JPH02277269A - Manufacture of nonvolatile memory - Google Patents

Abstract

PURPOSE:To reduce deterioration of memory characteristics by forming a tunneling insulating film, and then providing a step of implanting hydrogen ions. CONSTITUTION:A silicon oxide film 2, a silicon nitride film 3, and a field thermal oxide film 4 are formed on a substrate 1, the films 3, 4 are sequentially etched, a silicon oxide film 5 is then formed, ion implanted with photoresist 6 as a mask, and N-type diffused layers 8, 9 are formed. Then, the photoresist 6 is removed, the part of the film 5 on the layer 9 is opened, and a thin silicon nitride film 10 to become a tunneling medium is formed. Thereafter, a floating gate 11, a silicon oxide film 12, a control gate electrode 13, N-type diffused layers 14, 15 reformed, a silicon oxide film 16 are vapor grown on a whole surface, and hydrogen ions 17 are then implanted to the whole surface. Thus, the hydrogen content of the film 10 is increased to prevent the deterioration of memory holding characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for manufacturing a nonvolatile memory device having excellent memory retention characteristics and comprising a field effect transistor having a floating gate structure.

(Prior Art) Conventionally, electrically written and erased EEPROM (E
Electrically Erasable and
2. Description of the Related Art A nonvolatile memory device having a floating gate (hereinafter referred to as F gate) structure that can be written and erased by tunneling injection is known as one type of programmable ROM (ROM). This device tunnels charges from the semiconductor substrate side through a thin silicon oxide film, accumulates charges in the F gate electrode on the insulating film, and changes the threshold voltage of the transistor.

The principle is to memorize information.

FIG. 3 is a cross-sectional view showing a typical example of such a conventional F-gate structure nonvolatile memory.

Reference numeral 31 denotes a P-type silicon substrate, in which a drain region 32 made of an N-type diffusion layer is formed. It has a source region 33 and a silicon oxide film 34 formed over it, and a part of this film that contacts the upper part of the drain region 32 is opened to form a thin silicon oxide film 35 that becomes a tunneling medium over the entire surface. An F gate electrode 36. is provided on the upper surface of this silicon oxide film 35. It has a structure in which a silicon oxide film 37 and a control gate electrode 38 are sequentially laminated.

In recent years, in nonvolatile memory devices configured as described above, thin silicon oxide films (tunneling insulating films), which serve as the tunneling films, have been developed in order to lower the programming voltage or to reduce deterioration of memory characteristics due to rewriting. In place of 35, a thin silicon nitride film, a two-layer film of silicon oxide film-silicon nitride film, a three-layer film of silicon oxide film-silicon nitride film-silicon oxide film, or a silicon nitride film such as an oxynitride film It has been proposed to use a tunneling insulation crotch system.

However, in a nonvolatile memory device that uses a silicon nitride film-based tunneling insulating film, a high melting point metal such as a polysilicon film is usually used for the F gate electrode 36 and the control gate electrode 38, so the formation of the tunneling insulating film Afterwards, high heat treatment of about 900°C to too much°C is always required. Therefore, the film quality of the silicon nitride film-based tunneling insulator deteriorates significantly, resulting in deterioration of memory retention characteristics.

(Problems to be Solved by the Invention) In view of the above-mentioned conventional problems, the present invention aims to reduce the programming voltage and reduce the memory capacity associated with rewriting without deteriorating the memory retention characteristics of a nonvolatile memory device with an F-gate structure. An object of the present invention is to provide a nonvolatile memory device that can reduce characteristic deterioration.

(Means for solving problem a) The deterioration of the memory retention characteristics described above strongly depends on the film quality after the silicon nitride film is grown, and is particularly related to the content of hydrogen contained in the silicon nitride film, especially the content of 5i-It bonds. There is 5i-H
In silicon nitride films with many bonds, the number of 5i-H bonds decreases due to high heat treatment above the growth temperature, and 5 unstable traps are added and increased, increasing the electrical conductivity of the silicon nitride film and improving memory retention properties. As a result of investigation by the present inventors, it was found that the That is, deterioration in memory retention characteristics due to high heat treatment after forming a silicon nitride film largely depends on the hydrogen content at the time of forming the silicon nitride film.

Therefore, the present invention achieves the above-mentioned object by: - forming a tunneling insulating film including at least a silicon nitride layer in a conductive type semiconductor substrate, forming an F gate electrode on the upper surface thereof, and forming an insulating film on the electrode; This is achieved by providing a step of implanting hydrogen ions after forming the tunneling insulating film in a method of manufacturing a nonvolatile memory device including a step of forming a control gate electrode through the tunneling insulating film.

(Function) According to the present invention, by implanting hydrogen ions, the hydrogen content of the silicon nitride film is increased, the electrical conductivity is reduced, and excellent memory retention characteristics can be obtained without deterioration of memory retention characteristics. .

In addition, in a nonvolatile memory device with an F-gate structure, after forming a tunneling insulating film, an F-gate electrode made of a high-melting point metal such as a polysilicon film is usually formed, and then a source, drain, or surface protection film is formed. However, in order to indent the source and drain 2 and make the surface protective film denser, high-temperature treatment is performed at a temperature higher than the growth temperature of the silicon nitride film of the tunneling insulating film, so hydrogen ion implantation is performed after the high-temperature treatment. However, since the present invention performs activation after hydrogen ion implantation at a temperature lower than the silicon nitride film growth temperature, further effects can be obtained.

