JP2012079839A - Semiconductor nonvolatile memory device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrically erasable semiconductor nonvolatile memory device having high reliability by preventing degradation of a tunnel insulating film due to an edge portion thereof.SOLUTION: An electrode for transferring electric charge is disposed apart from an edge portion of a tunnel region on a tunnel insulating film, and the electrode for transferring electric charge and a floating gate electrode are electrically connected to each other.

Description

  The present invention relates to an electrically rewritable semiconductor nonvolatile memory device used in electronic equipment.

  An electrically rewritable semiconductor non-volatile memory cell (hereinafter abbreviated as an EEPROM cell) has an N-type source region and an N-type drain region arranged on a P-type silicon substrate via a channel region. A floating gate electrode is formed through a tunnel insulating film made of a thin silicon oxide film having a thickness of about 100 mm or less or a composite film of a silicon oxide film and a silicon nitride film, etc. on the floating gate electrode. A control gate electrode is formed through a control gate insulating film made of a thin insulating film, and the floating gate electrode is strongly capacitively coupled to the control gate electrode.

  The floating gate electrode and the control gate electrode are extended on the channel region, and the conductance of the channel region varies depending on the potential of the floating gate electrode.

  Therefore, information can be stored in a nonvolatile manner by changing the amount of charge in the floating gate electrode. By applying a potential difference of about 15 V or more with respect to the control gate to the drain region also serving as the tunnel region, electrons of the floating gate are discharged to the drain region through the tunnel insulating film of the tunnel region, or conversely to the floating gate electrode. Or can be injected.

  In this way, the charge amount of the floating gate is changed to function as a nonvolatile memory. A large number of nonvolatile memory semiconductor devices can be obtained by arranging a large number of such EEPROM cells in a matrix to form a memory array.

  Here, a tunnel region having a tunnel insulating film that allows electrons to pass through is particularly important, and it enables rewriting of memory cell information of hundreds of thousands of times, and long-term storage of memory information for several decades ( It plays a dominant role in the charge retention requirements.

  As a measure for improving the reliability of the tunnel region and the tunnel insulating film, an example in which a tunnel region having a different impurity concentration is provided adjacent to the drain region to improve the rewrite characteristics and the retention characteristics has been proposed (for example, see Patent Document 1). .

Japanese Patent Laid-Open No. 1-160058

  However, in the semiconductor device in which a dedicated tunnel region is provided separately from the drain region as in the improved example, there is a problem that the occupied area increases and the cost of the semiconductor device increases. Also, no consideration has been given to the edge of the tunnel region that significantly affects the rewrite characteristics and retention characteristics.

In order to solve the above problems, the present invention is configured as follows.
A channel which is the surface of the semiconductor region between the source region and the drain region, and the source region and the drain region of the second conductivity type provided on the surface of the semiconductor surface region of the first conductivity type and spaced apart from each other Forming region, floating gate electrode provided on the source region, drain region, and channel forming region via a gate insulating film, and a control gate capacitively coupled via the floating gate electrode and control gate insulating film In an electrically rewritable semiconductor nonvolatile memory comprising an electrode, a tunnel insulating film is provided in a tunnel region in the drain region, and is provided on an upper portion of the tunnel insulating film and at an edge portion of the tunnel region A charge transfer electrode is disposed at a position spaced from the electrode, and the charge transfer electrode and Serial The floating gate electrode, and the electrically erasable and programmable nonvolatile semiconductor memory device are electrically connected.

The charge transfer electrode and the floating gate electrode are electrically rewritable semiconductor nonvolatile memory devices formed of the same material.
The charge transfer electrode and the floating gate electrode are electrically rewritable semiconductor nonvolatile memory devices formed of polysilicon.

An electrically rewritable semiconductor non-volatile memory device in which a separation width between the charge transfer electrode and the edge portion of the tunnel region is equal to or greater than a film thickness of the gate insulating film.
Further, at least one of the tunnel insulating film or the control gate insulating film is an electrically rewritable semiconductor nonvolatile memory device that is a composite film of a silicon oxide film and a silicon nitride film.

