Epitaxial Process Of4H-SiC Bipolar Junction Transistors With Grading Doping Base

Epitaxial growth is key process to make SiC devices, and its quality directlydetermines the device performance. By studying the relationship between SiC epitaxialand the characteristics of BJT devices, the epitaxial growth process for the BJT deviceswas designed and optimized in this paper.First, the simulation result of BJT is provided. The Sentaurus software is used forthe relationship between BJT characteristics and material properties, doping andstructure of BJT. The4H-SiC material model and parameters are studied through thecomparison of the simulation and reported experimental results of BJT. Then we focuson the non-uniform base doping profile of BJT devices, the simulation results show thatthe DC gain is increased, the transit time through base region is decreased, as well asthe cut-off frequency of BJT is improved. It also shows that the difference in DC gaincaused by the gradient has some influence on the turn-on and turn-off delay time. So adouble layer with grading doping profile base is proposed in this chapter.And then the epitaxial growth process for the BJT devices is introduced. Theinfluence of SiC CVD process parameters for the quality of epitaxial layer is analyzed.And the common defects of epitaxial are summed up in the growth process, such asdeep-level defects, triangular defects, and basal plane dislocation. Further, the dopingcontrol principle in the epitaxial growth is elaborated. The process parameters are givenby some previous experiment in our equipment (VP508), and a proper process recipewas set in it.The BJT epitaxial film was characterization by kinds of methods. There are noobvious defects at the epitaxial layer surface characterized by optical microscopy. TheAFM show that the surface was planar and the Rms was only0.207nm. The goodcrystallization quality was proved by Raman and X-ray diffraction. At last, the profile ofthe epitaxial layer is provided by SIMS test, and results show that the doping profile ofepitaxial wafers meet the requirements of the BJT.