Study On The Alkali And Acid Etching Of Single-Crystalline Germanium Wafer

Due to the unique properties, bulk single crystalline germaniums are largely used in IC industry, such as lenses and windows for infrared (IR) optics, detectors for gamma radiation and substrates for solar cells, etc. The chemical etching is an important procedure, which has a great impact on the product quality and device yield of germanium. As common corrosive agents, HNO₃/HF system and NaOH/H₂O₂ system are widely used in etching of semiconductor materials. However, few reports on the alkali and acid chemical etching mechanism and characteristics of single-crystalline germanium are found. It is necessary to perform more detailed research on the alkali and acid etching of single crystalline germanium since it is the theoretical foundation for the process control and technology improvement.On the basis of systematic review of the application and development of germanium, this work studies the alkali and acid etching properties of single crystalline germanium in detail. First of all, acid and alkali etching orthogonal test were designed as a preliminary exploration. The orthogonal test confirms that the solution temperature, compositions concentration and etching environments are important factors that affect the etching process. According to the orthogonal tests, experiments are designed for detailed research of germanium etching mechanism and properties. Analysis of the etching conditions for the etching process provides experimental evidence and theoretical foundation for the etching of single crystalline germanium.Experiments show that the temperature is an important controllable condition, which influences the etching rate greatly either in acid etching or in alkali etching. The composition concentration is another important factor that affects both the etching rate and surface morphology of single crystalline germanium.During the acid etching of germanium wafer, temperature can only increase the etching rate of germanium. With the increasing proportion of acetic acid, wafer etching rate decreases while the surface roughness increases. It is difficult to achieve a polished germanium surfaces with a high proportion of acetic acid. Wafer etched in the solution without acetic acid has a much brighter surface with hill-shaped bulges, and a certain proportion of acetic acid can eliminate these bulges. The major functions of ultrasonication are causing the thermal and cavitational effect in etching agents. Ultasonication shows different performances under different temperature conditions,and mainly causes the cavitation effect at low-temperature.During the alkali etching process of germanium wafer, etching rate first increases and then decreases because of the rapid decomposition of H₂O₂ as the temperature increases. The alkali etching process of germanium is a non-preferential polishing etching as long as the concentration of H₂O₂ in the etchant is kept constant. In the non-preferred alkali etching process, wafer etching rate and surface smoothness increases first and then decreases as the increase of NaOH concentration; the increase of the adding amount of hydrogen peroxide per minute improves the etching rate and the surface smoothness. The decomposition of H₂O₂ increases with increasing concentration. Most of the oxygen ions coming from the decomposition of H₂O₂ release from the solution as oxygen, which improves the wafer polishing from the point view of dynamics. The use of vessel with smaller volume is also contributed to this process due to the increasing of the gas pressure may affect the final result of etching.