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Organosilicate glasses, also known as carbon-doped oxides (CDO), have been studied for application as interlayer dielectrics in microprocessors. Fourier-transform infrared (FTIR) spectroscopy is used here to monitor CDO film compositions prepared by plasma-enhanced chemical vapor deposition of dimethyldimethoxysilane. The Si–CH3/Si–O peak area ratios represent the relative content of these functional groups within the films, and indicate compositional changes in the films produced. Additionally, a close inspection of the C–H stretching modes shows a large peak at 2962 cm−1 due to the CH3 asymmetric stretch and a smaller shoulder to the right, made up of up to three other C–H stretching modes. The shoulder intensity divided by the asymmetric stretch intensity provides another metric that tracks compositional changes in the film. Product compositions indicated by FTIR also correlate well with physical properties such as dielectric constant, hardness, bulk modulus, and cohesive strength.

A technique for the measurement of brittle thin film toughness has been developed. It is based on the mechanics of channel cracking in thin films. Dielectric films including CVD silicon oxide and silicon nitride films were studied using this technique. To prevent channel cracks from propagating into silicon substrates, an aluminum layer was deposited prior to the deposition of the dielectric layer. By using a specially made bending fixture, the cracks were observed in situ when the samples were subject to well controlled stresses. It was observed that for each film, a well defined critical film stress level existed, beyond which the crack velocity accelerated very rapidly. The critical film stresses were obtained by superposition of the critical applied stresses and the residual stresses in the films due to deposition and thermal expansion mismatch. It was shown that this technique was highly consistent in critical stress measurement. A simple shear-lag model was used to obtain the film toughness values using the measured critical film stress data.

Silicon nitride thin films used for transistor spacer are usually under large tensile residual stresses. When a film is thick enough, it can crack by channel cracking mechanism. The toughness of these films, used in models for failure criteria, can be obtained by determining the critical thickness for channel cracking of blanket films with known residual stresses. However, depositing films of a range of different thickness to determine the critical thickness is tedious, and this process also introduces risks of producing particles in the deposition chamber when the film exceeds the critical thickness. An alternative technique is to deposit films of thickness below critical thickness and then to apply additional tensile stresses to the film by bending the substrate. A critical film stress can be determined for channel cracking from which the film toughness is obtained. This paper describes the experiments performed for a new SiN film and presents the results.

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