A Method for Estimating the Filling Rate of the Mold Cavity in Nanoimprint Lithography

When the dimensions of a microelectronic structure decrease, high manufacturing costs are inevitable. A low cost and high throughput manufacturing technique for nanostructures is desired. Nanoimprint lithography involves patterning the resist through physical deformation by using a mold at nanoscale and has the potential to meet these expectations. Therefore, nanoimprint lithography has been extensively studied in recent years. Many real time measurements have been proposed for enhancing the yield of nanoimprint lithography. Among these measurements, the application of surface plasmon resonance has the advantage of quick, highly accurate analysis. In surface plasmon resonance application, the mold contains a gold film for exciting surface plasmon resonance and an adhesion layer is applied to both sides of the gold film to increase the lifespan of the mold. However, the effect of the geometric characteristics of the adhesive layer on the surface plasmon resonance spectrum and the mechanical strength of the mold has not been extensively studied. To improve the detection accuracy and reliability of the measurement, this study investigated the aforementioned effect. Analytical and experimental investigations confirmed that the shape of the spectrum is influenced by the surface roughness and thickness of the titanium adhesion layer. To maintain the sharpness of the resonance dip, we suggest reducing the thickness of the titanium adhesion layer to below 6 nm and maintaining the surface roughness below 3 nm. Moreover, the proposed mold structure conforms to these requirements and is applied to estimate the filling rate. The measurement results demonstrate that the surface plasmon resonance spectrum is clearly affected by the mold filling. Specifically, the change in the surface plasmon resonance spectrum curve and resonance angle can indicate the quality of the imprinted pattern. This study demonstrates the effectiveness and high sensitivity of the proposed technique for estimating the filling rate of the mold cavity in nanoimprint lithography.