Passivation effect of silicon nitride against copper diffusion

Abstract

The use of Cu in ultralarge scale integrated ͑ULSI͒ conductors has resulted in the need to prevent Cu diffusion. We evaluated the passivation effect of plasma-enhanced chemical-vapor-deposited silicon nitride ͑PECVD-SiN͒ using secondary ion mass spectrometry and atomic absorption spectrometry. From these measurements, it was found that a large amount of Cu diffused through PECVD-SiN films during the heat treatments of the metallization process, probably due to the rapid diffusion paths along the microdefects of PECVD-SiN films. However, Cu contamination was barely detected in the current-voltage measurements and bias-temperature stressing tests of Cu/PECVD-SiN/SiO 2 /Si capacitors because the leakage current through SiN films slightly increased as a result of Cu diffusion. This result is attributed to the electric-field relaxation caused by a large number of electrons trapped in the PECVD-SiN films, of which the negative charge compensates the positive charge of Cu ions. Although the degradation of electrical characteristics is not explicitly observed in simulation using Cu/PECVD-SiN/SiO 2 /Si capacitors, Cu atoms reach Si devices in the actual process. Therefore, the passivation effect of PECVD-SiN films is insufficient to allow application to ULSI devices.

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

“…Based on these various methods, PECVD a-SiN:H has been shown to be an excellent Cu diffusion barrier. 36,37,73,75 Similar tests have also shown that a-SiC:H 59,60,64 and a-SiCN:H 44,45 can perform equivalently to a-SiN:H as Cu diffusion barriers with reduced values of dielectric permittivity as low as 4.2-4.9. 276,277 Recent studies have also indicated that dense a-SiCO:H dielectrics can also serve as Cu diffusion barriers with k values as low as 3.5.…”

“…This is a particularly germane question as the 2013 ITRS projects the thickness of the DB in a low-k/Cu interconnect will need to be only 1-2 nm thick in the next decade. 107 Unfortunately, early studies of the Cu diffusion barrier performance of a-SiN:H DB materials utilized relatively thick (>=100 nm) films, 37,73,75 and more recent studies of low-k DB materials have focused on evaluating Cu and H 2 O barrier performance at thicknesses of 30-100 nm. Only a few studies have attempted to investigate the ultimate limits in terms of DB thickness scaling.…”

“…The low-k ILD also provides some mechanical support to metal lines during downstream processing of multiple metal layers and packaging. The low-k DB/CCL/ES, however, serves these and many other additional integrated functionalities such as: preventing Cu out-diffusion into overlying metal layers, 36,37,[72][73][74][75][76] preventing in-diffusion of moisture [77][78][79] and other aqueous cleaning chemicals [80][81][82][83] that can corrode lower metal and ILD layers (see Figure 2), passivating the top surface of the Cu line to reduce/prevent electromigration, [84][85][86][87][88] halting/stopping the trench or via ILD etch to prevent over etching into the underlying metal layer and to facilitate unlanded vias (see Figure 3), 89,90 and prohibiting resist poisoning during next layer metal patterning (see Figure 2). 91,92 As these functionality requirements all relate to the material properties of the DB/CCL/ES, we briefly outline and review the basic electrical, mechanical, thermal and optical material property requirements for these layers in a general nano-electronic metal interconnect.…”

“…34,35 Depending on the details of the interconnect fabrication scheme, additional dielectrics were needed to serve as either a diffusion barrier (DB), 36 Cu capping layer (CCL), 37 etch stop (ES), 38 hard mask (HM), 35,38 and/or polish stop (PS). 39 In most cases, plasma enhanced chemically vapor deposited (PECVD) amorphous hydrogentated silicon nitride (a-SiN:H) 40 was initially utilized for these various applications.…”

Non-crystalline Zr–Si diffusion barrier for Cu/Si contact system under different sputtering power

“…A suitable diffusion barrier is crucial to suppress the diffusion and reaction taking place between copper and silicon at low temperatures for realizing thermally stable Cu/Si contact systems in current ULSI technology. For the material used as a diffusion barrier, it is required that the barrier should prevent the undesired diffusion and/or reaction, and also should be sufficiently low in resistivity [1,2]. Refractory metal binary and ternary nitrides are widely recognized as an attractive class of materials which can be used as diffusion barriers in metal-semiconductor contacts [3][4][5][6][7][8][9][10][11][12].…”