JPH02114568A - Manufacture of nonvolatile storage device - Google Patents

Abstract

PURPOSE:To lower a voltage of a programming voltage without worsening a storage retention characteristic and to reduce a deterioration of a storage characteristic by a rewrite operation by a method wherein, after a tunneling insulating film has been formed, a heat treatment in an atmosphere of hydrogen is executed. CONSTITUTION:An opening is made in one part of a silicon oxide film 4 on an N-type diffusion layer 15 by using an ordinary photoetching technique; a thin silicon nitride film 16 to be used as a tunneling medium is formed in the opening part by a low-pressure vapor growth method on the basis of a chemical reaction of dichlorosilane (SiH2Cl2) and ammonia (NH3); after that, a heat treatment is executed in an atmosphere of hydrogen. Thereby, a content of hydrogen in the silicon nitride film 16 is increased; an electric conductivity of the silicon nitride film 16 is reduced; it is possible to obtain an excellent storage retention characteristic which is worsened little.

Description

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

(Prior art) Conventionally, electrically programmable and erasable ROM (E
P ROM, E 1 electrically Era
sable and programmable ROM
) is known as a nonvolatile memory device with a floating gate structure in which writing and erasing is performed by tunneling injection.

This floating gate type nonvolatile memory device tunnels charges from the semiconductor substrate side through a thin insulating film, stores the charges in the floating gate electrode on the insulating film, and changes the threshold voltage of the transistor to store information. The principle is to memorize.

A conventional floating gate type nonvolatile memory device will be explained with reference to a structural cross-sectional view shown in FIG. As shown in FIG. 3, a drain region 2 and a source region 3 containing N-type impurities are formed in a P-type silicon substrate 1, and a drain region 2 and a source region 3 containing N-type impurities are formed on the silicon substrate 1. A silicon oxide film 4 is formed, and a thin silicon oxide IyA5 that can serve as a tunneling medium is formed in a portion of the silicon oxide film 4 above the drain region 2, and a floating gate electrode 6 is formed on the silicon oxide film 5. It has a structure in which a silicon oxide film 7 and a control gate electrode 8 are sequentially laminated.

In recent years, in nonvolatile storage devices as shown in Figure 3,
In order to lower the programming voltage and reduce deterioration of memory characteristics due to rewriting, a thin silicon nitride film or a silicon nitride film-silicon oxide film 5 is used instead of the thin silicon oxide film 5, which can serve as a tunneling medium.
M! It has been proposed to use a multilayer film of J, a three-layer multilayer film of a silicon oxide film, a silicon nitride film, and a silicon oxide film, or a tunneling insulating film made of silicon nitride threads such as an oxynitride film.

(Problem to be Solved by the Invention) However, in a nonvolatile memory device using a tunneling insulating film made of silicon nitride yarn, since a high melting point metal such as a polysilicon film is usually used for the floating gate electrode and the control gate electrode, the tunneling After forming the insulating film, high-temperature heat treatment of about 900 to 1000°C is necessary, which causes problems such as a significant change in the quality of the tunneling insulating film of the silicon nitride suction yarn and deterioration of memory retention characteristics. Ta.

In view of these problems, it is an object of the present invention to reduce the programming voltage and reduce the deterioration of memory characteristics due to rewriting in a floating gate nonvolatile memory device without deteriorating the memory retention characteristics. The goal is to provide a manufacturing method that can.

(Means for Solving the Problems) In order to achieve the above object, the present invention includes a step of selectively forming a tunneling insulating film containing at least a silicon nitride film on the surface of a semiconductor substrate of one conductivity type, and a step of forming a floating film on the tunneling insulating film. In a method for manufacturing a nonvolatile memory device, the method includes at least the steps of forming a gate electrode and forming a control gate electrode on the floating gate electrode via an insulating film, after forming the tunneling insulating film, It is characterized by carrying out a heat treatment.

