Patent Publication Number: US-2007115486-A1

Title: Film forming device, and production method for optical member

Description:
The present application is a Divisional Application of U.S. application Ser. No. 10/867,631, filed Jun. 14, 2004, which is a Continuation of PCT International Application No. PCT/JP02/13168 filed on Dec. 17, 2002, which is hereby incorporated by reference. 
    
    
     SPECIFICATION  
      1. Technical Field  
      The present invention relates to a film forming apparatus for forming a film consisting of a plurality of layers on the surface of a substrate, and a method for manufacturing an optical member which has a substrate and an optical thin film consisting of a plurality of layers that is formed on the surface of this substrate.  
      2. Background Art  
      In optical members such as optical filters, lenses, and reflective mirrors, optical thin films composed of a plurality of layers are often formed on the surfaces of such optical members for the purpose of adjusting the transmissivity or reflectivity at respective wavelengths to specified characteristics, adjusting the phase characteristics at respective wavelengths to specified characteristics, or providing anti-reflection properties. The number of layers in such films may reach several tens of layers, and specified optical characteristics are obtained by controlling the thicknesses of the respective layers constituting such optical thin films. A film forming apparatus such as a sputtering apparatus and a vacuum evaporation apparatus is used to form such optical thin films and other films.  
      In conventional film forming apparatuses, a visible region optical monitor which measures the spectroscopic characteristics in wavelength regions within the visible region according to the layers that are formed in the film is mounted, and an attempt is made to obtain a film with desired characteristics that are accurately reproduced by determining the film thicknesses of the respective layers that are formed on the basis of the spectroscopic characteristics measured by this visible region optical monitor, and by causing the film thicknesses of the respective layers of stages formed up to certain intermediate layers to be reflected in the film thicknesses of layers that are subsequently formed. For example, such a technique is described in Japanese Patent Application Kokai No. 2001-174226.  
      However, in such conventional film forming apparatuses, only a visible region optical monitor is mounted as an optical monitor for measuring the spectroscopic characteristics created by the layers that are formed. As a result, various inconveniences (which will be described below) have been encountered. In the following description, a case in which an optical thin film is formed will be described as an example; however, the facts described below also apply to films other than optical thin films.  
      For example, in optical members that are used in specified wavelength regions in the infrared region, such as optical members used for optical communications, the film thicknesses of the respective layers that constitute the optical thin film become greater as a result of the fact that the use wavelength is longer. When the respective layers of such optical thin films are successively formed so that the overall film thickness of the film that is formed increases, a large and abrupt repetitive variation with respect to changes in wavelength appears in the spectroscopic characteristics (e.g., spectroscopic transmissivity characteristics) in the visible region. The reason for this is that the reflected light at the boundaries of the respective layers in the short-wavelength region is superimposed so that higher-order interference occurs, and the spectroscopic characteristics created as a result of this interference generally have a steep wavelength dependence.  
      Meanwhile, the resolution of the visible region optical monitor is determined mainly by the resolution of the spectroscope, and has the following sensitivity distribution: specifically, the light that is detected as the amount of received light at a given wavelength is not only the light of this wavelength, but also light at wavelengths in a band centered on this wavelength. Consequently, even in cases where light which has wavelength characteristics with an ideal δ function type is incident on the light receiver, the observed spectroscopic characteristics do not have a δ function type, but are blunted.  
      Accordingly, when the overall film thickness of the film that is formed increases, visible region spectroscopic characteristics in which a large and abrupt repetitive variation appears with respect to changes in wavelength should be measured “as is”; however, the spectroscopic characteristics that are actually obtained using a visible region optical monitor are blunted characteristics which show no great variation with respect to changes in wavelength. Thus, when the overall film thickness that is formed increases, the measurement precision of the visible region optical monitor drops. Accordingly, in the conventional film forming apparatuses described above, when the overall film thickness that is formed increases, it becomes impossible to determine the film thickness with good precision, and therefore becomes difficult to obtain optical thin films with desired optical characteristics that are accurately reproduced.  
      Accordingly, in the conventional film forming apparatuses described above, the respective layers are actually also formed in the same manner on a monitoring substrate (e.g., a glass substrate), which is used as a dummy substrate for the measurement of the film thickness, in addition to being formed on the substrate of the optical member that is being manufactured. The spectroscopic characteristics of the monitoring substrate are measured using a visible region optical monitor, and when the overall film thickness of the layers or number of layers formed on the monitoring substrate exceeds a specified value during film formation, the monitoring substrate is replaced with a fresh monitoring substrate. In this case, even if the overall film thickness and number of layers of the optical thin film that is formed on the original substrate are large, the layer thickness and number of layers on each monitoring substrate are limited to specified values; accordingly, the film thicknesses of the respective layers can be measured with good precision. In this case, however, since time is required for the replacement of the monitoring substrate, the productivity drops.  
      Furthermore, in the conventional film forming apparatuses described above, only a visible region optical monitor is mounted; accordingly, in cases where an optical member used in a specified wavelength region in the infrared region is manufactured, as in optical members used for optical communications or the like, the optical characteristics in this specified wavelength region (the wavelength region in which the optical member is actually used) cannot be ascertained. Consequently, in the conventional film forming apparatuses described above, in cases where an attempt is made to obtain optical thin films having desired optical characteristics with better precision in a subsequent batch by determining the set film thickness values and film formation conditions of the respective layers that are used in this subsequent batch (i.e., that are used in the film formation of subsequent optical thin films on subsequent substrates) on the basis of information obtained for the current batch (i.e., information obtained during the formation of the current optical thin films on the current substrates), only the film thicknesses of the respective layers obtained for the current batch can be used as this information; the optical characteristics of the optical member in the actual-use wavelength region cannot be utilized. Accordingly, in the conventional film forming apparatuses described above, it is difficult from this standpoint as well to obtain optical thin films having desired optical characteristics that are accurately reproduced.  
     DISCLOSURE OF THE INVENTION  
      The present invention was devised in light of such facts; the object of the present invention is to provide a film forming apparatus and an optical member manufacturing method which make it possible to solve at least one of the various problems that arise in the conventional film forming apparatuses described above.  
      The first invention that is used to achieve this object is a film forming apparatus for forming a film consisting of a plurality of layers on the surface of a substrate, this film forming apparatus comprising a first optical monitor which measures the spectroscopic characteristics arising from the formed layers in a first wavelength region, and a second optical monitor which measures the spectroscopic characteristics arising from the formed layers in a second wavelength region.  
      The second invention that is used to achieve this object is the first invention, which is characterized in that the first wavelength region is a wavelength region within the visible region, and the second wavelength region is a wavelength region within the infrared region.  
      The third invention that is used to achieve this object is the first invention, which is characterized in that the first and second wavelength regions are wavelength regions within the infrared region, and the second wavelength region is a partial wavelength region within the first wavelength region.  
      The fourth invention that is used to achieve this object is the second or third invention, which is characterized in that the second wavelength region includes a specified wavelength region in which the film is used.  
      The fifth invention that is used to achieve this object is any of the first through fourth inventions, which is characterized in that the apparatus comprises means for determining the film thicknesses of the respective layers that are formed on the basis of the spectroscopic characteristics measured by the first optical monitor or the spectroscopic characteristics measured by the second optical monitor, or both.  
      The sixth invention that is used to achieve this object is any of the first through fourth inventions, which is characterized in that the apparatus comprises means for determining the film thicknesses of the respective layers that are formed on the basis of the spectroscopic characteristics measured by the first optical monitor, and memory means for storing data indicating the spectroscopic characteristics of at least a portion of the wavelength region among the spectroscopic characteristics measured by the second optical monitor in a state in which all of the layers constituting the film have been formed.  
      The seventh invention that is used to achieve this object is the sixth invention, which is characterized in that the apparatus comprises memory means for storing data indicating the spectroscopic characteristics of at least a portion of the wavelength region among the spectroscopic characteristics measured by the second optical monitor in a state in which only some of the layers among the layers constituting the film have been formed.  
      The eighth invention that is used to achieve this object is the second invention, which is characterized in that the apparatus comprises means for determining the film thickness of the layer formed as the uppermost layer following the formation of each layer on the basis of only the spectroscopic characteristics measured by the first optical monitor or the spectroscopic characteristics measured by the second optical monitor, and these means for determining the film thickness determine the film thickness of the layer formed as the uppermost layer on the basis of only the spectroscopic characteristics measured by the first optical monitor in cases where the total thickness of the formed layers or number of formed layers is equal to or less than a specified thickness or a specified number of layers, and determine the film thickness of the layer formed as the uppermost layer on the basis of only the spectroscopic characteristics measured by the second optical monitor in cases where the total thickness of the formed layers or number of formed layers exceeds a specified thickness or a specified number of layers.  
