Characterization of Sputtered Tantalum Carbide Barrier Layer for Copper Metallization

Abstract

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...

TaC as a diffusion barrier between Si and Cu

“…The reason for this is most likely that the very thin ͑7 nm͒ TaC layer is in nanocrystalline ͑i.e., nearly amorphous͒ state. Similar results indicating the amorphous nature of sputterdeposited TaC films have similarly been reported by Tsai et al 17 The formation of Cu 3 Si occurs at 600°C in these samples as displayed in Fig. 5.…”

“…Ta and Tabased diffusion barriers have been the subject of numerous investigations. [7][8][9][10][11][12][13][14][15][16][17] They fulfill rather well the overall requirements for diffusion barriers as summarized by Nicolet. 18 Among the most promising candidates to be used for this purpose are the binary tantalum nitrides and carbides.…”

“…Whereas Ta nitrides have been investigated widely, only few known reports have been published about TaC-based diffusion barriers. 16,17 Hence, there is a clear need for further investigation of these diffusion barrier layers, since they seem to offer a viable solution to the barrier layer problem associated with Cu metallization.…”

First-principles phase diagram calculations for the HfC–TiC, ZrC–TiC, and HfC–ZrC solid solutions

“…1,5,6 The transition-metal carbides have also been explored for a potential application as diffusion barriers in electronic devices. 7 Aside from the pure end members, solid solutions formed by these carbides are potentially of significant importance as properties can be optimized by varying the compositions in the binary-and higher order-systems.…”

MOCVD of Cr[sub 3](C,N)[sub 2] and CrSi[sub x]C[sub y] Films

“…Consequently, Cu must be isolated from its environment by a diffusion barrier. Because of their great similarity with the nitrides, carbides [20][21][22][23] and borides 24 of the same transition metals were also considered. In addition to being copper-tight, an ideal diffusion barrier must be entirely transparent to electrons.…”