元件尺寸對複晶矽薄膜電晶體效能之研究

Abstract

本論文主要在研究不同的通道尺寸對元件特性的影響。首先，我們以標準輕摻雜汲極製程製作出各種不同尺寸的薄膜電晶體；接著我們量測並觀察這些元件的基本電性，並配合鈍化處理和變溫量測以便更完整的呈現出元件特性。最後，根據所得的實驗結果，我們提出了合理的機制來解釋各種不同的尺寸變化對元件特性造成的影響。 本論文中元件的尺寸變化可歸納為三種: (1)窄通道元件: 這種元件的通道寬度從20微米縮小到0.9微米，而其通道長度維持20微米的定值；(2)短通道元件: 即元件的通道長度由20微米縮小到0.9微米，而通道寬度保持為20微米；(3)小尺寸元件: 這種元件的通道長度和寬度一樣，而且一起從20微米變化到0.9微米。 實驗結果顯示: 當通道寬度變窄時，元件的特性會變好，這應該是因為通道內的缺陷密度變小的原因。而當通道長度變小時，在n型通道的薄膜電晶體中會在汲極電壓加大時因為平行電場的增強而產生衝擊游離效應，這造成汲極電流大幅地增加、臨界電壓也非常明顯地下降；不過當汲極電壓不夠大或是在衝擊游離因素較低的p型通道元件中就不會產生衝擊游離效應。最後，在小尺寸元件的特性中我們發現電性機制將由缺陷密度和衝擊效應共同影響。

In this thesis, the poly-Si TFTs with different dimensions has been successfully fabricated and characterized. The mechanisms of dimension-related electrical behavior in n- and p-channel poly-Si TFTs are also proposed and compared with the experimental results. Our devices are divided into three groups: (1) narrow-width devices are devices with various channel widths and fixed channel length; (2) short-channel devices are devices with various channel lengths and fixed channel width; and (3) small-dimension devices are devices with both the channel length and width equally changed. Conventional top-gate light-doped-drain structure is used for this study. All the devices exhibit typical electrical characteristics. The experimental results show that device performances enhance as the width is reduced, which should result from the reduction of defect density. Avalanche multiplication occurs severely in short-channel n-type TFTs due to the high impact ionization of electrons and large amount of traps in the poly-Si. For short-channel p-type TFTs, only charge sharing is responsible for the degradation of device performances. In the case of small-dimension devices, both the impact ionization and reduction of defect density must be taken into account to explain the electrical behavior.