Abstract:
A non-contacting aligning method for planes in a three-dimensional environment is disclosed. The method includes: projecting a light beam in a predetermined incident angle onto a transparent first object and an opaque second object that are facing each other; and calculating a distance between the first and second objects basing on the tangent trigonometric function of the incident angle of the light beam.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Technical Field 
         [0002]    The present invention relates to methods for measuring overlay errors of facing objects, and more particularly to a non-contacting method for detecting overlay errors in X and Y axes between two objects facing each other, and detecting a vertical distance between the two objects (in Z axis) as well as parallelism therebetween. 
         [0003]    2. Description of Related Art 
         [0004]    As to the conventional lithography process, in course of transferring a pattern of a photo mask to a circuit substrate and transferring a pattern predefined on a photo mask to a wafer, measures for error measuring and object aligning are implemented so as to ensure accurate transfer of the patterns. On this note, X-Y positioning, Z positioning, and parallelism between two objects to be mutually overlaid are important. In addition to the lithography process, in course of installing a probe to a superconducting quantum interference microscope (SQUID Microscope), the relative distance and the parallelism between the probe and the assay sample have to be accurately controlled in order to ensure proper sensitivity of the device. 
         [0005]    Herein the lithography process is described as an example for illustrating how the prior art deals with the need of three-axis positioning. 
         [0006]    Using image capturing devices on the Z axis to monitor overlay between XY-axis marks of overlaid objects is known. Therein, a movable camera may be used to monitor images of overlaid objects in its focal plane and thereby achieve the Z-axis monitoring process. During the process, once the focus changes in the focal plane, it indicates that an inclining angle exists between the two facing objects. However, this known approach is infeasible to get the inclining angle accurately when the image definition of the camera is poor. 
         [0007]    Alternatively, two or more image capturing devices are arranged to take images from different view angles for comparison in order to obtain the distance in the Z axis. Nevertheless, this approach needs complicated calculation and operation, yet is defective in accurately giving the inclining angle between overlaid objects. 
       SUMMARY OF THE INVENTION 
       [0008]    One objective of the present invention is to provide a non-contacting aligning method for planes in a three-dimensional environment. This method adopts a non-contacting means to monitor a distance and parallelism between two objects facing each other, in conjunction with X-Y axis monitoring, to fully align the objects in a three-dimensional environment. 
         [0009]    The non-contacting means of the present invention primarily involves projecting a slantwise incident light beam to objects facing each other, calculating a distance between the two facing objects basing on an incident angle of the light beam and its tangent trigonometric function, and determining parallelism between the objects by checking parallelism between projected light strokes on an X-Y plane. When there is an included angle appearing between the two objects, an included angle appears between two said adjacent light strokes. The inclining angle between the two objects can be derived basing on the included angle and a trigonometric function. A known adjusting means may use the result to modify one of the objects so as to achieve the purposes of three-axis positioning and parallelism between the overlaid objects. 
         [0010]    A device for realizing the foregoing non-contacting means may comprises an image capturing device, a light-beam generating device and a computing device. The image capturing device is arranged on the Z axis of a first object and a second object that faces each other. The light-beam generating device generates a light beam that is projected onto the first object and the second object in a predetermined angle. The second object reflects the light beam to project a light stroke on the first object. Images of the light strokes on the first object and the second object are captured by the image capturing device. The computing device determines a distance between the two light strokes on the first object and uses a given incident angle of the light beam, by applying a tangent trigonometric function of the incident angle, to figure out the vertical distance between the first object and the second object. In addition, parallelism between the light strokes on the first and second objects can be used to determine whether the first and second objects are parallel with each other. Also, an inclining angle of the first object with respect to the second object can be calculated basing on the included angle between the light strokes on the first object and the second object and a trigonometric function so that the first object and the second object can be adjusted to have parallelism by using a known adjusting means according to the foregoing results. The image capturing device may also serve to take X-Y planar images of the first and second objects for facilitating determining alignment between overlay marks of the objects. Thereby, the non-contacting means of the present invention is effective in aligning planes in a three-dimensional environment. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The invention as well as a preferred mode of use, further objectives and advantages thereof will be best understood by reference to the following detailed description of illustrative embodiments when read in conjunction with the accompanying drawings, wherein: 
           [0012]      FIG. 1  is a lateral view of overlaid objects for illustrating how to calculate a vertical distance between the objects; 
           [0013]      FIG. 2  is a front top view of  FIG. 1  showing a route of a light beam passing the overlaid objects; 
           [0014]      FIG. 3  is a front top view of  FIG. 1  showing the route of the light beam changed when a distance between the objects changes; 
           [0015]      FIG. 4  is a lateral view of the objects with an inclining angle therebetween; 
           [0016]      FIG. 5  is a front top view of  FIG. 4  showing a route of a light beam with presence of the inclining angle between the objects; 
           [0017]      FIG. 6  and  FIG. 7  depict a device for achieving the present invention; and 
           [0018]      FIG. 8  is a top view of overlaid objects whose X-Y planes are provided with marks. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    Referring to  FIG. 1 , a way to calculate a vertical distance Z between two parallel matters, a first object  10  and a second object  20 , is illustrated. A slantwise incident light beam  30  is projected onto the transparent first object  10  and the reflective second object  20  in a predetermined angle (θ). Then the second object  20  further reflects the light beam to the first object  10 . Therefore, there are an incident light stroke  31  and a reflected light stroke  32  on the first object  10  while there is an incident light stroke  33  on the second object  20 . Assuming that a distance between the incident light stroke  31  and the reflected light stroke  32  on the first object  10  is 2×, the vertical distance Z between the first object  10  and the second object  20  can be derived from the following Equation 1: 
         [0000]    
       
