Abstract:
A positioning system for precise stage is provided. It includes a designed pattern on a stage; an electron beam column generating a focused electron beam to scan the designed pattern and produce electron signal; an electron detection unit to detect the electronic signal; and a control unit converting the electron signal to a clock signal to determine the relative position of the electron beam column and the designed pattern, so as to adjust the displacement of the stage. A nanometer scale positioning method for a precise stage is provided, which can resolve the problem of mechanical drift of the stage when the stage is multi-axis positioning or rotating.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a positioning system and method for a precise stage and more particularly to a positioning system and method for a precise stage by means of electron beam scanning. 
         [0003]    2. Description of the Prior Art 
         [0004]    With requirements of high precision for industrial machinery and measuring instruments, development of precision machinery, semiconductor industry, micron technology or nanotechnology all emphasize on micronization and precision, wherein positioning technique and instruments with high precision are necessary for processing machinery, semiconductor fabrication and electronic information device. 
         [0005]    Generally, when a high precision stage is rotating or multi-axis positioning, it may lead to a problem of mechanical drift. The state-of-art solutions and disadvantages thereof are described below:
       (1) Using an optical interferometer to detect precision movement of the moving stage for high precision positioning: it cannot be arranged on the rotating axis of the moving stage.   (2) Using an optical scale for calibration: precision thereof is insufficient and it is unable to measure eccentricity of the rotation.   (3) Using a mechanical axis with air bearing: although to 30 nm precision, it must be operated under standard atmosphere and is too large-sized to use in small space.   (4) Using a vacuum gauge for calibration: if the stage is designed for multi-dimensional movement with tilted angle, the mechanical design is very difficult and complex and therefore is unpractical.       
 
       SUMMARY OF THE INVENTION 
       [0010]    It is an aspect of the present invention to provide a positioning system and method for a precise stage and pattern used thereof, which can be applied to multi-dimensional moving stage with complex structure to nanometer scale and can overcome the problem of mechanical drift when the moving stage is rotating or multi-axis positioning. 
         [0011]    According to an embodiment, the positioning system and method for a precise stage comprises: a designed pattern placed on a moving stage, wherein the designed pattern comprises a plurality of gradually wider marks radially arranged with a space therebetween; an electron beam column, for generating a focused electron beam; a scanning unit connected to the electron beam column, for adjusting the focused electron beam to perform two-dimensional pattern scanning over the designed pattern so as to generate a reflected electron signal; an electron detection unit, for detecting the reflected electron signal; and a control unit connected to the moving stage, the electron beam column, the scanning unit and the electron detection unit, wherein the reflected electron signal is generated from the two-dimensional pattern scanning of the focused electron beam over the gradually wider marks and the space therebetween; the reflected electron signal is converted by the control unit to generate a clock signal, and the control unit adjusts the movement of the moving stage according to pulse width of the plurality of the clock signals, wherein the trace of the two-dimensional pattern scanning can be circle or ellipse. 
         [0012]    According to another embodiment of the present invention, in a positioning system for a precise stage, a designed pattern is placed on a moving stage and is maintained a constant distance from a specimen placed on the moving stage, wherein the designed pattern comprises: a plurality of gradually wider marks radially arranged with a space therebetween. 
         [0013]    According to another embodiment, the positioning method for a precise stage comprises: fixing a designed pattern on a moving stage, wherein the designed pattern comprises a plurality of gradually wider marks radially arranged with a space therebetween; using an electron beam to perform two-dimensional pattern scanning over the designed pattern so as to generate a reflected electron signal; detecting the reflected electron signal; and converting the reflected electron signal to a clock signal, and adjusting the movement of the moving stage according to the designed pattern, two-dimensional pattern scanning and pulse width of the plurality of clock signals. 
