Semiconductor devices and methods of manufacturing the same

A semiconductor device, comprising:

• a plurality of lower gate electrodes on a substrate in a first direction substantially perpendicular to a top surface of the substrate;
• a plurality of upper gate electrodes on the plurality of lower gate electrodes in the first direction, the plurality of upper gate electrodes spaced apart from one another in the first direction;
• and
• a plurality of channel structures, each channel structure of the plurality of channel structures extending through both the plurality of lower gate electrodes and the plurality of upper gate electrodes in the first direction, each channel structure of the plurality of channel structures including
• a lower channel structure penetrating through the plurality of lower gate electrodes,
• an upper channel structure penetrating through the plurality of upper gate electrodes, and
• a landing pad interconnecting the lower channel structure to the upper channel structure,
• wherein a first channel structure of the plurality of channel structures includes a first landing pad having a largest horizontal width of the first landing pad at a first vertical level,
• wherein a second channel structure of the plurality of channel structures that is closest to the first channel structure includes a second landing pad having a largest horizontal width of the second landing pad at a second vertical level,
• wherein the first landing pad includes a first lower connection on a first lower channel structure of the first channel structure, and a first pad on the first lower connection at the first vertical level, a horizontal width of the first pad being substantially greater than a horizontal width of the first lower connection and being the largest horizontal width of the first landing pad,
• wherein the second landing pad includes a second lower connection on a second lower channel structure of the second channel structure, and a second pad on the second lower connection at the second vertical level, a horizontal width of the second pad being substantially greater than a horizontal width of the second lower connection and being the largest horizontal width of the second landing pad,
• wherein the first and second channel structures have a same length in the first direction, the first and second lower channel structures have a same length in the first direction, and the first and second lower connections have different lengths in the first direction, such that the second vertical level is substantially lower than the first vertical level.

A semiconductor device, comprising:

• a plurality of lower gate electrodes on a substrate in a first direction substantially perpendicular to a top surface of the substrate;
• a plurality of upper gate electrodes on the plurality of lower gate electrodes in the first direction, the plurality of upper gate electrodes spaced apart from one another in the first direction;
• a first channel structure that extends in the first direction and includes a first lower channel structure penetrating through the lower gate electrodes, a first upper channel structure penetrating through the upper gate electrodes, and a first landing pad between the first lower channel structure and the first upper channel structure;
• and
• a second channel structure that extends in the first direction and is spaced apart from the first channel structure in a second direction parallel to the top surface of the substrate and includes a second lower channel structure penetrating through the lower gate electrodes, a second upper channel structure penetrating through the upper gate electrodes, and a second landing pad between the second lower channel structure and the second upper channel structure,
• wherein the first and second channel structures have a same length in the first direction, the first and second upper channel structures have different lengths in the first direction, and the first and second lower channel structures have a same length in the first direction, such that a bottom surface of the first upper channel structure contacts the first landing pad at a first vertical level and a bottom surface of the second upper channel structure contacts the second landing pad at a second vertical level substantially lower than the first vertical level.