Abstract:
A method for real-time monitoring thin film deposition using a dynamic interferometer is revealed. An optical monitoring extracting the temporal phase change of the reflection coefficient of the deposition film stacks. The dynamic interferometer, which gets rid of the influence of vibration and air turbulence, was used in the method to directly detect fluctuating phase of a deposition film stack. Combing with the reflectance or transmittance measurements, the real-time reflection coefficient under normal incidence of monitoring light can be found as well as optical admittance for enhancing the error compensation of the thin film deposition.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of Invention 
         [0002]    The present invention relates to a method for optical monitoring deposition and, in particular, to a method for monitoring thin film deposition using dynamic Interferometer. 
         [0003]    2. Related Art 
         [0004]    The optical monitoring method is generally thought better than other methods to manufacture optical filters, and for a costly optical filter manufacture, more precise optical monitor is necessary. 
         [0005]    In a deposition thin film stack, the refractive indices of materials usually change so that suitable thickness of each layer would not be the same as what we expected in the original design; hence the termination point of each thin film layer needs to be revised. However, the conventional monitoring methods never analytically solve this problem. In the most conventional monitor system for coating deposition, only the transmittance and reflectance are measured. The deposition of quarter-wave film stack is usually terminated when the transmittance or reflectance locus reaches a local extreme value. However, the signal near the extreme value changes little with respect to increased thickness, and th extreme value e monitoring sensitivity is low. Among most methods, the turning points of extreme value are used to estimate the termination point of deposition in each layer. Some other monitoring methods, such as ellipsometry and broadband spectrum monitoring, use some computing algorithm to obtain optical constant by fitting the measurements, since the measurement includes too many parameters and they are hard to be solved analytically. There is no clearer rule to terminate the deposition through these monitors. 
         [0006]    In this invention, a novel optical monitoring system is proposed to obtain the reflection coefficient, equivalent optical admittance, refractive index, and thickness of deposition film stacks analytically instead of applying numerical fitting. It provides higher precision in monitoring and more accurate error compensations. It helps the operator control the depositions more clearly, reduce the misjudgments of termination point of deposition, and improve the yield efficiency. 
       SUMMARY OF THE INVENTION 
       [0007]    The purpose of this invention is to provide a novel method for monitoring thin film deposition. By using a new-type polarization interferometer, the phase and magnitude of the reflection coefficients of monitoring light normally reflected from the deposition films can be acquired in real time, and the physical property changes of thin films can also be analytically found. 
         [0008]    This invention employs the dynamic interferometry to process monitor for thin film growth. It can provide reflection coefficient loci or equivalent optical admittance loci to do monitor and the corresponding error compensations. The change in thickness and refractive index can also be known for non-absorption films. For the termination points near the left cross point of the real axis, a phase shift of pi can be added on the measured phase, and recalculate the optical admittance in order to increase the sensitivity in monitoring. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The invention will become more fully understood from the detailed description given herein below illustration only, and thus is not limitative of the present invention, and wherein: 
           [0010]      FIG. 1  is a schematic diagram showing the monitoring device according to one preferred embodiment of the invention; 
           [0011]      FIG. 2  is a diagram showing the polarizer distribution on pixelated phase mask camera according to one preferred embodiment of the invention; 
           [0012]      FIG. 3  is a diagram showing the normal incident light reflections inside the substrate according to one preferred embodiment of the invention; and 
           [0013]      FIG. 4  is a flow chart according to one preferred embodiment of the invention. 
       
