Abstract:
The problem addressed by the present invention is easily and by means of a simple configuration to form a filter layer having a different film thickness at each position. The present invention is a method for producing a variable-transmission-wavelength interference filter ( 16 ) configuring a plurality of filter units ( 28 ), and is characterized by: using a mask member ( 75 ) that is interposed between a sputtering target ( 73 ) and a light reception element array ( 15 ) and that has an aperture ratio that differs at the positions corresponding to each filter unit ( 28 ); and causing the vapor phase growth of a dielectric multi-layer film ( 16 a) on the light reception element array ( 15 ) with the mask member ( 75 ) therebetween.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a method for manufacturing an optical filter that includes a filtering layer having different film thicknesses at the respective positions thereof and integrally constitutes a plurality of filtering portions having different transmission characteristics. 
       BACKGROUND ART 
       [0002]    As such an optical filter, a variable transmission wavelength interference filter has been known in which a filtering layer (multi-layer) is deposited so as to be gradually thicker toward the arrangement direction of light-receiving elements (see Patent Document 1). In addition, as such an optical filter, a variable wavelength interference filter has been known in which a filtering layer (dielectric film) is deposited so as to be gradually thicker toward a circumferential direction on a circular substrate (see Patent Document 2). As a method for manufacturing the filter, Patent Document 2 describes a method including using a circular mask partially opened in the circumferential direction and performing vacuum deposition via the mask while rotating the mask with respect to the circular substrate. According to the manufacturing method, the rotation speed of the mask is varied to control the passing time of the opening at respective positions in the circumferential direction to change the film thickness of the filtering layer at the respective positions in the circumferential direction. 
         [0003]    [Patent Document 1] JP-A-11-142752 
         [0004]    [Patent Document 2] JP-A-2000-137114 
       DISCLOSURE OF THE INVENTION 
     Problems that the Invention is to Solve 
       [0005]    However, the configuration in which the filtering layer having different film thicknesses at the respective positions thereof is formed using the manufacturing method described in Patent Document 2 requires a driving unit that rotates or moves the mask and a control unit that controls the speed of the mask, which results in the problem that the configuration of a manufacturing apparatus becomes complicated. In addition, there is a problem with the configuration in that the size of the optical filter, which may be manufactured, is limited in terms of structure. Moreover, in such an optical filter, the film thicknesses of respective filtering portions constituting a filtering layer are preferably each uniform (i.e., the respective filtering portions are preferably stepped) as shown in  FIG. 2 . However, the configuration described above for forming the filtering layer results in the problem that controlling becomes extremely complicated. 
         [0006]    The present invention has an object of providing a method for manufacturing an optical filter by which a filtering layer having different film thicknesses at the respective positions thereof can be easily formed with a simple configuration. 
       Means for Solving the Problems 
       [0007]    The present invention provides a method for manufacturing an optical filter constituting a plurality of filtering portions, the method comprising: using a masking member that is interposed between a source for radiating a vapor deposition material and a workpiece and has different opening ratios at positions thereof corresponding to the respective filtering portions; and vapor-depositing a filtering layer on the workpiece via the masking member. 
         [0008]    According to the configuration, the masking member has the different opening ratios at the respective positions thereof. Therefore, the radiated vapor deposition material is shielded at different shielding ratios at the respective positions. This results in a difference in the deposition amount of the vapor deposition material at the respective positions. Therefore, the filtering layer having the different film thicknesses at the respective positions thereof can be formed. Thus, the filtering layer can be formed with the simple configuration free from a driving unit and a control unit. In addition, the filtering layer can be easily formed only by vapor deposition in a state in which the masking member is disposed. Particularly, the filtering layer in which the film thicknesses of the respective filtering portions are each uniform can be easily formed. Therefore, the transmission characteristics of the respective filtering portions can be secured. 
         [0009]    In this case, the masking member preferably has a masking main body and a spacer that separates the masking main body and the workpiece from each other, and the filtering layer is preferably vapor-deposited in a state in which the masking member is arranged on the workpiece. 
