Nonuniformity in Selective Anodization of Silicon and its Application to Micro-Tip Fabrication
- PDF / 429,641 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 84 Downloads / 135 Views
J5.5.1
Nonuniformity in Selective Anodization of Silicon and its Application to Micro-Tip Fabrication S. Uehara, N. Negishi, and T. Matsubara Department of Electrical Engineering and Electronics, Seikei University, Musashino-shi, Tokyo 180-8633, JAPAN ABSTRACT Characteristics of selective anodization of p+-type Si have been studied. Temporal evolution of the etching front was visualized by periodic porosity modulated anodization. The etching front proceeded inside along the bottom of mask making its angle with the mask bottom face sharper and sharper. It was also found that the etching front proceeds forming a specifically angled facet. Selective anodization was applied to form Si micro-tips. Proper time of anodization for p+-type Si substrate with an n-type circular shape mask left a Si micro-tip formed on the substrate. A high resolution SEM observation revealed that the apex of the tip was composed of {110} facets. INTRODUCTION Micro-devices formed on Si substrates have been widely studied as a useful means of realizing elements for MEMS and field emitter arrays (EFA’s). Among a variety of fabrication methods proposed, a process using selective anodization of Si substrate is very attractive because of its simplicity and economical advantages: the process comprises only mask formation and anodization/etching steps and thus needs no complicated fabrication facilities. Several studies have been published on the fabrication of Si micro-devices using selective anodization of Si, including biomedical sensors [1], active light reflectors [2], air-suspended spirals for bolometer IR detectors [3] and EFA’s [4]. In contrast to the variety of studies on applications, little work has been done on the basic characteristics of the etching process. In this paper we report on our study to see how Si fine structures were formed by selective anodization. Temporal evolution of anodization etching fronts were visualized by use of a switching current method [5], in which porous layers were formed with porosity modulated periodic stacks. Each stack is composed of a low and a high porosity layers and the low porosity layer formed etching region while the thin high porosity layer acted as an etching front shape indicator. By applying the results obtained by the experiment we fabricated Si micro-tip arrays. The characterization as well as the fabrication of the micro-tips will also be reported.
TEMPORAL EVOLUTION OF ETCHING FRONT Sample Preparation
Highly doped p-type substrates are usually used to fabricate Si-micro-devices, so we used
(100) oriented p+-type wafers with 0.01-0.02 ΩӍcm resistivity as substrates. Stripe patterned n-type doped areas were used as a mask for selective anodization. 30-40 µm wide n-type doped stripes along the direction were formed using a photolithographic patterning and thermal diffusion process. N-type doping was carried out by thermal diffusion at 1000 °C for 50 min., using phosphorous doped oxide as source. The resulting n-type doping level was around
J5.5.2
5×1019 cm-3 with 1.4µm thickness. Ano
Data Loading...
