Ion beam neutral detection

An ion beam neutral detector system, an ion implanter system including the detector system and a method of detecting ion beam neutrals that ensures an ion implant is meeting contamination requirements are disclosed. The detector includes an energy contamination monitor positioned with in an ion implanter system. A method of the invention includes implanting the workpiece using an ion beam, and periodically detecting ion beam neutrals in the ion beam such that adjustments to the ion implanter system can be made for optimization.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The described apparatus and methods relate to detecting energetic neutrals of an ion beam. More particularly, the described apparatus and methods are directed for detecting neutrals of an ion beam in an ion implanter to minimize and prevent energy contamination of a workpiece.

2. Related Art

Deceleration of an ion beam reasonably close to a workpiece, such as a wafer, is a standard method of improving ion implanter productivity for low energy beams. The main benefit of deceleration is to reduce the distance the beam must travel at low energy where the efficiency of transporting the beam is poor. The closer the deceleration is to the workpiece, the more benefits result as far as increasing the beam current. However, ions that become neutral prior to the deceleration, but within a line of sight of the wafer, will be implanted at their undecelerated energy and are classified as energy contamination.FIG. 1illustrates how energy contamination may occur in an ion implanter. As an ion beam10propagates through the implanter, a bend magnet12may direct beam10toward drift space14. In drift space14, collisions with surfaces and background gas produce energetic neutrals. Through a deceleration stage16, ions are decelerated to a final energy in one portion18of beam10. A small flux of the higher energy neutrals remain as a second portion20of beam10. The neutrals that pass to a wafer22will implant significantly deeper than the ions to cause energy contamination. Only a small amount of energy contaminated ions are allowed to be implanted, typically on the order of 0.2% to 0.5%, before the implantation of the workpiece is adversely effected.

Known techniques for limiting energy contamination include an implanter architecture where an electrostatic or magnetic bend is placed between the deceleration stage and the magnet, increased pumping to limit the neutralization of beam ions by residual gas, an aperture and liner design to prevent neutrals formed by collisions with the structures inside the implanter from reaching the workpiece, and limiting the voltage allowed when running deceleration to reduce the implanted depth of the contaminant ions. The implanter may be designed to produce zero energy contamination by extracting the required low energy beams directly from the source, but this inherently runs at much lower beam currents. The other techniques allow for higher currents but do not provide any real time monitoring to ensure that they are effective in preventing energy contamination every time the implanter is run.

In view of the foregoing, it is desired to ensure that the implanter is meeting this contamination requirement at all times while the implantation productivity is maximized.

SUMMARY OF THE INVENTION

The invention includes an ion beam neutral detector system, an ion implanter system including the detector system and a method of detecting ion beam neutrals that ensures an ion implant is meeting contamination requirements. The detector includes an energy contamination monitor positioned within an ion implanter system. A method of the invention includes implanting the workpiece using an ion beam, and periodically detecting ion beam neutrals in the ion beam such that adjustments to the ion implanter system can be made for optimization.

A first aspect of the invention is directed to an ion implanter system comprising: a source for generating an ion beam for implanting a workpiece; and an ion beam neutral detector.

A second aspect of the invention is directed to a method of implanting a workpiece with an ion implanter system, the method comprising the steps of: implanting the workpiece using an ion beam; and periodically detecting ion beam neutrals in the ion beam.

A third aspect of the invention is directed to an ion beam neutral detector system comprising: a detection structure including: a chamber coupled to a bias voltage, a collector plate adjacent the chamber for receiving the ion beam, and a measuring device that measures a current at the collector plate.

The foregoing and other features of the invention will be apparent from the following more particular description of embodiments of the invention.

DESCRIPTION OF THE INVENTION

Embodiments of the present invention are directed to methods and apparatus for measuring the current of secondary electrons emitted due to the impact of the energetic neutral particles.FIG. 2Aillustrates a schematic diagram andFIG. 2Billustrates a cross sectional view of a detection structure108of an energy contamination monitor110(also referred to herein as an “ion beam neutral detector system”) according to embodiments of the present invention. Detection structure108includes: a chamber130, a collector plate140and a measuring device142. A container150may be provided to house and position collector plate140adjacent chamber130for receiving ion beam120, as will be described in more detail below. In addition, as shown inFIG. 2B, a mesh filter144is electrically connected to chamber130may be provided in front of collector plate140. Mesh filter144may include, for example, tungsten or tantalum.