         [0010]    According to the configuration, a specific structure (e.g., supporting member) for disposing the masking member is not required. Therefore, the filtering layer can be formed with the simpler configuration. 
         [0011]    In this case, the spacer and the masking main body are preferably made of a SOI wafer. 
         [0012]    According to the configuration, the masking member can be easily manufactured by the use of a SOI wafer. 
         [0013]    On the other hand, the filtering layer is preferably vapor-deposited by sputtering. 
         [0014]    According to the configuration, the filtering layer is formed by sputtering. Therefore, the optical filter with a high degree of precision can be provided. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a configuration view schematically showing a spectroscope according to an embodiment; 
           [0016]      FIG. 2  is a schematic view showing a variable transmission wavelength interference filter; 
           [0017]      FIG. 3  shows a determinant for calculating an intensity distribution; 
           [0018]      FIGS. 4A to 4C  show determinants for calculating a correction matrix; 
           [0019]      FIG. 5  is a configuration view schematically showing a filter manufacturing apparatus; 
           [0020]      FIG. 6  is a plan view showing a masking member; 
           [0021]      FIG. 7  is an explanatory view showing the radiation range of a vapor deposition material radiated from a sputtering target; 
           [0022]      FIG. 8A  and  FIGS. 8B to 8E  are a cross-sectional view schematically showing the masking member and cross-sectional views schematically showing a modified example of the masking member, respectively; 
           [0023]      FIGS. 9A and 9B  are schematic views showing modified examples of the variable transmission wavelength interference filter; and 
           [0024]      FIGS. 10A and 10B  are plan views showing modified examples of a light-receiving element array. 
       
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0025]    Hereinafter, a description will be given, with reference to the accompanying drawings, of a method for manufacturing an optical filter according to an embodiment of the present invention. The embodiment exemplifies a filter manufacturing apparatus and a manufacturing method for a variable transmission wavelength interference filter to which the present invention is applied. The manufacturing apparatus manufactures the variable transmission wavelength interference filter included in a spectroscope. Therefore, the variable transmission wavelength interference filter and the spectroscope having the variable transmission wavelength interference filter will be described prior to the manufacturing apparatus. The spectroscope represents a small semiconductor package manufactured according to a semiconductor manufacturing technology. In addition, the spectroscope is of a non-mobile type and represents an analysis apparatus that measures the intensity distribution (electromagnetic spectrums of light) of 18 wavelength regions obtained by dividing a visible light region into 18 regions. That is, the spectroscope measures the intensity distribution of the wavelengths of the respective 18 colors of incident light (inspection light). 
         [0026]    As shown in  FIG. 1 , a spectroscope  1  includes an incident portion  11  having a light shielding structure that forms an incident opening  11   a,  a diffusion plate  12  that diffuses incident light from the incident opening  11   a,  a light guiding plate  13  that deflects the diffused incident light, a collimator lens array  14  that converts the deflected incident light into parallel light, a light-receiving element array  15  constituting  18  light-receiving elements  25  that receive the parallel light, a variable transmission wavelength interference filter (optical filter)  16  formed on the 18 light-receiving elements  25 , and a control unit  17  the measures the intensity distribution of respective wavelengths based on the respective output values (photoelectric current values) of the 18 light-receiving elements  25 . After being diffused by the diffusion plate  12 , the incident light from the incident opening  11   a  is deflected by the light guiding plate  13  and guided to the 18 light-receiving elements  25  via the collimator lens array  14  and the variable transmission wavelength interference filter  16 . 
         [0027]    The light-receiving element array  15  is made of a photodiode array and has a P+ substrate  21 , a P-EPI layer  22  disposed on the P+ substrate  21 , an N-EPI layer  23  formed on the P-EPI layer  22 , and a plurality of N+ layers  24  formed side by side on the N-EPI layer  23 . Thus, the light-receiving element array  15  constitutes the  18  light-receiving elements (light-receiving portions) corresponding to the N+ layers  24  arranged side by side. The respective light-receiving elements  25  convert the received incident light to obtain photoelectric current values (output values). Then, the respective light-receiving elements  25  output the photoelectric current values to the control unit  17 . 
