Abstract:
A neutral beam is scanned across a workpiece surface and the beam angle is controlled in a manner that avoids variation in the beam source-to-workpiece distance during scanning.

Description:
BACKGROUND 
     1. Technical Field 
     The disclosure concerns treatment for material modification of a workpiece by a neutral beam. 
     2. Background Discussion 
     Treatment modification of surface material of a workpiece such as a semiconductor wafer using an ion beam is well-known. Such treatment may include localized film property modification by a directional beam to enable selectivity improvement. Surface properties may be altered to enhance or inhibit nucleation, deposition and etching of the material. Use of an ion beam for such purposes involves certain limitations. For example, there is no independent control of beam angle and beam energy for an ion beam. Further, the ion beam spreads as it propagates toward the workpiece due to space charge. More importantly, the ion beam charges the surface of the workpiece, which can lead to damage of features formed on the workpiece. One solution to such problems is to employ a neutral beam instead of an ion beam. One need is to provide for independent control of energy and impact angle at the workpiece of the neutral beam. 
     SUMMARY 
     A method of treating a workpiece comprises: producing a line beam comprising a sheet of neutral species by directing ions through an elongate slit of a neutralization grid of a neutral beam source; holding the workpiece in a path of the line beam to produce an elongate beam impact zone on a surface of the workpiece; translating the workpiece relative to the line beam in a scan direction transverse to the elongate beam impact zone; and setting a collision angle of the line beam relative to the surface of the workpiece to a desired value by rotating the neutral beam source. 
     In one embodiment, the operation of rotating comprises moving the neutral beam source in an orbital motion about a rotation axis external of the neutral beam source. In a further embodiment, the rotation axis coincides with the elongate beam impact zone on the surface of the workpiece. In a yet further embodiment, the rotation axis is a line corresponding to the beam impact zone. In one embodiment, the operation of rotating further comprises continually facing the elongate slit toward a stationary location on the surface of the workpiece. The stationary location can be the beam impact zone. 
     In accordance with another aspect, a method is provided for treating a workpiece, the method comprising: producing a plurality of respective line beams comprising respective sheets of neutral species by directing ions through respective elongate slits of respective neutralization grids of respective neutral beam sources; holding the workpiece in respective paths of the respective line beams to produce respective elongate beam impact zones on a surface of the workpiece; translating the workpiece relative to the respective line beams in a scan direction transverse to the elongate beam impact zones; and setting respective collision angles of the respective line beams relative to the surface of the workpiece to respective desired values by rotating the respective neutral beam sources. 
     In one embodiment, the operation of rotating comprises moving each of the neutral beam sources in respective orbital motions about respective rotation axes external of the respective neutral beam sources. In one embodiment, the rotation axes coincide with respective ones of the elongate beam impact zones on the surface of the workpiece. In one embodiment, the rotation axes comprise respective lines corresponding to the respective beam impact zones. In one embodiment, the operation of rotating further comprises continually facing the respective elongate slits toward respective stationary locations on the surface of the workpiece. The respective stationary locations may comprise the respective beam impact zones. 
     In accordance with a yet further aspect, a method of treating a workpiece is provided, the method comprising: producing a line beam comprising a sheet of neutral species by directing ions through an elongate slit of a neutralization grid of a neutral beam source; holding the workpiece in a path of the line beam to produce an elongate beam impact zone on a surface of the workpiece; translating the workpiece relative to the line beam in a scan direction transverse to the elongate beam impact zone; and setting a collision angle of the line beam relative to the surface of the workpiece to a desired value by positioning the neutralization grid at an angle relative to the surface of the workpiece at which the collision angle corresponds to the desired value. In one embodiment, the operation of producing comprises producing respective line beams comprising respective sheets of neutral species by directing ions through respective elongate slits of respective neutralization grids; the operation of holding comprises holding the workpiece in paths of the respective line beams to produce respective elongate beam impact zones on a surface of the workpiece; and the operation of setting comprises setting respective collision angles of the respective line beams relative to the surface of the workpiece to respective desired values by positioning the respective neutralization grids to respective angles relative to the surface of the workpiece at which the respective collision angles correspond to the respective desired values. 
