Uniformity of a scanned ion beam

One embodiment relates to an ion implanter. The ion implanter includes an ion source to generate an ion beam, as well as a scanner to scan the ion beam across a surface of a workpiece along a first axis. The ion implanter also includes a deflection filter downstream of the scanner to ditheredly scan the ion beam across the surface of the workpiece along a second axis.

BACKGROUND

In ion implantation systems, an ion beam is directed towards a work piece (e.g., a semiconductor wafer, or a display panel) to implant ions into a lattice thereof. Once embedded into the lattice of the workpiece, the implanted ions change the physical and/or chemical properties of the implanted workpiece region. Because of this, ion implantation can be used in semiconductor device fabrication, in metal finishing, and for various applications in materials science research.

An ion beam often has a cross-sectional area that is significantly smaller than the surface area of a workpiece to be implanted. Because of this, typical ion beams are scanned over the surface of the workpiece until a desired doping profile is achieved in the workpiece. For example,FIG. 1Ashows a cross-sectional view of a conventional ion implantation system100where an ion beam102traces over a scan path104to implant ions into the lattice of a workpiece106. While scanning the ion beam over the scan path104, the ion implanter makes use of a first axis108and a second axis110that collectively facilitate two-dimensional scanning over the workpiece surface. In this system100there are sufficient scans per unit time over the first axis108(e.g., fast axis) to ensure that small features (e.g., small feature150inFIG. 1B) on the second axis110(e.g., slow axis) are adequately scanned over the entire workpiece. However, when the fast scan speed is slowed to approach the slow scan speed, it is difficult to ensure dose uniformity when very sharp features are present in the beam profile (e.g., small feature150).

Therefore, aspects of the present disclosure relates to techniques for improving beam uniformity using a scanned ion beam.

SUMMARY

The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention, and is neither intended to identify key or critical elements of the invention nor to delineate the scope of the invention. Rather, the purpose of the summary is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.

One embodiment relates to an ion implanter. The ion implanter includes an ion source to generate an ion beam, as well as a scanner to scan the ion beam across a surface of a workpiece along a first axis. The ion implanter also includes a deflection filter downstream of the scanner to reduce energy contamination and dither the ion beam across the surface of the workpiece along a second axis.

The following description and annexed drawings set forth in detail certain illustrative aspects and implementations of the invention. These are indicative of but a few of the various ways in which the principles of the invention may be employed.

DETAILED DESCRIPTION

The present invention will now be described with reference to the drawings wherein like reference numerals are used to refer to like elements throughout, and wherein the illustrated structures are not necessarily drawn to scale.

FIG. 2shows a scanning technique utilizing an improved scan path in accordance with some aspects of the disclosure. As shown, to trace a scan path204over a workpiece surface206and thereby implant ions into a workpiece, an ion beam202is scanned back and forth over a first axis208while being simultaneously and ditheredly scanned over a second axis210. Thus, rather than scanning the ion beam202over the second axis210at a fixed unidirectional speed (as was done in the conventional scan technique shown inFIG. 1A), the ion beam202is scanned over the second axis with a superposition of a constant speed and a small amplitude, rapid oscillation. Most typically, the scanning of the beam along the first axis208is done with an electric or magnetic scanner, while the workpiece is mechanically translated along the second axis210. However, it is also possible to have the workpiece translated along both axes208,210, while the fast oscillation (dither) of the beam is achieved with an electric or magnetic beam scanner. Thus “dither” in this context can refer to the manner in which predetermined, random, or pseudo-random perturbations are used to prevent large-scale patterns such as “banding” or “striping” in the doping profile, which can be objectionable. Sharp features (e.g. sharp feature150inFIG. 1B) can cause striping and dithering effectively blurs these features, making them less sharp, and thus less detrimental to the uniformity of the implanted doping profile.

FIG. 3illustrates one embodiment of an ion implantation system300operable to carry out scanning techniques in accordance with some aspects of the invention. The ion implantation system300includes a source terminal302, a beamline assembly304, a scan system306, and an end station308, which are collectively arranged so as to inject ions (dopants) into the lattice of a workpiece310according to a desired dosing profile.

More particularly, during operation, an ion source316in the source terminal302is coupled to a high voltage power supply318to ionize dopant molecules (e.g., dopant gas molecules), thereby forming a pencil ion beam320.

To steer the pencil beam320from the source terminal302towards the workpiece310, the beamline assembly304has a mass analyzer322in which a dipole magnetic field is established to pass only ions of appropriate charge-to-mass ratio through a resolving aperture324. Ions having an inappropriate charge-to-mass ratio collide with the sidewalls326a,326b;thereby leaving only the ions having the appropriate charge-to-mass ratio to pass though the resolving aperture324and into the workpiece310. The beam line assembly304may also include various beam forming and shaping structures extending between the ion source316and the end station308, which maintain the pencil beam320in an elongated interior cavity or passageway through which the pencil beam320is transported to the workpiece310. A vacuum pumping system328typically keeps the ion beam transport passageway at vacuum to reduce the probability of ions being deflected from the beam path through collisions with air molecules.

