At its core, the RAP^TM technology involves the use of an atmospheric pressure plasma into which chemical precursors are injected. These precursors are broken down in the plasma to form desired chemical radicals that are then applied to a substrate placed downstream from the plasma.

An illustration of the plasma is shown using an Inductively Coupled Plasma (ICP) torch in the adjacent figure. A fluorine based precursor such as Sulphur Hexafluoride (SF₆) is then injected into the center of the plasma forming active fluorine (F) radicals. These radicals are then transported through an appropriate nozzle to the surface being processed which is located downstream of the plasma as illustrated. The substrate chemistry as well as the type of operation needed (cleaning, etching, doping, deposition etc.) determine the precursor(s) to be injected into the center of the plasma. The plasma serves as a source of both thermal and chemical flux. RAPT Industries, Inc. has developed innovative nozzle designs to minimize the thermal flux incident on the surface being processed while maximizing the chemical flux.

The resulting footprint is Gaussian due to the fluid flow nature both in the plasma and downstream and is fairly insensitive to positioning along the direction of the plasma for a certain nominal working distance. Typical footprints obtained with the RAP^TM torches are on the order of 10mm FWHM (Full Width Half Maximum). The numbers are similar for various operations such as etching, deposition or doping.

This Gaussian footprint is usually a fraction of the area of the surface being processed. The surface profile (shape, chemistry etc.) is then a function of the dwell time of the plasma over the instantaneous position on the surface. A deconvolution algorithm is then used to scan this footprint along the surface to etch/clean/deposit/dope the desired profile onto the surface. Such an approach is typically referred to as a sub-aperture process, with due respect to the optics industry, where this was first formalized. The Gaussian nature of the RAP^TM footprint desensitizes the process from positioning inaccuracies and thus reduces the precision demands on the positioning subsystem.

While, the Gaussian footprint prevents the introduction of higher spatial frequencies (and ringing effects) onto the surface, it is also limited in terms of its capability in processing high spatial frequency features. This limit is directly dependent on the "spot size". RAPT Industries, Inc. have since developed VirtuRAP^TM technology that allows the user to define virtually complex tool footprints, localize processing even further and greatly increase processing rates. VirtuRAP^TM technology uses the fact that the RAP^TM process is an Arrhenius rate reaction and involves two features:

• Use of a "cold" RAP^TM torch with very low heat flux incident on the substrate
• Use of a "local" heat source within the chemical flux field

The use of the "cold" torch ensures that the substrate temperature times the Boltzmann constant is below the surface activation energy, thus leading to zero or very low reaction rates. The local source of heat (such as a laser) then provides a rapid, controlled source of heat that can directly influence reaction rates within the thermalized region. Due to the difference in time constants between the laser heating and chemical diffusion, a virtual footprint can be defined within the chemical flux field as illustrated in the adjacent cartoon.

RAPT^TM Industries is continuously involved in enhancing its core technology and applying it to fields requiring rapid, damage-free processing of surfaces. RAPT^TM commercializes its technology through a combination of capital equipment sales, OEM module sales and technology licensing. For more information on adopting RAP^TM and VirtuRAP^TM technology in your manufacturing line, please contact sales@raptindustries.com.