Ultra-low-k materials

Bohm, O., et al., 2013. Novel k-restoring scheme for damaged ultra-low-K materials. Micro-electron. Eng. 112, 63—66. 

Typical nanopore materials are porous oxides or polymers that have an ultra-low dielectric constant (k < 2). Ultra-low k is significant in producing highspeed electronic devices such as the interconnect structure shown in Figure 13.8. Si02, which has a dielectric constant of about 4, is currently used as a dielectric material between interconnects in most microelectronic devices. When the packing density between multilevel interconnects increases, a low... 

Bremmer, J. A new class of insulating materials. Emergence of ultra low-k http //solidstate. archives.printthis.clickability.com/pt/cpt action= cpt expire= urlID=5079 (accessed Jan 2003). 

As a result, progress in the integration of new porous ultra-low-fe materials has been slow. The International Technology Roadmap for Semiconductors (ITRS) roadmap has been continuously revised and updated each year with k values inching upward from earlier predictions as illustrated in Figure 2.5. 

E. Bargeron, C. Schalk, P. Peck, A. Van Hove, M. Maex, K., A New Ultra-Low KILD Material Based On Otganic-Inoiganic Hybrid Resins , MRS Meetings, April 5,2002. 

The chemical component of CMP slurry creates porous unstable oxides or soluble surface complexes. The slurries are designed to have additives that initiate the above reactions. The mechanical component of the process removes the above-formed films by abrasion. In most planarization systems the mechanical component is the rate-limiting step. As soon as the formed porous film is removed, a new one is formed and planarization proceeds. Therefore, the removal rate is directly proportional to the applied pressure. To achieve practical copper removal rates, pressures greater than 3 psi are often required. These pressures should not create delamination, material deformation, or cracking on dense or relatively dense dielectrics used in silicon microfabrication on conventional dielectrics. However, the introduction of porous ultra-low-fc (low dielectric constant) materials will require a low downpressure (< 1 psi) polishing to maintain the structural integrity of the device [7-9]. It is expected that dielectrics with k value less than 2.4 will require a planarization process of 1 psi downpressure or less when they are introduced to production. It is expected that this process requirement will become even more important for the 45-nm technology node [10]. 

The technical importance of glass ceramics, produced under different trade names by various glass companies, was already mentioned in 2.9. With the code number 7971 Corning [61] developed an ultra low expansion titanium silicate glass, manufactured by flame hydrolysis. This glass, called ULE, is formed as large boules, typically 1.5 m in diameter by 0.15 m in thickness, from which virtually any size product can be fabricated using a variety of techniques. Both materials have a thermal expansion of even less than 0.2.1 O 7 K, 1 and are transparent between 0.5 and 2.3pm. 

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