MEMORY DATABOOK - Al Kossow's Bitsavers

RELIABILITY INFORMATION1. INTRODUCTIONSemiconductor memories play a leading role in theexplosive progress of semiconductor technology. Theyuse some of the most advanced design and manufacturingtechnology developed to date. With greaterintegration, diversity and reliability, their applicationshave expanded enormously. Their use in· large scalecomputers, control equipment, calculators, electronicgames and in many other fields has increased at a fastrate.A failure in electronic banking or telephone switchingequipment, for example, could have far reaching effectsand can cause incalculable losses. So, the demand, forstable high qual ity memory devices is strong.We, at Oki Electric is fully aware of this demand. Sowe have adopted a comprehensive quality assurancesystem based on the concept of consistency in development,manufacturing and sales.With the increasing demand for improvement in function,capability and reliability, we will expand ourefforts in the future. Our quality assurance system andthe underlying concepts are outlined briefy below.2. QUALITY ASSURANCE SYSTEMAND UNDERLYING CONCEPTSThe quality assurance system employed by Oki Electriccan be divided into 4 major stages: device planning,developmental prototype, production prototype, andmass production. This system is outlined in the followingblock diagram (Fig. 1-1).1 t Device plann ing stageTo manufacture devices that meet the market demandsand satisfy customer needs, we carefully considerfunctional and failure rate requirements, utilizationform, environment and other conditions. Once wedetermine the proper type, material and structure,we check the design and manufacturing techniques andthe line processing capacity. Then we prepare thedevelopment planning and time schedule.2) Developmental prototype stageWe determine circuits, pattern design, process settings,assembly techniques and structural requirements duringthis stage. At the same time, we carry out actual prototypereliability testing.Since device quality is largely determined during thedesigning stage, Oki Electric pays careful attention toquality confirmation during this stage.This is how we do it:(1) After completion of circuit design (or patterndesign), personnel from the design, process technology,production technology, installation' technologyand reliability departments get together fora thorough review to ensure design quality and toanticipate problems that may occur during massproduction. Past experience and know-how guidethese discussions.(2) Since many semiconductor memories involve newconcepts and employ high level manufacturingtechnology, the TEG evaluation test is often usedduring this stage.Note: TEG (Test Element Group) refers to thedevice group designed for stability evaluationof MaS transistors, diodes, resistors,capacitors and other circuit componentelement used in LSI memories.(3) Prototypes are subjected to repeated reliability andother special evaluation tests. In addition, thestabil ity and capacity of the manufactu ring processare checked.3) Production prototype stageDuring this stage, various tests check the reliability andother special features of the production prototype atthe mass production factory level. After confirmingthe quality of device, we prepare the various standardsrequired for mass production, and then start production.Although reliability and other special tests performedon the production prototype are much the same asthose performed on the developmental prototype, thepersonnel, facilities and production site differ for thetwo prototypes, necessitating repeated confirmationtests.4) Mass productionDuring the mass production stage. careful managementof purchased materials, parts and facilities used duringthe manufacturing process, measuring equipment,manufacturing conditions and environment is necessaryto ensure device qual ity first stipulated during thedesigning stages. The manufacturing process (includinginspection of the completed device) is followed by a lotguarantee inspection to check that the specified qualityis maintained under conditions identical to those underwhich a customer would actually use the device. Thislot guarantee inspection is performed in 3 differentforms as shown below.o25