Ion implanter and a method of implanting ions

An ion implanter comprising:

• an ion beam generator for generating a beam of ions to be implanted, in which said ions have a predetermined mass/charge ratio and are at an injection energy E, and
• a three gap linear accelerator stage into which said beam of ions is directed at said injection energy, said stage being arranged when energized for accelerating ions of said beam to a second energy, said stage comprising
• an entrance electrode held at a fixed potential and an exit electrode held at a fixed potential,
• first and second ratio frequency electrodes located in series between said entrance and exit electrodes, and
• a radio frequency generator to apply radio frequency voltages of opposite polarity and a predetermined frequency f respectively to said first and second electrodes,
• said entrance electrode and said first radio frequency electrode defining a first accelerating gap having a first center point, said first and second radio frequency electrodes defining a second accelerating gap having a second center point at a first predetermined spacing d1 from said first center point, and said second radio frequency electrode and said exit electrode defining a third accelerating gap having a third center point at a second predetermined spacing d2 from said second center point,
• wherein the injection energy E, the frequency f, and the gap spacings d1 and d2 are selected such that at amplitudes of the radio frequency energy below the maximum amplitude at which breakdown occurs across any of said gaps, injected ions of said beam cross the first gap when the radio frequency field across the first gap is rising from a maximum deceleration field to a maximum acceleration field, then cross the second gap during the maximum acceleration field across the second gap and cross the third gap when the field across the third gap is falling from a maximum acceleration field to a maximum deceleration field.

An ion implanter comprising an ion beam generator for generating a beam of ions to be implanted in which said ions are at a first energy, and a radio frequency linear accelerator assembly arranged when energized for accelerating ions of said beam to a second energy, said assembly comprising,

• a housing,
• electrodes mounted in the housing, said electrodes defining a series of gaps for changing the energy of ions of said beam, said electrodes having apertures through which the ions pass,
• at least one inductive coil electrically connected to at least one of said electrodes for energizing said at least one electrode at a radio frequency potential, and
• an electrically conductive enclosure around said coil,
• said coil, said at least one electrode, said housing and said conductive enclosure together constituting a radio frequency tank circuit having a predetermined resonant frequency,
• said coil comprising a self supporting rigid electrical conductor having at least first and second connecting arms, said linear accelerator assembly further including,
• a coil mounting fixture on said electrically conductive enclosure arranged to receive said first connecting arm for electrical connection to said enclosure and for supporting said coil at a desired location within said enclosure, and
• an electrically insulating mount locating said at least one electrode within said housing, said second connection arm extending from said enclosure into said housing to make radio frequency connection to said at least one electrode,
• said at least one electrode having a connection fitting providing a sliding fit connection with said second connecting arm, whereby thermal expansion and contraction of said coil is accommodated by sliding movement of said second arm in said fitting.

An ion implanter comprising an ion beam generator for generating a beam of ions to be implanted in which said ions are at a first energy, and a radio frequency linear accelerator assembly arranged when energised for accelerating ions of said beam to a second energy, said assembly comprising a housing, electrodes mounted in the housing, said electrodes defining a series of gaps for changing the energy of ions of said beam, said electrodes having apertures through which the ions pass, at least one inductive coil electrically connected to at least one of said electrodes for energising said at least one electrode at a radio frequency potential, and an electrically conductive enclosure around said coil, said coil, said at least one electrode, said housing and said conductive enclosure together constituting a radio frequency tank circuit having a predetermined resonant frequency, said coil comprising a tubular electrical conductor having an open end and a closed end, said linear accelerator assembly including a connecting fixture on said electrically conductive enclosure to receive said open end to enable access to said open end from outside said enclosure, and a double walled cooling tube extending in said tubular conductor from said open end to a position proximate said closed end, said cooling tube comprising an inner pipe which is open at said proximate position to the interior of said tubular conductor and an outer pipe which is closed at said proximate position, said inner and outer pipes providing a space between them along the length of said cooling tube, a source of vacuum connected to said outer pipe to evacuate said space between said inner and outer pipes, and a source of cooling fluid connected to one of said inner pipe and said open end of said tubular conductor to provide a flow of said cooling fluid along said tubular conductor.

