Strategies for Cost Effective Implementation of PFC Emissions Reduction Solutions in the Semiconductor Industry

PFC (perfluorocompound) gases such as CF₄, C₂F₆, C₃F₈, C₄F ₈, CHF₃, NF₃ and SF₆ are used as chemical precursors in semiconductor manufacturing, during the CVD (chemical vapor deposition) chambers cleaning process steps and for the plasma etching of interconnects materials. Once emitted in the atmosphere, PFC molecules contribute to the green house effect, due to their strong absorption of infrared radiations and high global warming potentials (GWPs). Further, PFC molecules are difficult to destroy, due to their strong chemical bonds, and can have very long atmospheric lifetimes. For example, SF₆ has a GWP of 23,900 and an estimated lifetime of 3,200 years in the atmosphere; CF₄ has a GWP of 6,500 and an estimated atmospheric lifetime of 50,000 years. PFC emissions from semiconductor manufacturing tools result for the most part from limited utilization efficiency of the gas during the etch or cleaning process. CF₄ and C₂F₆ can also be formed as byproducts of the destruction of other PFC molecules with a higher number of carbon atoms (i.e. CF₄ can formed from C₂F₆, CF₄ and C₂F₆ can be formed from C₄F₈...). CF₄ can also be produced as a byproduct of the cleaning or etching of carbon-containing materials (low-k). This paper provides an overview of the various PFC emissions reduction strategies and offers some guidelines to implement the most cost effective solutions in a manufacturing environment. We will review the environmental, cost and manufacturing productivity factors that must be taken into account to devise the best available PFC emission reduction solution. As we will see, there are multiple ways to arrive at an emission reduction target, through retrofit of existing factories or the implementation of PFC solutions for expanding semiconductor fabrication plants