An array process diagnosis
test structure for an
integrated circuit including a
transistor array composed of vertical FET
memory cell access transistors, which are formed into the depth of a substrate in the form of active webs which run parallel in the lateral direction of the circuit is disclosed.
Memory cell storage capacitors in the array
test structure are formed in deep trenches on the end faces of those sections of the active webs which form the vertical FET transistors. Word lines are arranged along the webs and along parallel intersecting bit lines of the array, outside of which, and on two mutually opposite edges, are located a first and second word line comb. The wordline combs are offset and connected alternately to different word lines. In addition, a first and a second
bit line comb are formed on the two other opposing edges of the
transistor array mutually offset and each connected to different bit lines. The
test structure provides a convenient means to carry out reliability investigations on the
gate oxide of the vertical FET transistors and on the
capacitor dielectric in the deep trenches,
capacitance measurements between the word lines, and between the word lines and other circuit
layers, as well as
capacitance measurements between the bit lines and between the bit lines and other circuit
layers, and thus facilitates diagnosis of possible fault sources arising during the production process.