Abstract:
An apparatus for effectively detecting and calibrating a sample of examination system. The apparatus has an optical-electronic assembly for detection of the sample initiated with a light projected to the sample and an elastic supporting assembly for providing motion freedoms to adjust the relative geometric conditions between the optical-electronic assembly and the sample. The elastic supporting assembly has a planer structure and a cubic structure, and provides both motion freedoms on a plane and motion freedoms vertical to the plane. The optics electricity optical-electronic assembly could analyze the received reflected light to get geometric information of the sample, and could adjust the light used to detect the sample.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a detecting apparatus, and more particularly, to a detecting apparatus capable of precisely detecting and calibrating the geometric information of a sample. 
     BACKGROUND OF THE RELATED ART 
     The critical dimension of semiconductor device is continuously decreased, such that the damage induced by any defect on a chip is continuously increased. Hence, high resolution examination (both review and inspection) is required to properly find and check the defect. For example, scanning electron microscope (SEM), as a more advanced examination system, is popularly used for examining chips. In general, a sample (wafer or photomask or semiconductor substrate) is located under a charged particle beam during the examination process. Clearly, whether the sample is correctly located is a key factor of the examining result. In general, one detector is located under the sample and on a base (such as the Z-stage of SEM). The detector will project or emit a light to the sample and analyze a reflected light from the sample. According to the analyzing result, the detector could acquire the geometric information (such as position, direction and angle) of the sample. 
     There are some drawbacks in the conventional design of the examination system. First, the detector is fixed on the base. Hence, once the base is improperly located (such as the top surface of the base is not parallel to the bottom surface of the sample located on a predetermined position), the detector usually can not properly detect the sample (such as the light is not properly projected from the detector onto the sample, such that the quality of the reflected light is degraded.) Second, only one detector is used to detect the geometric information of the sample. Hence, once the sample has a displacement around the light (or around an axis parallel to the light), the detector usually can not find the displacement. 
     Therefore, it is desired to develop some new designs of examination system to improve the above drawbacks. 
     SUMMARY OF THE INVENTION 
     An apparatus for detecting the geometric information of a sample in an examination system. The apparatus includes an elastic supporting assembly and an optical-electronic assembly. The optical-electronic assembly could project a light beam to the sample, receive a reflected light beam from the sample, and analyze the received reflected light beam to acquire messages about the geometric information (such as position, direction, and tilt angle) of the sample. The elastic supporting assembly could fix the optical-electronic assembly on a base (such as the Z-stage) and adjust the geometric condition of the optical-electronic assembly (such as moving along X-axis, moving along Y-axis, rotating on X-Y plane, tilting on X-Z plane and tilting on Y-Z plane.) 
     An application of the proposed detecting apparatus is exemplified herein. By adjusting the elastic supporting assembly, the geometric condition of the optical-electronic assembly could be adjusted, for example, the distance between optical-electronic assembly and sample and/or the direction of the light projected by the optical-electronic assembly. Thus, after the geometric condition of the optical-electronic assembly is adjusted to achieve an optimal reflected light from the sample, the elastic supporting assembly could be locked to fix geometric condition of the optical-electronic assembly corresponding to the base. After that, whenever a new sample is appeared to be detected, by comparing the difference(s) between the new reflected light and the optimal reflected light, it is easy to adjust the geometric condition of the new sample, until the new reflected light also is optimized. Moreover, when the examination system (such as SEM) is maintained, the apparatus also could be used to calibrate the relative geometric relation (such as relative distance, relative angle and relative direction) between the base (such as Z-stage) and the sample to be tested. For example, when the location of the sample is not changed but the location of the base might be changed during the maintain process, the apparatus could be used to calibrate the location of the maintained base by comparing the difference(s) between the new reflected light and the optimal reflected light. 
     Another application of the proposed detecting apparatus is exemplified herein. Because the proposed apparatus usually only projects a light to the sample along only one direction (such as Z-axis), the proposed apparatus only can detect the displacement (or motion) that has a non-zero displacement (or motion) along the direction but can not detect displacement (or motion) totally on a plane vertical to the direction (such as X-Y plane). Therefore, to effectively detect the displacement (or motion) of the sample, it is worth to use two apparatuses that separately projects lights to the sample along two different directions (such as one along X-axis and another along Y-axis). 
