Paper PS2-TuM4
XPS Sidewall Analyses of Poly Si/TiN/HfO₂ Gate Stack Etched with Chlorine and Fluorocarbon Based Chemistries

Tuesday, October 16, 2007, 9:00 am, Room 607

Patterning sub-40 nm metal gates on high k dielectrics is one of the biggest challenges for the fabrication of next generation devices. The metal gate etching step is, indeed, difficult: it must be highly anisotropic to maintain a tight CD control (≤ 2 nm) and must not damage the underlying high k material. In this work, we have investigated and compared the impact of the etching of the TiN layer in a Poly Si/TiN/HfO₂ gate stack using Cl₂/HBr and SF₆/CH₂F₂ based chemistries. The experimental work has been performed on a 200 mm etch platform connected, under vacuum, to an x-ray photoelectron spectroscopy surface analysis system. In order to better understand the etching mechanisms, we have used a technique based on X-ray photoelectron spectroscopy (XPS) to analyse the passivation layer deposited on the sidewalls of the patterns during the Polysilicon etching step and investigate its modification during the TiN etching step. We also used SEM pictures to analyse the gate profiles and determine the thickness of the passivation layer. The etching of polysilicon with a Cl₂/HBr based chemistry requires the introduction of O₂ in the plasma in order to form a SiOClBr layer which protects the polysilicon sidewalls. On the contrary, the etching of TiN must be O₂ free to prevent the metal oxidation. The absence of oxygen in the plasma gas phase during TiN etching can potentially lead to a modification of the passivation layer formed on the Polysilicon sidewalls. Nevertheless, We have shown that, using appropriate plasma conditions, the SiOClBr layer deposited on the chamber walls during Polysilicon etching is eroded during the TiN etch step, leading to an increase of the passivation layer thickness on the Polysilicon sidewalls. Same analyses using a SF₆/CH₂F₂ based chemistry will also be presented.