      In this eighth invention, when a distinction between cases is made according to the total thickness (overall thickness) of the layers that are formed, it is desirable that the specified thickness described above be set as a specified value in the range of 1 μm to 10 μm (more preferably a specified value in the range of 6 μm to 10 μm). This is for reasons that will be described below.  
      It was discovered that when the film thickness of the layer formed as the uppermost layer is determined following the formation of each layer on the basis of only the spectroscopic characteristics measured by the optical monitor that measures the spectroscopic characteristics in a wavelength region within the visible region, there is a particular deterioration in the film thickness measurement precision in cases where the overall film thickness exceeds a value of approximately 10 μm. It is thought that the reason for this is that when the overall film thickness is large, variations according to wavelength in the spectroscopic transmissivity or spectroscopic reflectivity that is used to measure the film thickness become extremely severe, so that these characteristics vary greatly with only a slight variation in the wavelength. Meanwhile, the wavelength resolution of commonly used spectroscopes is approximately 0.5 nm, and if an attempt is made to measure the film thickness with a precision of approximately ±0.1 nm in regions where the film thickness exceeds a value of approximately 10 μm, the measurement precision is insufficient in the case of a spectroscope having a wavelength resolution of approximately 0.5 nm.  
      However, in optical elements that are actually used, the difference between design values and actual values must be kept at approximately ±0.02% in most cases; furthermore, the wavelength resolution of spectroscopic transmissivity meters or spectroscopic reflectivity meters that can ordinarily be obtained is approximately 0.5 nm. From this standpoint, in order to ensure a precision of ±0. 1 nm, which is the thickness measurement precision that is actually required, it has been indicated by experiment that it is necessary to keep at least the overall film thickness at 10 μm or less in cases where film thickness measurements are performed on the basis of only the spectroscopic characteristics measured by an optical monitor that measures the spectroscopic characteristics in a wavelength region that is within the visible region.  
      Meanwhile, in cases where film thickness measurements are performed on the basis of only the spectroscopic characteristics measured by an optical monitor that measures the spectroscopic characteristics in a wavelength region within the visible region, a measurement precision of ±0.1 nm can be sufficiently ensured if the overall film thickness is less than 1 μm, and there is no great drop in the measurement precision even if the overall film thickness is 1 μm or greater, but less than 6 μm.  
      Accordingly, it is desirable that the specified thickness that is used as reference for distinguishing cases be set as a specified value in the range of 1 μm to 10 μm, and it is even more desirable to set this specified thickness as a specified value in the range of 6 μm to 10 μm.  
      The ninth invention that is used to achieve the object described above is the second invention, which is characterized in that (a) the apparatus comprises means for determining the film thickness of the layer that is formed as the uppermost layer following the formation of each layer on the basis of the overall spectroscopic characteristics combining both the spectroscopic characteristics that are measured by the first optical monitor and the spectroscopic characteristics that are measured by the second optical monitor, (b) these means for determining the film thickness determine the film thickness of the layer formed as the uppermost layer by fitting the corresponding spectroscopic characteristics calculated using various assumed thicknesses of the layer formed as the uppermost layer to the overall spectroscopic characteristics, and (c) these means for determining the film thickness perform the fitting described above while giving greater weight to the spectroscopic characteristics measured by the first optical monitor than to the spectroscopic characteristics measured by the second optical monitor in cases where the overall thickness of the layers that are formed or the number of layers that are formed is equal to or less than a specified thickness or a specified number of layers, and perform the fitting described above while giving greater weight to the spectroscopic characteristics measured by the second optical monitor than to the spectroscopic characteristics measured by the first optical monitor in cases where the overall thickness of the layers that are formed or the number of layers that are formed is greater than a specified thickness or a specified number of layers.  
      In this ninth invention, when a distinction between cases is made according to the total thickness (overall thickness) of the layers that are formed, it is desirable that the specified thickness described above be set as a specified value in the range of 1 μm to 10 μm (more preferably a specified value in the range of 6 μm to 10 μm). This is for reasons similar to the reasons described in connection with the eighth invention described above.  
      The tenth invention that is used to achieve the object described above is the eighth or ninth invention, which is characterized in that the second wavelength region includes the specified wavelength region in which the film is used.  
      The eleventh invention that is used to achieve the object described above is any of the fifth through tenth inventions, which is characterized in that the apparatus comprises adjustment means for adjusting the set film thickness values of layers that are formed subsequent to at least one of the layers constituting the film on the basis of the film thickness determined for this layer by the means for determining the film thickness in a state in which this layer has been formed as the uppermost layer.  
      The twelfth invention that is used to achieve the object described above is the first invention, which is characterized in that the second wavelength region includes the specified wavelength region in which the film is used, and the apparatus comprises means for determining the film thicknesses of the respective layers that are formed, means for judging whether or not the evaluation value of the deviation between the spectroscopic characteristics in the specified wavelength region measured by the second optical monitor in a state in which only some of the layers constituting the film have been formed and the spectroscopic characteristics calculated on the basis of the film thicknesses of these same layers determined by the means for determining the film thickness is within a specified permissible range, and means for stopping the film formation of layers subsequent to these layers in cases where it is judged by the judgement means that this evaluation value is not within the specified permissible range.  
      The thirteenth invention that is used to achieve the object described above is a method for manufacturing an optical member which has a substrate and an optical thin film consisting of a plurality of layers formed on top of this substrate, this method comprising a step in which the respective layers constituting the optical thin film are successively formed on the basis of set film thickness values for these respective layers, and a step in which the film thicknesses of the respective layers that are formed are determined on the basis of the spectroscopic characteristics measured by at least one optical monitor among a first optical monitor that measures the spectroscopic characteristics arising from the formed layers in a first wavelength region and a second optical monitor that measures the spectroscopic characteristics arising from the formed layers in a second wavelength region.  
      The fourteenth invention that is used to achieve the object described above is a method for manufacturing an optical member which has a substrate and an optical thin film consisting of a plurality of layers formed on top of this substrate, this method comprising a step in which the respective layers constituting the optical thin film are successively formed on the basis of set film thickness values for these respective layers, a step in which the film thicknesses of the respective layers that are formed are determined on the basis of the spectroscopic characteristics measured by a first optical monitor that measures the spectroscopic characteristics arising from the formed layers in a first wavelength region, and a step in which the set film thickness values or film formation conditions of the respective layers constituting the next optical thin film, which are used to form this next optical thin film on the next substrate, are determined on the basis of the spectroscopic characteristics for at least a portion of the wavelength region among the spectroscopic characteristics measured by a second optical monitor that measures the spectroscopic characteristics arising from the formed layers in a second wavelength region that differs from the first wavelength region in a state in which all of the layers constituting the optical thin film have been formed.  
      The fifteenth invention that is used to achieve the object described above is a method for manufacturing an optical member which has a substrate and an optical thin film consisting of a plurality of layers formed on top of this substrate, this method comprising a step in which the respective layers constituting the optical thin film are successively formed on the basis of set film thickness values for these respective layers, a step in which the film thicknesses of the respective layers that are formed are determined on the basis of the spectroscopic characteristics measured by a first optical monitor that measures the spectroscopic characteristics arising from the formed layers in a first wavelength region, and a step in which the set film thickness values or film formation conditions of the respective layers constituting the next optical thin film, which are used to form this next optical thin film on the next substrate, are determined on the basis of the respective spectroscopic characteristics for at least a portion of the wavelength region among the respective spectroscopic characteristics measured by a second optical monitor that measures the spectroscopic characteristics arising from the formed layers in a second wavelength region that differs from the first wavelength region in a state in which only some of the layers constituting the optical thin film have been formed and in a state in which all of the layers constituting the optical thin film have been formed.  
      The sixteenth invention that is used to achieve the object described above is any of the thirteenth through fifteenth inventions, which is characterized in that the method further comprises a step in which the set film thickness values of layers that are formed subsequent to at least one of the layers constituting the optical thin film are adjusted on the basis of the film thickness determined for this layer in the step in which the film thickness is determined in a state in which this layer has been formed as the uppermost layer.  
      The seventeenth invention that is used to achieve the object described above is any of the thirteenth through sixteenth inventions, which is characterized in that the first wavelength region is a wavelength region within the visible region, and the second wavelength region is a wavelength region within the infrared region.  
      The eighteenth invention that is used to achieve the object described above is any of the thirteenth through sixteenth inventions, which is characterized in that the first and second wavelength regions are wavelength regions within the infrared region, and the second wavelength region is a partial wavelength region within the first wavelength region.  
      The nineteenth invention that is used to achieve the object described above is the seventeenth or eighteenth invention, which is characterized in that the optical thin film is used in a specified wavelength region within the infrared region, and the second wavelength region includes the specified wavelength region in which the optical thin film is used.  