     Some optional improvements of the proposed apparatus are exemplified herein. The elastic supporting assembly could comprise a planar structure and cubic structure. The planar structure may make a restricted linear motion and/or restricted pivot motion relative to a base where the proposed apparatus is located. The cubic structure may make a restricted deformation. Hence, the optical-electronic assembly on the elastic supporting apparatus could be linear moved, pivot moved or tilted. 
     Some optional improvements of the proposed apparatus are exemplified herein. The optical-electronic assembly could comprise a light source module and an analyzing module. The optical-electronic assembly also could have other improvements, such as beam-splitting module, automatic gain control circuit, background eliminating circuit, and so on. Hence, not only the receive light could be effectively analyzed, but also the generation of light and elimination of noise could be effectively adjusted. 
     These and other aspects, features and advantages of the present invention can be further understood from the accompanying drawings and description of embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side-view diagram illustrating a system for detecting the geometric information of a sample in accordance with one embodiment of the present invention. 
         FIG. 2  is a schematic side-view diagram illustrating an elastic supporting assembly in accordance with one embodiment of the present invention. 
         FIG. 3A  is a schematic diagram illustrating the relative motion freedom(s) of the planar structure and the base by linear motion in accordance with one embodiment of the present invention. 
         FIG. 3B  is a schematic diagram illustrating the relative motion freedom(s) of the planar structure and the base by rotation in accordance with one embodiment of the present invention. 
         FIG. 4A  is a schematic side-view diagram illustrating a cubic structure in accordance with one embodiment of the present invention.  FIG. 4B  is a top view of the exemplary cubic structure in  FIG. 4A . 
         FIG. 4C  is a first side view of the exemplary cubic structure in  FIG. 4A . 
         FIG. 4D  is a second side view of the exemplary cubic structure in  FIG. 4A . 
         FIG. 4E  is a third side view of the exemplary cubic structure in  FIG. 4A . 
         FIG. 4F  is a fourth side view of the exemplary cubic structure in  FIG. 4A . 
         FIG. 4G ,  FIG. 4H ,  FIG. 4I ,  FIG. 4J , and  FIG. 4K  are top, a first side, a second side, a third side, and a fourth side views respectively of  FIG. 4A  when in operation in accordance with one embodiment of the present invention. 
         FIG. 5  is a schematic diagram illustrating an exemplary optical-electronic assembly in accordance with the present invention. 
         FIG. 6  is a schematic diagram illustrating an exemplary optical-electronic assembly in accordance with the present invention. 
         FIG. 7  is a schematic diagram illustrating an exemplary optical-electronic assembly in accordance with the present invention. 
         FIG. 8  is a schematic diagram illustrating an exemplary optical-electronic assembly in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a schematic side-view diagram illustrating a system for detecting the geometric information of a sample in accordance with one embodiment of the present invention. The exemplary system  10  comprises a holding apparatus  101  and at least one detecting apparatus  103 . The holding apparatus  101  is configured for holding a sample  23 . The detecting apparatus  103  separated from the sample  23  is for detecting the geometric information of the sample  23 . The detecting apparatus  103  comprises an elastic supporting assembly  20  and an optical-electronic assembly  21 . The optical-electronic assembly  21  projects a light beam  103   a  on the sample  23 , and then receives a reflected light beam  103   a  from the sample  23  and analyzes the reflected light beam  103   a . The elastic supporting assembly  20  supports the optical-electronic assembly  21 , fixes the optical-electronic assembly  21  to a base  201  (such as fixing on the top surface of the Z-stage) and adjusts a relative geometric relation (such as relative distance, relative angle and relative direction) between the optical-electronic assembly  21  and the sample  23 . Therefore, by using the elastic supporting assembly  20  to adjust the geometric condition of the optical-electronic assembly  21 , the light path of the light beam  103   a  can be adjusted to optimize the quality of the received reflected light beam  103   a.    
     As an example, the exemplary system  10  is equipped with a first detecting apparatus  103  for detecting the displacement/motion of the sample  23  on an X-Y plane. A second detecting apparatus  105  may be set such that a second light beam  105   a  is projected on another surface (such as the side of the sample  23 ) allowing the second detecting apparatus  105  to detect the position variation of the sample  23  on an X-Z plane or a Y-Z plane. In other words, because the sample  23  is a 3-dimensional object having a first edge, a second edge, and a third edge crossing a specific vertex of the sample  23 , at least two detecting apparatus  103 / 105  may be used to separately detect different displacements/motions of the sample  23 . For example, one detecting apparatus  103  which projects a light beam is used for detecting the displacement/motion on one plane defined by the first edge and the second edge, and another detecting apparatus  105  which projects another light beam is used for detecting the displacement/motion on another plane defined by the first edge and the third edge. Of course, the shape of the sample  23  is not restricted. Therefore, the first edge and the second edge could be the same edge if the shape of the surface defined by the first edge and the second edge is chosen from a group consisting of the following: circle, ellipse, oval, and combination thereof. 
