Nagarajan Rajagopalan

Robust TSV via-middle and via-reveal process integration accomplished through characterization and management of sources of variation

An overview is given of developments in unit-process and process-integration technology enabling the realization of through-silicon vias (TSVs) for 3D chip stacking. TSVs are expected to increase interconnect bandwidth, reduce wire delay due to shorter vertical signal path, and improve power efficiency [1-3]. The fabrication sequences for forming TSVs in the middle of the line (via-middle approach) and for revealing them from the backside in the far back end of the line are described with detailed attention to major unit processes of etch, dielectric deposition, barrier and seed deposition, electrochemical deposition, and chemical-mechanical planarization. Unit-process advances are described in relation to the structural and functional requirements of the TSVs, and examples are given of co-optimization among the interdependent steps of the integrated sequence. Emphasis is given to copper vias of diameter 4 to 10μm with aspect ratio between 8 and 12. For both the viaformation and via-reveal sequence, it is shown how integration problems were overcome by a comprehensive approach.

Development and Characterization of a PECVD Silicon Nitride for Damascene Applications

A silicon nitride film, Damascene Nitride™, is deposited in a plasma-enhanced chemical vapor deposition (PECVD) chamber with a conical hole faceplate using silane and ammonia as precursors. Fourier transform infrared analysis indicates that Damascene Nitride is similar to a high-density plasma nitride film. Hydrogen forward scattering spectroscopic analysis shows the films hydrogen content to be 13%, ~6% less than other PECVD nitride films, leading to a 20% improvement in etch selectivity to fluorinated silicate glass. Secondary ion mass spectrometric analysis shows that Cu diffusion is <250 A in the nitride; a low leakage current is confirmed through bias temperature stress testing. The higher density of Damascene Nitride leads to higher etch selectivity and better Cu barrier properties, allowing a thinner nitride film to be used. Thinner nitride layers, in addition to the lower dielectric constant (κ) of Damascene Nitride, leads to a 5-6% reduction in resistance-capacitance delay when Damascene Nitride is used with low-κ dielectric materials.

Reliability of dielectric barriers in copper damascene applications

The film properties of two PECVD deposited dielectric copper barrier films have been optimized to improve BEOL device reliability in terms of electromigration. Two critical aspects that affect electromigration are the dielectric barrier film hermeticity and adhesion to copper. We use a method to quantify the barrier film hermeticity of the BLO/spl kappa/ I low-/spl kappa/ dielectric film to be similar to that of silicon nitride. In addition, the interfaces between damascene nitride with copper, as well as BLO/spl kappa/ I with copper have been engineered to improve the interfacial adhesion energy to >10 J/m/sup 2/ for both damascene nitride and BLO/spl kappa/ I.

Reliability of Dielectric Barrier Films in Copper Damascene Applications

The film properties of two PECVD deposited dielectric copper barrier films have been optimized to improve BEOL device reliability in terms of electromigration. Two critical aspects that affect electromigration are the dielectric barrier film hermeticity and adhesion to copper. We use a method to quantify the barrier film hermeticity and have optimized the hermeticity of the BLOκ™ low-κ dielectric barrier film to be similar to that of silicon nitride. By using FT-IR we find that the film porosity has a much stronger effect than the film stoichiometry on hermeticity. In addition, the interfaces between Damascene Nitride™ with copper, as well as BLOκ with copper have been engineered to improve the interfacial adhesion energy to >10 J/m2 for both Damascene Nitride and BLOκ.

PECVD Silicon Nitride for Damascene Applications

A Pecvd silicon nitride film, Damascene Nitride™, is deposited in a PECVD chamber with a hollow cathode faceplate using silane and ammonia as precursor gases. Various techniques (FTIR, RBS-HFS, SIMS, TDS and BTS) were used to characterize the structure, composition, density and wet etch rate of the film. FTIR analysis indicates that Damascene Nitride is very similar to a high density plasma (HDP) nitride film. HFS analysis shows the films hydrogen content to be 13%,∼6% less than other PECVD nitride films, leading to a 20% improvement in etch selectivity to FSG. The film wet etch rate is 2 times slower than that of other PECVD nitrides, and the dielectric constant k was measured to be 6.8, which is lower compared to other PECVD nitrides and HDP CVD nitrides where k∼ 7.0 and 7.5, respectively. SIMS analysis shows that Cu diffusion is