Effects of vacuum ultraviolet photons, ion energy and substrate temperature on line width roughness and RMS surface roughness of patterned 193 nm photoresist

Abstract

We present a comparison of patterned 193 nm photoresist (PR) line width roughness (LWR) of samples processed in a well characterized argon (Ar) inductively coupled plasma (ICP) system to RMS surface roughness and bulk chemical modification of blanket 193 nm PR samples used as control samples. In the ICP system, patterned and blanket PR samples are irradiated with Ar vacuum ultraviolet photons (VUV) and Ar ions while sample temperature, photon flux, ion flux and ion energy are controlled and measured. The resulting chemical modifications to bulk 193 nm PR (blanket) and surface roughness are analysed with Fourier transform infrared spectroscopy and atomic force microscopy (AFM). LWR of patterned samples are measured with scanning electron microscopy and blanket portions of the patterned PRs are measured with AFM. We demonstrate that with no RF-bias applied to the substrate the LWR of 193 nm PR tends to smooth and correlates with the smoothing of the RMS surface roughness. However, both LWR and RMS surface roughness increases with simultaneous high-energy (⩾70 eV) ion bombardment and VUV-irradiation and is a function of exposure time. Both high- and low-frequency LWR correlate well with the RMS surface roughness of the patterned and blanket 193 nm PR samples. LWR, however, does not increase with temperatures ranging from 20 to 80 °C, in contrast to the RMS surface roughness which increases monotonically with temperature. It is unclear why LWR remains independent of temperature over this range. However, the fact that blanket roughness and LWR on patterned samples, both scale similarly with VUV fluence and ion energy suggests a similar mechanism is responsible for both types of surface morphology modifications.

Controlling VUV photon fluxes in low-pressure inductively coupled plasmas

“…The second includes synergistic effects that result from simultaneous fluxes of VUV photons and ion bombardment. For example, the roughening of photoresist has different characteristics as a function of temperature depending on whether the film receives only ion fluxes or fluxes of both ions and VUV photons [20,21]. The third includes photon-stimulated processes.…”

An atomic force microscopy-based method for line edge roughness measurement

“…The degradation can be explained be the softening of the PR bulk and the formation of a hard layer on the PR surface. [18][19][20][21][22] Despite the resist LER increase, the Si-ARC LER is decreased compared to the initial resist LER. It shows that the rough resist foot does not negatively affect the LER transfer into the Si-ARC layer.…”

Absolute radiometric calibration of a VUV spectrometer in the wavelength range 46–300 nm

“…However, the recent years show a growing interest in VUV spectroscopy especially for plasma diagnostic purposes in diverse contexts. VUV spectrometers allow monitoring of relevant impurities present in magnetically confined plasmas [2,3] and VUV photon fluxes were identified to be able to play a significant role in plasma surface treatment processes [4,5,6]. Quantification of VUV radiation is necessary for the control of arising VUV photon fluxes and hereinafter for an optimization of the specific application.…”