Electrical and mechanically robust, porous, ultra-low dielectric constant materials

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With the increasing demand of integrated circuits (IC) computational speed performance, new nano-fabrication techniques and novel materials are needed. One of the most noticeable recent developments in the IC industry is the deployment of copper interconnects and ultra-low dielectric constant (ULK) materials in back-end-of-line structures. Interconnect lines are nanometer-scale metal wires used to connect transistors together. To avoid electrical shorts between these nano-wires and to provide mechanical support for the IC devices, ULK materials are used to insulate these metal wires. The migration of copper/ULK from the out-dated aluminum/silicon dioxide technology is to reduce signal delay by the resistances of interconnect line and the capacitance cross-talks between them. In the future, IC technology with the characteristic transistor gate length smaller than 22 nm (22 nm technology node) will consist of ULK materials with target dielectric constants less than 2.1 To achieve this objective, the ULK will be incorporated with nanometer-scale empty voids or pores. This new class of material is commonly referred to as porous-ULK and can be produced by using the porogen-subtraction method. Organic template agents (porogen) are introduced into the silicate matrix material by using the plasma-enhanced chemical vapor deposition (PECVD) techniques. They will be subsequently removed by a vaporization process using UV radiation at high temperature in an ultra-high-vacuum chamber. Depending on the amount of porogen used during the PECVD process, the final porosity in the porous-ULK film can be in the range of 20% to 40%. However, this technique has drawbacks which limit its application. This includes the difficulty of producing pores with diameters smaller than 2 nm which is the 22 nm technology node requirement. The UV cure process may increase the dielectric constant of the porous-ULK by modifying its molecular structures. Finally, as expected, the introduction of porosity into the silicate film reduces its mechanical and fracture strength. It is the goal of this research to understand the causes of these degradations and provide solutions by inventing new fabrication techniques.