Mechanism of flat band voltage shift of organic material with low dielectric constant for ULSI interconnection

The flat band voltage shift (FBVS) and the variation of the chemical properties due to the backend process of the multilevel interconnection have been investigated by FTIR, thermal desorption mass spectrum (TDMS), and electrical CV measurement. The swelling reaction is the mechanism and key effect on the post-etching clean process which enhances the moisture content of an organic film with low dielectric constant. It is proposed that H2O and hydrogen ion should be the essential elements for the current leakage and FBVS. The substrate bias introduced from the PECVD process was employed to identify and establish the FBVS mechanism. It is concluded that the polarization and ion migration have the most important effect on FBVS at a temperature over 200 °C and room temperature, respectively. Any thermal process on the as-cured low-k film should be limited at a temperature as low as possible to avoid enhancing the hydrogen ion.