Abstract:
There is provided a deposition system ( 1 ) for yielding substantially uniform deposition of an evaporant material onto a substrate. The deposition system ( 1 ) comprises: a source ( 10 ) for generating a coherent energy beam; a substantially planar target ( 60 ) containing the evaporant material and disposed in spaced relation to the substrate; a focusing element ( 30 ) optically coupled to the source for focusing the coherent energy beam onto the target ( 60 ); and, an actuator ( 40 ) coupled to the focusing element ( 30 ) for reversibly translating the focusing element ( 30 ) along a scanning path directed substantially parallel to a target plane defined by the target ( 60 ). The focused coherent energy beam defines an impingement spot ( 14 ) on the target ( 60 ). The impingement spot ( 14 ) is displaced responsive to the translation of the focusing element ( 30 ) along the scanning path. The focus of the coherent energy beam on the target ( 60 ) thus remains substantially preserved.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The subject scanned focus deposition system is generally directed to a system for uniformly depositing an evaporant material onto a substrate. More specifically, the scanned focus deposition system is directed to a laser deposition system wherein the uniform deposition of evaporant material from a target onto a substrate is facilitated by optimally controlling the target material&#39;s consumption. 
     Generally in laser deposition techniques, an evaporant material source is excited by a coherent energy beam such that particles of the evaporant material are released from the source and deposited onto a proximally disposed substrate surface. In these deposition techniques, the evaporant source—or target—may be placed, along with a substrate, within a vacuum chamber. A pulsed laser beam generated by a source located outside the vacuum chamber is then directed by optical components into the vacuum chamber. The optical components include, among other things, a focusing element which focuses the laser beam to impinge upon the target, defining an impingement spot. The concentrated energy at the impingement spot causes the generation of a highly directed evaporant plume that emanates from the target toward the proximally located substrate. The particles of target material contained in the evaporant plume then deposit onto the substrate&#39;s surface. By sustaining this deposition process while the substrate is rotated or otherwise displaced in controlled manner, a coating of target material may be formed on the substrate. 
     In many applications of this technique, the uniformity of deposition is of paramount concern. Numerous factors bear on the uniformity that may ultimately be realized. Perhaps chief among them is the degree to which the release of the target&#39;s evaporant material is regulated. The target includes a given mass of evaporant material which ‘wears’ as the deposition process progresses. The progressive wear of evaporant material potentially yields ruts and divots formed in the surface of the target. Consequently, the regularity (concentration, direction of release, . . . ) with which particles of the evaporant material are released from the target is quickly disrupted unless adequate aversive measures are taken. There is, therefore, a need for a deposition system wherein such aversive measures are adequately taken to optimize the uniformity of deposition that the system may realize. 
     2. Prior Art 
     Deposition systems, including pulsed laser deposition systems, incorporating one or more aversive measures to minimize the detrimental effects of target wear are known in the art. The best prior art known to Applicant includes U.S. Pat. Nos. 5,654,975; 5,724,173; 5,606,449; 5,661,290; 5,374,817; 5,144,120; 4,568,142; 4,504,110; 4,327,959; 4,218,112; 3,642,343; and, 3,508,814. 
     One aversive measure incorporated in deposition systems known in the art is to rotate the target about a rotation axis normal thereto. Another is to simultaneously scan the laser beam impinging upon the target along, for instance, the target&#39;s radial extent. A system employing these measures is disclosed in U.S. Pat. No. 5,654,975 entitled “SCANNING LASER BEAM DELIVERY SYSTEM,” and assigned to the Assignee of the present invention. In that system, a laser beam source and a beam transfer assembly cooperatively generate and direct an optical path having a terminal segment that impinges upon a target evaporant. An automatically controlled scanning mechanism displaces the beam transfer assembly in appropriate manner to translate the terminal segment of the optical beam path in a direction substantially normal to the longitudinal direction along which it extends. 
