Nanometer resolution excimer laser ablat ion of thin polymer films

Abstract

An attractive aspect of excimer laser ablation of polymers is the ability to precisely control the depth to which material is removed by controlling the number of laser pulses. Recent work by the authors has shown that greater control of layer thickness (nanometer resolution) can be achieved when ablating sub-micron thick layers of polymers. This effect of improved depth control is presented for 1 µm thick SU-8 photoresist, and n-heptylamine plasma polymers (HAPP). The ablation process of HAPP shows such control that 90nm thick films were ablated to leave a uniform film of 1.5 nm thickness on a silicon wafer substrate. In both cases the minimum feature size reliably resolved was 2 µm in width. The threshold of ablation for SU-8 and HAPP occur at 50mJ/cm2 and approximately 100mJ/cm2 respectively.A model is also presented, which shows that the observed reduction in etch rate that occurs as the polymer film thickness decreases is a result of the thermal properties of the substrate material.An attractive aspect of excimer laser ablation of polymers is the ability to precisely control the depth to which material is removed by controlling the number of laser pulses. Recent work by the authors has shown that greater control of layer thickness (nanometer resolution) can be achieved when ablating sub-micron thick layers of polymers. This effect of improved depth control is presented for 1 µm thick SU-8 photoresist, and n-heptylamine plasma polymers (HAPP). The ablation process of HAPP shows such control that 90nm thick films were ablated to leave a uniform film of 1.5 nm thickness on a silicon wafer substrate. In both cases the minimum feature size reliably resolved was 2 µm in width. The threshold of ablation for SU-8 and HAPP occur at 50mJ/cm2 and approximately 100mJ/cm2 respectively.A model is also presented, which shows that the observed reduction in etch rate that occurs as the polymer film thickness decreases is a result of the thermal properties of the substrate material.