JPS5963764A - Manufacture of nonvolatile memory - Google Patents

Abstract

PURPOSE:To relax discontinuity, to reduce defects and strain and to stabilize the interface by forming an SiO2 thin-film on an Si substrate, nitriding the surface through treatment at a specific temperature in NH3 and vapor-growing an Si3N4 film up to predetermined thickness. CONSTITUTION:The SiO2 film 4 on an Si substrate 1 is bored and source and drain 3 are formed, and the opening is coated with the SiO2 thin-film 5 of approximately 25Angstrom . A thermally nitrided SiO2 film 8 is formed through treatment for thirty-five min at 700-1,000 deg.C in NH3, and the film 5 is further thinned. The film 5 is prepared in approximately 20Angstrom thickness, through which the film 5 can function as a tunnel medium, by selecting the conditions of growth of the film 5 and the conditins of NH3 treatment. When the Si3N4 film 6 is superposed through a vapor growth method, the defects and strain of the interface of the film 6 are reduced. An Al electrode 7 is formed, and the MNOS type nonvolatile memory is completed. According to the constitution, a threshold voltage value, memory holding characteristics, etc. hardly vary due to the defects and strain of the interface, and the nonvolatile memory can be manufactured with excellent accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing an MNOS (metal-silicon nitride film-silicon dioxide film-semiconductor) type nonvolatile memory device. The present invention provides a method for manufacturing a sexual memory device.

Conventional configuration and its problems The MNO8 type nonvolatile memory device has a thin silicon dioxide film applied from the semiconductor side to trap levels generated in the silicon nitride film at or near the interface between a silicon nitride film and a thin silicon dioxide film. The threshold voltage (Vth) of the field effect transistor increases due to the charge that is injected and accumulated by tunneling.
The most important challenge in manufacturing MNO8 type nonvolatile memory devices is to accurately and stably align the memory retention characteristics, and it is also a serious problem in practical use. It has become.

FIG. 1 is a process diagram illustrating a method of manufacturing a conventionally used MNO'S type nonvolatile memory device. first,
As shown in FIG. 1, a source region 2. After the drain region 3 is formed by selective diffusion technology and a predetermined portion of the silicon dioxide film 4 formed during the selective diffusion is opened by photoetching, a hole is formed in the hole portion.
A thin silicon dioxide film 5 having a thickness of approximately 200° C., which allows charge tunneling to occur, is oxidized in an oxygen atmosphere at a temperature of 700° to 800° C. to form the silicon dioxide film 5.

Next, as shown in FIG. 1), a silicon dioxide film 5 is formed.
A silicon nitride film 6 is formed on the silicon nitride film 6 by thermal decomposition from silane or a mixed gas of dichlorosilane and ammonia.
It is formed to a thickness of about 400 to SOO8 by a so-called vapor phase growth method, and then a metal electrode 7 such as aluminum is deposited thereon.

By the way, the electrical properties of the MNOS type nonvolatile memory device are as follows: (a) Charge accumulation and non-accumulation states in the silicon nitride at or near the interface between the silicon dioxide film and the silicon nitride film with respect to the gate applied voltage; The upper and lower widths of the hysteresis curve corresponding to ΔVtb' (the size of the L threshold voltage window).

(b) Memory retention characteristics of charges in accumulated and non-accumulated states.

(c) Deterioration characteristics in items (a) and (b) above after applying a relatively high gate voltage and repeatedly writing and erasing.

These properties are extremely important in practice, and these properties are influenced by the following physical parameters.

(1) Thickness of silicon dioxide film 5 2) Distribution of traps where charge is accumulated (3) Amount of charge accumulated (4) Electrical conductivity of silicon nitride film 6 (5) Silicon dioxide 5 - substrate 1 interface and , the state of the silicon dioxide 5-silicon nitride 6 interface The physical parameters described above vary significantly depending on the formation conditions of the silicon dioxide film 5 and the silicon nitride film 6, and conventionally, it has been extremely difficult to control them, and it has been difficult to control them with precision and stability. The major problem was that it was difficult to determine the electrical characteristics. In particular, in the method of forming the silicon nitride film 6 directly on the silicon dioxide film 5 by vapor phase growth as in the conventional example described above, the interface between the silicon dioxide film 5 and the silicon nitride film 6 has physical properties. It is a discontinuous surface where materials with different structures come into mechanical contact, and distortions and defects often occur at this interface. Such distortions and defects strongly affect items (2) and (6) among the physical property parameters mentioned above, and this makes it difficult to manufacture MNOS nonvolatile memory devices with uniform electrical characteristics in a stable manner, rather than with precision. This makes it extremely difficult in practice.

