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INDUSTRIAL PERSPECTIVES 11 process engineer. Acceptance of such a simulation package would set the stage for the use of more complex models by industrial engineers. RECOMMENDED PRIORITIES FOR DEVELOPMENT OF AN IMPROVED DATABASE Although there are many applications of plasmas to a wide variety of processes as noted above, it is appropriate to attempt to establish several applications that, from an industrial point of view, seem especially promising for modeling. These applications are listed in Table 1.2. The first application is polysilicon gate etching in chlorine- and bromine-containing gases. The second is SiO2 etching in hydrofluorocarbon-containing gases (i.e. CxFyHz), with various other gases added such as O2 and N2. The third is a common plasma-enhanced chemical vapor deposition (PECVD) application, SiO2 deposition. The primary gases for this application include SiH4, O2, N2O; SiH4, O2, Ar; and tetraethoxysilane (TEOS). Note that this list is not all-inclusive in that in some cases other gases are used in addition to the major gases listed in Table 1.2. TABLE 1.2 Recommended Priorities for Developing an Improved Database Application Gases Poly-Si etching Cls2, Br2, HBr, O2, N2 SiO2 etching CF4, CHF3, C2F6, O2, N2, CO, Ar SiO2 deposition SiH4, O2, N2O; SiH4, O2, Ar; TEOS The rationale for these choices is that all three are major applications with widespread interest in the industry, and they all appear to be applications that will persist for at least the next 3 to 5 years. Gate electrode etching is a key in controlling the effective channel length for complementary metal oxide semiconductor (CMOS) devices, and therefore plays a major role in the sorting of microprocessor speeds described above. This has a direct impact on chip profitability, and is in need of close attention as a result. Dielectric etching (mainly contacts and vias) is crucial because of the increasing aspect ratios (3-4 and above), coupled with a high degree of selectivity between the oxide and the silicon (50:1 is desired but difficult to achieve). Dielectric etching is also the largest segment of the plasma etching market. For PECVD, simultaneous deposition and etching offers the opportunity to fill gaps between metal interconnect lines. As the number of metalization levels increases, this application will become more important. Other PECVD oxide deposition applications include planarization layers. The list of recommended chemical systems and associated applications in Table 1.2 does not in itself constitute a "database." For each of these systems, the database consists of a choice of chemical species to include in the overall mechanism, the key reactive pathways by which the selected set of chemical species are created and destroyed, and, in addition, rate expressions and parameters describing the nature of the interactions between these selected species and with surfaces. These needs are discussed in greater detail in subsequent chapters. In this chapter, the emphasis is on identifying the general chemical systems that are related to a selected set of common industrial processes (i.e. those listed in Table 1.2), rather than on prioritizing individual collisional and/or reactive processes. It should be noted that, in addition to the recommended high-priority chemical systems listed in Table 1.2, there are many other chemical systems that are of interest in various applications of plasma processing in integrated circuit manufacture. These include physical vapor deposition techniques such as sputtering and reactive sputtering; conventional metal etching (Al/Cu alloys); photoresist stripping/ashing; plasma-enhanced chemical vapor deposition of a variety of materials; compound semiconductor etching; and emerging applications involving etching of ferroelectric materials and noble metals. These are all important applications of plasma processes, and it is likely that new applications will emerge in the future. Plasma modeling and simulation have the potential to significantly improve these applications as well as the ones listed as recommended priorities. Although the systems listed in Table 1.2 were judged to be the prime