In this study, a 3x-nm after development inspection (ADI) wafer with focus
exposure matrix (FEM) was inspected with both an advanced optical system and an
advanced electron beam inspection (EBI) system, and the inspection results were
carefully examined. We found that EBI can capture much more defects than optical
system and it also can provide more information about within reticle shot defect
distribution. It has high capture rate of certain critical defects that are insensitive to
optical system, such as nano-bridges. We also studied the critical dimension (CD) variations caused by the optical inspection and EBI.
In this study, a 3x-nm after development inspection (ADI) wafer with focus
exposure matrix (FEM) was inspected with both an advanced optical system and an
advanced EBI system, and the inspection results were carefully examined. We found that
EBI can capture much more defects than optical system and it also can provide more
information about within reticle shot defect distribution. It has high capture rate of certain
critical defects that are insensitive to optical system, such as nano-bridges.
KEYWORDS: Silica, Silicon, Selenium, Scanning electron microscopy, Monte Carlo methods, Defect inspection, Electron beams, Electron transport, Particles, Defect detection
Recently, a unique capability in highly sensitive detection of residue defects in photoresist patterns on a metal hard mask
has been verified experimentally [T. Hayashi et al., Proc. SPIE, 6922 (2008) 6922-129]. In order to reveal the
mechanism for the new defect inspection technique, the charging up induced by 300 eV - 2000 eV electron
bombardment of thin insulating layers (SiO2, ~tens of nm) on Si is studied by using a self-consistent Monte-Carlo
simulation of the transport of a primary electron and secondary electrons (SE) and the generation of an electric field due
to the charges in the layer. The calculation is compared with the contrast changes in the SEM images of thermally
oxidized layers (20~100 nm) on a Si wafer. Low-energy EB (or thick SiO2 layer) causes the positive charging of the
layer, whereas the high-energy EB, which penetrates under thin SiO2 layer, relaxes the charging of the layer due to
electron-hole recombination in Si. The thickness dependence of the SE yield for low- and high-energies is investigated,
which explains the observed changes in the SEM images of the insulating layers on Si.
Closed loop waveform acquisition methods on electron-beam probe systems have been used for many years. Its stability and linearity make it reliable and accurate to quantitatively measure the voltage at a probe point on the device under test (DUT). However, the feedback loop keeps decreasing the charging current to the integrator hence slowing the acquisition process. The open loop method can keep the charging current constant so as to speed up the waveform acquisition. Fast acquisition is desirable for productivity and to minimize electron beam induced contamination of the probe-point. By adjusting the loop gain and the filter mesh voltage properly, we developed a method to use the characteristics of the local linearity of S curve to make the open acquisition loop stable and reliable while significantly boosting the acquisition speed. The results show it can be approximately 25 times faster to acquire a waveform from the DUT. Also shown, the open loop method works ideally for measuring small amplitude (<EQ 1 volt) analog signals as well as logic waveforms.
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