      The twentieth invention that is used to achieve the object described above is a method for manufacturing an optical member which has a substrate and an optical thin film consisting of a plurality of layers formed on top of this substrate, this method comprising a step in which the optical thin film is formed on the substrate using the film forming apparatus constituting any of first through twelfth inventions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a diagram which shows in model form the rotating table of film forming apparatuses constituting respective embodiments of the present invention as seen from below.  
       FIG. 2  is a schematic sectional view which shows in model form the essential parts of film forming apparatuses constituting respective embodiments of the present invention along line A-A′ in  FIG. 1 .  
       FIG. 3  is a schematic sectional view which shows in model form the essential parts of film forming apparatuses constituting respective embodiments of the present invention along line B-B′ in  FIG. 1 .  
       FIG. 4  is a schematic sectional view which shows in model form one example of an optical member manufactured using the film forming apparatuses constituting respective embodiments of the present invention.  
       FIG. 5  is a schematic block diagram which shows the essential parts of the control system of the film forming apparatuses constituting respective embodiments of the present invention.  
       FIG. 6  is a schematic flow chart which shows one example of the operation of a film forming apparatus constituting a first embodiment of the present invention.  
       FIG. 7  is a schematic flow chart which shows the operation of a film forming apparatus constituting a second embodiment of the present invention.  
       FIG. 8  is another schematic flow chart which shows the operation of the film forming apparatus constituting a second embodiment of the present invention.  
       FIG. 9  is a diagram which shows an example of the measured spectroscopic transmissivity and the calculated spectroscopic transmissivity.  
       FIG. 10  is a diagram which shows an example of the tolerance setting of the first layer.  
       FIG. 11  is a diagram which shows an example of the tolerance setting of the fifteenth layer.  
       FIG. 12  is a diagram which shows an example of the tolerance setting of the fortieth layer.  
       FIG. 13  is a diagram which shows an example of the tolerance setting for a wavelength of 550 nm.  
       FIG. 14  is a diagram which shows an example of the tolerance setting for a wavelength of 1600 nm.  
       FIG. 15  is a diagram which shows an example of the tolerance setting in a three-dimensional depiction. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
      Preferred embodiments of the film forming apparatus and optical member manufacturing method of the present invention will be described below with reference to the figures.  
     FIRST EMBODIMENT  
       FIG. 1  is a diagram which shows in model form the rotating table of a film forming apparatus constituting a first embodiment of the present invention as seen from below.  FIG. 2  is a schematic sectional view which shows in model form the essential parts of the film forming apparatus constituting the present embodiment along line A-A′ in  FIG. 1 .  FIG. 3  is a schematic sectional view which shows in model form the essential parts of the film forming apparatus constituting the present embodiment along line B-B′ in  FIG. 1 .  FIG. 4  is a schematic sectional view which shows in model form one example of an optical member  10  manufactured using the film forming apparatus of the present embodiment.  FIG. 5  is a schematic block diagram showing the essential parts of the control system of the film forming apparatus constituting the present embodiment.  
      Before the film forming apparatus of the present embodiment is described, one example of an optical member  10  manufactured using this film forming apparatus will be described. In this example, the optical member  10  is an optical member that is used in a specified wavelength region (actual-use wavelength region) in the infrared region, as in the case of optical members used in optical communications, spacecrafts, satellites, or the like. For example, the actual-use wavelength region of the optical member  10  is 1520 nm to 1570 nm (i.e., the so-called C band).  
      This optical member  10  is constructed as an interference filter, for example, and is constructed from a substrate  11  that is a flat transparent plate (consisting of glass, etc., as this substrate), and an optical thin film  12  consisting of a plurality of layers M 1  through Mn (n is an integer of 2 or greater) that are formed on top of this substrate  11 . Of course, the optical member  10  is not limited to an interference filter, and may also be a lens, prism, mirror, or the like. For example, in the case of a lens, a glass member which has a curved surface, etc., is used as the substrate instead of the substrate  11 .  
      In the present example, the layers M 1  through Mn are alternating layers consisting of either a substance with a high refractive index (e.g., Nb 2 O 5 ) or a substance with a low refractive index (e.g., SiO 2 ), so that the optical thin film  12  is constructed from alternating layers of two different types of substances. Of course, the optical thin film  12  may also be constructed from layers consisting of three or more different types of substances.  
      Desired optical characteristics (in the following description, the desired optical characteristics are spectroscopic transmissivity characteristics; however, the desired optical characteristics are not limited to these characteristics, and may also be spectroscopic reflectivity characteristics or phase characteristics, etc.) are obtained in the optical member  10  by appropriately setting the materials, number of layers n and thicknesses of the respective layers M 1  through Mn.  
      The film forming apparatus of the present embodiment is constructed as a sputtering apparatus; as is shown in  FIGS. 1 through 3 , this sputtering apparatus comprises a vacuum chamber  1  used as a film forming chamber, a rotating table  2  which is disposed inside the vacuum chamber  1 , two sputtering sources  3  (only one of these is shown in the figures), and three optical monitors  4 ,  5  and  6 .  
      The rotating table  2  is arranged so that this table can be caused to rotate about a rotating shaft  7  by an actuator such as a motor, etc. (not shown in the figures). Substrates  11  that will constitute optical members  10 , and a monitoring substrate  21 , are attached via a holder (not shown in the figures) to the undersurface of the rotating table  2  in respective positions on a concentric circle centered on the shaft  7 . In the example shown in  FIGS. 1 through 3 , seven substrates  11  and one monitoring substrate  21  are attached to the rotating table  2 .  
      The two sputtering sources  3  are respectively disposed in two locations in the lower part of the vacuum chamber  1  which are such that these sputtering sources  3  can face the substrates  11  and  21  as the rotating table  2  rotates. In the present embodiment, particles of components that constitute the layers fly from these two sputtering sources  3 , and strike the surfaces of the substrates  11  and monitoring substrate  21 , so that layers are formed. In the present embodiment, the target materials are different in the two sputtering sources  3 , so that the substance with a high refractive index and substance with a low refractive index (described above) respectively fly from the two sputtering sources  3 .  
      For example, the monitoring substrate  21  consists of a transparent flat plate such as a glass substrate. Since flat substrates are used as the substrates of the optical members  10  as described above, the same substrates are used as the substrates  11  and monitoring substrate  21 . The monitoring substrate  21  is a dummy substrate used for film thickness measurement (i.e., a substrate that does not ultimately become an optical member  10 ); the thicknesses of the films that are formed on top of the substrates  11  under the same conditions are indirectly measured by measuring the thickness of the film that is formed on the surface of this monitoring substrate  21 . Depending on the case, it may not be absolutely necessary to use such a monitoring substrate  21 . However, in cases where the surfaces of the optical members  10  are curved surfaces, as when the optical members  10  are lenses, accurate measurement of the film thickness on such surfaces is difficult; accordingly, it is desirable to use a monitoring substrate  21 .  
      As is shown in  FIGS. 2 and 3 , three windows  14   b ,  15   b  and  16   b  are formed in the upper surface of the vacuum chamber  1 , and three windows  14   a ,  15   a  and  16   a  are formed in the lower surface of the vacuum chamber  1 . The pair of windows  14   a  and  14   b  are disposed so that these windows are located on either side of a specified position through which the substrates  11  and  21  pass as the rotating table  2  rotates. Another pair of windows  15   a  and  15   b , as well as the other pair of windows  16   a  and  16   b , are also similarly disposed.  
      The optical monitor  4  is constructed from a light emitting device  4   a  and a light receiving device  4   b  which splits and receives the light that is emitted from the light emitting device  4   a  and that passes through the window  14   a , substrate  11  or monitoring substrate  21 , and window  14   b ; this optical monitor  4  is arranged so that it can measure the spectroscopic transmissivity of the film formed on the surface of the substrate  11  or monitoring substrate  21 . Similarly, the optical monitor  5  is constructed from a light emitting device  5   a  and a light receiving device  5   b  which splits and receives the light that is emitted from the light emitting device  6   a  and that passes through the window  15   a , substrate  11  or monitoring substrate  21 , and window  15   b , and this optical monitor  5  is also arranged so that it can measure the spectroscopic transmissivity of the film formed on the surface of the substrate  11  or monitoring substrate  21 . Similarly, the optical monitor  6  is constructed from a light emitting device  6   a  and a light receiving device  6   b  which splits and receives the light that is emitted from the light emitting device  6   a  and that passes through the window  16   a , substrate  11  or monitoring substrate  21 , and window  16   b , and this optical monitor  6  is also arranged so that it can measure the spectroscopic transmissivity of the film formed on the surface of the substrate  11  or monitoring substrate  21 .  
