|
To use atomic force microscope (AFM) to measure dense patterns of 32-nm node structures, there is a difficulty in
providing flared probes that go into narrow vertical features. Using carbon nanotube (CNT) probes is a possible
alternative. However, even with its extremely high stiffness, van der Waals attractive force from steep sidewalls bends
CNT probes. This probe deflection effect causes deformation (or "swelling") of the measured profile. When measuring
100-nm-high vertical sidewalls with a 24-nm-diameter and 220-nm-long CNT probe, the probe deflection can cause a
bottom CD bias of 13.5 nm. This phenomenon is inevitable when using long, thin probes whichever scanning method is
used. We proposed a method to deconvolve this probe deflection effect. By detecting torsional motion of the base
cantilever for the CNT probe, it is possible to estimate the amount of CNT probe deflection. Using this information, we
have developed a technique for deconvolving the probe deformation effect from measured profiles. This technique, in
combination with deconvolution of the probe shape effect, enables vertical sidewall profile measurement.
We have quantitatively evaluated the performance of the proposed method using an improved version of a "tip
characterizers" developed at the National Institute of Advanced Industrial Science and Technology (AIST), which has a
well-defined high-aspect-ratio line and space structure with a variety of widths ranging from 10 to 60 nm. The critical
dimension (CD) values of the line features measured with the proposed AFM method showed good matches to TEMcalibrated
CD values. The biases were within a range of ±1.7 nm for combinations of three different probes, five
different patterns, and two different threshold heights, which is a remarkable improvement from the bias range of ±4.7
nm with the conventional probe tip shape deconvolution method. The static repeatability was 0.54 nm (3σ), compared to
1.1 nm with the conventional method. Using a 330-nm-deep tip characterizer, we also proved that a 36-nm-narrow
groove could be clearly imaged.
|
