Removal efficiency of metallic impurities on various substrates in HF-based solutions

In this study, the removal efficiency of metallic impurities with various substrate surfaces has been investigated. It strongly depends on the substrate conditions as well as the kind of metallic impurities. Copper (Cu) impurities deposited on an amorphous silicon (a-Si) surface are hardly removed by a hydrofluoric acid-hydrogen peroxide mixture (FPM) cleaning, while they are completely removed from a single crystalline silicon (c-Si) surface at a level lower than the detection limit. A hydrofluoric acid-hydrogen peroxide mixture with nonionic surfactant (FPMS) cleaning with high HF concentration, however, can efficiently remove Cu contaminants from both c-Si and a-Si surfaces. We postulate that both etching of the silicon by the FPM solution and surface passivation by the surfactant are essential to removing Cu contaminants from a-Si surface. Moreover, the Cu removal efficiency of FPMS solution is highly dependent on the nature of a-Si films. The range of high removal efficiency on a-Si film surface with inactivated phosphorus, when changing the chemical mixing ratio of an FPMS solution with 50 ppm nonionic surfactant, is much broader than that on undoped a-Si film surfaces, whereas it is not depending on the presence of hydrogen in a-Si film. In order to remove metallic impurities from all substrates including various a-Si film surfaces, a cleaning solution should have the etching capability of substrates and high dissolution rate of metallic contaminants. Much more attention should be given for HF-based solution process of various substrates with high etching rate. (C) 2001 The Electrochemical Society.