Thermal and dielectric stability of parylene X

Integrating pore sealing and barrier dielectric materials into back-end-of-the-line (BEOL) structures is challenging due to the requirements of high thermal stability, electrical stability (high breakdown, low leakage, and low dielectric constant), and barrier-like properties of the films. With Al etch-back metallization the dielectric needed to be stable up to 450°C due to Al reflow but now the thermal budget is shrinking with Cu metallization. The current limiting factors are solder and ultra-low k (ULK) dielectric cure temperatures. These temperatures may still require thermal anneals exceeding 400°C, which is very demanding on organic-based systems. Parylene X, a pore sealing chemical vapor depositable polymer, is deposited a room temperature via a precursor that allows the polymer to be self-initiated and without any byproducts. The deposition platform allows controlled penetration of the organic polymer that allows significant fracture toughness improvement for the ULK dielectric. The polymer starts to cross-link at 175°C with full conversion by 380°C as measured by FT-IR spectroscopy. The polymer is shown to be stable to 420°C with a dielectric constant of 2.7 and a leakage current of 0.5 × 10^-9 A/cm² at 0.67 MV/cm using MIMCAP structures. Parylene X was shown to have barrier-like properties in contact with both Ta and Cu metallization using bias-temperature stress (BTS) measurements at 0.5 MV/cm and 150°C. In a Cu/Ta/parylene X/ULK dielectric stack, Ta a carbide former, can be used as an adhesive layer linking Cu to parylene X or the organic-based surface since parylene X has barrier-like properties.