     While this system yields marked improvement over prior art deposition systems in the uniformity of deposition realized on a substrate, a number of shortcomings yet prevail. First, the strict lateral translation of the optical beam path terminal segment does not necessarily preserve the normal distance between the given focusing element and the target surface. In typical deposition systems, the planar front face of the target is not squarely oriented towards the incoming energy beam; for, the incident angle formed by the incoming beam relative to the target&#39;s front face must be something other than 90° if the resulting evaporant plume is to be directed towards the given substrate and not directly back towards the incoming energy beam, itself. Consequently, as the incoming beam is translated in a direction normal to its propagating direction, the focusing element is displaced either toward or away from that portion of the target&#39;s front facial plane on which it is to direct the energy beam. The beam&#39;s focus on the target is thus disturbed. That is, the effective shape and size of the impingement spot which the incoming energy beam forms on the target at a given instant in time is not preserved. 
     Another shortcoming prevails in the fact that the beam transfer assembly comprising all the optical components for forming at least the terminal segment of the energy beam is displaced in its entirety to effect the lateral translation of the beam path terminal segment. The practical inefficiencies inherent in such cumbersome manipulation of components are readily apparent. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to effect substantially uniform deposition of evaporant material contained in a target onto a substrate. 
     It is another object of the present invention to realize substantially uniform deposition of the target evaporant material onto a substrate using a pulsed laser deposition technique. 
     It is another object of the present invention to optimally regulate the consumption of the target evaporant material. 
     It is another object of the present invention to scan at least that portion of a coherent energy beam impinging upon the target in a manner that optimally preserves the beam&#39;s focus on the target. 
     It is yet another object of the present invention to effect the necessary scanning of a coherent energy beam in a simple and efficient manner. 
     It is still another object of the present invention to scan a coherent energy beam along the target by translating a focusing element along a scanning path that substantially preserves the beam&#39;s focus on the target. 
     These and other objects are attained in the present invention which provides a deposition system for substantially uniform deposition of an evaporant material onto a substrate. The deposition system comprises: a source for generating a coherent energy beam; a substantially planar target containing the evaporant material which is disposed in spaced relation to the substrate; a focusing element optically coupled to the source for focusing the coherent energy beam onto the target; and, an actuator coupled to the focusing element for reversibly translating that focusing element along a scanning path directed substantially parallel to a target plane defined by the target. The focused coherent energy beam defines an impingement spot on the target. The impingement spot is displaced responsive to the translation of the focusing element along the scanning path. The focus of the coherent energy beam on the target thus remains substantially preserved. 
     While enhanced uniformity of deposition may be realized in accordance with the present invention even without target rotation, the target is rotated in a preferred embodiment about a target rotation axis substantially normal to the target plane. Also in that embodiment, the actuator is adapted to translate the focusing element in reciprocal manner in accordance with a predetermined rate profile. The rate profile is defined based upon the position of the impingement spot relative to the target rotation axis. Preferably, the rate profile is defined by a substantially sinusoidal displacement profile, the rate of focusing element translation being inversely related to the displacement of the impingement spot from the target rotation axis. 
     In an alternate embodiment, the scanning path for the focusing element is described by a plurality of directional components. Each directional component in that embodiment is substantially parallel to the target plane. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view, partially cut-away, of one embodiment of the present invention in a typical application; 
     FIG. 2 is a detailed perspective view, partially cut-away, of a portion of the system shown in FIG. 1; 
     FIG. 3A is a schematic diagram illustrating an exemplary translation of the focusing element in an embodiment of the present invention; 
     FIG. 3B is a schematic diagram illustrating exemplary scan paths as projected on a target plane that may be realized in accordance with the present invention; 
     FIG. 3C is a graphic diagram illustrating exemplary displacement profile curves pertaining to exemplary application of the present invention; 
     FIG. 4 is an illustrative diagram showing an alternate embodiment of a portion of the present invention; 
     FIG. 5A is another alternate embodiment of a portion of the present invention; 
     FIG. 5B is an illustrative diagram of yet another alternate embodiment of a portion of the present invention; and, 
     FIG. 5C is an illustrative diagram of still another alternate embodiment of a portion of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning now to FIG. 1, there is shown an exemplary arrangement of components for one embodiment of the invention. System  1  generally includes a source  10  for generating a coherent energy beam  12 ; a focusing element  30  for focusing beam  12  onto a target (not shown) contained within a vacuum chamber  50 ; and, an actuator  40  for translating along a scanning path indicated by the bi-directional arrow  100 . System  1  also includes an assembly  20  of components for guiding and/or delivering energy beam  12  to focusing element  30 . 