         [0028]    As shown in  FIG. 2 , the variable transmission wavelength interference filter  16  is made of a dielectric multi-layer film (filtering layer)  16  in which high refractive materials (e.g., TiO 2 ) and low refractive materials (e.g., SiO 2 ) are alternately laminated together. The variable transmission wavelength interference filter  16  is such that the dielectric multi-layer film  16   a  is formed to be gradually thicker toward the arrangement direction of the light-receiving elements  25  and integrally constitutes 18 filtering portions  28  having different transmission peaks. That is, the dielectric multi-layer film  16   a  is formed such that the film thicknesses of the respective filtering portions  28  are each uniform. The 18 filtering portions  28  correspond to the 18 light-receiving elements  25 , respectively, and the light-receiving surfaces of the respective light-receiving elements  25  and the front surfaces of the corresponding respective filtering portions  28  are parallel to each other. Then, the 18 light-receiving elements  25  receive the incident light passing through the 18 filtering portions  28 , respectively. In addition, the 18 filtering portions  28  use the respective 18 colors described above as the transmission peaks. 
         [0029]    As shown in  FIG. 1 , the control unit  17  has a storage part  31  that stores a correction matrix and a calculation part  32  that calculates the intensity distribution based on the output values of the respective light-receiving elements  25  and the correction matrix. 
         [0030]    The storage part  31  is made of an EPROM (Erasable Programmable Read Only Memory) or the like and stores the correction matrix used to calculate the intensity distribution. The correction matrix is obtained by converting the coefficient matrix of transmission coefficients for the respective filtering portions  28  and the respective colors into an inverse matrix. The correction matrix is generated in advance by a calibration apparatus (not shown) and stored in the storage part  31 . 
         [0031]    The calculation part  32  calculates the intensity distribution of the wavelengths of the respective colors based on the output values (photoelectric current values) from the  18  light-receiving elements  25  and the correction matrix stored in the storage part  31 . Specifically, as shown in  FIG. 3 , the calculation part  32  calculates the intensity distribution (P 1 , P 2 , . . . ,P 18 ) of the wavelengths of the respective colors by multiplying the correction matrix a i,j (1≦i≦18, 1≦j≦18) by the column (l 1 , l 2 , . . . , l 18 ) of the respective photoelectric current values output from the 18 light-receiving elements  25 . 
         [0032]    As described above, in the spectroscope  1 , the storage part  31  stores the correction matrix in advance, and the 18 light-receiving elements  25  receive the incident light (inspection light) via the respective filtering portions  28 , respectively, and output the photoelectric current values to the control unit  17 . Then, the calculation part  32  calculates the wavelength intensities of the respective 18 colors based on the respective photoelectric current values output from the 18 light-receiving elements  25  and the correction matrix stored in the storage part  31 . That is, the spectroscope  1  measures the intensity distribution of the respective wavelengths. 
         [0033]    Here, the calibration processing of the spectroscope  1  will be described. The calibration processing is performed in such a way that the correction matrix of the spectroscope  1  is generated and stored in the storage part  31  of the spectroscope  1 . Specifically, first, 18 types of calibration light having different specific intensity distributions (e.g., monochromatic light having the wavelengths of the respective 18 colors described above) is generated and caused to be separately incident on the spectroscope  1  to obtain the respective output values (photoelectric current values) of the 18 light-receiving elements  25  at the incident of the light. Then, transmission coefficients for the respective filtering portions  28  and the respective 18 colors are calculated based on the respective photoelectric current values and the intensity distributions of the respective calibration light to be used as a coefficient matrix b ij (1≦i≦18, 1≦j≦18) ( FIG. 4A ). That is, with the respective incident calibration light, respective determinants shown in  FIG. 4B  are obtained. Based on the respective determinants, the respective columns of the coefficient matrix can be calculated from the respective photoelectric current values l 1 , l 2 , . . . , l 18  and the wavelength intensities P i  of the respective calibration light. Then, the calculated coefficient matrix b ij  is converted into an inverse matrix to calculate a correction matrix a ij  ( FIG. 4C ). The calculated correction matrix is stored in the storage part  31  to complete the calibration processing. 
