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

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.