     One embodiment further comprises providing different beam acceleration voltages within different ones of the respective neutralization beam sources, whereby the respective neutral beams have different energies, providing independent control of beam energy and beam angle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the exemplary embodiments of the present invention are attained can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. It is to be appreciated that certain well known processes are not discussed herein in order to not obscure the invention. 
         FIG. 1  depicts apparatus including a neutral beam source and a scanning support stage for carrying out a first embodiment. 
         FIG. 1A  is a plan view corresponding to  FIG. 1 . 
         FIG. 2  is a cross-sectional view of a semiconductor wafer and depicts material treatment in the embodiment of  FIG. 1 . 
         FIG. 3  depicts apparatus including two neutral beam sources and a scanning support stage for carrying out a second embodiment. 
         FIG. 4  depicts apparatus including three neutral beam sources and a scanning support stage for carrying out a third embodiment. 
         FIG. 5  is a cross-sectional view of a semiconductor wafer and depicts material treatment in the embodiment of  FIG. 3 . 
         FIG. 6  depicts apparatus including a neutral beam source and a scanning support stage for carrying out a fourth embodiment. 
         FIG. 6A  depicts apparatus including two neutral beam sources and a scanning support stage for carrying out a fifth embodiment. 
         FIG. 7  depicts apparatus including three neutral beam sources and a scanning support stage for carrying out a sixth embodiment. 
         FIG. 8  is a block diagram of method in accordance with an embodiment. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 and 1A , a neutral beam source  100  includes a plasma chamber  102  enclosed by side walls  104 , a ceiling  106  and a neutralization grid  108 . The neutralization grid  108  is a solid body of a thickness T formed of an electrically conductive material and has a single elongate slit  110  that opens into the interior of the plasma chamber  102 . Generally, the elongate slit  110  is the only opening through the neutralization grid  108 . The neutralization grid  108  may be connected to ground or may be connected to an RF or D.C. voltage source. The elongate slit  110  has opposing interior side walls  110   a  and  110   b  separated by a distance defining a width W of the elongate slit  110 . A plasma source power supply  120  provides power to a plasma source power applicator  122  on or adjacent the plasma chamber  102 . The plasma source power supply  120  may be an RF power generator with an impedance match or a D.C. power supply or a microwave generator, for example. The plasma source power applicator  122  may be an electrode or an RF-driven coil or a microwave waveguide, for example. A gas supply  124  provides a process gas into the plasma chamber  102 . Plasma source power is coupled into the chamber by the plasma source power applicator  122  and ionizes the process gas to generate a plasma within the plasma chamber  102 . Ions of the plasma exit the plasma chamber  102  through the elongate slit  110 , and their energy may be controlled (for example) by controlling a beam acceleration voltage within the neutral beam source  100 . This beam acceleration voltage may be (for example) the voltage difference between the plasma source power applicator  122  and the neutralization grid  108 . The ions undergo glancing collisions with the interior side walls  110   a  and  110   b  as they exit through the elongate slit  110 . Such collisions transform the ions to neutral species, producing a line beam  130  of neutral species emanating from the elongate slit  110 . The line beam  130  is generally a flat thin sheet of neutral species having a thickness corresponding to the width W of the elongate slit  110 . The direction of the line beam  130  coincides with the direction of the elongate slit  110 . 
     A support stage  134  supports a workpiece  136  in the path of the line beam  130 . The workpiece  136  may be a semiconductor wafer, for example. The line beam  130  impacts top surface  136   a  of the workpiece  136  in a thin elongate impact zone or line  138  depicted in  FIG. 1A . A scan servo  139  translates the support stage  134  in a scan direction S orthogonal (or transverse) to the line  138 , as depicted in  FIG. 1A . 
