RAPID THERMAL-OXIDATION OF SILICON WITH DIFFERENT THERMAL ANNEALING CYCLES IN NITROGEN - INFLUENCE ON SURFACE MICROROUGHNESS AND ELECTRICALCHARACTERISTICS

The influence of two different thermal annealing cycles on the microro ughness of the Si-SiO2 interface and on the electrical characteristics of the Si-SiO2 system has been investigated. Experiments were perform ed growing oxides by rapid thermal oxidation (RTO) and post-oxidation annealing in N-2 using a slow cooling ramp recipe (SCRR) or a conventi onal pulsed thermal annealing recipe (PTAR). Compared to PTAR, SCRR yi elded a more severe annealing in N-2 and slower temperature decay afte r RTO. The thickness of the as-grown oxides was measured by ellipsomet ry in the whole wafer area. Laser light scattering (LLS) at a grazing angle and atomic force microscopy (AFM) have been used for measuring t he Si-SiO2 interface topography after the SiO2 removal. LLS was mainly used for large-area scans (micrometric resolution) and AFM for small- size areas (atomic resolution). The results showed that oxides prepare d with SCRR exhibited a smoother Si-SiO2 interface at the nanometric s cale and protrusions up to 2.5 nm high and up to 100 nm wide ('large p rotrusions') at a submicrometre scale. On the other hand, the oxides p repared with PTAR resulted in an Si-SiO2 interface with protrusions up to 2 nm high and up to 5 nm wide ('sharp protrusions') at the nanomet ric scale and broad localized regions, sparsely distributed over the w afer area, with high root mean square (RMS) microroughness. By measuri ng the electrical parameters of a large number of MOS capacitors made with these oxides, we demonstrated evident experimental correlation of the electric breakdown field (E(bd)), charge to breakdown (Q(bd)), Si -SiO2 interface state density (D-it) and Al-SiO2 potential barrier hei ght (phi(0)) with surface microroughness and therefore with the therma l annealing cycle in N-2. The oxides prepared by SCRR exhibited improv ed overall electrical parameters as compared to the oxides prepared by PTAR.