Upon receiving the pencil beam320, a scanner330within the scan system306laterally diverts or “scans” the pencil beam back and forth in time (e.g., in a horizontal direction) to provide the scanned ion beam332. In some contexts, this type of scanned pencil beam may be referred to as a ribbon beam. In the illustrated embodiment, the scanner330is an electrical scanner that includes a pair of electrodes334a,334barranged on opposing sides of the scanned beam332. A control system336induces a change in a variable power source338to provide a time-varying current or voltage on the electrodes334a,334b,thereby inducing an oscillatory time-varying electric field in the beam path region and scanning the ion beam back and forth in time. In other embodiments, the scanner330can be a magnetic scanner that provides a time-varying magnetic field in the beam path region, thereby scanning the ion beam in time. In some embodiments, only a single electrode (rather than a pair of electrodes) can be used.

A parallelizer340in the scan system can redirect the scanned ion beam332so that the ion beam strikes a surface of the workpiece310at the same angle of incidence over the entire surface of the workpiece.

A deflection filter342, which is controlled by control system336and powered by a variable power source344, diverts the parallelized scanned ion beam along a second axis that can be perpendicular to the first axis. For example, inFIG. 3, the second axis could extend into the plane of the page or out of the plane of the page. The deflection filter342can impart a time-independent deflection and a time-dependent “dithered” deflection. Because the deflection filter342is downstream of the parallelizer340the working gaps of the corrector and deflection filter342are limited compared to solutions where a scanner is used to scan the ion beam in two dimensions before the correctors. This helps to reduce cost of the beam line by simplifying the parallelizer340and the deflection filter342. Also, because this solution limits the volume to be pumped down to vacuum, it can also in some instances improve the vacuum, which limits collisions between ions and air molecules and thus helps improve the resolution/accuracy of the beam.

In some embodiments, a quadrupole can be arranged between the scanner330and the deflection filter342, as shown by reference number346or348inFIG. 3, for example.

FIG. 5shows another embodiment where scanner electrodes502A,502B scan an ion beam back and forth, and deflection filter electrodes504A,504B deflect the beam and also introduce dither to the scanned ion beam. Voltages on the electrodes502A,502B,504A,504B change the beam trajectory so that the scanned beam passes through the center of beam resolving slits506downstream of the scanner.

FIG. 4Ashows an example of a first scan voltage402that can be applied to the scanner electrodes (e.g.,334a,334binFIG. 3), whileFIG. 4Bshows a second scan voltage404that can be applied to the deflection filter electrodes. In some systems the steady relative motion in the slow scan direction262is from mechanically moving the workpiece, while in other systems, these scan voltages can collectively trace the ion beam over the scan path illustrated inFIG. 4C. In some systems, the first scan voltage402scans the ion beam202back and forth on the first axis in time (e.g., between points A and G inFIG. 4C), while the second scan voltage404can introduce dither (e.g., vertical displacement inFIG. 4C). As shown inFIG. 4D, when a workpiece310is translated500along a second axis (e.g., top edge of workpiece310moves from point □ to point □ inFIG. 4D) and the first and second scan voltages are concurrently applied to the beam, the ion beam effectively traces over a 2-dimensional scan path that covers the surface of the workpiece.

AlthoughFIG. 4A-4Bdepict voltages that establish a time-varying electrical field to scan the beam, it will be appreciated that a time-varying magnetic field could also be used in other embodiments. In some embodiments, the scanner can use a time-varying electric field and the deflection filter can use a time-varying magnetic field, or vice versa.

Although the invention has been illustrated and described with respect to one or more implementations, alterations and/or modifications may be made to the illustrated examples without departing from the spirit and scope of the appended claims. For example, different types of end stations108may be employed in the ion implantation system300. In some embodiments, a “batch” type end station can simultaneously support multiple workpieces on a rotating support structure, wherein the workpieces are rotated through the path of the ion beam until all the workpieces are completely implanted. A “serial” type end station, on the other hand, can be used in other embodiments. Serial type end stations support a single workpiece along the beam path for implantation, wherein multiple workpieces are implanted one at a time in serial fashion, with each workpiece being completely implanted before implantation of the next workpiece begins. Further, althoughFIG. 3illustrated a ion implantation system where the beam was electrically or magnetically scanned in a first (X or fast scan) direction while the workpiece is mechanically scanned in a second (Y or slow scan) direction to impart the scanned ion beam over the entire workpiece; other systems could mechanically scan the ion beam along two different axes rather than using electrical or magnetic translation.