JPH0320086A - Manufacture of semiconductor storage device - Google Patents

Abstract

PURPOSE:To prevent a tungsten silicide film of high melting point from peeling by patterning a conductive layer which becomes a floating gate electrode to a specified shape and thereafter by flattening a stepped section whose edge section overrides a thick oxide film. CONSTITUTION:A LOCOS oxide film 12 and a gate oxide film 13 are formed on an Si substrate 11, and then a first layer of a polycrystalline silicon film 14 is made to grow through CVD method. A BPSG film 15 is formed as an insulating film and patterned. A section excepting a stepped section is removed through wet etching, and heat treatment is carried out in a high temperature oxide atmosphere of oxygen and hydrogen gas. A gate oxide film 16 is formed on a first layer of a polycrystalline silicon film 14 and a substrate 11 while the BPSG film 15 is thermally melted to flatten the stepped section. Then, a second layer of a polycrystalline silicon film 17 and a tungsten silicide film 18 of high melting point are formed. It is possible to prevent the tungsten silicide film 18 from peeling in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of manufacturing a highly reliable semiconductor memory device.

BACKGROUND OF THE INVENTION Conventionally, a nonvolatile semiconductor memory device has been well known as a type of semiconductor memory device, which has two gates, a floating gate and a control gate, in its cell gate, and maintains a written state by injecting electrons into the floating gate. ing. A manufacturing method for the above-mentioned EFROM as a storage device will be described.

FIG. 2 is a cross-sectional view of the manufacturing process of a conventional semiconductor memory device. A conventional method for manufacturing a semiconductor memory device will be described below with reference to FIG.

For example, the St substrate 21 is oxidized and a thick oxide film 22 (0.
After forming a thermal oxide film 23 (about 3001 mm thick). Thereafter, the first layer of polycrystalline silicon film 24 (0.000.
(approximately 3 μm), and then impurity diffusion is performed. Next, it is patterned into a predetermined shape using ordinary lithography technology and dry etching technology (see Fig. 2(a)).
)).

Next, a thermal oxide film 2-5 is formed on the polycrystalline silicon film 24 by a high temperature thermal oxidation method (FIG. 2(b)).

Next, a second layer of polycrystalline silicon film 26 (approximately 0.2 μm), which is a control gate, is grown using the CVD method.
Next, impurities are diffused. Next, a high melting point tungsten silicide film 27 (approximately 0.25 μm) is grown using the CVD method, and then patterned into a predetermined shape using ordinary phosphorography and dry etching techniques (FIG. 2(C)).

As described above, in the conventional semiconductor memory device, when the first layer polycrystalline silicon film 24, which is a floating gate, is patterned into a predetermined shape, the end portion 28 rides on the thick oxide film 22, resulting in a step. produce part. Next, when the second layer polycrystalline silicon film 26 and the high melting point tungsten silicide film 27, which are control gates, are grown, the end portion 28 of the first layer polycrystalline silicon film 24 forms a thick oxide film 22. Because it rides on top and creates a stepped portion, the adhesion of the high melting point tungsten silicide film 27 deteriorates.
Peeling of the film 31 and 32 (FIG. 3) may occur at the step portion with respect to the second layer polycrystalline silicon film 26, making patterning impossible.

Problems to be Solved by the Invention As described above, in the above-mentioned conventional configuration, the problem is that the adhesion between the second layer polycrystalline silicon film and the high melting point tungsten silicide film deteriorates at the stepped portion, resulting in peeling of the film. there were.

The present invention solves the above-mentioned conventional problems, and is a method for manufacturing a semiconductor memory device with excellent reliability by preventing peeling of the second layer polycrystalline silicon film and the high melting point tungsten silicide film at the stepped portion. The purpose is to provide

Means for Solving the Problems In order to achieve this object, the present invention provides a structure in which a conductive layer that becomes a floating gate electrode is patterned into a predetermined shape, and then the end portion of the conductive layer rests on a thick oxide film. An insulating film that can be thermally melted is formed so as to flatten the surface, and then the previous insulating film is melted by heat treatment, and a gate oxide film is simultaneously formed on the conductive layer that will become the floating gate electrode and on the semiconductor substrate. This is to flatten the area.

Function: This structure can prevent the second layer polycrystalline silicon film from peeling off from the high melting point tungsten silicide film at the stepped portion.

Example Examples will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view of the manufacturing process of a semiconductor memory device according to an embodiment of the present invention. First, as shown in FIG. 1 (al), one main surface of the Si substrate 11 was selectively oxidized and
An OGOS oxide film 12 is formed.

Thereafter, a gate oxide film 13 of 300 Å is formed in a high-temperature oxidizing atmosphere, and then a first layer polycrystalline silicon film 14 of 3000 Å is grown using the CVD method, and then impurities are diffused. Next, patterning is performed using photolithography technology, and butterninx is formed into a predetermined shape using reactive ion etching. Next, as an insulating film that can be thermally melted, 6
A BPSG film 15 of 0.0000000000000000000000000000 BPSG film 15 is grown by atmospheric pressure CVD method, patterned by photophosphorography technology, and portions other than the stepped portions are removed by wet etching (buffered hydrofluoric acid solution). Next, as shown in FIG. 1(b), a heat treatment is performed in a high-temperature oxidizing atmosphere of oxygen and hydrogen gas to thermally melt the BPSG film 15, and at the same time to melt the BPSG film 15 and the St substrate. A gate oxide film 16 is simultaneously formed thereon.

Next, as shown in Figure 1 (Cl), 200
2nd of 0A! An ri-th polycrystalline silicon film 17 is grown, and then impurities are diffused. Next, 2,500 high melting point tungsten silicide films 18 are grown using the CVD method, followed by patterning using photolithography and patterning into a predetermined shape using reactive ion etching.

Effects of the Invention The present invention has been developed by patterning a conductive layer that will become a floating gate electrode into a predetermined shape and then flattening the stepped portion where the end of the conductive layer rests on a thick oxide film. It is possible to prevent the melting point tungsten silicide film from peeling off, and to realize a highly reliable semiconductor memory device.

[Brief explanation of drawings]

FIGS. 1A to 1C are cross-sectional views of the manufacturing process of a semiconductor memory device showing an embodiment of the present invention, and FIGS. 2A to 2C are cross-sectional views of the manufacturing process of a semiconductor memory device showing an example of the conventional technology , 3rd
The figure is an enlarged view of FIG. 2(C) (a drawing in which peeling of the film has occurred). 11.21...Si substrate, 12.22...
...LOCOS film, 13.23... Gate oxide film, 14.24... First layer polycrystalline silicon film, 15... BPSG film, 16.25・・・・・・
... Gate oxide film, 17.26 ... Second layer polycrystalline silicon film, 18.27 ... High melting point tungsten silicide film, 28 ... First layer Edges of the polycrystalline silicon film, 31.32 . . . peeled portions of the film at step portions.

Claims (1)

[Claims] After patterning the conductive layer that will become the floating gate electrode into a predetermined shape, an insulating film that can be thermally melted is formed so as to flatten the stepped portion where the end of the conductive layer rests on the thick oxide film, and then heat treatment is performed to remove the previous insulation film. 1. A method of manufacturing a semiconductor memory device, comprising melting a film and simultaneously forming a gate oxide film on a conductive layer that will become a floating gate electrode and on a semiconductor substrate.