Method for SEM-guided AFM scan with dynamically varied scan speed
A method discloses topography information extracted from scanning electron microscope (SEM) images to determine the atomic force microscope (AFM) image scanning speed at each sampling point or in each region on a sample. The method includes the processing of SEM images to extract possible topography features and create a feature metric map (step 1), the conversion of the feature metric map into AFM scan speed map (step 2), and performing AFM scan according to the scan speed map (step 3). The method enables AFM scan with higher scan speeds in areas with less topography feature, and lower scan speeds in areas that are rich in topography features.
1. A method of varying scan speed of atomic force microscopy (AFM) imaging at each sampling point based on prior topography information extracted from a scanning electron microscopy (SEM) image, comprising:
(a) A method for producing a feature metric map based on image processing algorithms for identifying and locating topography features from the SEM image;
(b) A method for converting the feature metric map into an AFM scan speed map;
(c) A method for setting scan speed for each sampling point, based on the scan speed map, to use a high scan speed for locations on the sample with minimal topography feature, and use a low scan speed for locations on the sample with rich topography features.
2. The method of claim 1 , wherein said SEM images are captured using secondary electron imaging mode.
3. The method of claim 1 , wherein said algorithms used to generate the feature metric map is based on detecting rapid changing gray scale pixels within the SEM images.
4. The method of claim 3 , wherein said algorithm can be local entropy, local standard deviation, local range of gray level, and local magnitude of gradient.
5. The method of claim 1 , wherein said feature metric map quantitatively describes the amount of local topography features and distinguishes the feature-containing and feature-lacking regions in SEM images.
6. The method of claim 5 , wherein said feature metric map is normalized to allow direct comparison to the feature metric maps generated by other algorithms.
7. The method of claim 6 , wherein said feature metric map that best identifies topography features within a given sample is converted to the AFM scan speed map.
8. The method of claim 1 , wherein said speed map defines AFM XY scanner speed at each point on the sample.
9. The method of claim 1 , wherein said feature metric map is converted into ADA scan speed map through a mathematical transformation.
10. The method of claim 9 , wherein said mathematical transformation can be the scan speed map is proportional to the feature metric map to the power of gamma value, wherein the gamma value is a number larger than zero.
11. The method of claim 9 , wherein said speed map is filtered to provide smooth speed transitions.
12. The method of claim 11 , wherein a filtering method used can be low-pass filtering or Gaussian filtering.
13. A system for atomic force microscopy (AFM) imaging inside a scanning electron microscopy (SEM), comprising:
(a) An atomic force microscope (AFM) installed inside a scanning electron microscope (SEM);
(b) A host computer, which extracts topography information from SEM image to generate a speed map for AFM scanning process;
(c) An AFM controller, which controls scan speed of AFM using the information from the speed map, the AFM controller being connected through wire connection to the host computer;
(d) An AFM carrier, which scans a sample with dynamically varied speeds based on a control signal from the AFM controller, the AFM carrier being connected through wire connection to the AFM controller.