of relative optical output;  FIG. 16  is a view illustrating the output from a base substrate (substrate) in the first embodiment;  FIG. 17  is a view illustrating the output from a base substrate (substrate) in a second embodiment;  FIG. 18  is a view illustrating the output from a base substrate (substrate) in a third embodiment; and  FIG. 19  is a view illustrating the output from a base substrate (substrate) in a fourth embodiment. 
     A thin film forming apparatus  1  of the present embodiment forms an intermediate thin film on a substrate surface by performing a sputtering treatment of sputtering a target to attach a film raw material to a substrate surface so that a thin film comparably thinner than an intended film thickness is attached to the substrate surface and a plasma treatment of performing treatment such as oxidation on the film raw material to transform the composition of the thin film. The thin film forming apparatus  1  stacks a plurality of intermediate thin films by repeating the sputtering treatment and the plasma treatment several times to form a final thin film having an intended film thickness on the substrate surface. 
     Specifically, an intermediate thin film having an average film thickness of approximately 0.01 nm to 1.5 mm after the composition transform in the sputtering treatment and the plasma treatment is formed on the substrate surface, and a plurality of intermediate thin films is stacked by repeating the treatments every rotation of a rotating drum to form a final thin film having an intended film thickness of approximately several nm to several hundreds of nm. 
     As illustrated in  FIGS. 1 and 2 , main constituent components of the thin film forming apparatus  1  include a processing chamber  10  that includes a vacuum chamber  11  and a rotating drum  13 , a sputtering means  20 , a sputtering gas supply means  30 , a plasma generation means  40 , a reactive gas supply means  50 , and an optical film thickness measuring device  60 . In the figures, the sputtering means  20  is surrounded by dashed lines, the sputtering gas supply means  30  is surrounded by long dashed short dashed lines, the plasma generation means  40  is surrounded by dashed lines, and the reactive gas supply means  50  is surrounded by long dashed double-short dashed lines. 
     In a reaction process treatment, the plasma generation means  40  performs a plasma treatment on the film raw material attached to the surface of a base substrate (substrate) S in a film-formation process treatment to form an intermediate thin film made from a complete reactant or an incomplete reactant of the film raw material. 
     The plasma generation means  40  is configured to include a case member  41 , a dielectric plate  42 , an antenna  43 , a matching box  44 , and a high-frequency power supply  45 . The case member  41  has a shape such that the case member  41  covers an opening formed on a wall surface of the vacuum chamber  11 . The case member  41  is fixed to the wall surface of the vacuum chamber  11  so as to close the opening of the vacuum chamber  11 . In this way, the plasma generation means  40  is attached to the wall surface of the vacuum chamber  11 . 
     Main constituent components of the reactive gas supply means  50  include an oxygen gas cylinder  51  that stores oxygen gas, a mass flow controller  52  that adjusts a flow rate of the oxygen gas supplied from the oxygen gas cylinder  51 , an argon gas cylinder  53  that stores argon gas, a mass flow controller  54  that adjusts a flow rate of the argon gas supplied from the argon gas cylinder  53 , and a pipe  55  that introduces a mixed gas of the oxygen gas and the argon gas to a reaction process area. 
     Moreover, the plasma generation means  40  performs a plasma treatment on the film raw material attached to the surface of the base substrate (substrate) S by sputtering or the like to form an intermediate thin film made from a complete reactant or an incomplete reactant of the film raw material. 
     When power is supplied from the high-frequency power supply  45  to the antenna  43  in a state where oxygen gas is introduced into the reaction process area from the oxygen gas cylinder  51  and the argon gas cylinder  53  through an inlet port of the pipe  55 , plasma is generated in a region of the reaction process area being facing the antenna  43 . By this plasma, silicon (Si) in the film raw material formed on the surface of the base substrate (substrate) S or an incomplete silicon oxide (SiO x  (where, 0&lt;x&lt;2)) is oxidized, whereby an intermediate thin film made from a complete silicon oxide (SiO 2 ) or an incomplete silicon oxide (SiO x  (where, 0&lt;x&lt;2)) is obtained. 
     Next, the optical film thickness measuring device  50  according to an embodiment of the present invention will be described. The optical film thickness measuring device  60  measures a film thickness of a thin film formed on the surface of the base substrate (substrate) S. In the present embodiment, as illustrated in  FIGS. 2 to 7  and  12 , the optical film thickness measuring device  60  includes an emission side from which a measurement beam is emitted and a reception side on which the measurement beam having passed through the base substrate (substrate) S is received. 