       FIG. 2  is a simplified cross-sectional view of the workpiece  136 , depicting 3-dimensional features including openings  140  (which may be high aspect ratio openings) in the top surface  136   a  of the workpiece  136 .  FIG. 2  depicts how interior side wall surfaces  140   a  of the openings  140  are treated with the line beam  130 . 
     The angle A ( FIG. 2 ) at which the line beam  130  impacts the workpiece  136  relative to the interior side wall surface  140   a  determines the manner in which the neutral beam interacts with the interior side wall surfaces of the openings  140  for material modification. There is a need to set or control the angle A in accordance with process requirements. The problem is how to set or change the angle A without introducing non-uniformity or variations in the workpiece-to-beam source distance D as the workpiece is translated in the scan direction S. One choice may be to tilt the workpiece  136  and support stage  134 . However, such tilting can introduce non-uniformity or variations in the workpiece-to-beam source distance D as the workpiece is translated in the scan direction S by the support stage  134 . 
     The problem is solved by tilting the neutral beam source  100  about an axis until the desired tilt angle is reached, while not tilting the support stage  134  or workpiece  136 . By allowing the support stage  134  and the workpiece  136  to remain untilted, the introduction of non-uniformities in the workpiece-to-beam source distance during scanning is avoided, a significant advantage. This in turn enables the workpiece  136  and support stage  134  to be translated along the scan direction S while ensuring that the workpiece-to-beam source distance D remains uniform during the entire scan. 
     In one embodiment, the axis about which the neutral beam source is tilted (rotated) coincides with the line  138 . This requires an orbital-like motion of the neutral beam source  100  about the axis or line  138 . This feature provides the advantage of keeping the beam impact zone or line  138  stationary relative to a fixed frame of reference while the neutral beam source  100  is tilted (rotated). 
     In accordance with the foregoing, a tilt servo  160  coupled to the neutral beam source  100  can be provided to achieve the desired tilt angle of the neutral beam source  100 . In one embodiment, the tilt servo  160  moves the neutral beam source  100  in an orbital-like motion about an axis of rotation coinciding with the line  138 , until the desired tilt angle A is reached. This orbital-like motion is indicated in dashed line in  FIG. 1 . 
       FIG. 3  depicts an embodiment in which two neutral beam sources  100 - 1 ,  100 - 2  having respective parallel slits  110 - 1 ,  110 - 2 , overlie the support stage  134  and produce line beams  130 - 1 ,  130 - 2 , defining respective impact zones or lines  138 - 1 ,  138 - 2  on the top surface  136   a  of the workpiece  136 . Respective tilt servos  160 - 1 ,  160 - 2  move the respective neutral beam sources  100 - 1 ,  100 - 2  in respective orbital-like motions of the type described above with reference to  FIG. 1  about respective axes coinciding with the lines  138 - 1 ,  138 - 2  respectively. The neutral beam sources  100 - 1 ,  100 - 2  are independent and may be controlled to produce the respective line beams  130 - 1 ,  130 - 2  with different beam energies. This facilitates the simultaneous treatment of the workpiece  136  with two different beam energies at two different beam tilt angles. 
       FIG. 4  depicts an embodiment in which three neutral beam sources  100 - 1 ,  100 - 2 ,  100 - 3  having parallel slits  110 - 1 ,  110 - 2 ,  110 - 3 , respectively, overlie the support stage  134  and produce line beams  130 - 1 ,  130 - 2 ,  130 - 3 , defining respective beam impact zones or lines  138 - 1 ,  138 - 2 ,  138 - 3  on the top surface  136   a  of the workpiece  136 . Respective tilt servos  160 - 1 ,  160 - 2 ,  160 - 3  move the respective neutral beam sources  100 - 1 ,  100 - 2 ,  100 - 3  in respective orbital-like motions of the type described above with reference to  FIG. 1  about respective axes coinciding with the lines  138 - 1 ,  138 - 2 ,  138 - 3 , respectively. The neutral beam sources  100 - 1 ,  100 - 2 ,  100 - 3  are independent and may be controlled to produce the respective line beams  130 - 1 ,  130 - 2 ,  130 - 3  with different beam energies. This facilitates the simultaneous treatment of the workpiece  136  with three different beam energies at three different beam tilt angles, as depicted in  FIG. 5 . 
