Apparatus and methods for ion implantation

A system for implanting ions of a preselected chemical species into a plurality of semiconductor wafers, comprising:

• source means for producing an ion beam, including ions of said preselected chemical species at or above said preselected beam current level;
• beam analyzing means for receiving said ion beam and selectively separating various ion species in said beam on the basis of mass to produce an analyzed beam exiting said analyzing means;
• beam resolving means disposed in the path of said analyzed beam for permitting ions of said preselected chemical species to pass therethrough;
• beam accelerating means for accelerating said ions in said resolved beam in a prearranged direction defining one coordinate axis of a rectangular coordinate system;
• wafer scanning means for scanning a plurality of wafers through said accelerated ion beam;
• said analyzing means having an ion dispersion plane associated therewith;
• said source means having an associated ion emitting envelope including an area of substantial extension in a plane parallel to said ion dispersion plane and producing an ion beam characterized by a beam envelope which retains an area of substantial extension in a plane parallel to said ion dispersion plane throughout the region between said source and said analyzing means and by ions entering said analyzing means travelling substantially either toward or from a common apparent line object perpendicular to said ion dispersion plane;
• and
• said wafer scanning means comprising a vacuum chamber;
• means for 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 vacuum 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.

A system for implanting ions of a preselected chemical species into a plurality of semiconductor wafers comprising:

• source means for producing an ion beam, including ions of said preselected chemical species at or above said preselected beam current;
• beam analyzing means for receiving said ion beam and selectively separating various ion species in said beam on the basis of mass to produce an analyzed beam exiting said analyzing means;
• beam resolving means disposed in the path of said analyzed beam for permitting ions of said preselected chemical species to pass therethrough;
• beam accelerating means for accelerating said ions in said resolved beam in a prearranged direction defining one coordinate axis of a rectangular coordinate system;
• and
• wafer scanning means for scanning a plurality of wafers through said accelerated ion beam;
• said analyzing means having an ion dispersion plane associated ion emitting envelope including an area of substantial extension in a plane parallel to said ion dispersion plane and producing an ion beam characterized by a beam envelope which retains an area of substantial extension in a plane parallel to said ion dispersion plane throughout the region between said source and said analyzing means and by ions entering said analyzing means travelling substantially either toward or from a common apparent line object perpendicular to said ion dispersion plane;
• said wafer scanning means comprising 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 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:

• creating an ion beam analyzing field having an associated ion dispersion plane for separating various ion species in an ion beam on the basis of mass;
• producing and directing into said ion beam analyzing field an ion beam including ion or a preselected species at or above a beam current level of several milliamperes and having an associated overall ion beam envelope which retains an area of substantial extension in a plane parallel to said ion dispersion plane throughout the region of travel of said beam into said analyzing field;
• separating out of the analyzed ion beam exiting said analyzing field a beam of ions comprising said preselected chemical species;
• accelerating said separated ions to a prearranged energy;
• disposing a plurality of generally cylindrical heat sinks radially around a central hub with narrow spokes connecting said heat sinks to said hug;
• mounting a plurality of individual wafers on said heat sink elements with a wafer diameter substantially equal to that of 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 accelerated beam with a velocity which varies proportional to 1/r where r is the distance between said ion beam and said hub.

In a method for scanning semiconductor wafers through an ion beam, the steps of:

• creating an ion beam analyzing field having an associated ion dispersion plane for separating various ion species in an ion beam on the basis of mass;
• producing and directing into said ion beam analyzing field an ion beam including ions of a preselected species at or above a beam current level of several milliamperes and having an associated overall ion beam envelope which retains an area of substantial extension in a plane parallel to said ion dispersion plane throughout the region of travel of said beam into said analyzing field;
• separating out of the analyzed ion beam exiting said analyzing field a beam of ions comprising said preselected chemical species;
• accelerating said separated ions to a prearranged energy;
• 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:

• creating an ion beam analyzing field having an associated ion dispersion plane for separating various ion species in an ion beam on the basis of mass;
• producing and directing into said ion beam analyzing field an ion beam including ion of a preselected species at or above a beam current level of several milliamperes and having an associated overall ion beam envelope which retains an area of substantial extension in a plane parallel to said ion dispersion plane throughout the region of travel of said beam into said analyzing field;
• separating out of the analyzed ion beam exiting said analyzing field a beam of ions comprising said preselected chemical species;
• accelerating said separated ions to a prearranged energy;
• 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 other end of 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 in an orthogonal plane intersecting said other end of said pivot arm and said scan axis a triangle which is congruent with a triangle defined by an orthogonal plane intersecting said scan axis, said central axis and said ion beam 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 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.