         [0014]    The objective, technologies, features and advantages of the present invention will become more apparent from the following description in conjunction with the accompanying drawings, wherein certain embodiments of the present invention are set forth by way of illustration and examples. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The foregoing aspects and many of the accompanying advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
           [0016]      FIG. 1  is a schematic diagram illustrating the positioning system for a precise stage according to an embodiment of the present invention; 
           [0017]      FIG. 2  is a schematic diagram illustrating the designed pattern and the circle trace scanning according to an embodiment of the present invention; 
           [0018]      FIG. 3  is a schematic diagram illustrating a clock signal according to an embodiment of the present invention; 
           [0019]      FIG. 4   a  to  FIG. 4   c  are schematic diagrams illustrating corresponding relationship between the designed patterns and the circle trace scanning according to three embodiments of the present invention; 
           [0020]      FIG. 5   a  to  FIG. 5   c  are schematic diagrams illustrating the clock signals generated from circle trace scanning respectively according to  FIG. 4   a  to  FIG. 4   c;    
           [0021]      FIG. 6  is a schematic diagram illustrating the designed pattern and the circle trace scanning according to another embodiment of the present invention; 
           [0022]      FIG. 7  is a schematic diagram illustrating the clock signal according to another embodiment of the present invention; 
           [0023]      FIG. 8   a  and  FIG. 8   b  are schematic diagrams illustrating the designed pattern and the circle trace scanning according to another embodiment of the present invention; 
           [0024]      FIG. 9   a  and  FIG. 9   b  are schematic diagrams illustrating the clock signal generated from the circle trace scanning respectively according to  FIG. 8   a  to  FIG. 8   b ; and 
           [0025]      FIG. 10  is a flowchart illustrating the positioning method for a precise stage according to another embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0026]    The detail description is provided below and the preferred embodiments described are only for the purpose of description rather than for limiting the present invention. 
         [0027]      FIG. 1  is a schematic diagram illustrating the structure of the positioning system for a precise stage according to an embodiment of the present invention. As shown in  FIG. 1 , the positioning system for a precise stage  10  comprises a designed pattern placed on a moving stage  14 . Referring to  FIG. 2 , a schematic diagram illustrating the designed pattern according to one embodiment of the present invention, the designed pattern  12  comprises a plurality of gradually wider marks arranged radially; in one embodiment, there are four gradually wider marks, but not limited to this. The gradually wider mark is a fan-shaped mark  121  and there is a space  122  between two adjacent fan-shaped marks; an electron beam column  16  is arranged above the moving stage  14  for generating a focused electron beam  18  and using a scanning unit  26  to control the focused electron beam  18  to perform two-dimensional pattern scanning over the designed pattern  12  on the moving stage  14  to generate a reflected electron signal  20 . In one embodiment, the two-dimensional pattern scanning is circle trace scanning  28  or ellipse trace scanning, but not limited to this. As shown in  FIG. 2 , the fan-shaped mark  121  and the space  122  are scanned by the circle trace scanning  28 ; an electron detection unit  22 , for detecting scatter electron signal  20  which comprises secondary electron signal and backscattered electron signal, but not limited to this; and a control unit  24  connected to the moving stage  14 , the electron beam column  16 , the scanning unit  26  and the electron detection unit  22 . 
         [0028]    In one embodiment, the moving stage  14  comprises a three-axis moving stage and two rotating stages for horizontal rotation and vertical rotation, wherein the moving stage  14  is used for placement of a specimen (not shown in the picture) and the designed pattern  12  is arranged near the specimen with a specific distance so that the displacement of the focused electron beam  18  over the designed pattern  12  is equal to the displacement of the specimen. 
         [0029]    Continue the description above, the control unit  24  records the shape of the designed pattern  12  and outputs a control signal for controlling the scanning trace of the scanning unit  26  and further converting the electron signal  20  detected by the detection unit  22  to a clock signal  30  so as to adjust the displacement of the moving stage  14  according to time-varying offset of the designed pattern  12 , which can be calculated based on the shape of the designed pattern  12 , scanning trace and clock signals. 
         [0030]    In the present invention, because of distinctly different electrical properties between the designed pattern  12  and the space  122 , when the electron signal  20  generated from the circle trace scanning  28  of the focused electron beam  18  over the designed pattern  12  is converted to the clock signal  30  by the control unit  24 , as shown in  FIG. 3 , there is high and low voltage change of the clock signal  30 . In one embodiment, when the focused electron beam  18  scans over the fan-shaped mark  121 , the clock signal  30  appears as a square pulse  32  with high height and width and the digital value is displayed as 1; when the focused electron beam  18  scanned over the space  122  of the designed pattern  12 , there is no square pulse  32  fluctuated and the digital value is displayed as 0. 
