Abstract:
An article holder uses a gas flow, for example, a vortex, to hold the article in a desired position. The gas flow is substantially restricted to an article portion reserved for handling. The result of the processing is less sensitive to the condition (e.g. temperature) of that portion than to the condition of the rest of the article. Therefore, if the gas flow affects the condition (e.g., temperature) of the article portion contacting the gas flow, the processing result is improved.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to article holders suitable for holding articles being processed, and more particularly to holders which use gas flow to hold articles. 
     Holders that use gas flow are widely used in different industries including, for example, the semiconductor manufacturing industry. Examples of such holders are vortex holders described in PCT Publication WO 97/45862 “Non-Contact Holder for Wafer-Like Articles” (Dec. 4, 1997). Other examples are holders based on the Bernoulli principle. 
     It is desirable to provide improved article holders that use gas flow. 
     SUMMARY 
     The inventor has observed that the gas flow emitted by the holder can have a negative effect on the article processing by affecting the temperature or other conditions at different parts of the article. Of note, some semiconductor wafer processes, e.g. plasma etches, are quite sensitive to the wafer temperature. For example, a plasma etch of silicon dioxide may have an etch rate that changes by a factor of 10 as the wafer temperature changes from 100° C. to 300° C. Some plasma etches of silicon nitride are also sensitive to the wafer temperature. If, for example, a gas flow emitted by the holder cools the wafer non-uniformly, the etch becomes less uniform. 
     These problems are exacerbated in some processes in which the wafer temperature is supposed to change during processing in a predetermined fashion. The problems are exacerbated because it may become more difficult to adjust the gas temperature to reduce the processing non-uniformity. Examples of such processes include dynamic plasma treatment (DPT) described in PCT Publication WO 96/21943. In DPT, the plasma cross section is smaller than the wafer, and hence the plasma contacts at most a portion of the wafer at any given time. The wafer makes multiple passes through the plasma. With each pass, the plasma traces a path on the wafer surface, heating the wafer along the path. The wafer is cooled between the passes. In order for the process results to be uniform across the wafer, the temperature profile of these heating and cooling cycles may have to be uniform for different wafer points processed in different passes. This requirement makes it difficult or impossible to reduce the process non-uniformity by gas flow temperature control. 
     To reduce or eliminate such disadvantages, some embodiments of the present invention restrict the area in which a gas flow generated by the holder contacts the article. In some embodiments, that area is substantially restricted to the article portion reserved for article handling. For example, in many semiconductor manufacturing processes, each wafer has a peripheral area reserved for wafer handling. The wafer useful area is confined to the rest of the wafer. At least one gas flow generated by the holder does not contact the wafer useful area. Therefore, the temperature non-uniformity in the wafer useful area is reduced. 
     According to another aspect of the invention, at least one gas outlet in an article holder is positioned opposite to a periphery or a handling portion of the article. 
     In some embodiments, the holders hold articles which are not being processed. 
     Other features of the invention are described below. The invention is defined by the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-section illustration of a semiconductor wafer processing system according to the present invention. 
     FIGS. 2 and 3 are bottom views of wafer holders in different embodiments of FIG.  1 . 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a non-contact wafer holder  110  holding a wafer  120  during processing. Holder  110  includes gas flow generators  130  in holder body  110 B. Each gas flow generator  130  has an outlet  130 L in wafer facing surface  140  of holder body  110 B. A gas flow generated by a generator  130  flows through respective outlet  130 L and creates a reduced pressure (vacuum) area between wafer  120  and body  110 B to hold the wafer adjacent to the body. In some embodiment, each gas flow is a gas vortex generated by methods known in the art. See, for example, USSR inventor certificate 537924 (Feb. 9, 1977), USSR patent document SU 1812102 (Apr. 30, 1993), and PCT Publications WO 96/21943 (Jul. 18, 1996) and WO 97/45862 (Dec. 4, 1997). 