     Component assembly  20  may include as many or as few components as are necessary for a given application. It may, for example, include a filter  22 , a beam splitter or reflector  24 , and an aperture element  26 . These components  22 ,  24 ,  26 , however, are shown only for exemplary purposes, for assembly  20  may include any suitable components known in the art. In certain applications where system requirements permit, it may not even be necessary to employ assembly  20 . In such applications, energy beam  12  would be delivered by the given source  10  directly to focusing element  30 . 
     Preferably, coherent energy beam  12  is a pulsed laser beam that is generated by a pulsed laser source of any suitable type known in the art. 
     Focusing element  30  preferably includes a convex lens  31  characterized by a finite focal distance. It may be embodied in any of numerous configurations and forms other than that shown. It is important, however, that the focusing portion—or lens  31  in the embodiment shown—possess sufficient radial or transaxial extent such that as it is scanned along the range of displacement described by scanning path  100 , pulsed laser beam  12  remains fully directed through its focusing portion. 
     Focusing element  30  is supported by such suitable means as a neck  32  telescopically received within a base  33 . Focusing element  30  is initially positioned by its supporting structure at a sufficient distance from the given target (not shown) that the length of impingement beam segment  12 ′ generated by its lens  31  preferably approaches, if not equals, the lens&#39; characteristic focal distance. 
     Referring now to FIGS. 2-3B, impingement beam segment  12 ′ is thus substantially focused onto the given target  60 . Impingement beam segment  12 ′ impinges upon the front surface of target  60  to define thereon (at a given instant in time) an impingement spot  14  of a particular shape and size. The focused energy at impingement spot  14  then causes an evaporant plume  61  to form and emanate therefrom. The particulate constituents forming evaporant plume  61  are highly directed away from the substantially planar surface of target  60 , toward an opposing substrate for deposition into/onto that substrate&#39;s surface (not shown). 
     The directivity of an evaporant plume  61  thus formed is very much dependent upon the planar orientation of target  60 . It is, therefore, necessary that a substantially planar target plane defined by the target&#39;s front surface (facing the incoming energy beam) be oriented at an angle other than 90° relative to the incoming impingement beam segment  12 ′. Otherwise, the resulting evaporant plume  61  would be squarely directed back towards focusing element  30 . Any attempt to place the substrate in the path of the resulting plume  61  would then also necessarily place that substrate in the path of impingement beam segment  12 ′, obstructing further operation. For this reason, target  60  is retained by a support mechanism  62  such that it defines a target plane which forms an angle of 45°, or some other suitable value (in at least one dimension), relative to the axis of the incoming impingement beam segment  12 ′. This allows the substrate to be placed safely out of the path of impingement beam segment  12 ′. 
     As the evaporant material that forms target  60  is consumed by the process of generating successive evaporant plumes  61 , pits, ruts, divots, and other surface irregularities tend naturally to occur on target  60 . As discussed in preceding paragraphs, such surface irregularities tend to disturb significantly enough the directivity of subsequently formed evaporant plumes  61  that acceptable levels of deposition uniformity become virtually impossible to attain. 
     One preventive measure typically taken is to minimize the dwell time of impingement beam spot  14  on any particular portion of target  60  by scanning that impingement spot  14  along, for instance, a direction  200  as the target  60  itself is rotated by a predetermined angle ω about a target rotation axis X (preferably defined along the normal to the target plane defined by target  60 ). This leads to a gradually progressing, generally even wear, or consumption, of target  60 . This, in turn, leads to greater uniformity of deposition on the substrate. Ideally, the shape and size of impingement spot  14  is preserved, even as it travels through the range of displacements along an impingement spot scan path  200  between, preferably, a point at or near the rotation axis and a distal point  14 ′. That is, the focus of impingement beam  12 ′ on target  60  is substantially preserved despite the scanning. 