    
    
       [0014]    Attachment  1  is a diagram showing a phase shift of pi on the reflection phase and re-calculate the corresponding optical admittance. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    The present invention will be apparent from the following detailed description, which proceeds with reference to the accompanying drawings, wherein the same references relate to the same elements. 
         [0016]    Referring to  FIG. 1 , a thin-film monitor device  1  is set outside of a coater  12 , and is connected with a coater chamber  100 . The thin-film monitoring device  1  includes a light source  103 , a collimator  104 , a dynamic interferometer  10 , an imaging lens  115 , a pixelated phase mask camera  116 , a photo detector  120  and a processing unit  122 , wherein the photo detector  120  disposed in the coater chamber  100 , and a substrate  14  is also disposed in the coater chamber  100 . The dynamic interferometer  10  is combined by a Fizeau polarization interferometer  101  and a Twyman-Green interferometer  102  preferably, but the present invention is not limited to the embodiment. The Fizeau polarization interferometer  101  includes a beam splitter  113 , a quarter-wave plate  114 . The Twyman-Green interferometer  102  includes a polarizer  105 , a polarization beam splitter (PBS)  106 , two quarter-wave plates  107 ,  108 , two mirrors  109 ,  110 . 
         [0017]    The monitor system is set up outside the coater chamber  100 . A Fizeau polarization interferometer  101  combining with a pixelated phase mask camera  116  is used to extract the optical phase, as shown in  FIG. 1 . After the light is emitted from the light source  103 , it is then collimated by a collimator  104 . The collimated light will pass through a polarizer  105 , which is used to adjust the intensity ratio between the two orthogonally polarized lights. The polarization beam splitter (PBS)  106  will separate the two orthogonally polarized lights to different arms in the Twyman-Green interferometer  102 . The two quarter-wave plates  107 ,  108  placed around the polarization beam splitter  106  were oriented to convert S to P polarized beam reflected from one mirror  109  and P to S polarized reflected from the other mirror  110 , respectively. The lights come from two arms will be combined together again and go to the Fizeau cavity, that is our substrate. In our case, test surface  111  locates at the side where the thin film grows, and the other side of substrate is the reference surface  112 . The reflected light will be directed to a quarter-wave plate by the beam splitter  113 . 
         [0018]    The quarter-wave plate  114  in front of the camera is oriented to convert two polarized beams coming from two arms of interferometer into two orthogonally circular polarization states. This quarter-wave plate  114  will make the reflection coefficient phase of thin films be derived from arctangent function of measured intensities rather than arccosine form. It provides higher sensitivity than the case without quarter-wave plate. 
         [0019]    The lights go to the camera after passed through the imaging lens  115 . The camera  116  has CCD array where each pixel has a polarizer on it, as shown in  FIG. 2 . Let the test beam be left circularly polarized with a phase of φ L  and the reference beam be right circularly polarized with a phase of φ R . Further, let both beams be incident upon a linear polarizer oriented at an angle α with respect to the polarization direction of the reference beam. After passing through the polarizer, both the test and reference beams are linearly polarized at an angle α and a phase offset of +α has been added to the test beam, whereas a phase offset of −α has been added to the reference beam. The two beams are now collinear and will interfere to give an intensity pattern in accordance with: 
         [0000]        I=I   L   +I   R −2√{square root over ( I   L   I   R  )}cos(Φ+2α)  (1)
 
         [0000]    where Φ(x, y)=φ L −I L  and I R  are the intensities of left and right circle polarized beams. 
         [0020]    The linear polarizer acts as a phase shifting device between the two beams, were the phase shift, 2α, is equal to twice the orientation angle of the polarizer. 
         [0021]    The adjacent pixels on the camera have different orientation polarizer on them as shown in  FIG. 2 . There might be four different polarizers in a unit,  201 ,  202 ,  203 ,  204 , and the unit is distributed periodically in the CCD array. There were four different polarizers at 0°, 45°, −45°, 90°, respectively, on the camera, and they generate four different phase shifted interferograms at once for phase shifting algorithm. The phases can be thereby calculated by phase shifting algorithm simultaneously. 
         [0022]    The rays are drawn spatially separate and with a slight slant in the sketch,  FIG. 3 , but are all normal to the surface and collinear in the monitoring system. The numbers within the cavity indicate the number of test surface reflections of each beam has passed before it exited the cavity. 
         [0023]    Only the paired beams that are path matched and drawn in the same type of lines will interfere with each other, since the light has short coherence length. If we carefully adjust the translation stage of one arm of the Twyman-Green interferometer and let the distance to PBS  105  of the two mirrors  109 ,  110  have a difference of the optical thickness of substrate. Each successive reflection of the s-polarized beam off of the test surface is coherent with the p-polarized beam that has undergone one additional test surface reflection. Only the beam pair in which they undergo almost the same path lengths will have observable interference fringes; others will be suppressed due to low coherence. 
         [0024]    The path matched S 0  and P 1 , and S 1  and P 2 , etc. are drawn with the same type of lines (e.g. dashed line for S 0  and P 1 , dotted line for S 1  and P 2 ). The measured intensity can be presented as: 
         [0000]    
       
