Papers by Veerla Swarnalatha
Springer proceedings in physics, 2024
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Microsystem Technologies-micro-and Nanosystems-information Storage and Processing Systems, May 21, 2016
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Journal of Micromechanics and Microengineering, Jan 8, 2016
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Springer proceedings in physics, 2024
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ECS Journal of Solid State Science and Technology, 2019
Recently the effect of hydroxylamine (NH2OH) on the etching characteristics of alkaline solution ... more Recently the effect of hydroxylamine (NH2OH) on the etching characteristics of alkaline solution (e.g. potassium hydroxide (KOH) and tetramethylammonium hydroxide (TMAH)) is studied to obtain improved etching characteristics, especially high etch rate and enhanced undercutting at convex corners. Alkaline solution modified with NH2OH provides improved etch rate of silicon (Si), high etch selectivity between silicon and silicon dioxide (SiO2), considerably high undercutting at convex corner. As the addition of NH2OH alters the etching properties of alkaline solution dramatically, it is indispensable to investigate the effect of aging of NH2OH-added alkaline solution on its etching characteristics. In this work, the influence of aging of 15% NH2OH-added 20 wt% KOH, which is referred to as an etchant, on the etching characteristics of Si{100} and Si{110} is studied in detail. The results are systematically presented. The etch rate of silicon and the undercutting at convex corners decrease significantly with etchant aging at etching temperature, while the etch rate of silicon dioxide and etched surface morphology are not considerably affected with the age of the etchant. This study is significantly important for the researchers and industries where silicon wet anisotropic etching is used for silicon micromachining
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ECS Journal of Solid State Science and Technology, 2017
Potassium hydroxide (KOH) and tetramethylammonium hydroxide (TMAH) are most extensively used etch... more Potassium hydroxide (KOH) and tetramethylammonium hydroxide (TMAH) are most extensively used etchants for wet anisotropic etching process. Amongst these two etchants, KOH is a low cost etchant and provides high etch rate anisotropy between Si{111} and Si{100} planes. Increasing the etch rate is an important research problem for both academic and industrial applications. In this research, we study the effect of hydroxylamine (NH2OH) in 20 wt% KOH on the etching characteristics of Si{100}. This type of wafer orientation (i.e. Si{100}) is selected owing to its popularity in fabricating planar semiconductor devices (e.g. diode, transistor, complementary metal oxide semiconductor (CMOS), etc.) and MEMS components (e.g. cantilever, diaphragm, etc.). A systematic parametric analysis of various concentrations of hydroxylamine (from 0 to 20% in step of 5%) added 20 wt% KOH is carried out and its effect on the etching characteristics is discussed. We have found that the etch rate of Si{100} is increased threefold when 15% NH2OH is added to 20 wt% KOH solution. Additionally, this concentration also exhibits improved etching characteristics including undercutting rate, etch selectivity, and surface morphology. We have obtained improved etching characteristics when NH2OH is added to 20 wt% KOH. Due to an improvement in etching characteristics, present research is very useful to pave the path toward application in microfabrication industries as well as academic research laboratories.
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In wet anisotropic etching based silicon bulk micromachining, undercutting, which has both advant... more In wet anisotropic etching based silicon bulk micromachining, undercutting, which has both advantage and disadvantage, takes place at the convex corners of microstructures. In order to retain the desired shape of fabricated structure, corner compensation method is most commonly used to protect the convex corners. The design and shape of the compensation geometry depend on the type of etchant. In this work, various types of corner compensating structures to protect convex corners on Si{110} and Si{110} are studied in potassium hydroxide (KOH) modified by adding NH2OH solution. Silicon etch rate in NH2OH-added KOH is 3–4 times more than that in pure KOH solution, which is very useful for industrial application to improve productivity. Mesa shape structures are fabricated using different shapes corner compensating geometry to optimize the design to obtain best shape convex corner. Triangular shape and beam shape geometries are found most appropriate structures to obtain well-shaped convex corner on Si{100} and Si{110}, respectively.
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Springer proceedings in physics, 2019
In the present work, we have studied the etching characteristics of Si{100} and Si{110} in modifi... more In the present work, we have studied the etching characteristics of Si{100} and Si{110} in modified low concentration TMAH solution by adding different concentrations of NH2OH. The etch rate of silicon and thermal oxide, and etched surface morphology, which are important parameters to be known in the fabrication of MEMS structures using silicon wet bulk micromachining, have been studied in modified TMAH solution. In addition, the effect of aging time of the etchant solution on the etching characteristics is investigated.
