Method for productivity
and yield improvement in dry plasma etch and ash tools by using chemical-based
cleaning
�
Disclosed is a method for productivity
and yield improvement in dry plasma etch and ash tools by using chemical-based
cleaning. Benefits include improved
productivity, improved throughput, and improved reliability.
Background
� � � � � Any subtractive etch process (metal, poly silicon, silicon
oxide, silicon nitride) involve the use of halogen based reactive ion etch
technology in a plasma environment. Typically, in the aluminum etch process,
chlorine-rich plasma reacts with the exposed aluminum surfaces on the product
wafers to form volatile aluminum trichloride species.
� � � � � The bulk of this etch by-product is transferred out of the main
etch chamber via the pumping system. However, some portion of the volatile
aluminum subchlorides chemisorbs onto the chamber internal surfaces. Between
the wafer transfers, plasma chamber cleaning with oxygen is required to
minimize the corrosion effects of residual moisture in the transfer chamber.
During this step, aluminum chloride reacts with the oxygen to form solid-phase
aluminum oxide.
� � � � �
� � � � � The chemical reactions can be represented as follows:
Al + 3Clo � AlCl3�
and� AlCl3 + Oo
� AlxOyClz + AlxOy + Cl2
� � � � � With increases in the number
of wafers processed, the process of solid-phase aluminum oxide formation and
buildup on the chamber internal surfaces continues. In addition, cold surfaces
tend to accumulate buildup at a higher rate than the heated/warmer areas. Thermal
expansion/contraction due to heating/cooling cycles tend to shed off the
oxidized aluminum byproducts in the form of submicron to tens of micron size
particles on to the product wafers. Similar byproducts occur in the ash
chamber. They are generated during the ash process due to the oxygen plasma
reaction with the residual aluminum oxychlorides mixed with photoresist on the
wafers.
� � � � � The presence of the
aluminum oxide particles in the etch and ash chambers continue to present
manufacturing issues with regard to the tool availability for production and
also in the defects impacting the yield. Some tools require frequent
unscheduled and longer preventative maintenance (PM) cycles. Chamber parts
above (such as gas lines, orifices, and reflectors) and below (such as heated
base flanges and rings) the wafer surface are the significant contributors to
the wafer defects. The convectional/gravitational effects are caused by
potential fluctuations in the chamber temperature, pressure and gas-flow
dynamics.
� � � � � Conventionally, the best approach to preventing defects is to
maintain a clean chamber environment, using wet and dry cleaning techniques.
Wet cleaning is mechanically scrubbing off the adhered aluminum oxide
particles with scrub pads and deionized (DI) water, followed by a final wipe
with isopropyl alcohol (IPA). Wet cleaning is performed as appropriate, based on the number of
particles...