Sidewall Angle Research Articles

Application of a machine learning method to model-based library approach for critical dimension measurements using CD-SEM

A model-based library (MBL) method has already been established for the accurate measurement of the critical dimension (CD) of semiconductor linewidth using critical dimension scanning electron microscope (CD-SEM) images. In this work, the MBL method is further investigated by combining CD-SEM image simulation and a neural network algorithm. The secondary electron linescan profiles were first calculated using a Monte Carlo simulation method, enabling us to obtain the dependence of linescan profiles on the selected values of various geometrical parameters (e.g. top CD, sidewall angle and height) for Si and Au trapezoidal line structures. Machine learning methods have then been applied to predict the linescan profiles from a randomly selected training set of the calculated profiles. The predicted results agree very well with the calculated profiles with the standard deviations of 0.1% and 6% for the relative error distributions of Si and Au line structures, respectively. The findings show that the machine learning methods can be practically applied to the MBL method for reducing the library size, accelerating the construction of the MBL database and enriching the content of the available MBL database.

Nanoimprint lithography guiding templates for advanced magnetic media fabrication

Nanoimprint lithography presents unique opportunities for advanced magnetic storage media with ordered bit arrangements such as bit patterned media or heated dot magnetic recording. Providing sub-10 nm resolution and full disk imprinting capability, UV-nanoimprint lithography based on rigid quartz templates bears the entitlement for patterned recording media manufacturing with high throughput at low cost. However, a key challenge is the fabrication of the high-resolution template that can transfer the desired pattern onto the disk with high fidelity and low line edge roughness. In this article, we present fabrication routes and overcome challenges to the fabrication of quartz templates suitable for self-alignment and guiding purposes to be used for template replication toward full disk imprints. Guiding patterns down to 40 nm pitch are prepared using a rotary electron beam lithography tool. We compare three different process approaches to fabricate an etching mask for patterning the quartz. Two methods target chromium patterning, one with traditional lift-off and another by dry etching, both using an e-beam resist mask. The third approach is based on the development of a carbon-based Tri-layer hard mask. The template pattern profile is optimized for imprint-suitable sidewall angles using dry etching in a CF4/O2 chemistry. The templates were characterized using scanning electron microscopy and atomic force microscopy to evaluate the quality of the transferred pattern as well as line edge roughness. Our results show that the Tri-layer process using carbon resulted in the lowest line edge roughness of ≈0.65 nm at the imprinted disk level. In addition, we show that Tri-layer masking allowed for the use of conventional ZEP e-beam resist and fast writing speeds, while gaining high selectivity during quartz patterning.

Operational condition and furnace geometry for premixed C3H8/Air MILD combustion of high thermal-intensity and low emissions

MILD combustion is usually operated at relatively low thermal intensity to achieve uniform temperature field and low pollutant emissions, further understanding of its emission characteristics at high thermal intensity condition is required to widen its application. In the present numerical study of premixed C3H8/air MILD combustion, different operational conditions (equivalence ratio Φ and thermal input Pinput) and furnace geometries (side wall angle α and aspect ratio AR) are considered to reveal their correlations with pollutant emissions including CO, NOx and unburned hydrocarbon (UHC) at thermal intensities up to 1.06 MW/m3. By adopting reactor network calculation with detailed combustion chemistry, it is found that AR plays a notable role in controlling CO, NOx and UHC emissions, while NOx emission is insensitive to the variation of side wall angle. Both the CO and UHC emissions are related to the location of the internal recirculating vortex. Moreover, following the parametric study and NOx formation analysis, the optimized furnace geometry and operating condition of AR = 5, α = 0° and Φ = 0.6 are obtained to significantly reduce the pollutant emissions by 90 % for both C3H8 and CH4 fuels. The present investigation offers valuable insights into the high thermal intensity MILD combustion.

Modeling and algorithm of three-dimensional metrology with critical dimension scanning electron microscope

To address the challenges of accurate metrology of height and sidewall angle (SWA) of three-dimensional structures with critical dimension scanning electron microscopy, general modeling and algorithms based on tilted electron beam technology and the corresponding application skills are proposed, and the validity and error accuracy are evaluated as well. Three typical structures, the trapezoid, inverted trapezoid, and step, are investigated with Monte Carlo simulation. The maximum derivative method is used to extract key parameters from the secondary electron linescan. The efficiency of the proposed modeling, algorithms, and the accuracy of the calculated height and SWA are improved further with the application of wavelet transform.

