JPH04350969A - Semiconductor nonvolatile storage device and rewriting method thereof - Google Patents

Abstract

PURPOSE:To enable high speed rewriting and holding of data for a long period of time by providing two kinds of nonvolatile storage elements having a different rewriting speed characteristic and holding characteristic within a memory array. CONSTITUTION:A semiconductor nonvolatile storage device is constituted of a first block 11, 12 consisting of a first nonvolatile storage element 18 and a second block 13, 14 consisting of a second nonvolatile storage element 19 having the rewriting speed characteristic superior to that of the fist nonvolatile storage element 18 and the data holding characteristic inferior to that thereof. The first block 11, 12 has a first address region, while the second block 13, 14 has a second address region. Data writing of the first block 11, 12 is conducted by selecting an address of the first address region, while data writing of the second block 13, 14 is conducted by selecting an address of the second address region. Thereby, both high speed rewriting of data and data holding for a long period of time can be achieved at a time.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an electrically rewritable semiconductor non-volatile memory device and a method for rewriting the same.
In particular, it relates to improvements in rewrite time and memory retention of semiconductor nonvolatile memory devices.

0002

2. Description of the Related Art Conventionally, MNOS (Metal-Ni
tride-Oxide-Semiconductor
) type non-volatile memory element, for example, JP-A-2-10
MONOS (Met
al-Oxide-Nitride-Oxide-Se
Microconductor type nonvolatile storage devices are known. This MONOS type nonvolatile memory element is M
The surface of the silicon nitride film, which is the second layer gate insulating film of the NOS type nonvolatile memory element, is thermally oxidized to form a silicon oxide film to prevent carrier injection from the gate electrode side. In addition, a third layer of gate insulating film having a sufficient barrier height is provided. Non-volatile storage devices are MNOS type and MONOS
type non-volatile memory element and address MOS (Met
It has a memory array in which memory cells each made of an Al-Oxide-Semiconductor (Al-Oxide-Semiconductor) element are arranged in a matrix.

FIG. 2 shows a memory array of a conventional semiconductor nonvolatile memory device. As shown in FIG. 2, the memory array is an MNOS type or MON type connected to the word line 25.
OS type nonvolatile memory element 26 and address MOS
It has a memory cell consisting of an element 27.

Conventional semiconductor nonvolatile memory devices have slow rewriting speeds. This is due to the thickness of the gate insulating film of the built-in MNOS type non-volatile memory element or MONOS type non-volatile memory element, and the rewrite speed is slow for those with sufficient memory retention. be. Note that memory retention is the ability of a semiconductor nonvolatile memory device to retain stored data, and if the memory retention is poor, the data storage life will be shortened.

[0005] As a means to increase the rewriting speed, there are methods such as a block erase method and a chip batch erase method.
A method is known in which the rewriting speed is equivalently increased by erasing a plurality of nonvolatile memory elements at once in one erasing operation. These erasing methods will be explained using FIG. As shown in FIG. 2, the block erasing method is a method of erasing all nonvolatile memory elements 26 in each block 21, 22, 23, and 24 at once. The chip batch erasing method is a method for erasing all nonvolatile storage elements in a memory array at once.

[0006]

In the chip batch erasing method, blocks that do not need to be erased are also erased. For this reason, blocks that do not need to be erased must be rewritten, and rewriting takes longer than the block erasing method. However, even in the block erasing method, since the erasing speed of nonvolatile memory elements is slow, the time required for one erasing is long and the rewriting speed is slow.

[0007] MNOS type nonvolatile memory elements, MON
Rewriting of an OS-type nonvolatile memory element is performed by carrier tunneling in the silicon oxide film, which is the first layer of gate insulating film formed on the silicon substrate, so reducing the thickness of this silicon oxide film increases the rewriting speed. becomes faster. However, when the silicon oxide film is thin, memory retention deteriorates. Therefore, a semiconductor nonvolatile memory device with a high rewrite speed has poor memory retention. That is, it is difficult to achieve both high-speed rewriting and long-term memory retention.

An object of the present invention is to provide a semiconductor nonvolatile memory device that eliminates such problems, has a short rewrite time, and has a long memory retention life, and a rewrite method thereof.