         [0034]    Next, with reference to  FIG. 5 , the manufacturing apparatus and the manufacturing method for the variable transmission wavelength interference filter  16  will be described. The manufacturing apparatus (hereinafter referred to as a filter manufacturing apparatus  71 ) for the variable transmission wavelength interference filter  16  represents a sputtering apparatus that uses the light-receiving element array  15  as a workpiece and forms the dielectric multi-layer film  16   a  on the workpiece by sputtering. In addition, with a simple configuration, the filter manufacturing apparatus  71  is capable of easily manufacturing the dielectric multi-layer film  16   a  having different film thicknesses at the respective positions thereof by the use of a prescribed masking member  75 . 
         [0035]    As shown in  FIG. 5 , the filter manufacturing apparatus  71  includes a setting table  72  on which the light-receiving element array  15  is set, a sputtering target (source for radiating a vapor deposition material)  73  disposed opposing the setting table  72 , a magnet  74  disposed on the back surface side of the sputtering target  73 , the masking member  75  interposed between the light-receiving element array  15  and the sputtering target  73 , and a vacuum chamber  76  that accommodates the constituents described above. The masking member  75  is fixed and arranged on (the front surface of) the set light-receiving element array  15  in its positioned state and thus interposed between the light-receiving element array  15  and the sputtering target  73 . The masking member  75  is attached onto the light-receiving element array  15  by, for example, temporary crimping so as to be detachable. 
         [0036]    As shown in  FIGS. 5 and 6 , the masking member  75  includes a masking main body  81  that serves as a shielding portion and a spacer  82  that is joined to the masking main body  81  and separates the light-receiving element array  15  and the masking main body  81  from each other by a prescribed separation distance H. The masking main body  81  has opening portions  83  having different opening ratios at the positions thereof corresponding to the respective filtering portions  28  (respective light-receiving elements  25 ). The opening ratios of the respective opening portions  83  represent ratios at which the vapor deposition material radiated from the sputtering target  73  is shielded. Thus, the deposition amount of the vapor deposition material at the respective positions of the light-receiving element array  15  is adjusted, and the film thicknesses of the respective filtering portions  28  are controlled. By the control of the film thicknesses, the transmission characteristics of the respective filtering portions  28  on the respective light-receiving elements  25  are determined. For this reason, the opening ratios of the respective opening portions  83  are designed so as to suit the desired transmission characteristics of the respective filtering portions  28 . 
         [0037]    In addition, as shown in  FIG. 7 , a plate thickness T of the masking main body  81 , a separation distance L between the sputtering target  73  and the masking main body  81 , and a separation distance H between the masking main body  81  and the light-receiving element array  15  have an impact on the reaching amount and the reaching range of the vapor deposition material radiated from the sputtering target  73 . That is, the plate thickness T, the separation distance L, and the separation distance H have an impact on the deposition amount of the vapor deposition material over the entire light-receiving element array  15 . For this reason, the plate thickness T of the masking main body  81  and the height of the spacer  82  are designed based on the desired deposition amount, i.e., the desired film thickness of the vapor deposition material. 
         [0038]    Note that in the example of  FIG. 5 , the masking main body  81  is made of the SOI layer of a SOI (Silicon On Insulator) wafer, and the spacer  82  is made of the substrate layer of a SOI wafer and a BOX layer. Therefore, when the thickness of the SOI layer is represented as “T_soi,” the thickness of the substrate layer is represented as “T_sub,” and the thickness of the BOX layer is represented as “T_box,” the plate thickness T of the masking main body  81  and the separation distance H between the masking main body  81  and the light-receiving element array  15  are represented by the relationships T=T_soi and H=T_box+T_sub, respectively (see  FIG. 8A ). As described above, the masking main body  81  and the spacer  82  are made of a SOI wafer. Therefore, the masking member  75  can be easily manufactured. 
