Addressing the ESH Aspects of New Materials

Accompanying the introduction of new materials in almost every process module in semiconductor processing is a host of environmental, safety and health issues. And, because device manufacturers today are attempting to evaluate and introduce materials to the fab floor more quickly in efforts to stay competitive, the process requires faster evaluation of a variety of materials for copper plating, barrier metal deposition, low-k dielectrics, high-k gate dielectrics and metal gates.

At the 12th Annual Schumacher Dielectric and Metallization Symposium held earlier this year, individuals from Motorola (Austin, Texas) and Air Products' Schumacher Unit (Carlsbad, Calif.) discussed ways companies are dealing with the unprecedented introduction of new materials throughout the manufacturing process.

Laura Mendicino, manager of the Environmental Process Initiatives Department in Advanced Process Development for Motorola, explained the typical strategy for all new materials. Engineers look at the specific process, the process tool where the material will be used, tool location in the fab, storage location, and usage rates. The material must also be compatible with the tool's exhaust and/or drainage systems.

The engineer also considers the point of contact between the material and the user and the potential harm associated with varying levels of exposure to employees. Importantly, any new material that is being researched in the R&D lab or pilot line must undergo evaluations prior to use, even if the material winds up not being used in a production line. This has been one of the most challenging aspects of new material evaluations in semiconductor facilities.

Mendicino emphasized that an ESH strategy must focus on the entire process, not just the material itself. This includes the interaction between the chemical and other materials in reactor chambers, in exhaust ducts, in liquid disposal systems, etc. She suggested compiling as much data as possible during the R&D phase, so that if and when the material is transferred to production, the proper information is available to speed a material's adoption. Mendicino added that close work with gas and chemical suppliers is an absolute must, so that suppliers can provide the necessary support in the timeframe required by the device manufacturer.

ESH evaluations begin with a thorough review of the MSDS document, including the material's toxicity, flammability and reactivity, handling procedures, interactions with other chemicals, characteristics of similar materials, etc. During use, the engineer typically monitors process emissions using QMS, FTIR, RGA and other analytical tools. In some cases, point-of-use abatement becomes necessary.

The Table summarizes some of the metal CVD precursors, including the more common, commercially available materials such as TiCl₄ and TDMAT (tetrakis (dimethylamino) titanium), along with others, such as Zr t-butoxide and Hf t-butoxide and tetranitro titanium. The use of tetranitro titanium, often referred to as TN, requires work with suppliers to determine the properties and potential hazards upon exposure to air or water, solvents, or heat, for instance. TN is a corrosive, strong oxidizer that reacts with moisture to form HNO₃ in an exothermic reaction. Mendicino recommends the use of NO and NO₂ sensors in the cabinet and tool, and chamber cleaning with water, not IPA.

In general, metal CVD processes pose greater safety concerns than PVD. With CVD, there is the threat of exposure to dusts from Cu, Pb, Al, W and Ti byproducts.

In recent years, the Internet has somewhat simplified the materials' research process, making documents available from a number of industries worldwide. However, Mary Majors, senior EH&S specialist for Schumacher/Air Products Electronics Chemicals, warns against the quality of some information on the Internet. Majors also suggested the need for a formal forum in the semiconductor industry for sharing ESH information. She said that new materials evaluation is not just an ESH issue, but a market issue as well — to get data for a material that requires characterization, when it is required, even if the material never enters the fab.

Finally, with the use of many new materials, Mendicino was asked whether there were any materials that semiconductor manufacturers would not consider using in production facilities. She said that, aside from the obvious, radioactive chemicals, there was one gas, ClF₃, that Motorola decided not to use due to ESH issues. "However, you never know," she said. "I never thought we'd be using lead in our fabs, and now we are."