       FIG. 8  is an explanatory view illustrating an arrangement example of a projection lens on the emission side. The emission side includes a light source  61  that emits a measurement beam, a projection optical fiber  62  that transmits the measurement beam from the light source  61 , and a projection head  63  to which the measurement beam transmitted by the projection optical fiber  62  is guided. 
     The projection head  63  emits the measurement beam to a first beam splitter (BS 1 )  65   a , a second beam splitter (BS 2 )  65   b , and a first total reflection mirror  65   c  that are disposed within a rotating shaft. A projecting-side focusing lens  64  collects the measurement beam from the projection head  63 . 
       FIGS. 9 and 10  are explanatory views of a mirror unit, in which  FIG. 9  is an explanatory view of a mirror unit to which a contamination prevention shield is attached and  FIG. 10  is an explanatory view of a mirror unit in which the contamination prevention shield is detached. The total reflection mirror illustrated in  FIGS. 9 and 10  is a dielectric mirror. 
     In the present embodiment, the mirror unit includes the first beam splitter (BS 1 )  65   a  that allows a portion of the measurement beam from the projection head  63  to pass therethrough and guides a portion of the measurement beam to a product base substrate (substrate) S as a base substrate, the second beam splitter (BS 2 )  65   b  that allows another portion of the measurement beam having passed through the first beam splitter (BS 1 )  65   a  to pass therethrough and guides a portion of the measurement beam to the product base substrate (substrate) S, and the first total reflection mirror  65   c  that reflects the measurement beam having passed through the second beam splitter (BS 2 )  65   b . The projection optical fiber  62  is connected to the light source  61 , and one end of the projection optical fiber  62  is inserted into the light source  61  so that the measurement beam having passed through a filter of the light source  61  is incident on the end surface of the projection optical fiber  62  and guided to the projection head  63 . 
     The projection head  63  is disposed outside the vacuum chamber  11  on an upper side ( FIG. 2 ) of a rotating shaft  13   a  so as to face the first beam splitter (BS 1 )  65   a , the second beam splitter (BS 2 )  65   b , and the first total reflection mirror  65   c  that are disposed inside the rotating shaft  13   a . The measurement beam emitted from the projection head  63  enters from one end of the rotating shaft  13   a , passes inside the rotating shaft  13   a  along the axial direction thereof, and is emitted to the first beam splitter (BS 1 )  65   a , the second beam splitter (BS 2 )  65   b , and the first total reflection mirror  65   c.    
     The first beam splitter (BS 1 )  65   a , the second beam splitter (BS 2 )  65   b , and the first total reflection mirror  65   c  are configured so as to be fixed to a predetermined inner position of the rotating shaft  13   a , and in this case, the angular positions thereof can be adjusted. 
     Main constituent components of the reception side include a third beam splitter (BS 3 )  66   a , a fourth beam splitter (BS 4 )  66   b , and a second total reflection mirror  66   c  that reflect the measurement beam having passed through the base substrate (substrate) S toward the reception head  69 , a receiving-side focusing lens  68  that collects the measurement beam having passed through or reflected from the third beam splitter (BS 3 )  66   a , the fourth beam splitter (BS 4 )  66   b , and the second total reflection mirror  66   c , a reception head  69 , a receiving-side optical fiber  67  that transmits the measurement beam received by the reception head  69 , and a spectroscopic measurement device  71  that disperses the measurement beam transmitted by the receiving-side optical fiber  67 . That is, the reception side is configured to allow the measurement beam, which has passed through or reflected from the third beam splitter (BS 3 )  66   a , the fourth beam splitter (BS 4 )  66   b , and the second total reflection mirror  66   c  and has passed through the base substrate (substrate) S, to be reflected from or pass through the third beam splitter (BS 3 )  66   a , the fourth beam splitter (BS 4 )  66   b , and the second total reflection mirror  66   c  and guide the measurement beam to the spectroscopic measurement device  71  as a measurement beam. 
     Further, the light source  61 , the projection optical fiber  62 , and the projection head  63  correspond to a projecting unit of the present invention. Further, the reception head  69 , the receiving-side optical fiber  67 , and the spectroscopic measurement device  71  correspond to a light receiving unit. Moreover, the first total reflection mirror  65   c  corresponds to an inner optical reflection member, and the second total reflection mirror  66   c  corresponds to an outer optical reflection member. 
