Abstract:
An article which is being processed with plasma is moved during plasma processing so that the motion of the article comprises at least a first rotational motion, a second rotational motion, and a third rotational motion which occur simultaneously. The apparatus that moves the article comprises a first arm rotatable around a first axis, a second arm rotatably attached to the first arm and rotating the article around a second axis, and a rotational mechanism for inducing a rotational motion of the article in addition to, and simultaneously with, the rotation of the first and second arms.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to processing of materials, and more particularly to plasma processing. 
     Plasma processing is widely used to modify surface properties of materials. Thus, plasma is used in fabrication of integrated circuits to perform deposition, etch, cleaning, and rapid thermal anneal. Plasma-based surface processes are also used for hardening of surgical instruments and machine tools, and are used in aerospace, automotive, steel, biomedical, and toxic waste management industries. See, for example, M. A. Lieberman and A. J. Lichtenberg. “Principles of Plasma Discharges and Materials Processing” (1994), page 1. 
     For some applications there are unique advantages to etching a semiconductor wafer with plasma. For example, the backsides of semiconductor wafers are sometimes etched to make the wafers thinner after the components and circuitry have been fabricated on the frontside of the wafer. The wafer can then be separated into dice. Plasma etching is used for wafer thinning because other thinning techniques (e.g., grinding) create too much stress on the wafer and may damage the wafer. 
     A common goal in plasma processing is high throughput and high processing uniformity. 
     FIG. 1 shows a prior art plasma processing system  110  described in U.S. patent application Ser. No. 08/975,403 and PCT application WO 99/26796 which are incorporated herein by reference. Plasma source  114  generates a plasma jet  120  schematically shown by an arrow. Carrousel  124  has five wafer holders  130  (or some other number of wafer holders) each of which holds a semiconductor wafer. The wafers, not shown in FIG. 1, are positioned beneath the holders  130 . Plasma jet  120  flows upwards and impinges on the wafers bottom surfaces. Holders  130  may be non-contact vortex holders (these holders do not contact the wafers top surface), or they may be contact holders that hold the wafers by vacuum or by electrostatic or mechanical means. 
     Plasma processing occurs at atmospheric pressure. Plasma jet  120  is too narrow to cover an entire wafer, so the wafers are moved in and out of the plasma in a predetermined pattern aimed at achieving uniform processing. Each holder  130  is rigidly attached to a respective arm  140 A of an angle drive  140 . Angle drive  140  rotates the wafers around a vertical axis  140 X. Angle drive  140  has a body  140 B rigidly attached to an arm  150 A of an angle drive  150 . Drive  150  rotates the arm around a vertical axis  150 X. Control system  154  (e.g. a computer) controls the drives  140  and  150 . 
     Plan view FIGS. 2A-2C illustrate the wafer path. Only one wafer  134  is shown for simplicity. For each position of arm  150 A, wafers  134  sweep through a ring-shaped (donut-shaped) path  202  centered at axis  140 X. The actual path swept by the wafers is not a ring since drive  150  is not stationary, but a ring is a fair approximation of the wafer path if angular velocity W 1  of drive  150  is several times smaller than angular velocity W 2  of drive  140 . 
     Numeral  220  denotes a stationary horizontal line that intersects the axis  150 X and the center of plasma jet  120 . Angle Θ is the angle between the line  220  and the arm  150 A. 
     In FIG.  2 A. Θ=0. Axis  140 X is in its farthest position from plasma  120 . The arms  140 A,  150 A, and the distance between the center of plasma  120  and the axis  150 X, are dimensioned so that at Θ=0 the wafers do not pass over the plasma. This eliminates plasma processing during wafer loading and unloading. (Wafer loading and unloading occur at Θ=0.) 
     In the example of FIGS. 2A,  2 B,  2 C, arm  150 A rotates clockwise. In FIG. 2B, the angle Θ has increased to some value Θ 1 , and the outer edge  134 F of wafer  134  has entered the plasma  120 . (The “outer edge” refers to the most distant edge from axis  140 X.) As Θ continues to increase, the plasma processes wafer points closer and closer to axis  140 X. In FIG. 2C, the plasma processes the wafer edge  134 C closest to axis  140 X (Θ is some value Θ 2 ). When angle Θ is 180°, no plasma processing takes place. 
