|
Since mask design rule is smaller and smaller, Defects become one of the issues dropping the mask yield.
Furthermore controlled defect size become smaller while masks are manufactured. According to ITRS roadmap on
2007, controlled defect size is 46nm in 57nm node and 36nm in 45nm node on a mask. However the machine
development is delayed in contrast with the speed of the photolithography development.
Generally mask manufacturing process is divided into 3 parts. First part is patterning on a mask and second part is
inspecting the pattern and repairing the defect on the mask. At that time, inspection tools of transmitted light type are
normally used and are the most trustful as progressive type in the developed inspection tools until now. Final part is
shipping the mask after the qualifying the issue points and weak points. Issue points on a mask are qualified by using
the AIMS (Aerial image measurement system).
But this system is including the inherent error possibility, which is AIMS measures the issue points based on the
inspection results. It means defects printed on a wafer are over the specific size detected by inspection tools and the
inspection tool detects the almost defects. Even though there are no tools to detect the 46nm and 36nm defects
suggested by ITRS roadmap, this assumption is applied to manufacturing the 57nm and 45nm device.
So we make the programmed defect mask consisted with various defect type such as spot, clear extension, dark
extension and CD variation on L/S(line and space), C/H(contact hole) and Active pattern in 55nm and 45nm node. And
the programmed defect mask was inspected by using the inspection tool of transmitted light type and was measured by
using AIMS 45-193i. Then the marginal defects were compared between the inspection tool and AIMS. Accordingly we
could verify whether defect size is proper or not, which was suggested to be controlled on a mask by ITRS roadmap.
Also this result could suggest appropriate inspection tools for next generation device among the inspection tools of
transmitted light type, reflected light type and aerial image type.
|