     In accordance with the present invention, this preservation of focus is simply yet precisely realized by translating focusing element  30 —or at least the focusing lens portion  31  of focusing element  30 —along a scanning path  100  directed substantially parallel to the target plane defined by the front surface of target  60 . In the embodiment shown, this translation of focusing element  30  occurs only along the horizontal dimension. Note, however, that the translation may be along a composite scanning path having a non-zero component along both the horizontal and vertical dimensions, so long as the composite scanning path remains on a plane parallel to the target plane. Such an embodiment is indicated in FIG. 3B by the impingement spot scan path  200 ′ defining a range of impingement spot displacements from rotation axis X to a distal point  14 ″. 
     While not shown in the Drawings, the composite scan path may in certain embodiments map a complex and irregular pattern, where the available resources and applicable requirements permit. Where a programmable controller(s) is available, for instance, optimal patterns of high complexity may be automatically generated and implemented in the scan, dynamically or otherwise. 
     Any suitable measures known in the art may be employed to effect the necessary translation of focusing element  30  along the given scanning path  100 . In the exemplary embodiment of FIG. 1, the translation is effected automatically in reciprocal manner utilizing the mechanism shown in greater detail in FIG.  2 . Actuator  40  in this embodiment includes a base  41  on which is disposed an elongate rail  43 . A support block  42  is slidably engaged to rail  43  to be displaceable along the actuating direction indicated by bi-directional arrow  100 ′. Preferably, actuating direction  100 ′ is parallel to the scanning path  100 . 
     Coupled to support block  42  is a suspension arm  34  extending from the focusing element&#39;s base  33 . Suspension arm  34  is fixedly mounted to support block  42  by a suitable fastener  36  which may be released to adjust the position of suspension arm  34  relative to that support block  42 . 
     The displacement of support block  42  along rail  43  is controlled by a motor  44  or other comparable mechanism known in the art adapted to generate the force required for the displacement. The force generated by motor  44  is transferred to support block  42  via a substantially rigid transfer link  45  extending between a pin member  46  anchored to support block  42  and a pin member  47  anchored to motor  44 . Transfer link  45  is coupled by suitable means to pin members  46 ,  47  in angularly displaceable manner. 
     During operation, then, motor  44  generates a displacement of pin member  47 . Responsive to this displacement, pin member  46  is caused via transfer link  45  to undergo an accommodating displacement, which it imparts to support plate  42 . The direction of displacement is limited to actuating direction  100 ′ by the engagement of support plate  42  with rail  43 . The displacement of support plate  42  over rail  43  yields the displacement of focusing element  30  along scanning path  100 . 
     Referring again to FIG. 3B, the effective dwell time of impingement spot  14  at target rotation axis X cannot equal its effective dwell time at, for instance, point  14 ′ on target  60  which is radially offset from rotation axis X. Since target  60  is rotated about axis X, the instantaneous linear velocity at point  14 ′ on target  60  is necessarily greater than the instantaneous linear velocity at a second point on target  60  offset from target axis X by a lesser radial distance. Consequently, the effective dwell time of impingement spot  14  at point  14 ′, for instance, would invariably be less than the effective dwell time of impingement spot  14  at or near target axis X—unless the scanning rate is accordingly controlled. Preferably, therefore, the translation of focusing element  30  along scanning path  100  is carried out in accordance with a predetermined rate profile that is based upon the displacement profile of the resulting impingement spot  14  relative to target rotation axis X. 
