Architecture of RF Plasma Reactors

摘要

In order to achieve a complete understanding and ocntrol of plasma processes an appropriate knowledge of the structure of the particular glow discharge utilized is necessary. This is extremely important because the electrical potention inside a plasma reactor is not uniform and therefore, as a function of the reactor geometry and sample position, charged particles are accelerated from the plasma bulk to the substrate to be treated by different potential drops, i.e. they impinge on different surface with different eneryg. As it willb e extensively shown in this book of proceedings, the charged particle bombardment (by positive ions, in particular), along with the nature of the materals exposed to the glow, play a key role in most treatments and deposition processes and hence the electrical staturs of the sample surface and of the other parts of the materials exposed to the glow, play a key role in most treatments and deposition processes and hence the leectrical status of the sample surface and of the other parts of the reactor have to be always evaluated. An example pertinent with the contents of this NATO-ASI, is the plasma assisted deposition of luoropolymers in fluorocarbon fed glow discharges. It has been reported(1,2), that ion bombardment increases the polymerization rate as well as the crosslinking and the inorganic characteristi of deposited polymer, but if the usbstrate potential is too negative with resppect to the plasma bulk, the ion bombardment is extremely endrgietic and causes a reduction of the polymerization rate or a complete stop of deposition. I nthese conditions hard-like carbon films instead of fluoropolymers are obtaned(3). A suitable combination of ion bombardment and of materials exposed to the plasma can influence the quali-quantitative composition of the plasma and therefore can sometime be utilized to improve the process performances. This expedient is very often utilized in dry etching of silicon oxide in fluorocarbon plasma for microelectronics applications. In orfer to reduce drastically the plasma concentration of flurorine atoms and to achieve the needed etch rate selectrivity with respect to silicon and/or silicon nitride, some parts of the reactor, subjected to intense and energetic ion bombardment, are made of silicon. The rapid and quantitative reaction between silicion and fluorine, under the synergistic effect of ion bombardment, drastically and increases the effect of CFx radicals (oxide etchants) mproving the process selectivity. Very negative potentials, on the othe rhand, must be avoided on those parts of the reactor whic can be easily sputtered and release unwanted species in the gas phase (e.g. stainless steel, aluminium, etc.) which contaminate the surface of the sample to be treated.