Semiconductor manufacturing industry has reduced the size of wafer for enhanced productivity and performance, and Extreme Ultraviolet (EUV) light source is considered as a promising solution for downsizing. A series of EUV lithography procedures contain complex photo-chemical reaction on photoresist, and it causes technical difficulties on constructing theoretical framework which facilitates rigorous investigation of underlying mechanism. Thus, we formulated finite difference method (FDM) model of post exposure bake (PEB) process on positive chemically amplified resist (CAR), and it involved acid diffusion coupled-deprotection reaction. The model is based on Fick’s second law and first-order chemical reaction rate law for diffusion and deprotection, respectively. Two kinetic parameters, diffusion coefficient of acid and rate constant of deprotection, which were obtained by experiment and atomic scale simulation were applied to the model. As a result, we obtained time evolutional protecting ratio of each functional group in resist monomer which can be used to predict resulting polymer morphology after overall chemical reactions. This achievement will be the cornerstone of multiscale modeling which provides fundamental understanding on important factors for EUV performance and rational design of the next-generation photoresist.
Deformation characteristic of CFRP bi-stable composites according to negative initial curvature is discussed, and twisted
shape bi-stability of CFRP composites is introduced. Initial curvature of composites has effect on final curvature of bistable
composites. Positive initial curvature tailor final curvature linearly. However, some negative initial curvature
induces twisted shape bi-stability. CFRP laminated composites have three different final state (i.e. conventional shape bistability,
mono-stability, and twisted shape bi-stability) according to initial curvature. Twisted shape bi-stable composites
have different curvature changing characteristic from conventional shape bi-stable composites. In order to analysis effect
of initial curvature, analytical model that include force and moment equilibrium is proposed. FE simulation results and
analytical results are compared to verify the proposed analytical model. It is verified that some range of negative initial
curvature induce losing of bi-stability or twisted shape bi-stability by analytical model. Final state shape of three
different state is analyzed by FE simulation and analytical model. Final states shape from two different analyses are well
matched each other in three different state.
The self-folding of polystyrene sheet can be realized by the localized thermal absorption in narrow area, and it is easily achieved by light and black-colored line pattern printing. Lighting to polystyrene sheet provides thermal energy stored in infrared ray to black-colored area except transparent area, then the polystyrene sheet near black-colored area becomes glass transition state. The extreme thermal contraction deformation at black area results in folding deformation of polystyrene sheet. In this paper, various self-folding structure u sing the light-absorption folding technique of polystyrene sheet can be designed and manufactured . For prediction of light-activated folding behavior of polystyrene sheet, the cohesive line element is employed . In the cohesive line element, the additional nodes are defined at folded line, and the discontinued folding angles can be identified and be analyzed from finite element analysis .
For decades, downsizing has been a key issue for high performance and low cost of semiconductor, and extreme ultraviolet lithography is one of the promising candidates to achieve the goal. As a predominant process in extreme ultraviolet lithography on determining resolution and sensitivity, post exposure bake has been mainly studied by experimental groups, but development of its photoresist is at the breaking point because of the lack of unveiled mechanism during the process. Herein, we provide theoretical approach to investigate underlying mechanism on the post exposure bake process in chemically amplified resist, and it covers three important reactions during the process: acid generation by photo-acid generator dissociation, acid diffusion, and deprotection. Density functional theory calculation (quantum mechanical simulation) was conducted to quantitatively predict activation energy and probability of the chemical reactions, and they were applied to molecular dynamics simulation for constructing reliable computational model. Then, overall chemical reactions were simulated in the molecular dynamics unit cell, and final configuration of the photoresist was used to predict the line edge roughness. The presented multiscale model unifies the phenomena of both quantum and atomic scales during the post exposure bake process, and it will be helpful to understand critical factors affecting the performance of the resulting photoresist and design the next-generation material.
Shape Memory Alloy (SMA) spring has great potential as a component of compact actuating system. Trade-off between
recovery force and deformation range due to phase transformation is possible through the control of spring design
parameters such as spring diameter. Deformation behavior of SMA spring is complicated function in three-dimensional
space because its behavior is a combination of torsion, bending and stretching action. Therefore, three dimensional
analysis of SMA spring is the most accurate simulation procedure. In this paper, modified one-dimensional Brinson
model for SMA spring is proposed for more efficient and accurate simulation. In addition, numerical simulation of SMA
spring is validated by comparing it with the results of experiment.
