A composite layer of low k silicon oxide dielectric material is formed on
an oxide layer of an integrated circuit structure on a semiconductor
substrate having closely spaced apart metal lines thereon. The composite
layer of low k silicon oxide dielectric material exhibits void-free
deposition properties in high aspect ratio regions between the closely
spaced apart metal lines, deposition rates in other regions comparable to
standard k silicon oxide, and reduced via poisoning characteristics. The
composite layer of low k silicon oxide dielectric material is formed by
depositing, in high aspect ratio regions between closely spaced apart
metal lines, a first layer of low k silicon oxide dielectric material
exhibiting void-free deposition properties until the resulting deposition
of low k silicon oxide dielectric material reaches the level of the top of
the metal lines on the oxide layer. A second layer of low k silicon oxide
dielectric material, having a faster deposition rate than the first layer,
is then deposited over the first layer up to the desired overall thickness
of the low k silicon oxide dielectric layer. In a preferred embodiment,
the steps to form the resulting composite layer of low k silicon oxide
dielectric material are all carried out in a single vacuum processing
apparatus without removal of the substrate from the vacuum apparatus.
