HALOGEN UPTAKE BY THIN SIO2 LAYERS ON EXPOSURE TO HBR O-2 AND CL-2 PLASMAS, INVESTIGATED BY VACUUM TRANSFER X-RAY PHOTOELECTRON-SPECTROSCOPY/

Thin SiO2 layers were subjected to short exposures (10-40 s) to HBr/O- 2 and Cl-2 high-density plasmas, simulating the over-etching process e ncountered when polycrystalline Si gate electrodes are etched down to the gate oxide layer. Following this treatment, the samples were trans ferred under vacuum to an x-ray photoelectron spectrometer and spectra were recorded as a function of the take-off angle between the sample surface plane and the photoelectron collection lens. These angle-resol ved measurements were inverted, using a maximum entropy approach, to o btain depth profiles. After etching in Cl-2 or HBr plasmas at an ion e nergy of similar to 40 eV (obtained with a grounded stage and a plasma potential of 40 V), surface layers were formed with halogen areal den sities of similar to 2X10(15) cm(-2), distributed over a half-depth of 10-20 Angstrom. These results (both absolute areal densities and dept h distributions) are similar to those found previously for etching of Si under the same conditions. For SiO2, buildup of Cl or Br near the s urface is accompanied by a depletion of O. Addition of 10% O-2 to HBr plasmas decreases the Br content in the film by nearly a factor of 2 ( with the stage grounded), and dramatically slows the etching rate from similar to 30 to <2 Angstrom/min. Increasing the mean ion energy to s imilar to 150 eV by applying an rf bias (resulting in a de bias of -11 0 V) increases the etching rate in the 10% O-2/HBr plasma to about 10 Angstrom/min, and increases the Br areal density by 50. Implications f or etching of polycrystalline-Si gate electrodes and selectivity to Si O2 are discussed. (C) 1998 American Vacuum Society.