       FIG. 2  is a schematic side-view diagram illustrating an elastic supporting assembly in accordance with one embodiment of the present invention. The elastic supporting assembly  20  comprises a planar structure  202  and a cubic structure  203 . The optical-electronic assembly (not shown in the figure) may be loaded and fixed on the elastic supporting assembly  20 . In one option, the planar structure  202  is positioned between the base and the cubic structure  203 . Herein, the area between the planar structure  202  and the base is larger than the area between the cubic structure  203  and the planar structure  202 , such that the cubic structure  203  is fixed on the base through the planar structure  202 . Alternatively, the cubic structure  203  may be positioned between the base and the planar structure  202 . Herein, the area between the cubic structure  203  and the base is larger than the area between the planar structure  202  and the cubic structure  203 , such that the planar structure  202  is fixed on the base  201  through the cubic structure  203 . Clearly, the key is how to use both the planar structure  202  and the cubic structure  203  to provide the required motion freedom, how to combine the planar structure  202  and the cubic structure  203  is not a key of the invention. As an example, the planar structure  202  could be mounted with the cubic structure  203  by a way selected from a group consisting of the following: screw, glue, nail, tack, electric welding, and combination therefore. 
     Continuing the above description, the planar structure  202  is equipped with a plurality of fasteners  202   b  positioned within a plurality of holes  202   a  respectively. It is noted that all of the holes  202   a  usually are not designed on only one side of the planar structure  202 . For example, the holes  202   a  may be separately located but not limited to on the two opposite edges of the planar structure  202 . Alternatively, the holes  202   a  may all be located but not limited to on the same edge of the planar structure  202 . Moreover, the size of a hole  202   a  is larger than the size of a body of a fastener  202   b  passing through the hole  202   a  and is smaller than the size of an end of the fastener  202   b . Clearly, when the fastener  202  is located in the hole  202   a  but not locked, it is allowed to move in the hole  202   a  (for the body of fastener  202  is narrower than the hole  202   a ) to provide at least one motion freedom. Of course, when the fastener  202  is located in the hole  202   a  and locked (because the end of the fastener  202   b  is wider than the hole  202   a ), there is no motion freedom. As an example, the shape, the size and the geometric relation of the holes  202   a  and the fasteners  202   b  are adjusted to allow the optical-electronic assembly (not shown in the figure) loaded on the elastic supporting assembly to have at least one motion freedom before all of the fasteners  202   b  are locked. Herein,  FIG. 3A  and  FIG. 3B  shows an embodiment with two possible motion freedoms. Herein, the two motion freedoms may be chosen from a group consisting of the following: rotation/pivot on the locked fastener  202   b  (the dotted arc line with an arrow), rotation/pivot on a point between the fastener  202   b  and the planar structure  202 , linear motion along a direction parallel to a line crossing both of the holes  202   a , linear motion along a direction vertical to a line crossing both of holes  202   a  (the dotted straight line with an arrow), and combination thereof. Thus, the planar structure  202  may be crossed with or offset from the base as shown in  FIG. 3A  and  FIG. 3B , respectively. As an example, to provide the planar structure  202  with a significant motion freedom along the first direction ‘X’, the body of the fastener  202  can be made to be significantly smaller than the hole  202   a  along a first direction ‘X’ and slightly narrower than the hole  202   a  along a second direction ‘Y.” Furthermore, as an example, the shape of each hole  202   a  could be chosen from a group consisting of the following: quadrangle, oblong, circle, square, and the combination thereof, and each of the fasteners  202   b  may be chosen from a group consisting of the following: screw with nut, nail, tack and the combination thereof. 
