| The use of ultrathin dielectric in the ULSI (Ultra-Large Scale Itegration) era is curcial for device functionality and reliability. However, it is well known that conventional thermally grown pure oxides in the ultra-thin regime (40-60A) do not provide adequate electrical and reliability characteristics. The use of N{dollar}sb2{dollar}O gas in oxidation produces oxides (oxynitrides) with better dielectric integrity, lower defect density, less boron penetration and better process control, etc.. The N{dollar}sb2{dollar}O oxide is thus a better candidate for ultrathin oxide application.; Pre-oxidation surface preparation by conventional RCA clean increases surface microroughness and provides no passivation to the wafer surface. A new cleaning method based on methanol/HF has been developed and show improvement in the dielectric integrity of both oxides and oxynitrides. A microscopic model is also proposed.; The thickness dependent of stress-induced leakage current (SILC) was studied for pure oxides and N{dollar}sb2{dollar}O oxides. A "turn around" effect was observed such that for thickness going down from {dollar}sim{dollar}50A, SILC actually decreases. This effect is modeled by the two-step trap-assisted tunneling model where trap generation rate and tunneling time constants are the determining factors for the SILC.; Effects of oxide exposure, photoresist and gate dopant activation on the plasma damage immunity of ultrathin oxides were studied. It was found that not only charging damage and radiation damage are present during plasma exposure, photo-annealing by low energy UV light is competing with the damaging processes. The actual extent of damage depends on the plasma operating condition. It implies that using fully-covered MOSCAP structures is not an accurate indicator of the actual damage in integrated circuits. It was also found that photoresist quality affect plasma damage and patterning gate before ion implantation can reduce charging problem. Damage recovery effect of various RTA annealing processes is also studied.; The effects of different gate dopant species, concentration and microstructure on the electrical and reliability characteristics of ultrathin oxides and N{dollar}sb2{dollar}O oxynitrides are studied. Optimization of the gate doping level is based on poly depletion, charge-to-breakdown, and stress-induced leakage current. The optimization conditions for N+ and P+ gate are found to be very different. |
