AVS 52nd International Symposium
    Thin Films Wednesday Sessions
       Session TF-WeA

Paper TF-WeA2
PECVD Silicon Nitride Nucleation Kinetics Impact on Device Scaling

Wednesday, November 2, 2005, 2:20 pm, Room 306

Session: Fundamentals of Thin Films
Presenter: A. Raviswaran, Cypress Semiconductor
Authors: A. Raviswaran, Cypress Semiconductor
P. Keswick, Cypress Semiconductor
Correspondent: Click to Email
Plasma enhanced chemical vapor deposition of silicon nitride is a commonly used process in the microelectronics industry for etch stop and passivation layers. As the device dimensions continue to shrink along Moore's law, the silicon nitride thickness is also reduced to meet device requirements. So controlling the silicon nitride thickness and stoichiometry is critical as the gate length and contact width are affected by the thickness and etch rate of the silicon nitride layer used as etch-stop. The current study helps understand the initial stages of nucleation and growth of the PECVD silicon nitride and contributes significantly to better controlling the deposition of very thin silicon nitride layers used in device fabrication. Silicon nitride films with thickness ranging from 37 Å (deposition time of 1 sec) to 450 Å was deposited on Si wafers at 400 °C. Spectral data collected using an ellipsometer shows that as the thickness of the film increases, a transformation is observed in the spectral profile at about 200 Å thickness. AFM, SEM and cross section TEM show that the films are continuous (no 3D cluster growth) at 37 Å. In contrast to reports on LPCVD silicon nitride, the PECVD nitride deposition rate is found to increase with a reduction in deposition time and does not show an incubation time. The refractive index of these films is found to increase with a decrease in film thickness. XPS analysis shows that the thinner films are silicon rich. The 85 Å film with RI of 2.17 has a Si/N ratio of 0.947 and the 340 Å film with RI of 1.95 has a Si/N ratio of 0.928. Evaluation of hydrogen in the film by FTIR and HFS (in progress) will further help understand the impact of hydrogen on the nucleating film properties. The nucleation of a 2D Si-rich layer is attributed to high PECVD deposition rate (relative to surface diffusion) and lower bond strength of Si-H relative to N-H bonds in the reactant gases.