(Function) The present invention increases the hydrogen content in the silicon nitride film by performing hydrogen heat treatment, reduces the electrical conductivity of the silicon nitride film, and provides excellent memory retention properties with less deterioration of memory retention properties. It is something that you can wander around.

(Example) According to studies by the present inventors, deterioration of memory retention characteristics due to high-temperature heat treatment after forming a tunneling insulating film containing a silicon nitride film strongly depends on the film quality immediately after the silicon nitride film is grown.
In particular, the hydrogen contained in the silicon nitride film, especially 5i-I (
It is related to the content of bonds, and a silicon nitride film with many 5i-H bonds has a reduced number of 5i-H bonds by performing heat treatment at a high temperature higher than the silicon nitride film growth temperature.
It has been found that the addition of unstable traps increases and the air conductivity of the silicon nitride film increases, resulting in deterioration of memory retention characteristics. In other words, it has become clear that the deterioration in memory retention characteristics caused by high-temperature heat treatment in a step after forming the silicon nitride film is largely dependent on the hydrogen content during the formation of the silicon nitride film.

In addition, in a floating gate nonvolatile memory device, after forming a tunneling insulating film, a floating gate electrode and a control gate electrode made of a high melting point metal such as a polysilicon film are formed, and then a source, a train, and a protective film are formed. In these steps, heat treatment is performed at a high temperature higher than the growth temperature of the silicon nitride film, which is the tunneling insulating film, in order to push in the source and drain, make the protective film denser, etc. Hydrogen treatment must be performed after these high-temperature heat treatments are completed. Further, silicon nitride films are usually formed by chemical vapor deposition, and the growth temperature is usually 700 to 800°C.

It has been found that when such a silicon nitride film is used as a tunneling insulator, hydrogen treatment at a temperature of approximately 700° C. or higher is effective.

Next, specific embodiments of the present invention will be described using the drawings.

FIG. 1 is a process-order sectional view showing an embodiment of the present invention.

First, as shown in FIG. 1(A), 500 people formed a silicon oxide film 9 on the entire surface of a P-type silicon substrate 1.

After forming 1000 silicon nitride films 10, predetermined portions for element isolation are etched using a known photoetching technique.

Next, as shown in FIG. 1(B), a field oxide film 11 is formed to an IP level by a normal thermal oxidation method.

Next, as shown in FIG. 1C, the silicon nitride film 10 and the underlying silicon oxide film 9 are sequentially etched, and then 500 silicon oxide films 4 are formed using a conventional thermal oxidation method. Next, using the photoresist 12 as a mask,
Phosphorus ions 13 are implanted to form N-type diffusion layers 14 and 15. In this example, the implantation conditions were 100 keV, IXIO
It was carried out under the conditions of ``an-2''.

Next, as shown in FIG. 1(D), a photoresist 12
After removing the silicon oxide film 4 on the N-type diffusion layer 15
A part of the hole is opened using normal photoetching technology,
A thin silicon nitride film 1, which becomes a tunneling medium, is formed in this hole by a low pressure vapor phase growth method based on a chemical reaction between dichlorosilane (SiH2C1!) and ammonia (NH,).
Form 6. In this example, NH, /SiH, CIl
About 100 people formed the silicon nitride film 16 under conditions of , = 5 and 750°C.

Next, as shown in FIG. 1(E), a silicon nitride film 1 is formed.
About 5,000 polysilicon films doped with phosphorus (approximately 2XIO20m-3) are formed on 6 by vapor phase epitaxy, and then floating gate electrodes 6 made of polysilicon are formed by known photoetching techniques. . Then by normal thermal oxidation method.

A silicon oxide film 7 is formed on the floating gate electrode 6 to a thickness of about 400. Thereafter, approximately 4,000 polysilicon films doped with phosphorus (approximately 2XIO"an-3) were formed by vapor phase growth, and then control gate electrodes 8 made of polysilicon films were formed by known photoetching techniques. Form.

