FL&O_9_fabrication[1]

FL&O_9_fabrication[1] - Fabrication of integrated...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Fabrication of integrated circuits. The microprocessor chip of a modern computer contains about 500 million transistors on an area approximately 11 x 11 mm (about ½ inch square). Moore’s law is often cited in the development of computers. In 1965, Gordon Moore, a co-founder of Intel, predicted that the density of transistors on integrated circuits would double every 18 months. This is shown in figure I.1. Year of Introduction Transistors 4004 1971 2,250 8008 1972 2,500 8080 1974 5,000 8086 1978 29,000 286 1982 120,000 Intel386™ processor 1985 275,000 Intel486™ processor 1989 1,180,000 Intel® Pentium® processor 1993 3,100,000 Intel® Pentium® II processor 1997 7,500,000 Intel® Pentium® III processor 1999 24,000,000 Intel® Pentium® 4 processor 2000 42,000,000 Intel® Itanium® processor 2002 220,000,000 Intel® Itanium® 2 processor 2003 410,000,000
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Present research lets us expect this trend to continue at least for the next ten years, chips with 1.2 billion transistors are envisaged for the year 2007! This density, of course, dictates that the transistors be extremely small. In fact, the latest MOS transistors have a “gate pitch”, namely a distance between the centers of the source and drains of 0.25 micrometer. Their gate has a length of 35 nanometers and their gate oxide a thickness of 1.2 nanometer. How is it possible to manufacture 420 million microscopic transistors on a chip, and this for an affordable price? This is the subject of this chapter. Integrated circuits are fabricated by photolithography on the surface of a single crystal silicon wafer. The latter has a diameter of 300 mm (12 inches) and a thickness of less than one millimeter. The elements of each transistor (the source, the drain, the gate) are made on the surface of the wafer as shown in Figure 10.2. Each such element is a pocket of silicon that has been doped with boron to make it p-type or with phosphorous or arsenic to make it n-type. These pockets are extremely small. Figure 10.2 Schematic of a transistor on the surface of a silicon wafer. Left: Bipolar transistor, right: MOSFET transistor. In a modern transistor, the distance between the centers of the source and drain is 0.25 micrometer and the length of the gate is 35 nm. 1. Make a wafer of silicon: grow a silicon single crystal, cut it into thin wafers and polish them to remove all surface defects. 2. Grow and oxide layer on the surface of the wafer (by oxidation in a furnace) 3. Spread a photoresist on the surface of the wafer. A photoresist is a substance that is (usually a polymer) that becomes soluble where it is illuminated. 4. Apply a mask that has been designed to be transparent where one wants to make the doped pocket. The mask, of course, defines the area of a given element for all the transistors of one chip at the same time. 5. Illuminate the photoresist through the mask. One uses ultraviolet light with a wavelength of 139 nm. (The wavelength of visible light (400 to 600 nm) does not
Background image of page 2
provide sufficient resolution. This illumination is repeated for each chip on the wafer.
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 10/03/2009 for the course E E344 taught by Professor Libera during the Spring '09 term at Stevens.

Page1 / 18

FL&O_9_fabrication[1] - Fabrication of integrated...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online