We propose a scheme for generating pairs of de‐correlated photons in silicon nanowire waveguides. By properly engineering the geometrical dispersion of nanoscale waveguides we achieve both four‐wave‐mixing and group velocity matching. Factorable pure photon states are found that do not require spectral filtering. Highly anti‐correlated two‐photon states can be realized far from the Raman background of the waveguide. Our results hold promise for the realization of an integrated single photon source.