PROCESSING OF INTEGRATED CIRCUITS

1 2002 John Wiley & Sons, Inc. M. , Fundamentals of Modern Manufacturing 2/e PROCESSING OFINTEGRATED CIRCUITS Overview of IC PROCESSING (Part I) Silicon PROCESSING Lithography Layer Processes Use in IC Fabrication (Part II) Integrating the Fabrication Steps IC Packaging (Part III) Yields in IC PROCESSING 2002 John Wiley & Sons, Inc. M. , Fundamentals of Modern Manufacturing 2/e INTEGRATED circuit (IC)A collection of electronic devices such as transistors,diodes, and resistors that have beenfabricated andelectricallyintraconnectedonto a small flat chip ofsemiconductor material Silicon(Si)-most widely used semiconductormaterialfor ICs, due to its combination of propertiesand low cost Less common semiconductor materials: germanium(Ge) and galliumarsenide(GaAs) Since CIRCUITS are fabricated into one solid piece ofmaterial, the termsolid stateelectronics is used forthese devices 2002 John Wiley & Sons, Inc.

2 M. , Fundamentals of Modern Manufacturing 2/e Levels of Integration in MicroelectronicsIntegration levelNumber devicesApprox. yearSmall scale integration (SSI)10-501959 Medium scale integration (MSI)50-1031960sLarge scale integration (LSI)103-1041970sVery large scale integration (VLSI)104-1061980sUltra large scale integration (ULSI)106-1081990sGigascale integration109-10102000s 2002 John Wiley & Sons, Inc. M. , Fundamentals of Modern Manufacturing 2/e Overview of IC Technology An INTEGRATED circuit consists of hundreds, thousands,or millions of microscopic electronic devicesthathave been fabricated and electricallyintraconnectedon the surface of a silicon chip Achipis a square or rectangular flat plate that isabout mm ( in) thick and typically 5 to 25mm ( to in) on a side Each electronic device ( , transistor) on the chipsurface consists of separate layers and regions withdifferent electrical propertiescombined to perform theparticular electronic function of the device 2002 John Wiley & Sons, Inc.

3 M. , Fundamentals of Modern Manufacturing 2/e Figure of a transistor (specifically, a MOSFET)in an INTEGRATED circuit. Approximate size of the device is shown;feature sizes within the device can be less than 1 m withcurrent technology. 2002 John Wiley & Sons, Inc. M. , Fundamentals of Modern Manufacturing 2/e Packaging of ICs To connect the IC to the outside world, andto protectit from damage, the chip is attached to a lead frameand encapsulated inside a suitable package The package is an enclosure,usually made ofplastic or ceramic, that provides mechanical andenvironmental protection for the chip It includes leads by which the IC can beelectrically connected to external CIRCUITS 2002 John Wiley & Sons, Inc.

4 M. , Fundamentals of Modern Manufacturing 2/e Figure of an INTEGRATED circuit chip: (a) cutawayview showing the chip attached to a lead frame andencapsulated in a plastic enclosure, and (b) the package as itwould appear to a user. This type of package is called a dualin-line package (DIP). 2002 John Wiley & Sons, Inc. M. , Fundamentals of Modern Manufacturing 2/e PROCESSING Sequence for Silicon-based ICs Silicon PROCESSING -sand is reduced to very puresilicon and then shaped into wafers IC fabrication- PROCESSING steps that add, alter, andremove thin layers in selected regions to formelectronic devices Lithography is used to define the regions to beprocessed on wafer surface IC packaging-wafer is tested, cut into individualchips, and the chips are encapsulated in anappropriate package 2002 John Wiley & Sons, Inc.

