JPH0322485A - Field effect transistor for nonvolatile memory - Google Patents

Abstract

PURPOSE:To prevent disconnection of an electrode wiring by a method wherein a first gate insulation film, a floating gate electrode covered with the first gate insulation film and a control gate electrode provided on a second gate insulation film provided on the floating gate electrode are buried in the surface of a groove dug inward from one main surface of a semiconductor substrate. CONSTITUTION:An N-type impurity diffused layer is formed as a source 2 and a drain 3 in the surface of a P-type semiconductor substrate 1 (silicon), a groove is provided between the source 2 and the drain 3 by etching the P-type semiconductor substrate 1, the surface of the groove is covered with a first gate oxide film 4, and a first polycrystalline silicon layer 5 is buried, so as to form a floating gate electrode. Thereafter, a second gate oxide film 6 and a control gate electrode of a second polycrystalline silicon layer 7 are formed on the surface of the semiconductor substrate and on the first polycrystalline silicon layer 5 between the source 2 and the drain 3. By burying the first gate oxide film 4 and the floating gate electrode 5 in the groove dug inward from one main surface of the semiconductor substrate 1 between the source 2 and the drain 3, formation of an electrode wiring connected to the source 2 or the drain 3 over the control gate electrode 7 of a field effect transistor of a nonvolatile memory is facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a field effect transistor for non-volatile memory, and more particularly to a non-volatile memory cell having a floating gate.

[Conventional technology]

Conventional field effect transistors for non-volatile memory
As shown in the figure, a first gate oxide film 14, a floating gate electrode 15, a second gate oxide film 16, and a control gate electrode 17 are superimposed on the channel between the source 12 and the train 13 (that is, the entire life of the semiconductor substrate is 14, ] 5, 16 on the surface
, 1.7).

[Problem to be solved by the invention]

The conventional field effect transistor for non-volatile memory described above has a first layer on a flat channel region between the source and the drain.
a gate oxide film, a floating gate, a second gate oxide film,
Since the structure has a control gate, when an insulating film is formed on the control gate in an integrated circuit and an electrode wiring is formed to connect to the source or drain by going over the control gate, the electrode wiring is connected to the source or drain. Alternatively, the train portion may be curved, making it difficult to maintain its shape, and the electrode wiring may easily break, which may impede the yield and reliability of the semiconductor memory device.

[Means to solve the problem]

A field effect transistor for a nonvolatile memory according to the present invention includes a first gate insulating film covering the surface of a trench dug inward from the entire surface of a semiconductor substrate, and a trench covered with the first gate insulating film. The device has a floating gate electrode buried therein, a second gate insulating film provided on the floating gate electrode, and a control gate electrode provided on the second gate insulating crotch.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a longitudinal sectional view of a semiconductor chip showing an embodiment of the present invention.

An n-type impurity diffusion layer is formed as a source 2 and a drain 3 on the surface of a p-type semiconductor substrate 1 (silicon), and a groove is formed by etching the p-type semiconductor substrate 1 between the source 2 and the drain 3, and the surface is covered with grooves. A first polycrystalline silicon layer 5 is buried to form a floating gate electrode. Thereafter, a second gate oxide film 6 and a control gate electrode of a second polycrystalline silicon layer 7 are formed on the surface of the semiconductor substrate between the source 2 and drain 3 and on the first polycrystalline silicon layer 5. Note that the first gate oxide film 4 may be in good contact with the source 2 and drain 3.

The thicknesses of the first gate oxide film 4 and the first polycrystalline silicon layer may be, for example, 20 nm and 60 nm, respectively.

Source depending on the amount of charge injected and held in the floating gate electrode. It goes without saying that the resistance value between the drains changes based on the same principle as in the conventional example.

Since the floating gate electrode is buried, flatness is improved compared to the conventional example.

〔Effect of the invention〕

As explained above, the present invention provides an electric field for nonvolatile memory by embedding a first gate oxide film and a floating gate electrode in a trench dug inward from one principal surface of a semiconductor substrate between a source and a drain. It is possible to easily form an electrode wiring that goes over the control gate electrode of an effect transistor and connects to the source or train, and it is possible to flatten the semiconductor integrated circuit chip and eliminate defects in the cover film etc. formed on the surface of the semiconductor integrated circuit chip. This has the effect that a field effect transistor for nonvolatile memory suitable for integration into an integrated circuit can be obtained.

[Brief explanation of drawings]

FIG. 1 is a vertical sectional view of a semiconductor chip showing an embodiment of the present invention, and FIG. 2 is a vertical sectional view of a semiconductor chip showing a conventional example. 1, 11... p-type semiconductor substrate, 2, 12... source, 3, 13... drain, 4, 14... first gate oxide film, 5, 15... first multilayer Crystalline silicon layer (floating gate electrode), 6.16... second gate oxide film,
7.17...Second polycrystalline silicon layer (control gate electrode).

Claims (1)

[Claims] a first gate insulating film covering the surface of a trench dug inward from one main surface of the semiconductor substrate; a floating gate electrode filling the trench covered with the first gate insulating film; and a floating gate electrode on the floating gate electrode. a second gate insulating film provided on the second gate insulating film;
A field effect transistor for a nonvolatile memory, comprising a control gate electrode provided on a gate insulating film.