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Micro and Nano Systems Letters, Dec 1, 2022
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World Academy of Science, Engineering and Technology, International Journal of Chemical, Molecular, Nuclear, Materials and Metallurgical Engineering, Nov 1, 2017
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ECS transactions, Jul 7, 2017
Anisotropic wet etching is a low cost technique for silicon bulk micromachining to fabricate MEMS... more Anisotropic wet etching is a low cost technique for silicon bulk micromachining to fabricate MEMS components such as cantilevers, diaphragms, etc. It is inevitable for the fabrication of microstructures with slanted sidewalls and to remove underneath material for the realization of freestanding microstructures. Potassium hydroxide (KOH) is a popular etchant as it provides high anisotropy between {100}/{110} and {111} planes. In order to alter the etching characteristics, the effect of various kinds of additives such as isopropyl alcohol (IPA), surfactants (Triton X-100) in pure KOH is studied [1-3]. In this work, we studied the etching characteristics of ternary solutions composed of KOH + Triton X-100 + IPA. The concentration of KOH is varied from 5-40 wt% in step of 5 wt%, while the concentrations of Triton and IPA are kept fixed at 0.1 vol% and 15 vol%, respectively. In the different compositions of ternary solutions, the etch rate and etched surface morphologies of Si{100}, Si{110} and Si{111} are investigated. In addition to that the undercutting at convex corners, which is very important parameter for designing compensation structure to protect convex corner and to estimate etching to release the structure from the substrate, is measured. In order to explore the thermal oxide as mask and structural material, the etch rate of silicon dioxide is also measured. In the ternary solution comprising low concentration KOH, the etching characteristics are more significantly affected by Triton than IPA. However, in the case of ternary solution containing high concentration KOH, IPA influences etching characteristics more prominently than Triton. The systematic study of etch rate, etched surface roughness, and undercutting at convex corners in ternary solution presented in this work is very useful to select the composition of ternary solution for MEMS applications as per the requirement. References: [1] I. Zubel, M. Kramkowska, Sens. Actuators A 101 255-261 (2002). [2] P. Pal, A. Ashok, S. Haldar, Y. Xing, K. Sato, Micro Nano Lett. 10 224-228 (2015). [3] K.P. Rola, I. Zubel, J. Microelectromech. Syst. 22 1373-1382 (2013).
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ECS transactions, Jul 7, 2017
Wet chemical etching is extensively used in the fabrication of microelectromechanical systems (ME... more Wet chemical etching is extensively used in the fabrication of microelectromechanical systems (MEMS) owing to its several benefits such as low cost, easy handling, and bulk production [1, 2]. TMAH and KOH are most widely employed etchants for silicon anisotropic etching. In these two etchants, TMAH is preferred when complementary metal oxide semiconductor (CMOS) compatibility is a major concern and the oxide layer is used as mask material [2, 3]. Etching behavior of TMAH can be modified by the incorporation of different kinds of additives such surfactants, alcohol, etc. [2-4]. Significant amount of research has been done to modify the etching characteristics by adding some additives, however very less is reported on TMAH-based ternary solutions. Present research reports the anisotropic etching characteristics of silicon in various concentrations of TMAH (5 wt%, 15 wt%, and 25 wt%) solutions containing 10% NH2OH and Triton-X-100 ranging from ppb to ppm level. The etch rate, undercutting at convex corners, and etched surface morphology are investigated in different compositions of ternary solutions (TMAH+NH2OH+Triton). Optical microscope, scanning electron microscope (SEM), and three-dimensional (3D) measuring laser microscope are employed for the characterization of etched surface morphology and to measure the etch depth and undercutting at convex corners. Figure 1 presents the etch rate of Si{100} and the undercutting rate (U <110> = l <110> /d, l <110>: undercutting length along <110> direction, d: etch depth) at convex corners. High etch rate and undercutting are achieved in NH2OH-added 15 wt% TMAH, while significantly less undercutting with reasonably good etch rate of Si{100} (Er = 18 µm/hr) is obtained in 25 wt% TMAH+10%NH2OH+1ppm Triton. The high undercutting is desirable when freestanding structures are fabricated, while it is unwanted effect when microstructures with convex corners have to be fabricated such as mesa structure. The present research is very useful for engineering applications for the fabrication of microstructures using CMOS-compatible silicon bulk micromachining for MEMS-based devices. References: [1] I. Zubel, M. Kramkowska, J. Micromech. Microeng. 1 5 485 (2004). [2] P. Pal, and K. Sato. J. Micromech.Microeng. 19 055003 (2009). [3] A. Ashok and P. Pal, Microsy. Technol. 1-8 (2015). [4] Y.W. Xu, A. Michael, C.Y. Kwok, Sens. Actuators A 166, 164-171 (2011). Figure 1
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Micro and Nano Systems Letters, Jun 29, 2018
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Springer eBooks, Nov 21, 2022
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Micro and Nano Systems Letters
Silicon bulk micromachining is extensively employed method in microelectromechanical systems (MEM... more Silicon bulk micromachining is extensively employed method in microelectromechanical systems (MEMS) for the formation of freestanding (e.g., cantilevers) and fixed (e.g., cavities) microstructures. Wet anisotropic etching is a popular technique to perform silicon micromachining as it is low-cost, scalable, and suitable for large scale batch processing, which are the major factors considered in the industry to reduce the cost of the product. In this work, we report the wet anisotropic etching characteristics of Si{111} in sodium hydroxide (NaOH) without and with addition of hydroxylamine (NH2OH). 10M NaOH and 12% NH2OH are used for this study. The effect of NH2OH is investigated on the etch rate, etched surface roughness and morphology, and the undercutting at mask edges aligned along < 112 > direction. These are the major etching characteristics, which should be studied in a wet anisotropic etchant. A 3D laser scanning microscope is utilized to measure the surface roughness, e...
