Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having insulated gate
Reexamination Certificate
2001-06-05
2002-09-17
Weiss, Howard (Department: 2814)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having insulated gate
C438S263000, C438S264000
Reexamination Certificate
active
06451643
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor integrated circuit device and method of implementing the device and, in particular, to a technique for effectively implementing a semiconductor integrated circuit device having a non-volatile memory circuit, such as, in an Electrically Erasable Programmable Read Only Memory, for example, which employs single-element type field effect transistors as non-volatile memory elements.
2. Description of Related Subject Matter
A single-element type non-volatile memory element (memory cell) has been proposed as a non-volatile memory element in an Electrically Erasable Programmable Read Only Memory (EEPROM or (E
2
PROM). This non-volatile memory element (memory cell) is constituted by a field effect transistor having one gate electrode for the storage of information (a floating gate electrode) and another gate electrode as a control electrode thereof (a controlling gate electrode). The source region of the field effect transistor is connected to a source line, while the drain region thereof is connected to a data line.
The aforesaid non-volatile memory element, which is called a flash type non-volatile memory element, is constituted as being both a hot electron writing type and a tunnel erasing type. In other words, the information writing operation of the non-volatile memory element is performed by generating hot electrons in a high electric field near the drain region and injecting the hot electrons into the information storing gate electrode. On the other hand, the information erasing operation of the non-volatile memory element is performed by tunnel-discharge of the electrons stored in the information storing gate electrode to the source region.
An EEPROM which is constituted by such a flash type non-volatile memory element consisting of a single-element type memory cell, as noted above, makes it possible to reduce the cell area and, as such, this memory can be characterized as being able to attain a high integration density.
The aforementioned EEPROM is described in the publication 1985 IEDM Tech. Dig., on pp. 616-619 thereof, in an article entitled “A Single Transistor EEPROM Cell and Its Implementation in a 512K CMOS EEPROM.”
Having studied the above-mentioned EEPROM, the present inventors found that the following problems were evident or associated therewith.
(1) In order to improve the information erasing efficiency in the foregoing information erasing operation of the flash type non-volatile memory element, it is necessary to make the impurity concentration of the source region high and the junction depth thereof large. That is, if the impurity concentration of the source region is made high, it is possible to decrease the surface depletion of the source region and decrease the voltage drop of the same surface thereby making it possible to increase the amount of tunneling current. Further, if the junction depth of the source region is made large, the amount of diffusion of the source region to the channel-forming region side increases, the overlap area of the source region and the information storing gate electrode correspondingly increases and the tunneling area also increases, so that the amount of tunneling current can be increased. However, since the source and drain regions are formed during the same manufacturing process, the drain region, furthermore, also becomes high in impurity concentration and large in junction depth. That is, the coupling capacitance associated therewith increases because of an increase in the overlap area of the drain region and the information storing gate electrode. Consequently, in the information writing operation, an unselected memory cell, which has its controlling gate electrode connected to ground (biased at ground potential) and a drain electrode which is biased at a high potential, increases in potential at its information storing gate electrode because of the foregoing coupling capacitance, and the memory cell becomes conductive, so that the flow of leakage current occurs thereby resulting in a deterioration of the information writing characteristic of a selected memory cell.
(2) With an increase in impurity concentration of the drain region, the intensity of the electric field near the drain region becomes high. In the information writing operation, therefore, at a non-volatile memory element which is in an unselected state after having undergone a writing operation and which has been biased with a high potential only at its drain electrode, hot holes are generated thereby erasing the information which may have been previously stored and deteriorating its electrical reliability. Further, if the drain region is high in impurity concentration and large in junction depth, then in the information writing operation, at a non-volatile memory element which is in an unselected state after having undergone a writing operation and which has been biased with a high potential only at its drain electrode, it becomes easier for tunneling to occur between the information storing gate electrode and the drain region thereof which can effect an erroneous erasing operation which leads to deterioration of its electrical reliability.
(3) If the impurity concentration of the drain region is high and the junction depth thereof becomes large, the parasitic capacitance applied to the data line increases. Consequently, the speed of the information reading operation decreases, thus making it impossible to effect speed-up of the operation speed.
(4) The above problem (1) may be solved by making the channel length large to effectively reduce the coupling capacitance formed between the drain region and the information storing gate electrode. However, since an increase in the channel length would result in an increase in the area occupied by the non-volatile memory element, any attempt at attaining high integration would thus become an impossibility.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a technique which permits improvement of not only the information erasing efficiency but also the information writing characteristic in a semiconductor integrated circuit device having a non-volatile memory circuit.
It is another object of the present invention to provide a technique which permits improvement of electrical reliability in the above semiconductor integrated circuit device.
It is a further object of the present invention to provide a technique capable of attaining speed-up of the operation speed in the above semiconductor integrated circuit device.
It is a still further object of the present invention to provide a technique capable of decreasing the number of manufacturing steps required for the above semiconductor integrated circuit device.
A typical example of the invention disclosed in the present application will now be summarized.
In a semiconductor integrated circuit device having a non-volatile memory circuit, such as, constituted by a flash type non-volatile memory element which employs an additional gate as a floating gate, for example, the source region of a field effect transistor constituting the non-volatile memory element is high in its impurity concentration (heavily doped) and large in its junction depth, while the drain region of the said field effect transistor is low in its impurity concentration (lightly doped) and small in its junction depth.
According to the above means:
(1) Since the impurity concentration of the source region of the field effect transistor serving as the non-volatile memory element is made high, it is possible to reduce the surface depletion of the source region in the information erasing operation and decrease the voltage drop at the surface of the source region, thus making it possible to increase the amount of tunneling current and improve the information erasing efficiency.
(2) Since the junction depth of the above source region is made large, furthermore, it is possible to increase the amount of diffusion of the source region to the channel-forming region side and increase the overl
Kamigaki Yoshiaki
Komori Kazuhiro
Kume Hitoshi
Meguro Satoshi
Nishimoto Toshiaki
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Weiss Howard
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