     As Θ increases from 180° to 360°, the wafer path  202  returns to its position in FIG. 2A via a symmetric route. For each value Θ o  between 180° and 360°, the positions of ring  202  for Θ=Θ o  and Θ=360°−Θ o  are symmetric to each other relative to line  220 . 
     An advantage of the system of FIG. 1 is that there is no need to move the plasma source  114 . (In some earlier systems, a single wafer was positioned at the location of axis  140 X; the plasma source had to move towards and away from the axis  150 X to process the whole wafer.) 
     To achieve uniform processing, the system of FIG. 1 attempts to make each point on the wafer pass through the plasma the same number of times and spend the same amount of time in the plasma. The velocity W 1  of drive  150  varies so that the wafer points located farther from axis  140 X spend about the same time in the plasma as the points closer to the axis  140 X. The wafer passes multiple times over the plasma during each revolution of drive  150 . The paths traced by the plasma on the wafer surface in consecutive revolutions of drive  140  overlap. The overlap is particularly desirable because the plasma jet  120  may have non-uniform heat distribution across the jet&#39;s horizontal cross section. 
     It is desirable to further improve processing uniformity while maintaining high processing throughput. 
     SUMMARY 
     In the system of FIG. 1, processing uniformity may suffer at the wafer edges due to unstable plasma behavior when the wafer enters and exits the plasma. Another reason why the processing uniformity may suffer is as follows. As the wafer moves through the plasma, the processing byproducts are generated at the bottom surface of the wafer. These byproducts may impede the wafer processing near the wafer edge exiting the plasma. 
     To improve the processing uniformity, one can change the direction of the W 2  rotation during processing. This solution is described in U.S. patent application Ser. No. 09/315,122 filed May 19, 1999 by O. Siniaguine et al. and incorporated herein by reference. Disadvantageously, changing the direction of the W 2  rotation tends to increase the processing time. It is therefore desirable not to change the direction of the W 2  rotation, or at least to reduce the number of times that the direction of the W 2  rotation is changed. 
     Another problem noted in the U.S. patent application Ser. No. 09/315,122 relates to different cooling times obtained for the wafer points at different distances from the axis  140 X of drive  140 . As illustrated in FIGS. 2A,  2 B, and  2 C, the entire wafer is processed during each half-revolution of drive  150 . The wafer is processed once when θ changes from 0 to 180°, and once when θ changes from 180° to 360°. Each point P on the wafer&#39;s bottom surface is processed when θ is at or near some value θ P . When  0  increases past the value θ P , the point P is moved out of the plasma and is therefore cooled. The point P does not re-enter the plasma until θ reaches the value 360°−θ P  in the next half-revolution of drive  150 . Then the point P becomes processed again, and then is cooled again until the angle θ becomes equal to θ P . 
     As shown in the U.S. patent application Ser. No. 09/315,122, the cooling times may be different for different points on the wafer. To equalize the cooling times, U.S. patent application Ser. No. 09/315,122 proposes to suppress plasma processing during one half of each revolution of drive  150 . For example, plasma processing could take place only when θ changes from 0° to 180°, or only when θ changes from 180° to 360°. Disadvantageously, suppressing the plasma processing during one half of each revolution tends to increase processing time. 
     In some embodiments of the present invention, the wafer is subjected to a third rotation in addition to the rotation of drives  140  and  150 . For example, the wafer can be rotated around its axis, or some other axis, simultaneously with being rotated by drives  140  and  150 . The processing uniformity is improved because the processing byproducts affect the wafer processing more uniformly across the surface of the wafer. In addition, the cooling times for different points on the wafer surface also become more uniform. These advantages can be achieved without suppressing the wafer processing during one half of each revolution of drive  150 , and without changing the direction of rotation of drive  140 . The throughput is therefore increased. However, the direction of rotation may be changed, and the wafer processing may be suppressed during one half of each revolution of drive  150 , if desired. 
     Another advantage obtained in some embodiments of the present invention is illustrated in FIGS. 3,  4 . As shown in FIG. 3, each path  120 P traced by the plasma on the wafer surface in the system of FIG. 1 during a single revolution of drive  140  is approximately an arc with a center at axis  140 X. The path approximates the arc because the velocity W 2  is greater than W 1 . If the plasma processing is temperature sensitive (a temperature sensitive etch, for example) the processed wafer may have grooves and ridges extending in the direction of arcs  120 P. 