[0009]

[Means for Solving the Problems] In order to achieve the above object, the present invention employs the following semiconductor nonvolatile memory device and its rewriting method.

The semiconductor nonvolatile memory device of the present invention has MN
In a semiconductor nonvolatile memory device consisting of a plurality of blocks, in which memory cells each having at least an OS-type or MONOS-type nonvolatile memory element are arranged in a matrix, a first block consisting of a first nonvolatile memory element; , and a second block consisting of a second non-volatile memory element which has a faster rewriting speed than the first non-volatile memory element but has inferior memory retention, and each of the first block and the second block is made up of one block. Have more than blocks.

The method for rewriting a semiconductor non-volatile memory device of the present invention uses a first block consisting of a first non-volatile memory element, which has a faster rewrite speed than the first non-volatile memory element but has inferior memory retention. a second block consisting of a second non-volatile memory element;
each block has one or more blocks, the first block has a first address area, the second block has a second address area, and writing of the first block is performed in the first block.
Writing to the second block is performed by selecting an address in the second address area, and erasing is performed in units of each block.

0012

[Operation] The semiconductor nonvolatile memory device of the present invention has two types of memory arrays each having different rewriting speed and memory retention.
By having different types of non-volatile memory elements, in the case of high-speed rewriting, a non-volatile memory element with a high rewrite speed is used, and when long-term memory retention is required, a non-volatile memory element with excellent memory retention is used. This makes it possible to achieve both high-speed rewriting and long-term memory retention.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings. FIG. 1 is an example of a memory array of a semiconductor nonvolatile memory device according to the present invention. As shown in FIG. 1, the memory array includes first blocks 11, 12 and a second block 1.
It consists of four blocks, 3 and 14. The first blocks 11 and 12 have a memory cell consisting of a MONOS type or MNOS type first nonvolatile memory element 18 and a MOS element 17, and the second blocks 13 and 14 have a MOS element 17.
It has a memory cell consisting of a NOS type or MNOS type second nonvolatile memory element 19 and a MOS element 17. The first block 11 has a two-page structure consisting of two word lines 15 and 16. Similarly, the first block 12 and the second blocks 13 and 14 also have a two-page structure.

Note that in the memory array of this embodiment, the first block and the second block each consist of two blocks, and one block has a two-page structure. Each block is one or more blocks,
It is clear from the following explanation that the same effect can be obtained even if one block is one or more pages.

The second non-volatile memory element 19 is an element having memory characteristics such that the rewriting speed is faster than that of the first non-volatile memory element 18, but the memory retention property is inferior. In the case of MONOS type or MNOS type nonvolatile memory elements, it is easy to implement elements with different memory characteristics in the same memory array. That is, as already mentioned,
The thickness of the silicon oxide film, which is the first layer gate insulating film, of the second nonvolatile memory element 19 may be made thinner than that of the first nonvolatile memory element 18. In this way, by adjusting the film thickness of the silicon oxide film that performs carrier tunneling, a second nonvolatile memory element 18 is created which has memory characteristics that are faster in rewriting speed than the first nonvolatile memory element 18 but inferior in memory retention. A memory element can be realized.

FIG. 3 shows an example of a method for manufacturing nonvolatile memory elements with different memory characteristics within the same memory array. Note that FIG. 3 shows a method for manufacturing a MONOS type nonvolatile memory element. FIG. 3 shows a first nonvolatile memory element 31 having a first silicon oxide film 33 and a second nonvolatile memory element 31 having a second silicon oxide film 35 thinner than the first silicon oxide film 33. In this method, the device 32 and the device 32 are formed on the same silicon substrate 39.

First, as shown in FIG. 3A, a silicon substrate 39 is oxidized to form a first silicon oxide film 33, which is a first layer of gate insulating film. Next, as shown in FIG. 3B, the first silicon oxide film 33 is etched using the resist 34 as a mask, and the second silicon oxide film 35 is etched.
form. Next, as shown in FIG. 3(c), resist 3
4 is removed, and a silicon nitride film 36 serving as a second layer gate insulating film, a silicon oxide film 37 serving as a third layer gate insulating film, and polysilicon 38 serving as a gate electrode are formed. Next, as shown in FIG. 3(d), polysilicon 38,
Then, each gate insulating film is etched into a predetermined pattern to form a first nonvolatile memory element 31 and a second nonvolatile memory element 32.

