BEOL Reliability for More- Than-Moore Devices

A Temperature- and Aging-Compensated RC Oscillator With ±1030-ppm Inaccuracy From40 °C to 85 °C After Accelerated Aging for 500 h at 125 °C

“…Various resistors are available in standard CMOS technology, including poly, diffusion, and metal resistors, each governed by distinct aging mechanisms. The primary factor responsible for the shift in poly resistance is the depassivation of hydrogen at grain boundaries, coupled with hydrogen migration within an electric field [26], [27], [28], [29], [30], [31]. On the other hand, the alteration in metal resistance predominantly stems from electromigration (EM), a phenomenon that propels the migration of metal atoms and consequently leads to the formation of voids within the resistor's structure [31], [32], [33].…”

“…The primary factor responsible for the shift in poly resistance is the depassivation of hydrogen at grain boundaries, coupled with hydrogen migration within an electric field [26], [27], [28], [29], [30], [31]. On the other hand, the alteration in metal resistance predominantly stems from electromigration (EM), a phenomenon that propels the migration of metal atoms and consequently leads to the formation of voids within the resistor's structure [31], [32], [33]. Despite the divergence in their aging mechanisms, these resistors' anticipated time to failure (TTF) can be empirically modeled as follows:…”

“…where A is an empirically determined constant, J is current density (A/cm 2 ), n is the empirically determined current density factor, E a is the activation energy (eV), k is Boltzmann's constant, and T is the absolute junction temperature of the resistor during the aging stress. The TTF estimation can be achieved through Black's approach, as demonstrated by (1) [29], [31], [32], [33], or by employing an alternate model, as depicted in (2) [26], [29], [31] to accommodate low current density (J ) scenarios. E a represents a vital aging-associated parameter obtained by fitting aging experimental data with (1) or (2).…”

“…Compared with p-poly resistors, n-poly resistors have a higher E a of 0.68 eV and longer TTF, making them more suitable for the better long-term stability of the oscillators [26]. Metal interconnect or back-end-of-line (BEOL)-type resistors also have higher E a and exhibit smaller resistivity shifts under electrical and temperature stress than poly resistors [31], [34]. For instance, the copper interconnects and VIA chains are characterized by E a values spanning from 0.82 to 0.93 eV [34].…”