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標題: | 微波選擇性摻雜劑激活機制的發現及其在實現重 n 型摻雜矽接面穩定性的作用 Discovery of a novel microwave-selective dopant activation mechanism and its role in junction stability for highly n-doped silicon |
作者: | 蔡俊雄 Chun-Hsiung Tsai |
指導教授: | 李世光 Chih-Kung Lee |
關鍵字: | 施者失活,摻雜劑空位簇,微波回火,熱穩定結,摻雜劑激活,施者,磷空位簇,外延矽,退火, donor deactivation,dopant vacancy clusters,microwave annealing,thermally stable junctions,dopant activation,donors,phosphorus vacancy clusters,epitaxial Si:P,annealing, |
出版年 : | 2022 |
學位: | 博士 |
摘要: | 在現代 CMOS 3D 晶體管架構、FinFET 和環柵 (GAA) 納米片晶體管中,源漏形成需要原位重摻雜外延矽層來滿足器件性能要求。然而,在過去 30 年中,眾所周知,施者(donor)在高摻雜半導體中往往會失活。當矽中的施者濃度高於 2 x 1020 at/cm3 時,將漸漸開始觀察到施者的失活並導致電導率下降。相關研究工作表明施者喜好以圍繞空缺(Vacancy)組態出現, 而根據摻雜濃度的高低施者失活機制是由於低階PV通過遷移和動態聚集(DnV,n=1-4)轉變為更高階P2V、P3V. 甚至在濃度高到1 x 1021 at/cm3 可進一步轉化為P4V等施者空位簇 (donor-vacancy cluster)。這是由於其負形成能P3V 和 P4V 在熱力學上是較有利的配置。因此,Si中的施者濃度越高,其表現出的熱穩定性越低,這造成可用的自由載流子濃度因此受到限制並且不能隨著供體化學濃度的增加而增加。現代 FinFET 和環柵(GAA)納米片晶體管結構的源漏極中使用的典型磷濃度通常高於 2 x 1021 at/cm3,因此源漏結存在嚴重的熱穩定性問題。然而,據目前所知,儘管施者失活的機制透過過去四十年各方研究已得到完整的理解, 但到目前為止,施者失活仍被視為熱回火的本徵問題因此還沒有關於這種現像是否可以得到緩解和解決的討論。雖然通過最先進的閃光或激光退火進行額外的外延後摻雜劑活化是目前增加活化摻雜劑的唯一方法,但其回火後活化摻雜劑的熱穩定性問題仍然存在。本研究的目的是進一步揭示供體失活的機制並提供有關施者空位簇 (DnV) 的更有用的電子特性,以便能鑒往知來可以開發一種替代退火解決方案,該解決方案不僅可以激活摻雜劑,還可以解決熱穩定性問題。通過從頭計算(ab initio calculation),我發現了施者空位簇更多有用的電子特性,如偶極矩、晶格振動頻率和形成能。本研究逐步應用這些特性之間的關係來開發實用的退火解決方案,以克服長期存在的供體失活問題並將早期關於供體失活機制的研究,即磷空位簇(PnV,n = 1-4)動態聚集形成模型擴展到 PnV 偶極矩的從頭計算。結合已知的 PnV 形成能,理論計算證明熱不穩定的低階 PnV(n = 1-3)總具有非零偶極矩而熱穩定的高階PnV則不具有淨偶極矩. 這個特別偶極矩分佈可被用於透過與震盪電場選擇性的交互作用實現選擇性摻雜劑激活。通過穩定和不穩定摻雜劑-空位簇之間的偶極矩區別,本研究嘗試開發一種能量選擇性相互作用退火方法來實現高 n 摻雜 Si 的熱穩定結(Junction)。選擇性摻雜劑激活工藝方案的實施有望通過消除不穩定的 PnV 來實現回火後只存在熱穩定的P4V從而實現穩定結。但對於擇性摻雜劑激活所需震盪電場邊界條件並非簡單可得,本研究將通過引入各種感受器(susceptor)配置來探索各種微波腔設置,以探索在低於 700 攝氏度的最佳感受器配置下選擇性摻雜劑激活是否可被實現,在最佳感受器配置找到之後再根據微波腔中感受器設置的位置及其相對於諧振腔的臨界尺寸對微波場的分佈進行了建模。 得出的結論是,在三重平行感受器基座之間建立駐波的能力是將微波能量有效耦合到矽晶格中的非活性摻雜劑結構的關鍵。最後,通過涉及霍爾測量、二次離子質譜 (SIMS) 和 XRD 以及正電子湮沒技術的薄膜表徵技術,以實驗與分析方法驗證選擇性摻雜激活的機制。 In modern CMOS 3D transistor architectures, FinFETs, and gate-all-around (GAA) nanosheet transistors, source-drain formation requires in-situ heavily doped epitaxial silicon layers to meet device performance requirements. However, it has been known for the past 40 years that donors tend to be deactivated in highly doped Si. When the donor concentration of phosphorus in silicon is higher than 2 x 1020 at/cm3, deactivation of the donors will start to be observed and lead to a decrease in conductivity. Relevant research has shown that donors prefer to move toward and form a structure around vacancies. At the doping concentration of 2 x 1020 at/cm3, through the migration and dynamic aggregation of donors and vacancies, the deactivation mechanism can asymptotically transform donors into PV pairs, P2V, and higher-order P3V, etc. P3V can be further converted into donor vacancy clusters such as P4V at concentrations up to 1 x 1021 at/cm3. This effect is due to the negative formation energy, which leads to the thermodynamically favorable configuration of P3V and P4V. Therefore, the higher the donor concentration in Si, the lower its thermal stability. This results in the available free carrier concentration being thus limited and challenging to increase with increasing donor chemical concentration. Typical phosphorous concentrations used in the source-drain of modern FinFET and gate-all-around (GAA) nanosheet transistor structures are typically higher than 2 x 1021 at/cm3, so the source-drain junction has serious thermal stability issues. To the best of our knowledge, although the mechanism of donor