Abstract:
An apparatus rotates a sample to facilitate an accurate analysis of the sample. The apparatus includes a sample stage on which a plurality of samples are supported, a rotatable cap and a linearly movable plate for placing a selected one of the samples at an analysis position, and a rotating stage that supports the sample stage, rotatable cap and movable plate. The rotating stage is rotatable about an axis of rotation that intersects the analysis position. Once the selected sample is placed at the analysis position by the rotation of the cap and the linear movement of the plate, the selected sample is rotated by the rotating stage. The analysis process can be selectively or sequentially carried out with respect to the plurality of samples with a high degree of efficiency and without the associated drive mechanisms experiencing high loads.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the inspection of semiconductor substrates during the process of manufacturing semiconductor devices. More particularly, the present invention relates to an apparatus for rotating a sample while the sample is inspected so that the sample can be accurately analyzed. 
     2. Description of the Related Art 
     Currently, semiconductor memory devices are being developed at a rapid pace due to the widespread use of equipment, such as personal computers, for processing various types of information. Semiconductor devices must generally perform at high speeds and have the capacity to store large amounts of information. Accordingly, the current art is focused on developing and realizing semiconductor devices having a high degree of integration, response speed, and reliability. To this end, highly precise techniques are required for fabricating today&#39;s semiconductor devices. 
     More specifically, semiconductor devices are manufactured by repeatedly performing a series of precise unit processes, such as film deposition, patterning and metal wiring processes, on a semiconductor substrate. In addition, various inspection and analysis processes are carried out in the midst of these manufacturing processes. The inspection and analysis processes are carried out with respect to a semiconductor substrate to determine the density of a particular impurity that might be present in or on the surface of a film formed on the substrate, to check whether a bridge phenomenon is present in patterns formed on the substrate, and/or to check whether there is any disconnection in wiring formed on the substrate. 
     A scanning electron microscope (SEM), a transmission electron microscope (TEM) and a secondary ion mass spectroscope (SIMS) are used for the inspection and analysis processes. The secondary ion mass spectroscope is used for analyzing the composition or the profile of a film/film pattern formed on the semiconductor substrate. 
     When the profile of a film/film pattern formed on a semiconductor substrate is analyzed by using the secondary ion mass spectroscope, the sample is irradiated with an argon ion beam to thereby etch the sample. As a result, secondary ions are generated from the sample, and these secondary ions are analyzed by the secondary ion mass spectroscope to determine the profile of the film/film pattern. One example of such an analysis process using a secondary ion mass spectroscope is disclosed in U.S. Pat. No. 5,943,548, issued to Kim. 
     In this technique, the surface of the sample is etched irregularly by the argon ion beam. Such irregularities would limit the resolution of the apparatus in determining the profile of the film/film pattern. This problem can be overcome by rotating the sample. That is, the resolution of the inspection apparatus can be improved by rotating the stage on which the sample is supported. 
     To this end, the secondary ion mass spectroscope is provided with a sample rotating apparatus, which supports the sample, moves the sample to an analysis position, and rotates the sample. The sample rotating apparatus can move in x-axis, y-axis, and z-axis directions for allowing the sample to be placed at a prescribed coordinates defining an analysis position, and rotates the sample once the sample is located at the analysis position. 
     The sample rotating apparatus includes a sample stage, a first driving section for rotating the sample stage, and a second driving section for moving the sample stage linearly. The second driving section includes motors for moving the sample stage and the first driving section in x-axis, y-axis , and z-axis directions. The sample is placed on a central area of the sample stage at a position coinciding with the central axis of a rotating shaft of the first driving section. The second driving section moves the sample to the analysis position. Then the sample is rotated by the first driving section, the rotated sample is etched with the argon beam, and the resulting secondary ions are analyzed to determine the profile of a film/film pattern on the sample. 
