Abstract:
Most lithography techniques typically rely on repetitive processes of photoresist (PR) coating
(Multi-photoresist coating), exposure (Multi-exposure), development (Multi-development), and
etching (Multi-etching) as well as a utilization of costly detailed masks to produce a smaller and
higher density pattern. Although these tedious processes are time consuming, they are, in overall,
more cost effective compared to purchasing an advanced stepper system for a similar purpose.
This research thus aims to study the trimming lithography technique that is a time and cost saving
technique for pattern size reduction and pattern density and surface area enhancement. This
technique involves continuously multiple shifts of a target wafer associated with pre-defmed
multiple exposures under a single mask. The exposed film can later be developed in a single step. In
the experiment, the stepper with the resolution and the exposure wavelength of 0.5 um and 0.356
um respectively, are employed for multiple exposures on dense and isolated patterns Sumitomo
PFI-34A PR patterns with various linewidths.
It is shown that the dense and isolated patterns can be trimmed down successfully, especially for the
isolated pattern whose linewidth can be reduced from 0.8 um to 0.18 um and 0.14 um for dense and
isolated patterns respectively, which are in sub-resolution pattemning and sub-wavelengths
patterning. The line width and sidewall angle are well controlled; however, the PR thickness loss is
obvious and is believed to be enhanced by stronger interference and diffraction from smaller
openings. The pattern density and surface area of both dense and isolated patterns can also be
increased as expected; however, the actual patterns appear to deviate from the designed ones.
Therefore, the condition for multiple-exposures should be further refmed for practical applications.