Electrical Inspection of PROM Memory Links

Field programmable ROMs provide the electronics industry with a more versatile memory function by postponing final processing until after the seal operation. This report will focus on (1) a failure mechanism, unreported until now, which concerns the self-programming of an unprogrammed nichrome link during operation of the PROM under normal "read" conditions, and (2) an electrical screen for culling out links with a high probability for self-programming. The occurrence of these failures after many days of burn-in will be discussed along with the link programming set-up, failure analysis data, and documented history of high reliability screening procedures. It is important to note that these PROMs were programmed to the vendor's specifications, except that a single pulse fusing criterion was used. Additionally, an elaborate verification scheme followed each fusing attempt as a check for errors. Based on the results of the failure analysis study, the failures which are considered to be escapes from the die visual inspection screen will be shown to be due to a wafer process-related fault. A new electrical test procedure will be proposed which can be used to augment or partially supplant the visual screen now in practice. A general test scheme will be presented so that the prerequisite conditions of applicability to other manufacturers' PROMs can be defined. The general scheme will be then applied to the specific circuit implementation used by the manufacturer of the aforementioned failures.