US 4,804,852 A · Treating work pieces with electro-magnetically scanned ion beams

Abstract

A magnetic scanning technique for sweeping an ion beam across an implantation target, such as a semiconductor wafer, by means of modulating the energy of a beam and directing it through an analyzer magnet, which effects a scanning motion of the beam of constant intensity, the wave form for the modulation being selected to take into account that the areal density of the ions in the scanned beam varies dependently with the amount of displacement of the beam from a reference point. An ion scan can be obtained in which the ions travel in parallel paths and enter the target at a constant desired angle throughout the scan. The technique is applicable to targets held stationary or rotated during implant. By employing predetermined modulation wave forms which are adapted to other parameters of the selected system, a desired scan distribution of ions can be obtained, for instance a uniform distribution in X and Y directions. As applied to a semiconductor wafer rotated on a disc past the ion beam, the technique solves the problem of compensating for the fact that the area of a ring on the spinning disc depends linearly on the radius of the ring. The technique makes use of the properties of ion beams in uniform magnetic fields to produce a radial dependence of the density of the ion beam on the wafer which precisely cancels the radial dependence of circumferential length as a function of radius. The magnetic scanning technique is well adapted for use with large wafers held on rotating discs and has advantages over the conventional techniques of either electrostatic or mechanical scanning. The technique is readily adapted to a variety of other wafer transport systems including rotating conveyors and linear transports.

Claims35

Dependent claims

In an ion implanter having an ion beam source and a scanning device disposed in a beam line between the source and an implant target, said scanning device serving to cause a spatial distribution across the target of the ions being implanted, said scanning device comprising a beam energy modulator means provided with a source of modulating voltage having a cyclical wave form to modulate the energy of the ions of the beam over time, and an analyzer magnet means disposed after said modulator means in position to act upon the thus modulated ion beam to cause displacement of the beam in a repetitively scanned pattern, the improvement wherein, under conditions of operation in which the intensity of said ion beam is unchanging, said wave form of said modulating voltage is preselected to take into account the non-linear relationship between the deflection of said beam by said magnetic means and the modulation of the energy of said beam, so as to produce a uniform areal distribution of the number of ions implanted into the target.

a beam energy modulator means provided with a source of modulating voltage having a cyclical wave form to modulate the energy of the ions of the beam over time,
and an analyzer magnet means disposed after said modulator means in position to act upon the thus modulated ion beam to cause displacement of the beam in a repetitively scanned pattern,
a target carrier arranged to carry said implant target through the beam, the path of said carrier describing a circular arc, said scanning device and carrier being cooperatively related to orient the scanning motion of said beam upon said carrier in the direction of the radius of the arcuate motion of said carrier,
said carrier arranged to carry the implant target under the scanned beam in the arc of a circle whose centerline projects substantially through the point at which the modulated beam enters the analyzer magnet means,
said wave form of said modulating voltage being preselected to take into account the non-linear relationship between the deflection of said beam by said magnet means and the modulation of the energy of said beam and the dependence of the areal density of the ions being deposited on the implant target upon the position and motion of the target with respect to the beam position exiting from the said magnet means so as to produce an implant into a workpiece of high spatial uniformity.

2 more elements

a beam energy modulator means provided with a source of modulating voltage having a cyclical wave form to modulate the energy of the ions of the beam over time,
and an analyzer magnet means disposed after said modulator means in position to act upon the thus modulated ion beam to cause displacement of the beam in a repetitively scanned pattern
a target carrier arranged to carry said implant target through the beam, the path of said carrier decribing a circular arc, said scanning device and carrier being cooperatively related to orient the scanning motion of said beam upon said carrier in the direction of the radius of the arcuate motion of said carrier,
and means are provided to invert the beam from said magnet means and the axis of said carrier is parallel to a line projected substantially through the point where said beam enters said analyzer magnet means and is displaced therefrom an equal distance on the opposite side of said beam, said wave form of said modulating voltage being preselected to take into account the non-linear relationship between the deflection of said beam by said magnet means and the modulation of the energy of said beam and the dependence of the areal density of the ions being deposited on the implant target upon the position and motion of the target with respect to the beam position exiting from the said magnet means so as to produce an implant into a workpiece of high spatial uniformity.

1 more element

In an ion implanter having an ion beam source and a scanning device disposed in a beam line between a stationary source and a stationary implant target, said scanning device serving to cause a spatial distribution across the target of the ions being implanted, said scanning device comprising

a beam energy modulator means provided with a source of modulating voltage having a cyclical wave form to modulate the energy of the ions of the beam over time,
and an analyzer magnet means disposed after said modulator means in position to act upon the thus modulated ion beam to cause a displacement of the beam in a repetitively scanned pattern,
said source of modulating voltage has the wave form of a voltage ramp in which dV/dt=CV.sup.1/2 within the limits of V.sub.min and V.sub.max, where V is voltage, t is time and C is a constant,
there being two said analyzer magnet means set orthogonally to one another, each associated with a respective energy modulating means which precedes it, the ion beam exiting the first of said magnet means entering the second of said magnet means, said two magnet means and associated energy modulation means producing a scan of said beam in two orthogonal coordinates to produce a uniform areal distribution of the number of ions implanted into said stationary target.

1 more element

Dependencies are inferred from the claim text.

Treating work pieces with electro-magnetically scanned ion beams

Life of this patent

Treating work pieces with electro-magnetically scanned ion beams

Life of this patent

Abstract

Claims35