The present invention aims to solve these conventional problems, and provides a method for manufacturing a nonvolatile memory device that is particularly effective in stabilizing the interface state between silicon nitride and silicon dioxide and has good controllability. This is what we provide.

Structure of the Invention The present invention involves forming a thin silicon dioxide film on a silicon substrate surface, and then heating the film to 700 to 11oO in an ammonia gas atmosphere.
The surface of the silicon dioxide film is thermally nitrided by heating at a high temperature of °C, and then a silicon nitride film is formed to a predetermined thickness by vapor phase growth. By incorporating the interface into a thermally nitrided silicon dioxide film, it is possible to alleviate a kind of discontinuity and reduce defects and distortion. explain. FIG. 2 is a process diagram for explaining the manufacturing method of the present invention.

As shown in FIG. 2(5), a source region 2. The drain region 3 is formed by a well-known selective diffusion technique, and after photo-etching a predetermined portion of the silicon dioxide film 4 formed during the selective diffusion, 2 is etched in the opening portion.
A silicon dioxide film 5 having a thickness of about 5.8 mm is formed.

Next, as shown in Figure 2 (B), the tail was heated to 700-1100℃.
The surface of the silicon dioxide film 5 is thermally nitrided by heating at a high temperature for 30 to 6 minutes in an ammonia gas atmosphere to form a thermally nitrided silicon dioxide film 8.

Through this step, the surface of the silicon dioxide film 5 is nitrided, and the thickness of the silicon dioxide film 5 is reduced.

Therefore, the conditions for growing the silicon dioxide film and the conditions for the ammonia treatment are controlled so that the thickness of the silicon dioxide film 5 after thermal nitridation is approximately 20 degrees centigrade thick enough to serve as a tunneling medium.

Next, as shown in FIG. 2 (0), on the thermally nitrided silicon dioxide film 8, a silicon nitride film 6 of approximately 4° to 80° is formed by vapor phase growth.

Through the above-described steps, defects and distortions at the interface between the conventional silicon dioxide film 5 and silicon nitride film 6 are reduced.

Further, as shown in FIG. 2 (0), an aluminum electrode 7 is deposited on the silicon nitride film 6 by a normal vacuum deposition method.

Since the MNO8 type nonvolatile memory device obtained as described above forms a thermally nitrided silicon dioxide film, the discontinuity at the interface between the silicon dioxide film and the silicon nitride film is eliminated.
Defects and distortions at the interface are reduced, and as a result, MNO8 type nonvolatile memory devices produced by defects and distortions can be manufactured stably with high precision, with less variation in electrical properties such as threshold voltage and memory retention characteristics. It becomes easier to do.

In this example, a case has been described in which a metal (aluminum) gate type MNO8 type nonvolatile memory device in which the source and drain are formed by selective diffusion is manufactured.
A gate insulating film is formed by the manufacturing method of the present invention using a high melting point material such as polysilicon as a gate electrode,
It goes without saying that the source and drain may be formed using the well-known self-line technology.

Effects of the Invention As described above, the present invention, when forming a gate insulating film of an MNO8 type nonvolatile memory device, forms a thin silicon dioxide film that can serve as a tunneling medium and then heats it at high temperature in an ammonia gas atmosphere. , by thermally nitriding the surface of the silicon dioxide film and then forming a silicon nitride film to a predetermined thickness by vapor phase growth, the discontinuity at the interface between the silicon dioxide film and the silicon nitride film is eliminated;
Distortion and defects at the interface can be reduced. As a result, it is possible to eliminate the instability of the electrical characteristics of the MNO8 nonvolatile memory device by reducing distortion and defects at the interface, and to ensure accurate and stable production of the MNO8 nonvolatile memory device with uniform characteristics. This will greatly contribute to the

[Brief explanation of drawings]

FIG. 1 CAJω) is a sectional view of the manufacturing process of a conventional MNO8 type nonvolatile memory device, and FIGS. 2(3) to (C) are sectional views of the manufacturing process of the present invention. 1...Silicon substrate, 6...Silicon dioxide film, 6...Silicon nitride film, 8...
...Thermal nitrided silicon dioxide film. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
figure

Claims (1)

[Claims] (1) - Step of forming a silicon dioxide film of a desired thickness on the surface of a conductive type semiconductor substrate;
A nonvolatile method comprising the steps of heating at a temperature of ○ to 110° C. to form a thermally nitrided silicon dioxide film on the silicon dioxide film, and forming a silicon nitride film on the thermally nitrided silicon dioxide film. A method for producing a sexual memory device.