Abstract:
Techniques of swapping two samples with a mechanical arm that has no backlash, no friction, no particle contamination are described. With the unique structure and the material used for the cables, the mechanical arm provides considerable operating life. When used in a semiconductor inspection system, the mechanical arm, also referred to herein a cable drive robot mechanism, can be advantageously used to swap two wafers as part or within the inspection system. The two wafers, one examined and the other one yet to be examined, can be swapped between two chambers. During the exchanging process, the cable drive robot mechanism seamlessly picks up an examined wafer to exit one chamber while loading up an unexamined wafer to enter another chamber at the same time.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This is a continuation-in-part of co-pending U.S. application Ser. No. 14/730,136, entitled “Drive Mechanism for OPTO-Mechanical Inspection System”, filed on Jun. 3, 2015. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention is related to the area of semiconductor inspection system, and more particularly related to techniques of swapping two samples with a mechanical arm that has no backlash, no friction, no particle contamination and is of considerable operating life. The two samples may be two wafers, one has been examined and the other one is yet to be examined, where the mechanical arm, also referred to herein a cable drive robot mechanism, can be advantageously used to swap the two wafers as part or within an inspection system. 
         [0004]    2. Description of the Related Art 
         [0005]    Moore&#39;s Law states that the number of transistors on integrated circuits doubles every two years, which offers increased transistor density, cost scaling, and performance per watt. Shrinking of node sizes is essential for Moore&#39;s Law to work. With the shrinking sizes becoming tens of nanometers, the defects on a specimen have to be controlled within a certain range in order to ensure the function and yield of manufactured chips. 
         [0006]    With tighter design limits and the escalating need to increase yield and reduce semiconductor manufacturing costs, defect inspection to detect and classify defects in compound semiconductor processing is more critical than ever. As the size of defects becomes smaller and smaller along with the development of the integrated circuit (IC) designs, inspection of defects becomes increasingly difficult. For example, the resolution for an optical inspection tool is no long good enough to inspect hot spots smaller than 20 nm when the wavelength of the optical source is 193 nm. Accordingly, electron beam inspections are introduced and can provide a relatively high resolution to detect much smaller defects on a specimen for hot spots identification, inspection and review. 
         [0007]    Most of the defects that cause a silicon wafer defective are a result of contamination to the silicon wafer. Contamination is defined as a foreign material at the surface of the silicon wafer or within the bulk of the silicon wafer. The contamination can be particles or ionic contamination, liquid droplets and etc. Besides affecting the formation of geometric features in a designed circuit, particle contamination can cause a chip to lose proper functions, often leading to the complete failure of the chip. In general, there are three main sources in which particle contamination could happen: production environment, wafer transmission and wafer exchanging in process equipment. Among the three main sources, particle contamination in wafer exchanging in process happens the most. Therefore, effective particle control in wafer exchanging equipment is critical to yield enhancement. 
         [0008]    Charged particle beam inspection equipment is very important in semiconductor manufacturing process. It can quickly in-situ identify, inspect and further review hot spots on a specimen. It is required that the particles are introduced as little as possible when conducting defects inspection, otherwise the defects analysis would be affected and the lower yield of chips could happen. In an existing e-beam inspection system, particles may be generated when an examined wafer and an unexamined wafer are exchanged. In this disclosure, a cable drive robot mechanism used for wafer exchange is disclosed. 
         [0009]    The cable drive robot mechanism has no backlash, no friction, no particle contamination and with an infinite working life, because the cable material is with high strength and high stiffness. It is very useful for the charged particle beam inspection equipment, which requires high transmission accuracy and especially no-contamination. 
         [0010]    In this disclosure, a mechanical arm with cable drive rotation mechanism is described. One of the advantages, objectives and benefits of the cable drive rotation mechanism is of high precision in rotation, great reliability and durability, and has no backlash and no particle contamination. 
       SUMMARY OF THE INVENTION 
       [0011]    This section is for the purpose of summarizing some aspects of the present invention and to briefly introduce some preferred embodiments. Simplifications or omissions may be made to avoid obscuring the purpose of the section. Such simplifications or omissions are not intended to limit the scope of the present invention. 
         [0012]    In general, the present invention is related to techniques of swapping two samples with a mechanical arm that has no backlash, no friction, no particle contamination and is of considerable operating life. When used in a semiconductor inspection system, the mechanical arm, also referred to herein a cable drive robot mechanism, can be advantageously used to swap two wafers as part or within the inspection system. The two wafers, one examined and the other one yet to be examined, can be swapped between an inspection chamber and a preparation (e.g., load lock) chamber. During the exchanging process, the cable drive robot mechanism seamlessly picks up the examined wafer to exit the inspection chamber while loading up the unexamined wafer to enter the inspection chamber. 
