含氟氣體蝕刻二氧化鈦之研究

Abstract

近年來氮化鈦已經使用在雙硬遮罩雙鑲嵌銅導線製程中(dual-hardmask dual damascene patterning)的金屬硬遮罩，此結構可以有效的減少低介電常數介電層在去光阻製程(ashing)時因受到電漿攻擊和與光祖接觸所造成的傷害。然而，在蝕刻選擇比允許的情況下氮化鈦硬遮罩的厚度愈薄愈好，因為愈薄的遮罩會有愈小的應力殘留，進而避免導線受應力影響造成的彎曲，此外更薄的膜也可以擁有更好的光學穿透度以便有更好的校準度。經由上述的原因讓我們想到以二氧化鈦來取代氮化鈦來做金屬硬遮模，因為二氧化鈦擁有良好的可見光穿透度且二氧化鈦比氮化鈦有更強的化學鍵結，如此會有更好的蝕刻抵抗能力。 本論文中，藉由反應式離子蝕刻機(reactive ion etch)和生產用的蝕刻系統，我們研究二氧化鈦作金屬硬遮模在介電層蝕刻物質下(例如含氟為主的蝕刻劑)蝕刻的行為和機制。此外，藉由比較二氧化鈦和電漿輔助沉積的四乙氧基矽烷(PE-TOES)二氧化矽的蝕刻速率來當做蝕刻選擇比的研究，鈦化氮也做與PE-TOES蝕刻速率比較來判斷蝕刻選擇比。具體實驗上，我們使用在雙鑲嵌製程常用的借電層蝕刻劑，好比四氟甲烷混氧氣和藉由三氟甲烷混不同比例的碳氟化合物產生不同碳氟比氣體的蝕刻劑來做研究。本研究探討了不同氧氣比例的四氟甲烷混氧氣氣體的蝕刻速率和選擇比在不同能量和壓力下的影響，以及不同碳氟比對蝕刻速度和選擇的影響。在本研究中，二氧化鈦最高有15.8倍蝕刻選擇比於PETEOS，而在同樣的情況下氮化鈦只有8.1倍。

Titanium nitride (TiN) has been adopted as a metal hardmask in the dual-hardmask dual damascene patterning of dielectrics during the fabrication of copper interconnects. This minimizes plasma damage on the low-k interlayer dielectric, which is not exposed to photo-resist ashing steps. However, the thickness of TiN hardmask should be further reduced to avoid line-bending due to high residual stress and offers higher transparency for alignment, if the etch selectivity is high enough. This prompts us to explore TiO2 hardmask as the replacement for TiN because TiO2 is transparent in the visible light and may have better etch resistance due to its stronger chemical bonding. In this thesis, the etch behavior and mechanism of TiO2 as metal hardmask under dielectric etch chemistries, i.e. fluorine-based etchants were investigated using a reactive ion etch (RIE) and a commercial etch system. In addition, the etch selectivity of TiO2 relative to plasma enhanced tetraethylorthosilicate (PE-TOES) oxide in the dual damascene scheme was studied and compared to that of TiN hardmask. In specific, CF4/O2 and CHF3/CxFy at various F/C ratio were used as the etchants, which were the representative chemistries in the etching of dielectrics in the dual damascene patterning. The etch rate and etch selectivity as function of O2 ratio in CF4/O2 under different reaction conditions such as power and pressure were examined. The effect of F/C ration the etch rate and etch selectivity of TiO2 and TiN was also studied. In this study, TiO2 was found to have a high etch selectivity, 15.8 relative to PETEOS oxide, compared to 8.1 for TiN hardmask.