Systems and methods for ion implantation of semiconductor wafers

Claim 2

In a system for scanning semiconductor wafers through an ion beam, means generating an ion beam oriented in a prearranged direction defining one axis of a rectangular coordinate system relative thereto; a scan wheel assembly for carrying a plurality of semiconductor wafers and having a central axis; drive means for rotating said scan wheel assembly about said central axis to scan said wafers across said beam in one coordinate direction; scan means for producing relative scanning movement between said scan wheel and said ion beam in another coordinate direction; said scan wheel assembly comprising a central hub, a plurality of separate spoke arms mounted to said hub and extending radially outward therefrom; and a plurality of heat sink elements, each formed on the outer end of one of said spoke arms and including means for mounting a semiconductor wafer thereon, said spoke arms each having a width substantially less than the maximum width of said heat sink elements; said scan means overscanning said heat sink elements in and out of said ion beam so that said ion beam strikes only a portion of said spoke arms in one overscan position and the total heat load produced on said scan wheel assembly by said ion beam is substantially reduced.

Claim 3

The system of claim 1, wherein said drive means comprises a mounting drive means for mounting said scan wheel assembly with said central axis generally parallel to the direction of said ion beam but canted at a slight angle toward the origin of said ion beam in a plane defined by said central axis and said one coordinate axis and for rotating said scan wheel assembly at high rotational velocity about said central axis to scan said wafers across said beam in one coordinate direction; each of said heat sink elements defining a mounting surface region and being spaced by an associated spoke arm at a prearranged distance from said central axis; each of said wafer mounting means comprising a heat sink insert mounted to said heat sink element and defining a wafer mounting surface having a diameter at least as large as a prearranged size of semiconductor wafer to be carried thereon and being oriented at a prearranged angle relative to said one coordinate axis such that a line normal to said wafer mounting surface in said plane defined by said central axis and said one coordinate axis is either parallel to said one coordinate axis or is canted at a small angle to said one coordinate axis but in either event said normal line intersects said central axis to define a large acute angle, whereby rotation of said scan wheel assembly at said high rotational velocity produces a substantial component of centrifugal force normal to said wafer mounting surface so that a wafer thereon is held tightly against said mounting surface during said rotational scanning.

Claim 4

The system of claim 2, wherein each of said heat sink elements defines a wafer edge restraint adjacent said heat sink insert at the outermost radial point thereon to restrain said wafer on said wafer mounting surface when said scan wheel assembly is in rotation; and further comprising wafer clamping means mounted on said heat sink element for temporarily urging a wafer on said wafer mounting surface against said wafer edge restraint when said scan wheel assembly is not rotating at high rotational velocity.

Claim 5

The system of claim 3, wherein said wafer clamping means includes a pair of clamp finger means, means mounting said clamp finger means to said heat sink element on a side opposite said wafer mounting surface and including spring means urging said clamp finger means against an edge portion of a wafer on said wafer mounting surface and inertial means opposing said spring means when said scan wheel assembly is rotating at high velocity to retract said clamp finger means away from said edge of said wafer so that said wafer is retained on said wafer mounting surface solely by said component of centrifugal force normal to said wafer.

Claim 8

The system of claim 6, wherein each of said heat sink elements defines a wafer edge restraint adjacent said heat sink insert at the outermost radial point thereon to restrain said wafer on said wafer mounting surface when said scan wheel assembly is in rotation; and further comprising wafer clamping means mounted on said heat sink element for temporarily urging a wafer on said wafer mounting surface against said wafer edge restraint when said scan wheel assembly is not rotating at high rotational velocity; said wafer clamping means includes a pair of clamp finger means, means mounting said clamp finger means to said heat sink element on a side opposite said wafer mounting surface and including spring means urging said clamp finger means against an edge of a wafer on said wafer mounting surface and inertial means opposing said spring means when said scan wheel assembly is rotating at high velocity to retract said clamp finger means away from said edge of said wafer so that said wafer is retained on said wafer mounting surface solely by said component of centrifugal force normal to said wafer.

Claim 9

The system of claim 1, wherein said drive means and said scan means comprise a combined mounting drive means for mounting said scan wheel assembly in said vacuum chamber with said central axis oriented substantially parallel to said one axis, for rotating said scan wheel assembly about said central axis, and for translating said scan wheel assembly relative to said ion beam substantially in the direction of a second axis of said coordinate system to produce a two dimensional scan of said semiconductor wafer through said ion beam; said mounting drive means comprising a scan arm disposed within said chamber, first mounting means for mounting said scan wheel assembly at one end of said scan arm for rotation about said central axis, first drive means associated with said first mounting means for rotationally driving said scan wheel assembly, second mounting means for mounting said scan arm at the other end thereof for rotation about an axis generally parallel to said one axis including shaft means attached at one end to said scan arm and extending through a wall of said vacuum chamber, bearing means external to said chamber for journaling said shaft means for rotation, second drive means associated with said shaft means for rotating said shaft in said bearing, and vacuum sealing means cooperatively mounted between said vacuum chamber wall and said shaft means to provide a rotary vacuum-to-air shaft sealing arrangement.

