PLASMA DIAGNOSTICS OF A SF6 RADIOFREQUENCY DISCHARGE USED FOR THE ETCHING OF SILICON

The neutral molecules and the positive and negative ions issuing from a radiofrequency discharge have been identified and their concentrations measured by means of mass spectrometry and Langmuir probe, as a function of several parameters: pressure, gas flow rate, RF power, SF//6-Ar mixture, and the silicon area to be etched. The concentration of SF//4 produced in the reactor is correlated to the silicon area submitted to the discharge. The major positive ions are SF** plus //3 and SF** plus //5, the negative ions are SF** minus //3, SF** minus //5, F** minus and S//2F** minus //7. The electron and ion density measurements, obtained from Langmuir probe characteristics, give evidence of electron attachment. The rates of ionization, attachment and electron impact dissociation reactions have been estimated from these measurements. The kinetic scheme obtained shows that there are three sources for the atomic fluorine: attachment, ionization and dissociation from SF//6 and SF//4 molecules.