Applications of a low contact force polyimide shank bolometer probe for chemical and biological diagnostics

Abstract

This paper reports on the detection of nano-scale chemical variations in photosensitive polymers and biological variations in cancerous tumor cells that have been accomplished for the first time using scanning thermal probes that we have developed. It also reports on changes that have been made over older versions of this probe to help achieve these capabilities. The probe is fabricated by a 6-mask surface micromachining process using polyimide as the structural material. A unique assembly sequence that involves flipping over the probe accommodates the future integration of circuitry on the same substrate. The probe has measured spring constant 0.082 N/m for a 250μm×50μm×3 μm probe. It offers a tip diameter of 50 nm. Probes are used to study exposed but undeveloped photoresist latent images in features of 70 nm, the acid diffusion in chemically amplified photoresist during post exposure bake, and HeLa cells. Lateral spatial resolution of <50 nm, topographic resolution of <1 nm and thermal resolution of <1.2 mK are demonstrated. Wet scanning capability, which widens the possibility of biochemical applications, is also demonstrated for the first time. The structure, fabrication, and assembly of the probe and the interface circuit used for these experiments are described.