低介電常數材料HSQ與銅導線製程整合之應用

Abstract

隨著元件尺寸愈做愈小，元件速度主要受限於訊號在金屬導體連線間傳送的時間延遲，所以金屬內連線的時間延遲變成控制元件操作速度的主要原因。為了改善這個問題，一般都是用低介電常數材料和銅導線來取代傳統的二氧化矽和鋁導線，以降低金屬導體連線的電容值和電阻值，提高元件的速度。 由於銅原子很容易擴散到以二氧化矽為基礎的介電層中，造成電性不穩定，一般而言採用阻障層來抑制銅原子的擴散，但阻障層會使接觸電阻提高，進而降低積體電路的運作速度，所以在本論文中，我們採用電漿處理的方式來取代阻障層。首先研究經過高溫退火後，低介電常數材料HSQ和銅之間的作用，尤其是銅對於低介電常數材料的影響。研究發現在高溫退火後，銅原子會擴散到HSQ薄膜中，造成電性的不穩定；除此之外，為了阻擋銅原子的擴散，我們利用氫氣和氨氣電漿來處理HSQ薄膜表面，使薄膜表面緻密化，加強薄膜抵擋銅原子擴散的能力。研究中發現經過氫氣電漿處理過後的HSQ薄膜，在經過高溫退火後，漏電流變得比沒經過電漿處理的薄膜穩定，且銅原子比較不會擴散到介電層裡；經過氨氣電漿處理過後，由於表面形成氮化矽的薄膜，漏電流更穩定，而且銅原子也不會擴散到HSQ薄膜裡。經過電漿處理後，介電常數亦不會因為銅原子的擴散而大幅提高。

Hydrogen silsesquioxane (HSQ) is one of the most intensively studied low-k materials concerning both its basic properties as well as integration-related issue. The dielectric constant of HSQ is about 2.8. Also, copper is paid much attention for its lower resistivity and higher anti-electromigration capability comparing with Al. In this thesis, the reaction of low-k HSQ film and copper were investigated by using metal-insulation-semiconductor (MIS) capacitor. In addition, the different plasma treatments (H2 and NH3) were applied on HSQ films instead of conventional barrier layer for enhancing the resistance of HSQ film to copper diffusion. The structure of HSQ was significantly changed after subjected to a further thermal annealing. The bonding of Si-H was broken and the porosity of the HSQ film was decreased. Moreover, the degradation of dielectric properties due to copper diffusion in the HSQ film was severe after a high temperature annealing. These eventually caused the increase of the leakage current and dielectric constant. By applying the plasma post-treatments on HSQ, however, leakage current and dielectric constant were decreased with increasing treatment time when compared with those of untreated HSQ. For the H2-plasma treatment, the hydrogen radicals could recover the broken Si-H bonds and form a passivation layer at the surface of the HSQ film. This would maintain the porous structure and prevent low-k HSQ from moisture uptake and copper attack. Accordingly, both leakage current and dielectric constant were significantly decreased. On the other hand, NH3-plasma treatment provided nitrogen to form a thin SiNx layer at the surface of HSQ film. The thin SiNx layer was inert and also effectively blocked moisture uptake and copper diffusion into HSQ. Electrical characteristic measurements and material analyses were also consistent with our inference. In addition, the experimental results indicated that the plasma post-treatments (H2 and NH3) are effective methods in enhancing the barrier properties of HSQ for copper penetration into HSQ.