晶圓之場效電晶體機械應力之監測

Abstract

隨著越做越小，元件越來越敏感。除了漏電流、雜訊等等的影響,機械應力的效應已經不能被忽略了。當機械應力發生在上金屬層之前的絕緣層，或是金屬與金屬之間的絕緣層時。這將會造成:覆蓋在絕緣層上的金屬很容易發生原子漂移，或是絕緣層容易發生龜裂，特別在角落的部分更是容易發生。也就是說對於元件的可靠性有極大的衝擊。更嚴重的是，假如這發生在元件主動區，而主動區又跟應力的來源靠的夠近，機械應力將會造成驅動電流的下降。也就是說元件的工作效率將會比我們預料的還低，甚至還會造成晶片的不工作。 藉著轉角度元件，我們可以監測在晶圓上的機械應力。甚至在未來，我們可以在主要的工作晶片旁邊做一組這種測試元件。這樣一來，假如有完整機械應力的模型，我們就可以估計在這一個區域的機械應力有多大，進而得知他對於元件的工作會有多大的影響。換句話說,可以在Spice模擬器裡面加入這種模型(參數隨著晶圓以及製程會有變化)，得以事先調整元件尺寸來避免因為機械應力所造成的驅動電流下降的問題，或是改善製程來達到我們的要求。

The devices become more and more sensitive to stress along with their down-scaling trend. In addition to leakage current and noise, mechanical stress effect could not be ignored in device operation. When it appears in the PMD (Pre-Metal Dielectric) or IMD (Inter-Metal Dielectric), it may cause the metal layer over it easily to migrate or the isolation layer would be potential to crack, especially at the corner. It means a strong impact on the reliability issue. More seriously, when it happens to the active region, it may produce drive current degradation, if the active region is placed close to the stress source. Device performance will thereby be lower than our estimation, or even the function will fail ultimately. By means of the gate rotated devices in this work, we could monitor the mechanical stress on the whole wafer. Even in the future, such type of test devices close to the main functional devices are demanded due to increased stress. We could estimate the degree mechanical stress affects in this active region and the device operation, if a complete model has been set up in advance. In other words, we can include the stress factor with parameters varying from die to die in the Spice model to eliminate the drive capability degradation through modification of circuit design or improvement our fabrication process to meet requirements.