Methods for depositing silicon-containing thin films on a substrate in a reaction space are provided. The methods can include vapor deposition processes comprising at least one deposition cycle including sequentially contacting the substrate with a silicon precursor comprising a halosilane and a second reactant comprising an acyl halide. In some embodiments a Si(O,C,N) thin film is deposited and the concentration of nitrogen and carbon in the film can be tuned by adjusting the deposition conditions.