Surface modification of hafnia with polyelectrolytes based on the spin-coating electrostatic self-assembly method

In this paper, we describe organic surface modification and functionalization of a hafnia substrate, which has been extensively investigated as a replacement of the gate insulting SiO2 layer in field effect transistors. The surface state of the hafnia was assessed by water contact angle (θwater) measurement with comparison to that of the silicone during the layer-by-layer (LBL) deposition of poly(allyamine hydrochloride) (PAH)/poly(styrene sulfonate) (PSS) bilayers by means of the spin-coating electrostatic self-assembly, SCESA, method. The surface state of virgin hafnia (θwater = 73 ± 1°) turned hydrophilic (θwater = 8 ± 2°) after submission to the standard RCA cleaning process of silicon. The thickness of the multilayer films on the cleaned hafnia surface was found to grow linearly with an increase in the number of PAH/PSS bilayers (d = 2.2 ± 0.1 nm), indicating the consistency in the formation of uniform films. The average water contact angle of the PAH and PSS layers on hafnia alternately switched between 36.0 ± 0.7° and 29.7 ± 0.4° during the nine deposition cycles. The analysis of the surface topography by means of atomic force microscopy (AFM) indicated that the surface roughness of the first PAH layer deposited on the hafnia was strongly smoothed from 1.54 to 0.44 nm with increasing the LBL deposition of polyelectrolytes.