     The third beam splitter (BS 3 )  66   a , the fourth beam splitter (BS 4 )  66   b , and the second total reflection mirror  66   c  on the reception side are configured so as to be fixed to a predetermined position by a holding member (not illustrated) (for example, a rod-shaped member having an optional cross-sectional shape), and in this case, the angular positions thereof can be adjusted. 
     Moreover, reference numerals  100   a  to  100   c  designate optical path switching shutters that include a driving unit  101  and shielding plates  102   a  to  102   c.    
     The optical path switching shutters  100   a  to  100   c  have a configuration in which a servo motor (other actuators or the like) is used as the driving unit  101 , the shielding plates  102   a  to  102   c  are moved by the driving unit  101 , and the shielding plates  102   a  to  102   c  are moved to a position where the shielding plates  102   a  to  102   c  block the measurement beam from the emission side so as not to enter the third beam splitter (BS 3 )  66   a , the fourth beam splitter (BS 4 )  66   b , and the second total reflection mirror  66   c  and a position where the measurement beam is not blocked. The shape or the like of the shielding plates  102   a  to  102   c  is not particularly limited as long as the shielding plates  102   a  to  102   c  can block the measurement beam. In the optical path switching shutters  100   a  to  100   c , the driving unit  101  is provided outside the vacuum chamber  11  as a driving source. 
     The shielding plates  102   a  to  102   c  are configured so as to be moved to a position where the measurement beams from the beam splitters (BS 1 , BS 2 )  65   a  and  65   b  and the first total reflection mirror  65   c  are not blocked. The shielding plates  102   a  to  102   c  also have a role of preventing contamination. The driving unit  101  is disposed outside the vacuum chamber. 
     Moreover, the first total reflection mirror  65   c  and the second total reflection mirror  66   c  are members prepared by forming a thin film of aluminum or the like on a surface of a base substrate of glass or the like and have high reflectance of approximately 100% at least in the wavelength of the measurement beam. The total reflection mirrors of the present embodiment are formed of a plate-shaped member having an approximately square shape. The total reflection mirrors are arranged inside a hollow body of the rotating shaft  13   a  and are fixed to the inner wall surface of the rotating shaft  13   a  by welding, screwing, or the like. 
     The light source  61  of the present embodiment uses a halogen lamp, a white LED, or the like and is a device that is provided outside the vacuum chamber  11  so as to emit the measurement beam for measuring a film thickness. As illustrated in  FIG. 11 , the light source  61  includes a light-emitting element  61   a  that receives power supplied from a power supply (not illustrated) and emits light and a filter  61   b  that allows the light with a specific wavelength region in the light emitted from the light-emitting element  61   a  to pass there through. 
     An opening  13   c  that is cutout in a portion of a side wall is formed in a central portion of the rotating shaft  13   a , and the measurement beam reflected from the beam splitters (BS 1 , BS 2 )  65   a  and  65   b  and the first total reflection mirror  65   c  is emitted to the base substrate (substrate) S held on the rotating drum  13  through the opening  13   c . Moreover, in the present embodiment, although an example in which the opening  13   c  is formed is illustrated, a sealed structure may be created using a glass member through which the light can completely pass. 
     As described above, in the present invention, unlike the related art, the film thickness of a product substrate itself is directly measured without requiring a monitor substrate for measuring a film thickness. Moreover, unlike the related art, it is not necessary to use a transparent glass material as the monitor substrate or a plastic or the like as a material that allows the wavelength of the measurement beam to pass therethrough at a high transmittance. 
     The measurement beam emitted from the emission side to the base substrate (substrate) S is divided by the beam splitter into a measurement beam moving toward the base substrate (substrate) S and a passing measurement beam, which are finally reflected by the total reflection mirror. 
