This paper presents studies of the infrared (IR) absorbance and the intrinsic stress in thermally grown very thin films (60 to 700 Å) of SiO2. These data are combined with previously obtained data for thicker thermally grown films (∼1300 Å) to study the variation in intrinsic growth stress close to the Si/SiO2 interface. The combined data indicate that the intrinsic stress at Si/SiO2 interfaces extrapolates to the same relatively high values for oxides grown at 700 and 1000 °C, and that the distribution of Si–O–Si bond angles close to the Si/SiO2 interface, as deduced from the IR data, is quantitatively different than in the bulk of the oxide film. These two observations are explained in terms of a model based on a temperature dependent viscoelastic relaxation of the oxide stress. This model emphasizes differences in the thermal history of the SiO2 near the Si/SiO2 interface, as compared to the SiO2 that is well removed from that interface and is in the bulk of the film and/or close to the ‘‘top’’ surface of the film. The observed differences between the 700 and 1000 °C bulk oxides, and the associated Si/SiO2 interfaces are explained in terms of a renormalized time scale that is defined by the ratio of the growth time to the viscoelastic relaxation time at the growth temperature.

Articles you may be interested inInherent interface defects in thermal (211) Si / SiO 2 : 29 Si hyperfine interaction AIP Conf.This paper reports on a study of the intrinsic stress and strain in thin films ofSi0 2 prepared by the thermal oxidation of crystalline silicon. We focus on the relationship between the inhomogeneity of thin-film properties and the thermal history of the oxide film, including both film growth and thermal annealing. We show that this film can be inhomogeneous in the sense that oxide formed initially at the silicon-silicon dioxide (Si/Si0 2 ) interface has been annealed at the growth temperature for the time required for film growth, whereas newly formed oxide at the growth interface has not been annealed for any appreciable period. We demonstrate that thermal annealing cannot completely remove the thickness dependence in the strain induced by the mismatch between the molar volumes of silicon and silicon dioxide at the growth interface, subject to constraints introduced by the chemical bonding structure at that interface. Based on laser-beam deflection and photoreflectance measurements, we show that there is always a substantial residual intrinsic interfacial stress, and that is independent of the growth temperature, and thermal annealing. A time scale for describing thermal relaxation of stress and strain profiles is given by the ratio of process time to the viscoelastic relaxation time at the processing temperatures.

Selective silicon processing at 775 and 850~ using an SiH2C1JHC1/H2 based chemistry was studied. The selectivity of 2 each experimental condition was quantified by measuring the silicon nuclei density/cm on large blanket areas of SiO2. The morphology of the selective silicon films was examined for texture and hillocks. The roles of water vapor and atomic hydrogen on the microchemistry of an SiO2 surface was investigated. Thermodynamic modeling of the effect of different atmospheric leak rates on the water vapor and atomic hydrogen concentrations was carried out with the aid of the SOLGAS program. A new understanding of selectivity is proposed. An SiO2 surface is an interruption of the bulk continuous random network structure and, as such, has a characteristic density of defect sites. The degree of selectivity observed is determined by the type of species which terminate these defect sites, i.e., by the number of defect sites which are not chemically passivated against the adsorption of silicon species. A universal selective silicon processing regime is predicted and good agreement with a wide range of published selective silicon processes is shown.

Correlations between midgap interface state density (Dit) and thickness-averaged stress in thermally grown SiO2 thin films have been investigated by infrared spectroscopy, an optical beam deflection technique, and capacitance-voltage measurements. We find no correlations between Dit and either (i) the maximum stress in the Si or SiO2 at the Si/SiO2 interface or (ii) the stress gradient in the SiO2 film. By direct measurements of the strain-induced bending of the Si wafer, and by calculating the microscopic strain from the SiOSi bond-stretching vibrational frequency, we have established linear relationships between Dit and the thickness-averaged stress and strain in the oxide.

We have studied selected structure-dependent properties of thin films of SiO2 prepared by remote plasma-enhanced chemical vapor deposition (remote PECVD) and thermal oxidation of crystalline silicon, and have identified process-dependent differences in their local atomic structures. We have determined the frequency ν and linewidth Δν of the Si–O bond-stretching infrared-active vibration near 1075 cm−1, and have found that all relatively thick oxide films, t>1000 Å, prepared by either of these two techniques display the same linear relationship between Δν and ν. This behavior has been interpreted in terms of a central force model that gives the average bond angle 2θ at the oxygen atom sites, and attributes the linewidth to a distribution of vibration modes associated with a ±30° spread in 2θ. We have determined that (i) in remote PECVD films deposited at temperatures (Ts ) between 200 and 350 °C, 2θ varies between 140° and 144°; (ii) in thermal oxides grown over a temperature range (Tox ) between 800 and 1150 °C, 2θ varies from about 147° to 150°; and (iii) in thick oxide films, independent of the preparation method, Δθ/θ is equal to 0.21±0.01. We have compared other oxide properties as well: (a) the optical index of refraction n at 632.8 nm, (b) the intrinsic stress σi, and (c) the etch rate in buffered HF (6:1). In addition, we discuss the electronic properties of remote PECVD and thermally grown SiO2 films in metal–oxide–semiconductor (MOS) structures, where we have observed that the same device quality MOS properties can be obtained in structures employing both types of oxide films. Finally, we compare stress and strain in the remote PECVD and thermal oxides in the immediate vicinity of the Si/SiO2 interface, and the bulk of the oxide films, and correlate the differences we observe with fundamental differences in the two thin-film formation processes.