Positive ion species in high-density discharges containing chlorine and boron–trichloride

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We have used a quadrupole mass spectrometer to measure the positive ion species striking the wafer in a high-density plasma processing discharge containing chlorine and boron–trichloride. Since the relative transmission of our mass spectrometer versus ion mass is known, we are able to report the relative concentrations of the ion species striking the wafer. Our measurements were made in an inductively coupled Gaseous Electronics Conference Reference Cell operating at pressures between 15 and 50 mTorr and at electron densities up to 1011/cm3. The ion spectrum in these discharges is normally dominated by Cl+, Cl2+, BCl2+, and etch products. However, reactor wall or wafer surface conditions can strongly affect the ion species in the discharge. When a stainless steel “wafer” was replaced with a bare Si wafer, the dominant chlorine ion changed from Cl+ to Cl2+. A bare aluminum wafer strongly quenched both Cl+ and Cl2+ signals.