Evaluation of chemical kinetics in positive photoresists using laser desorption ionization

Abstract

Positive photoresists are photosensitive materials widely used in lithographic processes in microelectronics and optics for component relief manufacturing. When exposed to ultraviolet radiation, chemical reactions are induced that modify their physical–chemical properties. This work describes a novel technique to determine the kinetic rates of molecular structure changes of the positive AZ series photoresists after exposure to mercury arc lamp radiation. These positive photoresists consist of a photoactive compound (PAC), known as diazonaphthoquinone (DNQ), and a matrix material, which is a thick base resin. This positive AZ series photoresist was chosen because its technical information is well known while presenting potential for many applications. In the present work, we investigate these processes using laser desorption ionization (LDI) by a pulsed ultraviolet laser coupled to a high resolution time-of-flight mass spectrometer (ToF-MS). The LDI-ToF mass spectra present different relative intensities for some of the characteristic negative molecular ions of the positive photoresist after different exposure energies to the mercury arc lamp radiation. For measurement of the chemical kinetic mechanism, LDI-ToF mass spectrometry was used for the first time to obtain the fractional decay rate of the DNQ per unit of exposure radiation intensity. These results provide a novel use of LDI-ToF-MS to study the chemical kinetics of photosensitive materials.