     In some embodiments of the present invention, the third wafer rotation causes the plasma paths on the wafer to become more varied (FIG.  4 ). The processing uniformity is therefore improved. 
     The invention is not limited to the embodiments described above. Some embodiments provide a method for processing an article with plasma, the method comprising: 
     (a) generating the plasma; 
     (b) moving the article as the article contacts the plasma, wherein a motion of the article comprises at least a first rotational motion, a second rotational motion, and a third rotational motion which occur simultaneously. 
     Some embodiments provide an apparatus for moving an article through plasma, the apparatus comprising: 
     a first arm rotatable around a first axis; 
     a second arm rotatably attached to the first arm to rotate an article around a second axis; and 
     a rotational mechanism for inducing a rotational motion of the article in addition to, and simultaneously with, the rotation of the first and second arms. 
     Some embodiments provide articles processed by methods of the present invention. 
     Other features and advantages of the invention are described below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a prior art plasma processing system. 
     FIGS. 2A,  2 B,  2 C illustrate wafer trajectories in the system of FIG.  1 . 
     FIG. 3 is a bottom view illustrating a plasma path on the wafer in the system of FIG.  1 . 
     FIG. 4 is a bottom view illustrating plasma paths on the wafer in one embodiment of the present invention. 
     FIGS. 5-7 are side views of plasma processing systems according to some embodiments of the present invention. 
     FIG. 8 is a top view illustrating some features of one embodiment of the present invention. 
     FIG. 9 is a side view of a plasma processing system in one embodiment of the present invention. 
     FIG. 10 is a perspective view of a rim of a wafer holder in one embodiment of the present invention. 
     FIG. 11 is a side view of a plasma processing system of one embodiment of the present invention. 
     FIG. 12 is a bottom view of a wafer holder in some embodiments of the present invention. 
     FIG. 13 is a side view of a plasma processing system in one embodiment of the present invention. 
     FIGS. 14 and 15 are bottom views of wafer holders in some embodiments of the present invention. 
     FIG. 16 is a perspective view of an air motor used in a wafer holder of one embodiment of the present invention. 
     FIGS. 17A and 17B are perspective and cross-sectional views, respectively, of the vane impeller in the air motor of FIG.  16 . 
     FIG. 18 is a cross-sectional view of the assembly including the wafer holder, air motor, pin and wafer in the system of FIG.  16 . 
     FIG. 19 is a side view illustrating an embodiment wherein the pins are attached to a brim that rotates around the center of the substrate. 
     FIG. 20 is a detailed view of a vortex chuck. 
     FIG. 21 is a view of several vortex chucks oriented to impart a rotational movement to a wafer. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 5 illustrates a plasma processing system in which each wafer  134  rotates around axis  130 X of respective wafer holder  130 . Only one wafer is shown, though any number of wafers may be present. Wafer holders  130  are contact holders (for example, vacuum, electrostatic or mechanical chucks). Each wafer holder  130  is rotated by a respective angle drive  502 . Drive  502  has a body  502 B rigidly attached to and  140 A of drive  140 . A motor (not shown) inside the body  150 B rotates a spindle  502 S rigidly attached to holder  130 . As a result, the holder  130  rotates around some vertical axis  130 X defined by drive  502 . The angular velocity is shown as W 3 . The bottom surface of holder  130  may have a circular portion designed to receive the wafer  134 . In some embodiments, the axis  130 X passes through the center of that portion. Axis  130 X may pass through the center of mass of the wafer or the wafer holder or both. 
     Other arrangements of drive  502  relative to the holder are also possible. For example, transmission can be used to transfer the motion from the drive&#39;s motor to the holder. The motor can be a stepper motor or any other kind of motor, known or to be invented. 
     Drives  150  and  140  are arranged as in FIG.  1 . Drive  140  is shown at position Θ=0 (as in FIG.  2 A). Numeral  140 - 1  indicates the position of drive  140  at Θ=180°. Numberals  140 X- 1  and  130 X- 1  indicate respectively the positions of axes  140 X and  130 X at Θ=180°. 
     Except for the addition of drives  502 , the system can be identical to the system of FIG.  1 . The embodiment of FIG. 5 is different, however, with respect to position of plasma source  114  relative to the wafers. At Θ=180°, the wafer edge  134 C closest to axis  140 X does not pass over the plasma. Rather, the plasma processes the wafer points near the center of the wafer (at axis  130 X- 1 ). Thus, the plasma source is farther from the rest of the system than in FIG.  1 . 