     In addition to an analysis chamber in which the sample rotating apparatus is disposed, the inspection and analysis apparatus includes a sub-chamber connected to one side of the analysis chamber. The sample is loaded onto the sample stage in the sub-chamber, and is moved to the sample rotating apparatus provided in the analysis chamber. At this time, the analysis chamber is maintained at a pressure of about 10 −9  to 10 −10  Torr and the sub-chamber is maintained at a pressure of about 10 −6  to 10 −7  Torr. That is, the pressure in the sub-chamber is at atmospheric pressure when the sample is loaded in the sub-chamber, and the pressure in the sub-chamber is about 10 −6  to 10 −7  Torr when the sample is moved to the analysis chamber. On the contrary, once the sample has been moved into the sub-chamber after the sample has been analyzed, the pressure in the sub-chamber is adjusted to atmospheric pressure to facilitate the unloading of the sample from the sub-chamber. Accordingly, the pressure of the sub-chamber has to be adjusted every time a sample is transferred therethrough, and adjusting of the pressure of the sub-chamber requires a certain amount of time. 
     Therefore, a plurality of samples are loaded on the sample stage at once in order to make the process efficient. Then, a selected one of the samples is placed at the analysis position, and the profile analysis is carried out with respect to the selected sample. In this case, however, it is difficult to rotate the selected sample. The rotational axis of the drive shaft of the first driving section does not extend through the analysis position while the selected sample is being rotated. This shortens the useful life of the second driving section. That is, the second driving section may rotate the first driving section in a direction identical to the direction rotation of the first driving section so as to prevent the sample from being displaced from the analysis position. At this time, the motors of the second driving section are overloaded. As a result, the secondary ion mass spectroscope has high maintenance and repair costs and limits the efficiency of the overall manufacturing process. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to solve the problems of the prior art. Therefore, an object of the present invention is to provide an apparatus that is capable of supporting a plurality of samples, setting a selected one of the samples at an analysis position, and rotating the selected sample about an axis of rotation aligned with the analysis position once the selected sample has been set at the analysis position. 
     The apparatus for rotating a sample comprises a sample stage for supporting a plurality of samples, position adjusting means for moving the stage such that a selected one of the samples is located at the analysis position, and rotating means for rotating the sample stage and the position adjusting means about an axis that passes through the analysis position such that the selected sample is rotated at the analysis position. 
     The position adjusting means and rotating means are together mounted to a three-axis drive mechanism. Accordingly, the position adjusting means, rotating means, and sample stage are movable together along three axes orthogonal to one another. 
     According to another aspect of the present invention, the apparatus for rotating a sample comprises a sample stage for supporting a plurality of samples as spaced from one another along a circle, a moving member supporting the sample stage and movable in a radial direction of the circle such that the sample stage can be located at a position where the circle intersects an analysis position, a rotating cap having a main body disposed on said moving member and supported so as to be rotatable relative to the moving member about a first axis of rotation, a driving mechanism(s) that drives/drive the rotating cap and the moving member, and a rotating stage supporting the moving member and being rotatable about a central axis of rotation passing through the analysis position. 
     A first driving shaft extending along the central axis of rotation is connected to a lower portion of the rotating stage so as to transmit a driving force that rotates the rotating stage. 
     The moving member has a main body and a rack disposed on a lower surface of the main body. The rack extends in the radial direction of the circle along which the samples are disposed such that the moving member is moved in the radial direction when a driving force is transmitted to the rack. 
     The sample stage is mounted to the rotating cap such that the sample stage can be rotated while the circle intersects the analysis position. Thus, a selected sample supported on the stage is set at the analysis position through a combination of the rotational movement of the rotating cap and the linear movement of the moving member. In addition, the rotating cap has first gear teeth at a lower portion of the main body thereof. The first gear teeth are centered around the first axis of rotation such that the rotating cap is rotated relative to the moving body when a driving force is transmitted to the first gear teeth. 
     The driving mechanism is constituted by a driving gear that is selectively engageable with the first gear teeth of the rotating cap and the rack gear of the moving member, and a second driving shaft that extends through the first driving shaft and is connected to the driving gear. 
     The sample stage, rotating cap, moving member and rotating stage are together mounted to a three-axis drive mechanism. Accordingly, the sample stage, rotating cap, moving member and rotating stage are movable together along three axes orthogonal to one another. 
