Richard O. Tejeda

Finite element modeling of ion-beam lithography masks for pattern transfer distortions

As one of the Next Generation Lithographies, Ion-beam Projection Lithography (IPL) will be subject to strict error budgets for the sub-130 nm regime and will require high patter placement accuracy. Meeting these stringent conditions in a timely and cost-effective manner will depend upon accurate predictions of the mechanical distortions induced in IPL stencil masks during fabrication and pattern transfer. To simulate pattern transfer, finite element (FE) structural models of the stencil masks have been developed to predict distortions due to the fabrication of voids in stressed mask membranes. In this paper, an application of FE modeling for stencil masks has been demonstrated using both the IBM Falcon pattern and more uniform patterns.

Finite element simulation of ion-beam lithography mask fabrication

Fabrication of low distortion stencil masks is one of the key issues for ion-beam projection lithography (IPL). Identifying the sources of distortion and optimizing the processing techniques are essentical to meet the stringent error budgets. Since experiments are time consuming and expensive, it is desirable to develop accurate simulation procedures which can be used for analysis and design. This paper presents results to show that finite element analysis is a viable alternative.

Thermomechanical distortions of ion-beam stencil masks during exposure

Meeting the stringent requirements on pattern placement in the sub-130 nm regime will be a challenge for any Next Generation Lithography. A key issue for all technologies will be the development of a low distortion mask. This paper describes the thermomechanical simulations performed on the ion-beam projection lithography (IPL) mask to predict distortions during exposure. Pattern-specific global distortions are identified using equivalent modeling techniques, which are based upon the use of equivalent thermal properties are presented. Finite element heat transfer and structural models have been developed to employ these equivalent properties. To demonstrate the modeling procedures, predictions of the thermomechanical response of the stencil mask for the IBM Talon layout were performed. The finite element results illustrate that by optimizing the design parameters of the exposure system, IPL mask distortions can be controlled to meet the allotted error budgets.

Mechanical modeling of the reticle and chuck for EUV lithography

The reflective reticles used for extreme ultraviolet (EUV) lithography are subject to the stringent image placement and flatness requirements for 70 nm and smaller feature sizes. Stresses in the reflective multilayer coatings can produce substantial bowing of the reticle, and variations in the flatness and thickness of the reticle substrate, as well as entrapped debris particles, can contribute to flatness errors on the patterned surface after reticle chucking. Reticles will also be subjected to high stage accelerations and thermal loadings during exposure. The chuck in the exposure tool will be required to clamp the reticle flat, crush entrapped debris, remove absorbed EUV energy, and prevent slippage during stage accelerations. Additionally, the thermal and structural behavior of the chuck will influence the reticle response, and thus the reticle and chuck must be considered as a system. In order to determine reticle and chucking requirements, finite element models have been developed to analyze many of the key issues in the mechanical design of the reticle and chuck. The analyses are being used to support the development of reticle and chuck standards for EUV lithography.

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.

Mechanical modeling of ion beam lithography masks

The success of ion beam lithography in the sub-0.13 μm technology region is partially dependent on the development of a low distortion mask. To that end, finite element analyses have been performed to predict the distortions due to mounting of a stencil mask during exposure to the ion beam. In addition, modeling techniques which allow for the determination of in-plane distortions of specific pattern features during fabrication have been developed. Results can be used to perform Pattern Specific Emulation (PSE).

Modeling pattern transfer in ion-beam lithography masks

In an effort to maintain pattern transfer errors in stencil mask membranes within acceptable tolerances, finite element (FE) models and techniques are being developed at the University of Wisconsins Computational Mechanics Center in cooperation with Ionen Mikrofabikations Systeme (IMS), Vienna. FE calculations allow for detailed studies of various design scenarios before the efforts of physical implementation are required. Critical issues such as mask geometry, stencil pattern geometry, gravitational loading, and the SOI fabrication process can, therefore, be accurately addressed in a timely and cost-effective manner.

Determination of the Plastic Behavior of Low Thermal Expansion Glass at the Nanometer Scale

The nanometer-scale plastic behavior of two low thermal expansion glasses (ULE ® and Zerodur ® ) was determined through a combination of nanoindentation experiments and finite element modeling. The finite element models were then extended to investigate aspects of the performance of these materials as extreme ultraviolet lithography reticles.

Analysis, design, and optimization of ion-beam lithography masks

The error budget allotted to a lithographic mask is generally only a small fraction of the critical dimension of the device features. Consequently, ion projection lithography in the sub-0.13 micrometers technology regime will place large demands on image placement accuracy, a component of which is mask distortion. During the design stage then, it is desirable to identify those intrinsic loads which distort the mask pattern from its intended shape and, ultimately, to reduce those distortions to an acceptable level. This paper assesses the in-plane distortions (IPD) due to gravity as a function of the masks geometric parameters. The optimal mask geometry is identified by minimizing the IPD function.

Stress relief structures for ion-beam projection lithography masks

Next Generation Lithography (NGL) will require masks with high resolution and positioning accuracy to meet the requirements for sub-0.13 @mm technology. This paper focuses on the design and development of low distortion stencil masks for ion-beam projection lithography. With the stencil mask structure, one source of pattern placement errors is the in-plane distortion which occurs during the pattern transfer process. To address this issue, the use of stress relief structures to minimize distortion within the pattern area has been proposed. Results of the mechanical analysis, design, and optimization of these structures are presented.