同調雷射干涉技術作為圖案化12吋晶圓之全區薄膜應力量測

Abstract

在晶圓尺寸進入到12吋時，製程溫度1000C以上，晶圓即會進入不規則應變區域，傳統薄膜應力之量測方式是用光學聚焦作晶圓直徑掃瞄，偵測一截線之曲率，得到一平均應力值。此法難以量測局部性之應力，也不適用於圖案化之晶圓，因此只能應用於未圖案化,之測試晶圓。本技術為新型雷射干涉技術，可在全面晶圓上量測得到百萬點之局部應力值。使用X光繞射儀驗證此技術在連續膜晶圓的量測，局部六點的平均誤差在1.6%之內，而在雷射掃瞄機比較全區平均應力差異也在5%之內，在X、Y方向平均值量測再現性有小於2%的變動，在圖案化晶圓上使用晶圓正反面量測，正反面曲率呈現方向相反，顯示圖案面與連續面之量測有一致性，量測圖案化晶圓是可靠的。之後應用此技術觀察銅晶圓在退火及升溫時的應力，並得以改善銅退火製程的應力由180MPa降至135MPa，所以此干涉技術是監測 12吋晶圓應力的理想儀器。

When the wafer size from 200mm to 300mm, thin film stress will cause complicated deformation on wafer. There may be tensile stress and compressive stress existed in the same wafer. Therefore full field measurement with pattern wafer capability will be a new challenge to semiconductor manufacturer. Traditional method to measure stress is to do a laser diameter scan and calculate the curvature to get a average stress value, but it can not measure local stress and does not have pattern wafer capability. Coherent Gradient Sensing interferometry is developed to become a stress measurement tool for 300mm wafer. This technology can be used for full wafer stress mapping for 300mm wafer with more than 1 million sampling points, and it can do pattern wafer measurement. To verify local stress capability and full wafer average stress, X-ray diffraction and laser diameter scan technologies was adopted. XRD measurement for 6 local points has a 1.6% different for average value with CGS. Diameter scan for full wafer average stress has a maximum difference less than 5%.Repeatability measurement performance for CGS is less than 2%.For the pattern wafer stress measurement capability, front side and back side measurement prove the curvature information is correct. Then we apply this technology to measure copper wafer during annealing process and thermal process, annealing process stress has been improved from 180MPA to 135MPa by using this technology. So CGS will be a good metrology tool for stress measurement.