TEM Studies of Plasma Deposited Tungsten and Tungsten Nitride Barriers for Thermally Stable Metallization
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initial base pressure of 10- Torr. The deposition temperature is 350 'C and rf power density is 0.7 W/cm2 . 800 A thick W 67N33 thin film is deposited with H2/NH 3 /WF 6 flow ratio of 25/0.5/1 and 1500 A thick W thin film with H2/WF 6 flow ratio of 25/1. Resistivity and thickness are determined by 4-point probe, B-ray backscattering method, respectively and atomic concentration of N in Wl0o-XN. film is measured by Rutherford backscattering spectrometry (RBS). Furnace annealing is carried out at 850 °C for 30 min in Ar ambient after evacuating the initial pressure of furnace down to 10.4 Torr. Thermal stabilities of W67N 33 and W67N 33/Al are compared with the results of W, W/Al and TiN/Al with RBS and cross sectional transmission electron microscopy (XTEM). RESULTS AND DISCUSSION Solid line of Fig. 1 shows a typical RBS spectrum of W 10oo.N. film deposited with
H2/NH 3/WF 6 flow ratio of 25/0.5/1 to determine the stoichiometry. The RBS spectrum is obtained as following conditions; He acceleration energy is 2.42 MeV and its scattering angle is 1700. Tungsten signal can be seen at high energy of 2.4 MeV, and Si signal is around 1.2 MeV. N signal can be seen obviously around 0.7 - 0.65 MeV although the backscattering yield signal of N, whose atomic number is smaller than Si, is overlapped with Si signal. Tungsten yield from Wl00xN film is lower than the yield from W film (dot line of Fig. 1) because backscattering yield from W atoms is reduced due to N atoms existing in the W-N film. From the calculated result of RBS spectrum of W,..N , it is determined that the atomic ratio of W to N is W 67 N 33 .[6] For the W0o-.,Nx films deposited with various H 2/NH 3/WF 6 flow ratio from 25/0/1 to 25/1.0/1, varying NH 3/WF 6 ratio from 0 to 1 by 0.25 step, lattice constants and stresses are determined with N concentrations as shown in Fig. 2. Lattice constant increases from 3.165 to 4.144 while at. % of N increases from 0 to 49. This result implies that increasing N concentration up to 33 at. % of N, the measured lattice constant increases from 3.165 (bcc-W) to 4.126 (fcc-W 2N). Above 33 at. % of N, lattice constant of as-deposited W 10o-xN. film becomes saturated at the value that is slightly greater than 4.126. Stress of W1o0_xNx film is abruptly changed from tensile to compressive by the incorporation of N atoms. Compressive 2
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Fig. 1. RBS Spectra for W and deposited on Si.
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3.16 L 10 20 30 40 50 Atomic Concentration of N (%) L
Fig. 2. Lattice constants and stresses of W10ooxNx films ( x values are varied from 0 to 49 ).
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336
stress of Wloo-xN, is also saturated at 2.6 x 10-10 dyne/cm2 . These results mean that above 33 at. % of N as-deposited Wlo 1 -xNx films have fcc-W 2 N crystals along with some excess N on W2N grain boundaries. XRD patterns corresponding to N composition (Fig. 3) show that a
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