Self-aligned via (SAV) schemes are commonly used for back-end-of-line (BEOL) interconnect structures that have scaled to <; 90nm BEOL pitch [1]. In one implementation of this scheme, a TiN metal hard mask (MHM) is used for trench pattern definition, while the interconnect vias are patterned using a tri-layer resist mask such that the vias are self-aligned to the underlayer trench lines [2]. In this work, we describe a SAV etch process using RF pulsing in a capacitively coupled etch reactor that provides a solution to both via distortion / striation and critical dimension (CD) bias loading. Electrical results will be discussed.

Back-end-of line (BEOL) interconnect scaling has led to the implementation of self-aligned via (SAV) schemes for ≤ 90 nm BEOL pitches [1]. In one implementation of this scheme, a TiN metal hardmask (MHM) is used for the trench pattern definition while the interconnect vias are patterned using a tri-layer resist mask such that the vias are self-aligned to the underlayer trench lines [2]. In this work, we describe a SAV etch process that enables the use of thin (≤ 15 nm) TiN MHM. Key attributes of the via and trench etching process in a capacitively coupled etch reactor are described to meet physical performance requirements and eliminate tradeoffs between via chain yield and via-to-metal (M2-V1) bridging. Low-k sidewall damage, post-etch wet clean, and metallization are discussed. Finally, the physical etch performance is correlated to the device breakdown voltage (VBD) and time-dependent dielectric breakdown (TDDB) lifetime performance.

Silicon nitride films are grown by plasma enhanced chemical vapor deposition from tetrakis(dimethylamido)silicon, Si(NMe2)4, and ammonia precursors at substrate temperatures of 200-400 °C. Backscattering spectrometry shows that the films are close to stoichiometric. Depth profiling by Auger electron spectroscopy shows uniform composition and no oxygen or carbon contamination in the bulk. The films are featureless by scanning electron microscopy under 100,000X magnification.