<title>Mix And Match Of 10:1 Wafer Steppers With Die-By-Die Alignment To 1:1 Proximity And Projection Systems</title>

Abstract

We report here the use of automatic die -by -die alignment to overlay 10 :1 wafer-stepper images on patterns delineated by 1:1 proximity and projection systems. The motivation for these programs arises from considerations of cost -effectiveness and productivity while upgrading existing IC fab lines; 1:1 lithographic systems already in place can be used to generate non -critical layers, while the wafer steppers can be used to align and delineate the patterns of critical layers. Excellent intra -die overlay match is demonstrated, mixing with some of the more prevalent 1:1 systems.Practical issues relating to net wafer throughput are also illuminated.The motivation and the requirement The 10X wafer steppers available today are capable of producing images with resolution near 1 micron over a 1 -cm2 fi914, and with two -level overlay alignment near 0.1 micron when die -by -die alignment is used. ' These capabilities exceed what is required for the IC production lines of today, and probably for the next few years.There is always pressure to upgrade existing IC fab lines, however, in order to obtain higher yield, throughput, and performance of the IC chips. One cost -effective candidate for near -term upgrading of planned or existing IC production lines is the hybrid mix -and -match of 10X wafer steppers with iX exposure /alignment systems.The mix -and -match application assumes that the less -critical lithographic layers will be delineated by full -wafer IX exposures, while the critical layers will be aligned and delineated by the wafer steppers. Thus a near -term fab line might consist of a multitude of 1X printers, and only a few wafer steppers. The ratio of wafer steppers to 1X printers would be increased year by year, until finally only a few 1X printers (if any) would be in each fab area to delineate contact -pad openings in passivation coatings.The mixratio and timing for the scenario outlined above have been estimated by potential users, and the cost-effectiveness and productivity of the approach have been found to be attractive. 50There is no universal schedule that defines 30