     That is, a portion of the measurement beam emitted to the first beam splitter (BS 1 )  65   a  is reflected from the first beam splitter (BS 1 )  65   a  and then enters from a rear surface side (that is, the rotating shaft  13   a  side) of the base substrate (substrate) S and passes through the inside of the base substrate (substrate) S. The measurement beam that has passed through the first beam splitter (BS 1 )  65   a  without being reflected is guided to the next second beam splitter (BS 2 )  65   b , and a portion thereof is reflected from the second beam splitter (BS 2 )  65   b  and then enters from the rear surface side (that is, the rotating shaft  13   a  side) of the base substrate (substrate) S and passes through the inside of the base substrate (substrate) S. Further, the measurement beam that has passed through the second beam splitter (BS 2 )  65   b  without being reflected is guided to the first total reflection mirror  65   c . The first total reflection mirror  65   c  is formed of a member having high reflectance of approximately 100% in the wavelength of the measurement beam. These measurement beams emitted from the emission side are received on the reception side. 
     Similarly to the projection head  63 , the reception head  69  is disposed outside the vacuum chamber  11  on the upper side ( FIG. 2 ) of the rotating shaft  13   a , and the third beam splitter (BS 3 )  66   a , the fourth beam splitter (BS 4 )  66   b , and the second total reflection mirror  66   c  for reflecting the measurement beam emitted from the emission side so as to be guided to the reception head  69  are disposed in a predetermined position on a peripheral side of the rotating drum  13  that is disposed in the vacuum chamber  11 . In the present embodiment, as illustrated in  FIG. 2 , the reception head  69  is disposed at a position furthest from the sputtering means  20  and the plasma generation means  40 . As a result, the reception head  69  is configured to be rarely influenced by the sputtering means  20  and the plasma generation means  40 . 
     The reception head  69  is disposed at a position where the measurement beam reflected by the first beam splitter (BS 1 )  65   a , the second beam splitter (BS 2 )  65   b , and the first total reflection mirror  65   c  is incident, and one end of the receiving-side optical fiber  67  is connected to the reception head  69 , and the other end is connected to the spectroscopic measurement device  71 . The measurement beam having passed through the base substrate (substrate) S is reflected by the third beam splitter (BS 3 )  66   a , the fourth beam splitter (BS 4 )  66   b , and the second total reflection mirror  66   c , collected by the receiving-side focusing lens  68 , and incident on the reception head  69 . The incident measurement beam is guided to the receiving-side optical fiber  67  and input to the spectroscopic measurement device  71 . 
     As described above, since the projection head  63  and the reception head  69  are provided outside the vacuum chamber  11 , it is possible to prevent problems such as twisting or tangling of an optical fiber due to the rotation of the rotating drum  13  which may occur when the projection head  63  and the reception head  69  are disposed inside the rotating drum  13 . Moreover, the projection head  63  and the reception head  69  are disposed outside the vacuum chamber  11 , it is possible to eliminate a problem that the rotating drum  13  is heated in the course of film-formation, and the projection head and the reception head are thermally deformed by the heat. In this way, in the present invention, it is possible to prevent the twisting or tangling of the optical fiber and the influence of heat generated in the course of film-formation and to perform stable film thickness measurement. 
     The spectroscopic measurement device  71  is a device that measures the intensity of light of a predetermined wavelength in the reflection beam and has the same configuration as an existing spectroscopic measurement device used in measuring a film thickness. That is, as illustrated in  FIG. 11 , the spectroscopic measurement device  71  includes a light-dispersing element  71   b  that allows the light within a predetermined wavelength region in the reflection beam to pass therethrough, and a light-receiving element  71   a  that receives light having passed through the light-dispersing element  71   b  and outputs a current value corresponding to the intensity of the light. 
     The light-dispersing element  71   b  is formed of a member having a diffraction lattice such as a grating, for example, and allows the light within a predetermined wavelength region to pass therethrough. In the present embodiment, the light-dispersing element  71   b  allows the wavelength of the measurement beam to pass therethrough at least at the transmittance of approximately 100%. The light having passed through the light-dispersing element  71   b  is guided to the light-receiving element  71   a . The light-receiving element  71   a  is formed of a semiconductor element such as a photodiode, for example, and an element in which p and n-type semiconductors are bonded may be used, for example. When light strikes the bonding surface of the p and n-type semiconductors, a current corresponding to the intensity of the light is generated. The current is converted into a digital signal by an A/D conversion circuit in the spectroscopic measurement device  71 , and the digital signal is output from the spectroscopic measurement device  71  to a film thickness computing unit  80  described later. 
