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

(1)我们研究了从含HF的金属盐溶液中在n-Si晶片上化学置换沉积金属颗粒（Pt、Rh、Pd、Cu、Ag和Au）。金属的颗粒密度变化很大，取决于金属的种类。沉积金属可分为两种类型的形核行为。一种由铂族元素组成，其显示出比另一组元素更低的颗粒密度，并且取决于n-Si晶片的预处理类型。第二组由铜族元素组成，其显示出比第一组更高的颗粒密度，并且与预处理无关。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)金属颗粒增强的Si的HF蚀刻可以通过简单地将金属颗粒改性的Si浸入HF水溶液中而无需偏压或特定的氧化剂来产生微米尺寸的大孔和纳米尺寸的微孔Si。HF溶液中的溶解氧浓度和刻蚀过程中Si上的光照强度改变了Si的刻蚀速率和多孔Si的结构。对于n-Si，仅在晶片的金属颗粒沉积区域上形成多孔层。宏观和微孔层都形成在用Pt、金或银颗粒改性的n-Si晶片上。Pd颗粒表现出独特的行为，其中n-Si的蚀刻在黑暗条件下和不存在溶解氧的情况下以高速率进行伴随着析氢。对于Pt颗粒沉积的p-Si，通过HF浸渍形成多孔层。在连续光照射下，多孔Si主要形成在p-Si的非光照射侧表面上，与n-Si的光照射侧相反。

(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.