快速加熱低壓化學氣相沈積氧化鉭薄膜之製備與電性

Abstract

本篇論文探討應用於動態隨機存取記憶體（DRAM）之氧化鉭薄膜的製程與性質。主要利用快速加熱製程的化學氣相沉積法（RT-LPCVD）來成長薄膜，配合不同的後續退火程序，包括在氧氣氛及一氧化二氮氣氛中以不同的溫度做快速退火處理，以期改善薄膜的電性與探討其差異原因。 在氧化鉭厚度效應的研究中，我們發現厚膜比薄膜有更好的結晶性，介電常數也較高，可高達65左右，同時漏電流也會降低。而在快速高溫退火的處理探討上，於一氧化二氮中作快速加熱退火的薄膜電性比在氧氣氛中有更好的結果，原因在於退火處理過程中，一氧化二氮氣體在高溫下會分解出活化氧原子而快速地滲入氧化鉭的薄膜內，並能有效填補結構內的氧缺陷及大幅降低薄膜內碳、氫雜質的含量，故有助於漏電流之降低；此外，相對於在氧氣氛中熱處理，一氧化二氮處理之薄膜介電常數值也較高。結論是：對於採用RT-LPCVD方法製備氧化鉭薄膜而言，750oC、在一氧化二氮中快速加溫熱處理30秒鐘是退火處理製程的最佳條件。 最後，為瞭解氧化鉭薄膜缺陷所扮演的角色，吾人利用等效電路來分析複數平面之各項交流數據，以瞭解薄膜退化與鬆弛現象和薄膜內部缺陷的關係，並進一步對缺陷定量探討。

Tantalum oxide (Ta2O5) thin films have been demonstrated to be highly promising storage dielectrics in DRAM applications. Low-pressure chemical vapor deposition (LPCVD) method was employed to grow the thin film in this study. The objectives was to study the effect of film thickness and the effect of O2 and N2O annealing at various temperatures on the electrical and dielectric properties of Ta2O5 films. The experiment shows that film thickness affects the dielectric properties and leakage current density of Ta2O5 films. Thicker films have better crystallinity, higher dielectric constant (about 65), and lower leakage current density than thinner films have. The annealing effects show that the RTA in N2O can effectively improve the film quality and electrical properties of Ta2O5 CVD films. The reason is that it reduces the carbonhydrogen contamination more effectively than O2 gas does, and releases the oxygen atoms to fill the oxygen vacancies more effectively. It concludes that the rapid thermal annealing process of annealing at 750oC in N2O ambient is the most optimal condition for Ta2O5 CVD films growth. Finally, the dielectric relaxation and the defect analysis of Ta2O5 thin films at 750oC with and without O2 and N2O annealing were investigated. Through the measurement of dielectric dispersion as a function of frequency (100Hz≦f≦10MHz), we study the trapping dielectric relaxation and defect quantity of the films, and propose an equivalent circuit on the basis of the capacitance, admittance, and impedance spectra.