Hardening process for plasma deposited planar amorphous carbon films used in bilayer resists

A dry planarization process has been developed to produce planar amorphous carbon (a-C:H) films. These films provide a high degree of planarization over large distances, and they can be deposited at room temperature with low ion bombardment energy (10 V) and high deposition rate (300 nm/min). Depending on the deposition conditions and subsequent processing requirements, a hardening step may be needed. Various degrees of hardness can be obtained by heating the samples and/or exposing them to a low-power plasma. One effective hardening process is to expose the films to a low-power N₂ discharge (5-mW/cm² RF power and -10-V DC bias voltage) at 150°C and 500 mtorr for 30 min. Excimer laser projection lithography has been used to define submicrometer patterns in bilayers which consist of a wet or dry deposited inorganic photoresist applied on top of the planarization layers.