JPH0831563B2 - Manufacturing method of programmable element - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an electrically programmable programmable element incorporated in a semiconductor integrated circuit.

2. Description of the Related Art Among semiconductor integrated circuits, a so-called PROM (Programm
able ROM) is widely used because the desired content ROM (Read Only Memory) can be obtained immediately.

In the field of logic circuits, so-called contents can be electrically written after the user purchases it.
PLDs (Programmable Logic Devices) are used for similar purposes. In order to configure a PROM or PLD, it is necessary to use a programmable element in which the stored content can be electrically written from the outside and the stored content is retained even when the power is turned off.

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

2A to 2C are cross-sectional views in order of the steps, showing a conventional method for manufacturing a programmable element, which will be described with reference to FIG.

First, as shown in FIG. 2A, the P-type semiconductor substrate 1 is divided into a plurality of regions by the field insulating film 2, and the N ⁺ -type diffusion layer 3 to be the lower electrode of the programmable element is formed in the separated regions. .

Next, as shown in FIG. 2B, the diffusion layer 3 is thermally oxidized to form a programming oxide film 4 having a thickness of about 10 nm, and then a polycrystalline silicon film 5 is grown on the entire surface.

Then, as shown in FIG. 2C, a portion of the polycrystalline silicon film 5 is selectively removed by etching to form an upper electrode 51.

After that, electrical connection is formed to each of the diffusion layer 3 and the upper electrode 51 according to a normal semiconductor integrated circuit manufacturing process.

Programming is performed by applying an appropriate voltage between the upper electrode 51 and the diffusion layer 3 to break the insulation of the oxide film 4.

In the recent manufacture of semiconductor integrated circuits, a so-called dry etching method is generally used in order to improve the accuracy of processing size and shape. In the programmable element manufacturing method of, when the upper electrode 51 is processed by dry etching,
Since the thickness of the oxide film 4 as the base is as thin as about 10 nm, the etching easily reaches the diffusion layer 3, and the diffusion layer 3 is damaged, resulting in the problem that leakage current of the junction is likely to occur.

Further, at the end portion of the upper electrode 51, the electric field is concentrated when a voltage is applied, so that there is a problem that the oxide film 4 is destroyed at a voltage lower than the original dielectric breakdown voltage.

Means for Solving the Problems A method for manufacturing a programmable device according to the present invention for solving the above problems is to provide an insulating film including a silicon nitride film layer in a part to be a program part on a semiconductor substrate to be a lower electrode. A step of forming, a step of oxidizing the surface of the semiconductor substrate using the silicon nitride film as a mask and a surface of the silicon nitride film layer at the same time, and a step of forming an upper electrode that completely covers the surface of the insulating film. Is included.

Action In the method for manufacturing a programmable element according to the present invention, the thickness of the insulating film other than the part to be programmed can be increased, so that a sufficient process margin can be secured when etching the upper electrode. Further, 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 breakdown voltage can be obtained.

Example An example of a method of manufacturing a programmable element according to the present invention will be described with reference to FIGS.

First, as shown in FIG. 1A, a P-type semiconductor substrate 11 is divided into a plurality of regions by a field insulating film 12, and an N ⁺ -type diffusion layer 13 to be a lower electrode of a programmable element is formed in the separated regions. .

Next, as shown in FIG. 1b, the film thickness is partially formed on the diffusion layer 13.
A silicon nitride film 14 of about 10 nm is formed by a known method such as photoetching. 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 having a large selection ratio with respect to the underlying layer can be performed.

Then, as shown in FIG. 1C, the surfaces of the diffusion layer 13 and the silicon nitride film 14 are oxidized in an oxidizing atmosphere at a temperature of about 900 ° C. to form an oxide film 15 and an oxynitride film 16. When this oxidation is performed under the condition that the film thickness of the oxide film 15 is about 100 nm, the oxidation rate of the diffusion layer 13 is about three times as high as that in the case of low impurity concentration, and the silicon nitride film Since the oxidation rate of 14 is very small, the film thickness of the oxynitride film 16 is 1
It is about 2 nm. 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 15, the base is not damaged during the dry etching of the polycrystalline silicon film. Further, since the oxide film 15 has a structure in which the film thickness gradually increases at the end of the program portion 17, concentration of an electric field is avoided and a stable dielectric breakdown voltage can be obtained.

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

In the above embodiment, the program part is included for convenience of explanation.
Although 17 is a laminated film of the oxynitride film 16 and the silicon nitride film 14, this does not have to follow the configuration of the embodiment, and an oxide film obtained by oxidizing the semiconductor substrate 11 may be provided below the silicon nitride film. .

As described above, in the programmable element manufacturing method of the present invention, the insulating film other than the programmed portion can be made thicker than the programmed insulating film, so that the underlying semiconductor substrate is not damaged. Moreover, since the thickness of the insulating film gradually changes at the end of the programmed portion, the electric field is not concentrated and the dielectric breakdown voltage is stabilized. The result is a high performance, highly reliable programmable integrated circuit.

[Brief description of drawings]

1A to 1D are cross-sectional views in order of steps showing an embodiment of a method for manufacturing a programmable element according to the present invention, and FIGS. 2A to 2C are cross-sectional views in order of steps showing a conventional method of manufacturing a programmable element. 11 …… Substrate, 12 …… Field insulating film, 13 …… N ⁺ type diffusion layer, 14 …… Silicon nitride film, 15 …… Oxide film, 16 …… Oxynitride film, 17 …… Program part, 18 …… Upper electrode.

Claims (1)

[Claims] 1. A method of manufacturing a programmable element, wherein programming is performed by applying a voltage to an insulating film to break the insulation, and an insulating film including a silicon nitride film layer in a part to be a programmed portion on a semiconductor substrate to be a lower electrode. Forming a film, 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, and forming an upper electrode that completely covers the surface of the insulating film. The manufacturing method of the programmable element characterized by including the process.