銅/二氧化矽系統可靠性之研究

Abstract

本文分別以介電質劣化，及銅閘極金氧半結構中的銅離子遷移，來探討 銅/二氧化矽/矽系統之熱穩定性。我們測量銅/二氧化矽/矽結構經快速退 火後， 介電強度及矽/二氧化矽介面能階密度的變化， 來觀察此系統的 熱穩定性。 此結構經 300℃ 60 秒快速退火後， 電性便生劣化，其程度 隨退火溫度升高而加劇。 劣化原因可能來自退火過程中， 溶於二氧化矽 層中帶正電的銅離子。 銅離子在二氧化矽中的移動率則以加溫偏壓法求 之， 並以此法求得經快速退火處理後，銅離子在銅閘極金氧半結構的二 氧化矽層中之分佈。 我們發現銅離子在二氧化矽層中移動迅速,並可能在 到達二氧化矽/矽介面後擴散至矽基板中. Thermal stability of the Cu/SiO2/Si system was investigated with respect to the dielectric degradation and Cu ion migration in the Cu-gate MOS capacitor. We used the rapid thermal annealing (RTA) and the technique of bias-temperature stress in conjunction with the dielectric breakdown field (Ebd) and SiO2/ Si interface state density (Dit) measurements to characterize the thermal stability of the Cu/SiO2/Si system. We found that the Ebd degradation started to occur after Cu/SiO2/Si structure was annealed with 60 sec RTA at a temperature as low as 300℃; and the dielectric strength deteriorated progressively with the increase of annealing temperature. The dielectric degradation is presumably due to Cu dissolution in SiO2 layer in the form of positive ion. The mobility of Cu ion in the SiO2 layer was evaluated using the data obtained from the bias- temperature stress. The Cu ion concentration in the SiO2 layer of Cu-gate MOS capacitor resulting from RTA anneal was also evaluated using a simple extractation scheme. It is also concluded that Cu is a fast diffusion specises in SiO2 and may diffuse into Si substrate once it arrives at the SiO2/Si interface.