Gregg M. Gallatin

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

For the patterning of sub-100 nm features, a clear understanding of the origin and control of line edge roughness (LER) is extremely desirable, from a fundamental as well as a manufacturing perspective. With the migration to thin photoresists coupled with bottom antireflective coating (ARC)-hardmask underlayers, LER analysis of the developed resist structures is perhaps an inaccurate representation of the substrate roughness after the etch process, since those underlayers can play a significant role in increasing/decreasing linewidth variations during the image transfer process and hence can impact the device performance. In this article, atomic force microscopy is used to investigate the contribution of the imaging resist sidewall topography to the sidewall roughness of the final etched feature in thin photoresists, ARC, and hardmasks. Resist systems suitable for 248 and 193 nm lithography as well as fluorine-containing resists were processed using N2-H2 or fluorocarbon plasma etch. It is shown that the ...

Nonlinear laser dynamics : from quantum dots to cryptography

Semiconductor lasers-or diode lasers, as they are often called-are an integral part of modern technology. They are used in numerous devices from laser pointers to high-throughput laser printers to the light sources that power the optical-fiber communication behind the internet. At the fundamental level, a laser is a combination of a resonant optical cavity (such as a pair of mirrors facing each other a given distance apart so that only certain wavelengths can fit neatly between the mirrors) and a gain medium (which amplifies the light at one or more of those wavelengths). Turn up the gain to the point where it balances the losses due to absorption and leakage out of the cavity, and you have a laser.

Fundamental limits to EUV photoresist

Recent experimental results indicate that current resists lack the ability to simultaneously meet the 2005 International Roadmap for Semiconductors (ITRS) goals for Resolution, Line Edge Roughness (LER) and Sensitivity (RLS). This RLS tradeoff has also been demonstrated through modeling work. Here we use a model to explore the impact on the RLS tradeoff of anisotropic acid diffusion and increased quantum yield. We show that both these effects can significantly improve the RLS tradeoff.

Nanomanufacturing: A Perspective

Nanomanufacturing, the commercially scalable and economically sustainable mass production of nanoscale materials and devices, represents the tangible outcome of the nanotechnology revolution. In contrast to those used in nanofabrication for research purposes, nanomanufacturing processes must satisfy the additional constraints of cost, throughput, and time to market. Taking silicon integrated circuit manufacturing as a baseline, we consider the factors involved in matching processes with products, examining the characteristics and potential of top-down and bottom-up processes, and their combination. We also discuss how a careful assessment of the way in which function can be made to follow form can enable high-volume manufacturing of nanoscale structures with the desired useful, and exciting, properties.

Spatial scaling metrics of mask-induced induced line-edge roughness

Mask contributors to line-edge roughness (LER) have recently been shown to be an issue of concern for both the accuracy of current resist evaluation tests as well the ultimate LER requirements for the 22-nm production node. Problems arise from mask absorber LER as well as mask reflector or surface roughness leading to random phase variations in the reflected beam. Not only do these mask contributors effect to total measured LER in resist, but they also effect LER spatial characteristic such as the LER power spectral density and related descriptors of correlation length and roughness exponent. Noting that these characteristics are important in the understanding of LER, it is crucial to understand how mask effects impact these parameters. Moreover, understanding how these metrics respond to mask effects may lead to an experimental mechanism for experimentally evaluating the importance of mask contributors to LER. Here we use computer modeling to study the LER spatial metrics arising from mask effects. We further describe the effects of illumination conditions and defocus on the metrics and compare the results to those expected from intrinsic resist LER.

Film quantum yields of EUV& ultra-high PAG photoresists

Base titration methods are used to determine C-parameters for three industrial EUV photoresist platforms (EUV- 2D, MET-2D, XP5496) and twenty academic EUV photoresist platforms. X-ray reflectometry is used to measure the density of these resists, and leads to the determination of absorbance and film quantum yields (FQY). Ultrahigh levels of PAG show divergent mechanisms for production of photoacids beyond PAG concentrations of 0.35 moles/liter. The FQY of sulfonium PAGs level off, whereas resists prepared with iodonium PAG show FQYs that increase beyond PAG concentrations of 0.35 moles/liter, reaching record highs of 8-13 acids generated/EUV photons absorbed.