Research On Etching of Distributed Bragg Reflector

This study investigated the effect of etching process parameters on the sidewall morphology and bottom metal etching damage of Distributed Bragg Reflector (DBR), and analyzed the underlying mechanisms. By comparing the etching morphology under different RF power and pressure conditions, it was found that increasing RF power and reducing pressure can solve the problem of sidewall fracture and obtain a smooth sidewall morphology. By comparing the effect of different process gases on the sidewall angle, it was found that adding O2 can reduce the DBR/Photoresit selectivity and sidewall angle while adding BCl3 can increase the DBR/Photoresit selectivity and sidewall angle. Therefore, the sidewall angle can be adjusted by controlling the type and flow rate of the etching gas. By comparing the DBR/metal selectivity under different RF power, it was found that as the RF power decreases, the DBR/metal selectivity increases, which can prevent metal splashing caused by over-etching of metal. Therefore, in DBR etching, high RF power is used for main etching to obtain a smooth sidewall morphology and the sidewall angle can be adjusted by varying the gas type and flow rate, while low RF power is used for over-etching to improve the DBR/metal selectivity and prevent metal over-etching. This study has reference significance for the development of the inverted chip DBR process.

Enhancing light extraction efficiency and color stability for OLED by truncated micro-cone array films

A newly truncated micro-cone array film as light extraction layer for organic light emitting diodes (OLEDs) has been developed, which was fabricated by process combined with photolithography, polydimethylsiloxane (PDMS) molding, self-assembled anti-adhesion, and ultraviolet (UV) forming techniques. In this study, by varying the sidewall angle and fill factor of this film, their influences on the optical properties and light extraction efficiency for OLED are fully investigated. As a result, device performance of OLED employed truncated micro-cone array film, with a high fill factor and sidewall angle of 76.49⁰, was found to be significantly enhanced up to 52% compared with the reference OLED. Notably, the proposed truncated micro-cone array film also stabilized emissive color stability while the viewing angle changes from 0° to 70°, achieving an excellent angular shift with CIE-indices of (0.0025, 0.0066). Aforementioned findings contribute to the development in advanced OLEDs for display and lighting applications.

Advanced Etching Techniques of LiNbO3 Nanodevices.

Single LiNbO3 (LNO) crystals are widely utilized in surface acoustic wave devices, optoelectronic devices, and novel ferroelectric memory devices due to their remarkable electro-optic and piezoelectric properties, and high saturation and remnant polarizations. However, challenges remain regarding their nanofabrication that hinder their applications. The prevailing etching techniques for LNO encompass dry etching, wet etching, and focused-ion-beam etching, each having distinct merits and demerits. Achieving higher etching rates and improved sidewall angles presents a challenge in LNO nanofabrication. Building upon the current etching researches, this study explores various etching methods using instruments capable of generating diverse plasma densities, such as dry etching in reactive ion etching (RIE) and inductively coupled plasma (ICP), proton exchange-enhanced etching, and wet chemical etching following high-temperature reduction treatment, as well as hybrid dry and wet etching. Ultimately, after employing RIE dry etching combined with wet etching, following a high-temperature reduction treatment, an etching rate of 10 nm/min and pretty 90° sidewall angles were achieved. Furthermore, high etching rates of 79 nm/min with steep sidewall angles of 83° were obtained using ICP dry etching. Additionally, using SiO2 masks, a high etching rate of 108 nm/min and an etching selectivity ratio of 0.86:1 were achieved. Distinct etching conditions yielded diverse yet exceptional results, providing multiple processing paths of etching for the versatile application of LNO.

