Growth techniques and characterisation of Si_1_-_xGe_x heterostructures for pMOS applications

Increasing demands for faster switching frequencies require high current drives and consequently high Ge contents for Si_1_-_xGe_x hetero-MOSFETs. In addition, highly planar interfaces are a prerequisite for the successful incorporation of a Si_1_-_xGe_x layer into a Si CMOS technology, with stringent constraints being placed on layer thicknesses. The influence of MBE growth temperature has been investigated in order to kinetically suppress strain induced interface roughening associated with high Ge contents (x#>=#0.3). However, it has been shown that simply reducing the growth temperature leads to highly defected layers on the atomic scale (evidenced from PAS and low temperature Hall measurements). A two-stage growth technique has been developed employing a low temperature growth (LTG) stage to suppress the strain induced macro-roughening followed by a post growth in-situ anneal (PGA) stage to remove the grown in defects and consequently enhance the electrical characteristics. Using this novel growth technique highly planar alloy layers have been grown which can withstand the thermal budgets required for CMOS processing before the onset of alloy layer degradation. Complicated growth specifications in terms of layer thicloiess and doping levels accrue with submicron MOS device-processes to circumvent short channel effects. Exemplary FET characteristics have been obtained on devices working down to 0.35 #mu#m, processed on layers grown by the aforementioned LTG/PGA technique (HMOS1). In addition, growth techniques have been developed for B #delta# layer stabilisation against diffusion and segregation, required for valence band tailoring of the next generation devices working down to 0.15 #mu#m (HMOS2). Finally, preliminary work has been undertaken on the development of a novel growth technique for the production of thin virtual substrates with a smooth surface morphology. (author)SIGLEAvailable from British Library Document Supply Centre-DSC:DXN044699 / BLDSC - British Library Document Supply CentreGBUnited Kingdo