     The film thickness computing unit  80  is a means that computes the film thickness of a thin film formed on the base substrate (substrate) S based on the intensity of the measurement beam measured by the spectroscopic measurement device  71 . As illustrated in  FIG. 11 , the film thickness computing unit  80  includes a CPU  81  as a computing means, a hard disk  83  and a memory (specifically, ROM and RAM)  82  as a storage means, and an I/O port  84  as an input/output port used when transmitting and receiving signals to/from an external device or the like. The film thickness computing unit  80  corresponds to a film thickness computing unit of the present invention. 
     The film thickness computing unit  80  is electrically connected to the spectroscopic measurement device  71 , and the signal that represents the intensity of the measurement beam and is digitalized by the spectroscopic measurement device  71  is input to the hard disk  83  and the memory (specifically ROM and RAM)  82  as the storage means via the I/O port  84  of the film thickness computing unit  80 . For example, film thickness correlation data  83   a  in which a correlation between a change of the intensity of the measurement beam and the film thickness of the thin film formed on the base substrate (substrate) S and a film thickness computation program  83   b  that computes a film thickness based on the measurement beam intensity signal transmitted from the spectroscopic measurement device  71  and the film thickness correlation data  83   a  are stored in the hard disk  83 . The film thickness correlation data  83   a  and the film thickness computation program  83   b  may be stored in RAM, ROM, or the like. 
     Hereinafter, a principle of measuring the film thickness using the film thickness computing unit  80  will be described. A measurement beam emitted to the base substrate (substrate) S is reflected at the boundary between the base substrate (substrate) S and the thin film and the boundary between the thin film and the vacuum chamber. In this case, these reflection beams interfere with each other, and the intensity of the reflection beam is changed. 
     Here, a predetermined correlation is present between the intensity of the reflection beam or the transmission beam of the thin film and the film thickness. More specifically, it is known that when a refractive index of a thin film is n, a wavelength is λ, and a geometric film thickness is d, the intensity of a reflection beam exhibits peaks periodically whenever an optical film thickness nd becomes an integer multiple of λ/4. Since the height of peaks (peak value P) and a refractive index have a predetermined correlation, it is possible to obtain a refractive index by obtaining the peak value P. That is, the peak value P is obtained by measuring the intensity of the reflection beam, and the geometric film thickness d can be calculated from the optical film thickness nd based on the values of the refractive index n and the wavelength λ. 
     The film thickness computing unit  80  stores the wavelength □ of the measurement beam as a setting value in advance. Moreover, the film thickness computation program  83   b  obtains the height of the peak value P from the reflection beam intensity signal transmitted from the spectroscopic measurement device  71  to compute the refractive index n. Further, the film thickness computation program  83   b  calculates the geometric film thickness d based on the values of the refractive index n and the wavelength□. 
     The film thickness computing unit  80  is electrically connected to the film thickness controller  90 . The film thickness controller  90  includes a computing means such as a MPU, a storage means such as ROM and RAM, and an input/output port that transmits and receives an electrical signal to/from other devices. A film thickness (that is, a geometric film thickness d) measured by the film thickness computing unit  80  is input to the film thickness controller  90 . The film thickness controller  90  includes a film thickness control signal generation unit  91  and controls the film thickness by adjusting a film-formation rate and a film-formation period based on the film thickness signal generated by the film thickness control signal generation unit  91 . 
     Specifically, the film thickness controller  90  adjusts the film-formation rate based on the film thickness acquired from the film thickness computing unit  80  according to at least one of a method of increasing or decreasing the power supplied to targets  22   a  and  22   b  from the AC power supply  24   a  of the sputtering means  20 , a method of increasing or decreasing the amount of sputtering gas and reactive gas supplied to the film-formation process area by the sputtering gas supply means  30 , and a method of moving the film thickness correction plates  36   a  and  36   b  by correction plate driving motors  35   a  and  35   b . Reference numeral  36   c  is a film thickness correction plate, and the film thickness controller  90  corresponds to a film thickness adjustment means. 
