After finishing this chapter, the reader will be able to:
• give two reasons why silicon is more commonly used than any other semiconductor material
• list at least two preferred orientations of single-crystal silicon
• list the basic steps for making silicon wafers from sand
• describe the Czochralski (CZ) and the floating zone methods
• explain the purpose of epitaxial silicon layer deposition
• describe the epitaxial silicon deposition process
• list two ways to make a silicon-on-insulator (SOI) wafer
• identify the advantage of strained silicon
• describe the selective epitaxial process and its application in generating strained silicon.
Single-crystal silicon wafers are the most commonly used semiconductor material in IC manufacturing. This chapter explains why silicon wafers are used the most, and how to make them.
All materials are made from atoms. According to the arrangement of atoms inside solid materials, there are three different material structures: amorphous, polycrystalline, and single crystal. In an amorphous structure, there are no repeated patterns of atoms. A polycrystalline structure has some repeated patterns of atoms,
which form grains. All atoms are arranged in the same repeated pattern in a single-crystal structure. Figure 4.1 shows cross sections of the three different structures.
In nature, most solid materials are either amorphous or polycrystalline in structure. Only a few solids have a single-crystal structure, and they are usually gem stones, such as quartz (single-crystal silicon dioxide), ruby (single-crystal aluminum oxide with the presence of the element chromium), sapphire (single-crystal aluminum oxide with different impurities other than chromium), and diamond (single-crystal carbon).