     One such predetermined rate profile may be defined in accordance with a substantially sinusoidal displacement profile, with the scanning rate being inversely related to the radial displacement of impingement spot  14  from the target rotation axis X. The scanning rate, in accordance with that profile, is varied during a scan cycle to attain a minimum value at the radially outermost point(s) on target  60  reached by impingement spot  14  during its displacement along scan path  200 , and a maximum where impingement spot  14  is at its radially innermost point along that scan path  200 . The alternate embodiment of actuator  40  shown in FIG. 4 represents one exemplary means by which such sinusoidal profile may be effected. Note that scan path  200  may extend substantially across the diametric extent of target, traversing rotation axis X. 
     FIG. 3C graphically illustrates examples of substantially sinusoidal displacement profiles that may be employed in an exemplary embodiment of the present invention. As there shown, the instantaneous linear position of impingement spot  14  (in proportional units relative to the target&#39;s rotation axis X) is plotted against the corresponding instantaneous angle values within one complete cycle of the given scanning action. Curve  210  simply represents, for referential purposes, the cosine curve defined by the angle values within the scan cycle shown. Similarly, curve  212  effectively represents the ideal case—that is, where optimal target wear is realized given an infinitesimally small impingement spot  14  scanned through a path traversing the target&#39;s rotation axis X. 
     Curves  214  and  216  profile exemplary scanning actions that may be effected in accordance with the present invention. With LO denoting, for instance, the length of transfer link  45  and r representing the radial displacement of pin member  47  from the central shaft (not shown) of motor  44 , curve  214  represents the case where the ratio of l/r is rather low, equaling approximately 2 or so; whereas, curve  216  represents the case where the l/r ratio is relatively high, equaling approximately 8 or so. Note that the higher l/r ratio of curve  216  causes it to more closely follow the reference cosine curve  210 . 
     Among other things, it is graphically apparent from these curves that the instantaneous rate at which scanning occurs varies from a minimum value at the points of maximum linear displacement (from the target&#39;s rotation axis X) to a maximum value at the target&#39;s rotation axis X (where linear position equals 0). Given a motor  44  operating at a fixed frequency (at a fixed rpm), the angle values denoting instantaneous angular displacement positions within a motor shaft revolution would map linearly to a time reference. The instantaneous slope of each curve  214 ,  216 , which reaches a minimum at the given curve&#39;s amplitude extremes, is therefore indicative of (for instance, proportional to) the instantaneous scan rate. 
     Referring next to FIG. 4, there is illustrated an alternate embodiment  140  of the translation actuator. In this embodiment, actuator  140  includes a motor  141  that drives an axial shaft  142  to which a platform member  143  is coupled. A pin member  144  extends from platform member  143 , and a transfer link  145  couples pin member  144  to a pin member  146  extending from support block  142  (whose details, for the sake of clarity, are not shown). Where transfer link  145  is substantially rigid, suitable accommodating measures must be taken such as the rotatable coupling of pin members  144 ,  146  respectively to platform member  143  and support block  42 —or, alternatively, the angularly displaceable coupling of transfer link  145  to pin members  144  and  146 . The embodiment shown, however, permits transfer link  145  to be formed from a flexible material, thus obviating these accommodating measures. 
     Actuator  140 , in this embodiment, further includes a tension spring member  147  which extends between a pin member  148  affixed to support block  142  and a stationary pin member  149  affixed to base  41  (not shown) or some other fixed platform/surface. Spring member  147  possesses the properties sufficient for it to expand as the motor-driven rotation of platform member  143  indicated by the directional arrow  105  pulls transfer link  145  taut and, thereby, pulls support platform  142  along translation path  100 ′. During those phases of the platform member&#39;s rotation wherein pin member  144  is drawn towards pin member  146  (to relax the tension on transfer link  145 ), the tension of spring member  147  draws support block  142  in the opposing direction along translation path  100 ′. Spring member  147  thus serves to bias support block  42  towards stationary pin member  149 . Reciprocal translation of support block  42  in either direction along path  100 ′ may then occur even with motor  141  driving the translation in only one direction. 
