多孔隙低介電材料可靠度之研究

Study of Reliability Properties for Porous Low Dielectric Constant Materials

高楷傑(Kai-Chieh Kao)

指導教授 ： 鄭義榮

國立暨南國際大學/科技學院/電機工程學系/碩士(2014年)

摘要

在本論文中，我們將探討多孔隙低介電材料 (porous low-k) 可靠度之特性。研究主題有三個部分，分別為: (1) 不同時間紫外光 (UV) 照射對porous low-k 材料之影響；(2) 不同薄膜厚度對低介電材料 (low-k) 可靠度之影響；(3) 二氧化鉿 (HfO2) 覆蓋層作為 porous low-k 材料之表面封閉層與擴散阻擋層評估。
首先，我們將研究不同時間紫外光照射處理對 porous low-k 材料之材料特性、電性及可靠度變化。不同時間紫外光照射處理後，porous low-k 薄膜的化學成份分佈變化皆是相當均勻的。對於紫外光照射之固化過程中，首要去除與有機高分子 (porogen) 相關的 CHx 鍵結，同時也修改 Si-CH3 鍵結並且將 Si-O cage 鍵轉變為 Si-O network 鍵結，這導致經過300 s紫外光照射處理後的薄膜將擁有最低的介電常數。此外，原本摻雜 porogen 的 low-k 薄膜，當受到紫外光照射後將會轉變為較具疏水特性之薄膜，但是過多的紫外光照射又將會使薄膜的表面親水度稍微上升。另外，對於紫外光照射時間低於300 s之 low-k 薄膜，因為摻雜的 porogen 尚未完全遭到紫外光照射過程而去除，剩餘的殘留物將會降低 porous low-k 薄膜之電性與可靠性；然而照射時間大於300 s之 low-k 薄膜，其電性與可靠性都將被明顯的改善，但是並非隨著紫外光照射時間增加而持續改變。因此，雖然對 porous low-k 薄膜進行紫外光固化處理是 low-k 材料不可或缺的製程條件，但是固化時間的優化將是一個重要的課題。
其次，我們將探討兩種 low-k 薄膜在不同厚度下，其材料特性、電性及可靠性之變化。從材料分析中可發現，對於不同厚度之 low-k 薄膜，其鍵結結構並沒有明顯地改變，即使沉積厚度由100 nm增加至550 nm，而相同之結果亦可於介電常數量測中發現；而在金屬-絕緣層-半導體 (Metal-Insulator-Semiconductor，MIS) 結構之電性量測中可得到，low-k 材料的絕緣強度與其介電層的物理厚度將呈現反比變化，並以一逆冪次法則結合其薄膜之崩潰電場強度與其臨界厚度變化，充分地嵌合本實驗之結果。並且以未含有孔洞的 LK 薄膜表現出較高的冪次常數與較低的臨界厚度，表示崩潰電場強度變化受到薄膜厚度影響較為劇烈。
最後一部分的研究中，我們將評估以原子層沉積 (ALD) 的方式沉積HfO2薄膜作為 porous low-k 材料的孔洞封閉層與擴散阻擋層之可行性，並探討對其電性與可靠度之影響。實驗結果指出，HfO2 覆蓋層造成 porous low-k 薄膜整體介電常數由2.56增加為2.89，但漏電流密度與可靠度等性能將有效地改善，其原因為在使用 ALD 機台沉積 HfO2 薄膜時，將會封閉 porous low-k 薄膜表面的孔洞。另一方面，有 HfO2 覆蓋層之 porous low-k 薄膜也能較有效地對抗銅金屬的擴散性與氧氣電漿處理過程中所造成的損害。另外，我們將探討 HfO2 覆蓋層薄膜在不同退火溫度處理後其性能之優劣。實驗結果指出，含有 HfO2 覆蓋層之 porous low-k 薄膜並已經過400℃的退火溫度處理後，其堆疊薄膜將可以較顯著地減少銅金屬的擴散情形，並增加其薄膜之電性和可靠度性能。因此，以 ALD 方式沉積 HfO2 覆蓋層作為 porous low-k 材料的表面封閉層與銅擴散阻擋層將可行。

關鍵字

低介電材料 ； 孔洞 ； 紫外光 ； 銅 ； HfO2覆蓋層 ； 可靠度

並列摘要

In this thesis, we studed the reliability properties for porous low-k. The research topics are : (1) Effect of irradiation time on the porous low-k. (2) Effect of thickness on dense and porous low-k. (3) Evaluate HfO2 film as pore-sealing and Cu barrier film for porous low-k.
First, the effect of UVcurring time on the physical, electrical and reliability characteristics of the porous low-k dielectrics was comprehensively investigated in this study. After UV irradiation with various times, the depth profiles of the chemical composition in the low-k dielectrics were homogeneous. The UV curing process initially preferentially removed porogen-related CHx groups and then modified Si-CH3 and cage Si-O bonds to form network Si-O bonds. This leads to a lowest k value at UV curing time of 300 s. Moreover, the porogen-based low-k dielectrics transformed to be hydrophobic by UV irradiation and became more hydrophilic with an increase of UV curing time. For the shortest curing time (<300 s), porogen was not completely removed and the remaining residues caused the degrading reliability performance. For the longer curing time (>300 s), mechanical strength, electrical performance, and reliability all enhanced, but did not increased linearly with the UV time. Therefore, the UV curing process is necessary, but the process time optimization is essential for the porous low-k dielectrics.
Second, physical thickness-dependent dielectric electrical and reliability characteristics in the low-k films are studied in this study. The experimental results indicate that the deposition thickness change did not affect its molecular structure of low-k films, even if the deposition thickness increased from 100 nm to 550 nm. And the same result can also be found in the measurement of the dielectric constant. But the electrical properties obtained from MIS structures indicate that the dielectric strength of low-k dielectric films were inversely proportional to the dielectric physical thickness. A inverse power law combined with an critical thickness for dielectric breakdown strength was proposed and well-fitted the experimental results. The dense low-k films show a higher power law constant value and a lower critical thickness, indicating the breakdown behavior is seriously affected by the film thickness.
Last, we introduce an new scheme to improve the porous low-k dielectric film's characteristics by capping a HfO2 film using atomic layer deposition (ALD) method. The experimental results indicated that the dielectric constant of the porous low-k dielectric film can increase to 2.89 from 2.56 by capping HfO2 film because the pore on the film surface is sealed by Hf precursors. On the other hand, the leakage current density and reliability performance of the porous low-k dielectrics are greatly improved. Morever, the resistances to against Cu diffusion and oxygen plasma damage is also strengthened by the addition of the HfO2 capping film. However, the effect of the annealing temperatures of HfO2 films on the electrical and reliability of the porous low-k dielectrics is also investigated. The experimental results indicated that the low-k films containing HfO2 films that had with the annealing temperature of 400℃ can be significantly improved the situation of its copper diffusion, and increased its electrical properties, and reliability performance. Therefore, this capped ALD deposited HfO2 film can act as both pore-sealing layer and Cu barrier layer for the porous low-k dielectric film in the future technologies.

並列關鍵字

Low-k dielectric ； Porous ； UV light ； Copper ； HfO2 ； Reliability

參考文獻

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