     According to the present invention, a selected sample placed at the analysis position is rotatable about the central axis of rotation aligned with the analysis position. Accordingly, neither the sample rotating apparatus nor the three-axis drive mechanism supporting the sample rotating apparatus is overloaded. Therefore, the analysis process can be selectively or sequentially carried with high efficiency with respect to a plurality of samples and without significantly affecting the useful life of the three-axis drive mechanism. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments thereof made with reference to the attached drawings, of which: 
     FIG. 1 is a side view, partially in section, of one embodiment of a sample rotating apparatus according to the present invention; 
     FIG. 2 is a perspective view of a sample stage and a fixing ring of the sample rotating apparatus shown in FIG. 1; 
     FIG. 3 is a sectional view of a stopper of the sample rotating apparatus; 
     FIG. 4 is a bottom view of a rotating cap of the sample rotating apparatus; 
     FIG. 5 is a perspective view of the rotating cap; 
     FIG. 6 is a perspective view of a driving gear of the sample rotating apparatus; 
     FIG. 7 is a bottom view of a moving plate of the sample rotating apparatus; 
     FIG. 8 is a perspective view of a rotating stage of the sample rotating apparatus; 
     FIG. 9 is a side view of the sample rotating apparatus, showing the coupling between the rotating stage and the moving plate thereof; 
     FIG. 10 is a schematic diagram of a secondary ion mass spectroscope comprising the sample rotating apparatus of FIG. 1; 
     FIG. 11 is a perspective view of the sample rotating apparatus and a three-axis driving device; 
     FIG. 12 is a bottom view of the rotating cap of another embodiment of a sample rotating apparatus according to the present invention; 
     FIG. 13 is a sectional view of the rotating cap shown in FIG. 12; 
     FIG. 14 is a perspective view of the driving gear operatively associated with the rotating cap shown in FIG. 12; 
     FIG. 15 is a view similar to that of FIG. 1 but showing the linear movement of the sample stage; 
     FIG. 16 is a plan view of the sample stage showing the rotation thereof used to place a selected sample at the analysis position; and 
     FIG. 17 is a plan view of the sample rotating apparatus showing the rotation of the sample stage during the analysis of the selected sample. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, the present invention will be described in detail with reference to accompanying drawings. 
     Referring first to FIG. 1, the sample rotating apparatus  100  includes a sample stage  102  on which a plurality of samples  10  are placed, a position adjusting section  200  for allowing a sample  10   a  selected from the plurality of samples  10  to be placed at an analysis position, and a rotating section  300  for rotating the selected sample  10   a  and having a central axis coincident with the analysis position. 
     Referring to FIG. 2, the sample stage  102  includes an circular plate  104  on which the samples  10  are placed and a cylindrical body  106  disposed below the circular plate  104 . The sample stage  102  also has a clamping slot  108 , cooperating with a clamp  202  (refer to FIG.  1 ), in an outer wall of the cylindrical body  106 . The samples  10  are radially arranged on the circular plate  104  along the periphery of the circular plate  104 . A fixing ring  110  for fixing the samples  10  to the sample stage  102  is coupled to the upper portion of the circular plate  104  by means of bolts  112 . A plurality of threaded holes  114  corresponding to the bolts  112  are formed along the periphery of the circular plate  104 . The fixing ring  110  has the form of a flat annular plate, and a plurality of holes  116  corresponding to the threaded holes  114  are formed in the fixing ring  110 . Accordingly, the samples are arranged between the circular plate  104  and the fixing ring  110  coupled to the upper portion of the circular plate  104 . 
     Referring again to FIG. 1, the position adjusting section  200  includes a rotating cap  204  for supporting and rotating the sample stage  102 , a moving plate  206  for moving the rotating cap  204 , a driving gear  208  for transferring first and second driving forces to the rotating cap  204  and to the moving plate  206 , respectively, and a first drive shaft  210  connected to a lower surface of the driving gear  208 . 
     The rotating section  300  includes a rotating stage  302  disposed at the bottom portion of the moving plate  206 , and a second drive shaft  304  that supports the rotating stage  302  and transfers a third driving force to the rotating stage  302 . 
     The main body of the rotating cap  204  is in the form of a disc having a diameter identical to the diameter of the body  106  of the sample stage  102 , and a conical groove  212  in the bottom thereof. A first (toothed section) gear  214  extends along the conical groove  212 , and can be placed in meshing engagement with the driving gear  208 . In that state, rotation of the driving gear  208  causes the sample stage  102  and the rotating cap  204  to rotate. 
