text: Patent US6203661 - Brim and gas escape for non-contact wafer holder - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inPatentsThe present invention comprises a brim surrounding a wafer or wafer-like object during plasma etching in a non-contact wafer holder, such brim facilitating uniform flow of the plasma discharge around the edge of the wafer during plasma etching. The brim of the present invention avoids plasma instability...http://www.google.com/patents/US6203661?utm_source=gb-gplus-sharePatent US6203661 - Brim and gas escape for non-contact wafer holderAdvanced Patent SearchTry the new Google Patents, with machine-classified Google Scholar results, and Japanese and South Korean patents.Publication numberUS6203661 B1Publication typeGrantApplication numberUS 09/457,042Publication dateMar 20, 2001Filing dateDec 7, 1999Priority dateDec 7, 1999Fee statusLapsedAlso published asUS6667242, US20010002613Publication number09457042, 457042, US 6203661 B1, US 6203661B1, US-B1-6203661, US6203661 B1, US6203661B1InventorsOleg Siniaguine, Sergey Savastiouk, Alex BergerOriginal AssigneeTrusi Technologies, LlcExport CitationBiBTeX, EndNote, RefManPatent Citations (23), Referenced by (22), Classifications (11), Legal Events (7) External Links: USPTO, USPTO Assignment, EspacenetBrim and gas escape for non-contact wafer holder
  US 6203661 B1Abstract
  The present invention comprises a brim surrounding a wafer or wafer-like object during plasma etching in a non-contact wafer holder, such brim facilitating uniform flow of the plasma discharge around the edge of the wafer during plasma etching. The brim of the present invention avoids plasma instability and non-uniform flow typical of conventional plasma etching near the edges of the wafer being etched. The brim of the present invention, by facilitating uniform and stable plasma flows, decreases non-uniform etching. One embodiment of the present invention permits the brim to move in the axial direction from a position substantially. This permits the etching process to be controlled for more uniform and precise wafer etching as lowering the brim tends to shadow the edge region of the wafer from the plasma, reducing etching in the edge region while not significantly affecting etching in the central regions of the wafer. Another embodiment of the wafer includes a barrier on the upper side of the brim directed upward from the brim at an oblique angle away from the wafer. This barrier contacts the upper surface of the brim so as to leave a protrusion or debris-collecting shelf on the upper interior portion of the brim. This shelf in combination with the upward oblique barrier deflects the plasma and debris from plasma etching away from the wafer. Another embodiment of the invention includes a gas-controlling baffle in which gas flow around the edge of the wafer may be controlled to compensate for mechanical imprecision in the gap between the brim and the wafer and/or to provide an additional means of controlling etching in the vicinity of the edge of the wafer.
  Numerous areas of technology require that a workpiece be held in position while processes are performed thereon. The processing of semiconductor wafers into integrated circuits requires the wafer to be held by a suitable holder without impeding the processing steps directed to the exposed flat surface of the wafer. Following production of the integrated circuits, wafer processing is generally not finished. In particular, many areas of technology (cell phones, smart cards and the like) require that the integrated circuit providing the internal intelligence for the device be very thin. It is typically inconvenient to fabricate the integrated circuits directly on a thin wafer as distortion, non-uniform processing, perhaps even rupture, may occur during the several processing steps typically required for integrated circuit fabrication. Therefore, it is common practice for a wafer containing numerous fully fabricated integrated circuits thereon to be thinned by means of etching from the reverse side of the wafer. Plasma etching is the typical method for wafer thinning. For economy of language we will refer to the "face" of the wafer and intend thereby the face undergoing (or destined to undergo) etching, resulting in thinning of the wafer. The "opposite face" of the wafer denotes the face of the wafer not undergoing etching, typically having the integrated circuits thereon and lying in close proximity to the wafer holder.