         [0031]    There are four examples of fan-shaped marks in respect of the designed pattern, which are arranged radially and generate different clock signals based on the offset of the designed pattern. Referring to  FIG. 4   a , the four fan-shaped marks are respectively marked as the fan-shaped mark  121   a,    121   b,    121   c  and  121   d.  In one embodiment, the fan-shaped mark  121   a  and  121   c,  toward the X direction, and the fan-shaped mark  121   b  and  121   d , toward the Y direction, gradually grow wider away from the radiating center o, wherein the fan-shaped mark  121   a,    121   b.    121   c  and  121   d  are arranged with equal space therebetween. 
         [0032]    As shown in  FIG. 4   a , if the center of the circle trace scanning  28  corresponds to the radiating center o of the four fan-shaped marks  121   a ,  121   b,    121   c  and  121   d,  because the scanning trace of the focused electron beam  18  over each fan-shaped mark  121   a,    121   b,    121   c  and  121   d  is the same, the each square pulse  32   a,    32   b,    32   c  and  32   d  of the clock signal  30  as shown in  FIG. 5   a  has equal width and distance therebetween, which means the corresponding relationship between the designed pattern and clock signal is correct and therefore the clock signal is correct. 
         [0033]    When there is offset generated to the designed pattern (i.e. generated to the moving stage), the trace of the focused electron beam  18  scanning over the fan-shaped markers  121   a,    121   b,    121   c  and  121   d  changes. Take X direction offset of the designed pattern for example, as shown in  FIG. 4   b , the traces of the circle trace scanning  28  of the focused electron beam  18  over the fan-shaped marker  121   a  and  121   c  are different so that the width of the pulse  32   a ′ and  32   c ′ of the clock signal  30 ′ as shown in  FIG. 5   b  is different and the distance between the adjacent pulse  32   a ′,  32   b ′,  32   c ′ and  32   d ′ differ; time-varying offset of the moving stage  14  (as shown in  FIG. 1 ) can be deprived from comparison between the width of the pulse  32   a ′,  32   b ′,  32   c ′ and  32   d ′ of the clock signal  30 ′, and the width of the pulse  32   a,    32   b,    32   c  and  32   d  of the clock signal  30 , for adjusting the displacement of the moving stage  14 , which makes the designed pattern  12  on the moving stage  14  capable of generating the correct clock signal  30  (as shown in  FIG. 5   a ) when the designed pattern is scanned. 
         [0034]    In another embodiment, offset can be generated along the X direction and Y direction. As shown in  FIG. 4   c , the traces of the circle trace scanning  28  of the focused electron beam  18  over the fan-shaped marker  121   a,    121   b,    121   c  and  121   d  are different, thereby changing the width of the pulse  32   a ″,  32   b ″,  32   c ″ and  32   d ″ of the clock signal  30 ″ (as shown in  FIG. 5   c ); offset along the X direction and Y direction of the moving stage  14  can be derived from the change of the sequence and pulse width. 
         [0035]    Continuing the description above, in order to distinguish sequence relationship between the each pulse  32  of the clock signal  30  for better analysis, there is at least a groove formed on one of the fan-shaped markers  121 ; when the focused electron beam  18  scans over the fan-shaped marker  121  with the groove, the pulse  32  is not a smooth square wave but a rough square wave.  FIG. 6  shows a schematic diagram illustrating the designed pattern  12  and the circle trace scanning  28  according to another embodiment of the present invention, wherein the designed pattern  12  comprises the four fan-shaped markers  121   a,    121   b,    121   c,  and  121   d  and there is a groove  34  formed on the fan-shaped marker  121   d.    FIG. 7  shows a schematic diagram illustrating the clock signal  30  according to another embodiment of the present invention, wherein the focused electron beam  18  scans over the designed pattern as shown in  FIG. 6  and the center of the circle trace scanning  28  corresponds to the radiating center o of the four fan-shaped markers  121   a,    121   b,    121   c,  and  121   d.  As shown in  FIG. 7 , the width of the each pulse  32   a,    32   b,    32   c,    32   d  of the clock signal  30  and the distance therebetween is equal, wherein a fluctuation  36  appears over the wave top of the pulse  36  due to the groove  34  of the fan-shaped marker  121   d,  thereby confirming the corresponding relationship between the four fan-shaped markers  121   a,    121   b,    121   c,    121   d  and the each pulse  32   a,    32   b ,  32   c,    32   d  of the clock signal  30 . 
