利用N2+離子佈植處理複晶矽/非晶矽薄膜對矽化鈷熱穩定性改善之研究

Abstract

由於矽化鈷具有低阻值及較佳的化學穩定性,因此它被預期成為深次微米CMOS元件的矽化物材料。然而，矽化鈷在多晶矽上形成時，若經過製程中高溫的熱處理，會有分解而形成結塊(agglomeration)的現象產生。在本論文中，我們提出兩種不同於以往的矽化過程來改善二矽化鈷的熱穩定性:(1)將N2+離子植入複晶矽中(2)用非晶矽取代複晶矽薄膜。在N2+離子植入複晶矽後，從一矽化鈷(CoSi)到二矽化鈷(CoSi2)之轉換(transformation)的結核(nucleation)受到氮植入的抑制。因為結核溫度的提高，二矽化鈷在初形成時形成的並不完整，因而矽化鈷的晶粒尺寸是較小的，進而改善矽化鈷的熱穩定性。另外，當非晶矽取代複晶矽薄膜後，由於非晶矽比起複晶矽有較小的晶粒邊界密度(grain boundary density)及較少的擴散管線(diffusion pipeline)，因此可得到具有較佳熱穩定性的二矽化鈷。更進一步地，我們運用這些新的矽化製程到MOS閘極電容上。結果都可得到較佳的電性特質(electrical characteristic)。這說明了在本論文中所提出新的矽化製程，不但可抑制二矽化鈷結塊現象的產生，還可以得到較佳的閘極氧化層，有效的改善由傳統矽化過程所引起的閘極氧化層劣化。

Due to its low resistivity and better chemical stability, CoSi2 is more anticipated to be the silicide material of deep sub-micrometer dimension CMOS devices. However, CoSi2 films on polysilicon would be decomposed and agglomerated during post-formation annealing at high temperature. In this thesis, we present two kinds of silicidation processes to improve the thermal stability of CoSi2 films as follows: (1) using N2+ implantation into poly-Si films (CoSi2/Poly-Si with N2+ I/I), (2) using amorphous Si instead of poly-Si films (CoSi2/α-Si). In the CoSi2/Poly-Si with N2+ I/I case, the nucleation of CoSi2 transformation from CoSi is impeded by N2+ I/I. Since the nucleation temperature is increased, CoSi2 films are formed incompletely at the as-formed state so that the grain size of CoSi2 is small which improves the thermal stability. In the CoSi2/α-Si case, the better thermal stability is due to the amorphous-Si film results in less grain boundary density and fewer diffusion pipelines than the columnar polysilicon film. Moreover, we used these new silicidation process in polyside gated MOS capacitors. They all showed better electrical characteristics. This indicates that these new structures not only suppress the agglomeration of CoSi2, but also have more superior gate oxide integrity.