IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Plasma Science Thursday Sessions
       Session PS-ThA

Paper PS-ThA7
Determination of the Mechanisms Involved in the Creation of the Bowing during the Etching of Deep Anisotropic Trenches in an ICP Reactor

Thursday, November 1, 2001, 4:00 pm, Room 104

Session: Feature Profile Evolution
Presenter: P. Ranson, GREMI, CNRS-Universite d'Orleans, France
Authors: M. Boufnichel, GREMI, CNRS-Universite d'Orleans, France
F. Grangeon, GREMI, CNRS-Universite d'Orleans, France
S. Aachboun, STMicroelectronics, Tours
P. Lefaucheux, GREMI, CNRS-Universite d'Orleans, France
P. Ranson, GREMI, CNRS-Universite d'Orleans, France
Correspondent: Click to Email
In this study, we use a cryogenic technique instead of the polymerising one. The cryogenic method has two main advantages: it is faster and cleaner than the classical one, which uses polymerising gas such as C4F8. A cryogenic method with a SF6/O2 chemistry plasma in an Alcatel ICP (Inductively Coupled Plasma) reactor is used to achieve deep trenches with high aspect ratio (>10) and high anisotropy. The etching rate in 2 microns wide and 100 microns deep trenches is about 3.5 microns /min. The slope of the trenches can be adjusted from 88 ° to 90 ° and selectivity to oxide is higher than 300:1. However, profiles need to be improved, mainly by reducing the bowing and undercut effects. Bowing is a local lateral etching located on the side-walls and resulting in profiles destruction while undercut is a lateral silicon etching at the Si/mask interface resulting in trenches larger than the mask opening. One can notice that it is difficult to mask these defects with a cryogenic method without modifying the other features of the etching process such as the etch rate. Bowing creates the most severe damage as the change in profile slope due to bowed surfaces creating voids when it is necessary to refill the trench for a specific application. This study deals with improvements in these effects. We investigated the outcome of process parameters (pressure, bias voltage, temperature, gases flow rates) and mask characteristics (nature, thickness, side slope, trench width) in parallel with electrical and actinometrical measurements using respectively a langmuir probe and optical emission spectroscopy (OES). We also tested several more or less conducting masks (oxide, PSG, Aluminium,...). The different mechanisms responsible for bowing and undercut will be discussed and evaluated.