Over the recent years, extreme ultraviolet (EUV) lithography has demonstrated the patterning of ever-shrinking feature sizes (enabling the N7 technology node and below), whereas the EUV mask has remained unaltered, using a 70-nm tantalum (Ta)-based absorber. This has led to experimentally observed mask three-dimensional (M3D) effects at the wafer level, which are induced by the interaction between the oblique incident EUV light and the patterned absorber with typical thickness values on the order of several wavelengths. We exploit the optical properties of the absorber material of the EUV mask as an M3D mitigation strategy. Using rigorous lithographic simulations, we screen potential single-element absorber materials for their optical properties and optimal thickness for minimum best focus variation through pitch at the wafer level. In addition, the M3D mitigation by absorber material is evaluated by process window comparison of foundry N5-specific logic clips. To validate the rigorous simulation predictions and test the processing feasibility of the alternative absorber materials, we have selected the candidate single elements nickel and cobalt for an experimental evaluation on wafer substrates. We present the film characterization as well as the first patterning tests of these single-element candidate absorber materials.
Over the recent years EUV lithography has demonstrated the patterning of ever shrinking feature sizes (enabling the N7 technology node and below), while the EUV mask has remained unaltered using a 70nm Ta-based absorber. This has led to experimentally observed Mask 3D (M3D) effects at wafer level, which are induced by the interaction between the oblique incident EUV light and the patterned absorber with typical thickness values in the order of several wavelengths. In this paper we exploit the optical properties of the absorber material of the EUV mask as M3D mitigation strategy.
Using rigorous lithographic simulations, we screen potential single element absorber materials for their optical properties and their optimal thickness for minimum best focus variation through pitch at wafer level. In addition, the M3D mitigation by absorber material is evaluated by process window comparison of foundry N5 specific logic clips.
In order to validate the rigorous simulation predictions and to test the processing feasibility of the alternative absorber materials, we have selected the candidate single elements Nickel and Cobalt for an experimental evaluation on wafer substrates. In this work, we present the film characterization as well as first patterning tests of these single element candidate absorber materials.
This paper proposes a method for the characterization of multilayer defects from extreme ultraviolet (EUV) projection images at different focus positions. The transport-of-intensity equation is applied to retrieve the phase distribution of the reflected light in the vicinity of the defect. The defect-induced intensity and phase modifications and their dependency from defect geometry parameters are analyzed by several selected optical properties of multilayer defect. To reconstruct the defect geometry parameters from the intensity and phase of a defect, a principal component analysis (PCA) is employed to parameterize the intensity and phase distributions into principal component coefficients. In order to construct the base functions of the PCA, a combination of a reference multilayer defect and appropriate pupil filters is introduced to obtain the designed sets of intensity and phase distributions. Finally, an artificial neural network is applied to correlate the principal component coefficients of the intensity and the phase of the defect with the defect geometry parameters and to reconstruct the unknown defect geometry parameters. The performance of the proposed approach is evaluated both for mask blank defects and for defects in the vicinity of an absorber pattern.
This paper proposes a new method for the characterization of multilayer defects on EUV masks. To reconstruct the defect geometry parameters from the intensity and phase of a defect, the Principal Component Analysis (PCA) is employed to parametrize the intensity and phase distributions into principal component coefficients. In order to construct the base functions of PCA, a combination of a reference multilayer defect and appropriate pupil filters is introduced to obtain the designed sets of intensity and phase distributions. Finally, an Artificial Neural Network (ANN) is applied to correlate the principal component coefficients of the intensity and the phase of the defect with the defect geometry parameters and to reconstruct the unknown defect geometry parameters.
This paper proposes a new method for the characterization of multilayer defects of EUV masks. The method uses measured or simulated EUV projection images at different focus positions. The Transport of Intensity Equation (TIE) is applied to retrieve the phase distribution of the reflected light in the vicinity of the defect. An Artificial Neural Network (ANN) is applied to correlate the optical properties of the intensity and recovered phase of the defect with the defect geometry parameters and to reconstruct the defect geometry parameters from though-focus-images of unknown defects.