         [0013]    According to one aspect of the present invention, the mechanical arm includes a fixed pulley driven by a motor, a first pulley mounted with a first handler, a second pulley mounted with a second handler, and a first pair and a second pair of up-side and down-side cables. Both of the cables are made from a material that does not produce particles when in operation. Further both ends of the up-side and the down-side cables in the first pair are respectively secured on the first and the fixed pulleys, and both ends of the up-side and the down-side cables in the second pair are respectively secured on the second and the fixed pulleys. 
         [0014]    According to still another aspect of the present invention, the first and second pulleys are caused to rotate synchronously when the fixed pulley is driven to rotate, each of the first and second pulleys is pulled to rotate by one of the up-side and down-side cables respectively in the first and second pair. 
         [0015]    According to still another aspect of the present invention, the material of the up-side and down-side cables is metal. Depending on implementation, the metal is one of aluminum, tungsten, elgiloy steel and stainless steel. 
         [0016]    According to still another aspect of the present invention, a band or cable drive rotation mechanism is provided, there is no relative movement between a cable and a pulley so to minimize possible friction between the cable and the pulley. With a proper material selected for the cables and the pulleys, there are no contamination particles produced in the rotation process, the surface of samples being moved can be free of contamination all the time. 
         [0017]    According to yet another aspect of the present invention, the wear and tear is minimized on either the cable or the pulley. As a result, this driving mechanism enjoys an advantage of substantial operating life. It is an ideal driving mechanism for an inspection system that requires only less than one full rotation. 
         [0018]    Many objects, features, benefits and advantages, together with the foregoing, are attained in the exercise of the invention in the following description and resulting in the embodiment illustrated in the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
           [0020]      FIG. 1  shows a perspective view of an internal structure according to one embodiment of the invention; 
           [0021]      FIG. 2A  shows a perspective view of an exemplary cable drive robot mechanism according to one embodiment of the present invention; 
           [0022]      FIG. 2B  shows a corresponding cross-section view of the cable drive robot mechanism of  FIG. 2A ; 
           [0023]      FIG. 3  shows a view for the transmission principle of the cable drive robot mechanism of  FIG. 2A  or  FIG. 2B ; 
           [0024]      FIG. 4  shows a sketch illustrating the angle range that a cable drive robot mechanism can rotate in one embodiment; 
           [0025]      FIG. 5A  and  FIG. 5B  are two respective views for illustrating a spring loaded pushing force generating mechanism that may be used in the cable drive robot mechanism  104  of  FIG. 1 ; 
           [0026]      FIG. 6A, 6B and 6C  are respective views for illustrating another cable tension adjustment method used in the cable drive robot mechanism  104  of  FIG. 1 ; 
           [0027]      FIG. 6D  shown how an end of the cable may be winded; and 
           [0028]      FIG. 7  is a flow chart for explaining the wafer exchanging steps according to the embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0029]    The detailed description of the present invention is presented largely in terms of procedures, steps, logic blocks, processing, or other symbolic representations that directly or indirectly resemble the operations of mechanical devices. These descriptions and representations are typically used by those skilled in the art to most effectively convey the substance of their work to others skilled in the art. Numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will become obvious to those skilled in the art that the present invention may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuitry have not been described in detail to avoid unnecessarily obscuring aspects of the present invention. 
         [0030]    Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. 
         [0031]    Embodiments of the present invention are discussed herein with reference to  FIGS. 1-7 . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes as the invention extends beyond these limited embodiments. 
         [0032]    The present invention pertains to a mechanism that can be used advantageously for wafer exchanging, for example, in an inspection system (e.g., charged particle beam inspection equipment). According to one aspect of the present invention, the mechanism, also referred to as cable drive robot mechanism, has no backlash, no friction, no particle contamination and a substantial long working life if not infinite. As will be described further below, the material used in the cable drive robot mechanism is of high strength and high stiffness. Such a mechanism is very useful for the charged particle beam inspection equipment which requires high transmission accuracy and especially has no-contamination. 
         [0033]    Referring now to  FIG. 1 , it shows a perspective view of an internal structure  100  according to one embodiment of the invention. The structure  100  may be enclosed in or part of an inspection system, such as wafer inspection equipment or electronic beam inspection system. As shown in  FIG. 1 , the structure  100  comprises a main chamber  102 , a cable drive robot mechanism  104 , a gate valve  106 , a load lock chamber  108 , a wafer lift pin  110 , two wafers  112  and  113 , a stage  114  and an electrostatic chuck  116 . While the wafer  112  (labeled as Wa) is being examined under a focused beam (not shown) in the center of the main chamber  102 , an unexamined wafer  113  (labeled as Wb) is being prepared in the load lock chamber  108 . The two wafers  112  and  113  are to be swapped or exchanged when the wafer  112  is done with an inspection in the main chamber  102 . 
