284 Jin, Lin, and Wetzel Journal of ELECTRONIC MATERIALS, Vol. 30, No. 4, 2001 (Received November 17, 2000; accepted January 16, 2001) Special Issue Paper 284 INTRODUCTION Scaling of integrated circuit (IC) feature sizes has brought tremendous performance improvement and miniaturization in the past few decades. The primary contribution to the IC performance improvement has been coming from the device gate level. However, as device scaling continues into the deep-sub-micron region, metal interconnects become the bottleneck for continued IC performance improvement. The gain in device speed at the gate level is offset by propaga- tion delays at the metal interconnect due to the increased RC time constant. The RC time delay can be reduced by the incorporation of low dielectric con- stant (k) materials and/or high conductivity metals. The use of low-k dielectric materials also lowers power consumption and reduces crosstalk. 1 There are numerous low-k dielectric candidates available with the dielectric constant in the range of 2.5 and 4.1. 2 As predicted by the International Tech- nology Roadmap for Semiconductors, 3 continued scal- ing of devices will require ultra-low-k materials with dielectric constants as low as 1.5. One of the ways to obtain a lower dielectric constant is fluorination of either inorganic or organic dielectric materials. How- ever, the lowest dielectric constant available for flu- orinated dense materials is around k ~1.9 (Teflon ® ) and none of the current approaches using dense materials is expected to achieve k values lower than Evaluation of Ultra-Low-k Dielectric Materials for Advanced Interconnects C. JIN, 1,2 S. LIN, 1 and J.T. WETZEL 1 1.—International SEMATECH Inc., 2706 Montopolis Drive, Austin, TX 78741. 2.—Texas Instruments, Inc., MS-3701, 13570 N. Central Expressway, Dallas, Texas 75243 The International Technology Roadmap for Semiconductors predicts that con- tinued scaling of devices will require ultra-low-k materials with k values less than 2.5 for the 100 nm technology node and beyond. Incorporation of porosity into dense dielectrics is an attractive way to obtain ultra-low-k materials. Electrical and physical properties of ultra-low-k materials have been character- ized. Integration evaluations showed both feasibility and challenges of porous ultra-low-k materials. This paper discusses issues and recent progress made with porous ultra-low-k material properties, deposition processes, characteriza- tion metrologies, and process integration. Key words: Low-k, dielectric, porous low-k, interconnect, integration, porosity, thermal conductivity, Young’s modulus, sol-gel that. Air practically has the lowest dielectric constant possible—k ~ 1. Incorporation of air into dense mate- rials to make them porous is another attractive method to obtain ultra-low-k materials. The ultra low dielec- tric constant results from the incorporation of pores. For a porous material, the dielectric constant is a combination of air and that of the dense phase, and it has the potential to drive the dielectric constant significantly below 2. To meet performance goals, future technology nodes will require materials with progressively lower dielectric constant. A change in dielectric material for each technology node increases process and equipment complexity and development cost. It is desirable to have one class of material that can meet the requirements for multiple future tech- nology nodes. Porous dielectric materials offer the extendibility to multiple technology nodes because they have tunable dielectric constant. The dielectric constant variation with respect to porosity (volume fraction of pores) of porous silica xerogel is shown in Fig. 1. The figure includes predictions from the paral- lel model as well as bulk sample measurements. 4 Clearly, a dielectric constant of interest can be achieved by tuning the porosity to a proper level. POROUS DIELECTRIC FILM DEPOSITION AND CHARACTERIZATION At present, most porous low-k materials are pro- duced using either templated or sol-gel processes. In the templated approach, the precursor contains a composite of thermally labile and stable materials.