Disilane-based cyclic deposition/etch of Si, Si:P and Si_1−yC_y:P layers: I. The elementary process steps

Abstract

We have benchmarked the 550 • C, 20 Torr growth of Si:P and Si 1−y C y :P using SiH 4 and Si 2 H 6 . P segregation has prevented us from reaching P + ion concentrations in Si higher than a few 10 19 cm −3 using SiH 4 ; the resulting surface 'poisoning' led to a severe growth rate reduction. Meanwhile, [P + ] increased linearly with the phosphine flow when using Si 2 H 6 as the Si precursor; values as high as 1.7 × 10 20 cm −3 were obtained. The Si:P growth rate using Si 2 H 6 was initially stable then increased as the PH 3 flow increased. Mono-methylsilane flows 6.5-10 times higher were needed with Si 2 H 6 than with SiH 4 to reach the same substitutional C concentrations in intrinsic Si 1−y C y layers ([C] subst. up to 1.9%). Growth rates were approximately six times higher with Si 2 H 6 than with SiH 4 , however. 30 nm thick Si 1−y C y layers became rough as [C] subst. exceeded 1.6% (formation of increasing numbers of islands). We have also studied the structural and electrical properties of 'low' and 'high' C content Si 1−y C y :P layers (∼ 1.5 and 1.8%, respectively) grown with Si 2 H 6 . Adding significant amounts of PH 3 led to a reduction of the tensile strain in the films. This was due to the incorporation of P atoms (at the expense of C atoms) in the substitutional sites of the Si matrix. Si 1−y C y :P layers otherwise became rough as the PH 3 flow increased. Resistivities lower than 1 m cm were nevertheless associated with those Si 1−y C y :P layers, with P atomic concentrations at most 3.9 × 10 20 cm −3 . Finally, we have quantified the beneficial impact of adding GeH 4 to HCl for the low-temperature etching of Si. Etch rates 12-36 times higher with HCl + GeH 4 than with pure HCl were achieved at 20 Torr. Workable etch rates close to 1 nm min −1 were obtained at 600 • C (versus 750 • C for pure HCl), enabling low-temperature cyclic deposition/etch strategies for the selective epitaxial growth of Si, Si:P and Si 1−y C y :P layers on patterned wafers.

Chemical vapor deposition of Si:C and Si:C:P films—Evaluation of material quality as a function of C content, carrier gas and doping

“…The resistivity of the doped films with C tot ¼1.6% was 8.3 Â 10 À 4 Ohm cm while the resistivity of the film with C tot ¼2.3% was 1.5 Â 10 À 3 Ohm cm. The increase in resistivity with increasing C concentration is also reported by Hartmann et al, and Rosseel et al [12,35] and is explained by a loss in active P and the presence of many non-substitutional C related defects that might affect the carrier transport by scattering [36].…”

“…Realizing the S/D stressors for FinFETs requires selective epitaxial growth in the trenches with reduced defects. Hence, future work will focus on developing a selective process by the use of cyclic deposition and etching technique [10,12] and understanding the impact of CDE upon material quality.…”

“…Recently, there have been reports on the epitaxial deposition of Si:C using trisilane [10], neopentasilane [11] etc. The main problems associated with these gases are, i) their liquid phase which complicates their supply to the epi reactor, ii) the high cost especially for electronic grade quality [9,12], and iii) the concern for condensing into gas phase precipitates which may get incorporated into the growing epitaxial layer, leading to defect incorporation in the epitaxial layer [13]. In these aspects, the use of disilane, a gas phase precursor, is more beneficial and is also economic in comparison to other higher order silanes [12].…”

“…A couple of reports pertaining to the use of disilane to grow Si:C layers (in both gas-source Molecular Beam Epitaxy (MBE) as well as Chemical Vapor Deposition (CVD)), are already available [12][13][14][15][16][17][18][19]. Recently, Hartmann et al [19] have demonstrated a selective process for Si:C and Si:C:P deposition using disilane.…”

On the Evolution of Strain and Electrical Properties in As-Grown and Annealed Si:P Epitaxial Films for Source-Drain Stressor Applications

“…As P is an n-type dopant with a reduced covalent radius, Si:P films are expected to offer the combined advantages of better conductivity as well as tensile strain. [6][7][8][9] This motivation has led to a surge in the publications pertaining to the processing aspects of Si:P films 6,[8][9][10][11] and publications discussing the evolution of resistivities in the as grown and annealed Si:P films. 6,9,12 While the strain developed in the as-grown Si:P films increases with the total P concentration, the values of resistivity corresponding to those P concentrations were higher than the desired values for S/D applications i.e., higher than 0.3 mohm.cm.…”