         [0034]    In operation, after the wafer  112  is done for inspection, the stage  114  carrying the wafer  112 , assumed to be moving along x or y axis, is shifted to a wafer exchange position. The gate valve  106  is then opened. At the same time, the wafer lift pin  110  in the load lock chamber  108  vertically lifts the unexamined wafer  113  to the wafer exchanging position. A wafer lift pin (not shown) within the electrostatic chuck  116  in the main chamber  102  lifts the examined wafer  112  vertically to the wafer exchanging position. Next, the cable drive robot mechanism  104  is operated to move to the wafer exchanging position so as to exchange the wafers  112  and  113 . Afterwards, the two lift pins in both sides descend to the original position to put down the two wafers  112  and  113  on the cable drive robot mechanism  104 . Then the cable drive robot mechanism  104  is caused to rotate to an opposite wafer exchanging position, where the wafer  112  is in the load lock chamber  108  while the wafer  113  is in the main chamber  102 . Further, the two lift pins in both sides lift again to the wafer exchanging position, so the cable drive robot mechanism  104  can now be rotated to the initial position. Then the gate valve  106  is closed and the wafer lift pin within the electrostatic chuck  116  pulls down so that the unexamined wafer  113 , now in the chamber  102 , can be inspected. 
         [0035]    In operation, the x-y stage  114  is moved to the center of the main chamber  102  so as to start the examination of the wafer  113 . During this period, the examined wafer  112  is exited from the load lock chamber  108  while an unexamined wafer is newly introduced into the load lock chamber  108 . The examination for the new wafer follows as soon as the examination for the wafer  113  in the main chamber  102  is completed. 
         [0036]    As described above, the cable drive robot mechanism  104  is designed to exchange an examined wafer with an unexamined wafer at the same time. One of important features, objects and advantages of this design is to shorten the time required for wafer exchanging so as to enhance the throughput of an inspection system when employed therein. Referring now to  FIG. 2A , it shows a perspective view of an exemplary cable drive robot mechanism  200  according to one embodiment of the present invention.  FIG. 2B  shows a corresponding cross-section view of the cable drive robot mechanism  200 . The cable drive robot mechanism  200  may be used in  FIG. 1  to swap the two wafers  112  and  113 . As shown in  FIG. 2A , the cable drive robot mechanism  200  includes a rotating arm  201 , two wafer hands  202 A and  202 B, a servo motor  203 , a motor adapter  204 , a motor connector  205 , four cable  206 A,  206 B,  206 C and  206 D, a coupling  207 , a magnetic bearing  208 , a fixed pulley  209 , six roller bearings  210 , two rotating pulley  211 A and  211 B, two connecting shafts  212 A and  212 B. 
         [0037]    According to one embodiment, the fixed pulley  209  is mounted in the main chamber  102  of  FIG. 1 . Specifically, the fixed pulley  209  is mounted to the servo motor  203  through the motor adapter  204  and the motor connector  205 . The rotating arm  201  is connected with the magnetic bearing  208  which is connected with the coupling  207 . The servo motor  203  is also connected with the coupling  207 . So the rotating arm  201  is caused to rotate in association with the rotation of the servo motor  203 . The connecting shafts  212 A and  212 B are supported by the rotating arm  201  through the roller bearings  210  so as to be rotatable. Both the two wafer hands  202 A and  202 B and the two rotating pulley  211 A and  211 B are fixed to the connecting shafts  212 A and  212 B so that they can be rotated synchronously. According to one embodiment, one end of the cable  206 A or  206 B is fixed to the fixed pulley  209  and the other end of the cable  206 A or  206 B is fixed to the rotating pulley  211 A, the same is applied to the cable  206 C or  206 D, and the rotating pulley  211 B. As will be further detailed below, the four cables  206 A,  206 B,  206 C and  206 D should be arranged properly to ensure that they will not interfere with each other. 
         [0038]    In operation, when the rotating arm  201  is driven by the servo motor  203  to rotate, the two rotating pulley  211 A and  211 B are caused to rotate through the four cables  206 A,  206 B,  206 C and  206 D because the two ends of each cable are fixed. Further the two wafer hands  202 A and  202 B are rotated in association with the rotation of the two rotating pulleys  211 A and  211 B so that they can exchange an examined wafer and an unexamined wafer at the same time. 
