The Role of Surface Chemistry in Bonding of Standard Silicon Wafers

Abstract

Hydrophilic silicon surfaces become hydrophobic without microroughening after 2 00°C low energy hydrogen plasma cleaning. The fully hydrogen-terminated silicon surfaces do not bond to each other, not even by the application of external pressure. A subsequent 400 to 600°C, 4 mm thermal treatment in ultrahigh vacuum converts the wafer surfaces to hydrophilic and bondable which can be attributed to desorption of hydrogen from the surfaces. Hydrophobic silicon surfaces prepared by a dip in HF (without subsequent water rinse) are terminated by H and a small amount of F, or by H and a small amount of OH (after subsequent water rinse). Hydrogen bonding of Si-F (HF) H-Si or Si-OW (HOH) OH-Si across the two mating surfaces appears to be responsible for room temperature spontaneous hydrophobic or hydrophilic wafer bonding, respectively.

Artificial biomembrane based on DPPC — Investigation into phase transition and thermal behavior through ellipsometric techniques

“…were soaked with HF solution (1 %) during 2 minutes, followed by chromatography water wash [22]. Conversely, in order to remove the original silicon wafer native oxide, the substrates were cleaned through piranha solution (H 2 SO 4 :H 2 O 2 in a 7:3 ratio) during 30 minutes at 80 °C [23].…”

Optically pumped VECSELs: review of technology and progress

“…In particular, while direct hydrophobic wafer bonding can result in a bonding interface free of intermediate structures, as shown in [193], it can also be associated with an intermediate amorphous layer a few nm in thickness [194]. On the other hand, direct hydrophilic wafer bonding of silicon wafers usually comes with an intermediate oxide layer with a thickness of a few nm [164].…”

Low temperature bonding of microstructured fiber sensors

“…The chemical mechanism behind the bonding process is governed by the polymerization of the Si-OH groups on the pre-bonded substrates into strong equivalent Si-O-Si bonds under the release of H 2 O [7,8]. The effect of the pressure on the bonding strength is merely the contact surface enhancement between the two substrates, thereby changing the effective area where bonding will occur.…”