Lower Temperature and Shorter Curing Time of Methylsilsesquioxane for Application as a Dielectric

Spin-on dielectrics such as spin-on-polymer or spin-on-glass are used as intermetal dielectrics for isolation of metal lines in a semiconductor CMOS device. The customer had a problem of high RC delay, resulting in a poor performance.

200 mm p-type Si(100) wafer was first sent for RCA clean to remove any light organic residue, particles and metallic species. A 200A thermal oxide was grown on the substrate in an O2 / H20 ambient. Methylsilsesquioxane SOP was spin coated to a thickness of 4500 A. The SOP coated wafers underwent a baking sequence of 180 C, 200C and 250C with 1 minute duration each. The curing ambient is N2. Then the film was cured at 400C, 425C and 450C. The shrinkage was found to be 2%,5.6% and 8.4% respectively. The curing time was 1 hour. The dielectric constant was 2.44 at 450C. Then it was decided that the curing temperatures will be lowered and the time shortened. So data were collected for 350C and 375 C curing temperature and for curing time of 1 / 2 hour and 1 hour. Best result was obtained for 350C curing temperature and 1 / 2 hour curing time. The dielectric constant obtained was 2.4. The corresponding thickness shrinkage was 1.8%. The FTIR spectra has absorption at 2978 / cm (asymmetric CH3 stretch), 1275 / cm (Si-CH3 stretch), 1133 / cm and 1030 / cm (Si-O-Si) and 780 / cm Si-CH3). Lower curing temperature and time did not change the internal chemical structure of cured methylsilsesquioxane. Therefore, a baseline curing recipe with curing profile of 350C and 1 / 2 hour was optimized and recommended to reduce the thermal budget . This also reduced RC delay and improved the performance of the device.

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