Structural investigation of ultra-low resistance deeply recessed sidewall ohmic contacts for AlGaN/GaN HEMTs based on Ti/Al/Ti-metallization

This study presents a novel approach to forming low-resistance ohmic contacts for AlGaN/GaN HEMTs. The optimized contacts exhibit an outstanding contact resistance of approximately 0.15 Ω·mm. This is achieved by firstly recessing the barrier of the heterostructure to a depth beyond the channel. In this way, the channel region is exposed on the sidewall of the recess. The coverage of the Ti/Al/Ti ohmic metalization on the sidewall is ensured through tilting of the sample during evaporation. The annealing process is performed at a low temperature of 550 °C. The approach does not require precise control of the recess etching. Furthermore, the method is directly applicable to most barrier designs in terms of thickness and Al-concentration. The impact of recessed sidewall angle, thickness and ratio of Ti and Al layers, and the annealing procedure are investigated. Structural and chemical analyses of the interface between the ohmic contacts and epi-structure indicate the formation of ohmic contacts by the extraction of nitrogen from the epi-structure. The approach is demonstrated on HEMT-structures with two different barrier designs in terms of Al-concentration and barrier thickness. The study demonstrate large process window in regard to recess depth and duration of the annealing as well as high uniformity of the contact resistance across the samples, rendering the approach highly suitable for industrial production processes.

Analysis and control of self stable balance circle of surrounding rock of roadway in inclined coal seam

The asymmetric deformation of surrounding rock in inclined coal seam roadway is serious, and its stability is difficult to control. Based on the PU's arch theory and considering the development process of the progressive formation of the self stable balance circle (SSBC), this paper establishes a mechanical model of the SSBC for the right-angle trapezoidal roadway in the inclined coal seam. The mechanical analysis and morphological characterization of the forming process were carried out, and the numerical simulation and physical similarity simulation test were carried out to verify. On this basis, the stability control method of roadway in inclined coal seam is improved, and the asymmetric support scheme of roadway is optimized, which is verified by numerical simulation and field monitoring. The results show that the roadway surrounding rock forms a quasi elliptical SSBC after self stabilization, and the mechanical formula of the shape of the SSBC is derived and characterized. Through numerical simulation and physical similarity simulation experiments, the dynamic evolution process of SSBC is depicted, and the gradual forming evolution characteristics of SSBC are revealed. With the increase of the deformation of the surrounding rock, the effective height and width of the roadway gradually increase, and finally a quasi elliptical SSBC deflecting to the left side of the roadway is formed. Based on this, the asymmetric support principle that can control the stability of surrounding rock by improving the asymmetric stress concentration is proposed, and the asymmetric support scheme is designed, that is, "the anchor bolts (cables) are arranged to the right sidewall, and the sidewall angle weakening area is intensively supported". Through numerical simulation and field monitoring, the support effect is remarkable.

Simulation of the Entrance to the Escape of the Flood Branching from the Diyala River

The Diyala River is considered the third most important river in Iraq. However, in the recent period, Diyala Governorate has been subject to several floods. This study aims to simulate an efficient labyrinth weir at the flood escape entrance branching from the Diyala River to reach the best entrance through which the flood waves can pass safely. The discharge coefficient was calculated laboratory for five types of trapezoidal side labyrinth weirs with different sidewall angles. Results showed that the coefficient discharge for the trapezoidal labyrinth side weir with an angle of the sidewall is 75ᵒ and has a discharge coefficient greater than the rest of the labyrinth side weirs. The second part of this study is validating the laboratory work using the CFD technique, where the same laboratory channel was simulated with the weirs of the side trapezoidal labyrinth using the Ansys-Fluent program. The numerical study gave very close results compared with the experimental results with MSE, where the error percentage error was from 3.3% to 10%. The last part of the work is numerically simulating the trapezoidal labyrinth side weir with an angle of the sidewall of 75ᵒ at the flood escape entrance branching from the Diyala River. The results showed that the side labyrinth weir has a larger discharge capacity of 4.8% than the rest of the traditional weirs and is more effective in flood treatment.

Determination of influential springback parameters in U-bending test

AbstractU-bending tests are the most common method to predict springback and are influenced by the process and geometrical variables in addition to material behaviour. It needs a numerical study at a high level with many variables to reduce try-out time and loop. In this study, the U-bending test of DC01 steel has been researched numerically and experimentally to govern the influential parameters. The numerical analysis was conducted using AutoForm-Sigma code. The die radius has an excessive influence on the change of flange angle than the punch radius, but the punch radius has the greatest influence on the variation of the sidewall angle. The coefficient of friction played a great impact on both flange and sidewall angle deviation and its influence grows stronger as the blank holding force increases.

