A method for forming a ultralow dielectric constant layer with controlled biaxial stress is described incorporating the steps of forming a layer containing Si, C, O and H by one of PECVD and spin-on coating and curing the film in an environment containing very low concentrations of oxygen and water each less than 10 ppm. A material is also described by using the method with a dielectric constant of not more than 2.8. The invention overcomes the problem of forming films with low biaxial stress less than 46 MPa.