Introduction to VLSI Design Flow

To understand the VLSI design flow, we should be familiar with some basic concepts related to integrated circuits (IC). In this chapter, we explain them and introduce some terminologies that we use throughout this book.

VERY LARGE SCALE INTEGRATION (VLSI): AN HISTORICAL PERSPECTIVE

We connect various active and passive components such as transistors, diodes, resistors, and capacitors in an electronic circuit. However, with increasing complexity, interconnecting or assembling discrete components become expensive, time-consuming, and unreliable [1–3]. Therefore, the technology to build monolithic silicon chips containing several electronic components was invented in the early 1960s [1, 3]. These monolithic silicon chips are known as integrated circuits (IC).

IC technology: The invention of IC technology resulted in a tremendous decrease in the cost of electronic products and fueled the current information technology revolution [2, 4]. During the initial development of IC technology, the following problems were challenging to solve [1, 3]:

1. Isolating separate components electrically on a monolithic semiconductor was a challenge. We could accomplish this by employing reverse-biased p–n junctions that can block the unwanted flow of current through the semiconductor [5]. The technology to diffuse dopants directly into a semiconductor at precise locations using silicon dioxide (SiO2) mask was critical in solving this problem [4, 6].

2. Obtaining sufficiently high yield to be profitable was a challenge. Yield is the percentage of good ICs among all the fabricated ICs. A technique known as photolithography was critical in solving this problem. We will describe photolithography in detail in the following sections.

Many of the IC technology advancements relied on the discovery that the native oxide of silicon has an excellent interface property. These advancements culminated in developing the planar process of transistor fabrication [7].