Methods are described for forming and curing a gapfill silicon-and-carbon-containing layer on a semiconductor substrate. The silicon and carbon constituents may come from a silicon-and-carbon-containing precursor excited by a radical hydrogen precursor that has been activated in a remote plasma region. Exemplary precursors include 1,3,5-trisilapentane (H3Si—CH2—SiH2—CH2—SiH3) as the silicon-and-carbon-containing precursor and hydrogen (H2) as the hydrogen-containing precursor. The hydrogen-containing precursor may also be a hydrocarbon, such as acetylene (C2H2) or ethylene (C2H4). The hydrogen-containing precursor is passed through a remote plasma region to form plasma effluents (the radical hydrogen precursor) which are flowed into the substrate processing region. When the silicon-and-carbon-containing precursor combines with the plasma effluents in the substrate processing region, they form a flowable silicon-carbon-and-hydrogen-containing layer on the semiconductor substrate.