     The main body of the moving plate  206  is in the form of a disc having a diameter identical to the diameter of the rotating cap  204 . A rack  216  is integral with a lower portion of the main body of the moving plate  206 . The rotating cap  204  is rotatably supported on the moving plate  206  by a rotating shaft  218 . In particular, the rotating shaft  218  connects the rotating cap  204 , at a central portion of the conical groove  212 , to a central portion of an upper surface of the moving plate  206 . Therefore, the rotating shaft  218  supports the rotating cap  204  in such a manner that the rotating cap  204  can be rotated upon receiving the first driving force from the driving gear  208 . 
     A passage  220 , through which the driving gear  208  may be extended, is formed in the moving plate  206  at a location between the center and the periphery of the moving plate  206 . The rack  216  is disposed to one side of the passage  220  such that the rack  216  can be engaged with the driving gear  208 . The rack gear  216  moves the moving plate  206  in the radial direction thereof under the second driving force transferred to the rack  216  from the driving gear  208 . 
     In other words, the driving gear  208  engages the first gear  214  when it is moved upwardly through the passage  220 . In this state, rotation of the driving gear  208  rotates the rotating cap  204 . In addition, the driving gear  208  can be moved downwardly through the passage  220  and into engagement with the rack  216 . In this state, rotation of the driving gear  208  causes the moving plate  206  to move linearly in the radial direction thereof. 
     The length of the rack  216  is thus preferably longer than the radial distance between the center of the moving plate  206  and the passage  220 . In addition, the distance over which the moving plate  206  can be moved linearly, and which distance corresponds to the length of the rack  216 , is preferably greater than the radius of a circle  12  (refer to FIG. 2) along which the samples  10  are arranged. 
     Referring now to FIGS. 1 and 3, a stopper  222  is provided on the upper surface of the moving plate  206  for preventing the rotating cap  204  from being rotated while the driving gear  208  is engaged with the rack gear  216 . The stopper  222  includes a generally cylindrical housing  224 , a compression coil spring  226  accommodated in the housing  224 , and a ball  228  held within the housing  224  as seated on the coil spring  226 . The housing  224  is disposed on the upper surface of the moving plate  206 , diametrically across form the passage  220 . Part of the ball  228  protrudes from the housing  224  and is urged into contact with the first gear  214  by means of the coil spring  226 . 
     Referring now to FIGS. 4 and 5, the clamp  202  has a plurality of clamp arms integral with the main body of the rotating cap  204  to secure the sample stage  102  (refer to FIG. 2) to the rotating cap  204 . The clamp arms extend upwardly from the outer wall of the main body of the rotating cap  204  and have protrusions  230  at the upper ends thereof. The protrusions  230  fit within the clamping slot  108  formed in the cylindrical body  106  of the sample stage  102 . The clamp arms are made of an elastic material so that the sample stage  102  can be easily mounted on the rotating cap  204 . The protrusions  230  are rounded such that their sliding engagement with the body  106  of the sample stage  102  cams the clamp arms away from each other, thereby facilitating the mounting of the sample stage  102  to the rotating cap  204 . 
     Referring now to FIG. 6, the upper portion of the driving gear  208  has a frustoconical shape and constitutes a second (toothed section) gear  232  that is designed to mesh with the first gear  214  (refer to FIG. 1) of the rotating cap  204 . In addition, the periphery of the driving gear  208  constitutes a third (toothed section) gear  234  that is designed to mesh with the rack  216  (refer to FIG. 1) formed at the lower portion of the moving plate  206 . 
     FIG. 9 shows a state in which the rotating stage  302  and the moving plate  206  are drivingly coupled. 
