JPH0265277A - Non-volatile semiconductor memory device - Google Patents

Abstract

PURPOSE:To prevent the data written in a closed region from being erased out so as to retain it normally by a method wherein all of two or more EPROM elements selected from EPROM elements are covered being electrically insulated from other elements, and a light shielding layer not transmissive to light rays of specified wavelength is provided. CONSTITUTION:An EPROM element forming region is divided into two regions which are an open region 16 where a user is able to write and a closed region 17 where a manufacture write data. A light shielding aluminum layer 14 about 0.5-3Angstrom in thickness is formed on a passivation film 9 of the closed region 17. The whole element forming region including the upside of the aluminum layer 14 is covered with a second passivation film 15. As mentioned above, an Al light shielding film is formed as an optical barrier on the closed region 17 of an EPROM, even if the write and the erasure of data are performed onto an EPROM of the open region 16 two or more times, the data stored in an EPROM element of the closed region 16 can be retained without being erased out.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a nonvolatile semiconductor memory device that can be electrically written and optically erased. The present invention relates to a non-volatile semiconductor memory device.

[Prior Art] Non-volatile semiconductor memory (hereinafter referred to as EPR, OM) devices are widely used as electrically programmable and optically erasable read-only memories (ROM).

FIG. 3 is a cross-sectional view showing the structure of a conventional EPR, OM. EPROM elements 10, 11, 12, and 13 are formed on a silicon substrate 1 so as to be separated from each other.

(with a thickness of about 0.6 to 1 μn) on the surface of the silicon substrate 1
The relatively thick field 1-oxide film 2 and the memory element forming region surrounded by the field oxide film 2 have a thickness of about 10 mm.
0 relatively thin first cate oxidation JI! 3 is formed. Floating dandruffs 1 to 4 made of polycrystalline silicon are formed on the first goo 1 to oxide film 3, and furthermore, second goo 1 to oxide film 5 are formed on the floating dandruff 4. A control gate 6 made of polycrystalline silicon is also formed. A glabellar insulating film 7 is formed on the entire surface so as to cover the floating dandruffs 1 and 4 and the controllers 1 to 1 to 6. On this glabellar insulating film 7, metal wiring 8 such as Aρ is formed according to a predetermined wiring pattern. A part of this metal wiring 8 is connected to the source and drain impurity diffusion layers (not shown) of the transistor element formed on the surface of the substrate 1 through the contact hole provided in the interlayer insulating film 7. has been done. Further, the entire surfaces of the capacitive elements 1o to 13 are covered with a passivation plA9 for protection.

In the conventional EPROM described above, data is written by avalanche injection of electrons from the surface of the substrate 1 through the first gate oxide film 3 into the floating gate 4, and by accumulating the electrons in the floating gate 4. . Further, data is erased by irradiating the top of the EPROM with light (usually ultraviolet light). That is, this light passes through the passivation film 9 and forms the floating dandruff 1.
The electrons accumulated in the substrate 1 and the control gate 6 are excited by light, and the electrons are released into the substrate 1 and the control gate 6. As a result, the data written in the floating gate 4 is erased. This EPROM data can be erased using the EPR
This is done simultaneously for all elements in the OM region.

[Problems to be Solved by the Invention] Therefore, in the MO3 integrated circuit having the conventional EPROM element described above, due to its design, the memory area of the EPROM is an area where the user can freely write data (hereinafter referred to as an open area). (hereinafter referred to as "region") and the region (hereinafter referred to as "region") used by manufacturers to select system functions and optimize electrical characteristics, etc.
(referred to as a closed area). However, in such a system, it has been impossible for a user to erase data once written by the user in an attempt to modify the data. This is the conventional EPRO
This is because the structure of M, as described above, causes the data in all memory cells to be erased at the same time when data is erased, and even the data in the closed area is erased, causing the integrated circuit to malfunction.

Therefore, in the case of the above-mentioned design, the EPROM was only used as a so-called one-time PROM that limited data writing by the user to one time. For this reason, the conventional EPROM structure has been an obstacle to the development of integrated circuits that actively take advantage of the EPROM's ability to repeatedly write and erase data.

The present invention has been made in view of such problems, and includes:
It is an object of the present invention to provide a nonvolatile semiconductor memory device in which data written in a closed area is not erased and is normally retained even when data is erased in an open area (user area).

[Means for Solving the Problems] A nonvolatile semiconductor memory device according to the present invention includes a plurality of electrically writable and optically erasable EPROM elements.
It is characterized by having a light shielding layer which covers a selected part of the plurality of EPROM elements in a state where they are electrically insulated from each element and does not transmit at least light of a specific wavelength.

