VLSI Fabrication Technology

Integrated Circuits are widely regarded as one of the key components of today's world. The revolution of the change in VLSI fabrication and development of integrated circuits, is the result of first integrated circuits fabricated by Jack Kilbey in 1958. The market for Integrated Circuits has increased tremendously since. The basic steps involved in the fabrication of BJT and N-MOS are discussed in the last section of this chapter.

The first part of the chapter, discusses the contamination types and sources of contamination which affect the performance of the devices. The last section of the chapter discusses the perpetual generated contamination and wafer cleaning techniques.

In this chapter, first the silicon properties are mentioned then the Crystal Structure of silicon is discussed. The silicon structure used in the electronic industry, crystal perfection, purity and uniformity are not necessarily highest on the list of desirable attributes for crystalline S incorporated into commercial PV modules. The defects like point line, area and volume are also discussed in this chapter.

In the epitaxial growth process, the substrate wafer is the seed, high quality, single crystal films can be grown at temperatures 30% to 50% lower than the melting point, from the heteroepitaxial and homoexpitaxial silicon structure, the homoepitaxial silicon structure will remain popular design choices. Cleanliness of both chamber and growth process is critical to the success of process.

This chapter discusses thin film deposition techniques in detail. In deposition methods, physical vapour deposition and chemical vapour deposition are classified and the comparison of each other is also discussed.

During fabrication, to protect the underlying silicon oxidation is necessary. During which, a dioxide layer is formed over the silicon whenever the silicon comes in contact with oxygen. This layer is served as a mask during the etching process.

In this chapter, first the process of diffusion is discussed with the different types of diffusion and their comparative merits and demerits. A focused study of some common dopants like arsenic, boron, phosphorus is also carried out to develop a practical understanding for the readers. After that, the different types of diffusion systems used in the VLSI industries are discussed.

Photolithography transfers a pattern from a mask to a UV light sensitive photoresist on the wafer surface. Resolution is the smallest feature that can be patterned. Modern photolithography is based on optical lithography. Alignment and exposure is critical in lithography to meet critical submicron resolution requirement. Next-generation lithography is evaluating the lithography technology for eventually replacing optical lithography.

This chapter shows how etching is used to etch pattern films by selectively removing material with the help of mask layers. Anisotropy and throughput are the other etching parameters useful for the etching process.

Ion implantation is a doping process which introduces a dopant into silicon to modify its electronic properties. Ion implantation replaces the process of diffusion as ion implantation has many advantages over it.

The interconnection of circuits is made with metallization process in which the metallization material is used to interconnect the various device structures fabricated on the silicon substrate. Metallization includes a variety of components such as contact to active area global interconnects, local interconnect via interconnect levels, first level dielectrics and intermetal dielectrics etc.

In this chapter, technologies have been described that require hundreds of processing steps. The general trend for each individual technology has been towards smaller dimensions and more complicated processing. The shrinking of device dimensions has allowed improvement of device performance as well as an increase in the number of devices. The basic trend fro NMOS and CMOS development will continue to be driven by reducing device dimensions. Guidelines have been established for miniaturizing the dimensions of the MOS devices to maintain ideal transistor characteristics.

The rapid development of IC technology has created a critical need for packaging sealing and encapsulation using advanced polymeric materials for encapsulant, interlayer dielectrics and passivation layers. Recent advances in high performance polymeric materials, such as improved silicone elastomers, ultra soft silicone gels, low stress epoxies, low thermal expansion coefficient and photode-finable polymides and cyclobutenes have begun to provide polymers to meet reliability requirements of VLSI technology.

MEMS have a tremendous future in replacing the components of many commercial products used today. The medical, wireless (including cellular and network technologies), biotechnology computer, automotive and aerospace industries are only a few that will benefit greatly from MEMS. Furthermore, this enabling technology promises to not only transform most major industries but to create an entirely new categories of products. An almost infinite number of radical applications are possible because of its potential : nearly limitless functionality, infinitesimally small form factor, a phenomenal price / performance ratio, and an architecture that lends itself to mass production, all of which are advantages that drove the success of the integrated circuit. MEMS will be an indispensable factor for advancing technology in the 21st century world.