Claim 10

The system of claim 8, wherein said mounting drive means mounts said scan wheel assembly with said central axis generally parallel to the direction of said ion beam but canted at a slight angle toward the origin of said ion beam in a plane defined by said central axis and said one coordinate: each of said heat sink elements defining a mounting surface region and being spaced by an associated spoke arm at a prearranged distance from said central axis; each of said wafer mounting means comprising a heat fink insert mounted to said heat sink element and defining a wafer mounting surface having a diameter at least as large as a prearranged size of semiconductor wafer to be carried thereon and being oriented at a prearranged angle relative to said one coordinate axis such that a line normal to said wafer mounting surface in said plane defined by said central axis and said one coordinate axis is either parallel to said one coordinate axis or is canted at a small angle to said one coordinate axis but in either event said normal line intersects said central axis to define a large acute angle, whereby rotation of said scan wheel assembly at said high rotational velocity produces a substantial component of centrifugal force normal to said wafer mounting surface so that a wafer thereon is held tightly against said mounting surface during said rotational scanning.

Claim 11

The system of claim 9, wherein each of said heat sink elements defines a wafer edge restraint adjacent said heat sink insert at the outermost radial point thereon to restrain said wafer on said wafer mounting surface when said scan wheel assembly is in rotation; and further comprising wafer clamping means mounted on said heat sink element for temporarily urging a wafer on said wafer mounting surface against said wafer edge restraint when said scan wheel assembly is not rotating at high rotational velocity.

Claim 12

The system of claim 10, wherein said wafer clamping means includes a pair of clamp finger means, means mounting said clamp finger means to said heat sink element on a side opposite said wafer mounting surface and including spring means urging said clamp finger means against an edge of a wafer on said wafer mounting surface and inertial means opposing said spring means when said scan wheel assembly is rotating at high velocity to retract said clamp finger means away from said edge of said wafer so that said wafer is retained on said wafer mounting surface solely by said component of centrifugal force normal to said wafer.

Claim 14

13 . The system of any of claim 9 to 12,wherein each of said heat sink elements defines a cooling fluid channel therethrough; said scan wheel assembly includes piping means coupling cooling fluid to and from each of said cooling fluid channels in said heat sink assemblies to carry heat generated by said ion beam away therefrom; and each of said heat sink inserts comprises a conductive metal body defining a first mounting surface adjacent said heat sink assembly and a second second mounting surface facing said ion beam, a first layer of conductive elastomeric material mounted said first mounting surface, and a second layer of conductive elastomeric material mounted on said second mounting surface to serve as said wafer mounting surface, whereby said heat sink insert provides good thermal conductivity to said cooled heat sink assembly across the entire surface of a water mounted thereon when said scan wheel assembly s rotated at high velocity to produce said centrifugal force urging said wafer against said second layer of conductive elastomeric material.

Claim 15

14 . The system of any of claims 9 to 13, wherein each of said heat sjnk elements defines a wafer edge restraint adjacent said heat sink insert at the outermost radial point thereon to restrain said wafer on said wafer mounting surface when said scan wheel assembly is in rotation; and further comprising wafer clamping means mounted on said heat sink element for temporarily urging a wafer on said wafer mounting surface against said wafer edge restraint when said scan wheel assembly is not rotating at high rotational velocity; said wafer clamping means includes a pair of clamp finger means, means mounting said clamp finger means to said heat sink element on a side opposite said wafer mounting surface and including spring means urging said clamp finger means against an edge of a wafer on said wafer mounting surface and inertial means opposing said spring means when said scan wheel assembly is rotating at high velocity to retract said clamp finger means away from said edge of said wafer so that said wafer is retained on said wafer mounting surface solely by said component of centrifugal force normal to said wafer.

