Porous Silicon Formation by Means of Metal Particle Enhanced Etching and Its Structure Control

(1)我们研究了在含HF的金属盐溶液中化学置换沉积金属颗粒（Pt, Rh, Pd, Cu， Ag和Au）到n-Si晶片上。金属的颗粒密度随金属的种类而变化很大。沉积金属可分为两种成核行为。其中一种由铂族元素组成，其颗粒密度低于其他族元素，并取决于n-Si晶片的预处理类型。第二组由铜族元素组成，其颗粒密度高于第一组，且不受预处理的影响。随着颗粒密度的增加，沉积颗粒的尺寸从数百nm减小到10 nm。(2)金属颗粒增强HF对Si的蚀刻，通过将金属颗粒修饰的Si简单浸入无偏置或特定氧化剂的HF水溶液中，可以制备微米级的大孔和纳米级的微孔Si。蚀刻过程中，HF溶液溶解氧浓度和光照射强度改变了硅的蚀刻速率和多孔硅的结构。对于n-Si，多孔层只在晶圆的金属颗粒沉积区形成。宏观和微孔层都是在用Pt、金或银粒子修饰的n-Si晶片上形成的。Pd粒子表现出一种独特的行为，即在黑暗条件和没有溶解氧的情况下，n-Si的蚀刻以高速率进行，同时伴有氢的析出。对于pt颗粒沉积的p-Si， HF浸泡形成多孔层。在连续光照射下，多孔Si主要在p-Si的非光照射侧表面形成，而不是在n-Si的光照射侧形成。

(1) We investigate the electroless displacement deposition of metal particles (Pt, Rh, Pd, Cu, Ag, and Au) onto n-Si wafers from a metal-salt solution containing HF. The particle density of metals varies widely, depending on the kind of metal. Deposited metals can be classified into two types of nucleation behavior. One consists of the platinum group elements, which display lower particle densities than elements of the other group and depend on the type of pretreatment of the n-Si wafer. The second group consists of the copper group elements, which display higher particle density than the first group and are independent of pretreatment. The size of deposited particles decreases from hundreds nm to ten nm as the particle density increases.(2) Metal-particle-enhanced HF etching of Si can produce micrometer-sized macroporous and nanometer-sized microporous Si by simple immersion of metal-particle-modified Si in a HF aqueous solution without a bias or a particular oxidizing agent. The etching rate of Si and the structure of produced porous Si are changed by the dissolved oxygen concentration of the HF solution and the photoillumination intensity on Si during etching. For n-Si, porous layer is only formed on the metal particle deposited area of the wafers. Both macro and microporous layers are formed on n-Si wafers modified with Pt, gold, or silver particles. Pd particles show a unique behavior in which the etching of n-Si proceeds at a high rate accompanying hydrogen evolution under dark conditions and the absence of dissolved oxygen. For Pt-particle-deposited p-Si, porous layers are formed by HF immersion. Under continuous photoillumination, porous Si is formed mainly on the non-photoirradiation side surface of p-Si, as opposed to the photoirradiation side of n-Si.