Study On Reactive Ion Etching And Electrochemical Etching Of 4H-SiC

Silicon carbide(Si C) is a representative of the third generation semiconductor material and can be applied in high frequency and high power microelectronic and high temperature optoelectronic devices due to its outstanding semiconductor and physical properties such as large band gap, high breakdown electric field, and good thermal stability. As the preparation of Si C semiconductor material is becoming more and more mature with the continuous development of science and technology,not only the Si C based MEMS devices from bulk- but also NEMS devices from the nano-Si C have drawn more and more attention.In this master thesis, the n-type conductive 4H-Si C substrate is used. The thesis includes two parts. The first part is the reactive ion etching of Si C, and the formation mechanism and elimination method of spike residues are investigated. The second part is the piezoresistive effect of 4H-Si C nanowire. 4H-Si C nanowire is prepared by the electrochemical etching, and the origin of the piezoresistive effect of the nanowire is studied.The pattern transfer is achieved by using the traditional method, such as lithography, sputtering, and electroplating. The(000 1) C face and(0001) Si face of4H-Si C are etched, in the SF6/O2 gas mixture, by reactive ion etching(RIE) method.The spike residues with {1102}developing faces are observed on the etched C face by scanning electron microscopy(SEM) and atomic force microscopy(AFM), while the Si surface is smooth. The effects of etching parameters, such as working pressure,SF6:O2 flow ratio, etching time, and so on, on the formation of the spikes are systematically investigated. It is found that the work pressure and SF6:O2 flow ratio play an important role in the spike formation. The mechanism model of the spike formation is put forward based on the crystal structure of Si C. Silicon atoms are present in the {1102} planes and(0001) Si face, while carbon atoms are present in the(000 1) C face. The etching rate on the former faces is less than the etching rate of the latter, it is the reason why the spikes are formed on the etched C face. Thespike residues are completely eliminated by increasing the SF6:O2 flow rate and working pressure, both of which enhance the etching rate of {1102} planes.The 4H-Si C nanowires, with uniform thickness and smooth side wall, are prepared by the electrochemical etching method on the C face of the 4H-Si C substrate. The piezoresistive properties of single nanowires are characterized by the conductive atomic force microscopy(C-AFM). The piezoresistive coefficients of the4H-Si C nanowires with a radius of 33.96 nm and 66.11 nm, respectively, are in the range of 32.98 ~ 19.09×10-11 Pa-1 and 40.35 ~ 23.13×10-11 Pa-1, which are higher than those of bulk materials. The relationship between the 4H-Si C band gap Eg as well as electron mobility μ and ?ρ/ρ0 is studied. The piezoresistive effect of nanowires is mainly caused by the superimposition of the Eg and μ, in which the Eg is increased while the μ is decreased when the nanowires are exerted a sustained increase in stress.