Investigation for the structural stress of SiO2 thin films and its distribution on the large-wafer created by plasma enhanced chemical vapor deposition

Abstract

For a multilayered configuration of SiO2 film created by plasma enhanced chemical vapor deposition (PECVD), the thermal stress and growth-caused stress are two intrinsic stresses. In this work, based on the interactions of all the layers of film, a nonlinearly distributed structural stress over a large substrate is found. The numerical simulations for the nonlinear distribution of the structural stress and the uniform distributions of the two intrinsic stresses are carried out. As a result, the tensile structural stress decreases by ∼4x105MPa from center to edge of a 6” silicon wafer and the compressive growth-caused stress increases by ∼5x105MPa corresponding to the growth-rate increase of 40nm/s, which matches a ∼120MPa distribution of residual compressive stress obtained with in-situ measurements of film samples. In simulations, it is also discovered that the initial curvature of substrate has an impressive influence on the later grown film.

Study of Birefringence and Stress Distribution of SiO2 Film Optical Waveguide on Silicon Wafer

“…in Equations (13) and (14), both d i and E * i are the functions of radius r, so the key parameters t n and K f are certainly the functions of r. Therefore, from the definition model Equation 14of the structural stress of film, σ f ,thry is confirmed to be a function of r.…”

“…where δt is the time interval from the last sublayer to this grain-formed sublayer, ∆γ is the energy difference between the surface and grain boundary, L is the grain size, α is a constant depending on the deposition condition, δµ s is the increase in chemical potential of the surface because the film is not in equilibrium during deposition, Ω is the volume associated with adding an atom to the grain boundary, D is an effective diffusivity related to the rate of hopping from the surface into the triple junction, a is the normal size of the atom (same as the sublayer spacing), k is the Boltzmann constant, T is the absolute temperature, E i is the biaxial modulus of the i'th sublayer of film, and C s is a dimensionless concentration (fractional coverage) of mobile atoms on the surface that are free to make diffusive jumps into the triple junction. For the structural stress of a SiO 2 film, our theoretical model is based on the interactions among all the layers and the interaction in any layer is dependent on the radius on the wafer defined by [14]:…”

“…In our previous work, we found the structural stress of a multilayer coated thick SiO 2 film on a large wafer. The structural stress is originally formed by a deformation of the large multilayered wafer caused by the other two traditional stresses, the thermal stress and the growth-caused stress, but it is an independent stress and has a nonuniform distribution on the wafer from the center to the edge [14]. This progress has successfully explained why there is always a big discrepancy between the measured residual stress and the theoretically calculated sum of the traditional thermal stress and growth-caused stress defined by Chason.…”