不同前驅物質沉積的HfO2高介電材料特性及可靠度比較

本論文對高介電材料二氧化鉿 (HfO2) 材料特性、電性、以及可靠度的分析作一詳盡的研究。主要針對不同沉積厚度、不同前趨氧化劑、以及不同次數的沉積-退火製程等對二氧化鉿薄膜之影響；來了解高介電材料二氧化鉿在未來積體電路製程中應用上可行的方向。對於不同的二氧化鉿沉積厚度，可發現越厚的薄膜在退火後有越明顯的結晶狀態、較高的表面粗糙度、以及較低的薄膜密度；同時在電性上，其電容元件有較高的本體層介電常數、較高的 EOT、較高的遲滯、較小的平帶電壓、以及較低的漏電流密度；而在崩潰電場以及介電材料崩潰失效時間等可靠度，也是越厚的薄膜有較佳的特性；因此，當二氧化鉿厚度微縮時，二氧化鉿薄膜所造成的電性及可靠度影響將需要去考慮。利用氧化劑 O3 所沉積的二氧化鉿薄膜，相較於氧化劑 H2O 所沉積的二氧化鉿薄膜，除了有較厚的介面氧化層的缺點，在材料特性、電性、以及可靠度皆有較佳的性能。比較相同 EOT 值的二氧化鉿薄膜，氧化劑 O3 所沉積的二氧化鉿薄膜有較高的薄膜密度、較低的表面粗糙度、較低的結晶狀態、較理想的二氧化鉿比例、以及較少的雜質，因此在電性上有較小的漏電流、較小的平帶電壓、遲滯，同時在應力施加下有較少的電荷累積，造成有較長的可靠度壽命。使用多次沉積-退火的製程的二氧化鉿薄膜，可發現到經過多次沉積-退火步驟沉積出來的二氧化鉿薄膜晶相為單晶，其薄膜密度較接近理想，並且 EOT 值會下降，因此在電性上有較低的漏電流密度，較小的遲滯，以及在靜態與動態應力施加下可靠度也較佳。

關鍵字

原子層沉積；高介電質借電材料；二氧化鉿；可靠度；多次沉積-退火

並列摘要

In this thesis, three different experiments were used to study the physical properties, electrical characteristics, and reliability performance of high-k dielectric hafnium oxide (HfO2) deposited using atomic layer deposition method. The experimental topics are: (1) Effect of hafnium oxide deposition thickness, (2) Comparison of the different deposition oxidant (H2O versus O3) for hafnium oxide film, (3) Effect of multiple-step annealing (DADA) process on the hafnium oxide film. First, regarding to the thickness effects of HfO2 films deposited by ALD on the electrical properties and reliability, the experimental results shows that scaling the physical thickness of the HfO2 dielectric did not increase the capacitance as expected due to the thicker interfacial SiOx layer obtained by the oxidation process in thermal annealing. Additionally, extend of HfO2 crystallization is significantly reduced after the thermal annealing in scaling the HfO2 thickness. After thermal annealing, HfO2 crystallization increased with the thickness of HfO2 film, which then increases the dielectric constant for the bulk HfO2 film. The breakdown behaviors of the HfO2 gate dielectric film were not scaled to thickness, improved with HfO2 thickness until saturation. The reliability characteristics of the HfO2 dielectric under unipolar AC stressing were also evaluated. Dielectric breakdown failure time of unipolar AC stressing becomes longer in comparison to that stressed in constant voltage stress. As the thickness of the HfO2 dielectric increases, a larger lifetime enhancement is detected due to the effective charge de-trapping for thicker dielectrics under AC stressing. Second, the hafnium oxide film deposited with oxidant H2O has a thinner interfacial layer, but the bulk HfO2 layer has a worse quality as compared to the O3 oxidant. In the case of the annealed HfO2 films with a comparable equivalent oxide thickness (EOT), O3 oxidant-based HfO2 films have superior electrical properties and reliability performance. Furthermore, using the dynamic stress, including unipolar and bipolar stresses, increases the time to dielectric breakdown for both HfO2 films. However, a larger enhancement was observed in the HfO2 films grown using H2O oxidant under bipolar stress due to more de-trapping phenomenon. Third, the HfO2 films manufactured by DADA process not only have the single crystal phase and idea film density, but also decline the EOT value. Therefore, the resulting HfO2 films have a lower leakage current density and lower hysteresis on electrical properties. Moreover, they have better reliability under static and dynamic stress.