CHARGING EFFECTS IN LOW : VOLTAGE SCANNING ELECTRON MICROSCOPE METROLOGY

Abstract

With the reduction of IC features in semiconductor manufacturing, the need for higher resolution metrology tools increases. Low Voltage Scanning Electron Microscopy (LVSEM) is one of the most commonly used techniques in critical dimension (CD) measurement. This thesis presents the physical mechanisms, especially the charging effects and inspection of fine resist features in low voltage SEM. The beam-sample interactions parameters are measured in scanning electron microscope (SEM). The SE yield of Si and Au are measured at different primary beam energies and sample tilt angles. It is found that the SE yield dependence on beam incident angle is not only different between low and high SEM accelerating voltages, but also different between different atomic number elements. Charging of insulating materials are investigated through both experiments and computer simulations. An effective simulation package was used to study the charging dynamics in SEM. The electric field and charge accumulation at different charging status are shown. 'Sidewall charging' and 'proximity effect' are presented and are demonstrated by SE emission diagram, trajectories and the signal profiles. 'Sidewall charging' is caused by the SEs emitted from the substrate hitting the resist line sidewall. This kind of charging can reach an equilibrium gradually. As for proximity effect, the larger the distance between resist lines, the less the influence neighboring structure has on the electrons. Charging of resist results in signal blooming with negative charging and signal inversion with positive charging. This is shown both by simulation and captured SEM image profiles. Under positive charging the potential and charge accumulation reaches an equilibrium more quickly than that in negative charging. The signal profiles are less affected which means that the accuracy and precision of CD measurement are not affected much. A resist sample with fine features including line and space patterns is inspected and analyzed. Typical charging phenomena are observed. The charging process is captured and analyzed by dynamic signal recording. The linescan profiles of the sample are extracted. General issues of CD measurement in SEM are discussed. Initial approaches in linewidth measurement are performed and the results are analyzed.