Atomic force microscopy analyses on metallic thin films for optical MEMS

V. Merie, M. Pustan, G. Negrea, C. Bîrleanu
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Over the last decades, the attention of the researchers was focused on developing different devices known as microelectromechanical systems (MEMS) that are satisfying the demands of the customers. The properties of the materials employed for manufacturing such devices determine its properties and its performance [1]. The optical MEMS are a category of MEMS devices that are combining the optical, mechanical, and electronic properties in a single device. They are used in the manufacture of optical sensors, attenuators, micro-lenses, micro-mirrors, displays and so on [2-5]. Aluminum [6, 7], gold [8, 9] and silver [10, 11] are one of the most used materials for manufacturing optical MEMS due to their physical, chemical, mechanical, and optical properties. These materials can be obtained as thin films by different methods such as thermal evaporation [6], magnetron sputtering [7-9], electron beam deposition [12], and so on. Arrazat and his colleagues reported their results concerning the evolution of gold thin films deposited by sputtering on silicon substrates. They investigated the deposited films by electron back scatter diffraction analyses that allowed them to study the reliability of micro-switches manufactured using gold thin films [13]. The growth of aluminum thin films and the interfacial precipitation between such films and the silicon substrates were studied by Dutta and his coworkers. They pointed out that at the interface between the aluminum thin films and the silicon substrate during the heat treatment, some silicon precipitates are formed. According to them, these precipitates are supplying the driving force necessary for the deposit of the aluminum thin films [14]. Hojabri and his team worked on determining the influence of substrate temperature on the morphological and structural characteristics of silver thin films deposited by direct current magnetron sputtering on silicon substrates. Their results showed that the substrate temperature Powder Metallurgy and Advanced Materials – RoPM&AM 2017 Materials Research Forum LLC Materials Research Proceedings 8 (2018) 125-133 doi: http://dx.doi.org/10.21741/9781945291999-14 126 strongly influence the growth of the silver thin films, their surface roughness, as well as their grain size [15]. This research is an experimental study regarding the deposition and characterization of aluminum, gold, and silver thin films deposited by thermal evaporation on glass substrates, these films being suitable for manufacturing optical MEMS. Materials and Experimental Procedure Aluminum, gold and silver targets with purity of 99.99 % were employed for the deposition of the three metallic films by thermal evaporation. The films were deposited on glass substrate. The substrates were cleaned in high purity alcohol (99.9 %), in an ultrasonic bath in order to remove any possible impurities. Further they were blown with compressed air. We used resistance heated tungsten sources (“boat” type) and a vacuum atmosphere (5·10 torr). A current of 60-80 A was applied. A distance of 50 mm was kept constant between the substrates and the resistors. The deposited thin films have a thickness of about 70 nm that was determined using a JEOL JSM 5600 LV scanning electron microscope from the Materials Science and Engineering Department, Technical University of Cluj-Napoca. The so-obtained thin films were characterized from the topographical, tribological and mechanical point of view at nanoscale. The tests were performed on a XE70 atomic force microscope (AFM) from the Micro and Nano Systems Laboratory, Technical University of ClujNapoca, in a clean environment. An n-type silicon NSC35C cantilever was used for studying the topography and the tribological characteristics of the three metallic thin films. 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Theoretical formula Based on the data obtained for the deflection of the tip when scanning a probe by contact mode, the friction force between the AFM tip and the deposited films was calculated using the equation (1) [17]: s l b h G r d F z f ⋅ ⋅ ⋅ ⋅ ⋅ = 2 3","PeriodicalId":20390,"journal":{"name":"Powder Metallurgy and Advanced Materials","volume":null,"pages":null},"PeriodicalIF":0.0000,"publicationDate":"2018-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Powder Metallurgy and Advanced Materials","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.21741/9781945291999-14","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