  In the edge portion where the defects in the tunnel region that are remarkably affected in the rewritability and retention characteristics in the electrically rewritable semiconductor nonvolatile memory device are prone to occur, the upper portion of the tunnel insulating film, and from the edge portion of the tunnel region Since the charge transfer electrode is disposed at a spaced position, and the charge transfer electrode and the floating gate electrode are electrically connected, the floating gate electrode and the drain region are not connected in data rewriting or holding operations. Even when a high voltage is applied between them, a large electric field is not applied between the charge transfer electrode and the drain region separated from the edge of the tunnel region, and the substantial thickness of the tunnel insulating film is reduced. Because the structure is equivalent to the increased one, the power at the edge of the most stressed tunnel region It is possible to prevent the concentration, to improve the reliability of the tunnel insulating film, more or data rewrite count, it is possible to achieve data retention time.

  Further, since the charge transfer electrode and the floating gate electrode are formed of the same material widely used for manufacturing a general semiconductor device such as polysilicon, the manufacturing process is easy. Further, since the separation width between the charge transfer electrode and the edge portion of the tunnel region is equal to or greater than the thickness of the gate insulating film, a voltage that is the maximum applied voltage between the drain region and the floating gate electrode was applied. Even in this case, good characteristics can be maintained without destruction or deterioration.

In addition, at least one of the tunnel insulating film and the control gate insulating film is a composite film of a silicon oxide film and a silicon nitride film, improving reliability.
By these means, it is possible to prevent electric field concentration on the edge of the tunnel region where defects easily occur, which significantly affect the rewrite characteristics and retention characteristics in the electrically rewritable semiconductor nonvolatile memory device, and increase the occupied area. Therefore, it is possible to obtain a highly reliable electrically rewritable semiconductor nonvolatile memory device by suppressing deterioration of the tunnel insulating film.

1 is a schematic cross-sectional view of an electrically rewritable semiconductor nonvolatile memory device according to the present invention. 1 is a schematic plan view of an electrically rewritable semiconductor nonvolatile memory device according to the present invention.

  DESCRIPTION OF EMBODIMENTS Embodiments for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view of an electrically rewritable semiconductor nonvolatile memory device according to the present invention.

  A second conductivity type N-type source region 201 and a drain region 202 are provided on the surface of the first conductivity type P-type semiconductor substrate 101 at a distance from each other, and between the source region 201 and the drain region 202. On the channel formation region, the source region 201, the drain region 202, and the channel formation region on the surface of the P-type semiconductor substrate 101, for example, polysilicon or the like via a gate insulating film 301 made of silicon oxide and having a thickness of 400 mm A floating gate electrode 501 is provided. On the floating gate electrode 501, a control made of polysilicon or the like capacitively coupled via a control gate insulating film 601 made of a silicon oxide film, a silicon nitride film, or a composite film thereof. A gate electrode 701 is formed. A tunnel insulating film 401 made of a silicon oxide film, a silicon nitride film, or a composite film thereof is provided on the tunnel region 801 in the drain region 202. On the tunnel insulating film, a charge transfer electrode 521 made of polysilicon or the like is disposed from the edge portion 402 of the tunnel insulating film via a separation region 931.

  Next, FIG. 2 is a schematic plan view of an electrically rewritable semiconductor nonvolatile memory device according to the present invention. As shown in FIG. 2, a charge transfer electrode 521 made of polysilicon or the like is disposed on the tunnel insulating film 401 from the edge portion 402 of the tunnel region 801 through a separation region 931. Since the entire periphery of the charge transfer electrode 521 is separated from the edge portion 401, the charge transfer electrode 521 is disposed on the tunnel insulating film 401 in an island shape. The charge transfer electrode 521 and the floating gate electrode 501 are electrically connected by a conductor 991 formed of aluminum or another wiring material. The width of the separation region 931 between the tunnel region edge and the charge transfer electrode, which is the distance between the charge transfer electrode 521 and the edge portion of the tunnel region 801, is set to be equal to or greater than the thickness of the gate insulating film 301. ing. In this figure, the control gate insulating film and the control gate electrode are omitted and not drawn.

