Gerald A. Dicks

Modeling and simulation of membrane distortions in Next Generation Lithography (NGL) masks

Next Generation Lithographies will face major challenges to meet the allotted error budgets for sub-130 nm technologies. The development of low distortion masks will be essential. Using comprehensive finite element simulation models, mask distortions can be efficiently and accurately predicted. Pattern-specific distortions have been evaluated to investigate pattern placement accuracy and stability. For the three principal membrane mask technologies, typical pattern-transfer results are presented.

Controlling imprint distortions in step-and-flash imprint lithography

Step-and-Flash Imprint Lithography (S-FIL™) is a one-to-one imprinting process in which features are transferred from a template by lowering it onto a low-viscosity, photocurable, monomer solution that conforms to the template surface and is subsequently cured. The potential exists for both low cost and high throughput, making S-FIL a promising candidate for Next-Generation Lithography. However, there are many challenges that must be overcome in order to ensure the future viability of S-FIL. Mechanical distortion control is one of the principal challenges, and is addressed in this article. During the imprinting process, the viscous flow of the monomer liquid causes a significant pressure elevation within the fluid as it is forced to flow outwards through a small gap. These pressures cause out-of-plane distortions and in-plane distortions (OPD and IPD) of the template, which may be manifested as errors in the replicated pattern. A fluid-structure model was developed to predict the template distortion assoc...

Predicting microfluidic response during immersion lithography scanning

Immersion lithography has been proposed as a method of improving optical lithography resolution to 50 nm and below. The premise behind the concept is to increase the index of refraction in the space between the lens and wafer through the insertion of a high refractive index liquid in place of the low refractive index air that currently fills the gap. This paper presents three studies related to potential problem areas for immersion lithography. The first study investigates the entrainment of air as liquid flows over features in the wafer topology. Bubbles are undesirable because they introduce changes in the index of refraction in the optical path that can lead to imaging errors. The second investigation examines liquid heating due to the absorption of the incident energy by the fluid as well as heat transferred from the exposed wafer and viscous heating. This temperature elevation can lead to changes in the liquids index of refraction which may lead to optical degradation of the fluid. The final investigation examines the potentially significant normal and shear stresses induced on both the lens and wafer surface due to the increased viscosity and density of the liquid as compared with air. These mechanical loads may cause the lens to distort or shift in its mounting. This paper presents the results of the numerical thermal, flow, and structural simulations used to analyze these various critical issues.

Mask blank fabrication, pattern transfer, and mounting distortion simulations for the 8-in, format SCALPEL mask

Abstract The electron-beam projection lithography technique known as scattering with angular limitation projection electron-beam lithography (SCALPEL) is capable of producing linewidths of 100 nm and smaller, making it a leading candidate for replacing the current lithographic technique, deep ultraviolet (DUV). Critical to the success of SCALPEL is the creation of a low-distortion mask. Finite element modeling allows for the efficient identification of pattern-specific distortions of the mask membrane. Results pertinent to the current design of the 8-in. format mask are presented.

Mechanical Modeling of Projection Electron-Beam Lithography Masks

The production of microchips with circuit features in the sub-0.13 µm regime will require an advanced lithography technique such as SCattering with Angular Limitation Projection Electron Lithography (SCALPEL). The mask used in this technique is subject to intrinsic and extrinsic loads during fabrication, mounting, and exposure, giving rise to mechanical distortions which lead to pattern placement errors. In order to develop a low distortion mask, finite element models have been created to identify sources of distortion and quantify the resulting errors. The models are then used as predictive tools to optimize the design of the mask so that distortions do not exceed the error budget. The focus of this study was to investigate the mask membrane distortions induced during the fabrication process and pattern transfer for a preliminary test case of a SCALPEL mask. More specifically, out-of-plane and in-plane distortions were calculated and the sensitivity of this response to variations in mask design parameters was determined.

