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標題: 動態隨機存取記憶體鈦酸鍶鋇薄膜之研究
A Research on (Ba,Sr)TiO3 Thin Films for Dynamic Random Access Memory Applications
作者: 林晉慶
Lin, Chin-Ching
關鍵字: (Ba;鈦酸鍶鋇;Sr) TiO3;Plasma Etch;Electrode;Dynamic Random Access Memories;電漿蝕刻;電極;動態隨機存取記憶體
出版社: 精密工程研究所
高介電電容是高密度動態隨機存取記憶體之重要元件,鈦酸鍶鋇(BST)薄膜是製作電容之重要材料,而薄膜所使用之下電極材料更是影響其特性之關鍵。由於傳統的金屬電極及氧化物電極,存在著一些先天上的缺點,所以研究新電極有其必要性。在傳統電極中鉑(Pt)與銥(Ir)具有優於其他電極的電特性,但為了改善電極本身之缺陷使薄膜電容的特性更佳,所以使用Pt與Ir作為基礎電極材料,利用Pt/Ir多層結構之變化可研製出在工作電壓1.5 V時,其漏電流小於1×10-7 A/cm2及介電常數為240的理想下電極。
乾式蝕刻製程,為目前縮小元件積體化重要的關鍵技術之一,因此本論文使用高密度電漿技術對鈦酸鍶鋇與電極蝕刻機制與電漿導致的傷害進行一連串的研究,也以Langmuir探針電漿檢測系統對一些常用的電漿製程參數進行探討。從鈦酸鍶鋇蝕刻後的結果發現,在Ar/Cl2的混合氣體下,加入30% Cl2 、ICP功率800 W、rf功率100 W 和腔體壓力0.67 Pa時,可以得到蝕刻率佳(60 nm/min)且表面平滑沒有殘留物的表面。然而在蝕刻時會因一些電漿傷害而改變薄膜電容的特性,本論文以Pt/BST/Pt的電容結構針對漏電流與介電常數的變化探討其電漿導致傷害的機制,並對其電性恢復的方法進行研究。研究結果發現電漿會造成漏電流提高與介電損失,其中入射離子能量的提高可能為主要的影響因子。最後對於電漿傷害的元件,在經由氧氣600℃的熱處理後發現其可有效率的恢復元件電性,其漏電流在1.5 V的偏壓下可由原先的5×10-5 A/cm2改善至小於3×10-7 A/cm2。而在電漿蝕刻研究的後期,將其研究重心放在對電漿蝕刻所造成的損害補償上;在以電漿蝕刻鈦酸鍶鋇電容元件的上電極方面,以不同的恢復機制去探討蝕刻上電極對電容元件所造成之影響。
最後,研究使用不同電漿氣體對Pt/BST/Ir結構的電容的影響,由於以Ir金屬作為下電極之BST電容中其漏電流值偏高(5x10-5 A/cm2),所以使用電漿處理來改善其電特性。而在研究中發現此結構之薄膜電容在650°C氧氣環境下熱處理後,再以氧氣電漿進行表面處理可以降低漏電流至少兩個數量級,同時改善其可靠度在1.2 V的工作電壓下達十年以上,藉以提高BST薄膜電容之效能。

One of the key processing issues involved in the integration of Barium strontium titanate (BST) capacitor device into the existing dynamic random access memories (DRAMs) process is using for material of electrodes and the etching of these films. Due to the traditional electrodes are included the metal and oxidization electrodes exist some defect in natural. Therefore, we will consider developing the other novel electrodes. For the electric property of the platinum (Pt) and iridium (Ir) are better than the other electrodes, but in order to improve the defects of the Pt and Ir electrodes. Thus, we use the Pt and Ir metal to design the structure of bottom electrodes to conform to our ideal.
Moreover, in this study, the high-density plasma etch technique suitable for the BST films and related electrodes will be developed. A chemically assisted etch of BST was obtained under various Cl2/Ar gas mixtures. The etch profile along with etch anisotropy was observed as a function of etching parameters by scanning electron microscopy. A smooth surface with no residue was observed under 30% Cl2 in Ar/Cl2, ICP power of 800 W, RF power of 100 W, and 5 mTorr. However, the etching process may induce plasma damage, quantitative analysis of the etching damage was attempted to discuss the mechanism of leakage current density and dielectric constant with various rf power and ICP power on Pt/BST/Pt capacitor. In this work, this damage can be effectively recovered with annealed at around 600C in oxygen ambience and the leakage current density is less than 310-7 A/cm2 under applied voltage of 1.5 V. In order to comprehend the recovery effects for etching high-k capacitors. Therefore, the study will focus the issue on the recovered mechanisms after the etching process.
Finally, the effects of plasma treatment, using NH3, N2O and O2 gases, of (Ba,Sr)TiO3 films on the leakage and dielectric properties of the Pt/(Ba,Sr)TiO3/Ir capacitors were investigated. In this work, the oxygen plasma treatment could effectively improve the leakage current property and reliability for the BST films capacitor.
Appears in Collections:精密工程研究所

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