Film Property Requirements for Hermetic Low-k a-SiO_xC_yN_z:H Dielectric Barriers

Abstract

Continued reduction in resistance-capacitance (RC) delays in nano-electronic Cu interconnect structures will require new materials with increasingly lower dielectric constants (i.e. low-k). Significant reductions in RC delay can be achieved by reducing the dielectric constant of the relatively high dielectric constant Cu capping/etch stop layer. However, this risks comprising the required barrier performance of this material to the diffusion of Cu, H 2 O, and other species. In this regard, critical thresholds for the diffusion of water and solvents through low-k a-SiO x C y N z :H dielectrics of varying composition were investigated using a combination of X-ray reflectivity mass density and positronium annihilation lifetime spectroscopy pore size metrologies. It was observed that hermetic low-k a-SiO x C y N z :H dielectrics were achieved only at mass densities >2.0 g/cm 3 and when the pore diameter was less than twice the molecular diameter of water. The implications of these critical nano-porosity thresholds on continued scaling of low-k diffusion barrier and ILD materials are discussed as well as methods for overcoming these limitations.

Dielectric Barrier, Etch Stop, and Metal Capping Materials for State of the Art and beyond Metal Interconnects

“…369 Such an inverse correlation between k and electrical resistivity has been recently observed for a-SiC:H (see Figure 10). 77 In this case, the increase in resistivity also correlated with a decrease in paramagnetic defect density as measured by electron paramagnetic resonance (EPR) measurements. 370 This suggests that the variation in resistivity may also be tied to the presence of point defects in a-SiC:H along with the average coordina- tion.…”

“…This is due to fully dense / crystalline SiC having a higher k than fully dense / crystalline Si 3 N 4 . 77 For the a-SiC x O y :H system, a completely opposite trend for k vs. density has been observed. As shown in Figure 12 for another series of design of experiments involving various CO 2 /(CH 3 ) x SiH 4-x ratios, the k for a-SiCO:H has actually been observed to decrease with increasing mass density.…”

“…Detailed PALS investigation have shown that the diameter of nano-pores in robust DB materials are typically <0.4-0.5 nm. 52,56,77 For low-k ILD materials, SiO 2 network materials are preferred due to the more open network structure of SiO 2 and the corresponding lower starting k exhibited relative to SiC and Si 3 N 4 (see Figure 7a). 77 To make a low-k material from SiO 2 , terminal organic groups (most commonly methyl (CH 3 )) are incorporated in the film during deposition.…”

“…367,368 As shown in Figure 9, the nanoindentation Young's modulus for a-SiC:H exhibits an r 3/2 dependence for r > 2.4 but is invariant at r <2.4, consistent with rigidity and constraint theory predictions. 77 One interesting aspect of constraint theory is the prediction of increased resistance with decreasing r (or k). 369 Such an inverse correlation between k and electrical resistivity has been recently observed for a-SiC:H (see Figure 10).…”

Investigation of the Dielectric and Mechanical Properties for Magnetron Sputtered BCN Thin Films

“…The dielectric properties of the BCN films were investigated via low frequency (100 kHz) capacitance-voltage (CV) measurements performed with a Hg prober. 37 The dielectric constant of the films was determined by measuring the capacitance of the metal-insulatorsemiconductor when sweeping the semiconducting Si substrate into accumulation and using the elementary parallel plate capacitor equation and the film thickness to calculate k. The area of the Hg probe contact was calibrated by measuring the capacitance for a thermal oxide of known thickness and k (= 3.9). 38 Nanoindentation tests were performed with a Hysitron Triboindenter and a Berkovich diamond tip with a load range of 4 mN.…”