Nuclear-magnetic-resonance characterization of doped SiO2 films used in integrated circuits

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Abstract
Phosphorus‐doped silicon dioxide dielectric films, prepared by plasma‐enhanced chemical‐vapor deposition at low temperature (400 °C), play a critical role in the reliability of very large scale integration devices. The phosphorus in the phosphosilicate glass (PSG) neutralizes the effect of mobile ion species and improves the glass flow, resulting in better gap filling and improved planarization. To extract the maximum contribution from this and other doped films (boron and germanium doped) in advanced sub‐0.5 μm complimentary metal‐oxide‐semiconductor technologies, it is necessary to understand dopant incorporation and the effects of variation in the exposure to water, dopant concentration, and high‐temperature annealing. An analysis of PSG by 1H, 29Si, and 31P solid‐state nuclear magnetic resonance establishes the chemistry of the phosphorus dopant incorporation and the effect of moisture on the glass structures. Exposure to water results in a depolymerization of the PSG structures and a concurrent decrease in the crosslink density of the glass network. Similar concentrations of silanols are observed in both doped and undoped samples of SiO2. An increase in silanol concentration is found in P‐doped glass after exposure to moisture in air. The level of exposure to water will determine the extent of structural changes in the dielectric film. Variations in this exposure can be expected to produce variability in the glass flow and other properties of the dielectric.