Study on the Pulse Phase Lag Effect on Two Mask Holes During Plasma Etching

The charging effect seriously limits the quality of the pattern transfer from a mask onto the etched material in the plasma etching. This work investigated the effect of the pulse phase lag (sometimes called phase lag for short) of the dual-frequency pulsing between the bias power (2 MHz) and the source power (60 MHz) on the charging issue on the surface of two adjacent and asymmetrically-shaped mask holes based on a reliable modeling framework. This work first verified that various phase lags (0 to 180°) can result in different distributions of the electric-field (E-field) and the net charge density on the mask surface. Then next shows that the mask profile presents an increased deformation as the phase lag increases. The effect of the fluorocarbon passivation generated during the source pulse off-time was involved in the simulation of the profile evolution. In addition, the number of ions passing through the opening of these two mask holes varying with the phase lag was also examined, which shows an increasing trend with decreased pulse phase lag. These conclusions shed new light on the approach to reduce the mask damage and improve the high aspect ratio etching.