     Actuator  140  may, if necessary, further include a vertical actuator component  150  coupled to a base  151  of focusing element  30  in such manner that vertical displacement of focusing element  30  may be effected concurrently with the horizontal translation thereof. When thus combined with the horizontal translation, the concurrent displacement of focusing element  30  indicated by the directional arrows  110  and  100 ′ would, depending on the control employed, enable any of numerous effective beam scan paths to be described on the given target plane. In certain embodiments, vertical actuator component  150  may be programmable (as may the unshown control for motor  141 ). 
     Pertinent portions of another alternate embodiment  240  of the translation actuator are shown in FIG.  5 A. In this embodiment, the spring or other resilient element  147  and flexible translation link  145  are removed in favor of a transfer link  245  formed as a substantially rigid elongate arm member. Arm member  245  is coupled in angularly displaceable manner to a pin member  244  extending from platform member  243  and to a pin member  246  extending from support block  42 . The angularly displaceable coupling may be realized through any suitable means, such as a ball bearing joint  247 ,  248 . The reciprocating translation  42  is then fully driven by the rotation of platform member  243 . 
     Yet another embodiment  340  of the translation mechanism is shown in FIG.  5 B. As there shown, actuator  340 , in this embodiment, employs a platform member  343  shaped with a predetermined peripheral contour. Platform member  343  is rotatably driven by a motor  341  via a drive shaft  342 . The driven movement of platform member  343  is transferred to support block  42  by a substantially rigid transfer link member  345  that projects from a pin member  346  extending from support block  42  and engages the platform member&#39;s sidewall portion  343   a . At the opposing end of support block  42  is coupled a spring or other resilient member  347  of suitable properties which biases support block  42  away from a stationary member  349  affixed to either base  41  (not shown) or other stationary platform/surface. 
     As platform member  343  in the given configuration is driven to rotate, the biasing force of spring member  347  maintains the abutting engagement of the platform member&#39;s sidewall portion  343   a  and transfer link  345 . Consequently, the nature and extent of the support block&#39;s translation along the directions  100 ′ are determined by the contour described by the platform member&#39;s sidewall portion  343   a . That is, r(θ) is proportional to the instantaneous scanning rate, where parameters r and θ respectively represent the instantaneous distance from the axis of the platform&#39;s rotation to a point along the platform&#39;s peripheral outline and the instantaneous angular offset of a given radial extent from an angular reference. 
     Pertinent portions of still another alternate embodiment  440  of the translation actuator is shown in FIG.  5 C. Actuator  440  enables the adjustable re-configuration thereof necessary to vary the range of translation of support block  42  along path  100 ′. Actuator  440  includes a platform member  443   a  to which an adjustment member  443   b  is slidably coupled for adjustable displacement. Adjustment member  443   b  may thus be positioned on platform member  443   a  at any point along the range of displacement indicated by the bi-directional arrow  115 . A securing member  443   c  is provided to releasably lock member  443   b  at a selected position. 
     Actuator  440  further includes a pin member  444  coupled securely to adjustment member  443   b . The adjustable displacement of adjustment member  443   b  enables pin member  444  to be radially offset from the axis of the drive shaft  443  extending from the given motor  441 . Since the driving force generated by motor  441  is transferred to support platform  42  via a transfer link  445  engaging pin member  444 , the degree of movement transferred by actuator  440  is thus rendered selectively adjustable. 
     Note that this embodiment  440  of the translation actuator may be employed in combination with other features employed in a number of the preceding embodiments. Note also that by utilizing other suitable measures (not shown), the offset displacement of member  443   b  relative to platform member  443   a  may be controlled dynamically in further embodiments. Variability of the pin member  444  radial offset (along path  115 ) from the axis of drive shaft  442  could then be effected within a given drive cycle of motor  441 . This would permit great flexibility in customizing the system&#39;s scan profile. 
     Although this invention has been described in connection with specific forms and embodiments thereof, it will be appreciated that various modifications other than those discussed above may be resorted to without departing from the spirit or scope of the invention. For example, equivalent elements may be substituted for those specifically shown and described, and certain features may be used independently of other features, all without departing from the spirit or scope of the invention as defined in the appended claims.