高介電質材料氧化鑭之研究

Abstract

近年來，因為線寬的不斷縮小加上記憶體技術的快速發展，有相當多的研究投入高介電質材料的領域，亦已獲得了相當的成功。 有些高介電質材料技術已相當的成功，如鈦酸鍶鋇( BST, 介電質常數為200)，五氧化二鉭( Ta2O5, 介電質常數為30~75)等。 但，這些高介電質材料卻有一些缺點。 其中之一就是在高介電質材料與矽的界面上會產生互相擴散的現象。 對沉積在矽上的鑭直接氧化以形成氧化鑭作成的高介電質材料可消除這個現象。 我們作出了以此種高介電質材料作為閘極介電質的金氧半場效電晶體和電容。 藉著對電容的量測，可以得到厚度為33 Å的氧化鑭，其介電質常數為27，換算其等效厚度為4.8 Å。 從金氧半場效電晶體在閘極電壓為零時的高驅動電流及高電導值也證明了此材料擁有高介電質材料特性。 此材料之偏壓引起的漏電流(SILC, stress induced leakage current )及崩潰累積電荷的特性，與二氧化矽相比皆有相當好的表現，亦證明了其可靠度較佳。 之所以能達成如此的二氧化矽等效厚度，是因其對熱及氫氣回火時的穩定性高所致。

In recent years, there are large amounts of research and development of high K material for the reason of the scaling down and burst improvement of memory technology. The high K technology has reached a colossal success, just like BaSrTiO3 (BST, K=200), Ta2O5 (K=30~75), etc. But, there are several kind weaknesses of these developed high-K materials. One of them is the interfacial diffusion between the interface of the high K material and Si. For eliminating this effect, high K La2O3 gate dielectrics has been developed by using a process of direct thermal oxidization of deposited La. Using this high K material as the gate dielectric, MOSFETs and MOS capacitors have been fabricated. From the measurement of capacitance, the 33Å La2O3 has a K value of 27 that has an equivalent oxide thickness of 4.8 Å when considering the quantum correction. This high K is further evidenced from MOSFETs’ high current drive and high charge-to-breakdown comparable with SiO2 are obtained that demonstrates excellent reliability. Good dielectric integrity is evidenced from the low leakage current density of 0.06A/cm2 at -1V, high effective breakdown field of 13.5 MV/cm, low interface density of 3x1010ev-1cm-2. The achieved low equivalent oxide thickness is due to the high thermodynamic stability on Si and also stable for hydrogen annealing up to 550ºC. ENGLISH ABSTRACT………………………………… ii ACKNOWLEDGEMENT……………………………… iv CONTENTS………………………………………………v TABLE CAPTIONS………………………………………vi FIGURE CAPTIONS……………………………………vii CHAPTER 1 INTRODUCTION………………………… 1 CHAPTER 2 EXPERIMENTAL………………………… 4 CHAPTER 3 RESULTS AND DISCUSSION…………… 6 CHAPTER 4 CONCLUSIONS………………………… 11 REFERENCES……………………………………………12 TABLES…………………………………………………15 FIGURES……………………………………………… 16