5 M. , Fundamentals of Modern Manufacturing 2/e Figure of PROCESSING steps in the production ofintegrated CIRCUITS : (1) pure silicon is formed from the moltenstate into an ingot and then sliced into wafers; (2) fabricationofintegrated CIRCUITS on the wafer surface; and (3) wafer is cut intochips and packaged 2002 John Wiley & Sons, Inc. M. , Fundamentals of Modern Manufacturing 2/e Clean Rooms Much ofthe PROCESSING of ICs must be carried out ina clean room, the ambiance of which is more like ahospital operating room than a production factory Cleanliness is dictated by the microscopic featuresizes in an IC, the scale of which continues todecrease with each passing year 2002 John Wiley & Sons, Inc.

6 M. , Fundamentals of Modern Manufacturing 2/e Figure in device feature size in IC fabrication; alsoshown is the size of common airborne particles that cancontaminate the PROCESSING environment 2002 John Wiley & Sons, Inc. M. , Fundamentals of Modern Manufacturing 2/e Clean Room Classification SystemA number (in increments of ten) used to indicatethequantity of particles of size mor greaterin onecubic foot of air Aclass 100clean room must maintain a count ofparticles of size m or greater at less than 100/ft3 Aclass 10clean room must maintain a count ofparticles of size m or greater at less than 10/ft3 The clean room is air conditioned to21 C (70 F) and45% relative humidity 2002 John Wiley & Sons, Inc.

7 M. , Fundamentals of Modern Manufacturing 2/e Silicon PROCESSING Microelectronic chips are fabricated on a substrateof semiconductor material Silicon is the leading semiconductor material today,constituting more than 95% of all semiconductordevices produced in the world Preparation of silicon substrate can be divided intothree of electronic grade ofSiinto wafers 2002 John Wiley & Sons, Inc. M. , Fundamentals of Modern Manufacturing 2/e Electronic Grade Silicon Silicon is one of the most abundant materials in theearth's crust, occurring naturally as silica ( , sand)and silicates ( , clay) Principal raw material for silicon isquartzite, which isvery pure SiO2 Electronic grade silicon (EGS) is polycrystallinesilicon of ultra high purity-so pure that impurities aremeasured inparts per billion(ppb) 2002 John Wiley & Sons, Inc.

8 M. , Fundamentals of Modern Manufacturing 2/e Crystal Growing The silicon substrate formicroelectronic chips mustbe made of a single crystalwhose unit cell isorientedin a certain direction The silicon used in semiconductor devicefabrication must be of ultra high purity The substrate wafers must be cut in a directionthatachieves the desired planar orientation Most widely used crystal growing method is theCzochralskiprocess, in whicha single crystalbouleispulled upward from a pool of molten silicon 2002 John Wiley & Sons, Inc. M. , Fundamentals of Modern Manufacturing 2/e Figure for growing single crystal ingotsof silicon: (a) initial setup prior to start of crystal pulling,and (b)during crystal pulling to form theboule 2002 John Wiley & Sons, Inc.

9 M. , Fundamentals of Modern Manufacturing 2/e Shaping of Silicon into Wafers PROCESSING steps toreduce thebouleinto thin,disc-shaped (boule) preparation 2002 John Wiley & Sons, Inc. M. , Fundamentals of Modern Manufacturing 2/e Preparation of theBoule The ends of thebouleare cut off Cylindrical grinding is used toshape thebouleinto amore perfect cylinder One or more flats are ground along the length of theboule, whose functions, after thebouleis cut intowafers, are the following: Identification Orientation of ICs relative to crystal structure Mechanical location during PROCESSING 2002 John Wiley & Sons, Inc. M.

10 , Fundamentals of Modern Manufacturing 2/e Figure operations used in shaping the silicon ingot:(a) a form of cylindrical grinding provides diameter androundness control, and (b) a flat ground on the cylinder 2002 John Wiley & Sons, Inc. M. , Fundamentals of Modern Manufacturing 2/e Wafer Slicing Avery thin ring-shaped saw bladewith diamond gritbonded to internal diameter is the cutting edge TheID is used for slicing rather than the OD forbetter controlover flatness, thickness, parallelism,and surface characteristics of the wafer Wafers are cut mm ( in.) thick,greaterthicknessesfor larger wafer diameters To minimizekerfloss, blades are made very thin:about mm ( in.)