Gas-enhanced PFIB surface preparation enabled metrology and statistical analysis of 3D NAND devices

Process monitoring of critical dimensions and structural shapes in 3D NAND flash memory device manufacturing requires the precision, resolution, and speed of SEM image acquisition and metrology, with new challenges in the Z axis, as device capacity continues to grow. Automated, gas assisted PFIB surface preparation enables sampling at multiple, arbitrary heights in the memory cell stack at a rate fast enough support inline process control. This work reports on preparation and measurement of greater than 2000 devices, from three sites, at 3 layers, in <140 minutes from a commercially available 64 layer 3D NAND device. Automated SEM metrology is used as a fast and accurate method of surface analysis to determine the planar cell area, ellipsis, and position of the bits as a function of depth within the stack. These results and extended analyses provide insight into how the shape and size of the primary etch channel influences memory cell dimensional variation as a function of depth.