研究半導體光罩缺陷消除技術

Abstract

全球光罩都遭遇到析出物造成晶片缺陷的問題，尤其是愈先進製程的光罩愈嚴重(用於氟化氬193奈米雷射光源的光罩愈容易產生析出物)。當氟化氬(ArF)193奈米光罩因為產生析出物時，由於高階產品線寬越來越小，光罩上的析出物將容易在晶片上成像，進而造成晶片重複性缺陷，導致低良率或報廢，造成晶片生產廠商大量的損失。除此之外，當光罩因為產生析出物送修時，對高階產品順利量產及準時出貨將是非常大的挑戰。 析出物是一種光罩表面上的污染物，析出物有慢慢成長的特性，它的成長機制為由表面汙染物、殘留化學品(一般為硫酸及氨水)及曝光光源的能量所引起的光化學反應。析出物會造成光罩透明度的降低，造成晶片圖形成像品質不佳。 經驗上，當光罩析出物由2D惡化為1D後(定義的光罩缺陷代號，2D：淡/較小的析出物，對於在晶片上成像具有較低風險，1D：深/較大的析出物，對於在晶片上成像具有較高風險)，將會有在晶片上缺陷成像的高風險。所以如果我們可以提早消滅2D，就可以降低對晶片的衝擊，並延長光罩的使用時間。我們發現了一個以深紫外光(DUV) ArF 193奈米波長光源的創新光罩清潔製程，這個方法是藉由193奈米波長光源對光罩進行假(dummy)曝光，進而消滅光罩上的早期析出物(2D)。根據評估的結果，實施這個方法後將可增加光罩的壽命及晶片產出(每次送修區間增加1000片晶片產出)、降低光罩送修率(由8.8%降低至4.0%)以及改善晶片量產的時間(避免光罩送修的衝擊，48小時無法量產)。

The photomask (reticle) suffered serious haze (precipitate) defect in worldwide, especially for advanced technology reticles (ArF 193nm reticles occurred haze easily). Semiconductor manufacturer will have big impact when ArF 193nm reticles occurred haze. Because of advanced technology production line width become smaller and reticle haze defect will image formation on wafer easily. It will induce wafer repeating defect by field and cause wafer low yield or scrap. Besides, it is extremely higher challenge for mass production smoothly or delivery on time when 193nm reticles occurred haze and need to repair. Haze is a kind of contamination on the surface of reticle. Haze has a slowly growing characteristic and the growth mechanism is photochemical reaction induced by surface contamination、chemical residue (in general, sulfuric acid and ammonia) and energy of exposure light source. Haze caused reticle’s transmittance drop and poor pattern formation on wafer. As a matter of experience, haze will have high image formation risk on wafer when become worse from 2D to 1D (defined defect code, 2D: light/ smaller haze with low image formation risk, 1D: dark/ bigger haze with high image formation risk). So, we can reduce wafer impact and extend reticle lifetime if we can eliminate 2D first. We found a novel reticle cleaning process with DUV ArF 193nm wavelength light source. This method can eliminate early precipitate (2D) after dummy exposure by 193nm wavelength light source. After implementing this method, we can increase reticle lifetime and wafer output (increase 1000 pcs wafer per reticle repair)、reduce reticle repair rate (trend down from 8.8% to 4.0%) and improve wafer production cycle time (avoid impact by reticle repair around 48 hrs).