Transfer etching of bilayer resists in oxygen-based plasmas

Abstract

Thin film imaging offers the possibility of extending 248 nm lithography to sub 150 nm resolution. We have been working on a 248 nm bilayer imaging scheme which utilizes a thin Si-containing resist on top of a thick, planarizing underlayer. The image is developed in the top layer and transferred to the underlayer via O 2 -based plasma etching. This article focuses on three aspects of the critical transfer etch process: etch resistance of the imaging resist, profile control and resist roughening. The imaging resist thickness loss is very fast during the first few seconds of the etch after which the rate diminishes. The relative importance of three phenomena that can explain this nonlinear behavior: oxidation of silicon, deprotection of resist moieties, and plasma etching of resist, are discussed. Fourier transform infrared studies on imaging resist films indicate minimal deprotection-related film thickness losses. X-ray photoelectron spectroscopy analyses of etched films indicate that the extent of surface oxidation increases initially and then becomes constant. Thus, the etching of this category of resists can be described as a combination of the oxidation of the silicon species and sputtering of the oxide-like layer formed. Post-transfer etch profiles using an O 2 plasma are shown, and methods to reduce imaging resist faceting and thickness loss either by modifying the imaging layer silicon content or by using passivating plasma chemistries are discussed. The effect of different etching chemistries and processing conditions on imaging layer roughening and striation formation on underlayer sidewalls are explained with the aid of scanning electron microscopy micrographs and atomic force microscopy images of etched feature sidewalls. It is shown that the SO 2 -O 2 etch significantly reduces the sidewall roughness from the postlithograpy values. The ϳ3.5 nm rms sidewall roughness observed postetch is comparable to postdeveloped roughness values measured for mature single layer resists. The printing of 125 nm line/space patterns and 150 nm trench features with 10:1 aspect ratios in the underlayer is also demonstrated.

Effect of thin-film imaging on line edge roughness transfer to underlayers during etch processes

“…During the etching process, phenomena such as polymer deposition, ion bombardment, rise in wafer temperature, selective etching of film components, and micromasking can either increase or decrease the LER of the feature. Mahorowala et al 23 sist to localized agglomeration and evaporation of components from the resist and plasma fluoropolymer deposition on top leading to microscopic variations in etch rate. They also explained that the different thermal expansion coefficients of the resist and fluoropolymer can cause ''wiggling'' of resist lines under certain etching conditions; for example, inadequate substrate cooling.…”

“…Past work demonstrated the effect of SO 2 -O 2 plasma etch chemistry on the SWR of 248 nm bilayer systems. 23 In this work, we evaluated a silicon-containing 193 nm bilayer system as an example of such a patterning strategy. The presence of silicon in the polymer resin boosts the etch resistance of the ultrathin top layer ͑ϳ130 nm͒, allowing for a thicker organic underlayer ͑ϳ360 nm͒ to be introduced.…”

Impact of the double-patterning technique on the LER-induced threshold voltage variation in symmetric tunnel field-effect transistor

“…9k for the top view). It is observed that the LER profile (transferred through multiple etching processes) onto the substrate is not necessarily the same as the original LER profile onto the photoresist, Si-BARC, and hard mask [17,18,19,20,21,22]. Because the 2P2E technique uses multiple etching processes (e.g., from Si-BARC to hard mask, and from hard mask to silicon substrate), it is worthwhile to track the change in the LER profile.…”

Dendrimer‐Scaffold‐Based Electron‐Beam Patterning of Biomolecules

“…Although alignment is not an issue for biomolecule patterning based on polymer liftoff, [35] as it is an integrated process, this method involves extra steps of deposition and etching a polymer film, which increases the complexity of the process. Challenges are also encountered as the size of the photolithographic patterns decrease due to the increase in line-edge roughness (LER) [38,39] and the isotropic nature of oxygen plasma etch. [39] Patterned gold has been used for creating protein patterns using thiolbased linkers, [40] but gold surfaces cannot be tolerated in some biosensors [4][5][6]10] as gold interferes with the optical signal or conductivity of the sensor.…”

“…Challenges are also encountered as the size of the photolithographic patterns decrease due to the increase in line-edge roughness (LER) [38,39] and the isotropic nature of oxygen plasma etch. [39] Patterned gold has been used for creating protein patterns using thiolbased linkers, [40] but gold surfaces cannot be tolerated in some biosensors [4][5][6]10] as gold interferes with the optical signal or conductivity of the sensor. This technique also includes extra photolithographic and lift-off processing steps for patterning gold.…”