Resistivity of boron and phosphorus doped polycrystalline Si1−xGex films

Abstract

Sheet resistance, Hall mobility, and effective carrier concentration as a function of annealing parameters for boron or phosphorus ion implanted films of polycrystalline Si, Si0.75Ge0.25, and Si0.50Ge0.50 films are presented. The films were ion implanted with boron or phosphorus at dosages between 5×1014 and 4×1015 cm−2, and then thermally annealed between 550 and 650 °C from 0.25 to 120 min. Boron doped films showed decreasing minimum sheet resistance with increasing Ge fraction, while phosphorus doped films exhibited the reverse trend. Both boron and phosphorus doped films showed minima as a function of anneal time. This is attributed to the competing processes of damage annealing versus dopant segregation. Poly-Si0.50Ge0.50 films achieved minimum resistance faster than poly-Si films, and the lowest sheet resistances were measured in boron doped, poly-Si0.50Ge0.50 films.

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

“…In p-type polycrystalline SiGe, the resistivity decreases with increasing Ge content, which has been attributed to increases in both hole mobility and dopant activation with increasing Ge incorporation. 9,11 In contrast, it has been shown 9 that for n-type films containing less than 25% Ge, the Hall mobility increases, but the effective carrier concentration steadily decreases, with increasing Ge content. The net effect is a slight decrease in the resistivity at low Ge concentrations.…”

“…The net effect is a slight decrease in the resistivity at low Ge concentrations. For layers with Ge concentrations above 25%, a large drop in phosphorus activation combined with a drop in the Hall mobility is observed, 4,9 causing a large increase in resistivity. This was attributed to increased phosphorus segregation to the grain boundaries with increasing Ge content.…”

“…Several authors have shown that the addition of у25% Ge to polycrystalline Si 1Ϫx Ge x layers causes a significant increase in resistivity of n-type layers, and a corresponding decrease in p-type layers. [9][10][11] In polycrystalline Si, the dominant trap energy is close to the middle of the band gap, so that the effects of the carrier trapping are similar in both n-and p-type layers. In polycrystalline Ge, the dominant trap energy is close to the valence band, so that grain boundary energy barriers only appear in n-type material.…”

“…This was attributed to increased phosphorus segregation to the grain boundaries with increasing Ge content. 9 Polycrystalline Si 1ϪxϪy Ge x C y and Si 1Ϫy C y layers are of interest because they offer the possibility of an additional degree of freedom in band gap engineering not offered by Si 1Ϫx Ge x alone. A possible application for polycrystalline Si 1ϪxϪy Ge x C y and Si 1Ϫy C y layers would be as wide band gap emitters for bipolar transistors.…”

“…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.…”