Shape memory alloy (SMA) can exhibit interesting features such as the diverse material behaviors according to the induced temperature and stress. SMA changes its material properties progressively under cyclic loading conditions and finally reaches stable path(state) after a certain number of stress/temperature loading-unloading cycles, so called 'training' completion. The presence of permanent deformation, due to plastic strains or irreversible martensite variants during the material training, shifts the material characteristic curves of SMA wire. In this study, SMA wires that have been in a stable state through the training are used. Stress-strain curve of SMA wire at different temperature levels are measured. In addition, we observe other important effects such as the effect of mechanical/thermal training, rate effect according to thermal cycle times or strain rates, etc. Until now, the rate effect is not considered significantly in the SMA research and only extremely slow time rate is considered in most SMA experiments. It is common to use rate independent constitutive relations in the modeling and simulation of SMA behaviors. Therefore to make the actuators using an SMA wire which has the fast response or short-time thermal cycle environment, rate dependency should be properly considered. The result of two-way experiment at each (short or long) cycle time in phenomenological aspect shows that stress-strain-temperature relations and hysteresis characteristics depend upon the cycle time. In short-time cycle, strain-temperature curve moves in counterclockwise and the size of hysteresis envelop is large. As the time rate of the thermal cycle increases, the size of the hysteresis envelop is getting smaller and strain-temperature curve moves along the clockwise direction above a certain thermal cycle time. Above that thermal cycle time, hysteresis trajectory is fixed in the stable state. These new effects of SMA are investigated and the effect would be explained qualitatively. The present work presents the experimental test using 1-D SMA wire after training completion by mechanical/thermal cycling. Through these tests, we measure the characteristics of SMA. With the estimated SMA properties and effects, we compare the experimental results with the simulation results based on the SMA constitutive equation including the training and thermal rate effect.
A structure using the two-way shape memory effect (TWSME) returns to its initial shape by increasing or decreasing temperature under initial residual stress. Through the thermo-mechanical constitutive equation of shape memory alloy (SMA) proposed by Lagoudas et al., we simulate the behavior of a double actuator in which two SMA wires are attached to the tip of bar under the initially given residual stress. Through the numerical results conducted in the present study, the proposed actuator device is suitable for repeated actuation. The simulation algorithm proposed in the present study can be applied extensively to the analysis of the assembled system of SMA-actuator and host structure in practical applications.
One way Shape Memory Effect (SME) is not suitable mechanism for application to the repeated actuation of an Shape Memory Alloy(SMA) wire because the host structure does not return to its initial shape after it cools down. In the present study, the two-way SME under residual stress is considered. A structure using the two-way effect returns to its initial shape by increasing or decreasing temperature under an initially given residual stress. A thermo-mechanical constitutive equation of SMA proposed by Lagoudas et al. was employed in the present study. Laminated composite beams and plates are considered as simple morphing structural components. The modeling of beams and plates are based on first-order shear deformable laminated composite beam and plate theories with large deflections. Numerical results of fully coupled SMA-composite structures are presented. The proposed actuation mechanism based on the two-way SMA effect and a simulation algorithm can be used as a powerful morphing mechanism and simulation tool for structures.
Shape memory alloys (SMAs) are often used in smart materials and structures as the active components. Their ability to provide a high force and large displacement has been useful in many applications, including devices for damage control, active structural acoustic control, dynamic tuning, and shape control. The paper presents a macroscopic mathematical model which captures the thermomechanical behaviors and the two-way shape memory effect (TWSME) of SMAs, and SMA applications as an actuator to control the shape of a circular composite cylinder where a thin SMA layer actuator is bonded inside the cylinder is investigated numerically. The circular composite cylinder with the thin SMA layer was designed and analyzed to determine the feasibility of such a system for the removal of stiffeners from externally pressurized stiffened composite structures. SMAs start to transform from the martensitic into the austenitic state upon actuation through resistive heating, simultaneously recover the prestrain, and thus cause the composite cylinder to expand in the radial direction. The externally pressurized composite cylinder with the SMA actuators was analyzed using the 3-D finite element method.