Reduced pressure chemical vapor deposition of Si/Si[sub 1-y]C[sub y] heterostructures for n-type metal–oxide–semiconductor transistors.

We have grown by reduced pressure chemical vapor deposition Si/Si[sub 1-y]C[sub y]/Si heterostructures for electrical purposes. The incorporation of substitutional carbon atoms into Si creates a carrier confinement in the channel region of metal-oxide-semiconductor (MOS) transistors. Indeed, tensile strain Si[sub 1-y]C[sub y] layers present a type II band alignment with Si, with a conduction band offset of the order of 60 meV per at. % of substitutional carbon atoms. For small SiH[sub 3] CH[sub 3] flows, all the incoming carbon atoms are incorporated into substitutional sites. At 600 °C, when the SiH[sub 3] CH[sub 3] flow increases, the substitutional carbon concentration saturates at 1.12%. Meanwhile, the total carbon concentration C[sub T] still increases, following a simple law: C[sub T]/(1-C[sub T])=0.88 [sup *] [F(SiH[sup 3]CH[sub 3]) /F(SiH[sub 4])]. This is a sign that a growing number of C atoms incorporates into interstitial sites. The hydrogenated chemistry adopted does not enable one to achieve selectivity over SiO[sub 2]-masked wafers, but does not however generate any adverse loading effect. We have integrated Si/Si[sub 1-y]C[sub y]/Si stacks (which have been shown to be stable versus conventional gate oxidations and electrical activation anneals) into the channel region of ultrashort gate length (50 nm) nMOS transistors. Secondary ions mass spectrometry profiling has shown that C atoms segregate from the Si[sub 1-y]C[sub y] layer into the Si cap and the SiO[sub 2] gate, but also that they block the diffusion paths of B coming from the antipunch through layer towards the gate, generating very retrograde doping profiles. The addition of C leads to a degradation of the electron mobility which seems to be linked to the high amount of C atoms into interstitial sites. [ABSTRACT FROM AUTHOR]