Mask membrane distortions due to pattern transfer for electron-beam lithography (SCALPEL) masks

In order to successfully employ Scattering with Angular Limitation Projection Electron-Beam Lithography (SCALPEL) to produce integrated circuits with features below 0.13 @mm, mask membrane distortions (which lead to pattern placement errors) must not exceed the error budget. When designing a mask, finite element (FE) models are created to identify sources of distortion and quantify the resulting errors. Distortions arise during fabrication, mounting, and in situ exposure of the mask. The focus of this study was to determine the mask membrane distortions induced during the pattern transfer process for a large format SCALPEL mask. Three cases were investigated: the IBM Talon pattern, 100% removal of the scatterer layer, and 50% removal of the scatterer layer. The IBM Talon pattern was chosen to quantify typical pattern specific-distortions while the other two cases, 100% and 50% removal of the scatterer layer, were investigated to determine distortions corresponding to worst case situations.

Mechanical and thermal modeling of the SCALPEL mask

Scattering with angular limitation projection electron-beam lithography (SCALPEL) is being developed by Lucent Technologies for sub-130 nm lithography. The mask fabrication and exposure processes produce mask distortions that result in pattern placement errors. In order to understand these distortions, and determine how to reduce them to levels consistent with the error budget, structural and heat transfer finite element models have been generated to simulate the mechanical and thermal response of the mask. In addition, sensitivity studies of the distortions due to key design parameters that may be used to refine the SCALPEL mask configuration have been conducted.

Finite element modeling of SCALPEL masks

A virtual mask laboratory has been developed at the UW Computational Mechanics Center to aid in the design and optimization of the SCALPEL mask. Finite element models have been generated to simulate the thermomechanical response of the mask during fabrication, pattern transfer, mounting and exposure. Results on the mask-related distortions can be used to assess image placement accuracy and mask stability; examples of accurate procedures to vectorially sum in-plane distortion maps from the various sources are presented. In addition, experimental methods to provide material properties and stress characterization data are outlined, along with techniques to verify and benchmark the mechanical models.

Controlling template response during imprint lithography

Step-and-Flash Imprint Lithography (S-FILTM) is a principal candidate for the next-generation lithography at the 45-nm node (and below). In imprint lithography, a monomer solution is dispensed onto the wafer. The monomer fills small features in a template that is lowered onto the wafer. The monomer is cured, causing it to solidify so that a three-dimensional replica of the template features is produced and remains on the wafer after the template is removed. Because this is a one-to-one process, any distortions of the template during the squeezing process will be manifested directly as errors in the features that are imprinted on the substrate. A finite element (FE) structural model of the S-FIL template has been created to predict the distortions due to mounting, gravity, and the fluid pressure distribution that arises from the viscous flow of the polymer liquid during the imprint process. Distortions take the form of both in-plane and out-of-plane displacements. An axisymmetric, finite difference (FD) model is used to predict the pressure distribution over the template due to viscous flow and surface tension effects. The FE and FD models are coupled using an iterative process in which the pressure distribution and template distortions are calculated at progressing time intervals until the final, desired gap height is achieved, nominally 200 nm. The coupled models are capable of characterizing the fluid-structure interaction that occurs during the imprint process. The results of the model will facilitate the design of system components that are capable of meeting the stringent error budgets associated with the sub-45-nm nodes.

Characterizing the response of an EUV reticle during electrostatic chucking

Extreme Ultraviolet Lithography (EUVL) is one of the leading candidates for Next-Generation Lithography in the sub-45-nm regime. One of the key components in the development of EUVL is understanding and characterizing the response of the mask when it is electrostatically chucked in the exposure tool. In this study, finite element (FE) models have been developed to simulate the reticle / chuck system under typical exposure conditions. FE simulations are used to illustrate (a) the effects of the nonflatness of the reticle and chuck, (b) the image placement errors induced by back-side particulates, (c) the influence of the coefficient of friction between the reticle and chuck during exposure scanning, and (d) the effects of contact conductance on the thermomechanical response of the reticle. The focus of this paper is to illustrate that mechanical modeling and simulation has now become a fundamental tool in the design of electrostatic pin chucks for the EUVL technology.