Semiconductor memory device
View Patent ↗In a multiport SRAM memory cell of the present invention, an access transistor of a first port is disposed in a p-type well, and an access transistor of a second port is disposed in a p-type well. The gates of all of transistors disposed in a memory cell extend in the same direction. With the configuration, a semiconductor memory device having a low-power consumption type SRAM memory cell with an increased margin of variations in manufacturing, by which a bit line can be shortened in a multiport SRAM memory cell or an associative memory, can be obtained.
1. A method of forming a semiconductor device including static type memory cells having first and second load transistors, first and second drive transistors, first and second access transistors, and first and second transistors, comprising:
forming first to fifth impurity regions of a first conductive type in a first well of a second conductive type;
forming sixth to tenth impurity regions of the first conductive type in a second well of the second conductive type;
forming eleventh to fourteenth impurity regions of the second conductive type in a third well of the first conductive type, wherein the third well is arranged between the first and second wells;
forming a first gate layer having a first portion arranged over a portion between the first and second impurity regions to provide the first drive transistor, and a second portion arranged over a portion between the eleventh and twelfth impurity regions to provide the first load transistor, wherein the first gate layer is shared for gate electrodes of the first drive transistor and the first load transistor;
forming a second gate layer having a third portion arranged over a portion between the sixth and seventh impurity regions to provide the second drive transistor, a fourth portion arranged over a portion between the thirteenth and fourteenth impurity regions to provide the second load transistor, and a fifth portion arranged over a portion between eighth and ninth impurity regions to provide the first transistor, wherein the second gate layer is shared for gate electrodes of the second drive transistor, the second load transistor, and the first transistor;
forming a third gate layer having a sixth portion arranged over a portion between the second and third impurity regions to provide the first access transistor, and a seventh portion arranged over a portion between fourth and fifth impurity regions to provide the second access transistor, wherein the third gate layer is shared for gate electrodes of the first and second access transistors;
forming a fourth gate layer having an eighth portion arranged over a portion between the ninth and tenth impurity regions to provide the second transistor, the fourth gate layer functioning as a gate electrode of the second transistor;
forming an electrical connection of the first gate layer to the fifth and thirteenth impurity regions;
forming an electrical connection of the second gate layer to the eleventh impurity region;
forming an electrical connection of the eleventh impurity region to the second impurity region to provide a first storage node of the static type memory cell;
forming an electrical connection of the thirteenth impurity region to the seventh impurity region to provide a second storage node of the static type memory cell;
forming a first word line electrically connected to the third gate layer;
forming a second word line electrically connected to the fourth gate electrode;
forming a first bit line electrically connected to the third impurity region;
forming a second bit line electrically connected to the fourth impurity region; and
forming a third bit line electrically connected to the tenth impurity region.
2. The method of forming a semiconductor device according to claim 1 , further comprising:
forming a first wiring for supplying a power supply voltage to the eleventh and fourteenth impurity regions;
forming a second wiring for supplying a ground voltage to the first impurity region;
forming a third wiring for supplying a ground voltage to the sixth impurity region; and
forming a fourth wiring for supplying aground voltage to the eighth impurity region.
3. The method of forming a semiconductor device according to claim 2 , wherein
the first to fourth wirings and the first to third bit lines are arranged in parallel, and
the first and second word lines are arranged in parallel to each other and perpendicularly to the first to third bit lines.
4. The method of forming a semiconductor device according to claim 3 , wherein
the first word line is arranged over the first to third wells, and
the second word line is arranged over the first to third wells.
5. The method of forming a semiconductor device according to claim 1 , wherein
the second impurity region is shared for the first drive transistor and the first access transistor, and
the ninth impurity region is shared for the first and second transistors.