Abstract:
Electrostatic clamping devices and methods for reducing contamination to a workpiece coupled to an electrostatic clamping device are disclosed. According to an embodiment an electrostatic clamping device for coupling a workpiece comprises: an embossment portion on a surface of a body to contact the workpiece; and at least two electrodes within the body; wherein the two electrodes are separated by a separation portion below the embossment portion.

Description:
BACKGROUND OF THE DISCLOSURE 
   1. Technical Field 
   The present disclosure relates generally to integrated circuit processing, and more particularly, to electrostatic clamping devices for coupling a workpiece and methods for reducing workpiece contamination in the coupling. 
   2. Related Art 
   Electrostatic chucks are widely used to support/hold wafers for processing, e,g., ion implantation, in integrated circuit (IC) processing systems. An electrostatic chuck includes a chuck body having at least one electrode within the chuck body. When a voltage is applied to the electrodes, an electrical field is created adjacent to a surface of the chuck body such that a wafer can be clamped to the surface to be retained. The surface may include embossment portions, referred to as mesas, to support the wafer and to reduce physical contact with the wafer. 
   In the clamping, the backside of the clamped wafer has a physical contact with the chuck surface, e.g., mesas, of the electrostatic chuck. This contact may result an particles that contaminate the wafer and may contaminate the processing chambers of the wafer, which are generally referred to as backside particles. The contaminating backside particles usually damage devices manufactured from the wafer and cause yield losses. 
   SUMMARY OF THE INVENTION 
   A first aspect of the invention is directed to an electrostatic clamping device for coupling a workpiece, the electrostatic clamping device comprising: an embossment portion on a surface of a body to contact the workpiece; and at least two electrodes within the body; wherein the two electrodes are separated by a separation portion below the embossment portion. 
   A second aspect of the invention is directed to an electrostatic clamping device for coupling a workpiece, the electrostatic clamping device comprising: an embossment portion on a surface of a body to contact the workpiece: and at least two electrodes within the body, wherein the two electrodes are configured such that when a voltage is applied to the two electrodes, an electrical field adjacent to the embossment portion created by the two electrodes is substantially parallel to the surface of the body. 
   A third aspect of the invention is directed to a method for reducing contamination to a workpiece supported by an electrostatic chuck, the method comprising creating an electrical field substantially parallel to a surface of the electrostatic chuck adjacent to an embossment portion of the electrostatic chuck. 
   The foregoing and other features of the invention will be apparent from the following more particular description of embodiments of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The embodiments will be described in detail, with reference to the following figures, wherein like designations denote like elements, and wherein: 
       FIG. 1  shows a schematic planar view of an electrostatic clamping device according to an embodiment of the disclosure. 
       FIG. 2  shows a schematic cross-sectional view of the electrostatic clamping device of  FIG. 1  according to an embodiment of the disclosure. 
       FIG. 3  shows a schematic planar view of an electrostatic clamping device according to an alternative embodiment of the disclosure. 
   

   It is noted that the drawings of the disclosure are not to scale. The drawings are intended to depict only typical aspects of the disclosure, and therefore should not be considered as limiting the scope of the invention. In the drawings, like numbering represents like elements among the drawings. 
   DETAILED DESCRIPTION 
   The current disclosure is based on the finding that backside particles are located mainly around the positions that the wafer contacts the mesas of the electrostatic chuck. The current disclosure reduces backside particle contamination to a workpiece by creating an electrical field substantially parallel to a surface of the chuck body adjacent to the embossment portions on the surface. Any method may be used to create such a surface parallel electrical field, and all are included. For example,  FIG. 1  shows a planar view of an electrostatic clamping device (clamping device)  10  according to an embodiment of the disclosure,  FIG. 2  shows a cross-sectional view of electrostatic clamping device  10  of  FIG. 1 . 
   Referring to  FIGS. 1-2 , clamping device  10  includes a body  12  having a body surface  14 . Embossment portions (embossment)  16 , e.g., mesas, are on surface  14 . Embossments  16  may contact workpiece  30  (shown in phantom in  FIG. 2 ) coupled to clamping device  10 . At least two electrodes  18  are within body  12  in a layer under surface  14 . According to an embodiment, the at least two electrodes, e.g.,  18   a  and  18   b,  are separated by a separation portion  20 , e.g., a gap, below embossment  16 . Part of separation portion  20  is directly below embossment  16 . As such, as shown in  FIG. 2 , there is no electrode directly below embossment  16 . 
