AVS 53rd International Symposium
    Plasma Science and Technology Thursday Sessions
       Session PS1-ThA

Paper PS1-ThA1
Mechanisms and Selectivity for Etching of HfO@sub 2@ and Si in BCl@sub 3@ Plasmas

Thursday, November 16, 2006, 2:00 pm, Room 2009

Session: Plasma Processing for High-K/III-V’s and Smart Materials
Presenter: C. Wang, University of Houston
Authors: C. Wang, University of Houston
V.M. Donnelly, University of Houston
Correspondent: Click to Email
We have investigated etching of HfO@sub 2@ and poly-Si in BCl@sub 3@ plasmas as a function of substrate temperature (T@sub s@), source power, and substrate bias. The etching rates of both HfO@sub 2@ and poly-Si increase with increasing T@sub s@. An activation energy of 4.7 kJ/mol is obtained from an Arrhenius plot of HfO@sub 2@ etching rate vs. T@sub s@. This activation energy is much lower than the heat of vaporization of HfCl@sub 4@ (100 kJ/mol), hence desorption of this product is not rate limiting. The most likely mechanism is one in which the surface, disordered by ion bombardment, is terminated with Hf-O-BCl@sub 2@ and Hf-Cl groups. Etching is limited by chemical sputtering of this chemisorbed layer. Higher T@sub s@ modestly increases the rate at which reactions occur during ion "thermal" spikes. Similarly, the desorption of SiCl@sub 4@ is not limited by the vapor pressure of this product, which is orders of magnitude higher. The etching rate of Si in BCl@sub 3@ plasmas has an activation energy of 3±1 kJ/mol. Consequently, a small improvement in HfO@sub 2@ selectivity over Si can be realized at high temperature. At high (inductively coupled) power, a relatively thin BCl@sub x@ film (detected by vacuum-transfer to an XPS chamber) forms on partially etched HfO@sub 2@ and Si. At low (capacitively-coupled) power, a similar thickness films is present on HfO@sub 2@, but a much thicker BCl@sub x@ film is present on Si. BCl@sub 3@ dissociates in the plasma to yield Cl and BCl@sub 2@ at low power, and additionally, BCl, B, and Cl at high power. Apparently, the rate of BCl@sub x@ deposition on Si does not increase, or increases less than the rate of etching of Si as power increases, perhaps due to a lower sticking coefficient of BCl, compared to BCl@sub 2@, and the enhanced Cl flux. The BCl@sub x@ film formed on the Si surface likely inhibits the formation and sputtering of volatile SiCl@sub x@ species. Supported by SRC and AMD Inc.