Uncertainty evaluation of Monte Carlo simulated line scan profiles of a critical dimension scanning electron microscope (CD-SEM)

In recent years, precision and accuracy for a more precise critical dimension (CD) control have been required in CD measurement technology. CD distortion between the measurement by a critical dimension scanning electron microscope (CD-SEM) and a reference tool is the most important factor for a more accurate CD measurement. CD bias varies by a CD-SEM and a pattern condition. Therefore, it is urgently needed to identify, characterize, and quantify those parameters that may or may not affect the CD measurement by a CD-SEM. The sensitivity of the Monte Carlo simulated CD-SEM images with multiple physical modeling components has been studied previously. In this study, we demonstrate that the work function and elastic scattering potential models have a significant impact on secondary electron emission intensity, but their influence on the shape of the linescan profile is small, and other factors like the optical energy loss function and dielectric function models have even smaller effects. We have evaluated the uncertainty in the linescan profiles of Si line structures with different sidewall angles due to several different physical factors. It is found that when the CD is evaluated by a peak/valley method, the uncertainty of the CD is negligible. Therefore, it is concluded that the CD value and its related uncertainty are not critically related to the physical factors of the present Monte Carlo simulation model but rely dominantly on the line structure and electron beam parameters.

Etching mechanism of high-aspect-ratio array structure

Through-Silicon-Via (TSV) is an significant technology that is being widely employed in micro-electro-mechanical system (MEMS) manufactories. However, it is remain challenging to obtain a deep silicon etching with vertical-angle and smooth-sidewall characterizes by silicon-etching anisotropy through TSV technology. Herein, we use inductively coupled plasma (ICP) to obtain the deep silicon etching anisotropy. Chamber pressure, Bosch process cycles, bias powers, and the size of the etching pattern, which are the critical controllable process parameters, have been investigated to achieve the silicon-etching anisotropy. The results reveal that the sidewall angle of the array structure becomes increasingly slanted while raising chamber pressure from 2 to 15 Pa in the SF6 etching process of the first step of the cycle in the Bosch process. As the cycles increase from 60 to 240 cycles at the bias power of 100 w, the anisotropy decreases from 0.80 to 0.5. With RF bias powers rise from 200 to 400 w, the anisotropy enhances from 0.80 to 0.94. Due to the collision of active ions with each other, the sidewall angle and anisotropy of a high aspect-ratio array structure severely depend on the incidence angle of the active ions. The “Si etching balance model” has been established for the fabrication of TSV.

Enhanced light extraction efficiency of far-ultraviolet-C LEDs by micro-LED array design

AlGaN-based far-UVC light emitting diodes (LEDs) with an emission wavelength of 233 nm were fabricated in the form of micro-LED arrays with emitter diameters ranging from 1.5 to 50 μm. The mesa was plasma etched with a sidewall angle of 45°–50°, and insulator layers made of SiNx or SiO2 were deposited. While the external quantum efficiency (EQE) of the LEDs with SiNx showed only a small dependency on the micro-LED diameter, the LEDs using SiO2 showed an increase in the peak EQE by a factor of four as compared to large area devices. This enhancement is attributed to a strong increase in the light extraction efficiency due to total internal reflection and re-direction at the inclined mesa, allowing TM-polarized light emitted in the plane of the quantum well to be extracted through the sapphire backside of the chips.

Role of pixel design and emission wavelength on the light extraction of nitride-based micro-LEDs.

Micro-light emitting diodes (µ-LEDs) suffer from a drastic drop in internal quantum efficiency that emerges with the miniaturization of pixels down to the single micrometer size regime. In addition, the light extraction efficiency (LEE) and far field characteristics change significantly as the pixel size approaches the wavelength of the emitted light. In this work, we systematically investigate the fundamental optical properties of nitride-based µ-LEDs with the focus on pixel sizes from 1 µm to 5 µm and various pixel sidewall angles from 0∘ to 60∘ using finite-difference time-domain simulations. We find that the LEE strictly increases with decreasing pixel size, resulting in a LEE improvement of up to 45% for a 1 µm pixel compared to a 20 µm pixel. The ideal pixel sidewall angle varies between 35∘ and 40∘, leading to a factor of 1.4 enhancement with respect to vertical pixel sidewalls. For pixel sizes in the order of 2µm and smaller, a substantial transition of far field properties can be observed. Here, the far field shape depends severely on the pixel sidewall angle and affects the LEE within a solid angle of ±15∘. Moreover, we investigate the impact of emission wavelength and observe major differences in optical characteristics for blue, green and red emitting pixels, which is relevant for real-world applications. Finally, we discuss the implications of the assumptions we made and their significance for the design of µ-LEDs.