       FIG. 6  depicts a modification of the embodiment of  FIG. 1 , in which the neutralization grid  108  is angled relative to the ceiling  106  and side walls  104  of the plasma chamber  102  of the neutral beam source  100 . In  FIG. 6 , the desired tilt angle A of the line beam  130  relative to the workpiece  136  is achieved by orienting the neutralization grid  108  relative to the other components of the neutral beam source  100 .  FIG. 6A  depicts a modification of the embodiment of  FIG. 3  having the two neutral beam sources  100 - 1 ,  100 - 2 , in which neutralization grids  108 - 1  and  108 - 2  are each angled relative to the respective neutral beam sources  100 - 1 ,  100 - 2 . In  FIG. 6A , the desired tilt angles of the line beams  130 - 1  and  130 - 2  relative to the workpiece  136  are achieved by orienting the neutralization grids  108 - 1  and  108 - 2 .  FIG. 7  depicts a modification of the embodiment of  FIG. 4  having the three neutral beam sources  100 - 1 ,  100 - 2 ,  100 - 3 , in which the neutralization grids  108 - 1 ,  108 - 2  and  108 - 3  are each angled relative to the respective neutral beam sources  100 - 1 ,  100 - 2 ,  100 - 3 . In  FIG. 7 , the desired tilt angles of the line beams  130 - 1 ,  130 - 2  and  130 - 3  relative to the workpiece  136  are achieved by orienting the neutralization grids  108 - 1 ,  108 - 2  and  108 - 3  relative to the neutral beam sources  100 - 1 ,  100 - 2  and  100 - 3 . 
       FIG. 8  is block diagram illustrating a brief synopsis of the methods described above. In  FIG. 8 , a first operation is to produce a line beam comprising a sheet of neutral species by directing ions through an elongate slit of a neutralization grid of a neutral beam source (block  190 ). A next operation is to hold the workpiece in a path of the line beam to produce an elongate beam impact zone on a surface of the workpiece (block  192 ). A further operation is to translate the workpiece relative to the line beam in a scan direction transverse to the elongate beam impact zone (block  194 ). A yet further operation is to set a collision angle of the line beam relative to the surface of the workpiece to a desired value by positioning the neutralization grid at an angle relative to the surface of the workpiece at which the collision angle corresponds to the desired value (block  196 ). 
       FIG. 1  depicts a processor  400  (e.g., a computer) controlling the tilt servo  160 , the scan servo  139 , the plasma source power supply  120  and the gas supply  124 . A memory  410 , including computer-readable media, contains instructions executed by the processor  400 , the respective instructions corresponding to the respective operations of the method of  FIG. 8 . In one embodiment, the memory  410  may be provided within a network to which the processor  400  is coupled. The processor  400  implements the method of  FIG. 8  by carrying out the instructions stored in the memory  410 . 
     Advantages: 
     Embodiments described above provide a number of advantages. One advantage is that independent control of beam energy and beam angle is provided. The feature of tilting the neutral beam source  100  about an axis until the desired tilt angle is reached, while not tilting the support stage  134  or workpiece  136 , provides the advantage of avoiding the introduction of non-uniformities in the workpiece-to-beam source distance during scanning. Performing the rotation of the neutral beam source  100  about an axis coinciding with the beam impact zone or line  138  provides the advantage of keeping the beam impact zone or line  138  stationary relative to a fixed frame of reference while the neutral beam source  100  is tilted. 
     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.