JPS59155172A - Non-volatile semiconductor memory device - Google Patents

Abstract

PURPOSE:To thicken a tunnel insulating film, and to hold memory informations excellently by opposing a silicon substrate formed to a projecting shape and a floating gate through the tunnel insulating film and opposing the floating gate so as to coat the end section of a projecting type silicon substrate. CONSTITUTION:A mask material 12 for forming a projecting section is left on a P type silicon substrate 11 in a desired shape, the silicon substrate 11 is removed, and the projecting section is formed. An oxide film 13 is buried to the formed projecting section so as to coincide with the surface of the silicon substrate 11. A mask material 14 coating sections except a region containing the projecting section of the silicon substrate 11 and one part of the buried oxide film 13 is left, an N<+> layer 15 in the silicon substrate 11 is formed and one part of the oxide film 13 is removed, and the surface of the oxide film is retreated from the surface of the projecting section of the silicon substrate 11. A tunnel oxide film 16 is grown to the projecting section of the silicon substrate 11, and a floating gate 17 consisting of polycrystalline silicon is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a nonvolatile semiconductor memory device having a floating gate and a control gate, and particularly to an electrically rewritable memory device.

[Conventional technology and melting point]

As an electrically rewritable nonvolatile memory having a floating gate, for example, the one shown in FIG. 1 is known.

(8) in FIG. 1 is a plan view, and (bl) and (C) are cross-sectional views taken along line AA' and line B-B' in (a), respectively.

Formed on a P-type silicon substrate (IJ) -t: n layer m
(121) (122).

A memory transistor is constituted by the floating gate 0 control gate I stacked between these layers (121) and (122) with an insulating film interposed therebetween. Even more (122).

(123) and these n-layer layers (122), (123)
A selection transistor is constituted by a gate electrode (I5) formed with an insulating film in between. Memory contents can be rewritten by extending a floating gate (13) through a thin insulating film (16) through which a tunnel current flows over a layer (124) formed continuously with the n-layer IN (122). (1) is performed by transferring and receiving charges between the n-layer (124) and the n-layer (124). (17) is a field insulating film.

In a memory transistor with such a structure, normal write conditions (program voltage (pulse) pp=20
In order to rewrite the memory contents using the tunnel insulating film (161), it is necessary to reduce the thickness of the tunnel insulating film (161 to about 120 m5), which poses problems in the element formation method and in ensuring the memory contents and retention. Ta.

That is, if it is possible to change the memory contents by 1 under the above write conditions, it is desirable that the tunnel insulating film (161) be thicker.

[Purpose of the invention]

The present invention has been made in view of the above points, and an object of the present invention is to provide a memory element that can be rewritten under normal write conditions while maintaining a thick tunnel insulating film.

[Summary of the invention]

In the present invention, as shown in FIG. 2, a silicon substrate (11) formed in a convex shape and a floating gate (13) are opposite to each other with a tunnel insulating film 08 interposed therebetween. By facing each other so as to cover each other, an electric field is concentrated at the end, and even when a thick tunnel insulating film Oe is used, a memory element that can be rewritten under normal write conditions is realized. Note that FIGS. 2(a) and 2(b) show that in the memory element shown in plan view in FIG. 1(a),
In the case of using the present invention, A-A' and B, respectively.
-B' cross-sectional view is shown.

〔Effect of the invention〕

According to the present invention, since the thickness of the tunnel insulating film can be increased, device manufacturing is facilitated and the yield of device manufacturing is improved. Furthermore, since the floating gate is covered with a thick insulating film, the retention characteristics of stored information are good, and a highly reliable device can be realized.

[Embodiments of the invention]

Next, □The present invention will be explained using examples. Figure 3 (a
), after leaving a mask material (L) for forming a convex part on a P-type silicon substrate (11) in a desired shape, the silicon substrate 1B is removed and a convex part is formed.Next, An oxide film Q31 is buried in the formed recess so as to coincide with the surface of the silicon substrate (11) (bl. Next, as shown in C1, the convex part of the silicon substrate aυ and the buried oxide film u
A mask material (14) covering the area other than a part of 3 is left, and an n+ layer a9 is formed in the silicon substrate aυ and an oxide film (
13) is partially removed to retreat the oxide film surface from the convex surface of the silicon substrate aυ. Next, as shown in (d),
For example, 2 tunnel oxide films αe are formed on the convex portions of the silicon substrate U.
00^Floating gate a7) made of grown polycrystalline silicon
After that, control gates are stacked to form devices as is known in the art. In this embodiment, a case has been described in which the oxide film is buried in the recessed portion in the process shown in FIG. Can be done.

[Brief explanation of drawings]

Fig. 1 (al is a plan view for explaining the conventional example, (b)
(C) is a sectional view thereof, FIGS. 2(a) and 2(b) are sectional views for explaining the present invention, and FIGS. 3(a) to (dl) are sectional views showing one embodiment of the present invention. .Representative: Patent Attorney Noriyuki Chika (and 1 other person)

Claims (1)

[Claims] In an electrically rewritable non-volatile memory device having a floating gate and a control gate, charge is transferred to and from the floating gate through a process between the semiconductor substrate and a reverse trench type high concentration impurity region formed on the surface of the semiconductor substrate. The high concentration impurity region M is formed on the surface of a convex region formed on the semiconductor substrate, and is formed on the surface of a convex region formed on the semiconductor substrate. A non-volatile semiconductor memory device characterized in that the portion is filled with an insulating film so that the surface of the convex region protrudes.