Diffusion Barrier Characteristics of Zirconium Diboride Films Grown by Remote Plasma CVD
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J. SUNG*t, D.M. GOEDDE**, G.S. GIROLAMI** and J.R. ABELSON* *Department of Materials Science and Engineering, University of Illinois at Urbana Champaign, Urbana IL 61801 **Department of Chemistry, University of Illinois at Urbana Champaign, Urbana IL 61801 t JH-SUNG(&uiuc.edu
ABSTRACT
Low resistivity and fully conformal ZrB 2 thin films are deposited by remote plasma chemical vapor deposition using zirconium tetrahydroborate, Zr(BH 4)4. The problems with thermal CVD using this precursor -- excess B incorporation, oxygen contamination, and high resistivity -- are eliminated by injecting atomic hydrogen from a remote microwave plasma source onto the substrate. Using this technique, the films are stoichiometric, have - 40 jiQ-cm resistivity, < 4 at.% oxygen contamination, and are fully conformal in deep trenches and vias. We show that a 50 nm thick ZrB 2 film on c-Si (100) prevents Cu in-diffusion after 1 hour annealing at 650 C. INTRODUCTION Zirconium diboride has many useful properties: high hardness, high melting temperature, resistance to wear and corrosion, chemical inertness, and excellent electrical conductivity. Thick films are used as hard coatings for cutting tools, electrodes in aluminum extraction processes,
and coatings for high temperature nozzles and valves [1]. ZrB2 is potentially useful as an interconnect and diffusion barrier material for ultra large scale integrated (ULSI) circuits because it has a lower resistivity (9 pDQ-cm in bulk) and lower diffusivity for metal impurities compared with TiN, which is the most widely used material in current metallization schemes. Recently, the diborides ZrB 2 and HfB 2 have proven to make ohmic contacts, and to be good diffusion barriers, for metallization of GaAs and SiC [2,3]. To develop the next generation ULSI technology, with reduced feature size and increased aspect ratio, it is essential to develop a conformal CVD method to deposit barrier and metal layers. ZrB2 has the lowest resistivity among the materials tried thus far as a diffusion barrier for Cu metallization. However, conventional CVD of ZrB2 uses ZrCI4 as precursor, and the high deposition temperature and Cl contamination have been serious problems [4]. Zirconium tetrahydroborate, Zr(BH 4)4 , appears to be an excellent precursor for ZrB 2: it is a single source, has high vapor pressure at room temperature, contains no undesirable impurities such as C or Cl, and thermally decomposes at relatively low substrate temperatures. However, previous attempts to deposit films by thermal CVD using Zr(BH4 )4 had problems such as film peeling, impurity contamination, and high resistivity [5,6]. In this work, we show that ZrB2films with low resistivity (40-60 pQ-cm), excellent conformal coverage, and excellent diffusion barrier properties against Cu can be obtained at a substrate temperature lower than 300'C by injecting atomic hydrogen, generated by a remote microwave plasma discharge of H 2, into the CVD process. 39 Mat. Res. Soc. Symp. Proc. Vol. 563 ©1999 Materials Research Society
EXPERIMENT Fig. 1 s
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