Furthermore, using the control gate electrode 8 and field oxide film 11 as a mask, arsenic is implanted (50 keV,
4×101sc101s, N-type diffusion layers 2 and 3 which will become source and drain regions are formed.

Next, as shown in FIG. 1(F), a silicon oxide film 17 is deposited on the entire surface by a known vapor phase growth method.

Heat treatment is performed at 1000° C. in an N2 atmosphere to push in the source and drain and to make the silicon oxide film 17 dense. After that, in a hydrogen atmosphere, at 900℃,
Heat treatment was performed for 30 minutes. Finally, silicon oxide film 1
A contact hole is formed in the substrate 7 by a known photoetching technique to form an aluminum electrode 18, thereby producing a floating gate type nonvolatile memory device as shown in FIG. 1(F).

FIG. 2 shows an example of the memory retention characteristics of the floating gate nonvolatile memory device obtained as described above. The vertical axis shows the threshold voltage, and the horizontal axis shows the retention time. Second
As shown in the figure, the memory retention characteristics of the nonvolatile memory device fabricated by the manufacturing method of the present invention (actual @ 19) are much better than those without hydrogen heat treatment (dashed line 20). I know that there is.

In this example, a case is shown in which a single layer film of silicon nitride film is used as the tunneling insulating film.
It goes without saying that the same effect can be obtained when using a layered film, a three-layered film of silicon oxide film-silicon nitride film-silicon oxide film, or an insulating film made of silicon nitride suction, such as an oxynitride film.

(Effects of the Invention) As is clear from the above explanation, according to the manufacturing method of the present invention, programming voltage can be lowered without deteriorating memory retention characteristics, and deterioration of memory characteristics due to rewriting can be reduced. This will greatly contribute to improving the performance of floating gate type semiconductor memory devices.

[Brief explanation of the drawing]

Fig. 1 is a process-order sectional view for explaining an embodiment of the present invention, Fig. 2 is a memory retention characteristic diagram for explaining the present invention in detail, and Fig. 3 is a conventional floating gate type nonvolatile memory. FIG. 3 is a structural cross-sectional view of the device. 1... P-type silicon substrate, 2, 3, 14° 15.
...N-type diffusion layer, 4,7,9.17...silicon oxide film, 5,16...thin silicon nitride film that serves as a tunneling medium, 6...floating gate electrode, 8...control gate Electrode, 10... Silicon nitride film, 11... Field oxide film, 12.
... Photoresist, 13... Phosphorus ion, 18
...Aluminum electrode. Patent applicant: Matsushita Electronics Co., Ltd.＼-7 Figure 10 Nitride silicon 7I refreshing factor 8 Co> Draw J electrode 4.15...N1 cover 1 Figure old 17 Valuated silicon film °° Aluminum electrode Diagram

Claims (5)

[Claims] (1) selectively forming a tunneling insulating film containing at least a silicon nitride film on the surface of a semiconductor substrate of one conductivity type;
In the method for manufacturing a non-volatile memory device, the method includes forming a floating gate electrode on the tunneling insulating film, and forming a control gate electrode on the floating gate electrode via an insulating film, wherein the tunneling insulating film is formed. 1. A method of manufacturing a nonvolatile memory device, which comprises performing heat treatment in a hydrogen atmosphere after the above steps. (2) The method for manufacturing a nonvolatile memory device according to claim (1), wherein the tunneling insulating film is a laminated film of two types: a silicon nitride film and a silicon oxide film. (3) The nonvolatile memory device according to claim (1), wherein the tunneling insulating film is a three-layered film including a first silicon oxide film, a silicon nitride film, and a second silicon oxide film. manufacturing method. (4) The method for manufacturing a nonvolatile memory device according to claim (1), wherein the tunneling insulating film is an oxynitride film. (5) The temperature of the heat treatment in the hydrogen atmosphere is 700℃.
Claims (1), (2), characterized in that the temperature is at least ℃.
The method for manufacturing a nonvolatile memory device according to any one of (3) and (4).