Dopant Implantation and Activation in Polycrystalline-SiGe

Abstract

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.

N-Type Dopant Activation Behaviors in Poly Si[sub 1−x]Ge[sub x] Films with Ge Contents and Activation Temperatures

“…Since the diffusivity of arsenic became higher and the solid solubility limit of arsenic became lower with the increase of Ge content in the poly Si 1Ϫx Ge x films, the segregation of dopant increased and the activated carrier concentration decreased with the increase of Ge content, as shown in the Table II. 17,18 The sheet resistance of poly Si 1Ϫx Ge x films implanted with the dose of 1 ϫ 10 15 /cm 2 , 5 ϫ 10 15 /cm 2 and 1 ϫ 10 16 /cm 2 decreased with the increase of activation temperature and increased with the increase of Ge content, as shown in the Fig. 5.…”

The role of carbon on the electrical properties of polycrystalline Si1−yCy and Si0.82−yGe0.18Cy films

“…2 More recently, considerable interest has been shown in polycrystalline SiGe films [3][4][5][6][7] because of their increased dopant activation [8][9][10] and lower thermal growth budget. In MOS transistors, polycrystalline SiGe gates could be used to reduce gate depletion and to tailor the work function by varying the Ge content, allowing more freedom in the setting of threshold voltages.…”