ANISOTROPIC ETCHING OF CRYSTALLINE SILICON IN ALKALINE-SOLUTIONS .1. ORIENTATION DEPENDENCE AND BEHAVIOR OF PASSIVATION LAYERS
ANISOTROPIC ETCHING OF CRYSTALLINE SILICON IN ALKALINE-SOLUTIONS .1. ORIENTATION DEPENDENCE AND BEHAVIOR OF PASSIVATION LAYERS
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DOI：
10.1149/1.2086277
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发表时间：
1990-11-01
影响因子：
3.9
通讯作者：
BAUMGARTEL, H
中科院分区：
文献类型：
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作者：
SEIDEL, H;CSEPREGI, L;BAUMGARTEL, H
研究了单晶硅的各向异性刻蚀行为以及SiO2和Si3N4在乙二胺基溶液以及KOH、NaOH和LiOH水溶液中的刻蚀行为。包围蚀刻前沿的晶体平面及其蚀刻速率是温度、晶体取向和蚀刻剂成分的函数。在蚀刻速率和它们的活化能之间发现了相关性，缓慢蚀刻的晶体表面表现出较高的活化能，反之亦然。对于高浓度的KOH溶液，蚀刻速率随水浓度的四次方而降低。基于这些结果，提出了一个电化学模型，描述了硅在所有碱性溶液中的各向异性蚀刻行为。在氧化步骤中，四个氢氧根离子与一个表面硅原子反应，导致四个电子注入到导带中。由于空间电荷层的存在，这些电子停留在晶体表面附近。该反应伴随着背键的断裂，这需要热激发各自的表面态电子进入导带。这个步骤被认为是速率限制。在还原步骤中，注入的电子与水分子反应，形成新的氢氧根离子和氢。假设在硅表面产生的氢氧根离子在氧化反应中被消耗掉，而不是来自大块电解质的氢氧根离子，因为后者由于表面负电荷的排斥力而远离晶体。根据该模型，各向异性硅蚀刻剂的主要溶解产物是单硅酸Si (OH) 4。各向异性行为是由于背键表面态能级的微小差异作为晶体取向的函数。晶体硅的各向异性蚀刻剂早已为人所知（1-3）。他们的第一个应用包括在< 100>硅上蚀刻v型槽或在< 110>硅上蚀刻u型槽，以制造高功率和高电流密度的MOS晶体管(4)。在认识到这种蚀刻技术在微加工三维结构方面的独特能力后，人们越来越关注这种技术（5-9）。由于蚀刻速率与晶体方向和掺杂剂浓度有很强的依赖性，因此可以以高度可控和可复制的方式制备各种硅结构。典型的结构包括薄膜，深而窄的凹槽，以及带有单面或双面悬挂的悬臂。重要的应用领域包括制造无源机械元件、传感器和致动器，以及微光学元件（8,10）。其中最著名的例子是压力传感器(8)、加速度传感器（11）和流量传感器（12）
The anisotropic etching behavior of single-crystal silicon and the behavior of SiO2 and Si3N4 in an ethylenediaminebased solution as well as in aqueous KOH, NaOH, and LiOH were studied. The crystal planes bounding the etch front and their etch rates were determined as a function of temperature, crystal orientation, and etchant composition. A correlation was found between the etch rates and their activation energies, with slowly etching crystal surfaces exhibiting higher activation energies and vice versa. For highly concentrated KOH solutions, a decrease of the etch rate with the fourth power of the water concentration was observed. Based on these results, an electrochemical model is proposed, describing the anisotropic etching behavior of silicon in all alkaline solutions. In an oxidation step, four hydroxide ions react with one surface silicon atom, leading to the injection of four electrons into the conduction band. These electrons stay localized near the crystal surface due to the presence of a space charge layer. The reaction is accompanied by the breaking of the backbonds, which requires the thermal excitation of the respective surface state electrons into the conduction band. This step is considered to be rate limiting. In a reduction step, the injected electrons react with water molecules to form new hydroxide ions and hydrogen. It is assumed that these hydroxide ions generated at the silicon surface are consumed in the oxidation reaction rather than those from the bulk electrolyte, since the latter are kept away from the crystal by the repellent force of the negative surface charge. According to this model, monosilicic acid Si (OH) 4 is formed as the primary dissolution product in all anisotropic silicon etchants. The anisotropic behavior is due to small differences of the energy levels of the backbond surface states as a function of the crystal orientation.Anisotropic etchants for crystalline silicon have been known for a long time (1-3). Their first applications included the etching of V-grooves on< 100> silicon or U-grooves on< 110> silicon, in order to fabricate MOS transistors for high power and high current densities (4). Increasing attention has been paid to this etching technology, after recognizing its unique capabilities for micromachining three-dimensional structures (5-9). Due to the strong dependence of the etch rate on crystal direction and on dopant concentration, a large variety of silicon structures can be fabricated in a highly controllable and reproducible manner. Typical structures include thin membranes, deep and narrow grooves, and cantilevers with single or double sided suspension. Important fields of application include the fabrication of passive mechanical elements, sensors, and actuators, as well as micro-optical components (8, 10). Among the best known examples are sensors for pressure (8), acceleration (11), and flow (12), as