Virtual experiments for the assessment of data analysis and uncertainty quantification methods in scatterometry

Geometrical dimensions in nanostructures can be determined through indirect optical measurements carried out by a scatterometer. This includes solving a non-linear regression task in which a physical model is fitted to the observed optical diffraction pattern. We developed a virtual experiment which produces simulated diffraction patterns in coherent Fourier scatterometry measurements including perturbations due to various error sources. We utilize this virtual experiment to assess the suitability of data analysis and uncertainty quantification methods employed in scatterometry. In addition to investigating relevant physical parameters we explore the impact of deviations between the regression model utilized for the analysis and the scatterometry model used to produce the virtual diffraction pattern. We choose coverage probabilities of interval estimates of the geometrical dimensions as the main metric for the assessment. One of our findings is that the discretization level, expressed as the number of retained Fourier orders, can be relaxed up to order 9 in our case study, which is relevant as calculation times strongly depend on this parameter. Another result is that the least-squares approach considered here for solving the regression task in combination with the propagation of variances yields uncertainties which have somewhat lower coverage probabilities than the envisaged 95%. It turned out that it was critically important to model the oxide layer in order to get proper estimates of the width, or ‘critical dimension’, of the sample, while the uncertainty of the side wall angle had the largest impact on the uncertainty of the measurands. Our findings can help establishing traceability of Fourier scatterometry and underline the usefulness of high-quality virtual experiments in connection with complex measurement principles. At the same time the presented case study can be seen as a generic approach that could be followed for assessing uncertainty quantifications in other applications as well.

Assessing neutral transport mechanisms in aspect ratio dependent etching by means of experiments and multiscale plasma modeling

Since the onset of pattern transfer technologies for chip manufacturing, various strategies have been developed to circumvent or overcome aspect ratio dependent etching (ARDE). These methods have, however, their own limitations in terms of etch non-idealities, throughput or costs. Moreover, they have mainly been optimized for individual in-device features and die-scale patterns, while occasionally ending up with poor patterning of metrology marks, affecting the alignment and overlay in lithography. Obtaining a better understanding of the underlying mechanisms of ARDE and how to mitigate them therefore remains a relevant challenge to date, for both marks and advanced nodes. In this work, we accordingly assessed the neutral transport mechanisms in ARDE by means of experiments and multiscale modeling for SiO2 etching with CHF3/Ar and CF4/Ar plasmas. The experiments revealed a local maximum in the etch rate for an aspect ratio around unity, i.e. the simultaneous occurrence of regular and inverse reactive ion etching lag for a given etch condition. We were able to reproduce this ARDE trend in the simulations without taking into account charging effects and the polymer layer thickness, suggesting shadowing and diffuse reflection of neutrals as the primary underlying mechanisms. Subsequently, we explored four methods with the simulations to regulate ARDE, by varying the incident plasma species fluxes, the amount of polymer deposition, the ion energy and angular distribution and the initial hardmask sidewall angle, for which the latter was found to be promising in particular. Although our study focusses on feature dimensions characteristic to metrology marks and back-end-of-the-line integration, the obtained insights have a broader relevance, e.g. to the patterning of advanced nodes. Additionally, this work supports the insight that physisorption may be more important in plasma etching at room temperature than originally thought, in line with other recent studies, a topic on which we recommend further research.