     The wafer portion close to axis  140 X will be processed when this portion will be rotated by drive  502  to a position farther from axis  140 X. 
     This plasma positioning provides better wafer cooling. The wafer points close to axis  140 X have lower speeds and hence are not cooled as well as the wafer points farther from the axis  140 X. (We define “speed” as the magnitude of a linear velocity.) It is therefore desirable in temperature sensitive processing not to process the wafer points close to the axis  140 X in order to avoid overprocessing of these points. Also, the plasma is farther from drives  140 ,  150 , and from the wafer holders, so these parts are not heated as much. 
     In some embodiments, the angular velocity W 1  of drive  150  is such that drive  150  makes one revolution in a time period of 2 to 30 seconds. The angular velocity W 2  is 60 to 300 revolutions per minute. The angular velocity W 3  of wafer  134  is 0.1 to 3 revolutions per minute. In some embodiments, the wafer makes at least 3 to 5 W 3  revolutions during plasma processing. 
     In some embodiments, the velocity W 2  is constant. The wafer points farther from axis  140 X (such as point  134 F) move faster through the plasma than the wafer points closer to axis  140 X (such as point  134 C). The velocity W 1  is varied to compensate for this difference. When the plasma processes the wafer points farther from the axis  140 X, the velocity W 1  is lower than when the plasma processes wafer points closer to axis  140 X. Some W 1  patterns are described in U.S. patent application Ser. No. 09/315,122 filed on May 19, 1999, incorporated herein by reference. 
     The velocities W 1 , W 2 , W 3  can be controlled to achieve suitable heating and cooling cycles for plasma processing at atmosphere pressure. Such plasma processing is described in the U.S. patent application Ser. No. 09/315,122. 
     The present invention is not limited to any particular velocity values or relationships between velocities W 1 , W 2 , W 3 . The invention is not limited to the position of plasma source  114 . In some embodiments, the plasma source is positioned as in FIG.  1 . 
     In FIG. 5, R 1  denotes the distance between the axes  150 X and  140 X. R 2  is the distance between the axes  140 X and  130 X. In some embodiments with multiple wafer holders, the axes of all wafer holders  130  are at the same distance R 2  from axis  140 X. Dw is the wafer diameter. Dh is the diameter of wafer holder  130 , (which is substantially round). LP is the distance between the axis  150 X and the center of plasma jet  120 . LP 1  is the distance between the axis  150 X and the closest point of plasma  120  in the plane passing through the bottom surface of the wafer. (LP 1  may vary during the wafer processing as the wafer gets thicker or thinner.) 
     In some embodiments, the following equation holds true: 
     
       
           LP≦R   1 + R   2 + Dw /2  (1) 
       
     
     This equation means that at Θ=180° the wafer center is over the center of plasma jet  120  or to the right of the center of the plasma jet. 
     In some embodiments: 
     
       
           LP≦R   1 + R   2   (2) 
       
     
     This equation means that at Θ=180° the wafer edge  134 F farthest from axis  140 X is over the center of the plasma jet  120  or to the right of the center of the plasma jet. 
     In some embodiments: 
     
       
           LP   1 &gt; R   2 − R   1 + Dw /2  (3) 
       
     
     This means that at Θ=0, the wafers do not pass over the plasma. Therefore, plasma processing during loading and unloading is avoided if the loading and unloading are performed at Θ=0. Moreover, in some embodiments: 
     
       
           LP   1 &gt; R   2 − R   1 + Dh /2  (4) 
       
     
     This means that during loading and unloading the wafer holders do not pass over the plasma. Therefore, heating of the wafer holders is reduced. 
