Prem,

In our experience, the best method we've seen for a wet chemical
activation of surfaces prior to a direct bond is to use a reversed RCA
cleaning process, with the HF/BOE portion of the protocol removed.

So first clean the substrates using an RCA2 (HCl-H2O2-H2O) clean first,
followed by an RCA1 clean (NH4OH-H2O2-H2O), followed by a final DI
rinse. This will leave OH groups attached to the surface of the
substrates, which will enhance the initial Van der Waals bond force (via
hydrogen bonding).

Best Regards,
Chad Brubaker

EV Group
invent * innovate * implement
Senior Process Technology Engineer - Direct: +1 (480) 305 2414, Main: +1
(480) 305 2400 Fax: +1 (480) 305 2401
Cell: +1 (602) 321 6071
E-Mail: C.Brubaker@EVGroup.com, Web: www.EVGroup.com

Prem writes:

Dear all

I wish to perform the wafer bonding process between LPCVD deposited
nitride/oxide layers. Will it require cleaning prior to bonding using
RCA or Piranha solution? If yes, the cleaning in Piranha solution
(H2SO4+H2O2) is adequate for successful wafer bonding processAll kinds
of suggestions will be highly appreciated.

Best regards

Prem
Nagoya University