Impact of Defects in Silicon Substrate on Flash Memory Characteristics

Abstract

Floating-gate-type Flash memories are fabricated on Czochralski ͑CZ͒ silicon wafers. A large amount of residual misalignment in reticle shots at the photolithography process step and the programing failure are observed in the low oxygen concentration wafer. To investigate the origin of misalignment and programing failure, X-ray topography, optical microscope observation followed by preferential etching and laser scattering tomography observation are performed. Slip propagation from wafer edge to wafer center and surface dislocation are observed in the area where misalignment and programing failure are occurred. Misalignment and programing failure are explained by the plastic deformation of wafer by the relaxation of internal stress during the processes. In the high Oi wafer, we observed that oxygen precipitates ͑OPs͒ prevent the propagation of slip. We conclude that the OPs have a strong effect on the suppression of slip propagation, i.e., Flash memory characteristics.

Impact of Rapid Thermal Oxidation at Ultrahigh-Temperatures on Oxygen Precipitation Behavior in Czochralski-Silicon Crystals

“…In particular, for semiconductor devices that require complicated structural enhancements such as scaling and three-dimensional chip integration, new technology for controlling oxygen precipitates will gain more significance, specifically because endurance against the stress induced in Si wafers during device fabrication is becoming increasingly crucial. [4][5][6] The behavior of oxygen precipitates in Cz-Si crystals is closely related to point defects such as vacancies and interstitial Si atoms. [7][8][9] Vacancies promote the formation of oxygen precipitates because their nucleus is formed as a complex between oxygen atoms (O) and vacancies (Va); for instance, in the form of O 2 Va.…”

Dislocations in Crystalline Silicon Solar Cells

“…However, Nitecki et al and Hirano et al have discovered to occasionally cause punched-out dislocations that are harmful to the mechanical strength of CZ-Si wafers. [135,136] Moreover, if oxygen precipitates enter into the active region, it will raise the leakage current of device. Zeng et al have shown stress field interactions between precipitates and dislocations-which are more effective for platelet oxygen precipitates and perhaps less effective for polyhedral oxygen precipitates-frequently and effectively causing dislocation locking in CZ-Si.…”

Internal Gettering of Copper for Microelectronic Applications

“…The defect denuded zone and the microdefect density in the bulk defect zone should be tailored with respect to the device process. High densities of oxygen precipitates can cause plastic deformation of silicon wafers which results in overlay problems in photolithography steps [8,9]. Therefore, density and size of oxygen precipitates need to be carefully tuned to efficiently getter the metals without causing geometry problems.…”