2.5D+ plasma etching for a continuously adjustable sidewall angle in SiO2

We present a systematic investigation of an SiO2 etching process using a standard fluorocarbon chemistry ICP-RIE etch tool with a cryogenically cooled electrode. Our goal is to enable the control of the SiO2 feature morphology, i.e., the sidewall angle, in order to add a degree of freedom for the design of resonant micro-/nanooptical elements. For such elements as e.g., whispering gallery mode resonators with specific mode profiles, it is essential to maintain low surface roughness. To this end, we investigate a variety of gas compositions. For statistical evaluation, we use a surface response methodology for several parameters and investigate the influence of the substrate temperature on the sidewall angle. Different hypotheses from the literature for the cause of non-anisotropic etch behavior are discussed for our specific case. Various investigations based on the prior hypothesis are presented, which provide more information about the pseudo-isotropic etch profile. Finally, we present two use cases: firstly, a classical anisotropic etch with a high aspect ratio and very low roughness (<1 nm), and secondly, an etch process for the fabrication of whispering gallery mode resonators that confine the light at the bottom of the resonator.

Diffraction grating enhanced photoluminescence from etching-free erbium thin films.

Micro-structuration by etching is commonly used in integrated optics, adding complex and costly processing steps that can also potentially damage the device performance, owing to degradation of the etched sidewalls. For diffraction grating fabrication, different strategies have been developed to avoid etching, such as layer deposition on a structured surface or grating deposition on top of active layers. However, etching remains one of the best processes for making high aspect ratio diffraction gratings. In this work, we have developed fully structured diffraction gratings (i.e., like fully etched gratings) using lift-off based processing performed in pulsed laser deposited layers, since the combination of both techniques is of great interest for making micro-structures without etching. We have first studied the influence of the lithography doses in the lift-off process, showing that (1) micrometric spatial resolution can be achieved and (2) the sidewall angle can be controlled from 50° to 150° in 0.5 µm thick layers. Using such optimizations, we have then fabricated Er-doped Y2O3 uniaxial diffraction gratings with different periods ranging from 3 to 8 µm. The fabricated devices exhibit emission and reflectivity properties as a function of the collection angle in good agreement with the modeling, with a maximum luminescence enhancement of ×15 compared with an unstructured layer at a wavelength of 1.54 µm. This work thus highlights lift-off based processing combined with pulsed laser deposition as a promising technique for etch-free practical applications, such as luminescence enhancement in Er-doped layers.

Design, development, and analysis of a box type solar cooker with optimally reflecting side walls

A novel inclined sidewall box-type solar cooker is constructed, and its performance is evalu-ated. The Opto-geometrical design of the cooker was designed for Surat, a city in India. The design is modified by optimizing the inclination angles of the sidewalls so that an optimal thermal response may be generated by reflecting sun rays from the sidewalls, and the perfor-mance of the solar cooker is enhanced. The optimized sidewall angles due south, due north, due east, and due west are designed to be 67.30, 22.690, 35.440, and 35.440, respectively and side walls are made reflective with reflecting Aluminium sheets. The results are compared with a conventional cooker. The thermal performance of the newly built solar cooker was evaluated, and the merit F1 for no-load circumstances and the merit F2 for various loading conditions were determined. The results show that the maximum plate temperature, the figure of merit F1, and the maximum pot temperature of the newly developed solar cooker with optimally reflecting sidewalls during load test are higher than that of a conventional cooker. The max-imum plate temperature is found to be 760C and 650C in newly designed and conventional solar cookers, respectively. The temperatures are found to be about 16% more from 11:30 pm to 2:00 pm in the newly designed cooker compared to the conventional cooker. The maximum value of Figure of merit F1 is found to be 0.15 and 0.11 in newly designed and conventional solar cookers. The maximum value of Figure of merit F2 is found to be 0.59 and 0.30 in newly designed and conventional solar cookers. The maximum value of pot temperature is found to be 860C and 600C for newly designed and conventional solar cookers, respectively, during the load test, which is about 43% more in the newly designed cooker than the conventional cooker. The highest cooking temperature in the newly designed cooker was maintained at 90 0C for about 2 hours, and that in the conventional cooker was maintained at 60 0C for about 2 hours. In addition, the cooking test demonstrates that the food is thoroughly cooked in the newly built solar cooker, while it was discovered undercooked in the conventional cookerC thickness, respectively without heat recovery. The operating conditions and optimized geo-metric factors, based on result analysis and comparison, are discussed in detail.