Low dielectric constant silicon dioxide sandwich layer

Claim 1

A method for forming a composite dielectric layer with a selected composite dielectric constant on a semiconductor substrate having conductive lines defining a narrow gap, the method comprising the steps of: forming a first layer on the substrate and over the conductive lines using a plasma-enhanced chemical vapor deposition (PECVD) process combining reactants including TEOS, oxygen and a fluorine-containing compound, said first layer characterized by a first dielectric constant of less than about 4.0 and a first selected thickness sufficient to create compressive stress in said first layer and to partially fill the narrow gap between the conductive lines; and forming a second layer over said first layer using a non-plasma-enhanced, subatmospheric chemical vapor deposition (SACVD) process combining reactants including TEOS and one of oxygen and ozone, said second layer characterized by a second dielectric constant of about 4.0 or greater and a second thickness, wherein said first selected thickness is less than said second thickness and said first selected thickness and said second thickness are sufficient to produce a composite layer with the selected dielectric constant, said composite layer filling the gap between the conductive lines.

Claim 2

A method for forming a composite dielectric layer with a selected composite dielectric constant on a semiconductor substrate having conductive lines defining a narrow gap, the method comprising the steps of: forming a first layer on the substrate and over the conductive lines using a plasma-enhanced chemical vapor deposition (PECVD) process combining reactants including TEOS, oxygen and a fluorine-containing compound, said first layer characterized by a first dielectric constant of less than about 4.0 and a first selected thickness sufficient to create compressive stress in said first layer and to partially fill the narrow gap between the conductive lines; and forming a second layer over said first layer using a non-plasma-enhanced, subatmospheric chemical vapor deposition (SACVD) process combining reactants including TEOS and one of oxygen and ozone, said second layer characterized by a second dielectric constant of about 4.0 or greater and a second thickness, wherein said first selected thickness is less than said second thickness and said first selected thickness and said second thickness are sufficient to produce a composite layer with the selected dielectric constant, said composite layer filling the gap between the conductive lines.