An in situ aberration measurement technique based on an aerial image with an optimized source is proposed. A linear relationship between the aerial image and Zernike coefficients is established by the principal components and regression matrices, which are obtained in a modeling process through principal component analysis (PCA) and regression analysis. The linear relationship is used to extract Zernike aberrations from the measured aerial image in a retrieval process. The characteristics of regression matrix are analyzed, and the retrieval process of Zernike coefficients is optimized. An evaluation function for the measurement accuracy of Zernike aberrations is proposed, and then a fast procedure to optimize the illumination source is designed. Parameters of the illumination source are optimized according to the evaluation function and applied in our method. The simulators Dr.LiTHO and PROLITH are used to validate the method. Compared to the previous aberration measurement technique based on principal component analysis of an aerial image (AMAI-PCA), the number terms of Zernike coefficients that can be measured are increased from 7 to 27, and the measurement accuracy of Zernike aberrations is improved by more than 20%.
Defect parameters retrieval from diffraction-limited images is demonstrated. The parameters of defects in nanostructures
are retrieved from measured aerial images of high NA-projection systems. The difference between images of masks with
and without defects is used as a reference to reconstruct the parameters of the defect. An error function is defined, and
the whole retrieval procedure can be expressed as an optimization problem. The performance of the technique was
simulated by the lithography and imaging simulator Dr.LiTHO. The dependencies of the retrieval results on optimizers,
illumination settings, defect sizes, and reference images are presented. The evaluation of the performance of the
technique is performed by comparison of the retrieval errors for defect shapes, mask patterns, and types of noise.
Moreover, the sensitivity of the defect detection to Zernike aberrations of the optical image projection lens and the
retrieval accuracy for different mask models and types of defects are investigated.
In this paper, we propose an aberration metrology (AM) of a lithographic projection lens based on aerial images (AI) by using a quadratic relationship model (Quad) between the aerial-image intensity distribution and the Zernike coefficients. The proposed method (AMAI-Quad) uses principal component analysis and multiple linear regression analyses for model generation. The quadratic model is, then, used to extract Zernike coefficients by a nonlinear least-squares minimizing technique. The best linear constrain condition is estimated by optimizing the illumination settings. Compared with earlier techniques, based on a linear relationship between Zernike coefficients and AIs, the new method can extend the orders of Zernike coefficients measured. The application of AMAI-Quad to AIs, computed by lithography simulators PROLITH and Dr.LiTHO, demonstrated an extension of measurement range to 90mλ and an enhancement of measurement accuracy by more than 30 percent.
A novel technique (AMAI-Quad) for aberration extraction of lithographic projection based on quadratic relationship
model between aerial-image intensity distribution and Zernike coefficients is proposed. Zernike coefficients in this case
represent the imaging quality of lithographic projection lens in a semiconductor wafer exposure scanner. The proposed
method uses principal component analysis and multivariate linear regression analysis for model generation. This
quadratic model is then used to extract Zernike coefficients by nonlinear least-squares. Compared with earlier techniques,
based on a linear relationship between Zernike coefficients and aerial images, proposed by Duan, the new method can
extend the types of aberrations measured. The application of AMAI-Quad to computed images of lithography simulators
PROLITH and Dr.LiTHO for randomly varied wavefront aberrations within a range of 50mλ demonstrated an accuracy
improvement of 30%.
An in-situ aberration measurement technique based on aerial image with optimized source is proposed. A linear
relationship between aerial image and Zernike coefficients is established by principle component analysis and regression
analysis. The linear relationship is used to extract aberrations. The impacts of the source on regression matrix character
and the Zernike aberrations measurement accuracy are analyzed. An evaluation function for the aberrations measurement
accuracy is introduced to optimize the source. Parameters of the source are optimized by the evaluation function using
the simulators Dr.LiTHO and PROLITH. Then the optimized source parameters are adopted in our method. Compared
with the previous aberration measurement technique based on principal component analysis of aerial image
(AMAI-PCA), the number terms of Zernike coefficients that can be measured are increased from 7 to 27, and the
Zernike aberrations measurement accuracy is improved by more than 20%.
