A Practical Guide to SPM

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26 IX. Tip Shape Issues The SPM image is a result of the interaction of the tip shape with the surface topography. There are two primary features of the tip that affect the SPM image: the radius of curvature and the tip sidewall angles. The smaller the radius of curvature, the smaller the feature that can be resolved. A sharper tip will be able to laterally resolve smaller features than a dull tip with a larger radius of curvature (Figure 9-1). Figure 9-1. Schematics and image profiles of spheres scanned with a sharp (left) and dull (right) probe. The accumulation of debris on the end of the tip can also dull the tip and result in image distortion (Figure 9-2). Note: A dull or dirty tip may not affect the measurement of the vertical dimensions of these samples. Figure 9-2. Schematic and image profile of trenches scanned with a dirty tip. 35.0° 35.0° 17.0° 17.0° The ability to image steep sidewalls on a sample surface is determined by the sidewall angles of the tip (Figure 9-3); the tip is not able to profile sides of surfaces steeper than the sidewall angle of the tip. When scanning across features that are steeper than the sidewall angle of the tip, the sidewall angle in the images will reflect the sidewall angle of the tip. Tip Cantilever 35.0° Tip 35.0° Cantilever 25.0° 10.0° The following examples show the resulting angles and image profiles of a silicon nitride tip (Figure 9-4) and a silicon tip (Figure 9-5) scanned over trenches with 90° sidewall angles. Figure 9-3. Comparison of tip sidewall angles. Each tip was mounted in the cantilever at ~10°, so the angles measured with the front and back sides of the tip are skewed by ~10°. Scan line profile 45.0° 65.0° 10.0° 55.0° 55.0° Scan line profile Figure 9-4. Sidewall angle measurements of trench with vertical sidewalls acquired with silicon nitride probe. 10.0° Scan line profile 55.0° 90.0° Scan line profile 73.0° 73.0° Figure 9-5. Sidewall angle measurements of trench with vertical sidewalls acquired with silicon probe.
27 Resolution Issues The resolution of AFM images can be thought of in terms of lateral (X,Y) resolution and vertical (Z) resolution. Lateral Resolution Issues Tip Shape — As discussed in the previous section on tip shape effects, the radius of curvature of the end of the tip will determine the highest lateral resolution obtainable with a specific tip. The sidewall angles of the tip will also determine its ability to probe high-aspect-ratio features. Pixelization — The Samples/ line parameter in the Realtime menu determines the number of data points present in the image in the X and Y scan direction. These data points are commonly called pixels. Available choices are 512, 256, and 128. Pixelization affects resolution in that you cannot resolve features smaller than the pixel size of the image. For example, if you are acquiring a 50µm x 50µm image with the Samples/ line parameter set to 512, then the pixel size is 98nm (50µm÷512=0.098µm or 98nm). Thus, you will not be able to resolve features smaller than 98nm at a 50µm scan size. If you want to be able to see 10nm-sized features, you will need to choose a scan size
Page 1 and 2: A Practical Guide to SPM Scanning P
Page 3 and 4: A Practical Guide to SPM TABLE OF C
Page 5 and 6: 5 a sample surface, the sensed inte
Page 7 and 8: 7 The scanning tunneling microscope
Page 9 and 10: 9 Tuning forks also improve force s
Page 11 and 12: 11 Non-contact AFM Non-contact AFM
Page 13 and 14: 13 Figure 5-3 shows simultaneously
Page 15 and 16: 15 potential on the surface is diff
Page 17 and 18: 17 VI. Non-imaging Modes SPMs are m
Page 19 and 20: In the linear region of the curves
Page 21 and 22: 21 VII. The Scanner A piezoelectric
Page 23 and 24: 23 Aging The sensitivity of piezoel
Page 25: 25 Types of SPM Probes • Contact
Page 29 and 30: 29 In TappingMode, when operating o

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