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

• Published in: Meeting abstracts (Electrochemical Society) Vol. MA2016-02; no. 27; p. 1835
• Main Authors: Mehta, Sanjay C, Conti, Richard, Devarajan, Thamarai, Wright, Matthew P, Yao, Yiping, Cohen, Stephan A, Ryan, Todd, Haigh, Thomas J, Hall, Paul, Canaperi, Donald F, Tai, Leo
• Format: Journal Article
• Language: English
• Published: 01.09.2016
• ISSN: 2151-2043; 2151-2035
• DOI: 10.1149/MA2016-02/27/1835

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 effect is evident in Fig. 4a where FCVD oxide has been recessed using an etching technique. The oxide between fins is weaker and has recessed more than the oxide in the field region outside of the array (see reference lines). A two-step steam anneal was then developed to achieve uniform properties through film depth: 400°C for 1 hour followed by 500°C for 2 hours. Fig 4b shows a structure with oxide annealed in this way and then recessed through etching; it was observed that the recess is now equivalent in the field and between fins. The impact of UV power on the cure process was also explored. Fig. 5 shows the WERR as a function of thickness for blanket O 3 cured FCVD films and UV cured films after steam anneal. The UV cure again shows significantly lower WERR compared to O 3 cure, with more densification and improved film uniformity through depth with increased power. Fig. 6 compares cumulative electrical breakdown behavior for O 3 cured and UV cured films after steam anneal obtained using MIS structures. The UV cured films show a higher breakdown voltage (V bd ~10MV/cm) relative to O 3 cured films (~9MV/cm). Fig. 7 is a comparison of WERR between O 3 cured film and UV cured film inside the narrow STI Trench Features. The films were steam annealed followed by 2x900°C-1min soak RTA in N 2 . Data shows 30% lower in-trench WERR for UV cure compared to O 3 cure. In conclusion, UV cure has been demonstrated as a means to provide improved FCVD quality over O 3 cure as measured by wet etch rate ratio, in blanket films and within trenches for STI applications. This work was performed by the Research Alliance Teams at various IBM Research and Development Facilities. Figure 1