         
           
             
               
                 
                   
                     I 
                     = 
                     
                       
                         I 
                         
                           P 
                            
                           
                               
                           
                            
                           0 
                         
                       
                       + 
                       
                         I 
                         
                           S 
                            
                           
                               
                           
                            
                           0 
                         
                       
                       + 
                       
                         2 
                          
                         
                           
                             
                               I 
                               
                                 S 
                                  
                                 
                                     
                                 
                                  
                                 0 
                               
                             
                              
                             
                               I 
                               
                                 P 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                           
                         
                          
                         cos 
                          
                         
                             
                         
                          
                         ϕ 
                       
                       + 
                       
                         I 
                         
                           P 
                            
                           
                               
                           
                            
                           2 
                         
                       
                       + 
                       
                         I 
                         
                           S 
                            
                           
                               
                           
                            
                           1 
                         
                       
                       + 
                       
                         2 
                          
                         
                           
                             
                               I 
                               
                                 S 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                              
                             
                               I 
                               
                                 P 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                             
                           
                         
                          
                         cos 
                          
                         
                             
                         
                          
                         ϕ 
                       
                       + 
                       … 
                       + 
                       
                         I 
                         
                           P 
                            
                           
                               
                           
                            
                           n 
                         
                       
                       + 
                       
                         I 
                         
                           Sn 
                           - 
                           1 
                         
                       
                       + 
                       
                         2 
                          
                         
                           
                             
                               I 
                               Pn 
                             
                              
                             
                               I 
                               
                                 Sn 
                                 - 
                                 1 
                               
                             
                           
                         
                          
                         cos 
                          
                         
                             
                         
                          
                         ϕ 
                       
                     
                   
                    
                   
                     
 
                   
                    
                   
                       
                   
                    
                   
                     
                       If 
                        
                       
                           
                       
                        
                       n 
                     
                     → 
                     ∞ 
                   
                    
                   
                     
 
                   
                    
                   
                     I 
                     = 
                     
                       
                         
                           ( 
                           
                             
                               I 
                               S 
                             
                             + 
                             
                               I 
                               P 
                             
                           
                           ) 
                         
                          
                         
                           ( 
                           
                             
                               R 
                               r 
                             
                             + 
                             
                               
                                 
                                   
                                     ( 
                                     
                                       1 
                                       - 
                                       
                                         R 
                                         r 
                                       
                                     
                                     ) 
                                   
                                   2 
                                 
                                  
                                 
                                   R 
                                   t 
                                 
                               
                               
                                 1 
                                 - 
                                 
                                   
                                     R 
                                     r 
                                   
                                    
                                   
                                     R 
                                     t 
                                   
                                 
                               
                             
                           
                           ) 
                         
                       
                       + 
                       
                         2 
                          
                         
                           ( 
                           
                             1 
                             - 
                             
                               R 
                               r 
                             
                           
                           ) 
                         
                          
                         
                           
                             
                               I 
                               S 
                             
                              
                             
                               I 
                               P 
                             
                           
                         
                          
                         
                           
                             
                               R 
                               r 
                             
                              
                             
                               R 
                               t 
                             
                           
                         
                          
                         