         [0036]    Distinguishing standard, that is to say, the corresponding relationship between the fan-shaped markers and the clock signal, is not limited to the groove  34  formed on the fan-shaped marker  121 ; it also can be protrusion formed thereon. On the other hand, the fan angle of the fan-shaped marker may be too large or too small for sequencing the clock signal  30  so that a 45 degree fan angle of the fan-shaped marker  121  is designed for reducing deviation according to one embodiment. 
         [0037]    Four gradually wider markers arranged radially according to aforementioned embodiments are exemplified for specifications of the designed pattern, but not limited to this, wherein the designed pattern  12  can comprises two, three, four and above gradually wider markers.  FIG. 8   a  and  FIG. 8   b  shows schematic diagrams illustrating the designed pattern and the circle trace scanning, wherein the designed pattern  12  comprises three fan-shaped markers arranged radially, named the fan-shaped marker  123   a ,  123   b,    123   c,  which grow wider gradually away from the radiating center o and are arranged with a equal space therebetween. 
         [0038]      FIG. 9   a  and  FIG. 9   b  are schematic diagrams illustrating the clock signal  30  generated from the circle trace scanning  28  over the designed pattern  12  respectively according to  FIG. 8   a  to  FIG. 8   c . If the center of the circle trace scanning  28  corresponds to the radiating center o of the four fan-shaped marks  121   a,    121   b,  and  121   c,  because the scanning trace of the focused electron beam  18  (as shown in  FIG. 1 ) over each fan-shaped mark  121   a,    121   b,  and  121   c  is the same (as shown in  FIG. 9 ), the each square pulse  52   a,    52   b,    52   c  of the clock signal  30  has equal width and the distance therebetween, which means the corresponding relationship between the designed pattern  12  and clock signal  30  is correct and therefore the clock signal  30  is correct. When there is offset generated to the moving stage, as shown in  FIG. 9   b , the trace of the circle trace scanning  28  of the focused electron beam  18  over the fan-shaped markers  123   a,    123   b,  and  123   c  changes, and the width of the pulse  52   a ′,  52   b ′ and  52   c ′ also changes; offset of the moving stage  14  can be deprived from vector projection calculation based on change of pulse width and sequence. 
         [0039]    In the present invention, spot size of the focused electron beam generated from the electron beam column depends on resolution of the positioning system for a precise stage; current value of the focused electron beam is used for determining signal-to-noise ratio. Besides, in order to increase signal-to-noise ratio, multi-petal gradually wider markers can be adopted to increase sampling speed while scanning. 
         [0040]      FIG. 10  shows a flowchart illustrating the positioning method for a precise stage according to one embodiment of the present invention, wherein a positioning method for a precise stage comprises: fixing a designed pattern on a moving stage (Step S 40 ), wherein the designed pattern comprises 4 gradually wider markers arranged radially; using a focused electron beam to perform the two-dimensional pattern scanning over the designed pattern to generate a reflected electron signal (Step S 42 ); using an electron detection unit to detect the reflected electron signal (Step S 44 ); converting the reflected electron signal to a clock signal (Step S 46 ); and calculating the time-varying offset of the designed pattern according to the shape of the designed pattern, scanning trace and pulse width of the plurality of clock signals, for adjusting the displacement of the moving stage. 
         [0041]    The present invention uses the focused electron beam to scan the specific designed pattern to generate a reflected electron signal and uses the electron detection unit to detect the reflected electron signal, thereby further determining whether there is offset generated to the designed pattern so as to adjust the displacement of the moving stage, which enables default results of the clock signal while scanning the designed pattern via the adjusted scanning trace. This positioning system for a precise stage can be applied to nanoscale positioning of the multi-dimensional moving stage with complex structure and overcome the problem of mechanical drift when the stage is rotating or multi-axis positioning. 
         [0042]    While the invention is susceptible to various modifications and alternative forms, a specific example thereof has been shown in the drawings and is herein described in detail. It should be understood, however, that the invention is not to be limited to the particular form disclosed, but to the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the appended claims.