An impact of the layer-by-layer deposition method on forming the stoichiometric and conformal Cat-CVD SiN is presented. A Si-rich but conformal Cat-SiN thin film deposited with an NH3-deficient gas mixture of SiH4/NH3/H-2 is used as the unit layer for the layer-by-layer Cat-CVD, with each layer followed by in-situ post-treatment in an NH3-and/or H-2 ambient to cure the composition. To retrieve the stoichiometry, the in-situ Cat-H-2 treatment is of critical importance rather than the direct post-nitridation by the in-situ Cat-NH3 treatment. The film formation recipe properly engineered with respect to the thickness of unit layer and to the content of post-treatment gives a layered thick conformal Cat-SiN film having the stoichiometry, with the refractive index, being close to 2.000 and below. (c) 2005 Elsevier B.V. All rights reserved.