Chemistry Reference
In-Depth Information
concentration at various temperatures.
1005
Figure 4.10 plots the etch rate in SC-1 solu-
tion as a function of concentration.
1013
Residual oxide may be left in some microstructures at the end of etching and its
occurrence strongly depends on geometry, surface tension, and the contact angle of the
etchant.
13
It may be caused by the formation of air bubbles trapped in the structure when
the wafer is being immersed in the etchant. It has been found that etching of thermal
in a dilute aqueous solution of HF, 0.01% HF, proceeds down to ~20Å and beyond
this point a thin layer that is resistant to HF remains on the Si substrate.
368
This resid-
ual film, which is several nanometers thick with the oxygen content increasing toward
the surface, is hydrophobic. It has been suggested that this oxide layer near the inter-
face is relatively dense.
628
In etching of silicon oxide structures, the edge of a marked oxide step tends to
be etched also in the horizontal direction. The etching profile is independent of the com-
solutions but depends strongly on temperature as shown in Fig.
position of
4.11.
792
An oxide-covered wafer, after leaving the oxide etching tank, will continue to
etch faster in the initial stage in the rinse tank because of the residual etchant on the
surface.
97
Thus, the actual etch of in HF consists of etching in the HF tank and
etching in the rinse tank. The amount of oxide etched during the transfer and rinse
depends on the etchant. Determination of etch rates may thus be affected by the water
rinse step after the etching. Also, the etching may result in the final etched pattern being
U-shaped, with the center of the wafer etched more than the bottom and top.
The etch rate of thermally grown oxide may be altered by postoxidation
treatments. Ion implantation at a certain level, depending on the nature of damage
and distribution, has been found to increase the etch rate.
310
Also, an electric field, by
applying an anodic potential onto a thermally grown oxide film, is able to inject hydro-
xyls into the oxide.
427
The etch rate of the hydroxyl penetrated region, depending
on the hydroxyl concentration, is much faster than the unaffected thermal oxide
