游離輻射對N型電晶體的隨機電報雜訊之影響研究

Abstract

自1958年起積體電路的發明來，元件密度都依循著摩爾定律(Moore’s Law)以每18個月在同樣面積下的積體電路所容納的電晶體數目會以加倍的趨勢成長，而微影技術更是左右著此定律能否維持下去的一大主因。在10nm以下積體電路製程中，極紫外光微影技術是最有可能發展起來的微影技術，但當以極紫外光微影技術進行曝光微影，將使得製程中的元件直接暴露於輻射下而使得輻射損害不可忽略，且必須謹慎的評估。本論文中主要探討極紫外光所造成的游離輻射對NMOSFETs產生的影響進行研究。 經過極紫外光照射之後，金氧半電晶體的電性產生了許多明顯的變化，包括汲極電流(ID)-閘極電壓(VG)曲線變化、漏電流上升、臨界電壓位移、隨機電報雜訊(Random Telegraph Noise)的時間常數改變和功率譜密度(Power Spectral Density )的斜率變化。這些電性的變化代表元件經過極紫外光照射後，介電層中、淺溝渠隔離氧化物下方以及介電層和矽基板間介面的缺陷以及被捕捉到的電荷增加，這將使得原本沒有隨機電報雜訊的元件因為照射紫外光，而造成電路的不穩定性增加，此外我們發現到因輻射產生隨機電報雜訊的缺陷可能會在同一位置有深淺不同能階的缺陷，當電子損失能量時，會掉到較深的能階而讓電子待在缺陷的時間(τe)增長許多，但是當電子從深缺陷中釋放後，又開始回復原本與淺能階互動的情形。 本論文顯示極紫外光照射所引發的隨機電報雜訊現象將是研究人員得考量的因素，因為隨機電報雜訊對於元件操作在低電流時的影響更是嚴重，而讓穩定度受到很大的威脅。

Since Integrated circuit (IC) was invented in 1958, density of devices follows Moore’s law which means that the number of device in the same area is doubled every eighteen months. Lithography is an important factor for continuous scale-down of IC technology. However, below 10 nm technology node of the IC manufacturing, the extreme ultraviolet (EUV) technology is the most likely lithography technology to be employed. Lithography by EUV light source will make the device be directly exposed to irradiation so that the radiation damage can’t be ignored and should be considered carefully. This thesis focuses on the effect of ionizing radiation from EUV light source on random telegraph noise of NMOSFETs. After exposing to extreme ultraviolet radiation, the characteristics of NMOSFET exhibit many significant changes including variation of ID-VG characteristic, increase of leakage current, shift of threshold voltage, change of the time constant of random telegraph noise, and induce of random telegraph noise phenomenon. These variations of characteristics imply that the number of traps in gate dielectric, in field oxide of shallow trench isolation, and at the interface between gate dielectric and silicon increase after exposing to EUV. Random telegraph noise (RTN) phenomenon may be arisen on devices without random telegraph noise phenomenon before EUV irradiation, which resulting in increasing instability of the circuit. Furthermore, we found that the emission time constant of the EUV irradiation induced random telegraph noise trap has two quite different values. It may change from less than 1 second to longer than several tens seconds and then change back to less than 1 second. This phenomenon can be explained by the charge state of trap in HfO2. Therefore, it is suggested that the EUV irradiation produces trap which generates random telegraph noise in HfO2. We conclude that RTN resulting from EUV irradiation would be an important factor for further research especially when device is operated at low power and low current level.