         [0039]    Referring now to  FIG. 3 , it shows a view for the transmission principle of the cable drive robot mechanism  200  of  FIG. 2A  or  FIG. 2B . As shown in  FIG. 3 , there are eight tension devices  301  and eight fixing blocks  302 . The cables  206 A and  206 B are arranged in section A-A and the cable  206 B and  206 C are arranged in section B-B. One end of the cable is fixed to the fixed pulley  209  and the other end of the cable is fixed to either on of the two rotating pulley  211 A or  211 B with fixing blocks  301 . The tension devices  301  are respectively used for cable tension adjusting mechanism and installed at the end of the four cables  206 A,  206 B,  206 C and  206 D. 
         [0040]    Referring to section A-A, when the rotating arm  201  is rotated according to an arrow M the cables  206 B and  206 C shall twine onto the fixed pulley  209  in the circumferential direction. As a result, the cables  206 B and  206 C are released from the two rotating pulleys  211 A and  211 B because the cables are tense. Then the two rotating pulley  211 A and  211 B are rotated according to the arrows M. Referring to the section B-B, when the two rotating pulleys  211 A and  211 B are rotated according to the red arrow, the cables  206 A and  206 D are forced to release from the fixed pulley  209  and twine onto the two rotating pulleys  211 A and  211 B. Then the two wafer hands  202 A and  202 B are rotated in association with the rotation of the two rotating pulleys  211 A and  211 B. In the section B-B, when the rotating arm  201  is rotated according to an arrow N, the transmission principle is the same as when the rotating arm  201  is rotated according to the arrow M. 
         [0041]      FIG. 4  shows a sketch illustrating the angle range that a cable drive robot mechanism can rotate in one embodiment. The cable drive robot mechanism has three stop positions. When the x-y stage  114  is caused to carry an examined wafer and shift to a wafer exchange position, the rotating arm  201  is rotated to the wafer exchange position  1  according to the arrow M. Then the rotating arm  201  is rotated to the wafer exchange position  2  according to the arrow N. Eventually, the rotating arm  201  is rotated to the initial position according to the arrow M to wait for the next wafer exchanging operation. During the rotation, not only should the length of the four cables be arranged properly to ensure that they are not interfered with each other, but also the overlap length on the fixed pulley  209  and the two rotating pulleys  211 A and  211 B are long enough to meet the rotation angle. 
         [0042]    In one embodiment, the radio between the fixed pulley and the two rotating pulleys is set to 1:2. So the two rotating pulleys  211 A and  211 B are rotated to 150° when the fixed pulley  209  is rotated to 75° initially. Referring to the section A-A in  FIG. 3 , when the rotating arm  201  is rotated to the wafer exchange position  1  according to the arrow M, the tension device  301  and the fixing block  302  must be designed within 29° to ensure that the cable  206   b  and  206   c  would not interfere with each other after twining onto the fixed pulley  209 , where the tension device  301  and the fixing block  302  must be designed beyond 151° to ensure that the overlap length on the two rotating pulleys  211 A and  211 B is long enough after the cables  206 B and  206 C are released. 
         [0043]    Referring now to the section B-B in  FIG. 3 , when the rotating arm  201  is rotated to the wafer exchange position  1  according to the arrow M, the tension device  301  and the fixing block  302  must be designed within 29° to ensure that the overlap length on the fixed pulley  209  is long enough after the cables  206 A and  206 D are released, where the tension device  301  and the fixing block  302  must be designed beyond 151° to ensure that the cables  206 A and  206 D are not to be interfered with themselves after twining onto the two rotating pulleys  211 A and  211 B. The positions of the tension device  301  and the fixing block  302  are the same when the rotating arm  201  is rotated to the wafer exchange position  2  according to the arrow N, because they are symmetrical. 
         [0044]      FIG. 5A  and  FIG. 5B  are two respective views for illustrating a spring loaded pushing force generating mechanism that may be used in the cable drive robot mechanism  104  of  FIG. 1 . The spring loaded pushing force generating mechanism comprises a shoulder screw  501 , a spring holding block  502 , a stiff enough spring  503  and a fixing block  504 . The spring  503  is installed between the slot of a pulley and the spring holding block  502 . Then the shoulder screw  501  is used to hold the spring holding block  502  and the spring  503  on the right position. The spring holding block  502  is pushed by the compressed spring  503  to move outward in the direction of the radius of the pulley and the direction is guided by the shoulder screw  501  as well. The cable is lying inside of the notch designed on the spring holding block  502 , so the movement of the spring holding block  502  is pushing the cable to be tighter. The end of the cable and the fixing block  504  are welded together, then it is mounted on the pulley with screws after selecting the spring with the right stiffness to let the cable get an optimized tension. The cable tension is optimized by using the described tension adjustment method, so there is no-backlash in the driving mechanism, which is very critical to the high precision movement process in the e-beam inspection system. Two notches are machined on the outer surface of each pulley and work as tracks to confine the cable from running off the outer surface of the pulleys. 
