Dielectric material constants

Bonhote and co-workers [10] reported that ILs containing triflate, perfluorocar-boxylate, and bistrifylimide anions were miscible with liquids of medium to high dielectric constant (e), including short-chain alcohols, ketones, dichloromethane, and THF, while being immiscible with low dielectric constant materials such as alkanes, dioxane, toluene, and diethyl ether. It was noted that ethyl acetate (e = 6.04) is miscible with the less-polar bistrifylimide and triflate ILs, and only partially miscible with more polar ILs containing carboxylate anions. Brennecke [15] has described miscibility measurements for a series of organic solvents with ILs with complementary results based on bulk properties. 

Neirynck, J. M., Yang, G. R., Murarka, S. P., et al., Low Dielectric Constant Materials-Synthesis and Applications in Microelectronics, Materials Research Society Symposium Proceedings, Vol. 381,1995,pp. 229-234. 

An important class of materials that originates from the precursor core-shell particles is hollow capsules. Hollow capsules (or shells ) can be routinely produced upon removal of the core material using chemical and physical methods. Much of the research conducted in the production of uniform-size hollow capsules arises from their scientific and technological interest. Hollow capsules are widely utilized for the encapsulation and controlled release of various substances (e.g., drugs, cosmetics, dyes, and inks), in catalysis and acoustic insulation, in the development of piezoelectric transducers and low-dielectric-constant materials, and for the manufacture of advanced materials [14],... 

Power supply designers are usually aware that the most stable ceramic capacitance comes from materials dubbed COG material, also called NPO (for negative positive zero, referring to its near perfect temperature coefficient). But this is a low dielectric constant material, and unsuitable for modern miniaturization. So the common materials in use today are called X7R, X5R, and so on. There are others, starting with a Y or Z prefix, which no power supply designer worth his or her salt will ever use. 

B. D. Hatton, K. Landskron, W. Whitnall, D. D. Perovic and G. A. Ozin, Spin Coated Periodic Mesoporous Organosilica Thin Films Towards a New Generation of Low-Dielectric-Constant Materials, Adv. Fund. Mater., 2005, 15, 823. 

The development of low-dielectric-constant materials as ILDs is crucial to achieve low power consumption, reduce signal delay, and minimize interconnect cross-talk for high-performance VLSI devices. In one of the multilevel interconnect process routes, metal lines (e.g., A1—Cu or Cu) are patterned through reactive ion etching, and then dielectric films are filled in the trenches formed between these lines. These trenches can have widths in the sub-0.5 pm range and aspect ratios greater than 3. Therefore, small gap-filling capability is also required for such dielectrics. 

Chi-I Lang, Synthesis of new, vapor-depositable low dielectric constant materials for use as on-chip dielectrics, Doctoral Dissertation, Rensselaer Polytechnic Institute (1 995). 

The temperature coefficient of conductance is approximately 1-2 % per °C in aqueous 2> as well as nonaqueous solutions 27). This is due mainly to thetemper-ature coefficient of change in the solvent viscosity. Therefore temperature variations must be held well within 0.005 °C for precise data. In addition, the absolute temperature of the bath should be known to better than 0.01 °C by measurement with an accurate thermometer such as a calibrated platinum resistance thermometer. The thermostat bath medium should consist of a low dielectric constant material such as light paraffin oil. It has been shown 4) that errors of up to 0.5 % can be caused by use of water as a bath medium, probably because of capacitative leakage of current. 

The Problem Finding New High Dielectric-Constant Materials... 

The CCS approach is well matched to the synthesis part of the problem of the identification of new thin-film high dielectric constant materials for embedded DRAM applications. As noted above, low-temperature deposition is essential and the CCS approach provides in situ mixing at low temperatures. Samples are obtained in thin-film form and can be made in thicknesses that are similar to those that will actually be used. 

Although minimization in integrated circuits allows for faster device operation, propagation delays increase with increasing numbers of interconnects. To address this problem, lower dielectric constant materials have been prepared. 

Pore-generating materials, particularly p-cyclodextrins, were used by Lyu [5] with sUsesquioxane derivatives to prepare low dielectric constant materials. 

Since the discovery of ordered mesoporous materials, researchers have explored many possible applications that can take advantage of the unique compositional or structural features of mesoporous materials. In addition to apphcations in traditional areas such as catalysis, separation, and ion exchange, new applications that might involve mesoporous materials include stationary phases in HPLC, bio and macromolecular separations, low dielectric constant materials, enzyme immobilization, optical host materials, templates for fabrication of porous carbons, and reactions in confined enviromnents. 

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]. 

It is clear that, although there is not yet, a clear winner in the race for low dielectric constant materials, CVD polymers offer great potential as interlayer dielectric materials in future generation high density microchips. 

H. Treichel, B. Withers, G. Ruhl, P. Ansmann, R. Wurl, Ch. Muller, M. Dietlmeier, and G. Maier, Handbook of Low and High Dielectric Constant Materials and their Applications, Vol.l, 1999, p.l. 

Some other interesting applications include the CMP of high dielectric constant materials (e.g., BaTiOj) that could be used for increasing capacitance, high T -superconductors used for zero-resistance interconnections, and optoelectronic materials, especially waveguides, where surfaces will play an important role. There is considerable interest in these areas and there are quite a few challenges to encounter in each case. Unfortunately, very little is disclosed in the published literature. We shall review and discuss each of these areas in the following, with more focus on areas of immediate interest to microelectronic industry, the areas (a), (b), (c), (d), and (h). 

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