Flash memory device structure and manufacturing method thereof

Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode

Reexamination Certificate

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C257S315000, C257S330000

Reexamination Certificate

active

06770934

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a non-volatile memory (NVM) device. More particularly, the present invention relates to a flash memory device structure and manufacturing method thereof.
2. Description of Related Art
Flash memory is a memory device that allows multiple data writing, reading, and erasing operations. In addition, the stored data will be retained even after power to the device is removed. With these advantages, it has been broadly applied in personal computer and electronic equipment.
A typical flash memory device has a floating gate and a control gate fabricated using doped polysilicon. The control gate is set up above the floating gate with an inter-gate dielectric layer separating the two. Furthermore, a tunneling oxide layer is also setup between the floating gate and an underlying substrate (the so-called stack gate flash memory).
To write data into the flash memory, a bias voltage is applied to the control gate and the source/drain regions so that an electric field is set up to inject electrons into the floating gate. On the other hand, to read data from the flash memory, an operating voltage is applied to the control gate. Since the entrapment of charges inside the floating gate will directly affect the opening or closing of the underlying channel, the opening or closing of the channel can be construed as a data value of “1” or “0”. Finally, to erase data from the flash memory, the relative potential between the substrate and the drain (source) region or the control gate is raised. Hence, tunneling effect can be utilized to transfer electrons from the floating gate to the substrate or drain (source) via the tunneling oxide layer (the so-called substrate erase or drain (source) side erase) or from the floating gate to the control gate via the inter-gate dielectric layer.
FIG. 1
is a schematic cross-sectional view of the stack gate structure of a conventional flash memory (according to U.S. Pat. No. 6,214,668). As shown in
FIG. 1
, the flash memory comprises of a P-type substrate
100
, a deep N-well region
102
, a P-well region
104
, a stack gate structure
106
, a source region
108
, a drain region
110
, spacers
112
, an inter-layer dielectric layer
114
, a contact
116
and a conductive line
118
. The deep N-well region
102
is embedded within the P-type substrate
100
and the stack gate structure
106
is set up over the P-type substrate
100
. The stack gate structure
106
furthermore comprises a tunneling oxide layer
120
, a floating gate
122
, an inter-gate dielectric layer
124
, a control gate
126
and a gate cap layer
128
. The source region
108
and the drain region
110
are located within the P-type substrate
100
on each side of the stack gate structure
106
. The spacers
112
are attached to the sidewalls of the stack gate structure
106
. The P-type well region
104
is within the deep N-well region
102
and extends from the drain region
110
to the area underneath the stack gate structure
106
. The inter-layer dielectric layer
114
is above the P-type substrate
100
. The contact
116
passes through the inter-layer dielectric layer
114
and the P-type substrate
100
and short-circuits the drain region
110
and the P-type well region
104
. The conductive line
118
is positioned over the inter-layer dielectric layer
114
but is electrically connected to the contact
116
.
However, as the level of integration of integrated circuits increases and the miniaturization of devices continues, some problems arise. For example, in order to increase the level of integration of a memory device, dimension of each flash memory cell must be reduced. One method of reducing overall memory cell dimension is to shorten the gate length and the separation between data lines. However, reducing the gate length will shorten the channel layer underneath the tunneling oxide layer
120
rendering an electric punch-through between the drain region
110
and the source region
108
more probable. Should such electrical punch-through occur within the device, electrical performance of the memory cell will be seriously compromised. In addition, the photolithographic process used for fabricating the flash memory also has the so-called critical dimension problem, thereby setting a lower limit to the ultimate cell dimension. Furthermore, the drain region
110
and the P-well region
104
are short-circuited together and the P-type well region
104
extends from the drain region
110
into the area underneath the stack gate structure
106
. Hence, the P-type well region
104
may not have sufficient thickness in the lateral direction to enclose the drain region (N+ doped). When the memory cell is programmed, the source region receives a voltage of about 6V so that the drain region is at 0V. With this voltage setup, a NPN junction may break down leading to some adverse effect on a nearby flash memory cell. Thus, the ultimate level of integration in a conventional flash memory structure is severely limited.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a flash memory device structure and manufacturing process thereof capable of preventing punch-through between a source region (at 6V) and a drain region (at 0V) while performing a programming operation. In the meantime, the level of integration of the memory device is also increased.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a flash memory device structure. The flash memory device structure comprises a first conductive type substrate, a second conductive type first well region, a tunnel dielectric layer, a first floating gate, a second floating gate, an inter-gate dielectric layer, a first control gate, a second control gate, an insulating layer, a spacer, a source region, a drain region, a first conductive type second well region and a first conductive type pocket doping region. The first conductive type substrate has an opening and the second conductive type first well region is embedded within the first conductive type substrate. The tunnel dielectric layer covers the bottom area as well as the sidewalls of the opening. The first floating gate and the second floating gate are attached to the respective tunnel dielectric layer on the sidewalls of the opening. The inter-gate dielectric layer is set up over the first floating gate and the second floating gate. The first control gate and a second control gate are set up over the first conductive type substrate. The first control gate extends to cover the sidewall of the first floating gate and the second control gate extends to cover the sidewall of the second floating gate. The insulating layer is positioned within the space between the first control gate and the second control gate. The spacer is attached to the sidewall of the first control gate and the second control gate respectively. The source region is set up within the first conductive type substrate at the bottom section of the opening. The drain region is set up within the first conductive type substrate just below the spacer. The first conductive type second well region is set up within the second conductive type first well region and that the junction between the first conductive type second well region and the second conductive type first well region is higher than the bottom section of the opening. The first conductive type pocket doping region is set up within the first conductive type substrate adjacent to the opening sidewalls and the first conductive type pocket doping region is connected to the first conductive type second well region and the source region.
In the aforementioned structure, the drain region and the first conductive type second well region are electrically short-circuited together. The electrical short-circuit is achieved through a contact that passes through the junction between the drain region and the first conductive type second well region. Furthermore, th

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