Elastic properties of tensile nitrogen-plasma-treated multilayer silicon nitride films

International audienceIn the present article, we report a study on the mechanical behaviour displayed by hydrogen atoms and pores in silicon nitride (SiN) films. A simple three-phase model is proposed to relate the physical properties (stiffness, film stress, mass density, etc.) of hydrogenated nanoporous SiN thin films to the volume fractions of hydrogen and pores. This model is then applied to experimental data extracted from films deposited by plasma enhanced chemical vapour deposition, where hydrogen content, stress, and mass densities range widely from 11% to 30%, -2.8 to 1.5 GPa, and 2.0 to 2.8 g/cm(3), respectively. Starting from the conventional plotting of film's Young's modulus against film porosity, we first propose to correct the conventional calculation of porosity volume fraction with the hydrogen content, thus taking into account both hydrogen mass and concentration. The weight of this hydrogen-correction is found to evolve linearly with hydrogen concentration in tensile films (in accordance with a simple "mass correction" of the film density calculation), but a clear discontinuity is observed toward compressive stresses. Then, the effective volume occupied by hydrogen atoms is calculated taking account of the bond type (N-H or Si-H bonds), thus allowing a precise extraction of the hydrogen volume fraction. These calculations applied to tensile films show that both volume fractions of hydrogen and porosity are similar in magnitude and randomly distributed against Young's modulus. However, the expected linear dependence of the Young's modulus is clearly observed when both volume fractions are added. Finally, we show that the stiffer behaviour of compressive films cannot be only explained on the basis of this (hydrogen_porosity) volume fraction. Indeed this stiffness difference relies on a dual mechanical behaviour displayed by hydrogen atoms against the film stress state: while they participate to the stiffness in compressive films, hydrogen atoms mainly behave like pores in tensile films where they do not participate to the film stiffness

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“…[23][24][25] and details of the measurement on our samples are reported in Ref. 26. In our case, the precision on the measured stiffness is 2%.…”

Section: B Physical and Chemical Characterizationsmentioning

confidence: 56%

Dual mechanical behaviour of hydrogen in stressed silicon nitride thin films

Volpi

Braccini

Devos

et al. 2014

Journal of Applied Physics

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“…However, the reduction in mechanical properties has not been as severe with reported Young's moduli and fracture toughness values of 40-120 GPa 74,139,142 and 0.5-4 MPa √ m, [164][165][166][167][168][169] respectively. Compared to the Young's moduli of 100-200 GPa 135,140,142 and fracture toughness of 1-10 MPa √ m [170][171][172] reported for PECVD a-SiN:H, the low-k DB mechanical property reduction is fairly modest. Also as the reduced values for low-k DB materials are substantially higher than those for low-k ILD materials, there has been generally less concern for these properties when considering new low-k DBs.…”

Section: N3031mentioning

confidence: 63%

“…150 The original ILD material (SiO 2 ) utilized in damascene Cu interconnect structures exhibited reasonably robust Young's modulus and fracture toughness values of 60-80 GPa 141 and 0.6-0.8 MPa √ m, 129 respectively. However relative to SiO 2 , low-k a-SiOC:H ILD materials exhibit substantially reduced values for Young's modulus (3-20 GPa) [136][137][138][139][140][141][142][143][144][145][146][147] and fracture toughness / energy (≤0.2 MPa √ m). [151][152][153][154] Unfortunately, the reduction in mechanical properties scales with reductions in dielectric permittivity, 14,66, and is one of the contributing factors for why low-k ILD materials with increasingly lower values of k have been so challenging to integrate.…”

Section: N3031mentioning

confidence: 98%

“…[123][124][125][126][127][128] The low-k ILD and DB material properties most focused on from this viewpoint are Young's modulus and hardness as determined by nanoindentation. 129,130 Due to limitations in spatial resolution and substrate effects that have become increasingly significant as target film thicknesses decrease below 100 nm, 9,131 a number of alternative techniques have recently attracted attention such as contact resonance-atomic force microcopy (CR-AFM) [132][133][134] and bulge testing 135,136 as well as non-contact optical techniques such as picosecond laser ultrasonics (PLU), [137][138][139][140] Brillouin light scattering (BLS), [141][142][143][144][145][146] and surface acoustic wave spectroscopy (SAWS) 146,147 . However despite the extreme emphasis on measuring Young's modulus for low-k materials, the author is unaware of any established critical thresholds for these properties in either low-k ILD or DBs.…”

Section: Low-k Ildmentioning

confidence: 99%

“…For low-k ILD materials, this has resulted in numerous k vs. material property trends reported in the literature. Due to the extremely reduced thermal and mechanical properties exhibited by low-k ILD materials relative to SiO 2 , k vs. Young's modulus [136][137][138][139][140][141][142][143][144][145][146][147] and thermal conductivity [223][224][225][226][227][228][229][230][231][232][233][234][235] trends have been perhaps the most frequently reported in the literature. Correlations between porosity and low-k ILD thermal and mechanical properties have also been frequently reported in the literature owing to the interdependence of k and porosity and the exponential increase in difficulty associated with integrating low-k ILD materials with increasing levels of interconnected porosity.…”

Section: Current Status Of Low-k Db/ccl/es Materials and R And Dmentioning

confidence: 99%

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Over the past decade, the primary focus for improving the performance of nano-electronic metal interconnect structures has been to reduce the impact of resistance-capacitance (RC) delays via utilizing insulating dielectrics with ever lower values of dielectric permittivity. The integration and implementation of such low dielectric constant (i.e. low-k) materials has been fraught with numerous challenges. For intermetal and interlayer (ILD) low-k dielectrics, these challenges have been largely associated to integration with metal interconnect fabrication processes and well documented and reviewed in the literature. Although equally important, less attention has been given to other low-k dielectrics utilized in metal interconnect structures that are commonly referred to as low-k dielectric barriers (DB), etch stops (ES), and/or Cu capping layers (CCL). These materials present numerous challenges as well for integration into metal interconnect fabrication processes. However, they also have more stringent integrated functionality requirements relative to low-k ILD materials that serve only a basic purpose of electrically isolating adjacent metal lines. In this article, we review the integration challenges and associated integrated functionality requirements for low-k DB/ES/CCL materials with a focus on the current status and future direction needed for these materials to facilitate both Moore's law (i.e. More Moore) and More than Moore scaling.

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Elastic properties of tensile nitrogen-plasma-treated multilayer silicon nitride films

Cited by 9 publications

References 26 publications

Dual mechanical behaviour of hydrogen in stressed silicon nitride thin films

Dual mechanical behaviour of hydrogen in stressed silicon nitride thin films

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

Investigation of the Structural, Tribological, and Electrochemical Properties of Nitrided and Boronized AISI 316L Stainless Steel

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