Advanced Metallization Schemes

Advanced metallization schemes are required to obtain the performance benefits of scaling device dimensions into the sub-0.5 pm regime. This section discusses the origin of the interconnect delay and impact on IC electrical performance. Methods of reducing interconnect delay will be discussed, including MLM and the use of new metal and ILD materials. As additional metal layers are added, surface planarization requirements increase. This section discusses planarity requirements while subsequent sections discuss planarization schemes, including CMP. 

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As mentioned in Chapter 1, the present state of CMP is the result of the semiconductor industry s needs to fabricate multilevel interconnections for increasingly complex, dense, and miniaturized devices and circuits. This need is related to improving the performance while adding more devices, functions, etc. to a circuit and chip. This chapter, therefore, discusses the impact of advanced metallization schemes on the performance and cost issues of the ICs. Our discussions start with the impact of reducing feature sizes on performance and the need of various schemes to counter the adverse effect of device shrinkage on the performance of interconnections. An impact of continued device shrinkage on circuit delay is discussed. Then the need of low resistivity metal, low dielectric constant ILD, and planarized surfaces is established leading to the discussion of CMP. Finally various planarization techniques are compared to show why CMP is the process that will satisfy the planarity requirements of the future. 

ADVANCED METALLIZATION SCHEMES Table 2.2 Dielectric constant of Selected ILDs... 

Chapters 1 and 2 introduce the CMP process and historical motivations. The present status of CMP is discussed in Chapter 2, which focuses on establishing the need of advanced metallization schemes and planarization. There are a large number of variables that control the process these are discussed in Chapter 3. Chapter 4 presents the science of CMP— mechanical and chemical concepts important in understanding the CMP fundamentals. The CMP of the Si02 films, the most commonly used insulator interlayer dielectric, is discussed in Chapter 5. Chapters 6 and 7 cover the CMP of the two most studied metals, W and Cu, respectively. Chapter 8 examines the applicability of CMP to new materials, e.g., Al, polymers, and Si3N4 photoresists. Finally, Chapter 9 covers post-CMP cleaning science and technology. 

Catalytic, enantioselective cyclopropanation enjoys the unique distinction of being the first example of asymmetric catalysis with a transition metal complex. The landmark 1966 report by Nozaki et al. [1] of decomposition of ethyl diazoacetate 3 with a chiral copper (II) salicylamine complex 1 (Scheme 3.1) in the presence of styrene gave birth to a field of endeavor which still today represents one of the major enterprises in chemistry. In view of the enormous growth in the field of asymmetric catalysis over the past four decades, it is somewhat ironic that significant advances in cyclopropanation have only emerged in the past ten years. 

The four hitherto known routes of the C-H insertion are shown in Scheme 1. In general, the insertion by singlet carbenes proceeds via route a in one step, whereas the reaction by triplet carbenes proceeds sequentially via route b, i.e., hydrogen abstraction followed by recombination of the radical pairs.4 Other stepwise mechanisms are hydride abstraction (route c) and proton abstraction (route d), both being followed by the recombination of ion pairs. However, extended study on routes c and d for synthetic purposes had not been done before we started, except for a few earlier studies on carbanion-promoted P C-H insertion reactions.5,6 Recent advances in transition metal-catalyzed... 

Due to many impressive advances in metal-catalyzed transformations, both asymmetric and non-asymmetric, several efforts have been directed towards designing total synthesis routes that very heavily depend on various catalytic methods. These total syntheses benefit from the economic efficiency and environmental consciousness that are two of the inherent attributes of catalytic reactions. The total synthesis of wodeshiol 133 by Corey, discussed above (Scheme 19) is one such example. Two additional catalysis-based enantioselective total syntheses are briefly discussed below. In both efforts, all centers of asymmetiy are attained by a catalytic enantioselective method, and the synthesis is completed through the use of several other catalytic reactions. 

A diverse group of secondary and tertiary amines are readily synthesized from the reaction of primary and secondary amines with allylic carbonates in the presence of preformed iridium metalacycles, but the direct synthesis of primary amines via iridium-catalyzed allylic amination requires the use of ammonia as a nucleophile. The asymmetric allylation of ammonia had not been reported until very recently, and it is not a common reagent in other metal-catalyzed reactions. Nonetheless, Hartwig and coworkers developed the reactions of ammonia with allylic carbonates in the presence of la generated in situ [89]. Reactions conducted in the initial work led exclusively to the products from diallylation (Scheme 16). Further advances in... 

As part of this initiative, complex (80) (Scheme 11.10) has been advanced as a user-friendly catalyst for enantioselective metathesis [43]. Even when prepared in situ from commercially available solutions of the requisite metal complex and chiral ligand, (80) gives rise to high levels of efficiency and enantioselectivity. More recently, the first chiral solid-supported Mo alkylidene ((81), Scheme 11.10)... 

The state of the art has now advanced to the point that synchrotron sources are frequently not the hmiting factor in biological XAS. In particular, there is concern that sample measurement techniques have not kept pace with the development of new sources. Several new detection schemes are under development, however it may be several years before detectors will be available which are capable of fully utilizing the intensity available firom new sources. In addition, there is concern that very intense sources may compromise sample integrity. Taken together, these concerns suggest that it is not reasonable to extrapolate past experience when attempting to predict the effect of new sources on future concentrations limits. Metal ion concentrations below ca. 100 )tM are likely to remain inaccessible for many years. 

No readily acceptable mechanism has been advanced in reasonable detail to account for the decomposition of hydroperoxides by metal dialkyl dithiophosphates. Our limited results on the antioxidant efficiency of these compounds indicate that the metal plays an important role in the mechanism. So far it seems, at least for the catalytic decpmposition of cumene hydroperoxide on which practically all the work has been done, that the mechanism involves electrophilic attack and rearrangement as shown in Scheme 4. This requires, as commonly proposed, that the dithiophosphate is first converted to an active form. It does seem possible, on the other hand, that the original dithiophosphate could catalyze peroxide decomposition since nucleophilic attack could, in principle, lead to the same chain-carrying intermediate as in Scheme 4 thus,... 

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