         
           
             
               
                 
                   
                     tan 
                      
                     
                         
                     
                      
                     θ 
                   
                   = 
                   
                     x 
                     z 
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   1 
                 
               
             
           
         
       
     
         [0020]    Referring to  FIG. 2  and  FIG. 3 , the drawings show how the three light strokes  31 ,  32  and  33  locate on the first object  10  and the second object  20  and how a distance between the incident light stroke  31  and the reflected light stroke  32  on the first object  10  changes when the distance Z between the first object  10  and the second object  20  changes. The greater distance Z is, the greater the distance between the incident light stroke  31  and the reflected light stroke  32  is, vice versa. 
         [0021]    Referring to  FIG. 4  and  FIG. 5 , the drawings show variation among the three light strokes  31 ,  32  and  33  in response to inclination of the first object  10  with respect to the second object  20 . When an inclining angle φ exists between the first object  10  and the second object  20 , an included angle φ exists between the light stroke  31 ,  32  on the first object  10  and the incident light stroke  33  on the second object  20 , and the inclining angle φ can be derived from the following Equation 2: 
         [0000]    
       
         
           
             
               
                 
                   
                     tan 
                      
                     
                         
                     
                      
                     θ 
                   
                   = 
                   
                     
                       
                         tan 
                          
                         
                             
                         
                          
                         φ 
                       
                       
                         tan 
                          
                         
                             
                         
                          
                         ϕ 
                       
                     
                     ≅ 
                     
                       φ 
                       ϕ 
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   2 
                 
               
             
           
         
       
     
         [0022]    A known adjusting means may use the distance Z to modify the first object  10  and the second object  20  and achieve a desired value of the distance Z. Alternatively, the derived inclining angle φ may be used to adjust the first object  10  in order to make it become parallel with the second object  20 . 
         [0023]    Referring to  FIG. 6  and  FIG. 7 , a device for realizing the method of the present invention is illustrated. The device comprises an image capturing device  40 , a light-beam generating device  50  and a computing device  60  coupled to the image capturing device  40 . The image capturing device  40  is arranged on the Z axis of the first object  10  and the second object  20 . The light-beam generating device  50  generates and projects the aforementioned light beam  30 . The incident light stroke  31  and the reflected light stroke  32  on the first object together with the incident light stroke  33  on the second object  20  are captured as images by the image capturing device  40 . The computing device  60  then uses the captured images to determine a distance between the incident light stroke  31  and the reflected light stroke  32  on the first object  10 , and further applies a given incident angle θ of the light beam to Equation 1 to derive the distance Z between the first object  10  and the second object  20 . The light stroke  33  on the second object  20  and the light strokes  31 ,  32  are considered to determine whether the first and second objects are in parallelism. When the first and second objects are not parallel with each other, the computing device  60  uses Equation 2 to figure out the inclining angle φ of the first object  10  with respect to the second object  20 . 
         [0024]    The light-beam generating device  50  primarily comprises a light source  51 , an angle adjuster  52  on which the light source  51  is installed and adjusted in its incident angle, and an auxiliary device  53  that shapes light from the light source  51  into a beam of a predetermined width (about 500 μm). The light source  51  may be an LED unit, and the auxiliary device  53  is provided with a slot  54 , so that light of the LED unit passes through the slot  54  before focused by a convex  55  into the light beam  30  as wide as about 500 μm to be projected on the first object  10  and the second object  20 . The light source  51  may alternatively be a laser unit, and the auxiliary device  53  is a lenticular lens, so as to present the light beam as wide as about 60 μm for the first object  10  and the second object  20 . 
         [0025]    As the transparent first object  10  in the embodiment is glass of high transparency, for facilitating clear presentation of the light strokes  31 ,  32  on the transparent first object  10  (i.e. the glass), the first object  10  may have its surface ground with aluminum oxide powders into an imaging surface  11 , which has reduced transparency and is partially reflective. 
         [0026]    In another embodiment of the present invention, the first object  10  may have its surface coated to form a partially reflective imaging surface  11 , so that the incident light stroke  31  and the reflected light stroke  32  can show on the imaging surface  11  clearly. 
         [0027]    Referring to  FIG. 8 , the image capturing device  40  may also serve to take X-Y planar images of the first object  10  and the second object  20 . The images thus are useful in determining alignment between marks  15  of the objects. Thereby, the device can be used to realize the non-contacting aligning method for planes in a three-dimensional environment as claimed by the present invention. 
         [0028]    The present invention has been described with reference to the preferred embodiments and it is understood that the embodiments are not intended to limit the scope of the present invention. Moreover, as the contents disclosed herein should be readily understood and can be implemented by a person skilled in the art, all equivalent changes or modifications which do not depart from the concept of the present invention should be encompassed by the appended claims.