A Comparative Study on the Titanium Nitride (TiN) as a Diffusion Barrier Between Al/Si and Cu/Si: Failure Mechanism and
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to improve the adhesion between TiN and Cu. Post-anneals to test the diffusion barrier properties were conducted for 1 hour in an atmospheric pressure H 2 ambient in order to prevent the oxidation of Cu. The annealing temperature varied from 450 to 650 "C with an interval of 50 "C. It was measured by a thermocouple located directly above the sample. An initial survey of the reactions in Cu/TiN/Si structures was performed using sheet resistance measurements with a four-point probe. Reactions in these samples were characterized by x-ray diffractometry (XRD), etch-pit observations by scanning electron microscopy (SEM), and cross-sectional transmission electron microscopy (XTEM). For etch-pit observations, first the Cu and TiN layers were selectively removed using chemical solutions of IHNO 3 : H 20 = 1: 20 (for Cu) and NH 40H: H20 2 : H20 = 1: 2: 6 (for TiN). Then, Si surface was slightly etched by the Secco etching solution for about 5 seconds. For XRD analysis, a RIKAKU diffractometer equipped with a CuKI source was used operating at 50 kV and 100 mA. 1.6-MeV He+ source was used for RBS analysis. The backscattering angle was 170 o and the total accumulated charge was 6 lptC. For TEM analysis, Philips CM20 with a LaB 6 filament was used. RESULTS Characterizations of as-deposited and "stuffed" TiN film The electrical resistivity of the as-deposited TiN film was 700 itM-cm. This value is well agreed with the previous results, which reported the range from 20 to 2000 l[tQ-cm. 5 After annealing at 450 "C for 30 min in N 2 ambient, the resistivity of the TiN film increased to 1830 ý1 a-cm. Figure 1 shows the RBS spectra of the as-deposited and "stuffed" TiN films on Si substrates. In comparison with the as-deposited TiN film, the higher energy side of the titanium signal of the "stuffed" TiN film is significantly reduced and the oxygen signal is increased. This indicates that oxygen has been incorporated into the TiN film by "stuffing". The combined result of RBS (planar density) and XTEM (thickness) showed that the density of the two TiN films was 3.76 ± 0.20 g/cm3 (as-deposited) and 4.08 ± 0.20 g/cm3 ("stuffed"), respectively. This corresponds to about 70 % and 76 % of the bulk value (5.4 g/cm 3 )6 , respectively, indicating that significant densification of the TiN film occurs by "stuffing". The plan-view TEM micrograph of as-deposited TiN films is shown in Fig. 2(a). This micrograph clearly shows the structure of the individual grains as having a triangular shape and 50 0.450
Energy
0.6
0.8r
N V
1
40 -
(MeV)
1.0 1.2 ,0'-.-.i-.-qN-....
Si
0.4
Ti
..
Lnergy (MeV)
0.6
0.8
40
1.0
1.2
Si Ti
~3020
C o
>
30
~20
.TN4H SiTI]N L 1.6 MeV
-
S1uNý 1.6 MeV
10 -10
(a) 100
150
(b) 200
250 Channel
300
350
400
100
150
7•00
250 Channel
300
350
400
Fig. 1. Rutherford backscattcring spcctra of thc (a) as-deposited TiN/Si and (b) "stuffed" TiN/Si samples.
212
40 nm
40 nm Fig. 2. TEM micrographs of the as-depositcd TiN film: (a)focused, (b)300 nm under-focused, (c) 300 nm over-focused, and (d) s
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