Study on the oxidation and reduction of tungsten surface for sub-50 nm patterning process

Abstract

The oxidation characteristics of tungsten line pattern during the carbon-based mask-layer removal process using oxygen plasmas have been investigated for sub-50 nm patterning processes, in addition to the reduction characteristics of the WO x layer formed on the tungsten line surface using hydrogen plasmas. The surface oxidation of tungsten lines during the mask layer removal process could be minimized by using low-temperature (300 K) plasma processing for the removal of the carbon-based material. Using this technique, the thickness of WO x on the tungsten line could be decreased to 25% compared to results from high-temperature processing. The WO x layer could also be completely removed at a low temperature of 300 K using a hydrogen plasma by supplying bias power to the tungsten substrate to provide a activation energy for the reduction. When this oxidation and reduction technique was applied to actual 40-nm-CD device processing, the complete removal of WO x formed on the sidewall of tungsten line could be observed.

WO3 and W Thermal Atomic Layer Etching Using “Conversion-Fluorination” and “Oxidation-Conversion-Fluorination” Mechanisms

“…61 Somewhat thicker oxide thicknesses have been measured when using O 2 plasmas to oxidize tungsten at lower temperatures. 64,65 Tungsten oxidation at these lower temperatures is compatible with the temperature for WO 3 ALE and also is selflimiting at thin film thicknesses that are required for an ALE process.…”

“…At lower temperatures of <300 °C, the tungsten oxidation is limited to thin WO 3 films on the W substrate. ,, Oxide thicknesses of 10–16 Å have been reported after O 2 exposures on polycrystalline W substrates for 1 h at 23–200 °C . Somewhat thicker oxide thicknesses have been measured when using O 2 plasmas to oxidize tungsten at lower temperatures. , Tungsten oxidation at these lower temperatures is compatible with the temperature for WO 3 ALE and also is self-limiting at thin film thicknesses that are required for an ALE process.…”

“…There are also alternative methods to remove the WO 3 layer based on hydrogen reduction using H 2 or H 2 plasma exposures. 59,64,66 The self-limiting conditions for the BCl ALD, and HF is known to adsorb on Al 2 O 3 at the chamber wall temperature of 170 °C. 16 The O 2 /O 3 exposure may remove HF from the chamber walls.…”

“…These results indicate that the WO 3 layer on W can be removed with almost no effect on the W thickness. There are also alternative methods to remove the WO 3 layer based on hydrogen reduction using H 2 or H 2 plasma exposures. ,, …”