Canon KrF Scanner Overlay Study And Improvement

Semiconductor critical dimension getting shortens as the IC manufacture rapid development and advanced microlithography technical, but the critical dimension requires a better overlay. Overlay is one of the key design rules for the fine pattern alignment machine-scanner, and it's an important parameter in microlithography. A bad overlay will impact the production yield and quality, and better overlay will get better resolution and alignment accuracy in lithography process. This paper aimed to study the overlay in IC manufacture process and get the factor that impact overlay, so that we can improve it.In Lithography process, Overlay is the accuracy of overlap between the current layer and the pre-layer. If the overlay is out of the control limit, the circuit that we design will open or short, and the yield of the manufacture will be very low. There are several type of overlay error, such as translation, wafer rotation, wafer magnification, chip rotation, chip magnification.This paper aimed to study the factor that impact scanner overlay and improve it by theory analysis and test for lithography scanner. We will study it by three items: firstly, study the impacted of environment temperature to the wafer overlay, and modify scanner hardware to improve the overlay; Secondly, study the canner hardware configuration, understand the theory of wafer stage stepping accuracy, improve the overlay by increase the wafer stage stepping accuracy; thirdly, find the parameter that related the overlay error, and improve overlay by compensate the machine parameter.