     Moreover, the film thickness may be adjusted by adjusting the film-formation period. That is, when the film thickness of the base substrate (substrate) S acquired by the film thickness computing unit  80  is smaller than a preset film thickness, the film thickness controller  90  extends the film-formation period without ending the film-formation at a predetermined film-formation ending time to increase the film thickness to a preset film thickness. On the other hand, when the film thickness of the base substrate (substrate) S acquired by the film thickness computing unit  80  is larger than a preset film thickness, the film thickness controller  90  shortens the film-formation period by ending the film-formation before a predetermined film-formation ending time to end the film-formation at a preset film thickness. The film thickness may be adjusted by using only one of these film thickness control methods and may be adjusted by a combination of a plurality of methods. 
     As described above, the optical film thickness meter according to the present embodiment can automatically calculate the film-formation rate during the film-formation and control the film thickness. Moreover, by outputting a control signal to an automatic correction plate mechanism, it is possible to control the film thickness and the quality of an optical thin film product. For example, in the case of a stationary photometric method, it is possible to control the film thickness by analyzing the film thickness from the measurement results of the spectroscopic properties of the base substrate (substrate) S. 
     On the other hand, in the case of a rotating photometric method, the amount of the transmission beam of the base substrate (substrate) S is measured and the film thickness can be controlled. 
     First, a basic configuration of the present invention is configured as illustrated in  FIGS. 13 to 15 . That is, in the case of one branch, mirrors  1  and  2  are used during projection and reception. In the case of two branches, two BSs (BS 1 , BS 2 ) and two mirrors (mirrors  1  and  2 ) are used during projection and reception. In the case of three branches, four BSs (BS 1  to BS 4 ) and two mirrors (mirrors  1  and  2 ) are used. In the case of four branches, six BSs (BS 1  to BS 6 ) and two mirrors (mirrors  1  and  2 ) are used In the case of five branches, eight BSs (BS 1  to BS 8 ) and two mirrors (mirrors  1  and  2 ) are used. 
     The arrangements of the mirrors and the BSs, when the projecting unit and the light receiving unit are in the same direction and when they are in the opposite directions, are as follows. The mirrors are arranged to face each other when the projecting unit and the light receiving unit are in the same direction, and the mirrors are always arranged so as to face each other at the last reflecting position except for the case of one branch. In the case of mirrors in the opposite directions, the receiving-side mirror is fixed to the initially disposed position, and the projecting-side mirror is disposed at a position such that the mirror is moved sequentially downward for every additional branch. 
     Moreover, according to a method of calculating output light when the projecting unit and the light receiving unit are in the same direction, the relative optical output P=(100%/n)^2. That is, P=100% for one branch, n=2 and P=25% for two branches, and n=3 and P=11.1% for three branches. 
     Similarly, according to a method of calculating output light when the projecting unit and the light receiving unit are in the opposite directions, the relative optical output P=(50%)^n. That is, P=100% for one branch, n=2 and P=25% for two branches, and n=3 and P=12.5% for three branches. 
       FIG. 15  illustrates a table of comparison between the relative outputs for the case of respective branches. 
     The first to fourth embodiments will be described in detail with reference to  FIGS. 16 to 19 . 
     &lt;First Embodiment&gt; 
     The first embodiment is an example in which an aluminum reflection mirror with reflectance of 90% is used as the first and second total reflection mirrors  65   c  and  66   c . The first beam splitter (BS 1 )  65   a  has a reflectance/transmittance ratio of 18/82 and the second beam splitter (BS 2 )  65   b  has a reflectance/transmittance ratio of 45/55. The first total reflection mirror  65   c  and the second total reflection mirror  66   c  are aluminum reflection mirrors and have reflectance of 90%. The third beam splitter (BS 3 )  66   a  and the fourth beam splitter (BS 4 )  66   b  have a reflectance/transmittance ratio of 50/50. With the above mirrors and beam splitters, the transmittance values (efficiencies) of the measurement beam of the base substrate (substrate) S of the respective products on the upper, middle, and lower stages are 9%, 9.2%, and 9.1%, respectively. The optical path can be switched by the optical path switching shutters  100   a  to  100   c.    
     The transmittance values of the base substrate (substrate) S on the upper, middle, and lower stages of the drum are measured in the following order. 
     
