Fei Comapny

Bernd Rieger

Michiel Van Der Stam

Maarten Bischoff

Christiaan Kok

Marinus Johannes Van Der Zande

The invention relates to a method for adjusting a Ccorrector in a STEM using a crystalline sample. The method comprises recording a through-focus series, converting the obtained images to Fourier space, thus forming a set of images alike diffraction images. By then determining the symmetry of the Fourier images, the corrector can be tuned for better symmetry, and the transfer limit can be determined by determining the maximum distance of the spots from the center. By repeatedly performing these steps, the corrector can be tuned to its optimum performance.

Method for adjusting a stem equipped with an aberration corrector

The invention relates to a method of determining the distortions in the projection system of a TEM, and a method of correcting for these aberrations. The aberrations are determined by collecting a large number of images of a sample, the sample slightly displaced between each acquisition of an image. On the images sub-fields (-) showing identical parts of the sample are compared. These sub-fields (-) will show small differences, corresponding to differential aberrations. In this way the differential aberrations in a large number of points can determined, after which the aberrations for each point can be determined by integration. By now correcting the position of each detected pixel in an image to be displayed, the displayed image has much reduced aberrations. An advantage of the method according to the invention is that no highly accurate steps of the sample are needed, nor is a sample with known geometry needed.

Method for determining distortions in a particle-optical apparatus

A lens of particle-optical apparatus, such as the objective lens, suffers from aberrations. As is already known since decades Ronchigrams can be used to determine these aberrations of particle-optical lenses. Such methods rely e.g. on the determination of the 2derivative of the aberration function on the basis of local magnification in one or a set of Ronchigrams. Being dependent on the 2derivative the mathematics of these methods allow only (infinitesimal) small shifts between the Ronchigrams. However, this implies that e.g. the spatial quantization noise of the camera recording the Ronchigrams results in a large error. These conflicting requirements limit the accuracy and thus the usefulness of the known methods. The invention describes a set of algorithms which result in an improved method to quantify the lens aberration coefficients using a set of Ronchigrams.

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Delft, Netherlands

Bernd Rieger