         [0045]      FIG. 6A, 6B and 6C  are respective views for illustrating another cable tension adjustment method used in the cable drive robot mechanism  104  of  FIG. 1 . It comprises a worm gear  601 , a worm driver  602 , a mounting plate  603 , cross head screws  604  and a cable limit sheet  605 . As shown in  FIG. 6B  and  FIG. 6C , the worm driver  602  is first installed on the slot of the mounting plate  603 , then the worm gear  601  is installed on the mounting plate  603  and fixed by the cross head screws  604 . After that, one can insert the end of the cable through the hole in the worm gear  601  and wind the end of the cable according to  FIG. 6D . Some excess cable should be left to make sure that the cable can wind around the worm gear shaft a few (e.g., 3 to 4) rounds, otherwise the cable would loosen up after the cable drive robot mechanism is running for some time. Then the assembly can be installed on the two rotating pulleys  211 A and  211 B and fixed by the cross head screws  604  as shown in  FIG. 6A . Then the cable limit sheet  605  which confine the cable from running off the outer surface of the pulleys can be mounted on both of the rotating pulleys  211 A and  211 B by the cross head screws  604 . Then the worm driver  602  can be rotated by a tool (e.g., Allen wrench) to ensure that the cable tension is optimized. The worm gear mechanism is used in the cable tension adjustment method, because it has an interlock function which the worm gear  601  can be driven by the worm driver  602 , but the worm driver  602  cannot be driven by the worm gear  601 . So the cable will not loosen up after the cable tension is optimized by rotating the worm driver  602  using an Allen wrench. This is very critical to the high precision movement process in the driving mechanism. The cable tension adjustment method is easy to install and operate and have high reliability. 
         [0046]      FIG. 7  is a flow chart for explaining the wafer exchanging steps according to the embodiment of the present invention. It is assumed that the steps take place in an e-beam inspection system. Those skilled in the art can appreciate that the same or the substantially similar steps could be implemented in other devices. The initial state is assumed that a wafer is being examined under a focused beam in the center part of the main chamber  102  of  FIG. 1 , an unexamined wafer which will be examined next is being prepared in the load lock chamber  108   FIG. 1  and the cable drive robot mechanism is in its initial position. 
         [0047]    As shown in  FIG. 7  and in operation, the x-y stage  107  carrying the examined wafer  112  is shifted to a wafer exchange position and the gate valve  106  is opened so as to communicate the load lock chamber  108  with the main chamber  102 . Next, the wafer lift pin  110  in the load lock chamber  108  vertically lift the unexamined wafer  113  to the wafer exchanging position and the wafer lift pin within the electrostatic chuck  116  in the main chamber  102  vertically lift the examined wafer  112  to the wafer exchanging position. At this moment, the cable drive robot mechanism  104  is rotated to the wafer exchanging position  1 . The wafer lift pin  110  and the wafer lift pin within the electrostatic chuck  116  descend to the original position to put the two wafers  112  and  113  respectively on the wafer hands  202 A and  202 B. Next, the cable drive robot mechanism  104  is rotated to the opposite wafer exchanging position  2  according to the arrow N in  FIG. 4 . Next, the wafer lift pin  110  and the wafer lift pin within the electrostatic chuck  116  lift again to withdraw the wafers  112  and  113 . At this moment, the cable drive robot mechanism  104  is rotated to the initial position according to the arrow M in  FIG. 4 . Next, the gate valve  106  is closed and the wafer lift pin within the electrostatic chuck  108  pulls down so that the unexamined wafer  113  can be chucked. Next, the x-y stage  114  carrying the unexamined wafer  113  is moved to the center of the main chamber  102  so as to start the examination of the wafer  113 . Eventually, the examined wafer  112  is exited from the load lock chamber  108  while another unexamined wafer is introduced into the load lock chamber  108 . The examination for the new wafer continuously follows as soon as the examination at present is completed. 
         [0048]    The present invention has been described in sufficient details with a certain degree of particularity. It is understood to those skilled in the art that the present disclosure of embodiments has been made by way of examples only and that numerous changes in the arrangement and combination of parts may be resorted without departing from the spirit and scope of the invention as claimed. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description of embodiments.