      The optical monitor  4  is constructed so that it measures the spectroscopic transmissivity in a specified wavelength region in the visible region, e.g., 400 nm to 850 nm. The optical monitor  5  is constructed so that this optical monitor measures the spectroscopic transmissivity in a specified wavelength region in the infrared region, e.g., 1000 nm to 1700 nm. The optical monitor  6  is constructed so that this optical monitor measures the spectroscopic transmissivity in the actual-use wavelength region of the optical members  10  (this corresponds to the wavelength region described as the “specified wavelength region in which the film is used” in the sections titled “Claims” and “Disclosure of the Invention”), e.g., 1520 nm to 1570 nm. The respective optical monitors  4  through  6  are specially constructed for the respective measurement wavelength regions.  
      In the present embodiment, since the measurement wavelength region of the optical monitor  5  includes the actual-use wavelength region of the optical members  10 , which is the measurement wavelength region of the optical monitor  6 , the actual-use wavelength region of the optical members  10  can also be measured by the optical monitor  5 . Accordingly, it would be possible to omit the optical monitor  6  and to combine the function of the optical monitor  6  with the optical monitor  5 . However, if the optical monitors  5  and  6  are separately constructed as in the present embodiment, the resolution of the optical monitor  6  can be increased compared to the resolution of the optical monitor  5  since the measurement wavelength region of the optical monitor  6  is narrower than the measurement wavelength region of the optical monitor  5 . Accordingly, the spectroscopic transmissivity in the actual-use wavelength region can be measured with a high resolution, which is advantageous. Conversely, in cases where the spectroscopic transmissivity in the actual-use wavelength region of the optical members  10  can be used to determine the film thicknesses of the respective layers, it would be possible to omit the optical monitor  5  and to use the optical monitor  6  as a film thickness monitor as well.  
      In the following description, for the sake of convenience, the optical monitor  4  will be called the “visible region optical monitor,” the optical monitor  5  will be called the “film thickness measurement infrared monitor,” and the optical monitor  6  will be called the “actual-use wavelength region infrared monitor.” 
      As is shown in  FIG. 5 , the film forming apparatus of the present embodiment comprises a control and calculation processing part  17  constructed from (for example) a computer, which controls the overall apparatus and performs specified calculations and the like in order to realize the operation described below, an operating part  18  which is used by the user to input instructions and data, etc., into the control and calculation processing part  17 , and a display part  19  such as a CRT. The control and calculation processing part  17  has an internal memory  20 . Of course, it would also be possible to use an external memory instead of this internal memory  20 . Furthermore, like other universally known film forming apparatuses, the film forming apparatus of the present embodiment also comprises a pump which is used to place the interior of the vacuum chamber  1  in a vacuum state, a gas supply part which supplies specified gases to the interior of the vacuum chamber  1 , and the like. However, a description of these parts is omitted.  
      Nest, one example of the operation of the film forming apparatus of the present embodiment will be describe with reference to  FIG. 6 .  FIG. 6  is a schematic flow chart which shows one example of the operation of the film forming apparatus of the present embodiment.  
      Film formation is initiated in a state in which substrates  11  and a monitoring substrate  21  on which no films have yet been formed are attached to the rotating table  2 .  
      First, the user performs initial settings by operating the operating part  18  (step S 1 ). In these initial settings, setting information is input which sets the measurement mode of the film thickness monitoring optical measurements performed in step S 4  described below as either the visible region measurement mode (a mode in which film thickness monitoring optical measurements are performed by the visible region optical monitor  4 ) or the infrared region measurement mode (a mode in which film thickness monitoring optical measurements are performed by the film thickness measurement infrared monitor  5 ). Furthermore, in these initial settings, the set film thickness values, materials, number of layers n, film formation conditions, and the like for the respective layers M 1  through Mn are input which are such that the desired optical characteristics of the optical member  10  can be obtained, and which are predetermined according to advance design or the like.  
      Moreover, it would also be possible to provide the control and calculation processing part  17  with a design function for the optical thin film  12  so that when the user inputs the desired optical characteristics, the control and calculation processing part  17  automatically determines the set film thickness values, materials, number of layers n, film formation conditions, and the like of the respective layers M 1  through Mn in accordance with this design function. Furthermore, in these initial settings, setting information indicating the layer of film formation at which the optical measurement of the actual-use wavelength region is to be performed in step S 6  (described later), etc., is also input.  
      For example, the selection of this layer may be set as all of the layers M 1  through Mn, or may be set as only the uppermost layer Mn; alternatively, the selection may be set as the uppermost layer Mn and one or more other arbitrary layers (e.g., at every specified number of layers). A setting may also be used in which no layer is selected, and the optical measurement of the actual-use wavelength region in step S 6  is not performed for any layer; at the minimum, however, it is desirable to select the uppermost layer Mn.  
      Next, the control and calculation processing part  17  sets a count value m which indicates the number of the current layer as counted from the side of the substrate  11  at  1  (step S 2 )  
      Then, under the control of the control and calculation processing part  17 , the film formation of the mth layer is performed (e.g., by time control) on the basis of the set film thickness value and film formation conditions, etc., set for this layer (step S 3 ). In the case of the first layer M 1 , film formation is performed on the basis of the set film thickness value that has been set in step S 1 . However, in the case of the second or subsequent layers, if the set film thickness value has been adjusted in step S 9  (described later), film formation is performed on the basis of the most recently adjusted set film thickness value. During film formation, the rotating table  2  is caused to rotate, and only the shutter (not shown in the figures) disposed facing the sputtering source  3  that corresponds to the material of the mth layer is opened, so that particles from this sputtering source  3  are deposited on the respective substrates  11  and monitoring substrate  21 . When the film formation of the mth layer is completed, this shutter is closed.  
      Subsequently, under the control of the control and calculation processing part  17 , film thickness monitoring optical measurements are performed in the measurement mode that has been set in step S 1  (step S 4 ).  
      In cases where the visible region measurement mode is set in step Si, the spectroscopic transmissivity of the monitoring substrate  21  or substrate  11  in the specified wavelength region within the visible region described above is measured by the visible region optical monitor  4  in step S 4 , and this data is stored in the memory  20  in association with the current count value m. Measurements by the visible region optical monitor  4  are performed when the monitoring substrate  21  or substrate  11  in question is positioned between the light emitting device  4   a  and light receiving device  4   b  in a state in which the rotating table  2  is rotating, or are performed with the rotating table  2  stopped in a state in which the monitoring substrate  21  or substrate  11  is positioned between the light emitting device  4   a  and light receiving device  4   b.    
      On the other hand, in cases where the infrared region measurement mode is set in step S 1 , the spectroscopic transmissivity of the monitoring substrate  21  or substrate  11  in the specified wavelength region within the infrared region described above is measured by the film thickness measurement infrared monitor  5 , and this data is stored in the memory  20  in association with the current count value m. Measurements by the film thickness measurement infrared monitor  5  are performed when the monitoring substrate  21  or substrate  11  in question is positioned between the light emitting device  5   a  and light receiving device  5   b  in a state in which the rotating table  2  is rotating, or are performed with the rotating table  2  stopped in a state in which the monitoring substrate  21  or substrate  11  is positioned between the light emitting device  6   a  and light receiving device  5   b.    
      Basically, in step S 4 , the spectroscopic transmissivity characteristics of either the monitoring substrate  21  or substrate  11  may be measured in either measurement mode. Furthermore., for each layer, the spectroscopic transmissivitv characteristics of either the monitoring substrate  21  or substrate  11  may be arbitrarily set beforehand by the user as the spectroscopic transmissivity characteristics that are measured.  
      When the film thickness monitoring optical measurements performed in step S 4  are completed, the control and calculation processing part  17  judges whether or not the actual-use wavelength region optical measurements of step S 6  are to be performed when film formation has been performed up to the current mth layer (i.e., in the state in which the mth layer has been formed as the uppermost layer) (step S 5 ), on the basis if the setting information that has been set in step S 1 . If it is judged that the actual-use wavelength region optical measurements are not to be performed, the processing proceeds directly to step S 7 , while if it is judged that the actual-use wavelength region optical measurements are to be performed, the processing proceeds to step S 7  after passing through step S 6 .  
      In step S 6 , the spectroscopic transmissivity of the monitoring substrate  21  or substrate  11  in the actual-use wavelength region described above is measured by the actual-use wavelength region infrared monitor  6 , and this data is stored in the memory  20 . Measurements by the actual-use wavelength region infrared monitor  6  are performed when the substrate  11  is positioned between the light emitting device  6   a  and light receiving device  6   b  in a state in which the rotating table  2  is rotating, or are performed with the rotating table  2  stopped in a state in which the substrate  11  is positioned between the light emitting device  6   a  and light receiving device  6   b.    
