Tungsten Deposition by Metal-Chloride-Reduction Chemical Vapor Deposition

Abstract

We successfully developed a fluorine-free tungsten deposition technique on a Si substrate at a substrate temperature in the range from 450 to 520 C by metal chloride reduction chemical vapor deposition (MCR-CVD). In this process, we first prepared a tungsten coil as a source material that can be heated by passing a current directly in itself at a temperature of 800 C. In a reaction chamber, the heated tungsten coil is exposed to RF excited Cl radicals to produce W chlorides to be delivered to the Si substrate. The adsorbed W chlorides are reduced to W by the Cl radical and a W film is grown on the Si surface. The residual Cl and F levels in the deposited W film were measured under the detection limit by x-ray photoelectron spectroscopy. The deposited W exhibited very low resistivity in the order of 10 À5 X cm. The film conformality was examined using a trench-filling experiment, which suggests the suitability of the present process for the plug filling in VLSI production.Recent years due to the strong demands for higher integration in large scale integration (LSI), metal deposition has been developed as a plug filling process for interlayer connecting. W chemical vapor deposition (CVD) is extensively studied for the plug filling as W has a relatively good electrical conductivity and a high electromigration durability due to its high melting point of 3380 C. The conventional method was CVD with a precursor of WF 6 and reducing agents of In case of the W CVD using WF 6 , however, difficulties of interfacial Si consumption and corrosion of devices by HF gas as a byproduct have been reported. 5 To avoid the corrosion, all the surface to be protected should be coated with a barrier metal of TiN although this additional process is a disadvantage in the production cost. To avoid the byproduct, metal organic precursors have been investigated, though the deposited film exhibited unacceptably high resistivity due to the residual carbon in the film. 6 Ammerlaan et al. have reported a W CVD with tungsten hexachloride (WCl 6 ) with H 2 reduction in a temperature range 480-670 C, where deficiencies in the film uniformity and reproducibility were indicated. 7 Lai et al. investigated W deposition from W(CO) 6 using a low-pressure CVD at 375 C, though the film resistivity was still more than 1000 X cm, that is much higher than the W bulk resistivity of 5.6 X cm. 5 Additional vacuum annealing at 900 C was necessary to reduce the resistivity down to 19 X cm. 5 In the field of Cu CVD for metal wiring in the LSI production, on the other hand, Sakamoto et al. developed a unique metal CVD using metal chloride reduction (MCR). [8][9][10][11][12] In this process, bulk metal is exposed to Cl radicals to produce metal chloride species in the reaction chamber. The metal chloride species are delivered as gas molecules to the wafer to be reduced by the additional Cl radicals, where the pure metal film is grown on the surface. Since this process requires no organic precursors, the source material cost is very cheap. MCR-CVD has been applied to...