Title page for ETD etd-03122009-041754
|Type of Document
||Haque, Ashim Shatil
||Optimization of surface preparation technique for unipolar silicon direct bonding
||Master of Science
|Moore, Daniel J.
|Desu, Seshu B.
|Elshabini-Riad, Aicha A.
|Date of Defense
A special wafer bonding method called the Silicon Direct Bonding technique is
used to study the bonding of unipolar (n-type, <100> oriented) silicon wafers. The
primary objective of this thesis project is to find an optimum surface preparation technique
for subsequent silicon wafer bonding. Wafer cleaning and treatment methods are
investigated to understand the correlation between a high quality wafer surface and the
resulting high quality electrical conduction at the interface. Accordingly, in this project, a
preference for hydrophobic (less polar Si-OH surface) wafers is given to ensure a
minimized amount of oxide layer on the surface. Several key factors that govern the
quality of the wafer surfaces, such as the degree of hydrophobicity, HF etching time,
composition of HF etching solution and Dr water rinse, are examined with ellipsometric
and XPS measurements. An HF etching followed by a sputter etching has been selected to
pre-treat the wafer surfaces for bonding. A maximum allowable air exposure time (35
second) is also found which would allow bonding without significant re-growth of the
oxide layer. Bonding is performed under vacuum with a special mechanical fixture and the
resulting structures from a subsequent heat treatment process are examined with crack
propagation testing. Bond strength after annealing is sufficient to withstand a pull test,
however, with a 3 point bend testing, the crack propagated horizontally at the interface.
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