Real-time studies of surface roughness development and reticulation mechanism of advanced photoresist materials during plasma processing

Abstract

Surface roughness development of photoresist (PR) films during low pressure plasma etching has been studied using real-time laser light scattering from photoresist materials along with ellipsometric and atomic force microscopy (AFM) characterization. We show that evolution of the intensity of light scattered from a film surface can be used to study the development of surface roughness for a wide range of roughness starting from subnanometer to few hundred nanometers. Laser light scattering in combination with ellipsometry and AFM is also used to study the reticulation mechanism of 193 and 248 nm PRs during argon plasma processing. We employ a three-layer model (modified layer, rough layer, and bulk film) of the modified PR surface (193 and 248 nm PRs) to simulate and understand the behavior of ellipsometric Ψ-Δ trajectories. Bruggeman’s effective medium approximation is employed to study the roughness that develops on the surface after reticulation. When the glass transition temperature of the organic materials is reached during Ar plasma processing, the PR films reticulate and roughness develops rapidly. Roughness development is more pronounced for 248 nm PR than for 193 nm PR. Simulation of Ψ-Δ shows that the growth of roughness is accompanied by strong expansion in the materials, which is stronger for 248 nm PR than 193 nm PR. The leading factors responsible for reticulation are found to be compressive stress that develops in the modified surface layer as it is created along with strong molecular chain motion and expansion of the material when the temperature is increased past the glass transition temperature. Reticulation leads to a significantly different surface morphology for 248 nm PR as compared to 193 nm PR and can be related to differences in molecular structure and composition leading to different responses when a modified surface layer is formed by ion bombardment accompanying plasma etching.

Understanding the Roughening and Degradation of 193 nm Photoresist during Plasma Processing: Synergistic Roles of Vacuum Ultraviolet Radiation and Ion Bombardment

“…The characteristic buckling wavelength of 193 nm PR surface roughness resulting from plasma exposure above the T g in the presence of ion bombardment has also been studied 46. This roughness is on the order of micrometers and results in reticulation, a phenomenon that is not encountered in the present study.…”

Relationship between nanoscale roughness and ion-damaged layer in argon plasma exposed polystyrene films

“…UV-sensitive polymers show increased postplasma etch surface roughness compared to UV-insensitive polymers such as PS. 5,9 From wrinkling theory, a reduced underlayer elastic modulus would increase the magnitude of wrinkling that occurs during formation of the highly stressed, modified layer by ions. We suspect that the observed plasmagenerated UV damage 5,48 in UV-sensitive polymers ͓i.e., 193 nm PR, 5 poly͑␣-methylstyrene͒ 17 ͔ reduces their underlayer modulus and is responsible for the enhanced surface roughness compared to UV-insensitive polymers ͑i.e., 248 nm PR, 5 PS͒ observed under simultaneous ion bombardment and UV exposure.…”

“…This behavior has been observed in many types of polymers ͓e.g. poly͑methyl methacrylate͒ ͑PMMA͒, 8 193 and 248 nm photoresists 5,6,9,10 ͔ and has been described as a thin, highly crosslinked and graphitized layer. [4][5][6][11][12][13][14][15][16] We have previously shown that under energetic Ar + ion bombardment during plasma etching, a dense, amorphous carbonlike modified layer is formed at the surface of a wide range of polymers ͓polystyrene ͑PS͒, poly͑␣-methylstyrene͒, poly͑4-methylstyrene͒, PMMA, poly͑hydroxyadamantyl acrylate͒, and poly͑hydroxyadaman-tyl methacrylate͔͒ with a thickness of a few nanometers.…”

Validation of etching model of polypropylene layers exposed to argon plasmas

“…The plasma–material interactions were explored in this study using an ICP system (Figure a). Such a reactor has been thoroughly described elsewhere . Briefly, the plasma was induced in the vacuum chamber by powering a planar, water‐cooled brass coil, located on top of a quartz window, through an L‐type matching network with a power supply at a frequency of 13.56 MHz.…”