鉭電極與鈦酸鍶鋇薄膜電容之可靠性與製程整合研究

Abstract

本論文係採用射頻濺鍍的方式，在不同射頻瓦數(500 W, 700 W及 1000 W)及工作氣氛(Ar/O2 = 50/0, 40/10)下，沉積鈦酸鍶鋇(BaxSr1-xTiO3；BST)薄膜於Ta/SiO2/Si、Cu/TaN/SiO2/Si及Ta/Cu/TaN/SiO2/Si基材上。經不同條件的退火處理與電漿處理後，製備金屬-絕緣體-金屬(metal-insulator-metal；MIM)結構，探討可靠性與整合製程的性質。 實驗結果發現隨著射頻瓦數越高，表面粗糙度越低，Ta/BST(1000 W、Ar/O2 = 50/0)/Ta結構的漏電流在1 MV/cm的電場下更可達到1×10-8 A/cm2。此外，漏電流的對稱性也隨著射頻瓦數增加而變好，顯示射頻瓦數愈高，較不受到界面粗糙度的影響。從歐傑縱深成分分析的結果，經退火400℃後，鉭底電極與BST薄膜間所形成的氧化鉭(Ta2O5)很薄。而經退火500℃後，則形成一層較厚的Ta2O5，並對漏電流機制與電容密度的影響很大。 在漏電流機制上，預沉積BST薄膜(500 W、Ar/O2 = 50/0)及BST薄膜(500 W、Ar/O2 = 50/0)經退火400℃後在低電場時屬Schottky emission，而高電場則是Poole-Frenkel effect主導。BST薄膜(500 W、Ar/O2 = 50/0)經退火500℃後，則為介電鬆弛電流(dielectric relaxation current)；此外，1000 W、Ar/O2 = 50/0所沉積BST薄膜的漏電流機制亦屬dielectric relaxation current。 而BST/Cu結構在退火400℃後有產生hillocks，顯示銅已擴散至表面，但BST/Ta/Cu在退火400℃後並無產生hillocks且銅沒有向上擴散，此因鉭能阻礙氧擴散並抵擋銅擴散。在漏電流機制，Cu/BST/Cu與Cu/Ta/BST/Ta/Cu在低電場下為Schottky emission，高電場下則為Poole-Frenkel effect主導。

The deposited method in this thesis was adopted the R.F sputtering. The BaxSr1-xTiO3 (BST) thin films were deposited on the Ta/SiO2/Si, Cu/TaN/SiO2/Si and Ta/Cu/TaN/SiO2/Si substrates under the different R.F power (500 W, 700 W, 1000 W) and working gas (Ar/O2 = 50/0, 40/10). After the annealing and plasma treatment under different conditions, the characteristics of reliability and process integration were discussed. From the results, it was found that the BST thin films were smoother as the RF power increasing. The leakage current of Ta/BST(1000 W, Ar/O2 = 50/0)/Ta structure was 1×10-8 A/cm2 under 1 MV/cm. Moreover, the symmetry of the leakage current was better as the RF power increasing. It revealed that the roughness does not affect the symmetry under high RF power. From the results of depth profile of Auger electron spectrometer (AES), the formation of Ta2O5 was thinner between the Ta bottom electrode and BST thin films after annealing 400 ℃, however, it was thicker after annealing 500 ℃. The thicker Ta2O5 layer was strongly effect on the leakage mechanism and capacitance density. Under the lower electric field, the leakage current mechanism of the as-deposited BST thin films(500 W、Ar/O2 = 50/0) and BST thin films (500 W、Ar/O2 = 50/0) after annealing 400 ℃ were Schottky emission. Under the higher electric field, however, it was dominating by Poole-Frenkel effect. The leakage current mechanism of BST thin films (500 W, Ar/O2 = 50/0) after annealing 500 ℃ was the dielectric relaxation current. In addition, it was also the dielectric relaxation current for the as-deposited BST thin films deposited at 1000 W in Ar/O2 = 50/0 ambient. The BST/Cu structure after annealing 400 ℃, nevertheless, was formed the hillocks. It was indicated that the Cu atoms were out-diffused to the surface. It was not formed the hillocks for BST/Ta/Cu structure after annealing 400 ℃ because the Ta layer can efficiently resisted the diffusion of oxygen and Cu atoms. In the leakage current mechanism, the Cu/BST/Cu and Cu/Ta/BST/Ta/Cu structures were Schottky emission, and it was dominating by Poole-Frenkel effect.