Investigation of high resolution SPM alignment system

Alignment is a very basic and important process in manufacturing. An alignment process can affect a level of manufacturing precision and accuracy that in turn affects a product in terms of quality, yield and cost. This thesis is aimed at investigating an ultra-high resolution alignment system. As the atomic resolution of Scanning Probe Microscopy (SPM) is well established, we are interested in investigating the possibility of utilizing SPM as a part of an ultra high-resolution alignment system. Even though SPM itself has a high resolution, there are other issues that have to be resolved before the high-resolution potential of SPM can be realized. One of the problems is caused by the edge roughness of mark line. Even in a good system, the edge roughness varies from around 6nm to 30nm (3σ). Therefore, there is no absolute center for an alignment mark and it is difficult to position the mark without a not well-defined mark center. Also, in the existing SPM systems, raster scanning is commonly used to obtain a picture of the area scanned. However, this method if applied to alignment systems, becomes very time consuming and not efficient in locating an alignment mark. A Close Loop Scanning SPM Alignment System is proposed in this thesis. It is aimed at overcoming some of the above-mentioned problems. In order to conduct the investigation, a simulation approach has to be used due to the complexity of the uncertainties. A theoretical method for random mark edge generation with parameters determination based on real experimental measurements has been used. A simulation program has been written to examine the manner in which the roughness of the mark edge can affect alignment precision and accuracy. Different alignment methods based on the Close Loop Scanning are presented in this research. The simulation program helps to demonstrate that when the roughness of a line edge is around 6 nm the accuracy of our system achieved by using "Multi-Radius Scanning Method" could be under 0.25 nm and repeatability (3σ) of our system achieved by "Fixed-Radius Scanning Method" could be under 0.45 nm. Key Word: Alignment, Scanning Probe Microscopy (SPM), Close Loop Scanning, Alignment Mark.