銅化學氣相沈積之基板電漿前處理效應及銅膜應力之研究

Abstract

本論文以自行組建之多腔體式低壓銅化學氣相沈積(Cu CVD)系統，使用Cu(hfac)TMVS + 2.4 wt% TMVS當作先驅物(precursor)，分別探討基板的電漿前處理對銅膜沈積的效應、銅膜之成核特性以及銅膜的熱應力行為。在基板的電漿前處理部分，吾人將銅膜分別沈積在以物理性的氬氣電漿(Ar plasma)、化學性的氫氣電漿(H2 plasma)以及氬氣加氫氣電漿(Ar+H2 plasma)(先以氬氣電漿處理，再作氫氣電漿處理)處理過的TiN基板上，發現沈積在電漿處理過的TiN基版上之銅膜皆具有較小但形狀較規律的晶粒、較平坦的表面、以及較大的Cu(111)/Cu(200)晶向比。此外，在上述三種電漿處理後的基板上，由於基板的表面能增加(及/或銅膜與基板之間的界面能減少)，都使得銅成核角度(wetting angle)變小，尤其以Ar+H2電漿處理的效果最為明顯。然而，在氮氣電漿(N2 plasma)處理過的基板上之銅成核角度卻較未經過電漿處理者來得大。關於銅膜之熱應力行為的探討方面，吾人發現沈積在阻障層(TiN、Ta及TaN)上之銅膜的室溫殘留應力(room temperature residual stress)及熱循環過程中的熱應力變化(thermal stress variation)，均小於直接沈積在矽基板上的銅膜。在TiN、Ta及TaN三種阻障層中，沈積在TiN上的銅膜具有最小的室溫殘留應力及熱應力變化。本論文亦探討銅膜沈積溫度對銅膜熱應力行為的影響，結果發現在較高溫度沈積之銅膜具有較小的室溫殘留應力及熱應力變化。

This thesis consists of the studies of the effects of substrate plasma treatment on copper chemical vapor deposition (Cu CVD), the Cu grain nucleation on various substrates, and the film stress of CVD-Cu films. A liquid metalorganic compound of Cu(hfac)TMVS with 2.4 wt% TMVS additive was used as Cu precursor for Cu CVD in this study. Effects of Ar-, H2-, and Ar+H2-plamsa treatments on TiN substrate were investigated with respect to the properties of the CVD-Cu films. The Cu films deposited on these plamsa-treated TiN substrates all exhibit smaller and better regularly shaped grains, smoother film surface, and enhanced (111)-preferred orientation compared to that deposited on the bare TiN substrate. The wetting angle of Cu grain during nucleation is dependent on the substrate’s surface property. We found that the Ar-, H2-, and Ar+H2-plamsa treatments on the TiN, Ta and TaN substrates all resulted in decreased wetting angle, presumably because these plasma treatments all led to increase of substrate surface energy and/or decrease of Cu/substrate interfacial energy. On the other hand, N2-plamsa treatment resulted in increased wetting angle, implying that the N2-plamsa treatment led to decrease in substrate surface energy and/or increase in Cu/substrate interfacial energy. On the film stress of CVD-Cu films, it is found that, among the TiN, Ta and TaN barrier layers, TiN is the most efficient one in reducing the room temperature residual stress of Cu film and the stress variation during the 25 to 400℃ thermal cycling process. It is also found that the Cu film deposited at a higher temperature has a smaller room temperature residual stress and a smaller thermal stress variation during the thermal cycling process.