Solid State & Microelectronics Technology

In recent times, crystalline semiconductors have played a major role in device fabrication for all purposes, where crystal structure plays the most crucial role. Herein, all kinds of fundamental unit cell structures have been briefly discussed, whereas Miller indices have been introduced to illustrate the orientation of the crystal structures. Basic quantum mechanics have been introduced in order to explain the fundamental properties of semiconducting materials. In this context, Sommerfeld’ free electron theory has been considered. Although this model corroborates with a few experimental observations, but can’t differentiate between semiconductors, insulators and metals. Then Kronig – Penney, which successfully explains the deviation on the basis of the band concept, has been considered. Following the Kronig – Penney model, Bloch’s theory has been introduced, and it well explains the origin of conduction and valence bands. From this concept, different types of semiconducting materials, e.g., direct and indirect band gap semiconductors, n- and p-type semiconductors, etc., have emerged. Here, properties of charge carriers, such as their charge, effective mass etc., have also been discussed. Knowing these parameters, conductivity expression and related scattering phenomena influencing conductivity have been briefly elaborated. 

 In this chapter, fundamentals of the p – n junction, electric field across the junction, equilibrium carrier concentration on each side, etc., have been briefly discussed. Expression of built-in potential in terms of carrier density has been derived. Magnitudes of the current under zero, forward, and reverse biased conditions have been calculated. Unlike a resistor, p – n junction corresponds to static, dynamic and average ac resistance, and they have been briefly discussed here along with protocol to examine their values. These p – n junctions also exhibit capacitance, namely transition capacitance and diffusion capacitance. Herein, these parameters and their relevance in current-voltage characteristics of p – n junction and applicational aspects have been elaborated. 

Metal-Semiconductor-Junction is also called heterojunction since the material on each side of the junction is not identical. The normal pn junction diode concept can also be applied here. There are two probable types of metal semiconductor junctions: Schottky junction and ohmic junction. When the work function of metal is greater than the work function of a semiconductor, then this is called Schottky junction. Ohmic junctions are the junctions in which the work function of the metal is less than the work function of a semiconductor. Their band engineering discussed in detail the essentials of junction physics. 

FET is a resistor whose resistance value is controlled by the potential applied to the control terminal termed as Gate. The conducting region is called a channel which may be either p type or n type based on the substrate used. The channel conductivity mainly depends on the gate region. I-V characteristics are expressed in a detailed manner with necessary equations. JFET parameters are another crucial factor to understand its characteristics. The small signal model of JFET is illustrated in a very lucid manner. 

More or less than 17 years since D. Kahng and M. M. Atalla first conveyed the demonstration of a Si-SiO2 MOS transistor (MOSFET). In our regular lives, the impression of these MOS-based IC’s was imparted -just beginning to be felt. This incredible explosion has been caused by many inventions and countless numbers of perhaps small but crucial contributions by many researchers. Historical signs of progress of the metal-oxide-semiconductor field-effect transistor (MOSFET) during the last 60 years are appraised, from the 1928 patent disclosures of the field-effect conductivity modulation concept and the semiconductor triodes structures proposed by Lilienfeld to the 1947 Shockley-originated efforts which controlled to the laboratory demonstration of the modern silicon MOSFET 30 years later in 1960. A review is then made of the mileposts of the past 30 years leading to the latest submicron silicon logic CMOS (Complementary MOS and BICMOS (Combination of Bipolar-junction-Transistor and CMOS) arrays and the three-dimensional and ferroelectric extensions of Dennard‘s one-transistor dynamic random access memory (DRAM) cell. This chapter discusses the fabrication of MOSFET and its principal operations based on the concept of metal-oxide-semiconductor technology. Further, the discussion is focused on the details mathematical modeling of MOS capacitors, device characteristics, and the process of channel length modulation and its application. The conversation is continuing on the concept of CMOS technology and its combination with the transistor – the BiCMOS technology.

Semiconductor materials are beneficial in their performance and can be easily deployed by the addition of impurities known as doping. The resistivity of the semiconductor can be changed by incorporating the electric or magnetic field, light or heat, or mechanical distortion. Therefore, semiconductors can make excellent devices. Current conduction in a semiconductor happens due to free electrons and holes, jointly known as charge carriers. Doping of silicon significantly increases the number of electrons or holes within the semiconductor, making it “p-type” or “n-type.” This doping characteristic is a blessing to make a possible number of devices like LED, Tunnel diode, Solar cells, and many more, which have been discussed in this section.

This chapter introduces silicon as an electronic material for microelectronic device fabrication. It discusses, in-depth, the various aspects of crystalline silicon, wafer manufacturing and their identification techniques. Finally, the various steps involved in a microfabrication process are also discussed. From this chapter, the readers are expected to learn how to process a silicon wafer successfully and proceed with customized device fabrication. 

This chapter introduces the readers to the oxidation process focusing on silicon. It establishes the importance of oxidation in a silicon process and discusses the thermal oxidation process and its growth mechanism in depth. Towards the end, a detailed discussion on the oxide film characterization and its properties is provided. After reading this chapter, the readers are expected to have a sound knowledge of the oxidation process as a whole and its significance in the silicon processing industry.

This chapter introduces the readers to the diffusion process of doping intrinsic silicon. It discusses Fick’s Law of diffusion in-depth and the different types of diffusion that may be observed. Towards the latter part of the chapter, the diffusion process in semiconductors has been discussed in detail, explaining the diffusion-assisted doping process commonly employed for semiconductors, especially silicon

This chapter discusses the ion implantation process of silicon processing technology in depth. The chapter gives an in-depth insight into various aspects of the ion implantation process and ion-implanted silicon systems commonly encountered in a silicon process. After reading this chapter, the readers will have a sound understanding of the ion implantation process and its various aspects.

Micro-Electro-Mechanical Systems or MEMS, are an achievement of this era and revolutionized the semiconductor industry. It is the amalgamation of microelectronics with micromachining technology. Though the term mechanical is one of the keywords of MEMS but not necessarily, micromachined devices should not contain mechanical parts always. Machine means cutting tools. In MEMS technology, the micron-level substrates are cut down to fabricate the device. The primary purpose of MEMS technology is miniaturization with low power consumption. The term MEMS can be described in many ways. In a single sense, MEMS is a platform on top of which some common microscopic mechanical parts, e.g., channels, holes, cantilevers, membranes, cavities, and other structures, can be fabricated. Though micromachining is associated with MEMS, still the structures are not machined. Instead, they are created using micro-fabrication technology suitable for batch processing for integrated circuits. 

A few lithography techniques have been developed in the past few decades with improvements in lens systems and advanced radiation sources for exposure, such as photons, X-rays, electrons, ions, and neutral atoms. With each type of exposure source, the instrumental details significantly change. However, the fundamental principle behind the lithographic approaches remains the same. Photolithography is the most intensive technique in microelectronic fabrication, especially for the bulk production of integrated circuits (ICs). Below the different types of lithography techniques are described in detail.