Ion implantation is a high technology approach for modifying surface properties of materials. It is similar to a coating process, but it does not involve the addition of a layer on the surface. Originally developed for use in semiconductor applications, and still used extensively in that capacity today, ion implantation uses highly energetic beams of ions (positively charged atoms) to modify surface structure and chemistry of materials at low temperature. The process does not adversely affect component dimensions or bulk material properties.
Many surface properties can be improved with ion implantation including hardness and wear resistance, resistance to chemical attack, and reduced friction. The process can be applied to virtually any material, including most metals, ceramics and polymers; however, the effects of the process are typically material-specific. Examples of components treated with ion implantation are Ti and Co-Cr orthopedic prostheses, which are made harder and more wear resistant with the process (IonGuard®), and silicone rubber catheters, which are made less tacky and more water wettable for improved insertion and biological compatibility (Spi-Polymer™).
The ion implantation process is conducted in a vacuum chamber at very low pressure (10-4 to 10-5 torr). Large numbers of ions (typically 1016 to 1017 ions/cm2) bombard and penetrate a surface, interacting with the substrate atoms immediately beneath the surface. Typical depth of ion penetration is a fraction of a micron (or a few millionths of an inch). The interactions of the energetic ions with the material modify the surface, providing it with significantly different properties than the remainder of the material. Specific property changes depend on the selected ion beam treatment parameters, for instance the particular ion species, energy, and total number of ions that impact the surface.
Ion implantation offers numerous advantages for treating component surfaces. A primary benefit is the ability to selectively modify the surface without detrimentally affecting bulk properties, largely because the process is carried out at low substrate temperatures. The process is also extremely controllable and reproducible and can be tailored to modify different surfaces in desired ways. Although it is a line-of-sight process, specialized fixturing can be used to uniformly treat complex geometries.
Ions are produced in a multi-step process. Ions are initially formed by stripping electrons from source atoms in a plasma. The ions are then extracted and pass through a mass-analyzing magnet, which selects only those ions of a desired species, isotope, and charge state. The beam of ions is then accelerated using a potential gradient column. Typical ion energies are 10-200 keV. A series of electrostatic and magnetic lens elements shape the resulting ion beam and scans it over an area in an end station containing the parts to be treated.