The phase transformation and superelastic properties of NiTi thin films prepared by sputtering were studied. Thin films’ phase transformation process was analyzed with resistance temperature curves and X-ray diffraction spectroscopy. Meanwhile, the structure and transformation temperature were gained. In order to characterize their superelasticity, tensile and bulging and indentation test were performed.
TiNiCu thin film shape memory alloys are potential materials for microactuator. In our previous research, the various natural surface relief of crystallized TiNiCu thin film was observed, and it was related with compositions and the sputtering deposition conditions. In order to understand the origin and nature of the surface relief, the temperature-resistance measurement, X-ray diffraction and atomic fore microscopic study were performed. For Ti48.4Ni46.3Cu5.3 thin films, the transformation temperatures are below 0 degree(s)C, and the natural surface is smooth at 12 degree(s)C since the microstructure is austenite. For Ti51Ni44Cu5 thin films, two typical kinds of surface relief, e.g., chrysanthemum and rock candy, were observed at 12 degree(s)C. The chrysanthemum on the martensitic block relief is Ti-rich G.P. zone and will not disappear in thermal cycles later. It is also found that the Ti-rich G.P. zone is related with the thin films formed under lower sputtering Ar pressure. The rock candy relief is a typical martensite surface relief and will disappear when heating to the austenite phase. During crystallization process, the inherent compressive stress introduced under the condition of higher sputtering pressure is helpful to the transition from G.P. zones to Ti2(NiCu) precipitates and the increase of the transformation temperatures.
A novel design of a diaphragm microactuator prepared for micropump has previously been reported. The composite diaphragm consists of a silicon membrane and a patterned Titanium-Nickel (TiNi) thin film. In order to understand the actuation behavior of the diaphragm, modeling and thermal simulation of the diaphragm microactuator is performed with commercial finite element analysis (FEA) software ANSYS. In this paper, dynamic temperature distributions in thermal cycles are comparatively studied. During the thermal cycles, temperatures at the center and the border of the diaphragm and in the rounding silicon frames are monitored. The influences of the operational parameters such as current and duty ratio on the temperature distributions are quantitatively predicted. The optimal heating condition for the actuation can be inferred from the simulation results. Futhermore, diaphragm deflection profiles and stress distributions are illustrated by coupled thermomechanical analysis based on the thermal analysis. The experimental measurements of the deflection dependence on various power supplies can be explained in terms of the temperature variations in cycles. Finally, optimization of the patterned TiNi resistance strips is also proposed with respect to uniform temperature distribution and maximum deflection.
TiNi/Si diaphragm is a useful selection for reciprocating motion microactuator, since it needn't complex bias structure and special thermal-mechanical training. The TiNi/Si actuating diaphragm with patterned TiNi resistance strip can improve the dynamic response effectively. The several kinds of pattern of TiNi thin films with various shapes and sizes were designed and processed, and the influences of patterning and Si thickness on the characteristics of phase transformation were analyzed by measuring electrical resistance-temperature curves. Moreover, the stress distributions and maximum deflections of TiNi/Si diaphragms with different Si thickness were simulated by FEA. The results show that the phase transformation behaviors of the TiNi thin films with different Si thickness and various patterns are different. Based on these results, optimized actuating diaphragm with patterned TiNi/Si structure was developed. The thermal actuating results are agreed with simulating results of FEA.
Thin film shape memory alloy microactuators are the promising devices in MEMS. A kind of simple and effective micropump driven by bimorph thin film NiTi/Si diaphragm has been fabricated in our laboratory. This paper presents the optimization of the diaphragm structure with the finite element analysis package ANSYS. Maximum actuation deflections and stress distributions of five kinds of typical structures are analyzed. Simulation results show that patterned NiTi strips should be placed in the center of the silicon membrane to get uniform stress distribution, and there is an optimized distance between the boundaries of NiTi and Si to get maximum actuation deflection. The stress variances of NiTi films and silicon membranes in optimized structure during driving processes are limited in the range of elastic strain, which means the optimized NiTi/Si diaphragm structure has excellent actuation lifetime.
