Figure 3.2 This trench etch (0.2 µm wide by 4 µm deep) in single crystalline silicon shows the extraordinary capabilities of plasma processing. Such trenches are used primarily for device isolation and charge storage capacitors in memory devices. Only with plasmas can such features be fabricated economically. (Courtesy of Applied Materials, Inc.)

Figure 3.3 Schematic illustration of the difference between plasma (dry) and wet etching. Only plasma etching provides the needed anisotropic etching and high-fidelity pattern-transfer capability.

Feeding the electronics industry is the semiconductor industry, which had sales worldwide of $50 billion in 1990. Semiconductors are used in the fabrication of microelectronic integrated circuits or chips that are the principal components of electronic and telecommunication systems. Despite overall market growth, the United States consistently lost semiconductor market share throughout the 1980s and is expected to continue losing market share through the mid-1990s. In the world's largest semiconductor market—Japan—the United States has only a 10 percent share. Yet Japan has increased its U.S. market share from 5 to 30 percent since 1980.

Feeding the semiconductor industry is the equipment and materials industry, which had sales worldwide of $19 billion in 1990 (Figure 3.1). The ability to make large volumes of low-cost semiconductors depends directly on the quality of manufacturing equipment and materials. Plasma equipment and plasma processing are critical constituents in the equipment and materials industry. In fact, the microelectronics industry would not exist as we know it today were it not for plasma processing. For example, in the fabrication of 1-megabit dynamic random access memories (DRAMs), plasmas are used to "dry" etch patterns with vertical sidewalls and high aspect ratios (depth/width) into materials such as silicon, silicon dioxide, and aluminum. An example of a 0.2-mm-wide by 4-mm-deep (aspect ratio of 20) trench plasma etched in single crystalline silicon is shown in Figure 3.2.

To obtain high-density packing of microscopic circuit components, such anisotropic etching is essential. By contrast, wet chemical techniques used previously result in isotropic etching, where both vertical and lateral etch rates are comparable. As illustrated in Figure 3.3, only

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