Method for activated gaseous and vapor HF delivery methodologies for creating uniform low-K ILD systems

Method for activated gaseous and vapor HF delivery methodologies for creating uniform low-K ILD systems

Disclosed is a method for activated gaseous and vapor hydrogen fluoride (HF) delivery methodologies for creating uniform low-dielectric constant (K) interlayer dielectric (ILD) systems. Benefits include improved functionality, improved performance, and improved support for future technology.

Background

         Predictions for future technology requirements near the year 2010 include low-K ILDs with a dielectric constant lower than 2.0. Conventionally, no known method exists to successfully integrate such an ILD. A K value less than 2.0 must be porous in nature and/or contain relatively few bridging high-capacitance bonds (such as Si-O-Si). The porosity, due to size effects, complicates metals integration schemes, which require smooth side walls to maintain low Cu resistance.

         Conventionally, the semiconductor industry is working towards integrating porous ILDs to create low-K ILDs. Direct integration of low-K ILDs has been difficult because the porosity creates interconnects with high surface roughness. It dramatically increases the line resistance at dimensions lower than 100 nm. Interconnects are expected to be ~50-nm wide. Additionally, standard etch/cleans processing has the potential to change (increase) the K value of the ILD.

         Aqueous solutions of HF, including sonicated solutions, are successful at lowering K values in ILD films by replacing high dielectric Si-O bonds with Si-F bonds. Alternatively, etching/dissolving SiO₂ porogens creates pores in ILD films. A limiting factor for this approach is the lack of total depth-of-film uniformity, which is a result of surface tension effects in the delivery method (aqueous solution of etchant). Assuaging surface tension issues yields low-K films with higher uniformity and greater consistency.

General description

         The disclosed method is integrated, highly uniform, low K ILD systems. They are based on HF/H₂O vapor or activated gaseous HF. The ILD is saturated with HF gas, then ionized with H₂O vapor. The integration and processing scheme enables the creation of dual-damascene interconnects or direct patterning interconnects. A post-processing scheme lowers the dielectric constant of the film by replacing the Si-O bonds with Si-F bonds or internally etching SiO₂ porogens to create a porous ILD layer. The dissolution of the porogen post-dual-damascene processing creates voids in the ILD, which substantially lowers the K of the ILD.

         The HF delivery system is not hindered by the surface tension issues that aqueous solutions experience. As a result, the transformation of the ILD is more uniform.

         The key elements of the method include:

•         Low surface tension HF delivery methods to lower the K value of ILDs by:

-         Dissolving SiO₂ porogens to create a porous film, or

-         Maximizing Si-F bond formation and Si-O bond breaking

•         Physi...