Ion effects on CF2 surface interactions during C3F8 and C4F8 plasma processing of Si

Surface interactions of difluorocarbene (CF2) molecules were investigated using our LIF based imaging of radicals interacting with surfaces (IRIS) apparatus. LIF data of CF2 in C3F8 and C4F8 plasma molecular beams reveal that the relative densities of CF2 increase with increasing rf power and source pressure in both plasma systems. The surface reactivity of CF2 molecules during C3F8 and C4F8 plasma processing of room temperature Si substrates was also measured over a broad rf power range and at different pressures. A scatter coefficient (S) greater than one was measured for all unperturbed systems, indicating that CF2 molecules are produced at the substrate surface during film deposition. The same systems were also studied under ion-limited conditions, yielding S∼1, clear indication that ions are partially responsible for CF2 surface production. Plasma ions were identified using plasma-ion mass spectrometry. These data indicate that higher levels of CxFy+(x>1) are produced in the C4F8 plasmas. X-ray photoelectron spectroscopy analyses of treated substrates showed that amorphous fluorocarbon films were deposited during plasma processing of the substrates. A positive correlation was found between S(CF2) and film composition of FC materials deposited in both the IRIS apparatus and independent reactors.