Spin-On Glass Films Matias Lehtinen 16.3.2016

Spin-On Glass technology, SiO2 A so called sol-gel process SiO2 compunds most commonly used with semiconductors Process consists of: Film formation through spin coating Few thousand rpm Film thickness 50-500 nm, controlled with viscosity Drying the film Complete when no more weight loss Heat treatment Transition of hybrid inorganic-organic layers Water and solvent evaporate, strong film is formed http://doc.utwente.nl/14094/1/t0000009.pdf

Spin-On Glass Films Heat treatment of SiO2 films can be problematic High temperatures, fast treatment: Low decomposition rate of compounds High risk of cracking due to internal stress Low temperatures, slow treatment:  Susceptibility to moisture and decomposition Low risk of cracking due to internal stress Increase heat? Decerase heat?

Spin-On Glass Films Solution, Doping Adding dopants to modify the Si-O newtork Reduced internal stress during shrinkage Example, Phosphorus Doping gives more flexibility with temperature Engineering the host/dopant compound from the start can also solve this issue (e.g. Borazole) P-doped S-SOG Si-SOG Borazole structure http://doc.utwente.nl/14094/1/t0000009.pdf

Spin-On Glass Films Some compounds can only be heat treated in lower temperatures Use of ”Pore Capping”: The pores in the film are sealed before heat treatment High packing density layer over doped surface Capping prevents the reaction between atmosphere and the compound Oxidization Moisture https://www.researchgate.net/profile/O_Shilova/publication/225496629_Spin-on_glass_films_for_semiconductor_technology/links/0c9605310943535e8c000000.pdf

Information – sol-gel process A sol-gel process is a process involving a solution or sol that undergoes a sol-gel transition. Before transition the sol-gel solution is a stable single phased liquid. The transition transforms the single phased solution into a rigid two-phase system of solid and solvent-filled pores through destabilization, precipitation or supersaturation. The process happening after the spinning is not clearly understood, but the gels viscosity increases sharply. However, the main properties of the film are created through the heat-treatment, where water and solvents are evaporated through the pores and a strong film is created. The sol-gel transition is irreversible.

Information – Borazole (example) Dopant-organic compound (Boron-Nitrogen backbone polymer) The Borazole decomposes in the heat treatment process, into boron- nitrogen-hydrogen parts, which will react with the oxygen in the organic groups. The water from the Spin-On process or oxygen from the heat treatment process reacts further and B2O3 is formed. The process continues as B2O3 finally reacts with Si and the Boron gets diffused into the silicon substrate. The amount of unwanted reactions can be minimized with the help of Dopant-organic compounds.

References F. Horowitz. Towards Better Control of Sol-gel Film Processing for Optical Device Applications. Journal of Nonlinear Optical Physics and Materials Vol. 6, No. 1, 1997. p. 1-18. doi: 10.1142/S0218863597000022 Nguyen Nhu Toàn, 1999. Spin-on glass materials and applications in advanced IC technologies. ISBN: 90-365-12697 O. A. Shilova. ‘Spin-on glass’ films for semiconductor technology. Surface Coatings International Part B: Coatings Transactions 195 Vol. 86, Issue 3, 9/2003, p. 195–202, 9/2003. doi 10.1007/BF02699653