Claim 16

In a system for scanning semiconductor wafers through an ion beam, a vacuum chamber: means generating an ion beam and directing said ion beam into said vacuum chamber in a prearranged direction defining one axis of a rectangular coordinate system; a scan wheel assembly for carrying a plurality of semiconductor wafers and having a central axis; mounting drive means for mounting said scan wheel assembly in said vacuum chamber with said central axis oriented substantially parallel to said one axis, for rotating said scan wheel assembly about said central axis, and for translating said scan wheel assembly relative to said ion beam substantially in the direction of a second axis of said coordinate system to produce a two dimensional scan of said semiconductor wafer through said ion beam; said mounting drive means comprising a scan arm disposed within said chamber, first mounting means for mounting said scan wheel assembly at one end of said scan arm for rotation about said central axis, first drive means associated with said first mounting means for rotationally driving said scan wheel assembly, second mounting means for mounting said scan arm at the other end thereof for rotation about an axis generally parallel to said one axis including shaft means attached at one end to said scan arm and extending through a wall of said vacuum chamber, bearing means external to said chamber for journaling said shaft means for rotation, second drive means associated with said shaft means for rotating said shaft in said bearing, and vacuum sealing means cooperatively mounted between said vacuum chamber wall and said shaft means to provide a rotary vacuum to air shaft sealing arrangement.

Claim 17

In a system for scanning semiconductor wafers through an ion beam, a vacuum chamber: means generating an ion beam and directing said ion beam into said vacuum chamber in a prearranged direction defining one axis of a rectangular coordinate system; a scan wheel assembly for carrying a plurality of semiconductor wafers and having a central axis; mounting drive means for mounting said scan wheel assembly in said vacuum chamber with said central axis oriented substantially parallel to said one axis, for rotating said scan wheel assembly about said central axis, and for translating said scan wheel assembly relative to said ion beam substantially in the direction of a second axis of said coordinate system to produce a two dimensional scan of said semiconductor wafer through said ion beam; said mounting drive means comprising a scan arm disposed within said chamber, first mounting means for mounting said scan wheel assembly at one end of said scan arm for rotation about said central axis, first drive means associated with said first mounting means for rotationally driving said scan wheel assembly, second mounting means for mounting said scan arm at the other end thereof for rotation about an axis generally parallel to said one axis including shaft means attached at one end to said scan arm and extending through a wall of said vacuum chamber, bearing means external to said chamber for journaling said shaft means for rotation, second drive means associated with said shaft means for rotating said shaft in said bearing, and vacuum sealing means cooperatively mounted between said vacuum chamber wall and said shaft means to provide a rotary vacuum to air shaft sealing arrangement.

Claim 18

The system of claim 15, wherein said axis of said ion beam I said central axis of said scan wheel assembly A and said axis of said second mounting means B define a triangle having two fixed sides BA and BI and a third side AI which varies in length as said scan arm scans back and forth across said beam; said second drive arrangement comprising means for driving said scan arm so that the rate of change of the distance AI varies inversely with the magnitude of the distance AI, including a pivot arm mounted at one end to said shaft and a linear drive means mounted for rotation about an axis E and attached to the other end of said pivot arm at a point D so that said linear drive means translates said other end of said pivot arm toward said axis E; the positions of said axis E and said point of attachment D being preselected such that said points B, D, and E define a triangle BDE which is congruent to said triangle BAI; said second drive arrangement further including tracking means for signalling the distance DE as said linear drive means moves said pivot arm, and means for controlling the rate of drive of said linear drive means as a function of the inverse of said signalled distance DE so that the rate of change of the distance DE varies inversely with the magnitude of the distance DE and, because of triangular congruency, the corresponding rate of change of the distance AI varies inversely with the magnitude of the distance AI.

Claim 19

In a system for scanning semiconductor wafers through an ion beam, means generating an ion beam oriented in a prearranged direction defining one axis of a rectangular coordinate system relative thereto; a scan wheel assembly for carrying a plurality of semiconductor wafers and having a central axis; mounting drive means for mounting said scan wheel assembly with said central axis generally parallel to the direction of said ion beam but canted at a slight angle toward the origin of said ion beam in a plane defined by said central axis and said one coordinate axis and for rotating said scan wheel assembly at high rotational velocity about said central axis to scan said wafers across said beam in one coordinate direction; said scan wheel assembly including wafer mounting means comprising structural means defining a plurality of separate mounting surface regions disposed at radially arrayed locations spaced a prearranged distance from said central axis and a wafer support assembly mounted at each of said mounting surface regions and defining a flat wafer mounting surface having a prearranged angle relative to said one coordinate axis such that a line normal to said wafer mounting surface in said plane defined by said central axis and said one coordinate axis is either parallel to said one coordinate axis or is canted at a small angle to said one coordinate axis but in either event said normal line intersects said central axis to define a large acute angle, whereby rotation of said scan wheel assembly at said high rotational velocity produces a substantial component of centrifugal force normal to said wafer mounting surface so that a wafer thereon is held tightly against said mounting surface during said rotational scanning.