     In those embodiments in which a wafer edge  134 C can be processed with plasma: 
     
       
           LP   1 ≦ R   1 + R   2 − Dw   (5) 
       
     
     In FIG. 6, wafer holders  130  are non-contact vortex or Bernoulli holders. In a vortex holder, one or more gas vortices are emitted from the holder&#39;s body  130 B towards the wafer. A vacuum near the center of each vortex holds the wafer adjacent to the holder. Escaping gas also prevents the wafer from contacting the body of the holder. Suitable holders are described in the following U.S. Patent Applications, incorporated herein by reference: application Ser. No. 09/457,042, filed Dec. 7, 1999, entitled “Brim And Gas Escape For Non-Contact Water Holder”: application Ser. No. 09/456,135, filed Dec. 7, 1999, entitled “Non-Contact Workpiece Holder”: application Ser. No. 09/038,642, filed Mar. 10, 1998, entitled “Holders Suitable To Hold Articles During Processing And Article Processing Methods”. See also PCT application published as number WO 99/46805 on Sep. 16, 1999, incorporated herein by reference. Other vortex holders, and non-contact Bernoulli holders, can also be used. 
     The holder of FIG. 6 is provided with a limiter  602  rigidly attached to holder body  130 B rotated by drive  502 . Limiter  602  can be a continuous rim surrounding the wafer  134 . Alternatively, limiter  602  can be a number of discrete pins surrounding the wafer. The wafer is pressed against the limiter  602  by the centrifugal force developed by the W 2  rotation of the wafer around the axis  140 X. The friction between the limiter  602  and the wafer  134  causes the wafer to rotate with the wafer holder. The wafer rotates around an axis  134 X. 
     Axis  134 X is not necessarily stationary relative to wafer holder  130 . If wafer  134  is perfectly round, and the axis  134 X passes through the center of the wafer, the axis  134 X may be stationary relative to holder  130 . However, a semiconductor wafer may have a “flat”, that is, a linear boundary portion. In that case, the axis  134 X will not be stationary. The axis  134 X may be any vertical axis passing through the wafer. 
     In FIGS. 5 and 6, the rotations W 1 , W 2 , W 3  may be in the same direction (for example, all clockwise or counterclockwise) or in different directions in any combination (for example, rotations W 1 , W 2  may be clockwise and W 3  may be counterclockwise). The direction of rotation can be changed during plasma processing. 
     In FIG. 7, the W 3  rotation of the wafer holder  130  is actuated by drive  140 . The drive&#39;s motor (not shown) rotates a spindle  140 S rigidly attached to arm  140 A, as in FIGS. 5 and 6. The drive&#39;s cylindrical body  140 B does not rotate around axis  140 X, and is stationary relative to arm  150 A. A link  702 , for example a belt or a chain, runs around the cylindrical surface of body  140 B and also runs around a spindle  130 S rigidly attached to wafer holder  130 . Spindle  130 S passes through a slot in arm  140 A. Spindle  130 S can rotate freely around its axis  130 X. The rotation around the axis  140 X causes the spindle  130 S to drive the link  702  around the body  140 B. The body  140 B rolls along the inner surface of link  702  without slippage (although some slippage is admissible). This causes the link  702  to travel around the spindle  130 S. The link  702  travels around the spindle  130 S without slippage (although some slippage is admissible), causing the spindle to rotate. 
     The velocity W 3  is determined by the velocity W 2  and by the diameters of the cylindrical surfaces of body  140 B and spindle  130 S. The velocity W 3  can be changed by a transmission mechanism using known techniques. 
     If multiple wafer holders are used, a separate link  702  can be provided for each wafer holder. Alternatively, one link can be shared by a number of wafer holders. In FIG. 8, six wafer holders are shown. A link  702 . 1 , e.g. a belt or a chain, rotates three of the wafer holders, and link  702 . 2  rotates the other three of the wafer holders. Links  702 . 1 ,  702 . 2  are positioned at different heights. The W 2  rotation is clockwise. The spindles  130 S rotate counterclockwise around their respective axes. 
     The vertical axis of each spindle  130 S may pass through the center of holder  130  or wafer  134  or both, or through the center of mass of holder  130  or wafer  134  or both. 
     In FIGS. 7 and 8, links  702  can be replaced by other suitable mechanisms to transfer the rotation of arm  140 A around axis  140 X to the rotation of spindles  130 S around their respective axes. For example, a gear train can be used, with a gear or gears mounted on body  140 B and a gear mounted on each spindle  130 S. Combinations of gears, belts, chains, ropes, and other members, known or to be invented, can also be used. In some embodiments, a magnetic field is used to rotate the spindles. A magnetic member (not shown) is mounted on body  140 B. The magnetic member has areas of alternating magnetic polarities along the circumference of body  140 B. A similar magnetic member (not shown) is mounted on each spindle  130 S. Rotation of arm  140 A changes the position of the magnetic field relative to body  140 B and spindles  130 , and the changing field causes the spindles  130 S to rotate. Other mechanisms, know or to be invented, can also be used. 