      In step S 7 , the control and calculation processing part  17  determines the film thickness of the current mth layer on the basis of the spectroscopic transmissivity characteristics measured in step S 6 . In regard to the actual procedure that is used to determine the film thickness from the spectroscopic transmissivity characteristics, various types of publicly known procedures, or fitting similar to that performed in steps S 30  and S 31  (shown in  FIG. 7  described later), may be employed.  
      Next, the control and calculation processing part  17  judges whether or not m=n, i.e., whether or not film formation has been completed up to the final layer Mn (step S 8 ). If this film formation has not been completed, the set film thickness values for the layers from the (m+1)th layer on (i.e., the layers that have not yet been formed) are adjusted and optimized on the basis of the respective film thicknesses determined in step S 6  for each layer up to the mth layer so that the optical characteristics of the optical member  10  that will ultimately be obtained are adjusted to the desired optical characteristics (step S 9 ). For example, such optimization can be performed using various types of publicly known procedures. The set film thickness values for the layers from the (m+1)th layer on that are adjusted in this step S 9  are used in step S 3  when the layers from the (m+1)th layer on are formed. Following the adjustment performed in step S 9 , the count value m of the number of layers is increased by 1 (step S 10 ), and the processing returns to step S 3 .  
      On the other hand, if it is judged in step S 8  that film formation up to the final layer Mn has been completed, the spectroscopic transmissivity characteristics in the actual-use wavelength region measured in each step S 6 , and the film thicknesses of the respective layers determined in each step S 7 , which are stored in the memory  20 , are displayed on the display part  19  along with the associated count values m (information indicating which layer was formed as the uppermost layer at the time that the data was obtained), and if necessary, this data is output to an external personal computer, etc. (step S 11 ); with this, the formation of the optical thin film  12  on the substrate  11  is completed.  
      Optical members  10  can be manufactured in this manner.  
      Furthermore, on the basis of the film thicknesses of the respective layers and the spectroscopic transmissivity characteristics in the actual-use wavelength region that are displayed or output in step S 11 , the user determines the set film thickness values and film formation conditions of the respective layers that are to be set in step S 1  when the next optical thin film  12  is formed on the next substrate  11  (from a comparison of the above data with the initial set film thickness values of the respective layers and desired optical characteristics of the optical member  10 ) so that optical characteristics that are closer to the desired optical characteristics can be obtained when the next optical thin film  12  is formed on the next substrate  11 . When the next optical thin film  12  is formed on the next substrate  11 , the set film thickness values and film formation conditions of the respective layers thus determined are set in step S 1 .  
      Thus, in the present embodiment, feedback in which information that is obtained when the optical thin film  12  is formed on the current substrate  11  is reflected in the set film thickness values and film formation conditions for the respective layers that are set in step S 1  when the next optical thin film  12  is formed on the next substrate  11  can be performed via the user.  
      However, it is also possible to automate the processing by endowing the control and calculation processing part  17  with such a feedback function. In this case, for example, a look-up table or the like which shows the correspondence between the information that is obtained when the optical thin film  12  is formed on the current substrate  11  and the set film thickness values and film formation conditions for the respective layers that are to be initially set when the next optical thin film  12  is formed on the next substrate  11  may be constructed beforehand, and the system may be constructed so that the control and calculation processing part  17  performs the feedback described above by referring to this look-up table or the like.  
      The various advantages described below can be obtained in the present embodiment.  
      To describe the first advantage, in the present embodiment, regardless of which measurement mode is set as the measurement mode of the film thickness monitoring optical measurements performed in step S 4 , if the layer that determines the timing of the measurement of the optical characteristics in the actual-use wavelength region within the infrared region in step S 6  is set as the uppermost layer Mn in step S 1 , the spectroscopic transmissivity characteristics (in the actual-use wavelength region within the infrared region) of the optical member  10  having the entire optical thin film  12  finally formed are measured in step S 6 ; accordingly, feedback can be performed in which this information is reflected in the film formation of the next optical thin film  12  on the next substrate  11 . Consequently, an optical thin film  12  which has desired optical characteristics that are more accurately reproduced can be obtained. In particular, if the layer that determines the timing of the measurement of the optical characteristics in the actual-use wavelength region is set not only as the uppermost layer Mn, but also as one or more other layers, the spectroscopic transmissivity characteristics in the actual-use wavelength region in a stage in which the film has been formed up to the point of an intermediate layer are also measured, and feedback can be performed in which this information is also reflected in the film formation of the next optical thin film  12  on the next substrate  11 .  
      In this case, an optical thin film  12  which has desired optical characteristics that are reproduced much more accurately can be obtained. Furthermore, in the present embodiment, since an actual-use wavelength region infrared monitor  6  is installed separately from the film thickness measurement infrared monitor  5 , the characteristics in the actual-use wavelength region can be measured with an extremely high resolution. Accordingly, this is advantageous in that an optical thin film  12  which has desired optical characteristics that can be reproduced much more accurately can be obtained from this standpoint as well.  
      On the other hand, in a conventional film forming apparatus, since only a visible region optical characteristic monitor is mounted, the optical characteristics of the optical member  10  in the actual-use wavelength region within the infrared region cannot be measured, so that the feedback of information in the actual-use wavelength region as described above is completely impossible.  
      Secondly, in the present embodiment, if the measurement mode of the film thickness monitoring optical measurements that are performed in step S 4  is set as the infrared region measurement mode, then the film thickness monitoring optical measurements are performed by the film thickness monitoring infrared monitor  5  as described above, and the film thicknesses of the respective layers are determined from the spectroscopic characteristics in the infrared region obtained by these measurements. Since the wavelengths in the infrared region are longer than the wavelengths in the visible region, a large and abrupt repetitive variation with respect to changes in wavelength is less likely to appear in the infrared region than in the visible region, even if the total film thickness or number of layers formed is large.  
      Accordingly, in the present embodiment, if the measurement mode is set as the infrared region measurement mode, even if the total film thickness or number of layers formed is large, the film thicknesses of the respective layers can be determined with greater precision than in cases where the film thicknesses of the respective layers are determined from the spectroscopic characteristics in the visible region as in a conventional film forming apparatus; consequently, it is possible to obtain an optical thin film  12  with desired optical characteristics that are accurately reproduced. Thus, since the film thicknesses of the respective layers can be precisely measured in cases where the measurement mode is set as the infrared region measurement mode even if the total film thickness or number of layers formed is large, the need to replace the monitoring substrate  21  during film formation can be completely eliminated, or the frequency of such replacement can be reduced even if the total film thickness of the optical thin film  12  is large; consequently, the productivity is greatly improved.  
      In cases where the need to replace the monitoring substrate  21  is completely eliminated, if the substrate  11  that constitutes the optical member  10  is (for example) a flat plate, the spectroscopic characteristics of the substrate  11  may be measured by the film thickness monitoring infrared monitor  5 . In this case, since there is no need to use a monitoring substrate  21 , the productivity can be further improved.  
      Thirdly, in the present embodiment, if the measurement mode of the film thickness monitoring optical measurements that are performed in step S 4  is set as the visible region measurement mode, then the film thickness monitoring optical measurements are performed by the visible region monitor  4  as described above, and the film thicknesses of the respective layers are determined from the spectroscopic characteristics in the visible region obtained by these measurements. Accordingly, in cases where the total film thickness or number of layers of the optical thin film  12  is large, the monitoring substrate  21  must be replaced during film formation as in a conventional film forming apparatus in order to obtain the film thicknesses of the respective layers with good precision. Consequently, this embodiment of the film forming apparatus of the present invention is comparable to a conventional film forming apparatus in terms of productivity. However, since the wavelengths in the visible region are shorter than the wavelengths in the infrared region, the spectroscopic characteristics in the visible region can be measured with good sensitivity compared to the spectroscopic characteristics in the infrared region in cases where the total film thickness or number of layers formed is small.  
      Accordingly, if the measurement mode is set as the visible region measurement mode, although the productivity is inferior to that obtained when the measurement mode is set as the infrared region measurement mode in cases where the total film thickness or number of layers of the optical thin film  12  is large, the film thicknesses of the respective layers can be obtained with greater precision, so that an optical thin film  12  which has desired optical characteristics that can be reproduced with greater accuracy can be obtained. Of course, this advantage that is obtained in case where the measurement mode is set as the visible region measurement mode is an advantage that is also obtained in the conventional film forming apparatus described above. However, in the visible region measurement mode of the present embodiment, this advantage is obtained simultaneously with the first advantage describe above; accordingly, the technical significance of this advantage is extremely high.  
     SECOND EMBODIMENT  
       FIGS. 7 and 8  are schematic flow charts which illustrate the operation of a film forming apparatus constituting a second embodiment of the present invention.  