   According to an embodiment, as shown in FIG,  1 , separation portion  20  includes at least one first portion  22  directly below an embossment  16  and at least one second portion  24  extending from first portion  22  along the respective two electrodes (i.e., the two electrodes  18  separated by separation portion  20 )  18 , e.g.,  18   a  and  18   b.  That is, second portion  24  is below, but not directly below embossment(s)  16 . 
   According to an embodiment, as shown in  FIG. 1 , first portion  22  covers a planar area that encloses a planar area covered by embossment  16 . That is, if embossment  16  is projected onto the same plane as separation portion  20 , the planar area of embossment  16  will be totally within the planar area of first portion  22 . As such, as shown in  FIG. 2 , a distance  26  between electrodes  18   a  and  18   b,  in x-axis, at a location substantially directly below embossment  16  is larger than a planar dimension  28  of the embossment in the same x-axis. Preferably, the planar area of first portion  22  is only slightly larger, i.e., less than 10 percent larger, than the planar area of embossment  16 . 
   According to an embodiment, first portion  22  has a planar shape substantially similar to, but bigger than, a planar shape of embossment  16 .  FIG. 1  shows that embossment  16  and first portion  22  both have an oval/circular planar shape. However, the current invention is not limited to any specific shape of embossment  16  and/or first portion  22 . First portion  22  may have a height, i.e., in the z-axis, approximately twice of a height  25 , in the same z-axis, of embossment  16 . However, this is not necessary and other height  23  of first portion  22  relative to that of embossment  16  are also possible and included in the invention. In the current description, a “height” refers to a dimension in the z-axis that is perpendicular to surface  14  of electrostatic chuck  10 . 
   According to an embodiment, as shown in  FIG. 1  second portion  24  s narrower than first portion  22  in the x-axis along which electrodes  18   a  and  18   b  are separated. Correspondingly, at least one of the two electrodes,  18   a  and  18   b,  includes a recess portion  29  that is substantially directly below respective embossment  16 . As such, distance  26  between electrodes  18   a  and  18   b  at a location substantially directly below embossment  16  is larger than a distance  27  between electrodes  18   a  and  18   b  at another location, i.e., a location other than recess portion  29 . 
   According to an alternative embodiment, as shown in FIG,  3 , electrostatic clamping device  110  includes a second portion  124  that is substantially as wide as first portion  122  in the x-axis along which electrodes  118   a  and  118   b  are separated. 
   In the case that multiple embossments  16  are positioned in a line, as shown in, e.g.,  FIG. 1 , each first portion  22  directly below the multiple embossments  16  shares a second portion  24  with an immediately adjacent first portion  22 . As such, separation portion  20  includes multiple first portions  22  and multiple second portions  24  connected in a line along respective electrodes  18   a,    18   b.    
   As shown in  FIGS. 1 and 3 , according to an embodiment, around a first portion  22 / 122 , the respective two immediately adjacent electrodes, e.g.,  18   a / 118   a  and  18   b / 118   b,  are substantially parallel to one another. The inclusion of recess portions  29  does not affect the parallel position between electrodes  18   a  and  18   b.    FIGS. 1 and 3  show that electrodes  18   a / 118   a  and  18   b / 118   b  are substantially parallel to one another throughout the y-axis, which is a specific embodiment. The scope of the invention is not limited by the configuration shown in  FIGS. 1 and 3 . 
   According to an embodiment, two immediately adjacent electrodes  18  that are separated by separation portion  20 , e g,  18   a  and  18   b,  are connected to different polarities (illustrated by “+” and “−” in  FIGS. 1 and 3 ) of a voltage source (not shown). As a consequence, when a clamping voltage is applied to electrodes  18   a  and  18   b,  an electrical field adjacent to embossment  16  will be created, which is substantially parallel to surface  14  of body  12 . Any type of clamping voltage may be used, and all are included in the invention. For example, the clamping voltage may be one of a direct current (DC) and an alternating current (AC). Preferably, according to an embodiment, a bipolar square wave voltage having a peak-to-peak amplitude of at least 1000 volts and a frequency in the range of approximately 30 Hz to approximately 300 Hz may be used as the clamping voltage. As such, the “+” and “−” used in  FIGS. 1 and 3  do not limit any electrodes  18  to a specific polarity, but only indicate that adjacent electrodes  18 , e g.,  18   a  and  18   b,  are connected to different polarities of the clamping voltage. 
   The foregoing description of various aspects of the disclosure has been presented for purposes of illustration and descriptions. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously, many modifications and variations are possible. Such modifications and variations that may be apparent to a person skilled in the art are intended to be included within the scope of the invention as defined by the accompanying claims.