Structural and Strain‐Related Effects during Growth of SiO2 Films on Silicon

Abstract

We analyze various aspects of the stress/strain present at the normalSi/SiO2 interface during the growth of the oxide which arise from the volume change associated with the transfer of Si atoms from the substrate to the oxide. This volume change is so high (126%) that it cannot be accommodated simply by elastic strain. Previously suggested viscoelastic stress relief models are incompatible with several experimental observations, require unrealistically low viscosity values, and have a number of conceptual difficulties. Analyzing the situation from a structural/chemical point of view, we suggest that structural effects are of primary importance during growth. According to our model the noncrystalline SiO2 film grows on silicon with a high degree of short range order because of the influence of the crystalline substrate. The oxide near the interface resembles some high density crystalline polymorph of SiO2 , e.g., coesite; hence, this is a quasi‐epitaxial growth process. During subsequent growth, annealing takes place which results in a pseudo‐polymorphic transformation of the oxide to a lower density structure in a manner similar to the decompaction of pressure compacted silica glass. Structural rearrangement occurs preferentially normal to the interface, may involve variations in local conformations of the very flexible noncrystalline structure, and results in substantial accommodation of the oxidation strain. Stress relief can also occur on the silicon side of the interface by structural rearrangement in the upper layer of silicon atoms and/or by plastic flow. The latter could occur when the strain rate associated with oxide growth at a given temperature is so high that the yield point of silicon is exceeded.

Effect of physical stress on the degradation of thin SiO/sub 2/ films under electrical stress

“…By investigating the oxide etch rates in dilute HF, they showed that the interface stress in oxides grown in dry O is higher than those grown in pyrogenic steam. We attribute this to the fact that the viscosity of OH-containing SiO is about two orders of magnitude less than that of dry SiO [49]. An oxide with a lower viscosity results in a lower film stress and therefore a higher .…”

“…All the trends of furnace and RTP oxides in the previous section can be explained by examining the role of physical stress at the SiO /Si interface. During the thermal growth of SiO , there is a 128% volume expansion from Si to SiO [25], and therefore the SiO film is compressed. The newly formed SiO pushes the previously grown SiO upwards.…”

Electron beam induced conductivity in polymethyl methacrylate, polyimide, and SiO2 thin films

“…3 The thickness of this interfacial layer is on the order of 1 nm. However, the interface between a deposited oxide film and the underlying silicon is not nearly as perfect as that formed by thermal oxide.…”

Coupled mechanical-oxidation modeling during silicon thermal oxidation process

“…It has been observed that the uppermost one or two layers of silicon atoms beneath the silica scale were displaced up to about 0.015 nm (6.5%) from their lattice positions. 42 As mentioned above, the strains in the silica layer and silicon substrate are respectively due to elastic deformation and creep deformation. In such a case, the lattice of the silica scale is not obviously altered while the number of silicon atoms is changed, leading to the server deformation of the silicon lattice near the Si/SiO 2 interface.…”