The relationship between the magneto-impedance (MI) effect and the size of amorphous FeSiB film is reported in this paper. The MI change ratio of FeSiB film is different for the three samples with different widths, and increases with the increasing of sample length when the width is fixed. Experimental results can be explained in terms of stress anisotropy and different external inductance of the sample.
Combining sol-gel and Rf magnetron sputtering techniques, the smart PZT/NiTi/Ti/SiO2/Si and PZT/Pt/Ti/SiO2/Si heterostructures were prepared. Based on these material systems, two types of membrane actuators were designed and fabricated by using semiconductor micro-fabrication techniques. The 0.4 micrometers thick PZT thin films were used as actuator components, which were driven by sinusoidal or triangular wave current with different frequency. A single laser interference system was used to examine dynamic displacements. Compared with the PZT/Pt/Ti/SiO2/Si, the PZT/NiTi/Ti/SiO2/Si membrane actuators revealed more complexes and larger dynamic displacement. The highest deflect displacement of PZT/NiTi/Ti/SiO2/Si and PZT/Pt/Ti/SiO2/Si actuators occurred at the resonance frequency of 21.11 and 33.6 kHz respectively.
The internal stress in SMA/Si bimorph structure was investigate din this paper. The shape memory alloy (SMA) thin films were sputter-deposited onto single crystal silicon substrates at room temperature and thin annealed at high temperature for crystallization. The internal stresses in SMA films before and after crystallization were measured by substrate-curvature method based on S. Timoshenko's theory. The results show that the internal stress changes from compressive to tensile after film crystallization. The intrinsic stress in the sputter-deposited SMA films is almost relaxed completely during the crystallization annealing and the internal stress in crystallized SMA film is dominated by thermal stress. By varying the sputtering power during deposition, the interface status and intrinsic stress can be controlled and excellent SMA/Si bimorph actuation structure can be obtained.
A novel micropump actuated by NiTi/Si diaphragm has been developed. In order to optimize the actuating performance of the micropump, the dynamic actuating properties were studied in different actuating conditions such as different actuating currents, frequencies and duty cycles. The experimental result show that there is a maximum displacement when increasing the actuating current and frequency. The influence of duty cycle on maximum displacement when increasing the actuating current and frequency. The influence of duty cycle on maximum displacement with water flow and without water flow is different. The higher the displacement of the diaphragm is, the larger the flow rate is for a given frequency. The displacement of the pump diaphragm depends not only on the flow rate, but also on the moving frequency. The change of the resistance of NiTi strip indicates that the A - M phase transformation is completed partly during dynamic actuating processes. The maximum flow rate of 360 (mu) l/min was obtained in about 50Hz with 1:1 duty cycle in our experiment.
The patterning of nickel-titanium SMA thin films was one of critical micromachining issues during developing SMA film devices, now, an excellent etchant for etching of Ni-Ti SMA thin films was developed, therefore, this problem can be solved by photochemical etching easily. The etchant is based on the dilute hydrofluoric acid with several kinds of additives. The etching process is operated at room temperature with the etching rate of (1-5)micrometers /Min. The etched surface is very smooth and the edge of patterned SMA line is exactly the same as that of patterned photoresist. The etch factor is above 1.5 and might be enlarged furthermore. The etchant is stable and the repeatability is also good. This patterning method is compatible with IC processes, so it is easy to design and fabricate any magic pattern for MEMS applications.
A novel micropump actuated by thin film shape memory alloy has been designed, fabricated and tested. It is one of the membrane reciprocating micropumps which is driven by shape recoverable force of NiTi thin film and biasing force of Si membrane. The micropump is composed of a deformable chamber and two Si flap check valves. The structure of pump is simple. The pump was manufactured by Si surface and bulk micromachining technologies, Au-Si eutectic and epoxy bonding. The outer dimension of the micropump is 6*6*1.5 mm/mm/mm. The NiTi/Si composite actuator has an area of 3*3mm/mm with a thickness of 20micrometers Testing result show that the pump has extremely good performance, such as high pumping yield, low power consumption high working frequency. All these advantages are attributed to the patterning of NiTi thin film used as self-heating element and optimizing design of NiTi/Si actuated structure.