利用奈米壓痕與刮痕系統研究退火應變矽鍺磊晶薄膜之機械行為

Abstract

摘 要 半導體矽鍺合金材料，運用於異質接合雙極性電晶體(HBT)以及互補金屬氧化物半導體(CMOS)，其優異電子特性，故而可取代傳統矽材。而矽鍺合金與矽材存在著晶格不匹配，往往於熱處理製程中，讓薄膜內應力釋放從而表面不平坦進而發生缺陷擴散，此狀態將降低應變矽鍺原之特性。本研究提出對應臨界厚度矽鍺應變薄膜成長方式中，改變沉積條件與不同條件退火後之矽鍺薄膜，利用微應力施加之奈米壓痕與刮痕技術分析，探討其相對應磊晶薄膜之品質，分析結論如以下三部分: (I) 將單一層矽鍺合金試片(500奈米) 以400,500, 600度作退火處理，以原子力顯微鏡技術與奈米刮痕系統，並分別施力2000,4000, 6000 μN，分析矽鍺合金之耐磨耗破壞特性，繼之，微結構利用穿透式電子顯微鏡分析，結果顯示400度退火熱處理後，未退火試片的抗磨耗特性相對而言是增加的，其退火後內部應力釋放導致差排增生，將有助於臨界抗磨耗力之問題釐清，並證實退火後之黏着力與分層失效機制。 (II) 將矽鍺合金(530奈米的厚度)以400與 500度作退火處理，由奈米壓痕系統分析，多層次矽鍺合金得到部分的硬度提升，而斷面分布以原子力顯微鏡技術分析。實驗證實退火處理後之硬度、彈性模數效應，對應之力位移變化曲線，因壓痕導致內部差排之產生與滑移機制，與其相對應的多層界面結構之影響，將具有較佳的機械特性。 (III) 延續多層次矽鍺合金之主題，試片經由磨潤系統作動態測試，得到以下結論，第一:於探針進給線上與刮痕兩側，而較高之磨擦係數會發生於6000μN施力。第二:當探針刮痕伴隨之碎削減少，於高退火熱處理，體積變形較為穩定，可推論退火試片具較佳韌性。而犁削機制將主導刮痕的過程。內部差排顯著影響表面磨耗現象，同時也影響磨潤特性，故而可藉由差排機制改變，來分辨矽鍺合金之退火韌性與結合力的關係。 綜觀本論文實驗結果，由奈米刮痕技術分析，可觀察應變鬆弛及缺陷之現象，同時藉低溫退火，讓矽鍺薄膜對應之應力鬆弛，退火應變鬆弛將伴隨差排缺陷產生，從而觀察黏著與附著失效之機制，並證實硬度與彈性係數隨著熱處理溫度上升而增加。

Silicon-germanium (SiGe) material has recently become the most attractive semiconductor thin film in HBT (Heterojunction Bipolar Transistor) and CMOS(Completed Metal Oxide Semiconductor) because of its outstanding behavior. Nevertheless, due to the lattice mismatch between SiGe alloys and Si substrate, several phenomena after annealing, may occur in their growth and post-treatment including roughed surface, interdiffusion and partial strain relaxation of SiGe thin films. In this study, several conditions to analysis the quality of critical thickness in strained SiGe thin film by Nanoindentation and Nanoscrach system have been uesd. The conclusions are as below:

(I) The present study evaluates the wear performance of silicon-germanium (SiGe) epitaxial growth of thin films (a 500-nm-thick), in which the in situ scratch profile is followed by ex situ atomic force microscopy (AFM) examinations. The wear evaluation of SiGe films was carried out at different constant loads (2000, 4000, and 6000 μN) with the same sliding speeds after anneal(400,500,600°C). The results show that annealing treatments of SiGe films exhibit the highest scratch resistance at 400 °C compared to that of the as-deposited sample. The main characteristic of the SiGe film is its ability to withstand wear resistance; observations show that moderate compressive residual is beneficial to the film, since it can suppress crack initiation. The annealing treatments of SiGe films revealed the resultant adhesive and cohesive failure mechanism.

(II) Multilayer SiGe samples (a 530-nm-thick) for ex situ thermal treatments in the furnace system (400 and 500 °C) were uesd. The periodic multilayer SiGe with different annealing conditions measured by a commercial nanoindenter observed the slight increase in hardness. The cross-section profile and the microstructure of SiGe multilayer films were characterised by means of atomic force microscopy and transmission electron microscopy. The effect of the thermodynamics of the thin film/substrate system is evidenced by annealing treatment. It is demonstrated that the SiGe multilayer films are more susceptible to plastic deformation while annealing treatments are carried out. The misfit dislocations in the critical pileup event were observed in the periodical SiGe multilayer that can be relaxed at thermal annealing, thus providing the nanomechanical performance.

(III) Wear characteristics of thermal multilayer SiGe were also investigated. Firstly, the pile-up phenomena and different features happened on each sides of scratch line of SiGe films under variation of thermal conditions. Higher coefficients of friction were set at 6000μN, rather than 3000 μN. Second, the worn surface of the multilayered becomes tougher while the size of the debris becomes less. One can observed that cracking displays in the case of SiGe films while ploughing dominates during the scratching process. It is concluded that the thermal treatment not only produced misfit dislocations in the form of a significantly wavy sliding surface but also promoted wear behaviors; subsequently, dislocations glide may changes the performance of toughness and adhesion of SiGe films by nanoscratch system.