inactivation has been well understood through tremendous studies over the past four decades, donor deactivation has so far been regarded as an inherent problem of thermal annealing. Thus, no discussion existed on whether this phenomenon can be alleviated and resolved. Although additional post-epitaxial dopant activation by state-of-the-art flash or laser annealing is currently the only way to increase activated dopants, the problem of thermal stability of their post-annealing activated dopants persists. This study aims to reveal the mechanism of donor deactivation further and to investigate more useful electronic properties of donor vacancy clusters (DnVs) so that an alternative annealing solution beyond existing ones based purely on thermal effects can be developed. It not only activates dopants but also addresses long-term thermal stability issues associated with thermal-based annealing. Through ab initio calculations, several important electronic properties of donor-vacancy clusters, such as dipole moment, lattice vibrational frequency, and formation energy, are revealed in this work. The relationship between these properties will be used to develop practical annealing solutions to overcome the long-standing problem of donor deactivation. This work extended an earlier study on the mechanism of donor inactivation, namely the dynamic aggregation formation model of phosphorus-vacancy (PnV, n = 1-4) clusters, to calculate PnV dipole moments. Combining with the known PnV formation energies, theoretical calculations have demonstrated that thermally unstable lower-order PnVs (n = 1-3) always have a non-zero dipole moment while thermally stable higher-order PnV s do not have a net dipole moment. Particularly, the distribution of this dipole moment can be used to achieve selective dopant activation through selective interaction with Microwave oscillating electric fields. Due to the clear difference between stable and unstable dopant-vacancy clusters, I am trying to develop an energy-selective interaction annealing method to achieve thermally stable junctions of highly n-doped Si. Interaction of microwave electric fields with polar phosphorus vacancy clusters (PnV) is expected to eliminate unstable low-order PnV (n=1-3) structures, which are the major contribution to the de-activation process. As a result, the typical donor deactivation phenomenon can be effectively suppressed. However, the oscillating electric field boundary conditions required for selective dopant activation are not readily available. Various microwave cavity setups are explored by introducing various susceptor configurations to choose the optimal susceptor configuration. After finding the optimal susceptor configuration, selective dopant activation is successfully achieved. A model is also built for the microwave field distribution according to the location and dimension of the susceptor set in the microwave cavity. It is concluded that the ability to establish standing waves between triple-parallel pedestals is the key to the efficient coupling of microwave energy into inactive dopant structures in the silicon lattice. Finally, Hall measurements, secondary ion mass spectrometry (SIMS) and XRD, and positron annihilation techniques are applied for characterizations. It is experimentally and analytically verified to support the mechanism of selective doping activation. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/89676 |
DOI: | 10.6342/NTU202204032 |
全文授權: | 同意授權(全球公開) |
顯示於系所單位: | 應用力學研究所 |
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