                           ( 
                           
                             
                               ( 
                               
                                 1 
                                 - 
                                 
                                   R 
                                   r 
                                 
                               
                               ) 
                             
                             
                               1 
                               - 
                               
                                 
                                   R 
                                   r 
                                 
                                  
                                 
                                   R 
                                   t 
                                 
                               
                             
                           
                           ) 
                         
                          
                         cos 
                          
                         
                             
                         
                          
                         ϕ 
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where R r  and R t  are the reflectance from the reference and test surfaces, respectively. φ is the phase difference between the two beams in each interfering beam pair. 
         [0025]    The reflection phase of growing films coming from the test surface can be acquired by 4-step phase-shifting algorism in a single camera frame to freeze vibration effect: 
         [0000]    
       
         
           
             
               
                 
                   Φ 
                   = 
                   
                     arctan 
                      
                     
                       [ 
                       
                         
                           
                             I 
                             
                               
                                 - 
                                 45 
                               
                                
                               ° 
                             
                           
                           - 
                           
                             I 
                             
                               45 
                                
                               ° 
                             
                           
                         
                         
                           
                             I 
                             
                               0 
                                
                               ° 
                             
                           
                           - 
                           
                             I 
                             
                               90 
                                
                               ° 
                             
                           
                         
                       
                       ] 
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where Φ is the desired phase. 
         [0026]    The obtained data in several frames should be averaged to erase the air turbulence influence. 
         [0027]    Although the optical phase can be calculated in real-time and the distance between reference and test surface, that is the substrate thickness, should remain the same during coating process, the mechanical vibration of two mirrors in Twyman-Green can cause different tilts and shifts from time to time that will change the path difference between reference and test beams and influence the accuracy of calculated phase results. One part on the substrate test surface should be blocked and remain uncoated as a reference area. Since the beam coming from the reference area and tested film area pass through common path, the vibration effect can be cancel by subtracting the phase difference between the reference area and the monitored area before the deposition from that after the deposition; then the pure reflection phase of films can be acquired. 
         [0028]    There is a photo-detector placed under the coater to receive the transmitted light intensity change. The magnitude of the reflection coefficient, square root of the reflectance, can be further acquired. The reflectance can be measured by the camera and Eq. (2). 
         [0029]    After reflectance magnitude and phase are acquired, the reflection coefficient at normal incidence of light is known and optical admittance can be calculated by following relation: 
         [0000]    
       
         
           
             
               
                 
                   
                     γ 
                      
                     
                         
                     
                      
                     
                        
                       
                          
                          
                         
                             
                         
                          
                         θ 
                       
                     
                   
                   = 
                   
                     
                       
                         n 
                         0 
                       
                       - 
                       
                         ( 
                         
                           α 
                           + 
                           
                              
                              
                             
                                 
                             
                              
                             β 
                           
                         
                         ) 
                       
                     
                     
                       
                         n 
                         0 
                       
                       + 
                       
                         ( 
                         
                           α 
                           + 
                           
                              
                              
                             
                                 
                             
                              
                             β 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where γ and θ are the magnitude and phase of the reflection coefficient, and n 0  is the refractive index of the incident medium. 
         [0030]    In our case, the incident medium is substrate. Therefore, n 0  is equal to the refractive index of the substrate n s . α and β are given by follows. 
         [0000]    
       
         
           
             
               
                 
                   
                     α 
                     = 
                     
                       
                         
                           n 
                           s 
                         
                          
                         
                           ( 
                           
                             1 
                             - 
                             
                               γ 
                               2 
                             
                           
                           ) 
                         
                       
                       
                         1 
                         + 
                         
                           γ 
                           2 
                         
                         + 
                         
                           2 
                            
                           
                               
                           
                            
                           γ 
                            
                           
                               
                           
                            
                           cos 
                            
                           
                               
                           
                            
                           θ 
                         
                       
                     
                   
                   , 
                   
                     β 
                     = 
                     
                       
                         