     Wafer  120  has a peripheral portion  120 H reserved for wafer handling. Portion  120 H will be discarded after the integrated circuit manufacturing is complete, and thus no circuit elements to be used after the manufacturing are fabricated in that portion. Area  120 H extends along the wafer edge all around the wafer. The width pw of area  120 H is about 3 mm in some embodiments. 
     Advantageously, the gas vortices generated by generators  130  are substantially restricted to area  120 H because each outlet  130 L is positioned opposite (directly above) the area  120 H and does not laterally extend beyond the area. See FIG. 2 showing the bottom view of holder  110 . In FIG. 2, dashed line  120 B is the boundary of wafer  120 . Dashed line  120 HB is the inner boundary of peripheral area  120 H. Outlets  130 L do not extend beyond the area  120 H between the dashed lines  120 B and  120 HB. While gas can leave the vortex area and contact other parts of the wafer, the gas flow outside the area  120 H is slower than in the vortex and hence has a smaller effect on the wafer temperature than the vortex. Therefore, the impact of the gas flow on the wafer useful area  120 U is reduced. (Area  120 U is the entire wafer minus the peripheral area  120 H). 
     As shown in FIG. 2, the wafer facing surface  140  is slightly larger than the wafer, to accommodate slight variations in wafer sizes. In some embodiments, line  120 B represents the boundary of the intersection of all the wafer positions. Thus, the region inside the boundary  120 B is filled by wafer points, though the wafer can extend beyond the boundary  120 B. Dashed line  120 HB represents the outer boundary of the union (i.e., combination) of all the wafer non-handling positions. Thus, the annular region between the dashed lines  120 B and  120 HB is entirely occupied by the wafer handling area  120 H, though the handling area can extend beyond that annular region. Outlets  130 L are restricted in bottom view to the region between the boundary lines  120 HB,  120 B. In some embodiments, the distance between the dashed lines  120 HB,  120 B (the width of the annular region) is about 3 mm, and the diameter of each outlet  130 L is about 2 mm. 
     In FIG. 2, outlets  130 L are shown as circles. However, in some embodiments each outlet has annular or some other shape. 
     In FIG. 1, wafer  120  is being processed at atmospheric pressure with plasma jet  150  generated by plasma source  160 . The process involves deposition, etch, anneal, or some other operation. The process is described above and in the following documents: Yu. M. Agrikov et al., “Dynamic Plasma Treatment of HIC (Hybrid Integrated Circuit) Substrates”, Elektronnaya Tehnika, Ser. 10, 5(71), 1988, pages 30-32; PCT publications WO 92/12610 (published Jul. 23, 1992), WO 92/12273 (published Jul. 23, 1992), WO 96/21943 (published Jul. 18, 1996); P. P. Kulik, “Dynamic Plasma Treatment (DPT) of a Surface of a Solid Body”, Plazmohimiya-87, Part 2 (U.S.S.R. Academy of Science, Institute Neftehimicheskogo Sinteza im. A. V. Topchieva, Moscow, 1987), pages 4-13; Yu. M. Agrikov et al., “Foundations of a Realization of a Method of Dynamic Plasma Treatment of a Surface of a Solid Body” (same publication, pages 58-96); U.S. patent application Ser. No. 08/781,568 “Plasma Generation and Plasma Processing of Materials” filed Jan. 9, 1997 by O. Siniaguine, now U.S. Pat. No. 5,767,623 issued Jun. 16, 1998; U.S. patent application Ser. No. 60/030,425 “Back-Side Contact Pads” filed Oct. 29, 1996 by O. Siniaguine; PCT Application PCT/US97/18979 “Integrated Circuits and Methods for Their Fabrication” filed Oct. 27, 1997; U.S. patent application Ser. No. 08/975,403 pending “Plasma Processing Methods and Apparatus” filed Nov. 20, 1997 by O. Siniaguine. In particular, in some embodiments, holder  110  is attached to a rotating carousel (not shown) by arm  190 , and the holder and the wafer make multiple passes over the plasma jet  150  during processing, as described in the aforementioned U.S. patent application Ser. No. 08/975,403. The plasma cross section at the level of the wafer may or may not be smaller than the wafer. If the plasma cross section is smaller, the plasma contacts at most a portion of the wafer at any given time. In some embodiments, the wafer is held by a non-condact wafer holder during back-side etch. The wafer is diced into dice after the back-side etch. The dice contain integrated circuits. 
