Systems and methods for ion implantation of semiconductor wafers

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 vacuum chamber for journaling said shaft means for rotation, second drive means associated with said shaft means for rotating said shaft in said bearing means, 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.

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 axis and for rotating said scan wheel assembly at high rotational velocity about said central axis to scan said wafers across said beam generally in the driection of a second axis of said coordinate system;
• 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 axis such that a line normal to said wafer mounting surface in said plane defined by said central axis and said one coordinate axis 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.

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 central hub and rotatably mounting said hub on a scan arm itself mounted for pivotal movement about a selected point spaced from the hub;
• mounting a plurality of individual wafers on said heat sink elements;
• rotating said heat sinks and wafers around said central hub at a high velocity;
• and
• pivoting said scan arm to scan said heat sinks and wafers back and forth through said beam with a velocity which varies proportional to 1/r where r is the distance between said ion beam and said central hub.

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 scan 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 less than 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.

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 a scan 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, together with said other end of pivot arm and a point on said scan axis coplanar therewith, defines a triangle which is congruent with a triangle defined by points on said scan axis, said central axis and said ion beam in a plane mutually orthogonal thereto, said translating being at a velocity which is inversely proportional to the distance between said other end of said pivot arm and said fixed point so that said central axis of said scan wheel translates toward said ion beam with a velocity between said central axis and said ion beam which is inversely proportional to the distance therebetween because of said congruency.

In a system for scanning a semiconductor wafer through an ion beam,

• a scan wheel;
• means mounting said scan wheel for rotation about a central axis generally parallel to said ion beam;
• means for driving said scan wheel to a high rotational velocity in a plane generally parallel to the direction of gravitational forces;
• a heat sink element carried on said scan wheel and defining a mounting surface for carrying a semiconductor wafer on said heat sink, said mounting surface being disposed at a prearranged angle to said central axis such that a line normal to said mounting surface intersects said central axis to form a small acute angle;
• restraining means mounted adjacent said mounting surface for restraining a wafer carried thereon from flying off said mounting surface due to a high value component of centrifugal force on said wafer in the plane of said wafer during high rotational velocity of said scan wheel;
• and
• means for temporarily retaining said wafer on said mounting surface while said scan wheel is at rest or is spinning up toward high rotational velocity, said wafer being held tightly against said mounting surface by a component of centrifugal force normal to said wafer during high rotational velocity of said scan wheel.

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 accross said ion beam generally in the direction of a second axis of said rectangular coordinate system;
• scan means for producing relative scanning movement between scan wheel assembly and said ion beam generally in the direction of a third axis of said rectangular coordinate system;
• said scan wheel assembly comprising a central hub, a plurality of separate spoke arms mounted to and supported by said central hub and extending radially outward therefrom;
• and a plurality of heat sink elements, each supported 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;
• and 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 axis and for rotating said scan wheel assembly at a high rotational velocity about said central axis to scan said wafers accross said ion 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 for carrying a prearranged size of semiconductor wafer thereon and being oriented at a prearranged angle relative to said one axis such that a line normal to said wafer mounting surface in said plane defined by said central axis and said one axis 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 when said scan wheel assembly is rotating at high rotational velocity.