                           - 
                           2 
                         
                          
                         
                             
                         
                          
                         
                           n 
                           s 
                         
                          
                         γ 
                          
                         
                             
                         
                          
                         sin 
                          
                         
                             
                         
                          
                         θ 
                       
                       
                         1 
                         + 
                         
                           γ 
                           2 
                         
                         + 
                         
                           2 
                            
                           
                               
                           
                            
                           γ 
                            
                           
                               
                           
                            
                           cos 
                            
                           
                               
                           
                            
                           θ 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
         [0031]    For non-absorption films, refractive index and thickness variation at every moment can also be calculated. 
         [0032]    The optical admittance can be written down as: 
         [0000]    
       
         
           
             
               
                 
                   
                     α 
                     + 
                     
                        
                        
                       
                           
                       
                        
                       β 
                     
                   
                   = 
                   
                     
                       
                          
                          
                         
                             
                         
                          
                         n 
                          
                         
                             
                         
                          
                         sin 
                          
                         
                             
                         
                          
                         δ 
                       
                       + 
                       
                         
                           ( 
                           
                             
                               α 
                               E 
                             
                             + 
                             
                                
                                
                               
                                   
                               
                                
                               
                                 β 
                                 E 
                               
                             
                           
                           ) 
                         
                          
                         cos 
                          
                         
                             
                         
                          
                         δ 
                       
                     
                     
                       
                         cos 
                          
                         
                             
                         
                          
                         δ 
                       
                       + 
                       
                         
                           
                             ( 
                             
                               
                                  
                                  
                                 
                                     
                                 
                                  
                                 
                                   α 
                                   E 
                                 
                               
                               - 
                               
                                 β 
                                 E 
                               
                             
                             ) 
                           
                           n 
                         
                          
                         sin 
                          
                         
                             
                         
                          
                         δ 
                       
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where α E  and β E  are the real and imaginary part of the equivalent optical admittance of previously deposited film. δ is the optical phase thickness of newly deposited thin film, n is the corresponding refractive index. 
         [0033]    The solutions of Eq. (6) are: 
         [0000]    
       
         
           
             
               
                 
                   δ 
                   = 
                   
                     arctan 
                     [ 
                     
                       ± 
                       
                         ( 
                         
                           
                             
                               
                                 ( 
                                 
                                   α 
                                   - 
                                   
                                     α 
                                     E 
                                   
                                 
                                 ) 
                               
                                
                               
                                 ( 
                                 
                                   
                                     
                                       α 
                                       2 
                                     
                                      
                                     
                                       α 
                                       E 
                                     
                                   
                                   - 
                                   
                                     α 
                                      
                                     
                                         
                                     
                                      
                                     
                                       α 
                                       E 
                                       2 
                                     
                                   
                                   + 
                                   
                                     
                                       α 
                                       E 
                                     
                                      
                                     
                                       β 
                                       2 
                                     
                                   
                                   - 
                                   
                                     α 
                                      
                                     
                                         
                                     
                                      
                                     
                                       β 
                                       E 
                                       
                                         2 
                                         ) 
                                       
                                     
                                   
                                 
                                 ) 
                               
                             
                           
                           
                             
                               
                                 α 
                                 E 
                               
                                
                               β 
                             
                             + 
                             
                               α 
                                
                               
                                   
                               
                                
                               
                                 β 
                                 E 
                               
                             
                           
                         
                         ] 
                       
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
             
               
                 
                   
                       
                   
                    
                   
                     n 
                     = 
                     
                       ± 
                       
                         ( 
                         
                           
                             
                               
                                 ( 
                                 
                                   α 
                                   - 
                                   
                                     α 
                                     E 
                                   
                                 
                                 ) 
                               
                                
                               
                                 ( 
                                 
                                   
                                     
                                       α 
                                       2 
                                     
                                      
                                     
                                       α 
                                       E 
                                     
                                   
                                   - 
                                   
                                     α 
                                      
                                     
                                         
