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Chemically assisted ion beam etching, using Ar + ions and Cl2 as the reactive gas, has been investigated for the etching of common materials used in silicon-based microfabrication: SiQ, Si3N4, single-crystal St, and polycrystalline St. Two possible etch masks for etching the Si substrate have been characterized: SiO2 and TiW. Etch rates for all these materials and Si etch profiles have been studied as a function of ion energies from 300 to I000 eV, current densities between 0.05 and 0.15 mA/cm ~, and reactive C12 flow rates at substrate temperatures of 30 and 85~ Trenches etched into Si using TiW as a mask showed steeper profiles and less enhanced etching in the bottom corners than those with an SiO2 mask. These etch effects are attributed to a deposited layer on the trench sidewalls, when using TiW as a mask. This Si etch process has important applications in shallow trench isolation for deep submicron complementary metal oxide semiconductor integrated circuits.

The activation of dopants and theevolution of the microstructure of poly-SiGe films during the activation anneal are of interest for applications such as removable diffusion sources for shallow junctions in CMOS circuit processing, low resistance contact layers and elements for thin film transistors in active matrix flat panel displays. To study these effects, 2300A poly-SiGe films with Ge content between 20 and 48% were deposited on 600A poly-Si seed layers by APCVD on thermally oxidized Si substrates. Growth temperatures were between 600 and 700'C. These films were then implanted with B and As at energies of 40 and 80 keV, respectively, at two different doses of 5 x 101 3 /cm 2 and 5 x 106/cm2 . To activate the dopants, the samples were furnace annealed at temperatures from 600 to 1000'C in an N2 ambient. Additional samples were rapidly annealed at temperatures between 800 and 1050'C for times up to 120 seconds. The sheet resistance, measured using a four-point probe, of 5 x 10 16/cm2 arsenic implanted films increased by a factor of two as the Ge content in the film increased from 20 to 48%. The boron doped film, on the other hand, showed no increase in sheet resistance with Ge content. TEM showed that in all cases the grain size increased after anneal. However, the grain sizes of the annealed, arsenic doped samples were on average 5 times larger than those of the boron-doped samples with the same anneal. The sub-grain structure of these films also changed after implantation and annealing. In particular, the twin planes increased in size in boron doped samples and sub-grain twinning virtually disappeared in the arsenic doped samples. In 25x 10 /cm As implanted samples, precipitates were formed which may indicate that the As solubility limit in the films has been exceeded. These precipitates are believed to be As or Asrich and could be responsible for the sheet resistance increase with Ge fraction, since the maximum solubility for As in Ge is lower than in Si by about a factor often.

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