Chemical Mechanical Planarization (CMP)
is a process that can remove topography
from silicon oxide, metal and polysilicon
surfaces. It is the preferred planarization
step utilized in deep sub-micron IC
manufacturing. More recent scaling of
transistor critical dimension has required
the use of CMP for applications such as
shallow trench isolation (STI) and
trenched metal interconnection (Cu
damascene). CMP has also been utilized
for fabrication and assembly of Micro
Electro-Mechanical System (MEMS).
In principle, CMP is a process of
smoothing and planing surfaces with the
combination of chemical and mechanical
forces. It can, in a way, be thought of as a
hybrid of chemical etching and free
abrasive polishing. Mechanical grinding
alone may theoretically achieve
planarization but the surface damage is
high as compared to CMP. Chemistry
alone, on the other hand, cannot attain
planarization because most chemical
reactions are isotropic. However, the
removal and planarization mechanism is
much more complicated than just
considering chemical and mechanical
effects separately. CMP makes use of the
fact that high points on the wafer would be
subjected to higher pressures from the
pad as compared to lower points, hence,
enhancing the removal rates there and
achieving planarization