COATING$ ELSEVIER Surface and Coatings Technology 99 (1998) 274-280 An experimental study of chemical vapour deposition of tungsten on Ti/TiN adhesion bilayers: mechanical properties A. Mouroux ~'*, S.-L. Zhang a, C.S. Petersson a R. Palmans b K. Maex b T. Ahlgren °, J. Keinonen ° Royal Institute of Technology-Electrum, Deparnnent oJ'Electronics, Solid State Electronics, Box 229, S-164 40 Kista, Swe&'n b IMEC, Kapelreef'75. B-3001 Leut~en, Belgium Universio, of Helsinki, Accelerator Laboratory, Hiimeentie 100, SF-O0550 Hels#dci, FTnlamt Received 7 July 1997; accepted 23 September 1997 -- Abstract The mechanical properties of chemical vapour deposited tungsten (W-CVD) on Ti/TiN adhesion bilayers have been studied. Rapid thermal annealing (RTA) of the Ti/TiN bilayers has been found to strongly affect subsequentIy deposited W films. The stress in W is reduced as a consequence of the RTA treatment of Ti/TiN, and the stress reduction is especially pronounced for thin W films. However. the stress in the Ti/TiN bilayers deposited at 300 or 550 "C increases substantially after the RTA treatment at 650 °C, leading to appreciable increase in the total stress of the whole Ti/TiN/W stack. The nucleation deposition of W on the annealed Ti/TiN is somewhat hindered. The retardation of W growth on annealed Ti/TiN is discussed in terms of thermodynamics and classical nucleation theory in conjunction with the reduction of the interracial impurities (i.e. fluorine and oxygen) as a result of the RTA of Ti/TiN [A. Mouroux, R. Palmans, J. Keinonen, S.-L. Zhang, K. Maex, S. Petersson, in: Materials Research Society, MRS, San Francisco, CA, 1996], as well as the evolution of the W film texture with the W '~hickness. © 1998 Elsevier Science S.A. Keywords: Ti/TiN CVD-W; Stress: Impurity: Nucleation 1. Introduction As the dimensions of integrated circuits are scaIed down, the requirements of metallisation materials become more stringent. For contact via filling and interconnection applications in very large scale integ- ration (VLSI) technology, the chemical vapour depos- ition of tungsten (W-CVD) is an attractive solution [2], W-CVD by the reduction of WF6 provides three key features: (1) high-purity, (2) even step coverage, and (3) selective deposition. However, problems such as adhesion, void formation, high stress and impurities at interfaces can arise. Several papers have been presented on this subject with the aim of improving the W-CVD process [3-5]. In order to prevent W-CVD peeling from an oxide surface, an adhesion layer is needed. Among the different possibilities, TiN is a good alternative [6, 7]. TiN is a fairly good conductor with a resistivity of * Corresponding author. Tel.: +46 8 7521408: Fax: +46 8 7527782 e-mail: aliette@ele.kth.se about 50 f2. cm. It is also thermally stable, which makes it good diffusion barrier. W-CVD is typically deposited by the reduction of WE6 by H:: or Sill 4. The chemical process of W deposition has been widely studied [8-10] and the properties of the W deposited have been found to depend strongly on the preparation of the TiN adhesion layer. The properties of TiN determine not only the mechanical properties of W. but also the amounts of impurities present at the TiN-W interface. Proper heat treatment of TiN has been shown to improve its electrical properties [11]. Our recent results [1,12] demonstrate that rapid thermal annealing (RTA) of Ti/TiN adhesion bilayers prior to W deposition t~as a strong positive impact on W-CVD with regard to the reduction of stress in W and of impurities at the interface between W-CVD and TiN. However, the stress in the Ti/TiN bilayers increases as a result of annealing [ 1,12]. It appears that there exists an optimum anneal temper- ature at which the increase in the stress in the Ti/TiN bilayers is still under control but both the stress in W-CVD and the content of the interfadN1 impurities can be significantly reduced. 0257-8972/98/$19.00 ~D 1998ElsevierScienceB.V.All rights reserved. PII S0257-8972(97)00567-7