Semiconductor storage device
In a 4F 2 memory cell designed using an SGT as a vertical transistor, a bit line has a high resistance because it is comprised of a diffusion layer underneath a pillar-shaped silicon layer, which causes a problem of slowdown in memory operation speed. The present invention provides a semiconductor storage device comprising an SGT-based 4F 2 memory cell, wherein a bit line-backing cell having the same structure as that of a memory cell is inserted into a memory cell array to allow a first bit line composed of a diffusion layer to be backed with a low-resistance second bit line through the bit line backing cell, so as to provide a substantially low-resistance bit line, while suppressing an increase in area of the memory cell array.
1. A semiconductor storage device comprising:
a memory cell array formed using a vertical transistor which has a structure where a drain, a gate, and a source are arranged in a vertical direction with respect to a pillar-shaped semiconductor layer and a gate electrode surrounds the pillar-shaped semiconductor layer;
first bit lines formed by a first layer, said first bit lines being wired in a row direction so that each first bit line is connected to a sense amplifier;
second bit lines formed by a second layer, said second bit lines being wired in the row direction so that each second bit line is connected to a sense amplifier; and a plurality of vertical transistors formed on each first bit line, said vertical transistors including a first transistor for selecting a memory cell and a second transistor for connecting the first bit line and a corresponding one of the second bit lines,
wherein a gate electrode of the first transistor is connected to a corresponding one of first word lines wired in a column direction, and a gate electrode of the second transistor is connected to a corresponding one of second word lines wired in the column direction,
wherein when a first word line is selected, a corresponding second word line is also selected so that a second transistor connected to the corresponding second word line is conducted and a first bit line and a second bit line are therefore connected through the second transistor connected between the first and second bit lines.
2. The semiconductor storage device according to claim 1 , wherein each of the first transistor and the second transistor has a same structure.
3. The semiconductor storage device according to claim 1 , wherein each second bit line has a lower resistance with respect to each first bit line.
4. The semiconductor storage device according to claim 1 , wherein the memory cell array is configured to have a structure where a word line and a bit line intersect each other, and a memory cell is formed at the intersection of the word line and the bit line.
5. The semiconductor storage device according to claim 1 , wherein the memory cell is a dynamic memory formed by a single transistor consisting of the first transistor and a single capacitance element.
6. A semiconductor storage device comprising:
a memory cell array formed using a vertical transistor which has a structure where a drain, a gate, and a source are arranged in a vertical direction with respect to a pillar-shaped semiconductor layer and a gate electrode surrounds the pillar-shaped semiconductor layer;
first bit lines formed by a first layer, said first bit lines being wired in a row direction so that each first bit line is connected to a sense amplifier;
second bit lines formed by a second layer, said second bit lines being wired in the row direction so that each second bit line is connected to a sense amplifier;
a plurality of vertical transistors formed on each first bit line, said vertical transistors including a first transistor for selecting a memory cell and a second transistor for connecting the first bit line and a corresponding one of the second bit lines,
wherein a gate electrode of the first transistor is connected to a corresponding one of first word lines wired in a column direction, and a gate electrode of the second transistor is connected to a corresponding one of second word lines wired in the column direction,
wherein when a first word line is selected, a corresponding second word line is also selected so that a second transistor connected to the corresponding second word line is conducted and a first bit line and a second bit line are therefore connected through the second transistor connected between the first and second bit lines; and
a first contact formed above the first transistor and connected to a capacitance element formed above the first contact, and a second contact formed above the second transistor and connected to a corresponding one of the second bit lines formed in a lower-level layer than that of a capacitance element formed above the second contact,
wherein the first contact is formed between the second bit lines so that the first contact is electrically isolated from the second bit lines.
7. A semiconductor storage device comprising:
a memory cell array formed using a vertical transistor which has a structure where a drain, a gate, and a source are arranged in a vertical direction with respect to a pillar-shaped semiconductor layer and a gate electrode surrounds the pillar-shaped semiconductor layer;
first bit lines formed by a first layer, said first bit lines being wired in a row direction so that each first bit line is connected to a sense amplifier;
second bit lines formed by a second layer, said second bit lines being wired in the row direction so that each second bit line is connected to a sense amplifier;
a plurality of vertical transistors formed on each first bit line, said vertical transistors including a first transistor for selecting a memory cell and a second transistor for connecting the first bit line and a corresponding one of the second bit lines,
wherein a gate electrode of the first transistor is connected to a corresponding one of first word lines wired in a column direction, and a gate electrode of the second transistor is connected to a corresponding one of second word lines wired in the column direction,
wherein when a first word line is selected, a corresponding second word line is also selected so that a second transistor connected to the corresponding second word line is conducted and a first bit line and a second bit line are therefore connected through the second transistor connected between the first and second bit lines; and
a first contact formed above the first transistor and connected to a capacitance element formed above the first contact, and a second contact formed above the second transistor,
wherein the second contact is led out above a capacitance element through a contact hole formed in an electrode the capacitance element formed above the second contact to be connected to a corresponding one of the second bit lines formed by the second layer formed in a higher-level layer than that of the capacitance element.