AVS 45th International Symposium
    Plasma Science and Technology Division Monday Sessions
       Session PS-MoM

Paper PS-MoM2
Is Notch Formation Chemical or Physical?

Monday, November 2, 1998, 8:40 am, Room 318/319/320

Session: Feature Evolution
Presenter: N. Hershkowitz, University of Wisconsin, Madison
Authors: N. Hershkowitz, University of Wisconsin, Madison
A.K. Quick, University of Wisconsin, Madison
Correspondent: Click to Email
There is debate in the etching community about what mechanisms are most important in the formation of notches in phosphorous-doped poly-Si lines during Cl@sub 2@ plasma etching. Some researchers claim that the notch is formed by ion deflection due to differential charging. Others claim that the ion deflection causes only the removal of SiCl@sub 2@ passivating films which then allows neutral etching of the notch. They claim that stress at the poly-Si/SiO@sub 2@ interface opens up the poly-Si lattice to enhance the neutral etch rate. The goal of this talk is to help clear up this controversy. An experiment was performed in which poly-Si line and space patterns were etched in the presence of an electron beam to reduce differential charging. An electron beam of the correct energy and current density was found to suppress notch formation, indicating that this phenomenon is charge related. Analysis of the notch shape for a floating and 13.56 MHz RF biased substrate (without the electron beam) showed a characteristically larger notch opening for the biased case due to the low-energy peak in the bimodal ion energy distribution function. This shape difference provided evidence that the notching phenomenon is mainly from ion deflection. In addition, scanning electron microscope images of the inside of the notch showed ion tracks that could not have been made by neutrals. These findings, along with the notch supression in the electron beam are proof that the dominant etching species are ions. This work is supported by National Science Foundation Grant #EEC-8721545.