Paper EM-WeM10
Relation of Low-k Interconnect Si-based Dielectric Breakdown to Resistive Switching Behavior

Wednesday, October 21, 2015, 11:00 am, Room 210E

The relation between resistive switching (RS) and breakdown and reliability mechanisms are studied for metal-insulator-metal (MIM) structures with low-k dielectrics (SiOC:H, SiCOH, SiNC:H, SiCN:H, SiC:H, SiON:H, SiN:H) all 25 nm thick, with Ti, and Cu as electrode materials that are commonly used in the CMOS back-end process. The TDDB time is correlated with defect generation and related to mechanisms responsible for RS. Defect generation depends exponentially on E_a-bxE_el, where E_a is the activation energy, b is the bond polarization factor being proportional to the molecular dipole moment p_o, b=(2+k)/3p_o, and E_el is the electric field across the dielectric. The breakdown field E_bd is determined by E_a-bxE_bd=0, i.e. at high enough electric fields there is effectively no barrier impeding creation of defects. From this condition, the breakdown field E_bd=E_a/b is determined. We obtain, for SiC:H E_a=0.28 eV and p_o=10e-A, for SiCN:H E_a=0.26 eV and b=4e-A, for SiN:H, E_a=0.17 eV and p_o=1.2eA, for SiON:H p_o=1.5e-A. for SiOC:H we obtain E_a=1.67eV and p_o=15e-A. We find that E_a values of low-k dielectrics are very low compared with those for high-k dielectrics, e.g. E_a=4.4 eV for HfO₂ with k=21. On the other hand, the strength of the molecular dipole for low-k dielectrics is comparable to that for high-k dielectrics (e.g. p_o=11e-A for HfO₂). In terms of RS properties under a linear voltage sweep the low-k materials display varied behavior: SiNC:H does not exhibit resistive switching, i.e. under linear voltage stress it shows gradual decrease of resistance but the on-state is volatile, i.e. it evanesces when the cell is unpowered. A similar behavior is observed for SiCN:H, i.e. soft volatile breakdown with a volatile on-state. SiOC:H shows a sharp resistive switching that cannot be reversed - the cell is on permanently. The set voltage is high V_set=11.8V and it decreases significantly with increasing temperature. SiON:H shows comparable behavior as SiOC:H with slightly lower set voltages. SiC:H shows sharp resistive switching behavior at a moderate set voltage V_set=6.5V @ 300K. SiN:H displays also a sharp resistive switching but at much higher voltage, V_set=11.5V @300K. The high set voltages for SiC:H and SiN:H correlate well with high densities of those dielectrics, both at 2.5 g/cm³ and similar dielectric constant of k=7.2 and 6.5, respectively. The on-state is attributed to the formation of a Cu conductive filaments. The conductive filaments are cylindrical and difficult to rupture. The paper discusses correlation, differences, and commonalities between data obtained for dielectric breakdown and resistive switching mechanisms in terms of the film properties.