Damage of Low-k and Ultralow-k Dielectrics from Reductive Plasma Discharges Used for Photoresist Removal

Hydrogen-containing plasma discharges, used to remove photoresist in integrated circuit manufacturing, are compared for their damaging effect on porous ultralow- dielectrics. Such reductive ash processes studied are (A) a low- pressure chemistry, reactive ion etch (RIE)-type discharge; (B) a high-pressure chemistry, RIE-type discharge; and (C) a high-pressure remotely generated discharge. Two porous SiOCH dielectrics of differing porosity and values 2.5 and 2.2 are used in this comparative study. Diagnostic methods used for film analysis include Fourier transform infrared spectroscopy, thermal desorption spectroscopy, density, and -value measurements. Both RIE ash processes (A) and (B) were found to cause significant dielectric damage through film densification, loss, water gain, and dielectric constant increases. Film damage is noted to be more severe for the higher porosity film. In contrast, all measured parameters for both dielectric films showed low damage with use of the remotely generated discharge. Positronium annihilation lifetime spectroscopy is employed in this work to show pore collapse and surface densification with use of either RIE reductive ash.