Water sorbability of low-k dielectrics measured by thermal desorption spectroscopy

With the aim of collecting information for a reliability database, a method of quantitatively determining the amount of water that adsorbs on dielectric films was established that employs thermal desorption spectroscopy (TDS). The issues of measurement repeatability and the stability of the background level were examined, and a noble dehalogenation treatment was developed to improve these factors. In this study, the amount of water that adsorbs on SiLK∗ resin (∗Trademark of The Dow Chemical Company) and on porous silica film was measured and compared with values for p-TEOS and wet thermal SiO2 films. Samples stored in air in a clean room, stored in air with a relative humidity of 100%, and subjected to pressure-cook treatment were investigated by TDS. Reflecting the strong affinity to water, the amount of water that adsorbed on porous silica and p-TEOS films after pressure-cook treatments were 49 × 1016 and 30 × 1016 molecules/cm2, respectively. In contrast, the amount for SiLK resin was only 8 × 1016 molecules/cm2, which is very close to 6 × 1016 molecules/cm2 for thermally grown SiO2. These differences in water sorbability are discussed based on the chemical and physical properties of the materials.