Homma Takayuki, Sato Hirotaka, Mori Kentaro, Osaka Tetsuya, Shoji Shuichi
Department of Applied Chemistry and Department of Electrical Engineering and Bioscience, Waseda University, Okubo, Shinjuku, Tokyo 169-8555, Japan.
J Phys Chem B. 2005 Mar 31;109(12):5724-7. doi: 10.1021/jp045822n.
A photoassisted anodization process to fabricate arrays of uniform and straight macropores at selected areas of a Si wafer surface was developed. The front- and backside surfaces of n-type Si(100) wafers were coated with a thin Si(3)N(4) layer, and the frontside layer was micro-patterned using photolithography and reactive ion etching to form an array of microscopic openings at selected areas. The inverted pyramid-shape micropits were formed at these openings by anisotropic etching using aqueous KOH solution; these pits act as the initiation sites for the anodization to form macropores. The electrochemical etching was carried out in aqueous HF solution under illumination from the backside of the wafer, on which Au/Cr electric contact was formed following removal of the Si(3)N(4) layer. To improve the uniformity of the formation condition of the macropores at the selected area, holes were area-selectively generated by controlling the illumination condition during the anodization. For this, micropatterns were formed on the Au/Cr layer at the backside surface, which were aligned to those at the frontside surface. The parameters, such as HF concentration, current density, and wafer thickness, i.e., hole diffusion length, were optimized, and the arrays of uniform and high-aspect-ratio macropores were formed at the selected area of the domain at the silicon surface.
开发了一种光辅助阳极氧化工艺，用于在硅片表面的选定区域制造均匀且笔直的大孔阵列。n型Si(100)晶片的正面和背面均涂覆有一层薄的Si₃N₄层，并且使用光刻和反应离子蚀刻对正面层进行微图案化，以在选定区域形成微观开口阵列。通过使用KOH水溶液进行各向异性蚀刻，在这些开口处形成倒金字塔形微坑；这些微坑作为阳极氧化形成大孔的起始位点。电化学蚀刻在HF水溶液中从晶片背面进行光照的条件下进行，在去除Si₃N₄层之后在晶片背面形成Au/Cr电接触。为了提高选定区域大孔形成条件的均匀性，在阳极氧化过程中通过控制光照条件进行区域选择性地生成孔洞。为此，在背面的Au/Cr层上形成微图案，使其与正面的微图案对齐。对诸如HF浓度、电流密度和晶片厚度（即孔洞扩散长度）等参数进行了优化，并在硅表面区域的选定区域形成了均匀且高纵横比的大孔阵列。