                                     
                                      
                                     
                                       α 
                                       E 
                                       2 
                                     
                                   
                                   + 
                                   
                                     
                                       α 
                                       E 
                                     
                                      
                                     
                                       β 
                                       2 
                                     
                                   
                                   - 
                                   
                                     α 
                                      
                                     
                                         
                                     
                                      
                                     
                                       β 
                                       E 
                                       
                                         2 
                                         ) 
                                       
                                     
                                   
                                 
                                 ) 
                               
                             
                           
                           
                             α 
                             - 
                             
                               α 
                               E 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
         [0034]    We should always choose the set of answer whose n and δ are positive. Thus, the complete information about reflection coefficient, optical admittance, refractive index and actual thickness of the growing film stack at every moment can be observed through this optical monitor system. 
         [0035]    The monitoring sensitivity of monitoring of reflection coefficient or optical admittance loci, that is change amount per unit of optical phase thickness, should be analyzed in two parts, since the loci move in both two orthogonal directions, directions along the real and imaginary axis as thin film grows. The below equations show the sensitivities of optical admittance locus. Sensitivity X and Sensitivity Y represent sensitivities for real and imaginary parts of optical admittance, respectively. 
         [0000]    
       
         
           
             
               
                 
                   
                     Sensitivity 
                      
                     
                         
                     
                      
                     
                       X 
                       ( 
                       
                         S 
                         X 
                       
                       ) 
                     
                   
                   = 
                   
                      
                     
                       
                         α 
                         ( 
                         
                           
                             
                               ( 
                               
                                 
                                   2 
                                    
                                   
                                       
                                   
                                    
                                   cos 
                                    
                                   
                                       
                                   
                                    
                                   δ 
                                 
                                 - 
                                 
                                   2 
                                    
                                   
                                     β 
                                     n 
                                   
                                    
                                   sin 
                                    
                                   
                                       
                                   
                                    
                                   δ 
                                 
                               
                               ) 
                             
                              
                             
                               ( 
                               
                                 
                                   sin 
                                    
                                   
                                       
                                   
                                    
                                   δ 
                                 
                                 + 
                                 
                                   
                                     β 
                                     n 
                                   
                                    
                                   cos 
                                    
                                   
                                       
                                   
                                    
                                   δ 
                                 
                               
                               ) 
                             
                           
                           - 
                           
                             
                               
                                 α 
                                 2 
                               
                               
                                 n 
                                 2 
                               
                             
                              
                             sin 
                              
                             
                                 
                             
                              
                             2 
                              
                             
                                 
                             
                              
                             δ 
                           
                         
                         ) 
                       
                       
                         
                           ( 
                           
                             
                               
                                 ( 
                                 
                                   
                                     cos 
                                      
                                     
                                         
                                     
                                      
                                     δ 
                                   
                                   - 
                                   
                                     
                                       β 
                                       n 
                                     
                                      
                                     sin 
                                      
                                     
                                         
                                     
                                      
                                     δ 
                                   
                                 
                                 ) 
                               
                               2 
                             
                             + 
                             
                               
                                 
                                   α 
                                   2 
                                 
                                 
                                   n 
                                   2 
                                 
                               
                                
                               
                                 sin 
                                 2 
                               
                                
                               δ 
                             
                           
                           ) 
                         
                         2 
                       
                     
                      
                   
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
             
               
                 
                   
                     Sensitivity 
                      
                     
                         
                     
                      
                     
                       Y 
                       ( 
                       
                         S 
                         Y 
                       
                       ) 
                     
                   
                   = 
                   
                      
                     
                       
                         
                           
                             
                               
                                 
                                   
                                     
                                       ( 
                                       
                                         
                                           n 
                                           2 
                                         
                                         - 
                                         
                                           ( 
                                           
                                             
                                               α 
                                               2 
                                             
                                             + 
                                             
                                               β 
                                               2 
                                             
                                           
                                           ) 
                                         
                                       
                                       ) 
                                     