  According to the embodiment of the present invention, at the edge of the tunnel region 801 where the rewrite characteristic and the retention characteristic in the electrically rewritable semiconductor nonvolatile memory device are significantly affected, the defect is easily formed on the upper portion of the tunnel insulating film 401. The charge transfer electrode 521 is disposed at a position separated from the edge portion of the tunnel region 801 by a separation region 931 between the tunnel region edge and the charge transfer electrode. Are electrically connected, so that even when a high voltage is applied between the floating gate electrode 501 and the drain region 202 in the data rewrite or holding operation, the charge is transferred from the edge portion of the tunnel region 801. There is a large gap between the electrode 521 and the drain region 202. Since the field is not applied and the structure is equivalent to a substantial increase in the thickness of the tunnel insulating film 401, electric field concentration at the edge portion of the most stressed tunnel region 801 can be prevented. Thus, the reliability of the tunnel insulating film 401 can be improved, and more data rewrites and data retention times can be achieved.

  Further, since the charge transfer electrode 521 and the floating gate electrode 501 are formed of the same material widely used for manufacturing a general semiconductor device such as polysilicon, the manufacturing process is easy. Further, since the separation width between the charge transfer electrode 521 and the edge portion of the tunnel region 801 is equal to or larger than the film thickness of the gate insulating film 301, the voltage that becomes the maximum applied voltage between the drain region 202 and the floating gate electrode 501. Even when a voltage is applied, good characteristics can be maintained without the tunnel insulating film 401 being destroyed or deteriorated.

Further, at least one of the tunnel insulating film 401 or the control gate insulating film 501 is a composite film of a silicon oxide film and a silicon nitride film, and the reliability is further improved.
By these means, the electric field concentration on the edge portion where the defect of the tunnel region 801 which has a remarkable influence on the rewriting characteristics and the holding characteristics in the electrically rewritable semiconductor nonvolatile memory device is easily generated is prevented, and the occupied area is increased. Thus, it is possible to obtain an electrically rewritable semiconductor nonvolatile memory device with high reliability by suppressing the deterioration of the tunnel insulating film 401.

101 P-type silicon substrate 201 N-type source region 202 N-type drain region 301 Gate insulating film 401 Tunnel insulating film 402 Edge portion 501 Floating gate electrode 521 Charge transfer electrode 601 Control gate insulating film 701 Control gate electrode 801 Tunnel region 931 Tunnel Spacing region 991 between region edge and charge transfer electrode

Claims (5)

A source region and a drain region of a second conductivity type provided on the surface of the semiconductor substrate of the first conductivity type and spaced from each other, and the vicinity of the surface of the semiconductor substrate between the source region and the drain region. A channel forming region, a floating gate electrode provided on the source region, the drain region, and the channel forming region via a gate insulating film, and a control capacitively coupled via the floating gate electrode and the control gate insulating film In an electrically rewritable semiconductor nonvolatile memory composed of a gate electrode,
A tunnel insulating film is provided in the tunnel region in the drain region, and is located above the tunnel insulating film and at a position separated from an edge portion that is a boundary between the tunnel region and the gate insulating film. An electrically rewritable semiconductor nonvolatile memory device in which a charge transfer electrode is disposed, and the charge transfer electrode and the floating gate electrode are electrically connected.   The electrically rewritable semiconductor nonvolatile memory device according to claim 1, wherein the charge transfer electrode and the floating gate electrode are formed of the same material.   2. The electrically rewritable semiconductor nonvolatile memory device according to claim 1, wherein said charge transfer electrode and said floating gate electrode are formed of polysilicon.   The electrically rewritable semiconductor nonvolatile memory device according to claim 1, wherein a separation width between the charge transfer electrode and an edge portion of the tunnel region is equal to or greater than a film thickness of the gate insulating film.   2. The electrically rewritable semiconductor nonvolatile memory device according to claim 1, wherein at least one of the tunnel insulating film or the control gate insulating film is a composite film of a silicon oxide film and a silicon nitride film.

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