      The film forming apparatus constituting the present embodiment differs from the film forming apparatus constituting the first embodiment described above only in the following respect: namely, in the first embodiment described above, the control and calculation processing part  17  is constructed so that the operation shown in  FIG. 6  described above is realized, while in the present embodiment, the control and calculation processing part  17  is constructed so that the operation shown in  FIGS. 7 and 8  is realized. In all other respects, the film forming apparatus of the present embodiment is the same as that of the first embodiment described above. Here, therefore, the operation shown in  FIGS. 7 and 8  will be described; since other descriptions are redundant, such other descriptions will be omitted.  
      Film formation is initiated in a state in which the substrates  11  and monitoring substrate  21  on which no films have yet been formed are attached to the rotating table  2 .  
      First, the user performs initial settings by operating the operating part  18  (step S 21 ). In these initial settings, setting information indicating whether the film thickness determination mode is set as the mode using one wavelength region or the mode using both wavelength regions is input. Here, the term “film thickness determination mode” refers to the system used to determine the film thickness of the layer formed as the uppermost layer at the point in time in question. Furthermore, the term “mode using one wavelength region” refers to a system in which the film thickness of this layer is determined with only one type of spectroscopic transmissivity value among the spectroscopic transmissivity values measured by the visible region optical monitor  4  and the spectroscopic transmissivity values measured by the film thickness measurement infrared monitor  5  being selectively used as the measurement data. Moreover, the term “mode using both wavelength regions” refers to a system in which the film thickness of this layer is determined using both the spectroscopic transmissivity values measured by the visible region optical monitor  4  and the spectroscopic transmissivity values measured by the film thickness measurement infrared monitor  5 . Furthermore, the same film thickness determination mode is used for all of the layers M 1  through Mn.  
      Furthermore, in the initial settings in step S 21 , a tolerance Ti corresponding to each of the layer numbers m is set which is used in the mode using both wavelength regions. This point will be described in detail later.  
      Furthermore, in the initial settings in step S 21 , the set film thickness values, materials, numbers of layers n, film formation conditions, and the like for the respective layers M 1  through Mn are input which are such that the desired optical characteristics of the optical member  10  can be obtained, and which are predetermined according to advance design or the like. Moreover, it would also be possible to provide the control and calculation processing part  17  with a design function for the optical thin film  12  so that the control and calculation processing part  17  automatically determines the set film thickness values, materials, numbers of layers n, film formation conditions, and the like for the respective layers M 1  through Mn by means of this design function when the user inputs the desired optical characteristics.  
      Furthermore, in the initial settings in step S 21 , setting information indicating the layer of film formation at which the actual-use wavelength region optical measurements of step S 27  (described later) are to be performed (and the like) is also input. In the selection of this layer, for example, one or more arbitrary layers other than the uppermost layer Mn (e.g., layers separated by a specified number of layers) may be selected, the uppermost layer Mn and one or more other arbitrary layers may be selected, or all of the layers M 1  through Mn may be selected. Furthermore, the uppermost layer Mn alone may be selected, or a setting may be used in which no layer is selected, so that the actual-use wavelength region optical measurements of step S 27  are not performed for any of the layers. However, it is desirable to select at least one layer other than the uppermost layer Mn.  
      Next, the control and calculation processing part  17  sets a count value m which indicates the number of the current layer (i.e., the layer number) as counted from the side of the substrate  11  at  1  (step S 22 ).  
      Next, under the control of the control and calculation processing part  17 , the film formation of the mth layer is performed (for example) using time control on the basis of the set film thickness values and film formation conditions, etc., that were set for this layer (step S 23 ). In the case of the first layer M 1 , the layer is formed on the basis of the set film thickness value that was set in step S 21 ; however, in the case of layers from the second layer on, if the set film thickness value has been adjusted in step S 39  (described later), the layer is formed on the basis of the most recently adjusted set film thickness value. During film formation, the rotating table  2  is caused to rotate, and only the shutter (not shown in the figures) installed facing the sputtering source  3  corresponding to the material of the mth layer is opened, so that particles from this sputtering source  3  are deposited on the respective substrates  11  and monitoring substrate  21 . When the film formation of the mth layer is completed, this shutter is closed.  
      Subsequently, under the control of the control and calculation processing part  17 , the spectroscopic transmissivity of the monitoring substrate  21  or substrates  11  in the specified wavelength region within the visible region described above is measured by the visible region optical monitor  4 , and this data is stored in the memory  20  in association with the current count value m (step S 24 ). The measurements performed by the visible region optical monitor  4  are performed when the monitoring substrate  21  or substrate  11  in question is positioned between the light emitting device  4   a  and light receiving device  4   b  in a state in which the rotating table  2  is rotating, or with the rotating table  2  stopped in a state in which the monitoring substrate  21  or substrate  11  is positioned between the light emitting device  4   a  and light receiving device  4   b.    
      Next, under the control of the control and calculation processing part  17 , the spectroscopic transmissivity of the monitoring substrate  21  or substrate  11  in question in the specified wavelength region within the infrared region described above is measured by the film thickness measurement infrared monitor  5 , and this data is stored in the memory  20  in association with the current count value m (step S 25 ). The measurements performed by the film thickness measurement infrared monitor  5  are performed when the monitoring substrate  21  or substrate  11  in question is positioned between the light emitting device  6   a  and light receiving device  5   b  in a state in which the rotating table  2  is rotating, or with the rotating table  2  stopped in a state in which the monitoring substrate  21  or substrate  11  is positioned between the light emitting device  5   a  and light receiving device  5   b.    
      Next, on the basis of the setting information set in step S 21 , the control and calculation processing part  17  judges whether or not the actual-use wavelength region optical measurements of step S 27  are to be performed at the point in time at which film formation has been performed up to the current mth layer (i.e., in a state in which the mth layer has been formed as the uppermost layer) (step S 26 ). If it is judged that the actual-use wavelength region optical measurements are not to be performed, the processing proceeds directly to step S 28 ; if it is judged that the actual-use wavelength region optical measurements are to be performed, the processing proceeds to step S 28  after passing through step S 27 .  
      In step S 27 , the spectroscopic transmissivity of the monitoring substrate  21  or substrate  11  in the actual-use wavelength region described above is measured by the actual-use wavelength region infrared monitor  6 , and this data is stored in the memory  20 . The measurements performed by the actual-use wavelength region infrared monitor  6  are performed when the substrate  11  in question is positioned between the light emitting device  6   a  and light receiving device  6   b  in a state in which the rotating table  2  is rotating, or with the rotating table  2  stopped in a state in which the substrate  11  is positioned between the light emitting device  6   a  and light receiving device  6   b.    
      In step S 28 , the control and calculation processing part  17  judges whether the film thickness determination mode set in step S 21  is the mode using one wavelength region or the mode using both wavelength regions. If this mode is the mode using one wavelength region, the processing proceeds to step S 29 ; if the mode is the mode using both wavelength regions, the processing proceeds to step S 32 .  
      In step S 29 , the control and calculation processing part  17  judges whether or not the total film thickness of the layers from the first through mth layers is less than 10 μm. However, since the film thickness of the mth layer has not yet been determined at this point in time, the judgement of step S 29  is performed with the sum of the respective film thicknesses of the layers from the first through (m−1)th layers that have already been determined in step S 30  or step S 31  and the set film thickness value for the mth layer taken as the total film thickness of the layers from the first through mth layers.  
      The judgement reference value used in step S 29  is not limited to 10 μm; it is desirable to set this value as a specified value in the range of 1 μm to 10 μm, and it is even more desirable to set this value as a specified value in the range of 6 μm to 10 μm. The reasons for setting these values has already been described. Instead of judging the total film thickness in step S 29 , it would also be possible to judge the number of layers that have been formed up to the current time (i.e., the count value). In cases where a judgement is made on the basis of the number of layers, the approximate total film thickness can be calculated from the number of layers since the film thickness per layer shows no great variation.  
      Accordingly, a procedure in which the number of layers that produces a specified total film thickness is calculated, and the judgement reference value in step S 29  is set on the basis of this number of layers, is also included in the scope of the present invention. If the total film thickness is less than 10 μm, the processing proceeds to step S 30 , and if the total film thickness is 10 μm or greater, the processing proceeds to step S 31 .  
      In step S 30 , the control and calculation processing part  17  determines the film thickness of the mth layer using only the spectroscopic transmissivity in the visible region measured in step S 24 , without using the spectroscopic transmissivity in the infrared region measured in step S 25  by fitting the corresponding spectroscopic transmissivity calculated with the thickness of the mth layer assumed as various values to this measured spectroscopic transmissivity in the visible region.  
