Mechanisms for Microscopic Nonuniformity in Low-Pressure, High-Density Plasma Etching of Poly-Si in Cl_2 and Cl_2/O_2 Mixtures

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Etch anisotropy and microscopic uniformity have been investigated in low-pressure, high-density plasma etching environments. Polycrystalline Si films masked with a photoresist pattern of lines and spaces were etched in electron cyclotron resonance (ECR) Cl_2 and Cl_2/O_2 plasmas with additional rf biasing. Experiments were performed by varying the gas pressure, substrate temperature, and percentage of O_2 added. Moreover, the profile evolution during etching was simulated taking into account the transport of neutral and ionic species in microstructures and the following surface reactions: adsorption of neutral reactants, ion-stimulated desorption of reaction products, surface oxidation, and redeposition of etch products. The etched profiles obtained in ECR Cl_2 and Cl_2/O_2 plasmas were compared with simulated results, and interpreted in terms of the deposition of etch products and the surface oxidation that occur competitively during etching. Etch products desorbed from the surface in microstructures have a sticking coefficient S_p ≲ 0.1, while etch products arriving from the plasma have a much larger coefficient. S_p ≳ 0.5. It was also shown that the competitive surface oxidation by incoming oxygen atoms plays a more important role in achieving aspect-ratio-independent etching than the deposition of etch products: the increased deposition of etch products resulted in enhanced sidewall tapering with little change in vertical etch rate; the surface oxidation resulted in inverse reactive-ion-etching lag without significant change in sidewall tapering.
社団法人応用物理学会の論文
1997-04-30

Mechanisms for Microscopic Nonuniformity in Low-Pressure, High-Density Plasma Etching of Poly-Si in Cl_2 and Cl_2/O_2 Mixtures

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