Physical properties and thermal stabilities of tungsten nitride diffusion barrier produced by plasma enhanced chemical vapor deposition

Abstract

Stoichiometric tungsten nitride ($W_{100-x}N_x$) thin films have been deposited by plasma enhanced chemical vapor deposition (PECVD) at the temperature of 250 - $450\,^\circ\!$C, which is relatively lower than that of low pressure CVD (450 - $700^\circ\!$C). As controlling nitrogen content in $W_{100-x}N_x$ thin films from 15 to 72 at. \% with the variation of $NH_3/WF_6$ partial pressure ratio and deposition temperature, amorphous $W_{100-x}N_x$ and f.c.c. structure polycrystalline $W_{100-x}N_x$ films can be obtained. The resistivities of $W_{100-x}N_x$ films vary from 70 to $440 \mu \Omega-cm$ and surface roughnesses of the films decrease to $80\mbox{\AA}$ from $500 \mbox{\AA}$ for pure W as nitrogen composition changes from 15 to 75 at. \%. The density of $W_{67}N_{33}$ film deposited with $NH_3/WF_6$ ratio of 0.5 increase from 14.5 to $16.9 g/cm^3$ and surface roughness from 20 to $250 \mbox{\AA}$ as the deposition temperature increases from 250 to $450\,^\circ\!C$. PECVD-W and $W_{100-x}N_x$ thin films are applicable for the x-ray absorbing membrane. The reflectances of these films are as low as about 3 - 12 \% in the range of 200 - 800 nm in wavelength and the reflectances are nearly constant before and after annealing at $850\,^\circ\!C$ for 30 min even though $NH_3/WF_6$ partial pressure ratio varies from 0 to 2.0. These results are very promising characteristics for the x-ray absorbing membrane. The conversion of tensile to compressive stress has been found in PECVD-W thin films by the incorporation of N atoms. The stress varies from $6.25 \times 10^9$ to $-7.79 \times 10^9 dyne/cm^2$ as N concentration increases from 0 to 50 at. \%. In order to reduce the high tensile stress of W film, very thin $W_{67}N_{33}$ film is inserted between W and Si. As a result, the stress of $W_{67}N_{33}/W$ bilayer relaxes from $7.98 \times 10^9$ to $3.41 \times 10^9 dyne/cm^2$ after annealing at $900\,^\circ\!C$ for 30 min. The relaxation phenomena of $W_{67}N_{33}/W$ ...