260 Integrated circuits
Although these LSI circuits are being used in cal- extensive operator training, in-process tests
culators, automobiles, instruments, appliance controls spection with continual feedback, and a htigh asd,
and many other applications, realization of their po- of equipment calibration and control. Th h r
tential is just beginning. As the power of the corn- environment and operator attitude in an nte e py 1
puter is captured in the relatively inexpensive inte- cuit fabrication facility are important f gactors~
grated circuit, the role of integrated circuits will cessf ul operation.fatr o>
continue to expand rapidly. Processes. The basic relationship between thil' ',
Ron Btirghard; Youssef EJ-Mansy; Neil Berglund jor processes in integrated-circuit fabricat~tnis
schematically in Fig. 13. Film formation 1
FABRicATioti followed by impurity doping or lithography. ri4§
Integrated-circuit fabrication begins with a thin, raphy is generally followed by etching, which - *
polished slice of high-purity, single-crystal semnicon- is followed by impurity doping or film formation .,
ductor (usually silicon) and employs a combination of purity doping is normally followed by flilm fo ',"
physical and chemical processes to create the inte- or lithography. A complete integrated-circuitpm
grated-circuit structures described above. Junctions sequence requires many cycles through the flp'ow e'z
are formed in the silicon slice by the processes of gram in Fig. 13. For example, metal gate CMOs ,7-
thernal diffusion or high-energy ion implantation. quires seven cycles through lithography. The,,,".~
Electrical isolation between devices on the integrated plete flow time for a CMOS process is a~pprO~,
circuit is achieved with insulating layers grown by 2 to 6 weeks, depending on proces Unmlxit
thermal 'oxidation or deposited by chemical deposi- Film formation. Film formation employs therniaj01..
tion *. Conductor layers to provide the necessary elec- idation to produce silicon dioxide (SiO,) films C'ea, ."
trical connections on the integrated circuit are ob- ical vapor deposition to produce silicon, silicon de
talned by a variety of deposition techniques. Precision ide, or silicon nitride (Si3N4) films, fir Vaiu
lithographic' processes are used throughout the fabri- evaporation/sputtering to produce metal films.
cation sequence to define the geometric features re- The atoms on the surface of a silicon single szj
quired. from which integrated circuits are manufanctiýýJd .ý
Requirements. The integrated-circuit fabrication chemically bound only in the direction of the bulko
process is quite sensitive to both particulate and im- the crystal, and not in the other or free directio6~f.T',
purity contamination. Airborne particulates must be resultant so-called silicon dangling bonds are very re,
minimized during the fabrication sequence, since active and may bond to oxygen or nitrogen or oti
even small (1 -micrometer) particles on the wafer sur- impurities from the atmosphere, so that a large viainquy'
face can cause defects. A particulate-free fabrication of reactions can occur. Each of these reactions il~
ambient is normally achieved by the use of vertical result in different electrical properties for the'silitos
laminar-flow clean rooms or benches (Fig. 12). Lint- surface, a serious problem in designing a manufati..
free garments are worn to minimize operator-borne ing process in which extremely large nurnbers'iV'
particulates. To minimize impurity contamination ef- identically operating and reliable devices are-pm.
fects, the chemicals, solvents, and metals which are duced on silicon chips. The solution to this dilni~
used must be of the highest possible purity (electronic is to tie up the dangling bonds with a chemnicallý,st
grade). Yellow light is necessary in the clean room ble and electrically insulating film that will not iater-
because of the ultraviolet-sensitive photolithographic fere with the electrical characteristics of the sili~oi
processes employed, surface. A material with these properties that can t'
The precision and cleanliness requirements of inte- easily prepared in thin-film form on silicon is si66n
grated-circuit processing necessitate high discipline dioxide.
throughout the process sequence. This is achieved by The silicon dioxide film is made by the reacfiodil
F~~~g.~M 127et-a amnr
flo clanroofr Ite
gratd-cicuitfabrcatin.0
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