As described above, MONOS is used as a nonvolatile storage device.
Although the manufacturing method of the mold has been shown, in the MNOS mold, the third
The formation of the silicon oxide film 37, which is the gate insulating film of the layer, may be omitted.

In the above embodiment, non-volatile memory elements with different memory characteristics were realized by changing the film thickness of the first layer gate insulating film, but the second layer gate insulating film silicon The same effect can be obtained by changing the thickness of the nitride film 36 or the silicon oxide film 37 which is the third layer gate insulating film. This is because when the thickness of the silicon nitride film 36 or the silicon oxide film 37 is made thinner, the electric field applied to the first layer gate insulating film increases, which increases the probability of carrier tunneling and increases the rewriting speed. It is.

Conventionally, it has been believed that semiconductor nonvolatile memory devices require sufficient memory retention. However, depending on the application, the memory life may be short but high-speed rewriting may be required. Since the semiconductor nonvolatile memory device of the present invention has a high-speed rewrite area and a long memory life area,
Depending on the application, high-speed rewriting or long memory life can be selected. That is, according to the present invention, it is possible to both increase the rewriting speed of a semiconductor nonvolatile memory device and extend the memory retention life.

In FIG. 1, first blocks 11, 12
Writing to the blocks 13 and 14 is performed by selecting an address in the first address area, and writing to the second blocks 13 and 14 is performed by selecting an address in the second address area. The selection of the address in the first address area and the address in the second address area is determined by the selection of the address in the first address area and the address in the second address area.
This can be done by storing the address of the second address area and the address of the second address area. Therefore, the rewriting method of the present invention eliminates the need to provide a circuit for switching between the first blocks 11 and 12 and the second blocks 13 and 14 in the semiconductor nonvolatile memory device, simplifying the circuit configuration.

Further, since the semiconductor nonvolatile memory device of the present invention has a structure in which nonvolatile memory elements are different for each block, a block erasing method can be easily performed. therefore,
By performing erasing in block units, the erasing speed is equivalently increased, and the rewriting speed of the semiconductor nonvolatile memory device of the present invention can be further increased.

[0023]

As described above, the present invention makes it possible to increase the rewriting speed and extend the memory retention life in a semiconductor nonvolatile memory device as compared to the prior art. Furthermore, the rewriting method of the present invention simplifies the circuit configuration of the semiconductor nonvolatile memory device of the present invention, and erases each block, making it possible to further increase the rewriting speed of the semiconductor nonvolatile memory device of the present invention. becomes. In other words, a semiconductor nonvolatile memory device with high-speed rewriting and long memory life can be realized.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a memory array of a semiconductor nonvolatile memory device showing one embodiment of the present invention.

FIG. 2 is a circuit diagram of a memory array of a semiconductor nonvolatile memory device showing a conventional example.

FIG. 3 is a cross-sectional view showing an example of manufacturing nonvolatile memory elements with different memory characteristics in a memory array of a semiconductor nonvolatile memory device of the present invention.

[Explanation of symbols]

11 First block 12 First block 13 Second block 14 Second block 15 Word line 17 MOS element 18 First nonvolatile memory element 19 Second nonvolatile memory element 31 First nonvolatile memory element 32 Second nonvolatile memory element

Claims (2)

[Claims] Claim 1: A semiconductor nonvolatile memory device comprising a plurality of blocks, in which memory cells each having at least an MNOS-type or MONOS-type nonvolatile memory element are arranged in a matrix; It consists of a first block and a second block consisting of a second nonvolatile memory element that has a faster rewriting speed but inferior memory retention than the first nonvolatile memory element, and the first block and the second nonvolatile memory element 1. A semiconductor nonvolatile memory device having at least one block each of 2 blocks. Claim 2: A first memory device comprising a first non-volatile memory element.
and a second block consisting of a second non-volatile memory element which has a faster rewriting speed than the first non-volatile memory element but has inferior memory retention, and the first block and the second block each block has one or more blocks, the first block has a first address area, the second block has a second address area, and writing of the first block is performed by writing to the first block. 1, writing to the second block is performed by selecting an address in the second address area, and erasing is performed in units of each block. How to rewrite sexual memory.