Semiconductor memory device and method for inspecting the same

摘要

When the threshold voltage Vth of the transistor in the memory cell is within the allowable range is determined, a memory cell which does not have sufficient data retention characteristics is eliminated. In order to eliminate such a memory cell, the potential of a gate of the transistor is kept at an appropriate potential VGM and the potential of a drain of the transistor is set higher than or equal to VGM. When data is written to the memory cell in this state, the potential of a source of the transistor is expressed as a formula including the threshold voltage Vth, (VGM−Vth). By comparison between the level of the potential and the level of a reference potential, whether the threshold voltage Vth is within the allowable range can be determined.

主权项

1. A method for inspecting a semiconductor memory device comprising a memory cell including a capacitor and a transistor, one of a source and a drain of the transistor being connected to the capacitor, and the transistor including an oxide semiconductor, the method comprising the steps of:
a first step of turning on the transistor to accumulate electrical charge in the capacitor; a second step of turning off the transistor and setting the other of the source and the drain of the transistor to a floating state after the first step; and a third step of applying a voltage to a gate of the transistor and measuring a potential of the other of the source and the drain of the transistor to inspect a threshold voltage of the transistor after the second step.