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Journal of Micromechanics and Microengineering
Silicon wet bulk micromachining is an extensively used technique in microelectromechanical system... more Silicon wet bulk micromachining is an extensively used technique in microelectromechanical systems (MEMS) to fabricate variety of microstructures. It utilizes low-cost etchants and suitable for batch process that made it popular for industrial production. The etch rate and the undercutting at convex corner significantly affect the productivity. In wet anisotropic etching-based micromachining, Si{110} wafer is employed to fabricate unique shape geometries such as the microstructures with vertical sidewalls. In this research, we have investigated the etching characteristics of Si{110} in 10 M sodium hydroxide without and with addition of hydroxylamine (NH2OH). The main objective of the present work is to improve the etch rate and the undercutting at convex corners. Average surface roughness (R a), etch depth, and undercutting length are measured using a 3D scanning laser microscope. Surface morphology of the etched Si{110} surface is examined using a scanning electron microscope. The ...
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Micro and Nano Systems Letters
Silicon wet bulk micromachining is the most widely used technique for the fabrication of diverse ... more Silicon wet bulk micromachining is the most widely used technique for the fabrication of diverse microstructures such as cantilevers, cavities, etc. in laboratory as well as in industry for micro-electromechanical system (MEMS) application. Although, increasing the throughput remains inevitable, and can be done by increasing the etching rate. Furthermore, freestanding structure release time can be reduced by the improved undercutting rate at convex corners. In this work, we have investigated the etching characteristics of a non-conventional etchant in the form of hydroxylamine (NH2OH) added sodium hydroxide (NaOH) solution. This research is focused on Si{100} wafer as this orientation is largely used in the fabrication of planer devices (e.g., complementary metal-oxide semiconductors) and microelectromechanical systems (e.g., inertial sensors). We have performed a systematic and parametric analysis without and with 12% NH2OH in 10 M NaOH for improved etching characteristics such as ...
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Various process steps such as oxidation, diffusion, etching, lithography, etc. are employed for t... more Various process steps such as oxidation, diffusion, etching, lithography, etc. are employed for the fabrication of microstructures used in microelectromechanical systems (MEMS). In addition to these processes, micro-stereolithography (MSL), LIGA (a German acronym for Lithographie, Galvanoformung, Abformung), and micromachining are used in MEMS fabrication. Among these methods, micromachining is most widely used. It is further classified into two categories: surface micromachining and bulk micromachining. In these two techniques, bulk micromachining is a popular technique in MEMS fabrication and further divided into wet and dry bulk micromachining based on the type of chemical/process (wet chemical or gas/plasma/LASER) is employed. Wet anisotropic etching based micromachining is extensively used to fabricate various MEMS structures including suspended (e.g., microcantilever, diaphragm, etc.) and fixed (e.g., grooves, trenches, channels, etc.) structures. Wet anisotropic etching is used owing to its several benefits such as low cost, easy handling, orientation dependent etching, and bulk production capability over other techniques. Most importantly, it provides unique shape structures, which may not be possible by dry etching, for examples, the fabrication of freestanding microstructures using the undercutting process, slanted sidewalls for optical mirror application, etc. Tetramethylammonium hydroxide (TMAH) and potassium hydroxide (KOH) are the most widely employed etchants for silicon wet anisotropic etching. In these two etchants, TMAH is preferred when complementary metal oxide semiconductor (CMOS) compatibility is a major concern, and the oxide layer is used as a mask material. Although wet anisotropic etching has many advantages, industrial vii throughput is still limited due to the slow etch rate. In addition, slow etch rate increases the etching time and therefore mask material such as SiO2 is affected. Hence increasing the etch rate is an important research problem for both academic and industrial applications. In order to reduce the etching time to increase productivity, etchant must provide high etch rate. However, the etch rate attainable using the conventional etchants is limited and hence affects industrial productivity. Several methods have been proposed to increase the etch rate such