Lithographic Objective Research Articles

Global search algorithms in automated design of starting points for deep-UV lithography objective

Global search algorithms in automated design of starting points for deep-UV lithography objective

Optimization Design Method of a 6‐DOF Micromanipulation Mechanism for Extreme Ultraviolet Projection Lithography Objective Lens

Optimization Design Method of a 6‐DOF Micromanipulation Mechanism for Extreme Ultraviolet Projection Lithography Objective Lens

A Model-Based Approach for Measuring Wavefront Aberrations Using Random Ball Residual Compensation

The projection objective lens holds a pivotal role in lithography, directly influencing imaging system quality and, consequently, the lithography machine’s feature dimensions. Optical inspection methods for this lens require advancements in calibrating systematic error and enhancing alignment precision of auxiliary devices, given their impact on calibration accuracy. In the random averaging method, random ball can give rise to additional wavefront aberrations due to misalignment and numerical aperture mismatch. To mitigate these aberrations and enhance the accuracy of systematic error calibration, this paper introduces a random ball residual compensation (RBRC) model. Additionally, when combined with the random averaging technique, it elevates the calibration accuracy of the measured lens’s wavefront aberrations. The experimental results underscore the method’s effectiveness, accurately determining optical component eccentricities and numerical aperture errors. After eliminating these errors, more accurate values of lens wavefront aberrations are achieved. This research significantly contributes to enhancing error calibration of lithography objective lens systems.

Method to construct the initial structure of optical systems based on full-field aberration correction.

To meet full-field image quality requirements for extremely low aberration optical systems, an initial structure construction method for reflective optical systems based on full-field aberration correction is proposed. The aberration of the full field is used as the main evaluation criterion in this method. A multi-field evaluation function is established using the aberration values of multiple characteristic field points to represent the full-field imaging quality, and spatial ray tracing is introduced to constrain the optical system structure. Multi-objective optimization of the evaluation function is performed using a combinatorial nondominated sorting and metaheuristics algorithm; an initial optical system with a reasonable structure and corrected third-order aberrations over the full field is subsequently obtained. After optimization, an extreme ultraviolet lithography objective with a numerical aperture of 0.33 and root-mean-square wavefront error of 0.128 nm ($1/105\lambda, \lambda = 13.5\;{\rm nm}$) is obtained.

Process Optimization Based on Analysis of Dynamic and Static Performance Requirements of Ion Beam Figuring Machine Tools for Sub-Nanometer Figuring

Extreme ultraviolet lithography objective lenses require surface figure accuracy of approximately sub-nanometer root mean square (RMS). As the key equipment for sub-nanometer accuracy figuring, the dynamic and static performance of ion beam figuring (IBF) machine tools are critical. However, the related research is not sufficient and comprehensive. To this end, a general model of dynamic and static performance requirements on three-axis IBF machine tools was established. The requirements on dynamic and static performance under different figuring process for different surface shape were comprehensively analyzed. Analysis results revealed that the three-axis IBF machine tools require typical motion accuracy better than 100 μm and certain dynamic performance for achieving sub-nanometer accuracy. According to the theoretical and simulation results, a process optimization based on analysis of dynamic and static performance requirements of IBF machine tools for sub-nanometer figuring is proposed. To verify the proposed method, a Φ90 mm mirror with 2.594 nm RMS was figured to 0.251 nm RMS by optimizing the processing parameters to ensure that the IBF machine tool with measured performance (positioning error of 52.74 μm, 53.04 μm, 37.71 μm, and maximum acceleration of 1.0 m/s2, 1.3 m/s2, and 1.5 m/s2 for axes x, y, and z, respectively) meets the performance requirements. The proposed method can promote the application of three-axis IBF machine tools in sub-nanometer accuracy figuring.

Automatic design of an extreme ultraviolet lithography objective system based on the Seidel aberration theory.

In this paper, a method is proposed to solve the initial optical structure of an off-axis multimirror system for an extreme ultraviolet lithography (EUVL) application. By tracing the characteristic rays, the primary aberration can be expressed as a function of the distance and curvature based on the Seidel aberration theory. The initial structure with a favorable aberration performance is calculated when the function value is 0. We solve two different initial structures with an off-axis, six-mirror configuration with different optical powers. The NA of the finally optimized optical system is 0.25, the wavefront aberration rms value is less than 0.04λ, and the absolute distortion is below 1.2 nm.

Design of an extreme ultraviolet lithography projection objective with a grouping design method through forward and reverse real ray tracing.

