JP2649511B2 - Semiconductor storage device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a semiconductor memory device, and more particularly to a nonvolatile semiconductor memory device having excellent write / erase characteristics.

(Prior Art) Conventionally, as a typical nonvolatile semiconductor memory device, a semiconductor memory device having an MNOS (metal-nitride film-silicon oxide film-semiconductor) structure is well known. MNOS
In a semiconductor memory device, a relatively high voltage (about 15 to 25 V) is applied between the gate electrode and the semiconductor substrate, and the nitride film is formed near the interface between the ultra-thin silicon oxide film and the nitride film or in the vicinity thereof. The principle is that tunneling injection and accumulation of charges are performed from the semiconductor side to existing traps, and information is stored by changing the threshold voltage of the transistor.

FIG. 3 shows an example of a cross-sectional structure of a conventional n-channel MNOS type semiconductor memory device. Reference numeral 1 denotes a p-type silicon substrate, and 2 and 3 denote n-type selective diffusion regions, which are called source and drain regions. Reference numeral 4 denotes a thin silicon oxide film that can serve as a tunneling medium, 6 denotes a nitride film, and 7 denotes a gate electrode made of a polysilicon film.

(Problems to be Solved by the Invention) An example of the write / erase characteristics of the MNOS type semiconductor memory device having the conventional configuration as shown in FIG. 3 is shown by broken lines 8 and 9 in FIG. For example, when a pulse voltage of ± 20 V is used, the time required for writing / erasing is 2 ms or more for writing and 50 ms or more for erasing, and the erasing time is longer than the writing time. It has a drawback of being extremely long, which is a practical problem when applied to a large capacity memory.

SUMMARY OF THE INVENTION An object of the present invention is to provide a MNOS having a novel configuration in which write / erase characteristics, particularly erase characteristics, are significantly improved in view of the above problems.
It is an object of the present invention to provide a type semiconductor memory device.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides an insulating film, a nitride film, and a conductive film sequentially stacked in a predetermined region on a single conductivity type single crystal semiconductor substrate. In the semiconductor memory device, the semiconductor substrate adjacent to both sides of the predetermined region has a region of the opposite conductivity type to the semiconductor substrate,
The insulating film has a thickness of 15 to 30 °, is composed of a silicon oxide film and an oxynitride film, and the thickness of the oxynitride film is substantially half the thickness of the insulating film. It is assumed that.

(Operation) In the present invention, the thickness of the oxynitride film + silicon oxide film is 15 to 30 °, and the barrier against tunneling implantation can be reduced by making the silicon oxide film thinner than the conventional one. This makes it possible to improve the write / erase characteristics. Here, if the silicon oxide film is simply thinned, charges injected into and written into the nitride film thereon, particularly charges existing near the interface between the silicon oxide film and the nitride film, escape through the silicon oxide film. .

On the other hand, a thin oxynitride film has the properties of a nitride film that traps electric charges, as well as the properties of a silicon oxide film that tunnels electric charges.
Unless a voltage high enough to perform writing or erasing is applied to both ends of the film, the charge existing near the interface of the nitride film can be sufficiently held. As described above, the oxynitride film has a role of suppressing charge diffusion and maintaining a memory state.

(Example) A specific example of the present invention will be described with reference to FIG.
As shown in FIG. 1, the present semiconductor memory device has a thin silicon oxide film in a predetermined region on a single crystal p-type silicon substrate 1.
4, a thin oxynitride film 5, a nitride film 6, and a gate electrode 7 made of a polysilicon film are sequentially stacked, and source and drain regions 2, 3 each made of an n-type region are provided on both sides adjacent to this region, Source and drain electrodes 12 and 13 are formed thereon.

Thin silicon oxide film 4 that can be a tunneling medium
In order to effectively use the tunneling effect, the thin oxynitride film 5 has a total thickness of both films of 15 to
It is necessary to set the thickness to about 30 °. In this embodiment, the thickness is set to 10% for the silicon oxide film and 10% for the oxynitride film. A thin silicon oxide film is formed by oxidation of a known silicon substrate,
Further, as a method of forming the oxynitride film, (1)
A method of forming by a vapor phase growth method based on a chemical reaction of ammonia (NH ₃ ), dichlorosilane (SiH ₂ Cl ₂ ) and nitrous oxide (N ₂ O), (2) a silicon oxide film 4 such as ammonia (NH ₃ ) (3) Ammonia (N
There is a method of forming a nitride film by a vapor phase growth method based on a chemical reaction between H ₃ ) and dichlorosilane (SiH ₂ Cl ₂ ), and then oxidizing the nitride film. Formed by the method.

Next, on the oxynitride film 5, NH ₃ / SiH ₂ Cl ₂ =
A nitride film 6 was formed at a rate of 10 by a vapor phase growth method at 750 ° C. at about 500 °.

Next, a polysilicon film is formed on the nitride film 6 approximately.
The gate electrode 7 was formed by forming the electrode at 4000 °. Thereafter, phosphorus is implanted by ion implantation to form source / drain regions 2 and 3 and source / drain electrodes are formed thereon to obtain a semiconductor memory device having the structure shown in FIG. Can be.

The write / erase characteristics of this embodiment configured as described above are shown by solid lines 10 and 11 in FIG. For example, when a pulse voltage of ± 20 V is used, the write / read characteristics are lower than the characteristics of the conventional example (broken lines 8 and 9).
Erasure characteristics are improved, and remarkably improved especially on the erasure side.

(Effects of the Invention) As described above, according to the present invention, the write / erase characteristics can be significantly improved, and this greatly contributes to solving practical problems when applied to a large capacity memory. It is.

[Brief description of the drawings]

FIG. 1 is a sectional view of one embodiment of the present invention, FIG. 2 is a write / erase characteristic diagram for explaining the effect of the present invention, and FIG. 3 is a sectional view of a conventional MNOS type semiconductor memory device. FIG. 1 ... single crystal p-type silicon substrate, 2, 3 ... source and drain regions, 4 ... silicon oxide film, 5 ... oxynitride film, 6 ... nitride film, 7 ... gate electrode,
12,13 ... Source and drain electrodes.

Claims (1)

(57) [Claims] An insulating film, a nitride film, and a conductive film are sequentially laminated on a predetermined region on a single conductivity type single crystal semiconductor substrate, and the semiconductor film is formed on the semiconductor substrate adjacent to both sides of the predetermined region. In a semiconductor memory device having a region of a conductivity type opposite to a substrate, the insulating film has a thickness of 15 to 30 °, is composed of a silicon oxide film and an oxynitride film, and has a film thickness of the oxynitride film. Is a half of the thickness of the insulating film.