       
         
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Upper Stage 
                 Middle Stage 
                 Lower Stage 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Shielding 
                 off 
                 on 
                 on 
               
               
                   
                 Plate 102a 
               
               
                   
                 Shielding 
                 on 
                 off 
                 on 
               
               
                   
                 Plate 102b 
               
               
                   
                 Shielding 
                 on 
                 on 
                 off 
               
               
                   
                 Plate 102c 
               
               
                   
                   
               
             
          
         
       
     
     Alternatively, the average transmittance value of the base substrate (substrate) S of the products is measured as T (average)=(T1+T2+T3)/3 in a state where the shielding plates  102   a ,  102   b , and  102   c  are all in the off state. 
     More specifically, the transmittance from the base substrate (substrate) S of the upper-stage product to the base substrate (substrate) S of the lower-stage product via the base substrate (substrate) S of the middle-stage product is measured in the following order. 
     Regarding upper-stage product base substrate (substrate) S, middle-stage product base substrate (substrate) S, and lower-stage product base substrate (substrate) S, optical path switching shutter  100   a  is ON→OFF→ON, optical path switching shutter  100   b  is OFF→ON→OFF, and optical path switching shutter  100   c  is OFF→OFF→OFF. 
     A dark current is measured in the following conditions: 
     Dark Current  1 : Optical path switching shutter  100   a  is on, and Optical path switching shutters  100   b  and  100   c  are off; 
     Dark Current  2 : Optical path switching shutter  100   b  is on, and Optical path switching shutters  100   a  and  100   c  are off; and 
     Dark Current  3 : Optical path switching shutter  100   c  is on, and Optical path switching shutters  100   a  and  100   b  are off. 
     An average transmittance value of the base substrate (substrate) S of the products are measured as T(average)=(T1+T2+T3)/3 in a state where three optical path switching shutters  100   a  to  100   c  are in the off state. 
     The relative light intensities (%) of the upper-stage product base substrate (substrate) S, the middle-stage product base substrate (substrate) S, and the lower-stage product base substrate (substrate) S according to the first embodiment are as illustrated in  FIG. 16 . The measurement beam is very evenly distributed. 
     &lt;Second Embodiment&gt; 
     The first beam splitter (BS 1 )  65   a  and the third beam splitter (BS 3 )  66   a  according to the second embodiment are formed of a dielectric mirror and have a reflectance/transmittance ratio of 33.3/66.7 as illustrated in  FIG. 17 . The second beam splitter (BS 2 )  65   b  and the fourth beam splitter (BS 4 )  66   b  have a reflectance/transmittance ratio of 50/50. Moreover, the first total reflection mirror  65   c  and the second total reflection mirror  66   c  are formed of a dielectric mirror having reflectance of 99.9%. That is, in the first embodiment, an aluminum mirror having reflectance of 90% is used as the first and second total reflection mirrors  65   c  and  66   c . In contrast, in the second embodiment, a dielectric mirror having reflectance of 99.9% is used as the first and second total reflection mirrors  65   c  and  66   c.    
     In this way, in the second embodiment, a multi-work photometric optical system is used. Specifically, the first beam splitter (BS 1 )  65   a  has a reflectance/transmittance ratio of 33.3/66.7, the second beam splitter (BS 2 )  65   b  has a reflectance/transmittance ratio of 50/50, and the dielectric of the first total reflection mirror  65   c  and the second total reflection mirror  66   c  has reflectance ratio of 99.9%. The third beam splitter (BS 3 )  66   a  has a reflectance/transmittance ratio of 33.3/66.7, and the fourth beam splitter (BS 4 )  66   b  has a reflectance/transmittance ratio of 50/50. The transmittance values (efficiencies) of the measurement beam of the base substrate (substrate) S of the respective products on the upper, middle, and lower stages are all 11%, 11%, and 11%. The optical path can be switched by the optical path switching shutters  100   a  to  100   c.    
     The relative light intensities (%) of the upper-stage product base substrate (substrate) S, the middle-stage product base substrate (substrate) S, and the lower-stage product base substrate (substrate) S according to the second embodiment are as illustrated in  FIG. 17 . 
     &lt;Third Embodiment&gt; 
       FIGS. 4 and 18  illustrate the third embodiment, and  FIG. 4  illustrates the same partial cross-sectional perspective views as  FIG. 3 . The present embodiment illustrates an example in which a shutter device is not used, and five branches are used. The same materials, members, arrangements, and the like as those of the above embodiments will be denoted by the same reference numerals, and description thereof will not be provided. 
     The present embodiment illustrates an example in which four sets of beam splitters ( 165   a  to  165   d  and  166   a  to  166   d ) and one set of total reflection mirrors ( 165   e  and  166   e ) are used are used on the emission side and the reception side. With the configuration according to this example, it is possible to measure the film thicknesses of all base substrates (substrates) S provided on the holding portion. 
