AVS 57th International Symposium & Exhibition
    Plasma Science and Technology Wednesday Sessions
       Session PS1-WeA

Paper PS1-WeA11
Wet SiO2 Etch Rate Enhancement Due To Surface Fluorination By A Remote O2/CF4 Plasma

Wednesday, October 20, 2010, 5:20 pm, Room Aztec

Session: Plasma Surface Interactions (Fundamentals & Applications) II
Presenter: D.L. Gilbert, Mattson Technology Singapore PTE LTD
Correspondent: Click to Email
High Dose Implantation (HDI) for source/drain (S/D) is one of the critical steps for transistor formation. It becomes more complicated due to S/D junctions are designed to be shallower at proportional scaling down of the entire transistor. The photo resist (PR) mask is exposed to increasing number of implant species, higher dosages and energy levels. The top layer of the PR transforms to hard and cross-linked crust. Meanwhile, the sidewall of the PR mask collects a lot of spattered substrate (inorganic) materials. As a consequence, HDI photo resist strip (HDIS) is increasingly difficult to get residue free with controlled material loss and growth as required at lower node. One of widely used HDIS process solutions is remote O2/CF4 plasma followed by a wet chemical clean, such as dilute HF and/or SC1 solutions. However, these strip / clean processes also attack the underlying SiO2 films. It is critical to control such SiO2 loss for future IC production, as device sizes shrink. Therefore, a delicate balance is to be discovered between effectively cleaning the wafer surface and etching into the SiO2 substrate. This paper discusses the significant synergy between the O2/CF4 processes and subsequent wet clean. It has been observed that the overall oxide removal through combined O2/CF4 dry clean and wet chemical clean is significantly higher than the sum of the independent oxide loss through dry clean and wet clean. The effect on CF4 concentration in the plasma, O2/CF4 processing time, and temperature on the wet etch rate enhancement are explored. In an effort to reduce the etch rate enhancement, several post O2/CF4 processes such as a O2 only plasma, a forming gas plasma, and a simple water rinse are employed. Results show that the oxide loss enhancement is due to the presence of a highly fluorinated surface post O2/CF4 dry clean. This fluorinated oxide surface readily dissolves in wet etch chemistries. Furthermore, once desorbed from the wafer surface, the fluorine may increase the local concentration of species responsible for etching oxide films.