Thin Ti/TiN Barriers for ULSI Application
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Table I. Processing parameters for the collimated deposition of the Ti, TiN, and Ti/TiN films. Process Time (sec) Temperature (C) Power (KW) Ar Pressure Bias (V) (mTorr) Degas 30 400 0 2-3 0 Sputter etch 60 400 0.167 5 -700 Film Target thickness Temperature (C) Power (KW) %N(N2:Ar Bias (V) deposition (nm);Dep time (sec) sccm) Ti 5,10,20,30,50; 400 12 0 (0:27) 0 4.8,9.5,19,28.5,47.5 TiN 10,30,40,50,60; 400 20 67 (80:40) 0 6.8,20.3,27,33.8,40.5 Ti/TiN Combination of above Parameters are the same as above Note: The depositions are all shutterless and clampless. 216S Scanning UV was employed to measure specular reflectance at three different wavelengths of 246, 365 and 440nm, using Si as the reference. Bright field transmission electron microscopy (TEM) micrographs of cross-sectional view were taken on a Philips CM30. The X-Ray Fluorescence (XRF) measurement was conducted on a Tracor SpecTrace 5000. Ti(Ka) signal was collected. RESULTS AND DISCUSSION Weight Gain and Cross Sectional TEM Table II shows net weight gains of individual Ti and TiN, as well as composite Ti/TiN films. It should be noted that the thickness combination of the composite Ti/TiN films correspond to the thicknesses of each individual Ti and TiN films in each row. The composite films show excess net weight gain (A) from +0.93 to +1.44 mg as compared to the weight summation of two individual films. The thicker the films, the larger the , values. Little difference is expected between the individual Ti films and Ti in the composite Ti/TiN films since they were deposited on the same substrates using identical deposition conditions. From cross sectional TEM analysis (results are not shown), it was found that the oxide thickness at the surface of individual Ti films ranges from 3.0 to 4.5nm. In addition, all the TiN films were observed to have a columnar grain structure and an identical thickness for the films in the same row of Table II regardless of the substrates (Si0 2 or Ti). However, the grain sizes of the TiN on Ti in the composite films are larger than their corresponding individual TiN films on Si02. Therefore the positive A values are related to the higher density of the TiN films when they are deposited over Ti.
Individual Ti
Table II. Net weight gain for the Ti, TiN, and Ti/TiN films. Individual TiN Ti/TiN Composite
(nm)
Weight gain
(mg)
Thickness
(nm)
Weight gain
(mg)
A (mg) (composite individual
5 10 20 30 50
(nm)
0.31 0.77 1.93 3.25 6.09
m
combination)
10 30 40 50 60
0.84 4.47 6.05 7.91 9.60
5/10 10/30 20/40 30/50 50/60
2.08 5.99 9.21 12.28 17.13
0.93 0.75 1.23 1.12 1.44
Thickness Weight gain Thickness
496
Table II also shows that the net weight gain for the individual Ti and TiN in the thinner thickness regime are disproportionally small. It indicates that the initial nucleation of Ti or TiN on Si0 2 substrates are different from the bulk film growth, resulting in the initial thinner films to be less dense. Sheet Resistance Table III lists the sheet resistance (R,) measured for the individual Ti and TiN films, and co
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