  To be definite in our description of the invention, we will describe the common instance of the processing of semiconductor wafers as may typically occur in the production of integrated circuits or in wafer post-processing for thinning, etc. However, the processing of any wafer-like object in a non-contact holder is also a potential area of application for the present invention. Flat panel displays and other rectangular, circular, star-shaped or irregularly shaped planar objects may require processing by means of a non-contact holder. For economy of language we will refer to all such wafer-like objects herein as "wafers" recognizing that such objects may be large and need not be rectangular, circular or regular in shape. Since semiconductor wafers are expected to be an important area of application for the present invention, we will describe the primary features of the present invention in terms of semiconductor processing, not intending to limit the invention to this particular choice or particular example. Semiconductor wafers aptly illustrate the features of the present invention and permit obvious modification for use in processing other wafer-like objects.
  The present invention comprises a brim surrounding a wafer or wafer-like object during plasma etching in a non-contact wafer holder. This brim is preferably 20 mm to 25 mm in width, approximately 1.3 mm thick and the gap is substantially constant throughout the circumference of the wafer. The gap is preferably approximately 0.5 mm for etching of integrated circuit wafers. A brim so dimensioned and configured will facilitate the plasma discharge in flowing smoothly onto and off of the wafer, avoiding thereby the plasma instability and non-uniform flow typically of conventional plasma etching near the edges of the wafer being etched. The brim of the present invention, by facilitating uniform and stable plasma flows, decreases non-uniform etching.
  FIG. 1 depicts schematically and in cross section (but not to scale) a wafer-like object ("wafer") undergoing plasma etching. The wafer, 1, may optionally have integrated circuits or other structures, 2, fabricated on the face of the wafer nearer the wafer holder, 3. A common non-contact wafer holder, 3, could hold wafer, 1, (for example) by means of vortex-created partial vacuum attraction while providing an air (or similar gas) cushion, 4, preventing direct contact between wafer and holder. Wafer, 1, may be supported from above by vortex-created partial vacuum generated by numerous vortex "chucks" on the face of the wafer holder. These individual vortex chucks are not depicted in the figures. The air may exit from each vortex chuck preferentially in certain directions, merging in the region between wafer and holder into the overall partial vacuum support and air cushion in a complex flow pattern. The net flow of air around the wafer denoted as 4 in FIG. 1 may not exit from the gap between the wafer and holder completely uniformly in all radial directions. However, even in such cases, significant air exits from all regions of the circumference of the wafer holder to provide adequate separation of wafer and wafer holder, 7, typically 0.10 mm to 0.40 mm. The present invention is not limited to use with a particular form of non-contact wafer holder but may be used with advantage to stabilize the plasma and deflect etching debris in many types of non-contact holders.
  During processing, the wafer holder is typically one of several in a carousel rotating around a central axis. This results in a centrifugal force tending to push the wafer, 1, against the circumference of the carousel. Limiting pins are typically provided against which the wafer is centrifugally pressed to maintain a constant location within the holder during processing. One such limiting pin is depicted as 21 in FIG. 1. The limiting pins occupy only a very small fraction of the circumference of the wafer holder, having no significant effect on the gas dynamics described elsewhere herein. However, we depict in FIG. 4 one such limiting pin, 21, to illustrate that the limiting pin, not brim, 9, keeps the wafer in the holder, permitting brim, 9, to be displaced in the direction 16. FIG. 4 depicts brim, 9, in a lower position than in FIGS. 2, 2 a and 3. Thus, brim location may be adjusted to affect gas flow as may be desired by the process engineer. The width of the brim, 15 in FIG. 2, is typically 20 to 25 mm. In an embodiment of the present invention the brim can be moved to various axial positions with respect to the wafer. That is, the brim can be moved in direction 16. Lowering the brim (in the direction of the plasma) causes the brim partially to shield ("shadow") the edge of the wafer from the plasma, thereby lowering the etch rate in the edge region. Typically, in this embodiment of the present invention, the brim may be lowered to a position of approximately 1-3 mm. below the position of the wafer. Etch rate near the edge of the wafer can thus be controlled by suitable vertical positioning of the brim structure of the present invention.
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