AVS 60th International Symposium and Exhibition
    Plasma Science and Technology Tuesday Sessions
       Session PS1-TuA

Invited Paper PS1-TuA7
Time-resolved Optical and Electrical Diagnostics of Pulsed Plasmas Etching Processes

Tuesday, October 29, 2013, 4:00 pm, Room 102 B

Session: Plasma Diagnostics, Sensors and Control
Presenter: G. Cunge, Cnrs/ujf/ Cea - Ltm, France
Authors: G. Cunge, Cnrs/ujf/ Cea - Ltm, France
M. Brihoum, Cnrs/ujf/ Cea - Ltm, France
M. Darnon, Cnrs/ujf/ Cea - Ltm, France
E. Despiau-Pujo, Cnrs/ujf/ Cea - Ltm, France
A. Davydova, Cnrs/ujf/ Cea - Ltm, France
M. Haass, Cnrs/ujf/ Cea - Ltm, France
R. Blanc, Cnrs/ujf/ Cea - Ltm, France
N.St.J. Braithwaite, The Open University, UK
D. Gahan, Impedans Ltd, Ireland
S. Banna, AMAT
O. Joubert, Cnrs/ujf/ Cea - Ltm, France
N. Sadeghi, Cnrs/ujf/ Cea - Ltm, France
Correspondent: Click to Email
Pulsed ICP plasmas are a promising solution to several issues related to IC fabrication. Recent results are indicating that pulsing the ICP power and/or the RF biasing power allows to increase the etch selectivity, to reduce plasma induced damages and to minimize ARDE. However, the reasons for these improvements remain unclear. In particular, the impact of plasma pulsing on the radicals flux, on the ion flux and on the ion energy in electronegative plasmas has not been studied in details. We have used a capacitively-coupled planar ion flux probe to monitor the time variations of the ions flux in an industrial ICP etch reactor from AMAT. At the same time, the time-averaged IEDF are measured by an RFA analyzer. Finally the radicals’ densities are measured with a 10 µs time resolution by combining several diagnostic techniques: small polyatomic radicals are detected by broad band absorption spectroscopy (BBAS) in UV with highly stable LEDs as a light source, large closed shell molecules are detected by BBAS in the VUV and atomic species are monitored by threshold ionization modulated beam mass spectrometry. We discuss in detail the experimental set-up that we have designed to carry out such time resolved measurements. Results are presented for various electronegative (Cl2, BCl3, SiCl4, SF6, CF4) plasmas, that are synchronously pulsed (ICP and rf bias pulsed in phase) or in which only the rf bias power is pulsed. We will show that the duty cycle is the predominant parameter to control the ion flux, the ion energy and the plasma chemistry. These results are in good agreement with global models of electronegative Cl2 plasmas. In particular, we show that in chlorine based plasmas, both the radical densities and the ion flux drops dramatically when the duty cycle is reduced. As a result for the same rf biasing power, the ion energy is much higher in pulsed plasma than in a CW plasma. By contrast, in a pulsed ICP without bias power the time averaged ion energy is bimodal, with the predominance of a very low energy peak (1-5 eV). Therefore, plasma pulsing allows to reach new domains of ion energy and radical fluxes, thereby extending the operating range of ICP reactor to that of CCP plasmas and downstream plasmas. This has interesting applications for ultrathin layer etching, ranging from graphene cleaning to metal gate and nitride spacer etching processes. Finally, both radical and ions flux oscillations in the kHz range are observed by time resolved diagnostics in pulsed plasmas. We will show that they are due to the propagation of acoustic waves in the reactor, with potentially interesting effect on the process uniformity.