低熱預算處理之雷射濺鍍製備鈦酸鍶鉛薄膜之電性探討

Abstract

由於鐵電材料通常需要高溫後處理來得到好的結晶性及鐵電性質，不過高溫所造成的高熱預算將會導致許多問題，比如說鐵電材料與矽基材的交互擴散、摻雜載子介面處的變形等等。因此，為了使鐵電材料能夠匹配於矽製程中，降低其結晶溫度是不可或缺的。在此論文中，我們介紹了低溫及低熱預算的鐵電薄膜製備及後處理方法。 我們使用沈積於Pt/Ti/Ox/Si基底結構上之低結晶溫度(Pb,Sr)TiO3 (PST) 鐵電材料作為電容式1T-FeRAM之探討。此PST薄膜在低溫下採用雷射剝鍍方法於基版溫度200度下製備。首先，我們從傳統的後續熱處理方法（快速退火（RTA），爐管退火（FA））的結果得知，較大的熱應力造成表面龜裂及介面掀起。 因此，改採用新穎的後續熱處理方法（準分子雷射退火（ELA））來抑制上述的問題。PST薄膜以不同的雷射能量密度及雷射能量在基版溫度300度熱處理。我們從電性量測及物性分析可以得知明顯的鐵電特性改善，而且更進一步的瞭解再結晶的現象只有發生在表層區域。經由合適的雷射能量密度及雷射能量的控制可以得到較好的結晶特性的改善。 除此之外，ELA及RTA熱處理方法的結合可以大大改善整層薄膜的結晶性及鐵電性。在經過可靠度包括Fatigue, Imprint, TDDB的測試之後，經ELA及RTA結合熱處理的PST薄膜有著不錯的可靠度特質。最後，我們成功的利用低溫後續熱處理達到整層較好的結晶特性及鐵電特性，此一特性使之成為電容式1T-FeRAM的最佳選擇。

Since high temperature post-annealing for ferroelectric materials was usually required to get the fine crystallinity and ferroelectric characteristics. But many trouble issues was induced by the high thermal budget, such as the inter-diffusion of ferroelectric and substrate, and the deformation of junction profile etc. Therefore it is essential for the reduction of post-annealing temperature in order to make the ferroelectric material compatible the Si-base fabrication process. In this these, low temperature and low thermal budget for fabrication and post-annealing methods are introduced in this thesis. The (Pb,Sr)TiO3 (PST) ferroelectric material with low crystallization temperature was deposited onto the Pt/Ti/Ox/Si substrate for the research of capacitor type 1T-FeRAM. The PST thin film was fabricated by pulse-laser-deposition (PLD) method at low substrate temperature 200oC. At first, the results of conventional post annealing methods (Rapid Thermal Annealing (RTA), Furnace Annealing (FA) were acquired, witch surface cracks and interface lift were found by lager thermal stress. Therefore, novel post-treatment for Excimer Laser Annealing (ELA) method was introduced to suppress the above troubles. The PST thin films were irradiated with conditions of different laser energy density and shot number at low substrate temperature 300oC. The improvement of ferroelectric characteristic was apparently observed from electrical measurement and physical analysis, and it is further inferred that the crystallization phenomenon was occurred only on the surface region. The better improvement for crystallinity was found by appropriate control of laser energy density and shot number. Besides the larger improvement on crystallinity and characteristic of whole thin film were obtained with the combination of ELA and RTA post-treatment. The fine reliability properties for PST thin film with treatment of combination of ELA and RTA method were acquired after Fatigue, Imprint, and TDDB tests. Finally, the better crystallization and ferroelectric characteristic of the whole PST thin film treatments had been successfully achieved under low temperature post-treatment, and it is excellent for the most promising candidate in capacitor type 1T-FeRAM applications.