Reserch On The Measurement Technology Of Line Edge Roughness By AFM

With the development of "scaling" in Integrate Circuit, the critical dimension reduces continuously. It is expected half pitch of DRAM would be 45nm by 2010 according to the goal of International Technology Roadmap for Semiconductor(ITRS). In course of critical dimension reduction, line edge roughness (LER) becomes more and more impact on the electric character of component, which is even ignored before, the main reason is that LER does not decrease in scaling when critical dimension reduces. For example, LER occupies more than 50% of the line width error when critical dimension runs into 50nm. Hence, the measurement and control of LER has recently become a high interest topic in the semiconductor and lithography industry.Recently, atomic force microscope (AFM) is getting more and more attention and is applied widely in the industry area due to its 3-D imaging result in nano-scale resolution and as well its extensive adaptability on different measurement samples. AFM may be the most effective instrument to satisfy the demand of ITRS to improve the measurement precision constantly since its observed objects are not limited in nonconductor only.First, the working principle, imaging process, structure and working mode of AFM are studied. It is discussed and analyzed deeply in detail of the factors affecting on the measurement precision, such as AFM probe expansion, nonlinear of the piezo scanner, noise induced in scanning course. Several measuring LER methods are compared and analyzed. The conclusion is derived then, that is tilting measurement is the only feasible way to detect LER under the current measurement condition since it could gain topography information of line-edge surface as much as possible.Line width roughness(LWR) measurement, one of common ways to evaluate the sidewall topography, is studied in order to acquire the comparable results from using scanning electron microscopy. By using several image processing methods, such as histogram, threshold and the edge-detect operators, LWR of the step is derived. LWR measurement and evaluation procedures by using AFM with carbon nano-tube probe are given out. The conclusion is educed that LWR...