JPH0548113A - Nonvolatile semiconductor storage device and its manufacture - Google Patents

Abstract

PURPOSE:To provide a nonvolatile storage device which can be reduced in size and increased in degree of integration by reducing its cell area and the manufacturing method of the storage device. CONSTITUTION:This nonvolatile storage device has such a gate structure that a thin silicon oxide film 12 is formed as a tunneling medium on a channel area between a source area and drain area 19 provided on a semiconductor substrate 11 and a silicon nitride film 13 and the first gate electrode 14 are formed on the film 12. The gate structure contains side-wall insulating films 15 formed on the side wall of the structure and the second gate electrodes 17 formed adjacent to the films 15 with gate insulating films 16 in between on the semiconductor substrate 11.

Description

Detailed Description of the Invention

[0001]

The present invention relates to MNOS (gate electrode).
The present invention relates to a nonvolatile semiconductor memory device including a silicon nitride film-silicon oxide film-semiconductor substrate) type field effect transistor and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, an MNOS type nonvolatile semiconductor memory device is well known as one of electrically rewritable nonvolatile memories. The MNOS type non-volatile semiconductor memory device applies a voltage between a gate electrode and a semiconductor substrate to tunnel electrons or holes from the semiconductor substrate into a thin silicon oxide film that can serve as a tunneling medium and trap the electrons in a nitride film. Change the value voltage,
The principle is to operate as a memory element by the change of the threshold voltage.

A conventional MNOS type nonvolatile semiconductor memory device will be described below. FIG. 3 is a cross-sectional view of a conventional MNOS type nonvolatile semiconductor memory device. In FIG. 3, 1 is a P-type semiconductor substrate, 2 is a thin silicon oxide film serving as a tunneling medium, 3 is a silicon nitride film, 4 is a first gate electrode, 5 is a silicon oxide film, 6 is a second gate electrode, and 7 is A relatively shallow N-type diffusion layer, and 8 is an N-type diffusion layer to be a source region and a drain region. Further, in FIG. 3, the MOS transistor on the right side is called an MNOS transistor, and the MOS transistor on the left side is called a select transistor.

Normally, when reading the information stored in the MNOS transistor, a selection transistor is inevitably necessary in order to prevent erroneous writing in the MNOS transistor. Therefore, in order to operate as a non-volatile memory, two MOS transistor configurations of the MNOS transistor and the selection transistor have been required.

[0005]

However, in the above-mentioned conventional configuration, the demand for higher integration is increasing in the MNOS type nonvolatile semiconductor memory device as the capacity of the semiconductor memory is increasing in recent years. Two transistors, which are the selection transistors, have to be formed, which causes a problem that the cell area becomes large and miniaturization and high integration cannot be achieved.

The present invention solves the above conventional problems, and an object of the present invention is to provide a nonvolatile semiconductor memory device capable of reducing the cell area, enabling miniaturization and high integration, and a method for manufacturing the same. And

[0007]

In order to achieve this object, a nonvolatile semiconductor memory device of the present invention comprises a tunneling medium and a tunneling medium on a channel region sandwiched by a source region and a drain region provided on a semiconductor substrate. And a first insulating film made of at least one layer of a silicon nitride film on the thin silicon oxide film,
Formed on a sidewall of a gate structure in a nonvolatile semiconductor memory device having a MNOS (gate electrode-silicon nitride film-silicon oxide film-semiconductor substrate) structure having a gate structure having a first gate electrode on a first insulating film. The second gate electrode is provided via the formed second insulating film and the gate insulating film formed on the semiconductor substrate in contact with the second insulating film.

According to the method of manufacturing a nonvolatile semiconductor memory device of the present invention, a thin silicon oxide film is formed on a one conductivity type semiconductor substrate, a silicon nitride film is formed on the thin silicon oxide film, and a silicon nitride film is formed. Forming a first gate electrode made of a first polycrystalline silicon film on the silicon oxide film, and then performing an oxidation treatment to form a silicon oxide film on the semiconductor substrate and on the first gate electrode; Forming a second gate electrode on the side wall of the first gate electrode by depositing a second polycrystalline silicon film on the entire surface and performing anisotropic etching, and the first gate electrode and the second gate electrode. Is used as a mask to form a source region and a drain region.

[0009]

With this structure, since the second gate electrode, which is the gate electrode of the select transistor, is formed on the sidewall of the first gate electrode used as the gate electrode of the MNOS transistor, the second gate electrode is manufactured in a self-aligned manner. In addition, it is possible to make the MNOS nonvolatile semiconductor memory device finer and highly integrated.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of a MNOS type nonvolatile semiconductor memory device according to an embodiment of the present invention. In FIG. 1, 11 is a P-type semiconductor substrate, 12 is a thin silicon oxide film serving as a tunneling medium, 13 is a silicon nitride film, 14 is a first gate electrode, 15 is a sidewall insulating film, 16 is a gate insulating film, and 17 is a first insulating film. 2 is a gate electrode, 18 is a relatively shallow N-type diffusion layer, and 19 is an N-type diffusion layer serving as a source region and a drain region.