(Example) Hereinafter, the present invention will be explained with reference to a process sectional view of an example of the present invention shown in Figure @1.

First, a silicon oxide film 2 was formed on the entire surface of a P-type silicon planting board 1 to a thickness of 500 mm, and then a silicon nitride film 3 was formed.
A total of 1,000 samples are formed, and predetermined portions are photo-etched for element history [Figure (a)].

Next, a field thermal oxide film 4 with a thickness of about 1 μm is formed by normal thermal oxidation [Figure (b)], and then, as shown in Figure (c), a silicon nitride film 3. While sequentially etching the field thermal oxide film 4, the silicon oxide pancreas 5 is etched using the usual method.
After that, using photoresist 6 as a mask, phosphorus ions 7 are implanted to form N-type diffusion layers 8 and 9 at 100 k.
eV, I x 101 gcm −” (7).

Next, as shown in figure (d), the photoresist 6 is removed,
A part of the silicon oxide film 5 on the N-type diffusion layer 9 is opened,
A thin silicon nitride film 10, which will serve as a tunneling medium, is deposited on this layer by a low pressure vapor phase growth method based on a chemical reaction between dichlorosilane (SiH□CO,) and ammonia (NH3).
NH3/ 5iH2CO2” 5.1 at 750℃
Have 20 people form.

Next, as shown in Figure (e), approximately 2×10211. About 5,000 -3 doped polysilicon films were formed by vapor phase growth, and then.

An F gate electrode 11 made of a polysilicon film is formed by photoetching, and then a silicon oxide film 12 is formed on the F gate electrode 11 to a thickness of approximately 400 by thermal oxidation. Then add about 2 X t o 2 phosphorus
A polysilicon film doped with 0-7 is grown in about 4,000 phases, and a control gate electrode 13 made of polysilicon is formed by photoetching. Using this film and the field thermal oxide film 4 as a mask, arsenic ions are etched into the film. 4×101sC11+-2 implantation is performed at 50 keV to form N-type diffusion layers 14 and 15 in the source and drain regions.

Next, as shown in Figure (f), after vapor phase growth is performed on the entire surface of the silicon oxide film 16, in order to activate the source and drain and to make the silicon oxide film 16 dense, Heat treatment. Thereafter, hydrogen ions 17 are implanted into the entire surface.

In this example, H% ions were used as the hydrogen ion species,
The acceleration energy was 10 keV and the implantation amount was 5 x 10'' -2.Furthermore, the implanted ions were activated.

At a temperature below the silicon nitride film growth temperature of 700°C.

Heat treatment is performed in a N2 atmosphere for 20 minutes.

Finally, as shown in Figure 1(g), in order to provide electrodes for the N-heavy diffusions Nj 14 and 15 that constitute the source and drain regions, contact holes are formed in the silicon oxide film 16 by photoetching, and aluminum electrodes 18 are formed. By doing so, an F-gate type nonvolatile memory device is formed.

FIG. 2 is a diagram showing the memory retention characteristics of the F-gate type nonvolatile memory device formed as described above, in which the vertical axis represents the threshold voltage, the horizontal axis represents the memory retention time, and the solid line a represents 1 is a memory retention characteristic according to the present invention. It can be seen that the characteristics of the present invention are clearly superior to those of the conventional method, which is indicated by the broken line.

The present invention has been described in detail above using a single layer silicon nitride film as the tunneling insulating film, but this invention is not limited to a double layer film of a silicon nitride film and a silicon oxide film, or a silicon oxide film and a silicon oxide film.
It goes without saying that similar results can be obtained by using a three-layer film of a silicon nitride film and a silicon oxide film, or a silicon nitride film-based insulating film of an oxynitride film.

(Effects of the Invention) As is clear from the above description, the present invention realizes lower programming voltage and reduction of deterioration of memory characteristics due to rewriting without deteriorating memory retention characteristics.
This greatly contributes to improving the performance of F-gate type nonvolatile memory devices.

[Brief explanation of drawings]

Fig. 1 is a process sectional view explaining one embodiment of the present invention;
The figure shows its characteristics, and FIG. 3 is a cross-sectional view of the structure of a conventional example. 1...P-type silicon substrate, 2.5.12.16...
・Silicon oxide film, 3.10... silicon nitride film,
4... Field thermal oxide film, 6... Photoresist, 7... Phosphorus ion, 819.14.15
... N type diffusion layer, 11... Floating gate electrode (F gate electrode), ]3... Control gate electrode, 17... Hydrogen ion, 18... Aluminum electrode. Patent applicant: Matsushita Electronics Co., Ltd.

Claims (1)

[Claims] A step of forming a tunneling insulating film containing at least a silicon nitride film in a semiconductor substrate of one conductivity type, forming a floating gate electrode on the upper surface of the tunneling insulating film, and a step of forming a control gate electrode on the electrode via an insulating film. A method of manufacturing a non-volatile memory device comprising the step of implanting hydrogen ions after forming the tunneling insulating film.