       FIG. 4A  is a schematic side-view diagram illustrating a cubic structure in accordance with one embodiment of the present invention.  FIG. 4B  is a top view,  FIG. 4C  is a first side view,  FIG. 4D  is a second side view,  FIG. 4E  is a third side view, and  FIG. 4F  is a fourth side view of the exemplary cubic structure in  FIG. 4A . The cubic structure  203  is equipped with a first cavity  203   a , a second cavity  203   b , a first adjusting device  203   c  and a second adjusting device  203   d . The first cavity  203   a  is positioned between a top plate  205   b  and a bottom plate  205   a . The second cavity  203   b  is positioned between a top plate  205   c  and a bottom plate  205   b . The corresponding adjusting device, for example, the first adjusting device  203   c  comprises a first fastener (not shown in the figure) capable of passing through the top plate  205   b  to a top surface of the second plate (plate  205   a ) and a second adjusting device  203   d  comprises a second fastener (not shown in the figure) capable of passing through the top plate  205   c  and the second plate  205   b  to reach into a hole being terminated inside the bottom plate  205   a . Each of the adjusting devices ( 203   c  and  203   d ) could be chosen from a group consisting of the following: screw with nut, nail, tack and the combination thereof. The first fastener increases the angular magnitude of a corresponding opening when the first fastener is locked (the end of the first fastener contacts with the second plate, such that the second plate is pushed away when the first fastener is locked into the first plate), and the second fastener is capable of decreasing decreases the angular magnitude of the corresponding opening when the second fastener is locked (the end of the first fastener could be embedded into the second plate, such that the distance between the first plate and the second plate is decreased when the fastener is locked into the first plate). Further, the first portion of the cubic structure  203  forming the wall  203   e  of the first cavity  203   a  is partially overlapped with a second portion of the cubic structure forming the wall  203   f  of the second cavity  203   b . Herein, the first cavity  203   a  is with a first opening oriented towards a first direction and a second cavity  203   b  is with a second opening oriented towards a second direction that is different from the first direction, so that the deformation induced from the first cavity and the deformation induced from the second cavity is distributed over two different planes (or together forming a 3-dimension deformation). 
     Referring to  FIG. 4B ,  FIG. 4C ,  FIG. 4D ,  FIG. 4E , and  FIG. 4F , the first adjusting device  203   c  adjusts an angular magnitude of a first angle θ 1  of the first opening and the second adjusting device  203   d  adjusts an angular magnitude of a second angle θ 2  of the second opening. The first cavity  203   a  and the second cavity  203   b  are arranged along a specific direction (for example “Z”) to interact with the planar structure (not shown in the figure). Therefore, the deformation of the cubic structure  203  is not totally parallel to the top surface of the planar structure (i.e., the motion freedom(s) induced by the deformation is not totally parallel to the top surface of the planar structure). Herein, the angular magnitudes are in-measured along the specific direction. 
       FIG. 4G ,  FIG. 4H ,  FIG. 4I ,  FIG. 4J , and  FIG. 4K  are a top view, a first side, a second side, a third side, and a fourth side views respectively of  FIG. 4A  when the cubic structure is in operation in accordance with one embodiment of the present invention. In the case of compressing the angular magnitude of the second angle θ 2 , the first cavity  203   a  is compressed along the Y-Z plane. Similarly, in the case of stressing the angular magnitude of the first angle θ 1 , the second cavity  203   b  is de-compressed on the X-Z plane. According to the foregoing description in reference to  FIGS. 4A to 4K , the exemplary elastic supporting assembly may provide more freedoms for the adjustment of the optical-electronic assembly to enhance the qualities and precision of the alignment for the optical-electronic assembly. 
     Furthermore, the cubic structure  203  could be made of elastic material or could be formed to become an elastomer or an elastic structure. According to the configuration of the cubic structure  203  aforementioned, the shape, the size and the geometric relation of the cavities ( 203   a  and  203   b ) cooperated with the adjusting devices ( 203   c  and  203   d ) are adjusted to allow the optical-electronic assembly (not shown in the figure) loaded on the elastic supporting assembly  20  in  FIG. 2  to have at least one motion freedom before the adjusting devices ( 203   c  and  203   d ) are locked. The motion freedom is chosen from a group consisting of the following: tilting by varying the first angle θ 1  of the first opening, tilting by varying the second angle θ 2  of the second opening, and the combination thereof. 
     Accordingly, the adjustment of the relative geometric relation (such as relative position and relative angle) between the optical-electronic assembly  21  and the sample  23  may be achieved by cooperating the cubic structure  203  and the planar structure  202 . 