     In this case, similarly to the above-described embodiments, the beam splitter is selected so that the measurement beam to all base substrates (substrates) S has the same intensity. That is, in order to make the intensities of the measurement beams moving toward five base substrates (substrates) S to be the same, a beam splitter configured such that 20% of the measurement beam moves toward the base substrate (substrate) S is used as the first beam splitter (BS 1 )  165   a . Similarly, a beam splitter configured such that 20%, which is the same amount of beam reflected by the first beam splitter (BS 1 )  165   a , of the 80% measurement beam having passed through the first beam splitter (BS 1 )  165   a  moves toward the base substrate (substrate) S. In this manner, the beam splitters are used sequentially. In this way, in the last total reflection mirror  165   e , 20% of the original measurement beam is emitted to the base substrate (substrate) S. Moreover, on the reception side, a beam splitter having a configuration opposite to that of the emission side is used. With the above-described configuration, the optical path switching shutters  100   a  to,  100   c  are not necessary. 
     More specifically, the first beam splitter (BS 1 )  155   a  and the fifth beam splitter (BS 5 )  166   a  have a relative light intensity of 20%, the second beam splitter (BS 2 )  165   b  and the sixth beam splitter (BS 6 )  166   b  have a relative light intensity of 25%, the third beam splitter (BS 3 )  165   c  and the seventh beam splitter (BS 7 )  166   c  have a relative light intensity of 33.3%, and the fourth beam splitter (BS 4 )  165   d  and the eighth beam splitter (BS 8 )  166   d  have a relative light intensity of 50%. 
     The case of five branches or more can be handled. The relative optical output is as follows. 
     1 Branch: 100% 
     2 Branches: 25% 
     3 Branches: 11% 
     4 Branches: 6.25% 
     5 Branches: 4% 
     In the case of n branches, the relative optical output is P=(100%/n)^2. 
     Here, X1 =100%−100%/n and Y1 =X1 for the first beam splitter 1 (BS 1 ). 
     Y1:X1 is used for the first beam splitter 1(BS 1 ). 
     Similarly, X2=100%−100%/(n−1) and Y2=X2 for the second beam splitter 2 (BS 2 ). 
     X3=100%−100%/(n−2) and Y3=X3 for the third beam splitter 3(BS 3 ). 
     Thus, the i-th beam splitter i (BSi) is determined as Xi=100%−100%/(n−(i−1)) and Yi=Xi (i&lt;n). 
     &lt;Fourth Embodiment&gt; 
       FIG. 19  illustrates the fourth embodiment. As described above, the i-th beam splitter i (BSi) is determined as Xi=100%−100%/(n−(i−1)) and Yi=Xi (i&lt;n), and in this example, the case of four branches is illustrated. 
     More specifically, the first beam splitter (BS 1 ) and the fourth beam splitter (BS 4 ) have a relative light intensity of 75%, the second beam splitter (BS 2 ) and the fifth beam splitter (BS 5 ) have a relative light intensity of 33.3%, and the third beam splitter (BS 3 ) and the sixth beam splitter (BS 6 ) have a relative light intensity of 50%. 
       FIGS. 5 and 6  illustrate another embodiment of the device, in which  FIG. 5  is a similar cross-sectional explanatory view to  FIG. 2 , and  FIG. 6  is a partial cross-sectional perspective top view of the rotating drum of  FIG. 5 . In this embodiment, the same materials, members, arrangements, and the like as those of the respective embodiments above will be denoted by the same reference numerals, and description thereof will not be provided. 
     The present embodiment illustrates an example in which the beam splitters  166   a  to  166   d  and the total reflection mirror  166   e  on the reception side are attached within a cylindrical member  160  similarly to the rotating shaft  13   a  on the emission side. Moreover, the beam splitters  166   a  to  166   d  and the total reflection mirror  166   e  on the reception side are provided in the cylindrical member  160  by means of an existing means so that the tilt angles thereof can be adjusted. Further, an opening is formed at a position of the cylindrical member  160  corresponding to the optical path of the measurement beam so as not to interrupt the measurement beam moving to the beam splitters  166   a  to  166   d  and the total reflection mirror  166   e  on the reception side. In the present embodiment, although an example in which an opening is formed is illustrated, a sealed structure may be created using a glass member through which light can completely pass. 
     By configuring in this manner, just by attaching the cylindrical member  160  within the vacuum chamber  11 , the arrangement on the reception side can be realized and the attachment is easy. Moreover, it is possible to draw the cylindrical member  160  and perform adjustment, repair, and the like during maintenance. 
     &lt;Fifth Embodiment&gt; 
     Next, the fifth embodiment illustrated in  FIG. 7  will be described. In this example, in contrast to the first embodiment in which the light receiving unit and the projecting unit are in the same direction (or on the same surface), the light receiving unit and the projecting unit are on the opposite sides as illustrated in  FIG. 7 . In this embodiment, the same materials, members, arrangements, and the like as those of the respective embodiments above will be denoted by the same reference numerals, and description thereof will not be provided. 
     In this example, the first beam splitter (BS 1 )  65   a  and the second beam splitter (BS 2 )  65   b  have a reflectance/transmittance ratio of 50%, the total reflection mirrors  66   c  and  66   k  are formed of a dielectric mirror having reflectance of R&gt;99.9%, and the beam splitter (BS 3 )  661  and the beam splitter (BS 4 )  66   m  have a reflectance/transmittance ratio of 50%. Basically, the device has such a configuration as illustrated in  FIGS. 14 and 15 . 
     In this way, the projecting unit and the light receiving unit can be configured to be provided in the opposite directions of the optical thin film forming apparatus or on the opposite planar positions. Naturally, the configurations described in the second to fourth embodiments and illustrated in the respective figures can be applied to this embodiment. 
       FIG. 12  is a similar cross-sectional explanatory view to  FIG. 2 , illustrating another embodiment. In this example, the beam splitters  65   a  and  65   b  and the total reflection mirror  65   c  on the emission side are disposed inside the rotating shaft  13   a . The rotating shaft  13   a  is configured to be maintained as a vacuum by disposing a vacuum magnetic shield for maintaining vacuum. A glass window is disposed on the emission side so as to prevent entrance of foreign materials and impurities. With this configuration, it is not necessary to dispose a contamination prevention shield in the respective beam splitters.