     In FIG. 1, wafer  120  is positioned below the holder  110 , and the plasma jet  150  is positioned below the wafer to treat the bottom wafer surface. In other embodiments the wafer is positioned above the wafer holder and the plasma jet is positioned above the wafer to treat the top wafer surface. Other embodiments include non-plasma wafer processing. 
     In FIGS. 1 and 2, holder body  110 B has extensions  170  around the wafer to restrict the wafer lateral movement. Extensions  170  are one or more isolated fingers. One of fingers  170  is positioned against the flat edge  120 F of wafer  120  to prevent the wafer from rotating relative to holder  110 . In other embodiments, the wafer has a notch, and one of fingers  170  is positioned in the notch to prevent the wafer from rotating relative to the holder. 
     In some embodiments, extensions  170  form a continuous rim around wafer facing surface  140 . 
     While in FIG. 2 the wafer facing surface  140  has substantially the same shape as the wafer (except that the wafer facing surface is slightly larger than the wafer), in some embodiments the wafer facing surface is shaped differently from the wafer. For example, in some embodiments designed for circular wafers, the wafer facing surface is square with a side slightly larger than the wafer diameter. 
     In some embodiments, including the embodiments of FIGS. 2 and 3, more than one vortex generators  130  are provided. The vortex generators are positioned around the wafer periphery so as to balance the wafer. 
     In FIG. 2, four groups of outlets  130 L are provided. Each group  130 G. 1 ,  130 G. 2 ,  130 G. 3 ,  130 G. 4  has three outlets  130 L adjacent to one another. The gas vortices emitted from the adjacent outlets affect the gas motion in areas  210  between the outlets. The direction of each vortex is shown by an arrow such as  220 . All the gas vortices in any given group  130 G.i have the same direction. As a result, high gas pressure is created in areas  210  between adjacent vortices, and gas flows away from areas  210  towards the inside and the outside of the wafer as shown by respective arrows A and B for group  130 G. 2 . The gas flow in the direction of arrow B (towards the outside of the wafer) impedes the plasma from getting between the wafer and the holder  110 . This is advantageous in those embodiments in which only the wafer surface away from the holder (the bottom surface in FIG. 1) is to be processed. 
     In group  130 G. 2 , gas in each vortex flows clockwise, and in group  130 G. 4  gas flows in the opposite direction, i.e. counterclockwise. The opposite directions help avoid wafer rotation relative to the holder. Rotation is undesirable because it causes the wafer to rub against extensions  170  and because it makes it harder for the wafer to be loaded into the holder. The vortices in groups  130 G. 1  and  130 G. 3  also have different directions. 
     In FIG. 3, four pairs of adjacent outlets  130 L are provided. The gas vortices in the adjacent outlets have opposite directions. The directions are chosen so that between the adjacent vortices, gas flows towards the outside of the wafer (direction B). This impedes the plasma from getting between the wafer and the holder  110 . In addition, the opposite directions help avoid wafer rotation relative to the holder. 
     The invention is not limited by the embodiments described above. In particular, the invention is not limited by the kind of gas in the gas vortices. In some embodiments, the gas is air, nitrogen, or some other gas suitable for the process being used. Some embodiments use the Bernoulli effect generators  130  instead of, or in combination with, vortex generators. In some embodiments, articles  120  are flat panels such as video screens, or some other kind of articles. Other embodiments and variations are within the scope of the invention, as defined by the appended claims.