     Referring to FIGS. 1,  7 ,  8  and  9 , the rotating stage  302  comprises a main body in the form of a disc, and a pair of rails  306  disposed on the upper surface of the main body. The rails  306  are disposed at both sides of the rack  216  and the passage  220  of the driving gear  208 , and extend parallel to the rack  216  for supporting and guiding the moving plate  206 . Each of the rails  306  includes an upright portion, and a first protruding jaw  308  extending to one side of the upright portion, adjacent the periphery of the rotating stage  302 , to prevent the moving plate  206  from being separated from the stage  302 . A pair of guides  236 , corresponding to the rails  306  of the rotating stage  302 , extend downwardly from the lower surface of the disc-shaped body of the moving plate  206 . Each of the guides  236  includes a second protruding jaw  238  corresponding to and latched to the first protruding jaw  308  of one of the rails  306 . 
     On the other hand, the second driving shaft  304  for transferring the third driving force is connected to the bottom of the rotating stage  302  so as to rotate the rotating stage  302 . The first driving shaft  210  extends through the second driving shaft  304  and can be moved up and down within the second driving shaft  304  so as to selectively engage the first gear section  214  and the rack gear  216 . 
     FIG. 10 shows a secondary ion mass spectroscope having the sample rotating apparatus shown in FIGS. 1-9, and FIG. 11 is a perspective view of the sample rotating apparatus and a multi-axis driving device of the same. 
     Referring to FIGS. 1,  10 , and  11 , the sample rotating apparatus  100  and the multi-axis driving device  404  are disposed in an analysis chamber  402  of the secondary ion mass spectroscope. The multi-axis driving device  404  supports and moves the sample rotating apparatus  100 . In addition, the multi-axis driving device  404  applies the driving forces that operate the sample rotating apparatus  100 . More specifically, the multi-axis driving device  404  positions the sample rotating apparatus  100  in x-axis, y-axis and z-axis directions within the analysis chamber  402 , and provides the first, second and third driving forces to rotate or move the rotating cap  204  of the sample stage  102 , the moving plate  206  and the rotating stage  302 , respectively. For example, the multi-axis driving device  404  includes a three-axis (orthogonal coordinates) robot having a first motor for providing the first and second driving forces, second motors for moving the sample rotating apparatus  100  in the x-axis, y-axis and z-axis directions, and a lead screw. 
     A sub-chamber  406  in which samples  10  are loaded/unloaded onto/from the sample stage  102  is connected to one side of the analysis chamber  402 . The sample stage  102  loaded with samples  10  is moved from the sub-chamber  406  to the rotating cap  204  in the analysis chamber  402  by a conveying robot (not shown) and is clamped to the rotating cap by the clamp formed of clamp arms  202 . Generally, the profile analysis is carried out by the secondary ion mass spectroscope under a vacuum of 10 −9  to 10 −1  Torr. The sub-chamber  406  is provided to prevent impurities from entering the analysis chamber  402  when the samples are loaded/unloaded and to improve the efficiency of the analysis process. That is, the sub-chamber  406  allows a negative pressure to be constantly maintained in the analysis chamber  402 . A door (not shown) provided between the analysis chamber  402  and the sub-chamber  406  is closed when the samples  10  are loaded/unloaded. During these steps, the sub-chamber  406  is maintained under atmospheric pressure. However, when the sample stage  102  loaded with samples  10  is to be moved by the conveying robot into the analysis chamber  402 , the sub-chamber  406  is evacuated to a pressure of 10 −6  to 10 −7  Torr and then, the door is opened. Though not illustrated in the figures, a vacuum pump and a plurality of valves are connected to the analysis chamber  402  and the sub chamber  406  for regulating the respective pressures of the chambers. 
     In addition, an argon ion gun  408  for providing an argon ion beam is provided at one side of an upper portion of the analysis chamber  402 . Secondary ions are produced from the sample by the argon ion beam when the sample is irradiated with the beam. On the other hand, a mass spectroscope  410  for selecting ions of a predetermined type from the secondary ions produced from the sample, and a detector  412  for detecting the selected ions are connected to the other side of the upper portion of the analysis chamber  402 . 
     FIGS. 12-14 show a rotating cap and driving gear of another embodiment of an apparatus for rotating a sample according to the present invention. 
     Referring to FIGS. 12 to  14 , the rotating cap  500  has a vertical inner wall defining an circular groove  502  in the bottom of the cap  500 , and a set of gear teeth  504  formed along the inner wall for rotating the sample stage  102  (refer to FIG.  1 ). A set of gear teeth  512 , designed to mesh with the gear teeth  504 , are formed along an outer wall of a driving gear  510 . The gear teeth  512  can also mesh with those of the rack  216  of the moving plate  206 . 