         [0039]    Note that besides the configuration shown in the example of  FIG. 5  and  FIG. 8A , the spacer  82  may be made of a BOX layer and a substrate layer thinned by back grinding or the like as shown in, for example,  FIG. 8B . In this case, when the thickness of the thinned substrate layer is represented as “T_sub&#39;,” the plate thickness T of the masking main body  81  and the separation distance H between the masking main body  81  and the light-receiving element array  15  are represented by the relationships T=T_soi and H=T_box+T_sub&#39;, respectively. 
         [0040]    In addition, as shown in, for example,  FIG. 8C , the masking main body  81  may be made of a substrate layer, and the spacer  82  may be made of a SOI layer and a BOX layer. In this case, the plate thickness T of the masking main body  81  and the separation distance H between the masking main body  81  and the light-receiving element array  15  are represented by the relationships T=T_sub and H=T_box+T_soi, respectively. 
         [0041]    Moreover, as shown in, for example,  FIG. 8D , the masking main body  81  may be made of a substrate layer thinned by back grinding or the like, and the spacer  82  may be made of a SOI layer and a BOX layer. In this case, the plate thickness T of the masking main body  81  and the separation distance H between the masking main body  81  and the light-receiving element array  15  are represented by the relationships T=T_sub&#39; and H=T_box+T_soi, respectively. 
         [0042]    Moreover, as shown in, for example,  FIG. 8E , the masking main body  81  and the spacer  82  may be made of a SOI layer. Specifically, the SOI layer is recessed to be thinned at the central area thereof so as to make the upper half portion of the SOI layer serve as the masking main body  81  and the lower half portion thereof serve as the spacer  82 . In this case, when the thickness of the thinned portion of the SOI layer is represented as “T_soi&#39;,” the plate thickness T of the masking main body  81  and the separation distance H between the masking main body  81  and the light-receiving element array  15  are represented by the relationships T=T_soi&#39; and H=T_soi−T_soi&#39;, respectively. 
         [0043]    Next, an operation for manufacturing the variable transmission wavelength interference filter  16  will be described. The operation for manufacturing the variable transmission wavelength interference filter  16  is performed in such a way that the dielectric multi-layer film  16   a  is vapor-deposited by sputtering processing on the light-receiving element array  15  via the masking member  75  in a state in which the masking member  75  is fixed and arranged on the light-receiving element array  15 . 
         [0044]    Specifically, first, the vacuum chamber  76  is brought into a vacuum state, and an Ar gas (argon gas) serving as inert gas is introduced into the vacuum chamber  76 . After that, the Ar gas is converted into plasma, and the ionized Ar ion is caused to collide with the sputtering target  73  by the magnet  74 . By the collision of the Ar ion, the atoms (vapor deposition material) of the sputtering target  73  are radiated. Then, when the radiated vapor deposition material reaches the light-receiving element array  15  via the masking member  75 , the vapor deposition material is deposited on the light-receiving element array  15  (vapor deposition). 
         [0045]    At this time, the radiated vapor deposition material is partially shielded by the masking member  75  and deposited. However, since the opening ratios of the respective opening portions  83  are different from each other, the vapor deposition material is shielded by the masking member  75  at different shielding ratios and deposited on the respective light-receiving elements  25 . That is, on the light-receiving elements  25 , the deposition film is formed to be thicker at the opening portions  83  having larger opening ratios and formed to be thinner at the opening portions  83  having smaller opening ratios. As a result, the vapor deposition material having different film thicknesses is deposited on the respective light-receiving elements  25 . This results in a difference in the film thicknesses between the respective filtering portions  28 . 
