Imaging flow cytometry was used to analyze the self assembly of DNA-conjugated polystyrene microspheres. This technique enables quantitative analysis of the assembly process and thereby enables detailed analysis of effect of structural and process variables on the yield of assembly. In a demonstration of the potential of this technique, the influence of DNA strands base pair (bp) length was examined and it was found that 50 bp was sufficient to efficiently drive the assembly of microspheres, forming not only dimers but also chain-like structures. The effect of stoichiometry on yield was also examined. The analysis demonstrated that self assembly of 50 bp microspheres can be driven to near completion by stoichiometric excess in a manner similar to Le Chatelier’s principle in common chemical equilibrium.
Pitch division lithography (PDL) with a photobase generator (PBG) allows printing of grating images with twice the pitch of a mask. The proof-of-concept has been published in the previous paper [1,2] and demonstrated by others [1]. Forty five nm half-pitch (HP) patterns were produced using a 90nm HP mask, but the image had line edge roughness (LER) that does not meet requirements. Efforts have been made to understand and improve the LER in this process. Challenges were summarized toward low LER and good performing pitch division. Simulations and analysis showed the necessity for an optical image that is uniform in the z direction in order for pitch division to be successful. Two-stage PBGs were designed for enhancement of resist chemical contrast. New pitch division resists with polymer-bound PAGs and PBGs, and various PBGs were tested. This paper focuses on analysis of the LER problems and efforts to improve patterning performance in pitch division lithography.
The drive to sustain the improvements in productivity that derive from following Moore's law has led the semiconductor industry to explore new technologies that enable production of smaller and smaller features on semiconductor device. Pitch division techniques and double exposure lithography are approaches that print features beyond the fundamental resolution limit of state-of-art lenses by modifying the lithographic process. This paper presents a new technique that enables pitch division in the printing of gratings using only a single exposure that is fully compatible with the current manufacturing tools. This technique employs a classical photoresist polymer together with a photoactive system that incorporates both a photoacid generator (PAG) and a photobase generator (PBG). The PBG is added to the resist formulation in higher molar concentration than the PAG, but has a base production rate that is slower than the acid production rate of the PAG. The PBG functions as a dose-dependent base quencher, which neutralizes the acid in high dose exposure regions but not in the low dose regions. This photoactive system can be exploited in the design of both positive tone and negative tone resist formulations that provide a developed image of a grating that is twice the frequency of the grating on the mask. A simulation of this process was performed for a 52 nm line and space pattern using PROLITH and customized codes. The results showed generation of a 26 nm half pitch relief image after development. Through this new technique, a 45 nm half pitch line and space pattern was experimentally achieved with a mask that produces a 90 nm half pitch aerial image. This corresponds to a k 1 factor of 0.13. The principles, the materials design and the first lithographic evaluations of this system are reported.
ABSTRACT193 immersion lithography has reached its maximal achievable resolution. There are mainly two lithographic strategies that will enable continued increase in resolution. Those are being pursued in parallel. The first is extreme ultraviolet (EUV) lithography and the second is double patterning (exposure) lithography. EUV lithography is counted on to be available in 2013 time frame for 22 nm node [1] . Unfortunately, this technology has suffered several delays due to fundamental problems with source power, mask infrastructure, metrology and overall reliability [2] . The implementation of EUV lithography in the next five years is unlikely due to economic factors. Double patterning lithography (DPL) is a technology that has been implemented by the industry and has already shown the proof of concept for the 22nm node [3] .This technique while expensive is the only current path forward for scaling with no fundamental showstoppers for the 32nm and 22nm nodes. Double exposure lithography (DEL) is being proposed as a cost mitigating approach to advanced lithography. Compared to DPL, DEL offers advantages in overlay and process time, thus reducing the cost-of-ownership (CoO) [4][5] . However, DEL requires new materials that have a non-linear photoresponse. So far, several approaches were proposed for double exposure lithography, from which Optical Threshold Layer (OTL) was found to give the best lithography performance according to the results of the simulation [4][5] . This paper details the principle of the OTL approach. A photochromic polymer was designed and synthesized. The feasibility of the material for application of DEL was explored by a series of evaluations.
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