Nitridation of fine grain chemical vapor deposited tungsten film as diffusion barrier for aluminum metallization

Abstract

A novel tungsten nitride (WNx) film for diffusion barrier applications has been prepared by nitridation of a fine grain chemical vapor deposited tungsten (CVD-W) film. The fine grain CVD-W is deposited at 300 °C in a low pressure chemical vapor deposition reactor with a SiH4/WF6 flow rate of 12.5/5 sccm under a total gas pressure of 100 mTorr. The subsequent nitridation process is executed in nitrogen plasma at 300 °C without breaking vacuum. The thickness of WNx layer as examined by secondary ion mass spectroscopy is 50 nm after 5 min exposure to nitrogen plasma. X-ray photoelectron spectroscopy spectra shows that the atomic ratio of tungsten to nitrogen in WNx layer is 2:1. According to the analysis by Auger electron spectroscopy and the measurement of n+p junction leakage current, the Al/WNx/W/Si multilayer maintains excellent interfacial stability after furnace annealing at 575 °C for 30 min. The effectiveness of W2N barrier is attributed to stuffing grain boundaries with nitrogen atoms which eliminates the rapid diffusion paths in fine grain CVD-W films.

A study of structural and mechanical properties of nano-crystalline tungsten nitride film synthesis by plasma focus

“…Tungsten nitride coatings are one of them, have high hardness, high melting point and are chemically inert with high conductivity (1). These worthy properties of tungsten nitride films make them a suitable material for various applications such as hard, wear-resistant protective coatings (2)(3)(4) and diffusion barriers at elevated temperature in microelectronics devices (5)(6)(7)(8) and can also be used electrodes for field effect transistors and thin film capacitors. Various deposition techniques have been used for the synthesis of tungsten nitride films such as direct current/radio-frequency (DC/RF) sputtering (9), pulsed laser ablation (10), plasma focus (11), thermal chemical vapor deposition, cathodic arc (2), chemical vapor deposition, (6) etc.…”

Morphological and Compositional Studies on Al/Ti/TiN/Si, Al/TiN/Si, Al/W/Si, Al/WN/Si Systems to Test the Diffusion Barrier Properties of Nanoscale-Thick Layers between Al and Si

“…The typical materials fulfilling these requirements are refractory metals, having a high melting point (so as to minimize the formation of grain boundaries during the deposition step) and high chemical stability. Furthermore, impurities are often added to these metals, such as O, N, and C, which on the one hand increase the barrier stability and, on another hand, saturate the grain boundaries which are the main diffusion paths between Al and Si [ 1 , 4 , 5 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ]. These materials act as “sacrificial barriers”: the refractory metal reacts with the above-placed Al film ensuring that the formation of the corresponding compound avoids the diffusion of Al into the barrier and, subsequently, into the underlying Si (usually these material barriers do not react with Si because such reactions would require much higher temperatures than those used for the device processing).…”

“…However, the efficiency of TiN as a diffusion barrier was found to be strongly dependent on stoichiometry and on the deposition methodology, a phenomenon even more evident when using thin films, since the latter are normally synthesized in non-equilibrium conditions. W and WN constitute other materials exploited as diffusion barrier layers between Al and Si [ 5 , 7 , 18 , 19 , 20 ]; as previously mentioned, the addition of impurities such as N increases the chemical stability of W and saturates the grain boundaries, inhibiting Al grain boundaries diffusion. WN also belongs to the family of refractory metals and the structure of WN films strongly depends on the deposition parameters: for example, the structure of sputter-deposited WN films can be changed from the crystalline phase to the amorphous phase by the deposition power with a major impact on the layer performance as a diffusion barrier between Al and Si [ 18 , 19 , 20 ].…”

Microstructural properties of plasma-enhanced chemical vapor deposited WNx films using WF6–H2–N2 precursor system

“…Diffusion barrier properties of the WN x films depend on the crystalline phase; for example, W, W 2 N and WN layers of 25 nm thickness were found to successfully prevent intermixing of Cu wiring with Si substrate after annealing at 650, 790 and 500°C, respectively, for 30 min [1]. A variety of WN x deposition methods have been reported thus far, such as sputtering [6,7], chemical vapor deposition (CVD) [8][9][10], and post-nitridation of tungsten films [11]. Compared to the sputtered WN x films, the CVD films exhibit superior step coverage; therefore, they are more applicable to diffusion barriers for highaspect-ratio structures, such as W-plug contacts, vias for damascene interconnects, and plug-type high-e r metaloxide-metal capacitors.…”