         [0046]    The sputtering processing is alternately repeatedly performed using high refractive materials and low refractive materials, whereby the stepped dielectric multi-layer film  16   a  as shown in  FIG. 2  is deposited to form the respective filtering portions  28 . Thus, the operation for manufacturing the variable transmission wavelength interference filter  16  is completed. 
         [0047]    According to the configuration described above, the masking member  75  having different opening ratios at the positions thereof corresponding to the respective filtering portions  28  is used, and the dielectric multi-layer film  16   a  is vapor-deposited via the masking member  75 . Therefore, the dielectric multi-layer film  16   a  having different film thicknesses at the respective positions thereof can be formed. Thus, the dielectric multi-layer film  16   a  can be formed with the simple configuration free from a driving unit and a control unit. In addition, the dielectric multi-layer film  16   a  can be easily formed only by vapor deposition in a state in which the masking member  75  is disposed. Moreover, the masking member  75  may be reused by washing. 
         [0048]    Further, the masking member  75  is configured to have the masking main body  81  and the spacer  82  and configured be fixed and arranged on the light-receiving element array  15 . Therefore, a specific structure (e.g., supporting member) for disposing the masking member  75  is not required, and the dielectric multi-layer film  16   a  can be formed with the simpler configuration. 
         [0049]    Note that in the embodiment, the masking member  75  is configured to be fixed and arranged on the light-receiving element array  15  (workpiece). However, the masking member  75  may be configured to be attached to the side of the sputtering target  73 . Further, the masking member  75  may be configured to be supported by a separate supporting member and interposed between the sputtering target  73  and the light-receiving element array  15 . 
         [0050]    In addition, in the embodiment, the dielectric multi-layer film  16   a  is formed to be gradually thicker toward the arrangement direction of the light-receiving elements  25 . That is, the dielectric multi-layer film  16   a  is configured such that the film thicknesses of the respective filtering portions  28  become larger in an order in which the respective filtering portions  28  are arranged. However, any other configurations may be employed so long as the film thicknesses of the respective filtering portions  28  are each uniform. As shown in, for example,  FIG. 9A , a configuration may be employed in which the film thicknesses of the filtering portions  28  are arbitrarily set irrespective of the arrangement order of the respective filtering portions  28 . That is, the configuration may be such that the filtering portions  28  having desired transmission characteristics are formed in random order. Further, as shown in  FIG. 9B , a configuration may be employed in which the thickness of the dielectric multi-layer film  16   a  is formed by the manufacturing operation described above so as to be upwardly gradually thicker toward the arrangement direction of the light-receiving elements  25 . 
         [0051]    Moreover, in the embodiment, the plurality of light-receiving elements  25  is configured to be disposed side by side (in parallel). However, any other configurations may be employed. As shown in, for example,  FIG. 10A , a configuration may be employed in which the plurality of light-receiving elements  25  is disposed in matrix form. Alternatively, as shown in, for example,  FIG. 10B , a configuration may be employed in which the plurality of light-receiving elements  25  is disposed in ring form. The configurations described above are such that the dielectric multi-layer film  16   a  is formed so as to suit the arrangements of the plurality of light-receiving elements  25 . That is, the configurations are such that the plurality of filtering portions  28  is formed in matrix and ring form so as to suit the arrangements of the plurality of light-receiving elements  25 . 
         [0052]    Furthermore, in the embodiment, the dielectric multi-layer film  16   a  is configured to be vapor-deposited by sputtering. However, a configuration may be employed in which the dielectric multi-layer film  16  is vapor-deposited by deposition. 
       REFERENCE NUMERALS 
       [0053]      15 : light-receiving element array 
         [0054]      16 : variable transmission wavelength interference filter 
         [0055]      16   a : dielectric multi-layer film 
         [0056]      28 : filtering portion 
         [0057]      73 : sputtering target 
         [0058]      75 : masking member 
         [0059]      81 : masking main body 
         [0060]      82 : spacer