Kazuyuki Tsunokuni

Study of gate oxide breakdown caused by charge buildup during dry etching

Charge buildup and its effect on gate oxide breakdown have been studied for several types of etchers. In a barrel asher, the charging polarity during plasma treatment depends on the direction of the Si wafer with respect to electric fields. In a magnetron reactive ion etching and an electron cyclotron resonance (ECR) etcher, gate electrodes are positively charged. In the ECR etcher, the charge buildup depends on the frequency of the radio‐frequency generator connected to the wafer stage. The gate oxide breakdown during plasma treatment strongly depends on the charging polarity. A simple model is presented to successfully explain the phenomena with respect to gate oxide breakdown by charge buildup, and it is shown that gate oxide breakdown can be predicted by measuring the ΔVFB of the metal/silicon nitride/silicon dioxide/silicon capacitor and the time dependent dielectric breakdown characteristics of the gate oxide.

High rate and highly selective anisotropic etching for WSix/poly‐Si using electron cyclotron resonance plasma

High rate and highly selective anisotropic etching for tungsten polycide (WSix/poly‐Si) has been developed by fully utilizing such advantages of the electron cyclotron resonance plasma etcher, as high plasma density and independent control of ion energy and plasma density. Highly anisotropic etching with a WSix/poly‐Si etch rate of 400 nm/min and a poly‐Si/SiO2 selectivity of 50 was realized by adding O2 to Cl2 and reducing the ion energy. O2 addition increases the WSix etch rate and reduces the SiO2 etch rate, keeping the poly‐Si etch rate nearly constant. This leads to the same etch rate for WSix and poly‐Si, and a higher selectivity for poly‐Si/SiO2. The decrease in the SiO2 etch rate was found to be mainly caused by a deposition of SiOx on the surface. The role of the O2 was found to be not only increasing the WSix etch rate and the poly‐Si/SiO2 selectivity but forming a sidewall protection film to achieve an anisotropic etching.