Embodiments described herein relate generally to methods for forming low-k dielectrics and the structures formed thereby. In some embodiments, a dielectric is formed over a semiconductor substrate. The dielectric has a k-value equal to or less than 3.9. Forming the dielectric includes using a plasma enhanced chemical vapor deposition (PECVD). The PECVD includes flowing a diethoxymethylsilane (mDEOS, C5H14O2Si) precursor gas, flowing an oxygen (O2) precursor gas; and flowing a carrier gas. A ratio of a flow rate of the mDEOS precursor gas to a flow rate of the carrier gas is less than or equal to 0.2.