[Function] In the present invention, a selected part (closed area) of a plurality of EPROM elements of a non-volatile semiconductor memory device is entirely covered with this EPR,
It is covered with a light shielding layer electrically insulated from the 0M element. As a result, when the entire nonvolatile semiconductor memory device is irradiated with light, the data in the EPROM element covered with this light-shielding layer is saved, and the data on the EPROM element not covered with this light-shielding layer is saved.
Only the data of M elements is erased.

[Example] Next, an example of the present invention will be described with reference to the accompanying drawings.

FIG. 1(c) is a sectional view showing an EPROM according to the first embodiment, and FIGS. 1(a) and 1(b) are sectional views showing a manufacturing method thereof. Components in FIG. 1 that are the same as those in FIG. 3 are given the same reference numerals. As shown in Figure 1(c), the EPROM
The device is formed in a region surrounded by a field oxide film 2,
Floating gate 4 formed on first gate oxide film 3, second gate oxide film 5, control gate 6
, interlayer insulating film 7, metal wiring 8 and passivation film 9
It consists of

In this embodiment, E P formed on the semiconductor substrate 1
The ROM element itself has the same structure as a conventional EPROM element. The area where the EPROM element is formed is divided into an open area 16 that can be written by the user, and a closed area 17 where data is written by the manufacturer. On the passivation film 9 in the closed region 17, a light-shielding aluminum layer 14 having a thickness of about 0.5 to 3.0 mm is formed. The thickness of this aluminum layer 14 is thinner than the thickness of aluminum (about 10 mm) when the layer is normally used as wiring. And this aluminum layer]4
The entire element formation region including the second passivation film 15 is covered with the second passivation film 15.

According to this embodiment, since a light-shielding film of A°C is formed as an optical barrier on the closed area 17 of the EPROM, operations for writing and erasing data in the EPROM element in the open area 6 are performed multiple times. Even if you go, close area 16
The data stored in the EPROM element is retained without being erased.

Next, a method for manufacturing an EPROM according to this embodiment will be explained.

FIG. 1(a) shows an EPROM element on a silicon substrate formed in the same process as a conventional EPROM. After forming the device in this way, EPRO is performed at the level of a sea urchin fly.
Conduct electrical tests on integrated circuits, including tests on the M memory section, to eliminate defective products. After this electrical test, the data stored in the EPROM is erased by erasing ultraviolet light over the entire surface of the wafer.

Next, as shown in FIG. 1(b), aluminum is coated on the passivation film 9 on the EPROM element to a thickness of approximately 0.5 mm, which is thinner than that used for normal wiring (approximately 10 layers).
Aluminum layer 1 is sputtered to a thickness of
form 4. Thereafter, the aluminum layer 14 on the closed area remains and the aluminum layer on the open area 16 is removed by photolithography. As a result, the light-shielding aluminum N14 is placed on the cloth area 17.
is selectively formed.

Next, as shown in FIG. 1C, a second passivation film 15 is formed, for example, from a plasma nitride film, over the entire surface of the element formation region including the aluminum layer 14. This is to prevent the aluminum layer 14 from being oxidized. In this way, the EPR shown in FIG.
OIVI can be produced.

FIG. 2 is a sectional view showing a second embodiment of the invention.

In FIG. 2, the same parts as those in FIG. 1 are given the same reference numerals and their explanations will be omitted. This embodiment differs from the previous embodiment in that an optical filter 18 is disposed on the passivation film 9 in the closed region 17 using a suitable adhesive material.

This optical filter 18 has a characteristic of transmitting light of a specific wavelength and blocking light of other wavelengths. As a result, the EPROM in this embodiment can control the optical filter 1 by appropriately selecting the wavelength of the irradiated light.
When using light that does not pass through the filter 8, it is possible to erase only the data in the open area 16, and when using light that passes through the filter 18, it is possible to erase the data in both the open area 16 and the closed area 17. can.

The ability to select data to be erased depending on the situation increases the degree of freedom in designing a system including an EPROM, and is extremely beneficial.

[Effect of the invention] As explained above, according to the present invention, the manufacturer can
While retaining the data for function selection and optimization of electrical characteristics written in the closed area of the ROM, the user can erase the data once written in the open area and write new data. Therefore, it is possible to develop a system that maximizes the advantages of EPROM and actively utilizes EPROM for new applications.

[Brief explanation of the drawing]

1(a) to (c) are sectional views showing a first embodiment of the present invention, FIG. 2 is a sectional view showing a second embodiment of the present invention,
FIG. 3 is a sectional view showing the structure of a conventional EPROM. 1; Silicon substrate, 2; Field oxide film, 3 one - 10-

Claims (1)

[Claims] (1) Multiple E that can be electrically written and optically erased
In a nonvolatile semiconductor memory device including a PROM element, a plurality of E
A non-volatile semiconductor memory device comprising a light-shielding layer that covers the entire PROM element in a state where it is electrically insulated from each element and does not transmit at least light of a specific wavelength.