UV Cure Enabled Robust STI Oxide Gap Fill Solution for Thermally Limited Flow in Advanced Logic Devices

High mobility channel materials such as Si 1-x Ge x (x = 0.1-0.5) are important to achieve performance targets for FinFET devices at dimensions scaled beyond 14nm. Previously, flowable (FCVD) SiO 2 deposition processes have been developed to achieve adequate fill for Shallow Trench Isolation in FinFET structures. However, the thermal budget for curing FCVD oxide with SiGe fins must be limited to avoid out-diffusion of Ge. This restricts the processing options for achieving a robust material which is compatible with subsequent wets processing steps. FCVD oxide deposition employs an amine-based silicon precursor which, upon exposure to NH 3 radicals, forms short chain -Si-N-Si- oligomers with terminal Si-H or N-H bonds. These oligomers flow into and fill deep isolation trenches. Once the trenches are filled, it is critical to stabilize the film and initiate cross linking for densification to SiO2. To this end, a cure while still under vacuum, such as O 3 oxidation, is commonly used before a subsequent furnace steam anneal. This paper describes an alternate curing process using broadband UV light to densify FCVD oxide. Material properties were studied using cure by microwave-powered Hg lamps at 10 degC with broadband (200-450nm) spectrum and compared to the existing O 3 cure. To achieve the desired FCVD film properties, it is beneficial to remove -OH terminations during the post-dep cure to promote a dense final -Si-O-Si- matrix. Fig. 1 shows high frequency FTIR spectra from UV-cured FCVD oxide films as a function of UV power post-steam anneal. Data from O 3 cured FCVD oxide is plotted for comparison. The spectrum from the non-oxidizing UV cure process shows lower peak intensities for –OH and H-OH stretch peaks. For promoting densification, UV curing is also effective in breaking N-H bonds. The number of NH/NH 2 bonds is reduced with increasing UV power and a corresponding increase in Si-H bonding is observed. Figure 2 shows FTIR spectra of cured FCVD films treated with a subsequent steam anneal. The film with O 3 cure show more residual silanols (Si-OH) relative to UV cured films. Also, the -Si-O-Si- bonding peak is higher in UV cured films, suggesting a denser -Si-O-Si- network. During the steam anneal process, we observed that UV cured films densify more rapidly than O 3 cured films. For anneals at 500°C, a dense SiO 2 surface layer is formed, blocking further O 2 diffusion and leaving a less dense film below which has a higher wet etch rate (Fig. 3). This