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In recent years, various materials such as refractory metals as well as their compounds, and ternary metal-Si-N amorphous layers (e.g., Ta-Si-N, W-Si-N, etc.) have been investigated as diffusion barriers of Cu-based metallization for ultralarge scale integrated (ULSI) circuits. 1-4 Among these, Ta and Ta-based compounds (e.g., TaN x , 0 < x 0.2, TaC, Ta-N-O, Ta-Si-N, etc.) were the most promising candidates for Cu diffusion barriers because of their high melting points, high thermal stability, no interfacial reaction with Si, good electrical conductivity, and good adhesion to dielectrics. 5-7 In Tabased compounds, TaC possesses a very high melting point (ϳ3985ЊC) which suggests that the lattice diffusion of Cu through TaC is very slow, 8-10 in addition, TaC has a low electrical resistivity which is crucial for a diffusion barrier layer. Moreover, TaC x has similar electronic and optical properties with group IV nitride such as TiN which has been extensively studied as a diffusion barrier for Cu metallization. 9,11 In this work, we report for the first time on the characterization of TaC X thin films as diffusion barriers for Cu metallization. A dc magnetron sputtering process with a TaC target was used to deposit TaC X thin film on two types of substrates (n-Si and p ϩ n-Si). The physical properties and thermal stability of tantalum carbide films have been investigated in detail. The application of TaC X as a diffusion barrier is evaluated and discussed. ExperimentalThe Si substrates used in this work were phosphorous doped, (100) orientation with a resistivity of 1-10 ⍀ cm. After RCA cleaning the material analysis of unpatterned TaC x (600 Å)/n-Si structure was carried out by dc magnetron sputtering using a water-cooled TaC (50:50 wt %) target with 99.5% purity in pure Ar atmosphere. The base pressure of the reactor was around 9 ϫ 10 Ϫ7 Torr, and the deposition was carried out under a pressure of 7.6 mTorr. The target-tosubstrate distance is 15 cm. The applied dc power was 200 W, and deposition rate was measured to be around 0.3 Å/s. Prior to deposition, the TaC target was cleaned by a 10 min presputtering while the Si substrate was isolated by a shower plate. With the same deposition conditions, Cu (2000 Å)/TaC X (600 Å)/n-Si and Cu (2000 Å)/ TaC X (600 Å)/p ϩ n structures were prepared to examine the thermal stability of the TaC X barrier films for Cu metallization. The 2000 Å Cu film was deposited in situ followed by the TaC X layer. Finally, the deposited Cu/TaC layer was patterned by a lift-off technique in preparing the Cu/TaC X /p ϩ n structure. It is noted that the p ϩ n diode used in this study was formed by BF 2 ϩ implantation at an energy of 60 keV and a dose of 3 ϫ 10 15 cm Ϫ2 followed by a thermal annealing in N 2 ambient at 900ЊC for 30 min. The diode area and junction depth were measured to be 5.8 ϫ 10 Ϫ5 cm 2 and 0.3 m, respectively. To identify the physical properties of the deposited TaC X film, X-ray diffraction (XRD) analysis with Cu K␣ radiation and X-ray photoelectron spectroscopy (XPS) us...

This work investigated the thermal stability of tungsten carbide (WC x) films deposited by a sputtering process with a WC target as diffusion barrier layer between Cu and Si. The as-deposited WC x film has a nanocrystalline structure and a low electrical resistivity of around 227 ⍀ cm. Film characterization reveals that the WC x film was able to preserve the integrity of the Cu (2000 Å)/WC x ͑500 Å͒/n-Si structure without formation of Cu 3 Si, up to a 600°C annealing for 30 min. In addition, diode leakage current measurements on the same contact structure, but with a p ϩ n-Si substrate did not show deterioration of electrical characteristics up to a 550°C annealing. As the thickness of the WC x barrier was reduced to 150 Å, the WC x film retained the integrity of diodes up to 500°C without increasing the diode leakage current. The failure of WC x film after high temperature annealing is attributed to the Cu diffusion into the Si substrate through grain boundaries or local defects of the WC x barrier layer, in which some local defects may arise from the formation of W 5 Si 3 .

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