טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentGordon Nahum
SubjectSilicon Texturing under Negative Potential Dissolution
(NPD) Conditions
DepartmentDepartment of Materials Science and Engineering
Supervisors Professor Yair Ein-Eli
Dr. David Starosvetsky


Abstract

 A novel process for silicon texturing by electrochemical method is presented. Silicon texturing was carried out in electrolyte containing potassium hydroxide (KOH) with the use of Negative Potential Dissolution (NPD) conditions. The novel process was studied for as - cut p - type single- and multi- crystalline silicon and for Edge defined Film-fed Growth (EFG) multicrystalline silicon. Texturing of <100>, <110> and <111> oriented silicon, which was carried out by Negative Potential Dissolution (NPD) process, result in morphologies of pyramids, prisms and coined triangles, respectively. Effect of different parameters such as KOH concentration, negative potential, and time on the texturing process was studied.  KOH concentrations of 16 to 32 wt % were found to be the most suitable for texturing as - cut silicon. The research points that the application of a negative potential does not alters the anisotropic character of the dissolution, in comparison to dissolution at OCP (Open Circuit Potential), but rather it accelerates the process dramatically. Shifting the potential to - 10V decrease the etch rate in comparison to dissolution at OCP, while further shifting the potential to more negative potentials below - 20V accelerate the dissolution process exponentially. These results indicate that NPD mechanism is different from the mechanism at OCP. Possible mechanisms for silicon dissolution at extreme negative potential involve transfer of silicon atoms or negative silicon ions from the silicon surface to the solution.  Texturing of multicrystalline silicon, by the use of NPD, result in different morphologies formed on the same wafer. Texture of small pyramids was formed by the exposure of EFG multicrystalline silicon to - 50V in electrolyte containing 50 wt. % KOH.