1. Field of the Invention
Embodiments of the invention relate to the field of semiconductor device fabrication. More particularly, the present invention relates to an apparatus for regeneration of cryogenic ion implanter surfaces utilizing an optical heater.
2. Discussion of Related Art
Ion implantation is a process used to dope impurity ions into a semiconductor substrate to obtain desired device characteristics. An ion beam is directed from an ion source chamber toward a substrate. The depth of implantation into the substrate is based on the ion implant energy and the mass of the ions generated in the source chamber. One or more ion species may be implanted at different energy and dose levels to obtain desired device structures. In addition, the beam dose (the amount of ions implanted in the substrate) and the beam current (the uniformity of the ion beam) can be manipulated to provide a desired doping profile in the substrate. However, throughput or manufacturing of semiconductor devices is highly dependent on the uniformity of the ion beam on the target substrate to produce the desired semiconductor device characteristics.
FIG. 1 is a block diagram of an ion implanter 100 including an ion source chamber 102. A power supply 101 supplies the required energy to source 102 which is configured to generate ions of a particular species. The generated ions are extracted from the source through a series of electrodes 104 and formed into a beam 95 which passes through a mass analyzer magnet 106. The mass analyzer is configured with a particular magnetic field such that only the ions with a desired mass-to-charge ratio are able to travel through the analyzer for maximum transmission through the mass resolving slit 107. Ions of the desired species pass from mass slit 107 through deceleration stage 108 to corrector magnet 110. Corrector magnet 110 is energized to deflect ion beamlets in accordance with the strength and direction of the applied magnetic field to provide a ribbon beam targeted toward a work piece or substrate positioned on support (e.g. platen) 114. In some embodiments, a second deceleration stage 112 may be disposed between corrector magnet 110 and support 114. The ions lose energy when they collide with electrons and nuclei in the substrate and come to rest at a desired depth within the substrate based on the acceleration energy.
The ion source chamber 102 typically includes a heated filament which ionizes a feed gas introduced into the chamber to form charged ions and electrons (plasma). The heating element may be, for example, a Bernas source filament, an indirectly heated cathode (IHC) assembly or other thermal electron source. Different feed gases are supplied to the ion source chamber to obtain ion beams having particular dopant characteristics. For example, the introduction of H2, BF3 and AsH3 at relatively high chamber temperatures are broken down into mono-atoms having high implant energies. High implant energies are usually associated with values greater than 20 keV. For low-energy ion implantation, heavier charged molecules such as decaborane, carborane, etc., are introduced into the source chamber at a lower chamber temperature which preserves the molecular structure of the ionized molecules having lower implant energies. Low implant energies typically have values below 20 keV.
It has been discovered that a relatively low substrate or wafer temperature during ion implantation improves implant performance. In particular, lower wafer temperatures reduces the amount of damage caused when ions hit the substrate (damage layer). This decreased damage layer improves device leakage currents. This allows manufacturers to create abrupt source-drain extensions and ultra-shallow junctions needed for today's semiconductor devices. When the temperature of the wafer is decreased, the thickness of the amorphous silicon layer increases because of a reduction in the self-annealing effect. Typically, cooling reduces the temperature of the platen upon which the wafer is disposed in the range of between room temperature to about −100° C. Almost all existing low-temperature ion implanters cool wafers directly during ion implantation. However, lowering of the temperature of the wafer surface in an ion implanter tends to condense water molecules and other volatile compounds such as photoresist byproducts. Extended exposure of the vacuum chamber to low-temperature wafers may result in icing from the condensed water molecules. These unwanted conditions compromise implantation profiles as well as require incorporation of components configured to dispose of unwanted cryogenic byproducts.
A regeneration cycle is used to clean these cryogenic component surfaces which includes heating the surface of the affected components using electrical heaters and/or warm gas distributed over and/or through the component. However, these processes require the electrical heaters and gas flow devices to heat the component to a sufficient level which takes additional valuable system down time. Consequently, regeneration process cycles require long periods of equipment downtime which negatively impacts manufacturing throughput.