Radical-Driven Silicon Surface Passivation by Benzoquinone– and Hydroquinone–Methanol and Photoinitiators

5 years ago

Radical-Driven Silicon Surface Passivation by Benzoquinone– and Hydroquinone–Methanol and Photoinitiators

Robert L. Opila, Meixi Chen, James H. Hack, Kevin J. Jones, Abhishek Iyer

This work confirms that radical intermediates are the reactive species in quinhydrone/methanol (QHY/ME) passivation on silicon surfaces. The two constituent parts, p-benzoquinone (BQ) and hydroquinone (HQ), have been studied separately. BQ abstracts the hydrogen atom from methanol to become semiquinone radicals (QH*). Both QH* and the resulting methanol radical are responsible for the large, instantaneous increase in minority carrier lifetime in BQ/ME, obtaining the lowest surface recombination velocity of 1.6 cm/s. HQ releases a hydrogen atom to become QH*. The quinone derivatives containing a lower electronegativity group (Cl— or O═) on the benzene ring form radicals more easily, and give better passivation results. This radical-driven passivation mechanism is also valid on other radical sources. X-ray photoelectron spectroscopy (XPS) supports the radical mechanism in the observation of dominating BQ bonding after 1 h of BQ/ME treatment, and increasing methanol bonding with increasing immersion time, reaching a roughly 21% SiOSi, 13% ME, and 6% BQ monolayer coverage in 24 h for BQ/ME passivated silicon. Density functional theory (DFT) further confirms the thermodynamic possibility of radical bonding and proves that the “edge-on” single-bonded configuration is more energetically favorable than the “face-on” double-bonded configuration.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b05686

DOI: 10.1021/acs.jpcc.7b05686