The Study Of Silicon Etching In HF/HNO₃/H₂O System

The HF/HNO3/H2O system is wildly used in micro-electronics process and texturing for solar cells. The silicon etching process in this system is very complicated and the etching rate is hardly controlled. The silicon etching process in the HF/HNO3/H2O System and the influence of a new additive NH4F on silicon etching were mainly studied here.At first, the variation of etching rate under different temperate and ratio of HF to HNO3 was studied. The etching rate increased first, and then decreased with the increase of the volume ratio of HF to HNO3. If temperature increased, the etching rate increased quickly. The reaction is an exothermic reaction, so the temperature of solution increases quickly during the reaction. The reaction is easy to run away. On the basis of the above study, the silicon etching process in a controllable HF/HNO3/H2O System was studied. Since the etching rate and the reaction temperature were changing along with the time passed, the process could be divided into five phases. The variation of the etching rate was in the result of the coactions of three factors--the heat generated the concentration of the F+, and the heat exchange between the system and the environment. Then, the surface structure and reflectivity of silicon wafer during etching process was analyzed.At last, the influence of a new additive NH4F on silicon etching in this system was studied. When a few of NH4F was added into rich-HF system, the etching rate increased. This may be attributed to the decomposition of NH4NO2. Then, the etching rate decreased with the added NH4F increased because of the PH of solution increased. Using NH4F as diluents can effectively control the etching rate. The etching rate, the surface structure and the reflectance got a strong correlation.