JPH0320075A - Manufacture of programmable element - Google Patents

Abstract

PURPOSE:To avoid the concentration of an electric field and stabilize the dielectric breakdown voltage by adopting structure that the thickness of insulating films changes gradually at the ends of program sections. CONSTITUTION:A P-type semiconductor substrate 11 is separated into a plurality of regions by field insulating films 12, and N<+>-type diffusion layers 13 to be the lower electrodes of programmable elements are formed in the separated regions. Subsequently, nitride silicon films 14 are formed on parts of the diffusion layers 13, and oxide films 15 and oxide nitride films 16 are formed by oxidizing the surfaces of the diffusion layers 13 and nitride silicon films 14 in an oxidizing atmosphere. Then, the laminates of the oxide nitride films 16 with the nitride silicon films 14 make program sections 17. When the upper electrodes 18 are made out of polycrystalline silicon films after that, the oxide films 15 become to have structure being such that their film thickness increases gradually at the ends of the program sections 17. This avoids the concentration of an electric field and makes it possible to obtain stable dielectric breakdown voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of manufacturing an electrically programmable device incorporated in a semiconductor integrated circuit.

Among conventional semiconductor integrated circuits, there are so-called PROMs (PROMs) into which the contents can be electrically written after purchase by the user.
ogrammable ROM) is a ROM with the desired content.
(Read Only Memory) is widely used because it can be obtained immediately.

Even if we are in the field of logic circuits, there is also so-called P, which allows the user to electrically write the contents after purchasing it.
LD (Programmable LogicDe
vice ) is used for similar purposes.

In order to construct a FROM or a PLD, it is necessary to use a programmable element that allows storage contents to be written electrically from the outside and that retains the storage contents even when the power is turned off.

Conventionally, a manufacturing method suitable for manufacturing such a programmable element has been, for example, as shown below.

FIGS. 2A to 2C are step-by-step cross-sectional views showing a conventional method of manufacturing a programmable device.

1. As shown in FIG. 2a, a P-type semiconductor substrate 1 is separated into a plurality of regions by a field insulating film 2, and an N+-type diffusion layer 3, which will become a lower electrode of a programmable element, is formed in the separated regions. Admonish the formal precepts.

Next, as shown in FIG. 2b, after thermally oxidizing the diffusion layer 3 to form a programming oxide film 4 with a thickness of about 10 mm, a polycrystalline silicon film 6 is formed over the entire surface. .

Then, as shown in FIG. 2C, a portion of the polycrystalline silicon film 5 is selectively etched away to form an upper electrode 61.

Thereafter, electrical connections to each of the diffusion layer 3 and the upper electrode 61 are formed according to a normal semiconductor integrated circuit manufacturing process.

Programming is performed by applying an appropriate voltage between the upper electrode 61 and the diffusion layer 3 to break down the insulation of the oxide film 4.

Problems to be Solved by the Invention In recent manufacturing of semiconductor integrated circuits, it is common to use so-called dry etching methods to improve the accuracy of processing dimensions and shapes. In the conventional method of manufacturing a programmable element, when attempting to process the upper electrode 61 by dry etching,
Since the thickness of the underlying oxide film 4 is as thin as about 10 mm, etching easily reaches the diffusion layer 3, causing damage to the diffusion layer 3, resulting in a problem in that leakage current at the junction is likely to occur.

Furthermore, since the electric field is concentrated at the end portion of the upper electrode 61 when a voltage is applied, there is also the problem that the oxide film 4 is broken down at a voltage lower than the original dielectric breakdown voltage.

Means for Solving the Problems In order to solve the above-mentioned problems, the method for manufacturing a programmable element of the present invention includes forming an insulating film containing a silicon nitride film layer on a portion of the semiconductor substrate that will become the lower electrode and will become the program area. The method includes a step of forming an upper electrode, an oxidizing step, and a step of forming an upper electrode completely covering the surface of the insulating film.