As the logic node gets more and more advanced, the performance of extreme ultraviolet (EUV) objective projection is required to be higher and higher in a large field of view. It is known that a good initial structure can greatly reduce the dependence on the experience of optical designers. In this paper, a grouping design method through forward and reverse real ray tracing is proposed to design the aspheric initial structure for the EUV objective system. The system is first divided into three groups, and each spherical group is designed separately. Then, the three groups are connected as a whole spherical initial objective system. Through forward and reverse real ray tracing, each spherical group is recalculated to an aspheric structure in turn. Finally, an iterative process is applied to improve the performance of the aspheric initial structure. The aspheric initial structure calculated by this method can be taken as a good starting point for further optimization. As verification of the design method, a six-aspheric-mirror EUV lithography objective with a numerical aperture of 0.33 has been designed, whose root mean square (RMS) wavefront error is less than 0.2 nm and distortion is less than 0.1 nm.

Nonlinear Effects of Pulsed Ion Beam in Ultra-High Resolution Material Removal.

Ion beam sputtering is widely utilized in the area of ultra-high precision fabrication, coating, and discovering the microworld. A pulsed ion beam (PIB) can achieve higher material removal resolution while maintaining traditional ion beam removal performance and macro removal efficiency. In this paper, a 0.01 s pulse width beam is used to sputter atom layer deposition (ALD) coated samples. The nano-scale phenomenon is observed by high-resolution TEM. The results show that when the cumulative sputtering time is less than 1.7 s, the sputtering removal of solid by ion beam is accompanied by a nonlinear effect. Furthermore, the shortest time (0.05 s) and lowest thickness (0.35 nm) necessary to remove a uniform layer of material were established. The definition of its nonlinear effect under a very small removal amount guides industrial ultra-high precision machining. It reveals that PIB not only has high removal resolution on nanoscale, but can also realize high volume removal efficiency and large processing diameter at the same time. These features make PIB promising in the manufacturing of high power/energy laser optics, lithography objective lens, MEMS, and other ultra-high precision elements.

Grouping design method dependence on an illumination system and large off-axis distance for an anamorphic extreme ultraviolet lithography objective

High-numerical-aperture (NA) anamorphic extreme ultraviolet lithography (EUVL) is the next-generation technology to achieve a 3 nm node and below. Current EUVL anamorphic projection objectives in publications are designed with small off-axis distance of the field of view (FOV). Further, the ray path of the illumination system will be obscured by the last mirror of the objective. In fact, as the NA increases, the diameter of the last mirror of the objective becomes larger. Thus, the off-axis distance of the FOV should be larger to ensure that the ray path of the illumination system is not obscured by the objective. It is well known that the design of an anamorphic EUVL objective with large off-axis distance is very challenging. In this paper, a high-NA anamorphic EUVL objective with large off-axis distance is designed. The value of the large off-axis distance that satisfies the unobscured constraint is first analyzed. Then an 8× demagnification isomorphic objective with large off-axis distance is designed by a grouping design process. Finally, the XY polynomial surface is adopted to achieve a 4× demagnification perpendicular to the scanning direction. This method is implemented to design a NA 0.55 anamorphic EUVL objective with large off-axis distance. The performance of the designed objective demonstrates that this design method is very effective and will provide a good structure of the objective for the illumination system design.

Design of X-Y Flexible Adjustment Mechanism for Moving Mirror in Lithographic Projection Objective

Design of X-Y Flexible Adjustment Mechanism for Moving Mirror in Lithographic Projection Objective

Study on rapid convergence strategy of nano-precision optical surface by ion beam figuring

Ion beam figuring (IBF) provides a deterministic figuring method for fabricating ultra-high precision optical components such as lithographic objective lenses. But in the previous IBF process, the convergence of surface accuracy is often uncertain. Therefore, the iterative processing methods are mostly adopted. In the iterative process, the convergence ratio (the ratio of root mean square before and after figuring) of single figuring is relatively low. With the improvement of machining accuracy, the convergence ratio continues to decrease. The study analyzes the factors that limit the convergence ratio of single processing and the influence form and degree of each element on the convergence ratio. Furthermore, we present an IBF strategy with a high convergence ratio based on an optimized removal function. Based on this strategy, we complete the figuring experiment. The convergence ratio is much higher than the previous level. Compared with the surface of iterative figuring, the surface is simple and more favorable to figuring to sub-nanometer precision. The experimental results show that we can optimize the removal function to achieve rapid optical surface fabrication with nanometer precision.

