Method for productivity and yield improvement in dry plasma etch and ash tools by using chemical-based cleaning

Method for productivity and yield improvement in dry plasma etch and ash tools by using chemical-based cleaning

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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.

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� � � � � The chemical reactions can be represented as follows:

Al + 3Cl^o � AlCl₃� and� AlCl₃ + O^o � 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...