     Wafer holders  130  of FIGS. 7 and 8 can be non-contact holders, as in FIG. 6. A mechanism  702  can be used to drive the rim  602  rigidly attached to the body of the holder. 
     In FIG. 9, the wafer holder  130  is also a non-contact holder, but its rim  602  can rotate freely around the holder&#39;s body  130 B. The holder&#39;s body  130 B is rigidly attached to arm  140 A. Angle drive  502  has a body  502 B rigidly attached to the wafer holder body  130 B. A motor (not shown) inside the body  502 B rotates a bobbin  502 R around a vertical axis. This rotation is transferred to rim  602  by direct coupling (as in FIG. 9) or through a transmission. The outer edge of the wafer is pressed against the rim  602 , so the wafer rotates around an axis  134 X. 
     The invention is not limited to any particular positioning of drive  502  or other drives in FIG. 9 or in other figures. For example, the bobbin  502 R may contact the rim  602  from inside the rim. The rim may extend above the body  130 B. Other arrangements may also be possible. 
     Rim  602  may be a continuous rim. Alternatively, as shown in FIG. 10, the top portion  602 T of the rim may be continuous, and the bottom portion  602 P may be made in the form of protrusions or pins. The top portion contacts the bobbin  502 R. The bottom portion contacts the wafer  134 . The top portion may be provided with additional openings to make it easier for the gas holding the wafer to escape. 
     FIG. 11 shows another system using non-contact wafer holders. Here the limiters  602 . 1 ,  602 . 2 ,  602 . 3  are individual pins. Each pin is rotated by its own angle drive  502  having a body  520 B rigidly attached to the holder&#39;s body  130 B. All the pins rotate in the same direction. In FIG. 11, three pins are shown. Any number of pins can be provided. The wafer contacts only a pin or pins positioned on the outside of the holder, that is, the pin or pins farthest from the axis  140 X. In some other embodiments, only these pins rotate. The remaining pins, such as pin  602 . 3  in FIG. 11, are provided to restrain the wafer during loading and unloading. During loading and unloading, the W 3  rotation of the wafer is not needed. Therefore, in some embodiments, pin  602 . 3  is rigidly affixed to the holder body  130 B. In other embodiments, pin  602 . 3  is freely rotatable, but is not driven. Allowing all the pins to rotate, and providing them drives, is believed to be beneficial for uniform, controllable W 3  rotation of the wafer during plasma processing, because the wafer may accidentally touch the inner pins (such as pin  602 . 3 ) during the plasma processing. 
     FIG. 12 shows a bottom view of a wafer holder, with three rotatable pins  602  and three non-rotable pins. 
     In FIG. 13, the pins  602 . 1 ,  602 . 2  are rotated using the energy of drive  140 , in a way similar to that of FIG. 7. A single link  702 , e.g. a belt or a chain, may be used to rotate a number of pins on a single holder (two pins in FIG.  13 ). Other types of mechanisms can also be used. A transmission can be used to adjust the velocity of the pin rotation. All the pins driven by mechanisms  702  rotate in the same direction. 
     Pin  602 . 3  is freely rotatable but is not driven. 
     In FIG. 14, a link  702 , e.g. a belt or a chain, drives three of the six pins  602  of holder  130 . (Other mechanisms can also be used instead of a single link.) The other three pins are not driven. Some of these three pins may be freely rotatable, while others may be rigidly affixed to the body of the holder. 
     In FIG. 15, a single link  702 , e.g. a belt or a chain, drives pins  602  of two wafer holders  130 . Other mechanisms (not shown) may be used to drive the pins of other wafer holders that may be present in the system. A single link may drive pins on more than two wafer holders. 
     The embodiments of FIGS. 5-15, the motion of wafer  134  includes at least three rotational motion components. The first rotational motion (W 1 ) is a rotation around the axis  150 X. The system including the arm  150 A, the drive  140 , and the wafer holders  130  rotates around this axis. The second rotational motion (W 2 ) is provided by the rotation of drive  140  and the wafer holders  130  around the axis  140 X. In addition, a rotational mechanism (including, for example, drives  502 , limiters  602 , mechanisms  702 ) provides the third rotational motion of the wafer in the wafer holder. 
