介面處理對鉿氧化物之抗極紫外光輻射損傷之影響研究

Abstract

本研究探討極紫外光輻射對金屬閘極/高介電常數介面層的影響。選用氮化鈦為金屬閘極材料，及選用二氧化鉿搭配不同的三種介面處理方式，另外也使用二氧化鉿製作了金氧半場效電晶體(MOSFET)來驗證極紫外光對電晶體的影響。 電容器經極紫外光照射後有明顯的電容-電壓特性變化，包括平帶電壓漂移、電容-電壓曲線變形、還有遲滯現象的劣化。平帶電壓向左漂移表示有正電荷產生，電容-電壓曲線變形表示介面能態增加，遲滯現象的劣化代表邊界陷阱增加。綜合以上結果，顯示二氧化鉿搭配化學氧化的電容確實抑制了電容-電壓曲線漂移及變形。除此之外，二氧化鉿搭配快速熱氧化的電容也稍微改善抗極紫外光能力。以二氧化鉿作為介電質的電晶體經極紫外光照射後，電晶體的電流-電壓特性也和電容器一樣產生漂移，此現象可以呼應電容器電容-電壓曲線漂移，顯示在介電層有正電荷的捕捉。另外，也探討了電晶體可靠度(PBTI)在照射前後的改變狀況。電晶體在關閉下的漏電流，因極紫外光照射後隔離氧化物下產生介面能態，導致激發電流。 本研究也討論經過極紫外光照射後的元件是否具有自我修復的現象。元件在室溫之下長時間儲存，電容器以及電晶體中因為極紫外光產生的傷害會逐漸減少，但是無法回復到照射前的特性，我們再利用400度氮氣混合氫氣作退火，仍然無法回復到照射前的特性。因此，極紫外光微影製程必須考慮對元件性能的影響 ，如何修復極紫外光照射帶來的損傷是需要進一步的探究。

In this study, we investigate EUV radiation effects on the interface between the high dielectric constant (high-k) dielectric with the metal gate. TiN is selected as the metal gate electrode. HfO2 dielectric with different interface engineering are evaluated. Besides, we use HfO2 as the gate dielectric for a metal-oxide-silicon-field -effect-transistor (MOSFET) in order to study the EUV radiation damage effects. After EUV irradiation, the C-V curves of MIS capacitors have significant changes. There are flatband voltage shift, C-V curve distortion, and hysteresis increase. The flatband voltage shifting to the negative direction exhibits that positive charges are generated. The C-V curve distortion exhibits that the interface states increase. Hysteresis increase exhibits that border traps raise. Among these MIS capacitors, HfO2 with the chemical oxide shows that chemical interfacial layer can suppress the shift and distortion. Moreover, HfO2 with RTO shows a little effect on radiation hardness. The Id-Vg curve of a MOSFET shifts the like C-V curve shift of a MIS capacitor after EUV irradiation. It means that positive charges are trapped in the dielectric. We also study the reliability of MOSFET on PBTI stress condition before and after EUV irradiation. The leakage current in the off-state increases after EUV irradiation, because the increase of interface states under the isolation oxide excites the leakage current. In this study we also investigate whether devices can self-annealing. After devices are stored for a long time, the radiation damage will recover little by little. Samples do not recover even using additional 400℃ H2 + N2 annealing. EUV radiation damage on the devices at the EUV lithography technology nodes should be progressively investigated.