多孔性二氧化矽薄膜表面電漿改質在奈米積體電路超低介電材料之應用研究

Abstract

當積體電路的密度增加，元件尺寸縮小，導線的電阻值與金屬間介電層的電容值乘積所形成的功率損，將延遲訊號的傳遞時間。當製程進入深次微米領域時，元件閘極層次的速度增益，將因增加電阻電容時間常術所引起之內連線傳導延遲而抵銷，進而限制晶片效能的提升。為了解決內連線延遲問題，早期以線路設計的方式增加層數及關鍵部分的線徑與空間來改善，然而如此將增大積體電路的尺寸，造成產率與成本的負擔，為了改善這些問題，使用低介電常數材料做為導線間的介電層為必要選擇。

本研究中所使用的低介電常數材料為奈米孔洞二氧化矽薄膜。然而，由於高孔隙率的關係，衍生出許多製程上的問題，增加實際導入生產製程上的困難，如吸水性、蝕刻氣體滲入孔洞、以及銅鑲嵌結構製程中，氣體前驅物分子可能經由孔洞滲透擴散至介電層中，由於前驅物中含有金屬組成，金屬原子一旦進入介電層，將會嚴重劣化材料的介電性質。

因此，我們嘗試將開孔性薄膜表面的孔洞再次封合，來減少後續製程上所衍發的問題。本研究將利用不同的電漿對奈米孔洞二氧化矽薄膜做前置處理，以期其離子轟擊效應能使薄膜表面的孔洞結構崩壞，形成緻密結構，而內部的高孔隙率性質依舊存在。研究的重點包括：經電漿處理後的奈米孔洞二氧化矽薄膜抵抗金屬原子擴散的能力同時探討因電漿處理而造成薄膜基本性質的改變。

在本研究中發現經過電漿處理之奈米孔洞二氧化矽薄膜可於表面產生一層緻密結構的二氧化矽薄膜，而在薄膜內部依舊維持著高孔隙率，且可抵抗後續金屬化製程中的金屬擴散行為，而介電常數值僅些微上升，顯示電漿處理為一可用的孔洞封合技術。

While the semiconductor industry continues to scale down device sizes for better performance, lower power consumption and higher packing density, the interconnect delay and cross-talk between adjacent metal lines must be reduced. The performance of an IC chip can be degraded by interconnect RC delay and power consumption. In order to alleviate the problems, low dielectric constant (k) materials are used to replace the conventional intermetal dielectric (IMD), SiO2.

In this research, low-k nanoporous silica dielectrics was selected as the ultra-low k IMD material for nanoscaled integrated circuit technology. However, integration of the porous ultralow-k dielectric into Cu interconnect processes is subjected to impurity diffusion through pore channels and moisture uptake on the pore surface due to high porosity. Because of the very low mass density and enormously large and active surface area, low-k nanoporous silica dielectrics are extremely susceptible to plasma damage during etch and CVD processes. Without appropriate pore-sealing treatment, these materials are not suitable for application for Cu interconnect technology.

In the study, plasma treatments were implemented to seal open pores of porous ILDs by forming a thin dense layer on the dielectric surface. Ion bombardment on the dielectric surface during the plasma treatment will result in the collapse of the pore structure near the surface region, thereby forming a dense surface layer while making the porous bulk intact. In the surface layer, chemical and microstructure properties were dramatic different from that of the bulk. The changes in the film chemistry, mechanical properties, and resistance to metal diffusion were studied by various spectroscopies and microscopies, such as x-ray diffractometry, electron nicroscopies, and x-ray photoelectron spectroscopy.