Extreme ultraviolet (EUV) lithography is one of the most promising techniques in the semiconductor industry to enhance resolution, line edge roughness (LER) and sensitivity of chemically amplified resist (CAR) pattern. Post exposure bake (PEB) process, a major process in EUV lithography, has been studied by experimental approach, but they are confronted by time-consuming tasks for massive combinatorial research. Also, theoretical models have been reported to explain fundamental mechanism of the process, but the single-scale simulation studies show obvious limitations for accurate prediction of photo-chemical reactions in photoresist (PR) matrix and the resulting morphology of line pattern. In order to settle the problem, a multiscale model (density functional theory (DFT)-molecular dynamics (MD)-finite difference method (FDM) integration) was developed to simulate chemical reactions including PAG dissociation, acid diffusion, and deprotection of photoresist in our previous study, which is based on two-components system (PAG and PR). Herein, we propose the multiscale model for three molecular components consisting of PAG, PR, and photo-decomposable quencher (PDQ) which is widely used for fine PR pattern fabrication by neutralizing acid in unexposed region of the resist. The newly constructed model reflects more realistic acid diffusion and chemical reactions on PEB process. This achievement will be helpful to identify critical design parameters and suggest optimized design materials in EUV lithography process.
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.
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.
The availability of defect-free masks remains one of the key challenges for inserting extreme ultraviolet lithography
(EUVL) into high volume manufacturing. Recently both blank suppliers achieved 1-digit number of defects at 60nm in
size using their M1350s. In this paper, a full field EUV mask with Teron 61X blank inspection is fabricated to see the
printability of various defects on the blank using NXE 3100. Minimum printable blank defect size is 23nm in SEVD
using real blank defect. Current defect level on blank with Teron 61X Phasur has been up to 70 in 132 X 132mm<sup>2</sup>. More
defect reduction as well as advanced blank inspection tools to capture all printable defects should be prepared for HVM.
3.6X reduction of blank defects per year is required to achieve the requirement of HVM in the application of memory
device with EUVL. Furthermore, blank defect mitigation and compensational repair techniques during mask process
needs to be developed to achieve printable defect free on the wafer.
Amplitude defects (or absorber defects), which are located in absorber patterns or multilayer surface, can be repaired
during mask process while phase defects (or multilayer defects) cannot. Hence, inspection and handling of both defects
should be separately progressed. Defect printability study of pattern defects is very essential since it provides criteria for
mask inspection and repair. Printed defects on the wafer kill cells and reduce the device yield in wafer processing, and
thus all the printable defects have to be inspected and repaired during the mask fabrication. In this study, pattern defect
printability of the EUV mask as a function of hp nodes is verified by EUV exposure experiments. For 3x nm hp nodes,
defect printability is evaluated by NXE3100. For 2x nm hp node, since resolution of a current EUV scanner is not
enough, SEMATECH-Berkeley actinic inspection tool (AIT) as well as micro-field exposure tool (MET) in LBNL are
utilized to verify it,. Furthermore those printability results are compared with EUV simulations. As a result, we define
size of defects to be controlled in each device node.