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Abstract

This paper is a study on three metallic thin films usable for manufacturing optical MEMS. The films were deposited by thermal evaporation on glass substrates. They were characterized from the topographical, tribological and mechanical point of view at nanoscale. The results pointed out that the silver thin films present higher values of the tribological and mechanical properties than the other two films when testing at room temperature. Increasing the testing temperature from 20 to 100 °C caused a decreased of both hardness and Young’s modulus with about 30 up to 55 %. Introduction The optical microelectromechanical systems (MEMS) are formed in general by multi-layers of metallic thin films characterized by good optical properties. Over the last decades, the attention of the researchers was focused on developing different devices known as microelectromechanical systems (MEMS) that are satisfying the demands of the customers. The properties of the materials employed for manufacturing such devices determine its properties and its performance [1]. The optical MEMS are a category of MEMS devices that are combining the optical, mechanical, and electronic properties in a single device. They are used in the manufacture of optical sensors, attenuators, micro-lenses, micro-mirrors, displays and so on [2-5]. Aluminum [6, 7], gold [8, 9] and silver [10, 11] are one of the most used materials for manufacturing optical MEMS due to their physical, chemical, mechanical, and optical properties. These materials can be obtained as thin films by different methods such as thermal evaporation [6], magnetron sputtering [7-9], electron beam deposition [12], and so on. Arrazat and his colleagues reported their results concerning the evolution of gold thin films deposited by sputtering on silicon substrates. They investigated the deposited films by electron back scatter diffraction analyses that allowed them to study the reliability of micro-switches manufactured using gold thin films [13]. The growth of aluminum thin films and the interfacial precipitation between such films and the silicon substrates were studied by Dutta and his coworkers. They pointed out that at the interface between the aluminum thin films and the silicon substrate during the heat treatment, some silicon precipitates are formed. According to them, these precipitates are supplying the driving force necessary for the deposit of the aluminum thin films [14]. Hojabri and his team worked on determining the influence of substrate temperature on the morphological and structural characteristics of silver thin films deposited by direct current magnetron sputtering on silicon substrates. Their results showed that the substrate temperature Powder Metallurgy and Advanced Materials – RoPM&AM 2017 Materials Research Forum LLC Materials Research Proceedings 8 (2018) 125-133 doi: http://dx.doi.org/10.21741/9781945291999-14 126 strongly influence the growth of the silver thin films, their surface roughness, as well as their grain size [15]. This research is an experimental study regarding the deposition and characterization of aluminum, gold, and silver thin films deposited by thermal evaporation on glass substrates, these films being suitable for manufacturing optical MEMS. Materials and Experimental Procedure Aluminum, gold and silver targets with purity of 99.99 % were employed for the deposition of the three metallic films by thermal evaporation. The films were deposited on glass substrate. The substrates were cleaned in high purity alcohol (99.9 %), in an ultrasonic