AVS 45th International Symposium
    Plasma Science and Technology Division Friday Sessions
       Session PS-FrM

Paper PS-FrM11
Operating High Density Plasmas in a Low Density Range : Applications to Metal Etch Processes

Friday, November 6, 1998, 11:40 am, Room 318/319/320

Session: Plasma-Surface Interactions - II
Presenter: P. Czuprynski, France Telecom CNET/DTM/TFM, France
Authors: P. Czuprynski, France Telecom CNET/DTM/TFM, France
O. Joubert, France Telecom CNET
L. Vallier, France Telecom CNET
M. Heitzmann, CEA LETI, France
N. Sadeghi, CNRS, France
J.P. Booth, CNRS, France
Correspondent: Click to Email
In metal etching where complicated and thick metal stacks have to be etched on severe topography, selectivity between metal and resist is a critical problem. In practice, using standard Cl@sub 2@/BCl@sub 3@ etching chemistries and inductively coupled plasma sources (ICP) dedicated to metal processes, metal/resist selectivity higher than 3 are difficult to obtain. In this paper, we present a new way of operating high density plasma sources which greatly improve the selectivity issue of metal etch processes. The principal of the technique is to operate a high density plasma source in a low density mode (by strongly decreasing the RF power injected in the source, typically by a factor of 4) while keeping unchanged the RF power injected in the chuck to bias the wafer. Different techniques are used to compare the low density and high density modes. First, optical emission techniques are used to compare the dissociation efficiency of both modes and therefore get some information on the relative fluxes of Cl@sub 2@ and Cl species in the discharge. The ion current density (J@sub i@) and ion energy are also measured when the plasma source is operated in the low and high density modes (using identical chuck power conditions). The ion current density is measured using a new type of electrostatic probe whereas ion energy is simply estimated by measuring the self-bias voltage in the matching network of the chuck. The influence of low and high density modes on metal etch processes are evaluated using Cl@sub 2@/HCl chemistries. A strong increase in resist/metal selectivity is measured when the source is operated in the low density mode while perfectely anisotropic etching profiles of the metal stacks are still obtained. Finally, a simple model taking into account the chlorine coverage on the resist surface (as measured by in situ XPS), the ion density and ion energy is proposed to describe the resist etching rate. This simple model is useful to explain why operating ICP sources in a low density mode allows the resist consumption to be strongly decrease during etching processes. @FootnoteText@ This work has been carried out within the GRESSI consortium between CEA-LETI and France Telecom-CNET.