Plasma-based area selective deposition for extreme ultraviolet resist defectivity reduction and process window improvement

Abstract

Extreme ultraviolet (EUV) lithography has overcome significant challenges to become an essential enabler to the logic scaling roadmap. However, it remains limited by stochastically driven defects, such as line breaks and line bridges for aggressive pitches. This is especially relevant for the back end of line, which requires the most aggressive scaling. Stochastic defects reduce device yield and may push device manufacturers to move to EUV multipatterning beyond 36 nm pitch single exposure, which is a costly option. While the lithography and patterning stack can be optimized to provide the largest process window with the lowest number of defects, process margins decrease as smaller pitches are required. Currently, for some lithography stacks, especially spin-on glass based trilayer stacks, the defect-free process window beyond 36 nm pitch is limited by line collapse. Reduction in resist thickness may mitigate pattern collapse, but it may also increase the number of line breaks—trading one killer defect for another. In this paper, we expand on an area selective deposition (ASD) process in situ of an etch chamber to selectively deposit material on the EUV photoresist prior to transferring the pattern downstream. We demonstrate mitigation of resist line notching and breaks while maintaining deposition-free open areas and clear alignment marks. Due to the inherent chemical selectivity of the deposition process as opposed to a purely aspect ratio driven deposition process, thinner resists that, with a normal etch condition would result in line breaks, can now be considered. This drives down flopover defect issues seen with thicker EUV resists and enables several underlayer systems that could otherwise not be considered. Finally, we demonstrate that defectivity levels measured by e-beam inspection post lithography and post pattern transfer and yield are both improved at 30 nm pitch when this ASD process is used.

Atomic layer deposition and its derivatives for extreme ultraviolet (EUV) photoresist applications

“…Lutker-Lee et al determined that line breaks were the dominant form of defects across various exposure dosages when resist thickness was reduced, wherein the number of defects increased by up to two orders of magnitude compared to the standard resist thickness. 30) When post-lithography ASD treatment was applied, the defect density of thinner resist was comparable to that of the standard thickness photoresist, as shown in Fig. 3(b).…”

“…Over the years, there has been an increasing number of reported studies utilizing ALD and its modified forms to improve the EUV patterning process and develop advanced inorganic-organic hybrid resist technology. For example, besides improving the feature roughness of patterned organic EUV resist, [27][28][29] ALD-based techniques can also increase the thickness of resist pattern/ mask for reactive ion etching as well as the intrinsic etch resistance by either selectively adding more materials on the pattern surface, [29][30][31] or infusing inorganic elements into the patterned organic resist matrix. 32,33) On the other hand, instead of modifying the already patterned EUV resist, ALD and its modified techniques can be leveraged to synthesize novel hybrid EUV resist thin films that can be then subjected to EUVL.…”

“…This technique has been widely employed in the semiconductor industry for various applications, like selective epitaxial growth, 38,39) and selective cobalt capping of copper. 40,41) It has recently been proposed to expand the usage of ASD in conjunction with EUVL, [29][30][31][42][43][44] in which materials can be selectively deposited after the development step on the patterned EUV resist or the substrate surface, as shown in Fig. 2(b).…”

“…Since the sidewall roughness of line patterns tends to be directly transferred to the substrate during the etching process, the ASD of materials on patterned EUV resist can help repair the sidewall damages, resulting in a more robust and defect-mitigated pattern transfer process for greater device performance eventually. 30) Wada et al reported the use of plasma-based ASD as a post-EUV lithography treatment and effectively lowered the line width roughness (LWR) and LER of 36 nm-pitch line patterns by ∼26% and ∼35%, respectively [Fig. 3(a)].…”