Function: In the method for manufacturing a programmable element of the present invention, the thickness of the insulating film other than the portion to be programmed can be increased, so that sufficient margin can be taken in the process when etching the upper electrode. Since the thickness of the insulating film changes smoothly at the end of the programmed portion, there is no concentration of electric field and a stable dielectric breakdown voltage can be obtained.

Embodiment An embodiment of the method of manufacturing a programmable element according to the present invention will be described with reference to FIG.

As shown in FIG. 1a, a P-type semiconductor substrate 11 is separated into a plurality of regions by a field insulating film 12, and an N+-type diffusion layer 13, which will become the lower electrode of the programmable element, is formed in the separated regions. do.

Next, as shown in FIG. 1B, a silicon nitride film 14 having a thickness of about 10 nm is formed on a portion of the diffusion layer 13 by a well-known method such as photo-etching.

Since this silicon nitride film 14 is thin, it can be etched without damaging the underlying diffusion layer 13. Further, since the cross-sectional shape is not so important, wet etching with a high selectivity to the underlying layer can be performed.

Then, as shown in FIG.
The surface is oxidized to form an oxide film 16 and an oxynitride @16. If this oxidation is performed under conditions such that the thickness of the oxide film 16 is about 100 nm, the oxidation rate of the diffusion layer 13 is about three times higher than when the impurity concentration is low. Since the oxidation rate of the film 14 is very low, the film thickness of the oxynitride lIi 16 is about 1 to 2 nm. Among them, the stacked layer of the oxynitride film 16 and the silicon nitride film 14 becomes the program portion 17.

Next, as shown in FIG. 1d, an upper electrode 18 made of a polycrystalline silicon film is formed. At this time, if the end of the upper electrode 18 is placed on the oxide film 16, the underlying layer will not be damaged during dry etching of the polycrystalline silicon film. In addition, since the oxide @16 forms a structure in which it falls at the end of the derogom part 17 and its film thickness gradually increases,
Concentration of electric field is avoided and stable breakdown voltage can be obtained.

Thereafter, electrical connections to each of the diffusion layer 13 and the upper electrode 18 may be formed according to a normal semiconductor integrated circuit manufacturing process.

In the above embodiment, for convenience of explanation, program part 1 is
7 is a laminated film of an oxynitride film 16 and a silicon nitride film 14, but this need not follow the structure of the embodiment, and even if there is an oxide film where the semiconductor substrate 11 is oxidized under the silicon nitride film. good.

Effects of the Invention As described above, in the programmable device manufacturing method of the present invention, the insulating film in the part other than the programmed part can be made thicker than the insulating film in the programmable part, so that the underlying semiconductor substrate is not damaged. Also, since the thickness of the insulating film gradually changes at the edge of the program area,
There is no concentration of electric field and the breakdown voltage is stable. The result is a programmable integrated circuit with high performance and high reliability.

[Brief explanation of drawings]

FIGS. 1A to 1D are step-by-step sectional views showing an embodiment of the programmable element manufacturing method of the present invention, and FIGS. 2A to 2C are process-order sectional views showing a conventional programmable device manufacturing method. 11...Substrate, 12...Field insulating film, 13...N-type diffusion layer, 14...
・Silicon nitride film, 16...Oxide film, 16...
... Oxynitride film, 17 ... Program portion, 18 ... Upper electrode.

Claims (1)

[Claims] In a method for manufacturing a programmable element that performs programming by applying voltage to an insulating film to break the insulation,
A step of forming an insulating film including a silicon nitride film layer on a part of the semiconductor substrate that will become a lower electrode and will be a program part, and oxidizing the surface of the semiconductor substrate using the silicon nitride film as a mask and simultaneously oxidizing the surface of the silicon nitride film layer. A method for manufacturing a programmable element, comprising the steps of: oxidizing the insulating film; and forming an upper electrode completely covering the surface of the insulating film.