Propagation of Vortex Electron Wave Functions in a Magnetic Field

The physics of coherent beams of photons carrying axial orbital angular momentum (OAM) is well understood, and such beams, sometimes known as vortex beams, have found applications in optics and microscopy. Recently electron beams carrying very large values of axial OAM have been generated. In the absence of coupling to an external electromagnetic field, the propagation of such vortex electron beams is virtually identical mathematically to that of vortex photon beams propagating in a medium with a homogeneous index of refraction. But when coupled to an external electromagnetic field, the propagation of vortex electron beams is distinctly different from photons. Here we use the exact path integral solution to Schrodingers equation to examine the time evolution of an electron wave function carrying axial OAM. Interestingly we find that the nonzero OAM wave function can be obtained from the zero OAM wave function, in the case considered here, simply by multipling it by an appropriate time and position dependent prefactor. Hence adding OAM and propagating it can in this case be replaced by first propagating then adding OAM. Also, the results shown provide an explicit illustration of the fact that the gyromagnetic ratio for OAM is unity. We also propose a novel version of the Bohm-Aharonov effect using vortex electron beams.

Modeling the effects of acid amplifiers on photoresist stochastics

The tradeo between Resolution, Line Edge Roughness (LER) and Sensitivity, the so called RLS tradeo, continues to be a dicult challenge, especially for EUV lithography. Acid ampliers have recently been proposed as a method to improve upon the overall RLS performance of EUV resists. Here we discuss a simulation approach to study the issue. The model extends the standard reaction diusion equation to explicitly capture the stochastic behavior of exposure, photo-acid generation and acid amplication. Using this model the impact acid ampliers have on the RLS tradeo is studied under a variety of resist conditions.

Effect of resist on the transfer of line-edge roughness spatial metrics from mask to wafer

Mask contributors to line-edge roughness (LER) have recently been shown to be an issue of concern for extreme ultraviolet lithography both in terms of the accuracy of current resist evaluation tests and in terms of the ultimate LER requirements for the 22 nm production node and beyond. More recently, it has been shown that the power spectral density of the mask-induced roughness is markedly different from that of intrinsic resist roughness and thus potentially serves as a mechanism for distinguishing mask effects from resist effects in experimental results. However, the evaluation of stochastic effects in the resist itself demonstrates that such a test would only be viable in cases where the resist effects are negligible in terms of their contribution to the total LER compared with the mask effects. Moreover, the results presented here lead the authors to the surprising conclusion that it is indeed possible for mask contributors to be the dominant source of LER while the spatial characteristics of the LER...

Resist Requirements and Limitations for Nanoscale Electron-Beam Patterning

Electron beam lithography still represents the most effective way to pattern materials at the nanoscale, especially in the case of structures, which are not indefinitely repeating a simple motif. The success of e-beam lithography depends on the availability of suitable resists. There is a substantial variety of resist materials, from PMMA to calixarenes, to choose from to achieve high resolution in electron-beam lithography. However, these materials suffer from the limitation of poor sensitivity and poor contrast. In both direct-write and projection e-beam systems the maximum beam current for a given resolution is limited by space-charge effects. In order to make the most efficient use of the available current, the resist must be as sensitive as possible. This leads, naturally, to the use of chemically amplified (CA) systems. Unfortunately, in the quest for ever smaller feature sizes and higher throughputs, even chemically amplified materials are limited: ultimately, sensitivity and resolution are not independent. Current resists already operate in the regime of 2 . In this situation detailed models are the only way to understand material performance and limits. Resist requirements, including sensitivity, etch selectivity, environmental stability, outgassing, and line-edge roughness as they pertain to, high-voltage (100 kV) direct write and projection electron-beam exposure systems are described. Experimental results obtained on CA resists in the SCALPEL® exposure system are presented and the fundamental sensitivity limits of CA and conventional materials in terms of shot-noise and resolution limits in terms of electron-beam solid interactions are discussed.