Manufacturingofmicroprocessor-120813121945-phpapp02.pptx

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Manufacturing of Microprocessor Farooq Ahmad Shah Preliminary Discussion • • Integrated circuit: An electronic circuit designed to perform some function, in which the electronic components (transistors, resistors, diodes, capacitors, etc.) are miniaturized, built into a small chip made of silicon and interconnected through tiny strands of aluminum. !ore commonly referred to as microchips, or I" chips# $he chip found inside of a musical birthday card contain only a few dozen components, whereas a Pentium processor today contains o%er &'' million transistors *hen an integrated circuit is e+tremely comple+, it is usually nown as a microprocessor. Preliminary Discussion • (contd.) Microprocessors are manufactured in clean rooms, the ambiance of which cleaner than a hospital operating room.  –  –  –  The air in the clean room is air conditioned to a temperature of 21C !"F# and $%& relati'e humidit(.  The air is passed through a high)e*cienc( particulate air +-A# lter to capture particle contaminants worers must be co%ered from head to toe in specialized garments, called bunny suits, designed to trap particles. -utline of the processing steps e/uence of processing steps in the production of integrated circuits: (0) pure silicon is formed from the molten state into an ingot and then sliced into wafers1 (2) fabrication of integrated circuits on the wafer surface1 and (3) wafer is cut into chips and pacaged. ilicon Ingot • $o pro%ide uniform electrical properties throughout, the silicon must be almost totally pure and a perfect crystal. Ingot diameter 3''mm(02 in) and up to 3m(0' ft) long $he "zochralsi process for growing single4crystal ingots of silicon: (a) initial setup prior to start of crystal pulling, and (b) during crystal pulling to form the boule. ilicon Ingot (contd.) 5rinding operations used in shaping the silicon ingot: (a) a form of cylindrical grinding pro%ides diameter and roundness control, and (b) a flat ground on the cylinder. ilicon *afers *afer slicing using a diamond abrasi%e cutoff saw. ilicon *afers (contd.) $wo of the steps in wafer preparation: (a) contour grinding to round the wafer rim, and (b) surface polishing. I" 6abrication • • • • 7epeated se/uential steps (2'' times or more). 8ayering: Adding new material on top of or into the silicon lie dopants, insulators, conductors. Photolithography: 9y e+posing a light sensiti%e chemical (photoresist) through a mas, the desired pattern is transferred onto the current top layer. tching: 7emo%es the material to gi%e the desired pattern. I" 6abrication (contd.) A;  Ions of arsenic are bombarded using ion implantation to create a n4type doped region. 8ayer of i-2 is grown using o+idation. 8ayer of photoresist is applied. • photoresist is an organic polymer sensiti%e to light radiation in a certain wa%elength range1 the sensiti%ity causes either an increase or decrease in solubility of the polymer to certain chemicals. I" 6abrication (.g. contd.) +pose photoresist using appropriate lithographic mas. De%elop the photoresist. tch photoresist and silicon dio+ide. Implant boron 7emo%e silicon dio+ide I" 6abrication (contd.) (A) A p4type wafer (silicon doped with 9oron) has a epilayer of n4type (silicon doped with Phosphorous or Arsenic) (9) A mas is used to implant ilicon Dio+ide, for the insulator (") Acceptor atoms (9oron) are diffused into the window in the ilicon Dio+ide (D) ?sing another mas additional ilicon Dio+ide is grown. and donor atoms (elements lie Arsenic with e+cess electrons) are implanted. () Another mas is used to grow additional ilicon Dio+ide. Another mas is then used to implant Pacaging • • • • • *afer $esting: a computer4controlled needle probes contacts the chip connection pads and a series of D" tests are carried out to indicate short circuits and other faults1 the failed chips are mared with an in dot1 these defects are not pacaged. "hip eparation: A thin diamond4impregnated saw blade is used to perform the cutting operation. $he sawing machine is highly automatic and its alignment with the streetsBB between circuits is %ery accurate. Die 9onding: Automated handling systems pic the separated chips and place them for on the die. po+y is applied to the base of the chip. *ire 9onding After the die is bonded to the pacage, electrical connections are made between the contact pads on the chip surface and the pacage leads. Cideo $han you. Ion Implantation 6irst a gas containing the desired dopant is ionized by bombarding it with electrons, producing charged atoms. $his process will also produce ions of other types, are screened out. 9y carefully adusting the field, the desired ions are gi%en the correct arc to e+it the mass spectrometer. Ions that are hea%ier will cur%e too wide and ions that are lighter will cur%e too sharply to escape. $he dopant ions are then accelerated through a %ery strong electric field and fired at the wafer. A patterned layer of photoresist or other material is used to bloc the dopant atoms from areas where they are not needed. In areas of silicon that are e+posed, the ions crash into the surface at high rates of speeds. $he total dose of dopant depends upon how many ions are fired into the silicon. *afer must be annealed to allow the doper atoms and silicon atoms to position themsel%es in their proper places. Photolithography Photolithography, also nown as optical lithography, uses light radiation to e+pose a coating of photoresist on the surface of the silicon wafer1 a mas containing the re/uired geometric pattern for each layer separates the light source from the wafer, so that only the portions of the photoresist not bloced by the mas are e+posed. $he mas consists of a flat plate of transparent glass on to which a thin film of an opa/ue substance has been deposited in certain areas to form the desired pattern. $hicness of the glass plate is around 2 mm ('.'&' in), whereas the deposited film is only a few mm thicEfor some film materials, less than 0 mm.$he mas itself is fabricated by lithography, the pattern being based on circuit design data, usually in the form of digital output from the "AD system used by the circuit designer. tching tching is usually done selecti%ely, by coating surface areas that are to be protected and lea%ing other areas e+posed for etching. $he coating maybe an etch4resistant photoresist, or it maybe a pre%iously applied layer of material such as silicon dio+ide. *et "hemical tching in%ol%es the use of an a/ueous solution, usually an acid, to etch away a target material. $he etching solution is selected because it chemically attacs the specific material to be remo%ed and not the protecti%e layer used as a mas. Dry Plasma tching uses an ionized gas to etch a target material. $he ionized gas is created by introducing an appropriate gas mi+ture into a %acuum chamber. and using radio fre/uency (76) electrical energy to ionize a portion of the gas, thus creating a plasma. $he high4energy plasma reacts with the target surface, %aporizing the material to remo%e it.