Specific Process Knowledge/Lithography/EBeamLithography/JEOLPatternPreparation: Difference between revisions

If alignment is needed it is vital to consider this already at the process design and mask design level to ensure that a visible mark is produced. Alignment is done using the electron beam in either SEM mode or beam scan mode. It is vital that the mark produced is visible in a 100 kV SEM or from a 100 kV beam scan. For this purpose marks made by heavy metals or etched trences with an aspect rate of at least 1 is preferable. In SEM mode the stage is moved to the expected alignment mark position and the user will manually observe the SEM image and adjust stage position to center the mark at as high magnification as required by alignment tolerance of the design. In beam scan mode the user sets up a routine that will scan the beam across the expected mark position and the Backscatter Electron Detector (BED) will detect the backscattered signal. This is done in both x- and y-directions and the system will calculate the mark center based on the second derivative of the backscatter signal.

The advantage of SEM mode is that it is fairly straight forward to do. It is however also very slow as it requires constant user input to move the stage at higher and higher magnification levels until position is sufficiently determined. Due to the time it takes it is hardly realistic to do chip alignment, only global wafer alignment should be done in this way.