Claim 20

In a system for scanning semiconductor wafers through an ion beam, means generating an ion beam oriented in a prearranged direction defining one axis of a rectangular coordinate system relative thereto; a scan wheel assembly for carrying a plurality of semiconductor wafers and having a central axis; mounting drive means for mounting said scan wheel assembly with said central axis generally parallel to the direction of said ion beam but canted at a slight angle toward the origin of said ion beam in a plane defined by said central axis and said one coordinate axis and for rotating said scan wheel assembly at high rotational velocity about said central axis to scan said wafers across said beam in one coordinate direction; said scan wheel assembly including wafer mounting means comprising structural means defining a plurality of separate mounting surface regions disposed at radially arrayed locations spaced a prearranged distance from said central axis and a wafer support assembly mounted at each of said mounting surface regions and defining a flat wafer mounting surface having a prearranged angle relative to said one coordinate axis such that a line normal to said wafer mounting surface in said plane defined by said central axis and said one coordinate axis is either parallel to said one coordinate axis or is canted at a small angle to said one coordinate axis but in either event said normal line intersects said central axis to define a large acute angle, whereby rotation of said scan wheel assembly at said high rotational velocity produces a substantial component of centrifugal force normal to said wafer mounting surface so that a wafer thereon is held tightly against said mounting surface during said rotational scanning.

Claim 21

In a method for scanning semiconductor wafers through an ion beam, the steps of: disposing a plurality of generally cylindrical heat sinks radially around a central hub with narrow spokes connecting said heat sinks to said hub; mounting a plurality of individual wafers on said heat sink elements with a wafer diameter larger than the heat sink so that only the surface of the wafer and the spokes are presented to the beam; rotating said heat sinks and wafers around said hub at high velocity; and scanning said heat sinks and wafers back and forth through said beam with a velocity proportional to 1/r where r is the distance between said ion beam and said hub.

Claim 22

In a method for scanning semiconductor wafers through an ion beam, the steps of: disposing a plurality of generally cylindrical heat sinks radially around a central hub with narrow spokes connecting said heat sinks to said hub; mounting a plurality of individual wafers on said heat sink elements with a wafer diameter larger than the heat sink so that only the surface of the wafer and the spokes are presented to the beam; rotating said heat sinks and wafers around said hub at high velocity; and scanning said heat sinks and wafers back and forth through said beam with a velocity proportional to 1/r where r is the distance between said ion beam and said hub.

Claim 23

In a method for scanning semiconductor wafers through an ion beam, the steps of: disposing a plurality of wafer mounting surfaces on a scan wheel with each at a common prearranged first angle to a major plane of said wheel; mounting said scan wheel for rotation about an axis which is canted toward the origin of said ion beam direction by a small acute angle which is of value equal to or greater to said first angle; and rotating said scan wheel about said axis at high angular velocity to provide a component of centrifugal force normal to said wafer surface even when said second angle is equal to said first angle.

Claim 24

In a method for scanning semiconductor wafers through an ion beam, the steps of: disposing a plurality of wafer mounting surfaces on a scan wheel with each at a common prearranged first angle to a major plane of said wheel; mounting said scan wheel for rotation about an axis which is canted toward the origin of said ion beam direction by a small acute angle which is of value equal to or greater to said first angle; and rotating said scan wheel about said axis at high angular velocity to provide a component of centrifugal force normal to said wafer surface even when said second angle is equal to said first angle.

Claim 25

In a method for scanning semiconductor wafers through an ion beam,the steps of: mounting said wafers on prearranged radially arrayed positions on a scan wheel; mounting said scan wheel for rotation about a central axis thereof on one end of a scan arm; mounting the other end of said scan arm for rotation about an axis generally parallel to said central axis and generally parallel to said ion beam; mounting a pivot arm at one end to said scan arm to drive said scan arm about said scan axis; and translating the other end of said pivot arm toward a fixed point in space which defines with said pivot arm end and said scan axis a triangle which is congruent with a triangle defined by said scan axis, said central axis and said ion beam at a velocity which is inversely proportional to the distance between said other end and said fixed point so that said scan wheel translates toward said ion beam with a velocity between said central axis and said beam which is inversely proportional to the distance therebetween because of said congruency.

Claim 26

In a method for scanning semiconductor wafers through an ion beam,the steps of: mounting said wafers on prearranged radially arrayed positions on a scan wheel; mounting said scan wheel for rotation about a central axis thereof on one end of a scan arm; mounting the other end of said scan arm for rotation about an axis generally parallel to said central axis and generally parallel to said ion beam; mounting a pivot arm at one end to said scan arm to drive said scan arm about said scan axis; and translating the other end of said pivot arm toward a fixed point in space which defines with said pivot arm end and said scan axis a triangle which is congruent with a triangle defined by said scan axis, said central axis and said ion beam at a velocity which is inversely proportional to the distance between said other end and said fixed point so that said scan wheel translates toward said ion beam with a velocity between said central axis and said beam which is inversely proportional to the distance therebetween because of said congruency.