Test Structures

For vertical calibration, use the TGS01 grating set. It comprises TGZ01, TGZ02, and TGZ03 gratings. These gratings have steps of various heights. Choose the grating with the step height approximately equal to the characteristic height of your sample (20, 100, or 500 nm). Scan the grating and make sure that your microscope measures height correctly in this range of heights (Fig. 1). If necessary, update the calibration factor.

Fig.1a 20x20 µm image of TGZ02.

Fig.1b Image of one step of TGZ02. For vertical calibration of your microscope, determine the distance between the lower and upper levels of the step. It should be equal to the size specified in the grating certificate.

Verify that your microscope is correctly calibrated in both the fast-scan and slow-scan directions. Determine how scanning speed and feedback parameters influence the imaging. Find optimum parameters.

Pay close attention to distortions caused by such parasitic effects as nonlinearity, hysteresis, and creep (Fig. 2). Follow the links at the top of the page for more information.

Fig.2a 18.5x18.5 µm image of TGZ02. Note the distortions caused by creep.

Fig.2b Cross section of a TGZ02 scan. Note the distortions caused by creep.