高密度金氧半電晶體超大型積體電路動態存取記憶元件之高可靠性二氧化矽/氮化矽/二氧化矽複層膜的新製程技術─製程及分析

Abstract

本文研究等效厚度自69埃到138埃的氧氮氧動態記億電容的特性及可靠度。與傳統的熱二氧化矽薄膜比較，氧氮氧薄膜具有較小的漏電流及較大的崩潰電場，此種特色隨厚度之變薄而愈加明顯。在氧化矽及氮化矽層內各有不同的傳輸機構，且對溫度的變化有不同的反應。根據時間依賴介電質崩潰的方法，可預測氧氮氧記億電容的生命期。由固定電壓應力測量．可得其電場加速崩潰因素。由固定電流應力測量，可得陷阱效應的特性，並可得氧氮氧記億電容的電子通量。 電子通量較低是氧氮氧記億電容的主要缺點，在本實驗中利用：一、降低上層氧化溫度及縮短氧化時間；二、雙步驟低壓氣相沉積氮化矽；三、底層氧化矽加以氮化的技術，來舒解氧化矽和氮化矽間應力的問題，並將電子通量提高二十倍以上。

In this paper, the characteristics and reliability of the stacked oxide/nitride/oxide (ONO) films used in high-density DRAM charge storage capacitors (Teq=69A∼138A) have been studied. The SONOS capacitors are shown to have lower leakage current and higher field strength than the thin oxide capacitors, especially for the thinner SONOS capacitors. Fowler-Nordheim field-enhanced tunneling current is the dominant transport mechanism in oxide and Frenkel-Poole thernmal hopping current is the dominant transport mechanism in Si3N4, so they show different responses to temperature. The lifetime of SONOS was extracted from time-dependent-dielectric breakdown (TDDB) measurement. The field acceleration factor of SONOS was deduced from constant-voltage-stress. From constant-current-stressed V-t, we got electron fluence and trapping characteristics of SONOS. Since the major disadvantage of SONOS is its lower electron fluence, we use: (1) lower top oxidation temperature and shorter top oxidation time, (2) two-step LPCVD Si3N4, and (3) bottom oxide nitridation to increase the electron fluence of SONOS at least 10 times than the conventional SONOS.