Effect of aging on wettability of silicon surfaces modified by Ar implantation

Abstract

The contact angles of most surfaces modified by ion implantation change with the passage of time. The aim of this experiment is to better understand the mechanism leading to the aging of argon implanted silicon oxide surfaces. Coupons of silicon with its native oxide layer have been irradiated by means of 3 keV Ar ions with a fluence of 1.8×1016 Ar/cm2. Some of the implantations have been performed under oxygen partial pressure (∼5×10−5 Torr). The samples have been characterized at different periods of time after the implantation, by means of contact angle hysteresis measurements and angle resolved x-ray photoelectron spectroscopy (ARXPS). Irradiation with Ar ions has produced a more hydrophilic surface immediately after implantation. With the passage of time, the contact angles have increased both in ambient air and in argon atmosphere. Characterization by means of XPS has shown that there is with time a small increase of the O concentration as well as a small decrease of the quantity of Ar in the silicon oxide surfaces. The shape of the C 1s and Si 2p spectra and their details are also slightly modified with the passage of time. A model using the ARXPS measurements suggests that for the samples implanted without oxygen, the aging would be principally due to the spreading of a natural carbonaceous surface layer dispersed into islands after the Ar implantation. The layer being more hydrophobic than the silicon oxide, its spreading would increase the apparent contact angles. On the other hand, the increase of the carbon concentration in the carbonaceous layer would produce a more hydrophobic surface and would be responsible for the aging of the samples implanted in O2 partial pressure. Results obtained by means of a simple model and the Cassie’s equation suggest that for the samples implanted without O2 gas, the contact angles of the substrate and the carbonaceous layer are 5° and 110°, respectively. The apparent contact angle obtained with the Cassie’s equation is in good agreement with the experimental measurements.

Correlation of surface roughness and surface energy of silicon-based materials with their priming reactivity

“…Notably, the Ar-IMP-TEOS SiO 2 surface did not become more hydrophilic during cleaning: already the Ar implantation yielded a surface energy of 75 mN m -1 , which could not be further increased. The increase of the surface energy during implantation processes was also observed for native SiO 2 layers and quartz, but is not yet unequivocally explained on the atomic level [25]. Surface priming of the above-mentioned silicon-based materials was carried out with HMDS in the vapor phase at 90°C either before or after a cleaning step.…”

Selective areain situconversion of Si (0 0 1) hydrophobic to hydrophilic surface by excimer laser irradiation in hydrogen peroxide

“…The quantity of SiO 2 and SiOH is greater for the irradiated site (figure 4(f )) than that for the non-irradiated material (figure 4(e)). Depending on the O/Si ratio, the minimum CA values of SiO 2 -coated Si have been reported to be 45 • -55 • (Chasse and Ross 2002), while the minimum CA of 13 • has been reported for a SiOH monolayer covered Si surface (Chen et al 1991). Thus, the increase in SiOH plays a dominating role in decreasing CA to 14 • at 500 pulses.…”

Selective Area Modification of Silicon Surface Wettability by Pulsed UV Laser Irradiation in Liquid Environment

“…The quantities of SiO 2 and SiOH on the site irradiated by KrF laser are greater ( Figure 3C) than those on the non-irradiated (Figure 3B). The Si surfaces coated with SiO 2 were always reported to have minimum CA values of 45°-55°, as referenced 11 , depending on the O/Si ratio. However, a superhydrophilic SiOH monolayer covered Si surface was reported with a minimum CA of 13°, as referenced 30 .…”

“…However, as Si has an elevated texturing threshold, requiring irradiation with pulse fluence to induce surface texturing in excess of its ablation threshold (~500 mJ/cm 2 ) 9 , texturing of Si surface has frequently been assisted by employing reactive gas atmospheres, such as that of a high pressure SF 6 environment 4,7,8 . Consequently, to modify wettability of the Si surface, numerous works have focused on chemical treatment by depositing organic 10 and inorganic films 2 , or using plasma or electron beam surface treatment 11,12 . It is recognized that hydrophilicity of Si originating from the existence of singular and associated OH groups on its surface could be achieved by boiling it in a H 2 O 2 solution at 100 °C for several minutes 13 .…”