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Plasma etch properties of organic BARCs

Plasma etching is an integral part of semiconductor integrated circuit (IC) processing and is widely used to produce high-resolution patterns and to remove sacrificial layers. Bottom anti-reflective coatings (BARCs) under the resist absorb light to minimize reflectivity during lithography and are typically opened during pattern transfer using plasma etching. High etch selectivity is required in the BARC opening process to minimize resist loss to allow further substrate etching. Because the plasma etch process combines physical bombardment and chemical reaction, the factors affecting etch rate and selectivity are complex. The results are related to etch conditions and the chemical nature of polymer. This paper addresses plasma etch properties as they relate to polymer type and etch gas composition. Polyacrylate, polyester, and polymers containing nitrogen and halogens have been investigated. The research was carried out by a series of designs of experiments (DOEs), which varied the flow rate of Ar, CF4, and O2 in plasma gas. The selectivity of BARC to resist depends not only on the carbon content but also on the different ways polymer compositions and structures respond to an oxidizing gas, a reducing gas, and plasma bombardment. Based on a polymer decomposition mechanism, we discuss what could happen physically and chemically during the polymer's exposure to the high-energy reactive plasmas. We also modified the Ohnishi parameter for the polymers containing nitrogen and halogen using our polymer decomposition theory. The contribution of nitrogen and halogen in the etch equation can be positive or negative depending on the chemical properties of the plasma.