A relatively shallow N-type diffusion layer 18, a source region and a drain region 19 are formed on the P-type semiconductor substrate 11, and a thin oxide serving as a tunneling medium is formed on the region sandwiched by the relatively shallow N-type diffusion layer 18. The silicon film 12, the silicon nitride film 13, and the first gate electrode 14 are sequentially stacked to form a first gate structure. A sidewall insulating film 15 is formed on the sidewall of the first gate structure. The sidewall insulating film 15 is formed on the P-type semiconductor substrate 1 on both sides of the first gate structure.
1 and the gate insulating film 16 formed on the first insulating film 16.
Further, the second gate electrode 17 is formed on the sidewall of the first gate structure with the sidewall insulating film 15 and the gate insulating film 16 interposed therebetween.

Next, a method of manufacturing the MNOS type semiconductor memory device of the present invention will be described. 2A to 2D are process cross-sectional views of the MNOS type semiconductor memory device in one embodiment of the present invention. First, as shown in FIG. 2A, a thin silicon oxide film 12 of about 2 nm that serves as a tunneling medium is formed on a P-type semiconductor substrate 11 by oxidation in an oxygen atmosphere, and then a chemical reaction of dichlorosilane and ammonia is performed. A silicon nitride film 13 is formed to a thickness of about 20 nm by a vapor phase growth method based on the above, and then a polycrystalline silicon film to which phosphorus is added is deposited to a thickness of about 300 nm on the entire surface to be the first gate electrode 14. Next, by a known etching technique using a photoresist, the first
The gate electrode 14, the silicon nitride film 13 and the thin silicon oxide film 12 are etched to form a first gate structure. Next, as shown in FIG. 2B, a sidewall insulating film 15 and a gate insulating film 16 having a thickness of about 20 nm are simultaneously formed by a treatment in an oxygen and hydrogen atmosphere, and then a phosphorus film is formed on the entire surface to be the second gate electrode 17. A polycrystalline silicon film added with about 200 nm is deposited. Next, as shown in FIG. 2C, the first
The polycrystalline silicon film is removed by a known anisotropic etching technique so that a part of the polycrystalline silicon film to be the second gate electrode 17 remains on the side wall of the gate structure to form the second gate structure. Next, as shown in FIG. 2D, using the first gate structure and the second gate structure as a mask, phosphorus ions are implanted into the semiconductor substrate 11 under the conditions of 30 keV and 1 × 10 ¹³ cm ^-2 , and a relatively shallow N The mold diffusion layer 18 is formed. Next, using the photoresist as a mask, arsenic ions are implanted into the semiconductor substrate 11 under the conditions of 40 keV and 4 × 10 ¹⁵ cm ^-2 ,
The source region and the drain region 19 are formed. Thereafter, although not shown, the MNOS is subjected to various steps such as deposition of an interlayer insulating film, opening of contact holes, deposition and patterning of an aluminum wiring layer, and deposition of a protective layer.
Type nonvolatile semiconductor memory device is completed.

The MNO of this embodiment constructed as described above
In the S-type non-volatile semiconductor memory device, since the second gate structure is formed on the side wall of the first gate structure of the MNOS transistor, the second gate electrode can be manufactured in a self-aligned manner, and it can be miniaturized and high in size. Integration can be achieved.

In the above embodiment, the case of the N channel MOS transistor is explained, but the P channel MO transistor is used.
It may be an S transistor. Although the two-layer structure of the silicon oxide film and the silicon nitride film is used as the gate insulating film, a three-layer structure of the silicon oxide film, the silicon nitride film, and the silicon oxide film may be formed by oxidizing the top of the silicon nitride film.

[0015]

As described above, according to the present invention, by providing the selection transistor on the side wall of the MNOS transistor,
It is possible to realize an excellent non-volatile semiconductor memory device that can easily achieve miniaturization and high integration of memory cells and a manufacturing method thereof.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a MNOS type nonvolatile semiconductor memory device according to an embodiment of the present invention.

2 (a) to (d) are M in one embodiment of the present invention.
Process sectional view of the NOS type semiconductor memory device

FIG. 3 is a cross-sectional view of a conventional MNOS type nonvolatile semiconductor memory device.

[Explanation of symbols]

 11 P-type semiconductor substrate (semiconductor substrate) 12 Thin silicon oxide film 13 Silicon nitride film (first insulating film) 14 First gate electrode 15 Side wall insulating film (second insulating film) 16 Gate insulating film 17 Second gate electrode 19 N-type diffusion layer (source region and drain region)

Claims (2)

[Claims] 1. A thin silicon oxide film serving as a tunneling medium is provided on a channel region sandwiched by a source region and a drain region provided on a semiconductor substrate, and a thin silicon nitride film is formed on the thin silicon oxide film. Non-volatile semiconductor memory device having an MNOS (gate electrode-silicon nitride film-silicon oxide film-semiconductor substrate) structure having a gate structure having a first gate electrode on the first insulating film. A nonvolatile memory having a second gate electrode provided via a second insulating film formed on a sidewall of the gate structure and a gate insulating film formed on the semiconductor substrate in contact with the second insulating film. Semiconductor memory device. 2. A thin silicon oxide film is formed on a semiconductor substrate of one conductivity type, a silicon nitride film is formed on the thin silicon oxide film, and a first polycrystalline silicon film is formed on the silicon nitride film. Forming a first gate electrode made of, and then performing an oxidation treatment to form a silicon oxide film on the semiconductor substrate and on the first gate electrode; and a second polycrystalline film on the silicon oxide film. A step of forming a second gate electrode on the sidewall of the first gate electrode by depositing a silicon film on the entire surface and performing anisotropic etching; and a source region using the first gate electrode and the second gate electrode as a mask. And a step of forming a drain region, a method of manufacturing a nonvolatile semiconductor memory device.