Method for preparing TEM sample

A method for preparing a transmission electron microscope (TEM) sample, comprising the following steps:

• step 1, providing a chip sample having a metal protective layer, the metal protective layer being formed on a first surface of the chip sample;
• step 2, fixing the chip sample on a sample table of a focused ion beam (FIB) system;
• step 3, performing a first time of FIB cutting on the metal protective layer using a FIB, so as to form a groove, wherein a first direction is a width direction of the subsequently formed TEM sample, and a second direction is a direction perpendicular to the first direction in the first surface,
• a direction of the first time of FIB cutting is the first direction, and the groove extends along the first direction,
• an inner side surface of the groove on a section along the second direction is arc-shaped, and
• in the second direction, the groove is located in an area for forming the TEM sample, a thickness of the metal protective layer at each position on the inner side surface of the groove gradually changes, and, from a top to a bottom of the groove, the thickness of the metal protective layer gradually decreases at various positions on the inner side surface of the groove;
• and
• step 4, performing a second time of FIB cutting on the chip sample using the FIB, the second time of FIB cutting thinning the chip sample and forming the TEM sample, wherein
• a direction of the second time of FIB cutting is a third direction, and the third direction is a direction from the metal protective layer to the chip sample, wherein, in the second time of FIB cutting, a cutting rate at a corresponding position is adjusted by means of the thickness of the metal protective layer, so as to adjust a width of the TEM sample, wherein, in an area for forming the groove, the width of the TEM sample gradually changes due to a feature that the thickness of the metal protective layer gradually changes, from the top to the bottom of the groove, utilizing the characteristic of gradually decreasing thickness of the metal protective layer at the various positions on the inner side surface of the groove, the cutting rate at each position on the inner surface of the groove gradually increases, and the width of the TEM sample corresponding to each position on the inner surface of the groove gradually decreases, an optimal observation area for TEM analysis is obtained from the gradually changing width of the TEM sample.