       FIG. 5  is a schematic diagram illustrating an exemplary optical-electronic assembly in accordance with the present invention. The optical-electronic assembly  21  comprises a light source module  211  capable of emitting a light beam  214  to the sample  23 , and an analyzing module  212  capable of analyzing a reflected light beam  215  from the sample  23 . 
       FIG. 6  is a schematic diagram illustrating an exemplary optical-electronic assembly  21  in accordance with the present invention. In the example, the light source module  211  comprises an electrostatic discharge device  211   a  electrically coupled with at least one external signal line that receives at least one external signal from an external environment, such that the noise (or the damages induced by electrostatic discharge) from the external environment through the external signal line is effectively blocked. Furthermore, as an example, the light source module  211  comprises a laser diode  211   b  driven and controlled by a laser diode driver. The laser diode  211   b  is configured for emitting a laser beam as the light beam  214 . 
     Further, the optical-electronic assembly  21  optionally comprises a beam splitting module  216  capable of splitting the light beam  214  and the reflected light beam  215 . The beam splitting module  216  could be positioned between the sample  23  and the light source module  211 , and/or between the sample  23  and the analyzing module  212 . As one example, as shown in  FIG. 7 , the beam splitting module  216  comprises a first beam splitter  216   a  which reflects the first portion  214   a  of the light beam  214  and reflects the first portion  215   a  of the reflected light beam  215 , and allows the second portion  214   b  of the light beam  214  to pass through for projecting on the sample  23  and forms the reflected light beam  215 . As another example, as shown in  FIG. 8 , the beam splitting module  216  may comprise a second beam splitter  216   b  and a third beam splitter  216   c  located separately and in sequence between the light source module  211  and the sample  23 . The second portion  214   c  of the light beam  214  is reflected by the second beam splitter  216   b . The third portion  214   d  of the light beam  214  passes through the second beam splitter  216   b  and the third beam splitter  216   c  and projects on the sample  23  to form the reflected light beam  215 . Then the first portion  215   c  of the reflected light beam  215  is reflected by the third beam splitter  216   c , the second portion  215   d  of the reflected light beam  215  passes through the third beam splitter  216   c  and the third portion  215   e  of the reflected light beam  215  is reflected by the second beam splitter  216   b . Different light splitting modules  216  correspond to different designs of the optical-electronic assembly  21 , especially correspond to different designs of the analyzing module  212 . 
     Next, as an example, the analyzing module  212  comprises a position sensor device  212   a  and an automatic gain control (AGC) circuit  212   b  coupled with the position sensor device  212   a  as shown in  FIG. 6  or coupled with a first detector  212   d  capable of receiving the third portion  215   e  of the reflected light beam  215  as shown in  FIG. 8 . The position sensor device  212   a  the first portion  215   a  of the reflected light beam  215  and outputs a processed detected signal  218  which is a function of both the incident angle of the second portion  214   b  of the light beam  214  on the sample  23  and a projected position of the second portion  214   b  of the light beam  214  on the sample  23 . Herein, by using proper position sensor device  212 , such as a commercial position sensor device  212  having four detectors for providing quadrantal detection independently, it is easy to decide whether the second portion  214   b  of the light beam  214  is properly projected on the sample  23  and whether the sample  23  is properly located on the predetermined position with predetermined angle. The automatic gain control circuit  212   b  outputs an adjusting signal  219  to the light source module  211  according to a light intensity of the first portion  215   a  of the reflected light beam  215  or the third portion  215   e  of the reflected light beam  215 . Then, by referring to the output of the automatic gain control circuit  212   b , the light source module  211  decreases the light intensity of the light beam  214  when the light intensity of the light beam  214  is larger than a higher threshold. Similarly, the light source module  211  increases the light intensity of the light beam  214  when the light intensity of the light beam  214  is smaller higher than a lower threshold. Thus, the light source module  211  adjusts the light intensity of the light beam  214  according to the adjusting signal  219 , such that the light intensity of the first portion  215   a  of the reflected light beam  215  could be optimal for proper operation of the analyzing module  212 . 