An ion implanter comprising:

• an ion beam generator for generating a beam of ions to be implanted in which said ions are at a first energy, and
• a radio frequency linear accelerator assembly arranged when energized for accelerating ions of said beam to a second energy, said assembly comprising,
• electrodes defining a series of gaps for changing the energy of ions of said beam, said electrodes having apertures through which the ions pass,
• at least one magnetic quadrupole located along the beam adjacent at least one of said electrodes for controlling beam divergence,
• a unitary block providing a vacuum housing for the assembly, said unitary block having a through channel for said beam to pass through,
• at least first and second electrode mounting points at spaced locations along said through channel for mounting said electrodes to define a plurality of said gaps along the length of said through channel, and
• at least one magnetic quadrupole mounting point located between said first and second electrode mounting points for mounting said magnetic quadrupole.

A method of implanting ions into a target substrate comprising the steps of:

• generating a beam of the ions at a first energy, and
• changing the energy of ions in the beam to a second energy using a radio frequency (rf) linear accelerator assembly having at least first and second booster stages in tandem along the beam direction, each of the booster stages comprising entrance and exit electrodes and at least one intermediate rf electrode defining a series of gaps for changing the energy of ions of said beam, the exit electrode of the first booster stage and the entrance electrode of the second booster stage defining between them a drift distance between the stages over which beam ions are not subject to rf fields, said drift distance being greater than the length of the first booster stage between the entrance and exit electrodes thereof, wherein the arrival time at the second booster stage of bunches of ions from the first booster stage, relative to the rf field waveform in the gaps of the second booster stage, is controlled by
• maintaining the phases of the rf fields in said first and second booster stages locked to fixed phase values, and
• adjusting the speed of said bunches over said drift distance so that said bunches arrive at the second booster stage at a desired region of said field waveform.

An ion implanter comprising:

• an ion beam generator for generating a beam of ions to be implanted, in which said ions are at a first energy, and
• a radio frequency (rf) linear accelerator assembly arranged, when energized, for accelerating ions of said beam to a second energy, said assembly comprising at least first and second rf booster stages in tandem along the beam direction, each of said booster stages comprising,
• entrance and exit electrodes,
• at least one intermediate rf electrode defining a series of gaps for changing the energy of ions of said beam,
• the exit electrode of the first booster stage and the entrance electrode of the second booster stage defining between them a drift distance between the stages over which beam ions are not subject to rf fields, said drift distance being greater than the length of the first booster stage between the entrance and exit electrodes thereof, and
• a controller arranged to control the arrival time at the second booster stage of bunches of ions from the first booster stage, relative to the rf field waveform in the gaps of the second booster stage, by maintaining the phases of the rf fields in said first and second booster stages locked to fixed phase values and adjusting the speed of said bunches over said drift distance so that said bunches arrive at the second booster stage at a desired region of said field waveform.

An ion implanter comprising:

• an ion beam generator for generating a beam of ions to be implanted in which said ions are at a first energy, and
• a radio frequency linear accelerator assembly arranged when energized for accelerating ions of said beam to a second energy, said assembly comprising at least first and second rf booster stages in tandem along the beam direction, each of said booster stages comprising,
• entrance and exit electrodes,
• at least one intermediate rf electrode defining a series of gaps for changing the energy of the ions of said beam, and
• an adjacent pair of magnetic quadrupoles located between said first and second booster stages,
• said electrodes having apertures through which the ions pass, all the electrodes of all said booster stages being contained in a length L and the apertures of the electrodes having respective largest dimensions transverse to the beam which are not less than D, where L/D is less than 25.