     Hereinafter, the process of inspecting and analyzing the sample using the secondary ion mass spectroscope having the sample rotating apparatus according to the present invention will be described with reference to the accompanying drawings. 
     First, a plurality of samples  10  are radially arranged on the sample stage  102  in the sub-chamber  406 , and are fixed to the sample stage  102  by means of the fixing ring  110 . Then, the sample stage  102  loaded with the samples  10  is set by the conveying robot on the upper surface of the rotating cap  204  within the analysis chamber  402 . Accordingly, the sample stage  102  is clamped to the rotating cap  204  by the clamp arms  202 . 
     Then, the multi-axis driving device  404  moves the sample rotating apparatus  100  in x-axis and y-axis directions to align the central axis of the second driving shaft  304  with an analysis position, and moves the sample rotating apparatus in the z-axis direction until the center of the circle  12  along which the samples  10  are arranged is located at the analysis position. At this time, the center of the circle  12  is located along the central axis of the second driving shaft  304  and the driving gear  208  is engaged with the rack  216 . 
     Referring to FIG. 15, the moving plate  206  is moved radially by the first driving shaft  210  and the driving gear  208  until the analysis position is located along the circle  12  itself. At this time, the second driving shaft  304  is not rotated. The arrow in FIG. 15 represents the direction of movement of the moving plate  206 . 
     Referring to FIG. 16, the rotating cap  204  and the sample stage  102  are rotated by the first driving shaft  210  and the driving gear  208  so as to position a first one of the samples, namely a selected sample  14 , at the analysis position. To this end, the driving gear  208  is engaged with the gear  214 , the driving gear  208  is rotated to rotate the cap  204  and the stage  102  about the central axis of shaft  218 , and the second driving shaft  304  is not rotated. The arrow shown in FIG. 16 represents the direction of rotation of the sample stage  102 . 
     Referring next to FIG. 17, the first sample  14  is rotated at the analysis position by the second driving shaft  304  while the argon ion beam from the argon ion gun  408  irradiates the surface of the first sample  14 . The first sample  14  is etched by the argon ions of the beam, whereby secondary ions are generated from the first sample  14 . Among the secondary ions, ions of a predetermined type appropriate for analysis are selected by the mass spectroscope  410  and detected by the detector  412 . At this time, the driving gear  208  is engaged with the rack  216  and the first and second driving shafts  210  and  304  rotate at the same angular speed. Accordingly, the moving plate  206  is prevented from moving in the radial direction thereof. In addition, the stopper  222  prevents the rotating cap  204  from rotating relative to the central axis of shaft  218 . 
     When the profile analysis of the first sample  14  has been completed, the argon beam is shut off, the rotation of the sample stage  102  is stopped, and the driving gear  208  is moved upwardly into engagement with the gear  214  of the rotating cap  204 . Then, the rotating cap  204  and the sample stage  102  are rotated by the first driving shaft  210  and the driving gear  208  so as to place a second sample  16  at the analysis position. 
     These steps may be repeated such that the samples  10  are sequentially analyzed. In addition, various portions of each selected sample  14  can be analyzed because the sample stage  204  and the moving plate  206  can be rotated and moved linearly in the radial direction thereof. 
     As mentioned above, the sample rotating apparatus according to the present invention includes a position adjusting section for placing the selected sample on the sample stage at the analysis position, and a rotating section for rotating the selected sample while its axis of rotation remains aligned with the analysis position. Accordingly, the motor operating the rotating section experiences a low load. As a result, the multi-axis driving section has low maintenance costs and does not require frequent repairs. 
     Finally, although the present invention has been described in detail with reference to the preferred embodiments thereof, the present invention is not so limited. For instance, various transmission elements, other than the first gear and the driving gear, can be provided to rotate the sample stage. In addition, various linear driving mechanisms, such as pneumatic or hydraulic cylinders, may be employed for moving the moving plate. Therefore, various changes, substitutions and alterations to the preferred embodiments, as will become apparent to those skilled in the art, are seen to be within the true spirit and scope of the invention as defined by the appended claims.