bath in order to remove any possible impurities. Further they were blown with compressed air. We used resistance heated tungsten sources (“boat” type) and a vacuum atmosphere (5·10 torr). A current of 60-80 A was applied. A distance of 50 mm was kept constant between the substrates and the resistors. The deposited thin films have a thickness of about 70 nm that was determined using a JEOL JSM 5600 LV scanning electron microscope from the Materials Science and Engineering Department, Technical University of Cluj-Napoca. The so-obtained thin films were characterized from the topographical, tribological and mechanical point of view at nanoscale. The tests were performed on a XE70 atomic force microscope (AFM) from the Micro and Nano Systems Laboratory, Technical University of ClujNapoca, in a clean environment. An n-type silicon NSC35C cantilever was used for studying the topography and the tribological characteristics of the three metallic thin films. Its characteristics as the manufacturer mentioned are: length of 130 μm, thickness of 2 μm, width of 35 μm and force constant of 5.4 N/m. The set point used during tests was of 10 nN. The determination of the adhesion parameters was realized using a PPP-NCHR cantilever by spectroscopy in point. The relative humidity was 31 % and the testing temperature was varied between 20 and 100 oC, increasing it with 20 oC per testing. As the manufacturer indicated, the characteristics of this cantilever are: tip radius smaller than 10 nm, cantilever thickness of 4 μm, its width of 30 μm and length of 125 μm, tip height between 10 and 15 nm, force constant of 42 N·m-1. A TD21464 nanoindentor was employed for determining the mechanical characteristics (hardness and Young’s modulus) of the deposited films. The tests were carried out at a relative humidity of 31 % and at different temperatures namely 20, 40, 60, 80 and 100 °C. The characteristics of this nanoindentor – as given by the manufacturer are: cantilever stiffness of 156 N/m; tip thickness of 19 μm; tip height of 103 μm; tip radius smaller than 25 nm and cantilever length of 581 μm. The tests were performed at a force limit of 50 nN. The obtained curves were interpreted using the XEI Image Processing Tool for SPM (scanning probe microscopy) data by both the Oliver and Pharr (for determining the values of the hardness) and the Hertzian (for determining the values of the Young’s modulus) methods [16]. Theoretical formula Based on the data obtained for the deflection of the tip when scanning a probe by contact mode, the friction force between the AFM tip and the deposited films was calculated using the equation (1) [17]: s l b h G r d F z f ⋅ ⋅ ⋅ ⋅ ⋅ = 2 3
光学MEMS金属薄膜的原子力显微镜分析
本文研究了三种可用于制造光学MEMS的金属薄膜。薄膜是通过热蒸发沉积在玻璃衬底上的。从形貌、摩擦学和力学角度对其进行了表征。结果表明,在室温条件下,银薄膜的摩擦学性能和力学性能均高于其他两种薄膜。将测试温度从20℃提高到100℃,硬度和杨氏模量都下降了约30%至55%。光学微机电系统(MEMS)一般是由具有良好光学性能的多层金属薄膜构成的。在过去的几十年里,研究人员的注意力集中在开发不同的器件,即微机电系统(MEMS),以满足客户的需求。用于制造这种装置的材料的性质决定了它的性质和性能[1]。光学MEMS是将光学、机械和电子特性结合在单个器件中的一类MEMS器件。它们被用于制造光学传感器、衰减器、微透镜、微镜、显示器等[2-5]。铝[6,7]、金[8,9]和银[10,11]由于其物理、化学、机械和光学性能,是制造光学MEMS最常用的材料之一。这些材料可以通过热蒸发[6]、磁控溅射[7-9]、电子束沉积[12]等不同的方法得到薄膜。Arrazat和他的同事报告了他们关于在硅衬底上溅射沉积金薄膜的演变的结果。他们通过电子反向散射衍射分析研究了沉积的薄膜,这使他们能够研究使用金薄膜[13]制造的微开关的可靠性。Dutta和他的同事研究了铝薄膜的生长和这种薄膜与硅衬底之间的界面沉淀。他们指出,在热处理过程中,铝薄膜与硅衬底之间的界面处形成了一些硅沉淀。他们认为,这些沉淀物为铝薄膜b[14]的沉积提供了必要的驱动力。Hojabri和他的团队致力于确定衬底温度对在硅衬底上通过直流磁控溅射沉积的银薄膜的形态和结构特征的影响。他们的研究结果表明,衬底温度对银薄膜的生长、表面粗糙度和晶粒尺寸[15]有很大的影响。粉末冶金与先进材料- RoPM&AM 2017材料研究论坛LLC材料研究进展8 (2018)125-133 doi: http://dx.doi.org/10.21741/9781945291999-14 126。本研究是对热蒸发法在玻璃基板上沉积铝、金、银薄膜的实验研究,这些薄膜适合制造光学MEMS。材料和实验方法采用纯度为99.99%的铝靶、金靶和银靶热蒸发法制备了三种金属薄膜。薄膜被沉积在玻璃衬底上。底物用高纯度酒精(99.9%)在超声波浴中清洗,以去除任何可能的杂质。然后用压缩空气吹。我们使用电阻加热钨源(“船”型)和真空气氛(5.10托)。施加了60- 80a的电流。衬底与电阻器之间保持50mm的恒定距离。用克卢日纳波卡工业大学材料科学与工程系的JEOL JSM 5600 LV扫描电子显微镜测定了沉积薄膜的厚度约为70 nm。从形貌、摩擦学和力学等方面对制备的薄膜进行了表征。测试在克卢纳波卡技术大学微纳米系统实验室的XE70原子力显微镜(AFM)上进行,环境干净。采用n型硅NSC35C悬臂梁对三种金属薄膜的形貌和摩擦学特性进行了研究。其特点如厂家所述:长度为130 μm,厚度为2 μm,宽度为35 μm,力常数为5.4 N/m。测试时使用的设定点为10 nN。采用点内光谱法,利用PPP-NCHR悬臂梁实现了附着参数的测定。相对湿度为31%,测试温度在20 ~ 100℃之间变化,每次测试增加20℃。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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