From "Dust Control" to Contamination-Free Processing
Laura Peters, Senior Editor -- Semiconductor International, 12/1/1998
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In early issues of Semiconductor International, experts referred to the need for "dust control" in fabs to minimize defects on wafers primarily due to operator interaction and the environment. Today, the cleanroom and operator can induce such low levels of contamination that the main culprits of defectivity are the processing equipment and processes themselves. For instance, high density plasma (HDP) deposition and etching equipment requires frequent chamber cleaning; contamination control in CMP is critical (and not too well understood), and sputtering and ion implantation processes are susceptible to resist contamination. To get from 1978's views of particle contamination to today's more sophisticated methods of contamination-free manufacturing requires new ways of thinking about contamination and defects.
What evolved over 20 years was a better understanding of the relationship between particle levels (or particulates) and defects. Importantly, the focus of contamination control migrated from the fab itself to wafer-level contamination. Minienvironment concepts, expected by many to reach widespread adoption at the 200 mm wafer level, are still being scrutinized yet appear to be a foregone conclusion for 300 mm processing. Integrated processing, which provides better contamination control, is generally only adopted in vacuum chambers when clearly superior process results such as improved film quality are demonstrated. Integrated stepper/track approaches, first attempted in the late 1970s, are now commonly found in fabs around the world.
 What evolved over 20 years was a better understanding of the relationship between particles and defects.
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The demise of wet cleaning stations is not expected in the near future, though a variety of vapor-phase cleans, cryogenic cleans and laser-based cleans are finding use in fabs. All-dry metalization sequences are being explored. Cleaning sequences are becoming very level-specific. Cleaning engineers also focus on the systematic elimination of unwanted chemicals such as sulfuric acid, HCl and many solvent-based strippers. Ozone-based cleans show great promise in these areas. The development of copper-compatible cleans is critical today, as is cost-effective cleaning following CMP. Point-of-use chemical generation, which can provide even cleaner chemicals than can be otherwise purchased, is being gradually adopted.
Gas distribution system technology is rapidly advancing, with new integrated
component systems, new valves and controllers for more precise, contamination-free
delivery. Today, that includes not only inert bulk gases such as N2
and Ar; specialty gases such as silane, diborane, phosphine and WF6
and etchants such as HCl and HBr, but also new liquid-source gases such as trichlorosilane
and metalorganic sources, which require heated distribution systems and control
over leakage and vibration. As the complexity of these systems increases, the
need to deliver a variety of gases for purging, in-situ cleans and processes
must also become more exacting. In the long run, integrated component systems
may provide not only enhanced purity and reliability, but possibly significant
savings in cost-of-ownership as well. 
