Epitaxial Si/SiGe growth studies in view of novel logic devices using an alternative Ge precursor gas

With the continuous evolution of logic devices, metal-oxide-semiconductor field effect transistors (MOSFET) have progressed from conventional planar architectures to three-dimensional (3D) structures, where stacked horizontal channels, commonly referred to as nanosheets (NS), are used to integrate p-type and n-type devices.

NS devices, as well as their vertical stacking in complementary field effect transistors (CFET), are now considered as the main device architecture for the most advanced technology nodes. In this configuration, boron-doped Si_1-xGe_x (Si_1-xGe_x:B) and phosphorus-doped Si (Si:P) are used as p- and n-type source/drain (S/D) materials, respectively. These layers have to be grown exclusively on the exposed NS sidewalls, while avoiding growth on the surrounding masking materials, thereby achieving selective epitaxial growth (SEG). This selectivity is hence achieved by the introduction of chlorine in the growth chemistry.

Chlorine-based precursors have emerged as particularly promising candidates for enabling such selective growth. In this context, GeCl₄ is considered as an attractive candidate to enable the SEG of Si_1-xGe_x material. However, despite the common usage of Si_1-xGe_x:B as a p-type S/D material, its growth using GeCl₄ has received relatively limited attention. In particular, the influence of this alternative precursor on the boron incorporation and the resulting active dopant concentration in Si_1-xGe_x:B SEG is yet to be clarified.

Additionally, GeCl₄ is known to enable high growth rate of lowly-defective Si_1-xGe_x layers. Thereby, GeCl₄ also appears as a promising precursor to enable thick Si_1-xGe_x layers of high crystalline quality. The internship student will start with the growth of undoped Si_1-xGe_x layers using GeCl₄ to study chemical vapor deposition, Si_1-xGe_x material properties/characterization including the growth selectivity and strain relaxation mechanisms. The study will be extended to Si_1-xGe_x:B selective growth. The candidate will be introduced to several standard material characterization techniques like XRD, XRR, micro-Hall effect, etc. The student will contribute to the selective epitaxial growth studies of doped materials by applying the different characterization techniques.