Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having insulated gate
Reexamination Certificate
1999-11-05
2001-06-12
Tsai, Jey (Department: 2812)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having insulated gate
C438S634000
Reexamination Certificate
active
06245611
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a semiconductor integrated circuit device and a technique for manufacturing the same and, more particularly, to a technique which is effective when applied to a semiconductor integrated circuit device having an SRAM (Static Random Access Memory).
BACKGROUND OF THE INVENTION
The CMOS SRAM, in which are combined a high resistance load type or complete CMOS (Complementary Metal-Oxide-Semiconductor) type memory cell and a peripheral circuit composed of a complementary MISFET (Metal-Insulator-Semiconductor Field-Effect-Transistor) (CMOSFET), has been used for a cache memory of a computer or workstation of the prior art.
The memory cell of the CMOS SRAM is composed of a flip-flop circuit for storing information of 1 bit, and two transfer MISFETs. The flip-flop circuit of the high resistance load type is composed of a pair of driver MISFETs and a pair of resistance elements, whereas the flip-flop circuit of the complete CMOS type is composed of a pair of driver MISFETs and a pair of load MISFETs.
In recent years, the SRAM of this kind has been required to miniaturize the memory cell size to increase the capacity and speed and to lower the operating voltage to reduce the power consumption of the system. However, to meet the requirement, a problem that the resistance to soft error due to alpha rays (d-ray) must be solved.
The soft error due to alpha rays is a phenomenon that alpha rays (He nuclei) contained in cosmic rays or emitted from radioactive atoms contained in the resin materials of LSI packages, come into the memory cell to break the information retained in the information storage section.
An alpha particle has an energy of 5 eV and produces an electron-hole pair when it is incident upon the silicon (Si) substrate. When an alpha ray comes into a storage node at a “High” potential level, of the memory cell, the electron produced by the alpha-ray, flows to the storage nodes so that the hole flows to the substrate. As a result, the charge and potential of the storage node instantly decrease to invert the information of the memory cell with a certain probability.
In the case of an SRAM, the increase in the storage node capacitance of the memory cell is effective in improving the aforementioned resistance to soft error due to alpha rays.
U.S. Pat. No. 5,483,083 discloses a TFT (Thin Film Transistor) complete CMOS SRAM in which the load MISFETs are made of two-layered polycrystalline silicon film formed over the driver MISFET. In the SRAM, as disclosed, the gate electrode of one of the load MISFETs is partially extended to above the source or drain region of the other of the load MISFETs, and a capacitor element is formed of the gate electrode, the source or drain region and a insulating film interposed between the former two so that the storage node capacitance may be increased.
SUMMARY OF THE INVENTION
Thus, in the high resistance load SRAM and the TFT complete CMOS SRAM, countermeasures have been taken in the prior art to increase the storage node capacitance of the memory cell.
It has been considered that in the case of the so-called bulk CMOS SRAM, out of the complete CMOS SRAM, in which all the six MISFETs consisting a memory cell are formed in the semiconductor substrate, any countermeasure to increase the storage node capacitance is unnecessary.
The reason will be described in the following. A bulk CMOS SRAM having load MISFETs formed in a semiconductor substrate has a high current driving ability and a large storage node capacitance because the area of the load MISFETs is relatively large. As a result, sufficient charge can be fed to the storage node even if the potential of the storage node is fluctuated by the incidence of a alpha ray.
However, we have found out the following fact. In the bulk CMOS SRAM, too, the current driving ability of the load MISFETs drops if the miniaturization of the memory cell size further advances. If the operation voltage further drops, the amount of charge stored in the storage node drops, so that the potential fluctuation of the storage node due to alpha rays cannot be suppressed, deteriorating the soft error resistance.
An object of the present invention is to provide a technique capable of improving the soft error resistance of an SRAM adopting the bulk CMOS type.
Another object of the present invention is to provide a technique capable of promoting the miniaturization of the SRAM adopting the bulk CMOS type.
The foregoing and other objects and novel features of the present invention will become apparent from the following description to be made with reference to the accompanying drawings.
The representatives of the invention to be disclosed herein will be summarized in the following.
According to the semiconductor integrated circuit device of the present invention, in a complete CMOS SRAM in which the gate electrodes of a pair of driver MISFETs, a pair of load MISFETs and a pair of transfer MISFETs constituting a memory cell are composed of a first conductive film formed over the principal face of a semiconductor substrate, a capacitor element is composed of a second conductive film formed over the memory cell, an insulating film (dielectric film) formed over the second conductive film, and a third conductive film formed over the insulating film, the second conductive film and one of the storage nodes of the memory cell are electrically mutually connected, and the third conductive film and the other storage node of the memory cell are electrically connected.
In the semiconductor integrated circuit device, the one electrode of the capacitor element and the one storage node are electrically connected to each other through one of a pair of metal wiring lines composed of a first metal film formed over the third conductive film, and the other electrode of the capacitor element and the other storage node are electrically connected to each other through the other of the paired metal wiring lines.
In the semiconductor integrated circuit device of the present invention: the second conductive film constituting the one electrode of the capacitor element and the third conductive film constituting the other electrode of the capacitor element are individually composed of n-type polycrystalline silicon films; the one electrode of the capacitor element is electrically connected to the drain region of one of the paired driver MISFETs through a first contact hole and to one of the paired metal wiring lines through a second contact hole made above the first contact hole; and the other electrode of the capacitor element is electrically connected to the drain region of the other of the paired driver MISFETs through a third contact hole and to the other of the paired metal wiring lines through a fourth contact hole made above the third contact hole.
In the semiconductor integrated circuit device of the present invention: the second conductive film constituting the one electrode of the capacitor element and the third conductive film constituting the other electrode of the capacitor element are individually composed of n-type polycrystalline silicon films; the one electrode of the capacitor element is electrically connected to the one metal wiring line at the side wall of a fifth contact hole for connecting one of the paired metal wiring lines to the drain region of one of the paired driver MISFETs electrically; and the other electrode of the capacitor element is electrically connected to the other metal wiring line at the side wall of a sixth contact hole for connecting the other of the paired metal wiring lines and the drain region of the other of the paired driver MISFETs electrically.
In the semiconductor integrated circuit device of the present invention: the second conductive film constituting the one electrode of the capacitor element and the third conductive film constituting the other electrode of the capacitor element are composed of an n-type polycrystalline silicon film and a p-type polycrystalline silicon film respectively; the one electrode composed of the n-type polycrystalline silicon film
Hashimoto Naotaka
Hoshino Yutaka
Ikeda Shuji
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Tsai Jey
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