Transient dynamical-thermal-optical system modeling and simulation

In modern high resolution optical systems like astronomical telescopes or lithographic objectives, performance degradations can be caused by various disturbances. Holistic optical system simulation is required to predict the performance or the high precision systems. In this paper a method for transient dynamical-thermal-optical system modeling and simulation is introduced. Thereby, elastic deformation, rigid body motion, and mechanical stresses due to dynamical excitation are calculated using elastic multibody system simulation and temperature changes are determined using thermal finite element analysis. The deformation, the motion, and the mechanically and thermally induced stress index changes are then considered in a gradient-index ray tracing. Finally, the presented method is applied in a dynamical-thermal single lens system.

Design method for off-axis aspheric reflective optical system with extremely low aberration and large field of view.

This paper proposes a grouping design method based on a combination of spatial ray tracing and aberration correction to construct the initial structure for an off-axis multi-reflective aspheric optical system. This method establishes a mathematical parameter model of the optical system to satisfy the aberration balance and multi-constraint control requirements. The simulated annealing particle swarm algorithm is applied to calculate the initial optical system structure. Finally, an extreme ultraviolet (EUV) lithography projection objective with six-reflective aspheric mirrors is used as an example to verify the reliability and effectiveness of this method. A 0.33 numerical aperture EUV lithographic objective with wavefront error better than 1/70λ(λ=13.5nm) root mean square (RMS) is obtained.

组合倍率极紫外光刻物镜系统梯度膜设计方法

组合倍率极紫外光刻物镜系统梯度膜设计方法

Optimization techniques applied to initial designs of ultraviolet lithographic objectives

The optimization of lithographic objectives is a quite challenging task due to many conflicting constraints, limitations and numerous variables. We describe the optimization techniques of starting designs for ultraviolet objectives which were previously generated by the global search algorithm. The powerful tools for the global optimization as Automatic Element Insert feature and Saddle points construction were applied to starting points, examining the applicability limited by design considerations. The ray tracing failures and critical lenses in starting designs caused by automatic decisions of the global search algorithm are fixed and replaced by Saddle point construction. The results of this work and presented techniques of the global optimization are valid and relevant for any on-axis complex optical system.

Starting point selection in grouping design method for lithographic objectives

This work aims on method development for obtaining initial designs for ultraviolet (UV) and deep-ultraviolet (DUV) objectives through global search algorithm. We studied a global search based algorithm tending to obtain the feasible local minima of lens design landscape. One of the major challenges of our work is writing macro input related to a number of lenses, the length of objective, and glass material. The obtained results show the main advantages and efficiency of the design approach based on the global search algorithm. As an output, we developed a method and criteria for successful selection of the starting point of micro-lithographic objectives

高数值孔径自由曲面极紫外光刻物镜光学设计

高数值孔径自由曲面极紫外光刻物镜光学设计

16 nm极紫外光刻物镜热变形对成像性能影响的研究

16 nm极紫外光刻物镜热变形对成像性能影响的研究

Design of a hyper-numerical-aperture deep ultraviolet lithography objective with freeform surfaces

We have proposed and developed a design method of a freeform surfaces (FFSs) based hyper-numerical-aperture deep ultraviolet (DUV) projection objective (PO) with low aberration. With an aspheric initial configuration, lens-form parameters were used to determine the best position to remove elements and insert FFSs. The designed FFSs PO reduced two elements without increasing the total thickness of the glass materials. Compared with aspheric initial configuration, the wavefront error of the FFSs PO decreased from 0.006λ to 0.005λ, the distortion reduced from 1 to 0.5 nm, and the aspheric departure decreased from 1.7 to 1.35 mm. The results show that the design method of the FFSs PO is efficient and has improved the imaging performance of PO. The design method of FFSs PO provides potential solutions for DUV lithography with low aberrations at 10–5 nm nodes.

Influence of model order reduction methods on dynamical–optical simulations

In this work, the influence of model order reduction (MOR) methods on optical aberrations is analyzed within a dynamical–optical simulation of a high precision optomechanical system. Therefore, an integrated modeling process and new methods have to be introduced for the computation and investigation of the overall dynamical–optical behavior. For instance, this optical system can be a telescope optic or a lithographic objective. In order to derive a simplified mechanical model for transient time simulations with low computational cost, the method of elastic multibody systems in combination with MOR methods can be used. For this, software tools and interfaces are defined and created. Furthermore, mechanical and optical simulation models are derived and implemented. With these, on the one hand, the mechanical sensitivity can be investigated for arbitrary external excitations and on the other hand, the related optical behavior can be predicted. In order to clarify these methods, academic examples are chosen and the influences of the MOR methods and simulation strategies are analyzed. Finally, the systems are investigated with respect to the mechanical–optical frequency responses, and in conclusion, some recommendations for the application of reduction methods are given.