Influence of the reactor wall composition on radicals' densities and total pressure in Cl2 inductively coupled plasmas: I. Without silicon etching

Laser absorption at 355nm is used to monitor the time variations of the Cl2 density in high-density industrial inductively coupled plasma. This technique is combined with the measurement of the gas temperature from the Doppler width of the 811.5nm line of argon, added as a trace gas and with the measurement of the total gas pressure with a Baratron gauge. These measurements permit to estimate the mole fractions of Cl2 and Cl species in Cl2 inductively coupled plasmas in a waferless reactor. The impact of the chemical nature of the reactor wall coatings on the Cl and Cl2 mole fractions is studied systematically. We show that under otherwise identical plasma conditions, the Cl mole fraction is completely different when the plasma is operated in SiOCl, AlF, CCl, or TiOCl coated reactors, because the homogeneous recombination probability of Cl atoms is strongly surface dependant. The Cl atom mole fraction reached at 100W radiofrequency power in SiOCl coated reactor (80%) is much higher than that obtained at 900W in a “clean” AlF reactor (40%). A simple zero-dimensional model permits to provide the recombination coefficient of Cl atoms, γrec: 0.005 on SiOCl film and about 0.3 on the other three coatings. It is proposed to get benefit of this very high sensitivity of Cl2 dissociation rate to the wall coating for the control of the chamber wall status from the Cl2 density measurements in standard conditions.