- 學位論文
含氟介面之二氧化鉿閘極介電層特性研究
Characterization of HfO2 Gate Dielectric with Fluorine Doped Interface
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摘要
本文是以有機金屬化學氣相沉積系統(MOCVD)來成長出高介電係數的二氧化鉿(HfO2)，並以離子佈植方式將氟離子摻雜在二氧化鉿薄膜及此二氧化鉿薄膜與矽基板之界面處，利用電流-電壓和電容-電壓曲線之量測技術於室溫下進行分析，比較出以有摻雜與無摻氟的二氧化鉿做成的金氧半電容元件(MOSC)的電性與可靠度差別。 氟離子的佈植可以減少界面狀態的懸空鍵結(interface dangling bond)還可以有效減少此薄膜層的電荷捕捉情形，而進一步的有效改善二氧化鉿薄膜的特性。HfO2薄膜的結晶溫度因為太低，所以退火溫度在高於500℃時會造成結晶化的問題，使其絕緣特性降低。因此，將氟離子摻入薄膜中使其反應為HfOxFy，會具有在高溫退火時的抗結晶化特性來改善HfO2薄膜的熱穩定性。所以在漏電流的比較中，可看出在摻氟之後的二氧化鉿有獲得改善，並且由C-V圖中可看出有摻氟的二氧化鉿在累增區的電容值也因漏電流值改善而皆高於無摻氟的二氧化鉿。在平能帶電壓遲滯量圖中看出有摻氟的HfO2遲滯量較無摻氟的HfO2來的低，可歸因於界面層的缺陷捕捉電荷現象因摻氟而減少。 對有摻氟及無摻氟的二氧化鉿MOSC元件給予定電流(CCS)及定電壓(CVS)應力，可觀察出有摻氟和無摻氟的二氧化鉿在定電流(CCS)及定電壓(CVS)應力下的可靠度。在高頻的C-V曲線下，摻氟的HfO2在平能帶電壓偏移量和stretch out的現象獲得改善而變小，這是因為氟離子摻入在HfO2/Si界面中，使鍵結更強並減少因電性應力下所造成的鍵結破壞。這可從mid-gap interface trap density的結果中可被證實，有摻氟的HfO2閘極介電層的mid-gap interface trap density (ΔDitm)會比無摻氟HfO2閘極介電層低。 從實驗的數據中，可以發現摻雜氟離子的最佳濃度。氟離子摻雜劑量超過5E15 ions/cm2時，會使得漏電流、遲滯量以及CVS、CCS應力下的平能帶電壓偏移量、界面陷阱濃度改善效果降低。因此，若我們特地的將氟摻入MOS元件中，可以增加元件的可靠度。
並列摘要
In this thesis, metal-oxide-semiconductor capacitors (MOSC) with high-k dielectric HfO2 deposited by metal-organic chemical vapor deposition (MOCVD) were fabricated, and fluorine ions were deliberately implanted into the HfO2 and HfO2/Si interface. Room temperature current-voltage (I-V) and capacitance-voltage (C-V) characteristics were obtained to compare the differences of the electrical and reliability properties of the MOSC with HfO2 gate insulator having and having not fluorine doped interface. It is known that fluorine incorporation at the interface of gate insulator can reduce the dangling bonds at the interface and passivate the bulk traps in the HfO2 gate dielectric, hence improve the HfO2 thin film characteristics. Since the re-crystallization temperature of HfO2 film is low, an annealing at temperature higher than 500℃ might cause HfO2 thin film to re-crystallize and thus weaken the insulation property of the gate dielectric. When fluorine is incorporated, the HfO2 film will transform into HfOxFy which has higher re-crystallization temperature than has the HfO2. Therefore, another advantage of fluorine incorporation in high-k dielectric is thermal stability improvement. It is found that the gate leakage current can also be decreased effectively after fluorine is introduced into the high-k gate dielectric HfO2, which can be inferred from the obvious increase in the accumulation capacitance of the MOSC. The hysteresis can also be reduced for the samples with fluorine incorporation due to the interface trap passivation. In this work, both the constant voltage stress (CVS) and constant current stress (CCS) were applied to all the samples to check the reliability issues caused by fluorine incorporation. We found that the fluorine-implanted samples exhibited smaller flan-band voltage shift and less stretch out in the high-frequency C-V curves. This is due to the incorporated fluorine ions at the silicon/dielectric interface enhance the bond strength and therefore decrease bond breakage during the application of stresses. This can be confirmed from the reduction of mid-gap interface trap density in fluorine-implanted samples as compare with those non-fluorine implanted samples. It is found that there exists an optimum concentration for fluorine incorporation. From our experimental data, we see that the improvement in leakage current, hysteresis, flat-band voltage shifts, and interface trap density vanishes when the incorporated fluorine concentration is larger than 5 X 1015 cm-2. Therefore, care should be taken if fluorine incorporation is to be used to improve the reliability of high-k dielectric in MOS devices.
參考文獻
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