                                     n 
                                   
                                    
                                   cos 
                                    
                                   
                                       
                                   
                                    
                                   2 
                                    
                                   
                                       
                                   
                                    
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                                 - 
                                 
                                   2 
                                    
                                   
                                       
                                   
                                    
                                   β 
                                    
                                   
                                       
                                   
                                    
                                   sin 
                                    
                                   
                                       
                                   
                                    
                                   2 
                                    
                                   
                                       
                                   
                                    
                                   δ 
                                 
                               
                               
                                 ( 
                                 
                                   
                                     
                                       ( 
                                       
                                         
                                           cos 
                                            
                                           
                                               
                                           
                                            
                                           δ 
                                         
                                         - 
                                         
                                           
                                             β 
                                             n 
                                           
                                            
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                                            
                                           
                                               
                                           
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                                       ) 
                                     
                                     2 
                                   
                                   + 
                                   
                                     
                                       
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                                         2 
                                       
                                       
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                                      
                                     
                                       sin 
                                       2 
                                     
                                      
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                                 ) 
                               
                             
                             + 
                           
                         
                       
                       
                         
                           
                             
                               
                                 
                                   
                                     ( 
                                     
                                       
                                         
                                           
                                             ( 
                                             
                                               
                                                 n 
                                                 2 
                                               
                                               - 
                                               
                                                 ( 
                                                 
                                                   
                                                     α 
                                                     2 
                                                   
                                                   + 
                                                   
                                                     β 
                                                     2 
                                                   
                                                 
                                                 ) 
                                               
                                             
                                             ) 
                                           
                                           
                                             2 
                                              
                                             
                                                 
                                             
                                              
                                             n 
                                           
                                         
                                          
                                         sin 
                                          
                                         
                                             
                                         
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                                          
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                                       + 
                                       
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                                          
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                                          
                                         
                                             
                                         
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                                         2 
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                                     ) 
                                   
                                 
                               
                               
                                 
                                   
                                     ( 
                                     
                                       
                                         
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                                                
                                               
                                                   
                                               
                                                
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                                           ) 
                                         
                                          
                                         
                                           ( 
                                           
                                             
                                               sin 
                                                
                                               
                                                   
                                               
                                                
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                                             + 
                                             
                                               
                                                 β 
                                                 n 
                                               
                                                
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                                                
                                               
                                                   
                                               
                                                
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                                           ) 
                                         
                                       
                                       - 
                                       
                                         
                                           
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                                             2 
                                           
                                           
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                                             2 
                                           
                                         
                                          
                                         sin 
                                          
                                         
                                             
                                         
                                          
                                         2 
                                          
                                         
                                             
                                         
                                          
                                         δ 
                                       
                                     
                                     ) 
                                   
                                 
                               
                             
                             
                               
                                 ( 
                                 
                                   
                                     
                                       ( 
                                       
                                         
                                           cos 
                                            
                                           
                                               
                                           
                                            
                                           δ 
                                         
                                         - 
                                         
                                           
                                             β 
                                             n 
                                           
                                            
                                           sin 
                                            
                                           
                                               
                                           
                                            
                                           δ 
                                         
                                       
                                       ) 
                                     
                                     2 
                                   
                                   + 
                                   
                                     
                                       
                                         α 
                                         2 
                                       
                                       
                                         n 
                                         2 
                                       
                                     
                                      
                                     
                                       sin 
                                       2 
                                     
                                      
                                     δ 
                                   
                                 
                                 ) 
                               
                               2 
                             
                           
                         
                       
                     
                      
                   
                 
               
               
                 