      Here, the corresponding spectroscopic transmissivity is the spectroscopic transmissivity of a multi-layer film model (thin film model) comprising layers from the first through mth layers. In the calculation of the spectroscopic transmissivity of this multi-layer film model, the film thicknesses that have already been determined in step S 30  or step S 31  are used as the respective film thicknesses of the layers from the first through (m−1)th layers. When step S 30  is completed, the processing proceeds to step S 34 .  
      Here, one example of the spectroscopic transmissivity in the infrared region measured in step S 25  is shown as the measured transmissivity in  FIG. 9 . Furthermore, the spectroscopic transmissivity calculated with the film thickness of the uppermost layer assumed to be a certain thickness (corresponding to the measured transmissivity) is shown as the calculated transmissivity in  FIG. 9 . In the example shown in  FIG. 9 , since the assumed film thicknesses show a considerable deviation from the actual film thicknesses, there is a considerable deviation between the measured spectroscopic transmissivity and the calculated spectroscopic transmissivity.  
      In the fitting of the calculated spectroscopic transmissivity to the measured spectroscopic transmissivity, an evaluation value which evaluates the deviation between the respective values (or conversely, the degree of fitting) is calculated. This evaluation value is calculated for each film thickness with the film thickness of the mth layer assumed as various values. Furthermore, the film thickness that is assumed when the evaluation value (among all of the evaluation values) that shows the smallest deviation (the minimum value in the case of the merit value MF described later) is calculated is determined to be the film thickness of the mth layer. This is the concrete content of the fitting processing.  
      In the present embodiment, a merit value MF based on a merit function is used as the evaluation value that is used in the fitting of step S 30 . Of course, it goes without saying that evaluation values that can be used are not limited to such a merit value MF. The definition of this merit value MF is shown in the following  
               Equation   ⁢           ⁢       (   1   )     .       ⁢                                   MF   =         1   N     ⁢       ∑     i   =   1     N     ⁢       (         Q   i   target     -     Q   i   calc         T   i       )     2                   (   1   )             
 
      In Equation (1), N is the total number of targets (total number of transmissivity values at respective wavelengths in the measured transmissivity characteristics). i is a number corresponding to the wavelength in a one-to-one correspondence, and is a number that is attached to quantities relating to a certain wavelength. This number may have any value from 1 to N. Q target  is the transmissivity value in the measured transmissivity characteristics. Q calc  is the transmissivity value in the calculated transmissivity characteristics. T is the tolerance (the reciprocal of this value is generally called the weighting factor).  
      When Equation (1) is applied in step S 30 , Q target     1    through Q target     N    in Equation (1) are the transmissivity values in the spectroscopic transmissivity in the visible region measured in step S 24 . Furthermore, in the present embodiment, in cases where the merit value MF is used in step S 30 , the tolerance values Ti (i is 1 through N) are all set at 1, and none of the data of the respective transmissivity values is weighted, so that these sets of data are all treated equally.  
      Referring again to  FIG. 7 , in step S 31 , the control and calculation processing part  17  determines the film thickness of the mth layer using only the spectroscopic transmissivity in the infrared region measured in step S 25 , without using the spectroscopic transmissivity in the visible region measured in step S 24 , by fitting the corresponding spectroscopic transmissivity that is calculated with the thickness of the mth layer assumed as various values to this measured spectroscopic transmissivity in the infrared region. In the present embodiment, the processing of step S 31  is the same processing as the processing of step S 30 , except for the fact that the spectroscopic transmissivity in the infrared region measured in step S 25  is used instead of the spectroscopic transmissivity in the visible region measured in step S 24 . When Equation (1) is applied in step S 31 , Q target     1    through Q target     N    in Equation (1) are the transmissivity values in the spectroscopic transmissivity in the infrared region measured in step S 25 . When step S 31  is completed, the processing proceeds to step S 34 .  
      In cases where the film thickness determination mode set in step S 21  is the mode using both wavelength regions, the control and calculation processing part  17 , in step S 32 , determines the tolerance Ti corresponding to the current layer number m (this layer number m indicates the number of layers currently formed) from the tolerances set in step S 21 .  
      Subsequently, in step S 33 , the control and calculation processing part  17  determines the film thickness of the mth layer using the overall spectroscopic transmissivity that combines both the spectroscopic transmissivity in the visible region measured in step S 24  and the spectroscopic transmissivity in the infrared region measured in step S 25 , by fitting the corresponding spectroscopic transmissivity calculated with the thickness of the mth layer assumed as various values to this measured overall spectroscopic transmissivity. When step S 33  is completed, the processing proceeds to step S 34 .  
      In the present embodiment, the merit value MF is used as the evaluation value in the fitting of step S 33  as well. When Equation (1) is applied in step S 33 , Q target     1    through Q target     N    in Equation (1) are the transmissivity values in the spectroscopic transmissivity in the visible region measured in step S 24  and the transmissivity values in the spectroscopic transmissivity in the infrared region measured in step S 25 .  
      In steps S 30  and S 31 , the tolerance values Ti (i is 1 through N) were all set at 1, so that none of the data of the respective transmissivity values was weighted. In step S 33 , on the other hand, the tolerance values Ti determined in step S 32  are used, and the data of the respective transmissivity values is weighted by appropriately setting the tolerance Ti for each of the layer numbers m in step S 21 . In the present embodiment, in cases where the number of layers m currently formed is equal to or less than a specified number of layers, the tolerance Ti for each of the number of layers m is set in step S 21  so that fitting is performed in step S 33  with a greater emphasis on the spectroscopic transmissivity in the visible region measured in step S 24  than on the spectroscopic transmissivity in the infrared region measured in step S 25 , and in cases where the number of layers m currently formed is greater than this specified number of layers, the tolerance Ti for each of the number of layers m is set in step S 21  so that fitting is performed in step S 33  with a greater emphasis on the spectroscopic transmissivity in the infrared region measured in step S 25  than on the spectroscopic transmissivity in the visible region measured in step S 24 . Here, the term “emphasis” refers to weighting of the data of the evaluation value described above. In cases where the evaluation value is the merit value MF, this refers to a relative reduction of the tolerance.  
      Here, a concrete example of the setting of the tolerance Ti for each of the number of layers m in step S 21  will be described in combination with a description of the significance of the tolerance setting.  
      In the concrete example described below, the wavelength range of the overall transmissivity characteristics obtained by the visible region optical monitor  4  and film thickness measurement infrared monitor  5  is 400 nm to 1750 nm. The tolerance in the merit function (Equation (1)) that is used when the film thickness is determined by fitting to the transmissivity characteristics thus obtained is positively controlled. Since the tolerance can be set for the transmissivity characteristics values at each wavelength, relative reduction of the tolerance means that it is desired to increase the degree of fitting to the measured value of the transmissivity at the wavelength in question. Conversely, a relative increase in the tolerance means that the degree of fitting to the measured value of the transmissivity at the wavelength in question may be relatively poor.  
      For example, in cases where the total film thickness of the multi-layer film on the monitoring substrate  21  or substrate  11  is not very large, the visible region transmissivity characteristics obtained by the visible region optical monitor  4  are emphasized; accordingly, the tolerance in the visible region is reduced to a tolerance that is smaller than the tolerance in the infrared region. As the total film thickness of the multi-layer film on the monitoring substrate  21  or substrate  11  increases, the tolerance in the visible region is increased, and the tolerance in the infrared region is reduced. By proceeding in this way, it is possible to suppress the error that is caused mainly by the resolution of the optical monitor, so that film formation can be continued without causing a drop in the precision of film thickness determination.  
      Values that varied linearly with wavelength were used as the set tolerance values in a case where a 41-layer film in which the thicknesses of all of the layers were more or less the same was actually formed on the monitoring substrate  21  (the layer film thickness was approximately 15 microns). The tolerance settings for the first layer, fifteenth layer and fortieth layer are shown in  FIGS. 10, 11  and  12 , respectively. Furthermore, the tolerance setting for the layer number at a wavelength of 550 nm is shown in  FIG. 13 , and the tolerance setting for the layer number at a wavelength of 1600 nm is shown in  FIG. 14 .  
       FIG. 15  is a diagram in which these tolerance settings are shown comprehensively in three dimensions. By varying the first-order slope of the tolerance vs. wavelength as the layers progress, it is possible to change from an emphasis on the visible region transmissivity characteristics to an emphasis on the infrared region transmissivity characteristics in the determination of the film thickness as the total film thickness of the multi-layer film on the monitoring substrate  21  increases. The linear variation of the tolerance shown here is merely one example; in regard to the manner of this variation, it goes without saying that the tolerance can be varied in the most appropriate form in accordance with the film construction of the multi-layer film and the conditions of the optical monitors, etc.  
