Plasma Treated Ta, Ti, and Hf-based Diffusion Barriers for Copper Metallization System
|關鍵字:||擴散阻障層;金屬化;鉭;鈦;鉿;電漿處理;Diffusion barrier;Metallization;Ta;Ti;Hf;Plasma treated|
本研究主要探討氮氣電漿處理的鉭(Ta)擴散阻障層薄膜在銅製程上的熱穩定性。其中分別以氮氣電漿處理Ta (TaNx/Ta) 擴散阻障層及未處理的Ta、TaN擴散阻障層薄膜特性作比較。經分析發現，經氮氣電漿處理後，在Ta的薄膜表面有非晶質層的形成。此外，與未處理的Ta，TaN薄膜比較分析得知，電漿處理後的Ta薄膜具有較低的電阻率及細小的晶粒，使得氮氣電漿處理後的薄膜，具有較佳的熱穩定性及抵抗銅原子的擴散能力。故經氮氣電漿處理的Ta (TaNx/Ta)擴散阻障層薄膜比Ta及TaN擴散阻障層薄膜，具有更好的熱穩定性。
然而當元件尺寸越來越小，物理氣相沉積因受限於階梯覆蓋性的問題，逐漸被化學氣相沉積所取代。TiCl4目前廣被用來作為化學氣相沉積鈦及氮化鈦的反應前趨物，但因以TiCl4作為反應前趨物所沉積的鈦(Ti)及氮化鈦(TiN)，目前所採用的製程，一般都於高溫下(>600 oC)進行。在如此的高溫製程下，熱應力容易造成元件的破壞。此外，高溫下沉積的Ti (或TiSi2)與氮化鈦大都會以多晶相結構存在，而多晶相結構中的晶界，即是一個極佳的銅原子快速擴散通道。故本研究中亦針對極大型積體電路製程應用需要，發展一具備低溫、低電阻、高階梯覆蓋性及高擴散阻障性的擴散阻障層製程。經穿透式電子顯微鏡(TEM)觀察發現，剛沉積的鈦擴散阻障層為非晶質薄膜層，而經電漿處理後，在鈦薄膜表面有另一非晶質層的形成，成為疊層非晶質的Ti/TiNx薄膜阻障層結構。經電漿處理後的非晶質Ti/TiNx薄膜阻障層，具有較低的電阻率122 mW-cm及細小的晶粒，使得電漿處理後的薄膜具有較佳的熱穩定性及抵抗銅原子的擴散能力。以Cu/TiNx/Ti/Si的結構進行650°C、一小時的退火發現，其片電阻並無明顯的上升，得知在650°C高溫下，其並無高電阻值的銅矽(Cu-Si)化合物形成。此外，Cu/TiNx/Ti/n+-p接面二極體經500°C的高溫退火破壞考驗後，仍具整流的特性，此乃因非晶質Ti/TiNx阻障層薄膜具有較長的晶界擴散路徑，使得較傳統以物理氣相沉積方式沉積的Ti及TiN薄膜，具有較佳的熱穩定性及電性。此利用化學氣相沉積方式所沉積的非晶質Ti阻障層薄膜，於小尺寸高深寬比的凹槽結構中，展現其具有極佳的的階梯覆蓋性。
In this thesis, in order to promote barrier properties to apply in copper metallization, various diffusion barriers and surface treatments on deposited barrier films were prepared. The contents includes the optimum condition of Ta and TaN barrier films was set up, thermal stability of optimum condition for TaN barrier films was discussed in copper metallization, The barrier properties of CVD-Ti and TiN barrier films were discussed in thermal stability and step coverage for small trenches, various plasma treatments were performed on barrier layers to improve the thermal stability in copper metallization, and physical and electrical properties of Hf and Hf-N barrier films were also investigated. First, thermal stability of Ta barrier films with and without plasma treatments in copper metallization was discussed. Ta and TaN barrier films were comparison with plasma treated TaNx/Ta barrier films. Based on the analyses, an amorphous layer was formed on the Ta film surface with N2 plasma treatment. In addition, TaNx/Ta barrier film possessed lower resistivity and finer grains. The amorphous layer (TaNx) induced the better thermal stability and against Cu diffusion. Hence, barrier properties of TaNx/Ta films were better than that of Ta and TaN films. Secondly, various nitrogen flow ratios TaN barrier films were performed to discuss optimum conditions and thermal stability was advance discussed. Furthermore, O2 and N2 plasma treated process were also performed onto TaN barrier films. Based on the investigation, finer grains were found after TaN barrier films with O2 and N2 plasma treatments. The amorphorization phenomenon was observed on TaN(O)/TaN barriers. A thin amorphous layer was also observed on TaN surface after plasma treatments. TaN(O) and TaN(N) amorphous layers can improve barrier thermal stability. With shrinking the feature sizes of ULSI devices, physical vapor deposition for such kind of application has been replaced by chemical vapor deposition (CVD), because of the increased conformability of the film as compared with PVD films. CVD Ti and TiN layers can be deposited using TiCl4-based CVD process. Nevertheless, this process requires high-temperature (>600°C) substrates to achieve the depositions, which sometimes cause thermal damage to the deposited films and thermal diffusion of materials not suitable for devices. Moreover, deposited films are polycrystalline and provide inadequate protection because grain boundaries may presumably serve as fast diffusion paths for copper. In this paper, a low-temperature (<500°C) plasma enhanced chemical vapor deposition was used to deposit ultrathin (10 nm) Ti films. Furthermore, in-situ NH3 plasma was further employed to posttreat PECVD-Ti films. The resulted films had a multilayered amorphous Ti/TiNx structure and high thermal stability. Moreover, the effective resistivity of resulted Ti/TiNx film reduces to 122 mW-cm. Improved barrier capability against Cu diffusion is found for the Ti/TiNx barrier layer since the Cu/TiNx/Ti/n+-p junction diodes retain low leakage current densities even after annealing at 500°C for 1 hour. Ti/TiNx barrier layers present lengthened grain structures to effectively impede Cu diffusion, and thus act as much more effective barriers than conventional Ti and TiN films. Better step coverage is also observed for PECVD-Ti films deposited on small trenches defined by electron beam lithography. Finally, hafnium and hafnium nitride barriers films with lower resistivity were discussed in thermal stability. Phase transformation existed as nitrogen was incorporated with hafnium films. Various thermal stability of Hf and Hf-N barrier films was investigated.
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