     FIG. 17 shows a detailed view of one embodiment of drive  502  (FIG.  11 ). The drive is actuated by an embodiment of air motor. Shown are a vane impeller  638 , a blower  640  and a flow duct  642 . Pin  602  is attached concentrically to vane impeller  638 . Air from a pressure source is introduced into blower  640  and is emitted through a nozzle (not shown) in blower  640  against one side of van impeller  638 . Flow duct  642  guides the air around vane impeller  638 , causing van impeller  638  and pin  602  to spin at an angular velocity W 4 . Since the edge of wafer  134  (FIG. 11) is in contact with pins  602 , the wafer  134  also rotates at the angular velocity W 3 , the relationship between W 3  and W 4  being governed by the following equation:        W4   =     W3        (     Dw     D   Pin       )                              
     where Dw and D Pin  are the diameters of wafer  134  and pin  602 , respectively. In one embodiment the air supplied to blowers  640  is from the same pressure source (e.g., 20 psi) that is used to supply the vortex chucks that clamp wafer  134  to holder  130 . The nozzles in blowers  640  have an opening 0.020 mm in diameter. 
     FIGS. 17A and 17B are perspective and cross-sectional views, respectively, of vane impeller  638 , FIG. 17B being taken at cross-section  17 B— 17 B shown in FIG.  17 A. Pin  602  is mounted in an internal bore  641  of vane impeller  638  by means of a set screw (not shown) that is threaded into tapped hole  639 . In one embodiment vane impeller  638  is 1 inch in diameter. 
     FIG. 18 is a cross-sectional view of the assembly that includes wafer holder  130 , pin  602 , air motor  502 , and wafer  134 . As indicated, wafer  134  “floats” below wafer holder  130  by means of vortex chucks, one of which is shown as  637 . Pin  602  is mounted in a bearing  639 . The arrows show the path of the air leaving the vortex chuck  637 . 
     FIG. 19 shows a detail of an embodiment of FIG.  6 . Pins  602  are rigidly attached to a brim  650  that rotates around wafer holder body  130 B. The brim helps obtaining good processing uniformity at the wafer edges. See U.S. patent application Ser. No. 09/457,042, mentioned above, incorporated herein by reference. Another possibility is that the pins  602  could be rotated by a propeller (not shown) driven by the air flow created as arms  140 A rotate around axis  140 X. 
     In other embodiments the pins are free to rotate (i.e., mounted in bearings) but are not driven, and the air from the vortex chucks is used to rotate the substrate. 
     FIG. 20 shows a single vortex chuck  637  in detail. The air swirling through the opening creates a vacuum (labeled“V”) at the center of the opening. After the air leaves the vortex chuck, it flows outward in a radial pattern  704  sometimes referred to as a “rooster tail”. 
     As shown in FIG. 21, if the “rooster tails” are oriented in a single angular direction around the center of a wafer, a rotational force may be imparted on the wafer. By adjusting the size and number of vortex chucks and the air pressure through them, the wafer can be caused to rotate at a desired angular velocity W 3 . In this case the pins  602  rotate freely, constraining the wafer in position over the surface of the holder but allowing the water to rotate. 
     The above embodiments illustrate but do not limit the invention. The invention is not limited by any dimensions, velocity values or relationships between the dimensions and the velocity values. The invention is not limited to systems in which a plasma jet is too narrow to cover the entire wafer. The invention is not limited to the dynamic plasma treatment or to plasma processing at atmospheric pressure, and is applicable to plasma processing in vacuum. Plasma source  114  does not have to be stationary, it may move during wafer processing. Axis  150 X may also move. In some embodiments, the wafers arc positioned above the holders, and the plasma flows downward. The invention is not limited to semiconductor wafers or to round articles. The invention is applicable to processing of flat screens or other articles, known or to be invented. In some embodiments, a holder  130  holds a semiconductor chip, or a number of chips, obtained from a semiconductor wafer through dicing. Each chip may include circuitry. 
     The invention is not limited to any particular motors used for the drives  140 ,  150 ,  502 . Stepper motors, servo motors, or other motors, known or to be invented, may also be applicable. In some embodiments, a single motor drives the arm  150 A around the axis  150 X and the carrousel  124  around the axis  140 X. The invention is defined by the appended claims.