Fabrication Processes for Capacity-Equalized Mold with Fine Patterns

Abstract

The variation of residual layer thickness (RLT) by the difference of pattern density is a difficult problem in UV nanoimprint lithography (NIL). A capacity-equalized mold was proposed to solve the problem, and the effectiveness of the concept was validated using a mold with various pattern sizes of hundreds of micrometers. However, the effectiveness should be evaluated at nanometer scales to prove the concept. Here the first challenge has been to fabricate and evaluate a two-step-depth mold with tens of nanometer patterns for the capacity-equalized mold. A two-step-depth mold with sub-100 nm patterns was fabricated by a combination of electron beam lithography and laser beam lithography. We succeeded in fabricating a two-step-structure with a width of around 40 nm, and the widths of the deeper grooves were found to have slightly increased during the second RIE process. The differences in widths were found to vary approximately from 10 to 30 nm. UV nanoimprint was carried out using the two-step-depth mold in order to examine its depth modulation, and to judge whether it could be applied to a NIL process, including a residual-layer-removal process. Fine patterns of 40 nm width were successfully transferred onto the underlying Si wafer from two-step-height resin patterns that were fabricated by UV nanoimprint.

Uniform Residual Layer Creation in Ultraviolet Nanoimprint Using Spin Coat Films for Sub-100-nm Patterns with Various Pattern Densities

“…We also developed a mold fabrication process for the two-step structures with sub-100-nm wide patterns using electron beam (e-beam) lithography and laser beam lithography. 22) In this work, a capacity equalized mold with sub-100-nm wide patterns was fabricated based on the developed processes and verified the applicability of the capacity equalized mold to UV nanoimprint in sub-100-nm dimensions.…”

“…In a previous study, a Cr film was sputtered by physical dry etching using CHF 3 gas. 22) In this study, the Cr etching method was replaced by a chemical dry etching (using Cl 2 and O 2 gases) through thin SiO 2 mask patterns. The SiO 2 thin film served as an etching mask in the Cr etching process to keep the grooves from becoming wider during the Cr dry etching using Cl 2 and O 2 gases.…”

“…In a previous study, the linewidth fabricated using a two-step-depth mold clearly varied according to the two-step structures. 22) However, we can now create lines with a constant linewidth using a capacityequalized mold even in the dimension less than 100 nm.…”

Chip-scale pattern modification method for equalizing residual layer thickness in nanoimprint lithography

“…The fabrication process of a two-step-depth quartz CE mold that utilizes electron beam (EB) lithography and self-alignment etching has already been published. 28) One of the key processes is the reuse of the etch mask utilized in the first etching step as a support mask for the second etching step. Therefore, the complexed second EB writing pattern can be simplified to a solid square area because all surfaces except patterned areas are protected by the etch-stop layer for the first etching step.…”

“…As an alternative, we have proposed the use of a capacityequalized (CE) mold, in which deeper complementary cavities are added to the original trench pattern areas to achieve a uniform pattern capacity per unit area throughout an entire mold with varying pattern density. [26][27][28][29][30][31][32] One of the key advantages of this method is that the pattern capacity can be equalized without changing the original pattern layout. To enhance the possibility of the industrial use of CE molds, we develop an automated design method using software programs, which is applicable to real device patterns where variations in pattern density and shape are severe.…”