中子轉換摻雜技術 (Neutron Transmutation Doping，NTD) 由於具有高度摻雜均勻性及摻雜濃度易於掌控的特性，已被公認是一種在半導體製程技術中無可取代的摻雜方法。NTD的作用原理係藉由中子照射，使材料中的特定同位素吸收中子後，透過一核反應轉化為新元素。以矽而言，其同位素30Si透過（n, ）反應轉變成31P；而鍺則是由其同位素70Ge、74Ge及76Ge分別轉變成71Ga、75As及77Se。然而進行中子照射過程中不可避免地會引入晶格損傷，因此需透過合適的退火條件修復損傷並活化載子。本論文藉由電性以及缺陷分析，來探索矽、鍺兩種半導體材料在中子照射之後，經由不同退火條件下的摻雜特性及缺陷行為，希望藉此能夠更深入了解中子轉化摻雜的各項影響因子。
本研究所使用的試片樣品為本質矽以及本質鍺晶片，中子照射實驗進行於清華大學所屬的THOR (Tsing Hua Open-pool Reactor) 水池式反應器，在反應器功率運轉於1.5 MW時進行照射，並分別接受不同通量與不同能譜的中子照射。中子照射後，分別對矽及鍺試片進行氮氣氛圍下的等時退火，矽試片退火條件為400～800 oC，持溫0.5～2小時；鍺試片則為300～500 oC，持溫1～6小時。接著，使用四點探針、霍爾量測儀及微波光電導量測來進行試片的摻雜特性分析，藉此得到材料的電阻率、載子濃度、載子電性、載子遷移率以及少數載子生命期等特性；藉由電子自旋共振光譜儀，來辨識晶格內部的缺陷組態；最後，透過展阻分析儀來驗證材料內部的自由載子摻雜之均勻性。
實驗結果顯示，後續的退火處理可有效的修復晶格損傷以及活化載子。矽試片中由30Si轉化而成的31P可使載子電性呈現n型摻雜，而鍺試片中轉換出的71Ga、75As及77Se可使載子電性呈p型。為使晶格缺陷有效修復及載子活化，矽的退火溫度至少須達800 oC，鍺至少須達500 oC；值得一提的是，由於鍺的熱中子吸收截面較矽來得高，故在同樣的中子照射通量之下，鍺材料會得到較高的載子濃度。此外，當退火未能完全修復材料損傷時，其晶格缺陷仍會主導材料電性。最後，由展阻分析結果驗證了中子轉化摻雜可具有絕佳的摻雜均勻性。

Neutron transmutation doping (NTD) has been considered as a superior approach in introducing dopants in semiconductors due to its advantages of good controllability and extreme homogeneity in dopant concentration. The mechanism of NTD is based on the nucleus transmutation by neutron irradiation of semiconductors. In NTD-Si, 31P dopants can be transmuted through the（n, ）nuclear reaction of the isotope 30Si, while NTD-Ge relies on the transmutation of three isotopes of 70Ge, 74Ge, and 76Ge into three stable nuclides of 71Ga, 75As, and 77Se, respectively. However, neutron irradiation would induce lattice damage in semiconductors, and an adequate thermal annealing process is thus needed to recover the damage as well as to activate the transmuted dopants. For this reason, the purpose of this study is to establish the process of NTD such that the temperature-dependent doping properties and lattice defect behavior in NTD-Si and NTD-Ge can be investigated in depth by the electrical measurements and spectroscopic defect analyses.
The specimens employed in this study were intrinsic silicon and germanium wafers. The neutron irradiation experiments of the specimens were carried out using the Tsing Hua Open-pool Reactor (THOR) operated at 1.5 MW. The specimens were irradiated with different thermal neutron fluences and neutron spectra. After neutron irradiation, the isochronal annealing was performed to anneal the irradiated specimens in N2 ambient. For silicon specimens, the annealing process were annealed at 400-800 oC for 0.5-2 hours, and for germanium ones were annealed at 300-500 oC for 1-6 hours. Four-point probe, Hall Effect analyzer, and microwave photoconductance decay (µ-PCD) were employed to determine the doping properties of the specimens, such as resistivity, carrier concentration, carrier type, mobility, and minority carrier lifetime. The lattice defects in NTD specimens were detected by electron paramagnetic resonance (EPR). Finally, the carrier density versus depth was identified by spreading resistance probe system (SRP).
The results revealed that subsequent thermal annealing treatments can repair the lattice damage and activate the transmuted dopants. The transmuted 31P dopants in the NTD-Si specimens lead to the n-type electrical conduction. In NTD-Ge ones, the transmuted 71Ga, 75As, and 77Se dopants lead to the p-type electrical conduction. The NTD-Si specimens require an annealing temperature of 800 oC to well recover the lattice defects and activate the dopants, while the NTD-Ge ones require an annealing temperature of 400 oC. Due to the fact that germanium corresponds to a larger neutron absorption cross section than silicon does, a higher dopant concentration can be achieved in NTD-Ge than that in NTD-Si under the same neutron irradiation time. In addition, when the annealing temperature is lower than that for full recovery, the residual lattice defects would form defect levels and dominate the electrical properties of specimens. Also, the excellent doping homogeneity of NTD process can be verified from the results of SRP analysis. 

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