                   ( 
                   11 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where α and β are the real and imaginary part of the equivalent optical admittance of previous film stack, respectively. δ is optical phase thickness, and n is refractive index of thin film. 
         [0036]    The sensitivity is low at the termination points of deposition at the left side of the circle of the locus, but in that case, the sensitivity can be greatly improved if we simply adding a phase shift of pi on the reflection phase and re-calculate the corresponding optical admittance, as shown in attachment  1 . 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 refractive 
                   
                 reflection 
                 optical 
               
               
                   
                 index 
                 thickness 
                 coefficient 
                 admittance 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 The 
                 2.119 
                 39.039 nm 
                 −0.20708 − 0.34514i 
                 1.6405 + 
               
               
                 invention 
                   
                   
                   
                 1.3513i 
               
               
                 Ellipsometer 
                 2.168 
                  39.04 nm 
                 −0.23321 − 0.35071i 
                 1.6939 + 
               
               
                   
                   
                   
                   
                 1.4443i 
               
               
                   
               
             
          
         
       
     
         [0037]    Table 1 shows the comparison between the measurement results by monitor system and ellipsometer. Their results are very close to each other. 
         [0038]    Referring to  FIG. 4 , the monitoring method of the invention is used to monitor the thin film deposition in real time, and whether the coating thin film is terminated or not is determined by the real time monitoring. As the step S 100 , a low coherence light of the light source  103  is used to irradiate substrate  14  for suppressing the spurious interference fringes. Adjusting the mirror  109  or  110  of the Twyman-Green interferometer  102  to make the length difference between the two arms be in accordance with the optical thickness of the substrate  14  to make only the specific beam pairs be phase matched and have interference with each other. It makes the calculation reflection phase of thin films easier. The adjusting manner of the interferometer for getting the better perspicuity of the interfering light is common sense, so here is no more explanation. As the step S 102 , calculating the phase in accordance with the intensity measurement from the pixelated phase mask camera  116 , unwrapping the phase of the intensity measurement, removing the tilt factor and aberration of the intensity measurement, and averaging the phase of 15 frames and more captured from the pixelated phase mask camera  116 . It is to say, unwrapping the phase difference between the interfering beam pairs, removing the tilt factor and aberration of the phase, and averaging data of the several frames for removing the influence of the air turbulence to the phase. As the step S 104 , record the intensity &amp; the phase difference between coated area and blocked area as initial phase difference and initial intensity, respectively. As the step  106 , Starting the thin film deposition, and then the step  108  is executed. As the step  108 , unwrapping the phase of the measurement from the pixelated phase mask camera  116 , removing the tilt and aberration of the measurement, averaging phases of 15 frames and more from the pixelated phase mask camera  116 . 
         [0039]    Then, as the step S 110 , acquiring transmittance and the measured phase difference between coated area and blocked area of the substrate  14  for obtaining the reflection phase of the thin film. As the step S 112 , compare the initial phase difference with the measured phase difference to obtain and the reflection phase change, and compare the measured intensity with the initial intensity. It is to say, to subtract the initial phase difference from the measured phase difference for acquiring the reflection phase change of the grown thin film. The transmittance of the thin film is calculated by comparing the measured intensity with initial intensity. Then, as the step S 114 , calculate the reflection coefficient or optical admittance of the grown thin film, and record the loci as thin film deposition. As the Step S 116 , determining whether the loci reach the termination point of the thin film deposition or not according to the result of the Step S 114 . When the determination is yes, the next execution is the step S 118 . When the determination is no, the next execution is the step S 108  to continue monitoring of the thin film deposition. Finally, as the step S 118 , terminate the thin film deposition. 
         [0040]    Moreover, the real-time refractive index and thickness of deposition films can be analytically obtained. It provides a global and precise monitor for fabrications of thin film elements. 
         [0041]    The reflection coefficient loci and optical admittance loci as thin film grows can be thereby monitored in this system. From these loci, operators can directly find better error compensations of depositions than transmittance or reflectance loci, since they include both magnitude and phase information of the films. Furthermore, a way to increase the sensitivity of the optical admittance loci monitoring is also proposed in this invention. 
         [0042]    Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments, will be apparent to persons skilled in the art. It is, therefore, contemplated that the appended claims will cover all modifications that fall within the true scope of the invention.