      Returning again to the description in the flow chart, the control and calculation processing part  17  judges in step S 34  whether or not the actual-use wavelength region optical measurements of step S 27  have already been performed at the time that the film was formed up to the current mth layer (i.e., in a state in which the mth layer was formed as the uppermost layer). In cases where the actual-use wavelength region optical measurements have been performed, the processing proceeds to step S 35 ; in cases where the actual-use wavelength region optical measurements have not been performed, the processing proceeds to step S 38 .  
      In step S 35 , the control and calculation processing part  17  calculates the evaluation value of the deviation between the spectroscopic transmissivity in the actual-use wavelength region measured in step S 27  and the corresponding spectroscopic transmissivity that has been calculated. Here, the corresponding spectroscopic transmissivity is the spectroscopic transmissivity of a multi-layer film model (thin film model) comprising layers from the first through mth layers. In the calculation of the spectroscopic transmissivity of this multi-layer film model, the film thicknesses already determined in steps S 30 , S 31  or S 33  are used as the respective film thicknesses of the layers from the first through mth layers.  
      For example, the merit value MF can be used as the evaluation value that is calculated in step S 35 . In cases where the merit value MF is used as this evaluation value, since weighting has no particular meaning, the tolerance values Ti (i is 1 through N) may all be set at 1. When Equation (1) is applied in step S 34 , Q target     1    through Q target     N    in Equation (1) are the transmissivity values in the spectroscopic transmissivity in the actual-use wavelength region measured in step S 27 .  
      Subsequently, the control and calculation processing part  17  judges whether or not the evaluation value calculated in step S 35  is within the permissible range (step S 36 ). If this value is within the permissible range, the processing proceeds to step S 38 . On the other hand, if this value is not within the permissible range, the spectroscopic transmissivity characteristics in the actual-use wavelength region measured in each step S 27 , and the film thicknesses of the respective layers determined in each step S 30 , S 31  and S 33 , which are stored in the memory  20  are displayed on the display part  19  along with the associated count values m (information indicating which layer was formed as the uppermost layer at the time of this data). If necessary, furthermore, this data is output to an external personal computer or the like (step S 37 ), and film formation is stopped. Accordingly, even if the mth layer is an intermediate layer, the film formation of the layers from the (m+1)th layer on is not performed.  
      In cases where film formation is thus stopped at an intermediate point, the user appropriately adjusts (for example) the refractive index dispersion data constituting one of the conditions of the multi-layer film model calculated in steps S 30 , S 31  and S 33 , and forms the next optical thin film  12  on the next substrate  11 .  
      In step S 38 , the control and calculation processing part  17  judges whether or not m=n, i.e., whether or not film formation has been completed up to the final values of the layers from the (m+1)th layer on (layers that have not yet been formed) are adjusted and optimized on the basis of the respective film thicknesses of the layers up to the mth layer determined in steps S 30 , S 31  or S 33  for each layer so that the optical characteristics of the optical member  10  that is ultimately obtained are the desired optical characteristics (step S 39 ). For example, such optimization can be accomplished using various universally known procedures. The set film thickness values of the layers from the (m+1)th layer on that are adjusted in step S 39  are used in step S 23  in the film formation of the layers from the (m+1)th layer on. Following the adjustment of step S 39 , the count value m of the number of layers is increased by  1  (step S 40 ), and the processing returns to step S 23 .  
      On the other hand, in cases where it is judged in step S 38  that film formation has been completed up to the final layer Mn, the formation of the optical thin film  12  on the substrate  11  in question is completed after processing similar to that of step S 37  is performed in step S 41 .  
      An optical member  10  can be manufactured in this manner.  
      In the present embodiment, advantages similar to those of the first embodiment are obtained; in addition, the following advantages can also be obtained:  
      In the present embodiment, in the case of mode using one wavelength region, the film thicknesses of the respective layers are determined on the basis of the spectroscopic transmissivity in the visible region measured by the visible region optical monitor  4  when the total film thickness is less than 10 μm, and are determined on the basis of the spectroscopic transmissivity in the infrared region measured by the film thickness measurement infrared monitor  5  when the total film thickness is 10 μm or greater. Since the wavelengths in the infrared region are longer than the wavelengths in the visible region, a large and abrupt repetitive variation with respect to changes in wavelength is less likely to appear in the infrared region than in the visible region even if the total film thickness or number of layers formed is large. Accordingly, in the present embodiment, if the measurement mode is set as the infrared region measurement mode, the film thicknesses of the respective layers can be determined with greater precision than is possible in cases where the film thicknesses of the respective layers are determined from the spectroscopic characteristics in the visible region as in a conventional film forming apparatus, even if the total film thickness or number of layers formed is large. Consequently, an optical thin film  12  with desired optical characteristics that are accurately reproduced can be obtained. Thus, since the film thicknesses of the respective layers can be precisely measured even if the total film thickness or number of layers formed is large, the need to replace the monitoring substrate  21  during film formation can be completely eliminated, or the frequency of such replacement can be reduced even if the total film thickness of the optical thin film  12  is large; consequently, the productivity can be greatly improved. In cases where the need to replace the monitoring substrate  21  is completely eliminated, the spectroscopic characteristics of the substrate  11  that constitutes the optical member  10  can also be measured by means of the film thickness monitoring infrared monitor  5  if this substrate  11  is (for example) a flat plate. In this case, there is no need to use a monitoring substrate  21 , accordingly, the productivity can be increased even further.  
      Furthermore, in the present embodiment, in the case of the mode using both wavelength regions, fitting is performed with a greater emphasis on the spectroscopic transmissivity in the visible region measured by the visible region optical monitor  4  than on the spectroscopic transmissivity measured by the film thickness measurement infrared monitor  5  in cases where the number of layers formed is equal to or less than a specified number of layers, and fitting is performed with a greater emphasis on the spectroscopic transmissivity measured by the film thickness measurement infrared monitor  5  than on the spectroscopic transmissivity measured by the visible region optical monitor  4  in cases where the number of layers formed is greater than this specified number of layers.  
      Accordingly, advantages that are basically the same as those obtained in the case of the mode using one wavelength region are also obtained in the case of the mode using both wavelength regions. In the case of the mode using both wavelength regions, unlike the case of the mode using one wavelength region, there is no complete switching between the use of the spectroscopic transmissivity in the visible region and the use of the spectroscopic transmissivity in the infrared region; instead, the contributions of both regions can be freely varied by appropriately setting the tolerance. Accordingly, the film thicknesses can be determined with higher precision in the case of the mode using both wavelength regions than in the case of the mode using one wavelength region.  
      Furthermore, in the present embodiment, the processing of steps S 35  and S 36  is performed, and in cases where the evaluation value of the deviation between the spectroscopic transmissivity in the actual-use wavelength region and the corresponding spectroscopic transmissivity that is calculated is outside a permissible range, film formation is performed only up to an intermediate layer, and the film formation of the remaining layers is stopped. Accordingly, in the present embodiment, a check can be made at an intermediate stage in the film formation of the multi-layer film in order to ascertain if the performance of the optical multi-layer film that will ultimately be obtained has no prospect of satisfying the performance requirements. In cases where there is no prospect that these requirements will be satisfied, the wasteful formation of the remaining layers up to the final layer can be avoided Accordingly, the production efficiency can be greatly improved by using the present invention.  
      Respective embodiments of the present invention were described above. However, the present invention is not limited to these embodiments.  
      For example, it would also be possible to modify the first embodiment so that only the infrared measurement mode described above is always performed. In this case, the visible region optical monitor  4  can be eliminated.  
      Furthermore, it would also be possible to modify the first embodiment so that only the visible region measurement mode described above is always performed. In this case, the film thickness monitoring infrared monitor  5  can be eliminated.  
      Moreover it would also be possible to modify the second embodiment so that only the mode using one wavelength region or only the mode using both wavelength regions is always performed.  
      Furthermore, in the second embodiment, it would also be possible to devise the system so that tolerance values Ti are set for respective total film thicknesses in step S 21  in  FIG. 7 , and the tolerance value Ti corresponding to the total film thickness is determined in step S 32 .  
      In addition, in the first and second embodiments, the optical monitors  4  through  6  were all monitors that measure the spectroscopic transmissivity. However, at least one of the optical monitors  4  through  6  may be an optical monitor that measures the spectroscopic reflectivity.  
      Furthermore, the first and second embodiments were examples of a sputtering apparatus. However, the present invention may also be applied to other film forming apparatuses such as vacuum evaporation apparatuses.  
     INDUSTRIAL APPLICABILITY  
      The film forming apparatus of the present invention can be used to form optical thin films and the like. Furthermore, the optical member manufacturing method of the present invention can be used to manufacture optical members that have optical thin films.