EUV lithography scanner for sub-8nm resolution

Abstract

EUV lithography for resolutions below 8 nm half pitch requires the numerical aperture (NA) of the projection lens to be significantly larger than the current state-of-the-art 0.33NA. In order to be economically viable, a throughput in the range of 100 wafers per hour is needed.As a result of the increased NA, the incidence angles of the light rays at the mask increase significantly. Consequently the shadowing deteriorates the aerial image contrast to unacceptably low values at the current 4x magnification.The only solution to reduce the angular range at the mask is to increase the magnification. Simulations show that we have to double the magnification to 8x in order to overcome the shadowing effects. Assuming that the mask infrastructure will not change the mask form factor, this would inevitably lead to a field size that is a quarter of the field size of current 0.33NA step & scan systems. This would reduce the throughput of the high-NA scanner to a value significantly below 100 wafers per hour unless additional measures are taken.This paper presents an anamorphic step & scan system capable to print fields that are half the field size of the current full field. The anamorphic system has the potential to achieve a throughput in excess of 150 wafers per hour by increasing the transmission of the optics as well as increasing the acceleration of the wafer-and mask stage. This makes it an economically viable lithography solution. Furthermore, the simulated imaging behavior of the system is demonstrated and its impact on the rest of the lithographic system is discussed.

Emulation of anamorphic imaging on the SHARP extreme ultraviolet mask microscope

“…For experiments where higher sampling is desired, the highest magnification with 6.5 pixels per resolution element can be used. 4 Like SHARP's standard zoneplates, the 0.55 4x/8x NA zoneplates are patterned with e-beam lithography and electroplated using 35 nm of gold on a 100-nm silicon nitride membrane. The SEM-images in Fig.…”

“…Both of these options are considered economically not viable. 4 Zeiss and ASML have proposed an anamorphic projection optic with increased mask-side NA perpendicular to the plane of incidence and increased demagnification in the plane of incidence. 5 Such a design avoids high angles of incidence on the photomask in the plane of incidence (that would degrade image quality) while preserving the demagnification perpendicular to the plane of incidence.…”

Photolithography reaches 6 nm half-pitch using EUV light

“…If the secondary electron blur is lower, the resolution might be further increased down to 5 nm HP. For high volume manufacturing (HVM), EUV scanners with 0.55 NA optics might be able to achieve 6 nm HP resolution [25]. This requires suitable photoresists with much higher sensitivity than that of HSQ.…”

EUV high-NA scanner and mask optimization for sub-8nm resolution

“…Moving away from the 4x isomorphic mask towards the 4x/8x anamorphic mask has several impacts for the mask and for the lithography tool [16]. In section 6.1 the main differences for the mask will be discussed.…”