     Furthermore, as an example, the analyzing module  212  may further comprise a background eliminating circuit  212   c  electrically coupled with the position sensor device  212   a . The background eliminating circuit  212   c  eliminates the effect of a background light which is received with the first portion  215   a  of the reflected light beam  215  by the position sensor device  212   a  simultaneously. There are different approaches to achieve the object of the background eliminating circuit  212   c , based on the fact that the light source module  211  usually use laser as the light source. According to a first example, the background eliminating circuit  212   c  filters to obtain the required first portion  215   a  of the reflected light beam  215  by only allowing a portion of the received light within specific frequencies (corresponding to the frequencies of the light source module  211 ) to pass and blocking the other portion of the received light. According to a second example, background eliminating circuit  212   c  divides the received light into a continuous portion which spans over continuous frequencies (corresponding to the backlight) and a discrete portion which discretely distributes only within some specific frequencies (corresponding to the reflected light). Then, the background eliminating circuit  212   c  also produces a simulated light which is essentially out-phase with the continuous portion over all frequencies, such that the continuous portion is cancelled by the simulated light and only the discrete portion is passed. 
     Furthermore, as an example shown in  FIG. 7 , for properly adjusting the light intensity of the light beam  214  with reference to the reflected portion of the light beam  214  and the operation of the light source module  211 , the optical-electronic assembly  21  may further comprise a photo receiver  220  capable of receiving the first portion  214   a  of the light beam  214  and producing a corresponding output signal  220   a . A focus lens  222  may be optionally set for focusing the first portion  214   a  of the light beam  214  on the photo receiver  222 . Optionally, the a power limitation circuit  221  produces a power limitation signal  221   a  according the output signal  220   a  (which is detected) and a reflection-transmission ratio of the first beam splitter  216   a  (which is known when a specific beam splitter is used to form the first beam splitter  216   a ). The power limitation signal  221   a  is proportional to the actual intensity of the light beam  214 . according to which the light source module  211  adjusts the light intensity of the light beam  214 . For example, to avoid the risk that only a very small portion of the second portion  214   b  of the light beam  214  is reflected (the sample  23  might have a very low reflection coefficient) and then the automatic gain control (AGC) circuit  212   b  generates the adjusting signal  219  driving the light source module  211  to overly increase the light intensity of the light beam  214 , the power limitation signal  221   a  could be used to restrict the adjusted light intensity of the light beam  214  to be smaller than or equal to a maximum allowable light intensity of the light source module  211 . 
     Alternatively, as shown in  FIGS. 5˜8 , the optical-electronic assembly  21  may comprise a light adjusting module  217  capable of adjusting the propagation of the light beam  214  and the reflected light beam  215 . The light adjusting module  217  may be positioned between the sample  23  and the light source module  211 , and/or between the sample  23  and the analyzing module  212 . In one example, the light adjusting module  217  comprises a collimator lens  217   a  capable of adjusting propagation of the light beam  214  for ensuring propagation of the light beam  214  with less divergence. The light adjusting module  217  may comprise a first plate  217   b  with a first aperture for ensuring the uniform light intensity of the light beam  214  within a specific cross-sectional area, such that only essentially parallel light is projected on the sample  23  (or such that only incident light within a specific cross-section area and with a specific light strength intensity could pass through the first plate  217   b ). The light adjusting module  217  may further comprise a second plate  217   c  with a second aperture for ensuring the uniform light intensity of the reflected light beam  215  within a specific cross-sectional area (e.g. only incident light within a specific cross-section area and with a specific light intensity could pass through the second plate  217   c ). Hence, if the sample  23  is significantly improperly located (such as the sample  23  is far away from the predetermined position or the sample  23  is significantly tilted), the reflected light beam  215  will be blocked by second plate  217   c  and then the light adjusting module  217  will receive no light, such that it easily finds the significantly displacement of the sample  23 . Alternatively, the light adjusting module  217  may further comprises a first focusing lens  217   d  located between the second beam splitter  216   b  and the first detector  212   d , which focuses the third portion  215   e  of the reflected light beam  215  into the first detector  212   d.    
     The optical-electronic assembly means an assembly of the optical device, optoelectronic device and the electronic device. In one embodiment of the present invention, the optical-electronic assembly  21 , as shown in  FIG. 6  to  FIG. 8 , may include an optical device including the light adjusting module  217  and the beam splitting module  216 , an optoelectronic device including the laser diode  211   b  and the position sensor device  212   a , and an electronic device including the electrostatic discharge device  211   a , the automatic gain control (AGC) circuit  212   b  and the background eliminating circuit  212   c    
     Although the present invention has been explained in relation to some embodiments, it is to be understood that other modifications and variation can be made without departing the spirit and scope of the invention as hereafter claimed.