as ultrasonic agitation and microwave irradiation during etching, adding some additives, oxidizing agents, various ion and non-ionic typed surfactants, etching at the boiling point of the etchant. Each method has its own pros and cons such as the ultrasonic method may rupture the fragile structures, and microwave irradiation causes damage. The present thesis work is focused on investigating a non-conventional etchant in the form of NH2OH-added in 5 wt% TMAH to determine its etching characteristics. A systematic and parametric analysis with concentrations of NH2OH varying from 5% to 20% in step of 5%, all in 5 wt% TMAH, to obtain the optimum concentration for achieving improved etching characteristics including higher etch rate, higher undercutting at convex corners, and smoother etched surface morphology is performed. To study different etching characteristics, various kinds of mask patterns are used on Si{100}, Si{110}, and Si{111} wafers. As the lower concentration TMAH (2-5 wt%) provides high etch in comparison to higher concentration TMAH (20-25 wt%), 5 wt% TMAH is selected to improve its etching characteristics. Average surface roughness (Ra), etch depth, and undercutting length are measured using 3D scanning laser microscope. Surface morphology of the etched surfaces is examined using a scanning electron microscope (SEM), and the thickness of the oxide layer is determined using spectroscopic ellipsometry. The etch rate of silicon with the addition of NH2OH in TMAH solution enhances viii significantly. Additionally, the incorporation of NH2OH significantly improves the etched surface morphology of Si{100} and the undercutting at the convex corner, which is highly desirable for the quick release of microstructures from the substrate. Moreover, the addition of NH2OH in TMAH increases etch selectivity between thermal oxide and silicon. 10% NH2OH is found to be an optimal concentration for addition in 5 wt% TMAH to achieve favorable etching characteristics. The optimal etchant composition (i.e., 10% NH2OH + 5 wt% TMAH) is used to study the effect of etchant age on the etching characteristics. Moreover, the effect of different concentrations of Triton in 10% NH2OH + 5 wt% TMAH is investigated. The etching mechanism in NH2OH-added alkaline solution is investigated. An in-depth analysis of possible etching mechanism in modified alkaline solutions is presented by considering NH2O- and OH- ions as catalysts and H2O as the reactive molecule. It accounts for the rise in etch rate in NH2OH-added alkaline solution. It also justifies the reasonable explanation of the etching mechanism in pure alkaline solution. In the…
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The present research reports the investigation of fast etching of silicon for the fabrication of ... more The present research reports the investigation of fast etching of silicon for the fabrication of microelectromechanical systems (MEMS) structures using silicon wet bulk micromachining. Low concentration tetramethyl-ammonium hydroxide (TMAH) and hydroxylamine (NH<sub>2</sub>OH) are used as main etchant and additive, respectively. The concentration of NH<sub>2</sub>OH is varied to optimize the composition to achieve best etching characteristics such as high etch rate, significantly high undercutting at convex corner for the fast release of the microstructures from the substrate, and improved etched surface morphology. These etching characteristics are studied on Si{100} and Si{110} wafers as they are most widely used in the fabrication of MEMS structures as wells diode, transistors and integrated circuits.
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2018 IEEE SENSORS, 2018
In wet anisotropic etching based silicon bulk micromachining, undercutting, which has both advant... more In wet anisotropic etching based silicon bulk micromachining, undercutting, which has both advantage and disadvantage, takes place at the convex corners of microstructures. In order to retain the desired shape of fabricated structure, corner compensation method is most commonly used to protect the convex corners. The design and shape of the compensation geometry depend on the type of etchant. In this work, various types of corner compensating structures to protect convex corners on Si{110} and Si{110} are studied in potassium hydroxide (KOH) modified by adding NH2OH solution. Silicon etch rate in NH2OH-added KOH is 3–4 times more than that in pure KOH solution, which is very useful for industrial application to improve productivity. Mesa shape structures are fabricated using different shapes corner compensating geometry to optimize the design to obtain best shape convex corner. Triangular shape and beam shape geometries are found most appropriate structures to obtain well-shaped con...
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Papers by Veerla Swarnalatha