低介電常數碳氧化矽阻障層與銅金屬整合之電性可靠度研究

Abstract

本論文探討三種電漿輔助化學氣相沈積法成長之低介電常數碳氧化矽(silicon-oxycarbide， SiCO)阻障層與銅金屬整合之電性可靠度。論文首先探討這些低介電常數介電層的物理特性及其熱穩定性，再利用金屬絕緣層半導體(MIS)結構來分析他們與銅金屬整合所衍生的電性可靠度問題。吾人發現這些介電材料隨其組合成分中氧濃度的升高，介電材料的密度、反射係數和介電常數皆有所降低。這是因為較高的含氧量傾向形成「鳥籠型」的矽-氧-矽鍵結，導致較為疏鬆的微結構。這三種介電層在經過30分鐘500℃的熱退火處理後，均展現極佳的高溫熱穩定性。在500oC以上溫度的高溫退火後，則由於水氣的熱脫附，使介電常數有所下降。在電性的探討方面， 吾人發現TaN/Cu/SiCO/Si電容結構經過30分鐘400℃的熱退火處理後，在室溫下測量的漏電流都沒有改變，顯示這三種介電層在沒有外加電場的情況下，即使在400oC的高溫也能有效延緩銅的穿透。吾人亦以電容結構研究室溫下的漏電流機制，發現隨著電場的增強，導電機制由低電場時的歐姆傳遞，轉變成Frenkle-Poole發射，然後在高於0.36 MV/cm電場時發生electric breakdown等三種機制。 再者，吾人利用加溫偏壓法(BTS)施加於TaN/Cu/SiCO/Si及Al/SiCO/Si電容結構， 迫使銅加速擴散至介電層，藉以探討低介電常數碳氧化矽的電性可靠度。測試結果顯示，介電層SiCO-A具備優越的抗銅擴散能力以及熱穩定性，在溫度200oC電場強度1 MV/cm的BTS測試15小時後，仍能維持原有的漏電流大小。介電層SiCO-B在相同條件的BTS測試15小時， 鋁電極的電容展現良好熱穩定性，漏電流維持不變，然而銅電極的電容在BTS測試的16分鐘內即全數崩潰，推測是由於SiCO-B的鳥籠型微結構較為疏鬆，無法阻擋銅的擴散之故。此外.介電層SiCO-C由於介電質本身的強度過於脆弱，即使鋁電極的電容在200oC施加1MV/cm電場強度的BTS下很快便崩潰，而銅電極的電容則無法在200oC支撐過0.8 MV/cm電場強度的測試。 總結本論文之研究結果顯示k值約為4的碳氧化矽SiCO-A具有極佳的抗銅性與熱穩定性，是極具潛力的銅鑲嵌製程之介電阻障材料，有機會取代目前通用的高介電常數之氮化矽(k~7)，應用於銅鑲嵌製程。

This thesis studies the thermal stability and physical property for three PECVD low-k (k-value less than 4) amorphous silicon-oxycarbide (α-SiCO:H) dielectric barrier films with different elemental compositions designated as SiCO-A (SiC1.19O0.73), SiCO-B (SiC1.12O0.77) and SiCO-C (SiC1.34O0.85). More importantly, this study also explores the electrical reliability of integrating these silicon-oxycarbide dielectric barrier films with Cu metallization using planar MIS capacitor structure. It is found that the film density, dielectric constant and refractive index all decrease with increasing content of oxygen in the dielectric composition; this is presumably because higher content of oxygen tends to make the Si-O-Si bond of the dielectrics forming a cage-like bonding, which is a relatively loose microstructure. All of the three dielectrics are thermally stable up to 500oC (in N2 ambient for 30 min). However, the dielectric constant of the α-SiCO:H films decreases slightly at temperatures above 500oC because the H2O outgassing at the elevated temperatures would diminish the ionic and dipolar polarization, and thus the dielectric constant. Leakage current of the dielectrics at room temperature exhibited different conduction mechanisms at different electric fields, including ohmic conduction at very low electric fields, Frenkle-Poole emission at low electric fields, and electric breakdown generally at electric fields above 0.36 MV/cm. All the three α-SiCO:H dielectric films are presumably capable of retarding Cu diffusion at temperatures up to 400oC without an applied electric field because no difference in room temperature leakage current was observed between the Al-gated and TaN/Cu-gated MIS capacitors, whether as-fabricated or 400oC-annealed. The SiCO-A dielectric film exhibited a good dielectric barrier property against Cu penetration; its MIS capacitors were able to withstand BTS at 200℃ under 1 MV/cm electric field up to at least 15h. This indicates that the SiCO-A dielectric is a potential candidate to replace the higher dielectric constant SiN film as a Cu-cap barrier and etching stop layer in the Cu damascene structure. The SiCO-B dielectric, presumably due to its loose and more cage-like Si-O-Si bonding structure, can not prevent Cu from diffusion into the film under the BTS (at 200oC with 1 MV/cm electric field). The SiCO-C dielectric has an even weaker dielectric strength; in fact, breakdown occurred to the 400oC-annealed TaN/Cu/SiCO-C/Si MIS capacitor under an electric field of 0.8 MV/cm at 200oC.