As shown inFIGS. 2A-2B, ion beam120of ions and neutrals enters container150through an aperture152in a shield160, which is coupled to container150. In one embodiment, detection structure108is substantially cylindrical in shape, although this is not necessary. In this case, however, chamber130is substantially cylindrical and collector plate140is substantially circular. Chamber130is connected to a bias voltage supply132and collector plate140is connected to measuring device142, which measures the collector current Icol(FIG. 3) at collector plate140. Chamber130, collector plate140and mesh filter144are isolated from container150by insulation154(FIG. 2B). Ion beam120includes a flux of ions Iionat energy Eionand a flux of neutrals Ineutrals. Aperture152allows beam120to pass toward collector plate140and the bias applied to chamber130allows portions of the collector current to be distinguished, namely the ion current, Iionthe secondary electrons generated by ions, and the secondary electrons generated by the neutrals, Ineutrals.

Chamber130is designed to a sufficient length and diameter to direct beam120to collector plate140while subjecting beam120to the electric field produced by biasing chamber130. Considerations should be made to minimize the completed size of detection structure108so that it may fit relatively unobtrusively within a beam-generating device, such as an implanter. For example, chamber130may be of a length of about 2″ and a diameter of about 1″ to provide dimensions for meeting these constraints. Also, chamber130, collector plate140, and shield160should be made of materials compatible with the environment. For example, chamber130and collector plate140may be made of aluminum or like material, and shield60may be made of graphite or like material.

The bias voltage (V) applied to chamber130may be positive, negative or grounded as illustrated in the graph ofFIG. 3. In region1, a negative bias is applied to chamber130. In region1, the measured collector current (Icol) is due to ions and Il=Iion. At a sufficiently high voltage in region3, the measured collector current (Icol) results from neutrals, and I3=Ineutral·γneutral, where γneutralis the secondary electron emission coefficient for neutrals. In region2, the bias voltage (V) applied to chamber130(FIGS. 2A-2B) is positive but less than the voltage applied in region3, which is required to prevent ions from reaching collector plate140(FIGS. 2A-2B). The measured collector current (Icol) results from both neutrals and ions such that I2=Iion+Iion·γion+Ineutral·γneutral, where γionis the secondary electron emission coefficient for ions.

The currents for each of the operating regions can be manipulated to give:

By assuming that the secondary electron emission coefficients for neutrals (γneutral) and ions (γion) are the same, the relation is derived:

As illustrated inFIG. 4, detection structure108may be incorporated into an ion implanter system400according to an embodiment of the present invention. In this case, ion beam neutral detection system110also includes a detector support assembly460for moving detection structure108between a use position and a non-use position within ion implanter system400although configurations may be found that allow the detector to remain in a fixed position. Ion implanter system400of the present embodiment includes a source410for generating an ion beam. In addition, system400may also include a directing magnet420of, e.g., 90°, for directing the beam, a deceleration stage430for decreasing the energy level of the beam, a corrector magnet440for directing the beam, a final stage of deceleration444and an end station450where the beam is directed to the workpiece. The end station450includes detection system110, which is connected to support system460, which may include, for example, robotics for moving detection system110as generally indicated by the double-ended arrow.

In operation, detection system110is moved toward the use position A for obtaining energy contamination measurements during set up, i.e., prior to implanting, or at predetermined intervals (periods). Detection system110is moved away from the workpiece to a non-use position B since energy contamination measurements will not be made when the workpiece is being implanted. Periodic detection or measurements of ion beam neutrals in the ion beam during stoppage of ion implanting can then be input into a computer or processor (not shown) for use in optimizing (i.e., through adjustment) the operation of implanter system400, i.e., prior to implanting or during implanting. For example, if the energy contamination measurements are outside of specification values, implanter system400can be re-tuned or stopped until the implanter system400is brought back to within the specifications.

The described invention provides process assurance and maximizes implantation productivity when running in deceleration to low energies. Changing conditions in implanter system400(FIG. 4), vacuum pressure and maintenance, for example, may lead to differing levels of contamination when running the same recipe. Present practices limit the output of an implanter system to provide some margin for potential changes in operating conditions. Real time detection of energy contamination minimizes contamination due to poor operating conditions and thereby reduces the margin required for safe operation.

Detector system110according to the above-described embodiments of the present invention measures the current of secondary electrons emitted due to the impact of the energetic neutral particles. Other neutral detectors could be substituted for the neutral detector based on the same principle or another like calorimetry.

Although the methods and systems have been described above relative to specific embodiments, the present invention is not so limited. Obviously, many modifications and variations may become apparent in light of the teachings. Many additional changes in the details, materials, and arrangement of parts, described and illustrated herein, can be made by those skilled in the art.