Non-volatile memory and non-volatile memory cell having asymmetrical doped structure

A non-volatile memory cell comprising a substrate, a charge-trapping layer, a control gate, a first conductive state of source and drain, a lightly doped region and a second conductive state of pocket-doped region. The charge-trapping layer and the control gate are disposed over the substrate. A dielectric layer is disposed between the substrate, the charge-trapping layer and the control gate. The source and drain are disposed in the substrate on each side of the charge-trapping layer. The lightly doped region is disposed on the substrate surface between the source and the charge-trapping layer. The pocket-doped region is disposed within the substrate between the drain and the charge-trapping layer. Because there are asymmetrical configuration and different doped conductive states of implant structures, the programming speed of the memory cell is increased, the neighboring cell disturb issue is prevented, and the area occupation of the bit line selection transistor is reduced.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a non-volatile memory device. More particularly, the present invention relates to a non-volatile memory with non-volatile memory cell having asymmetrical doped structure and method of operating the memory cell.

2. Description of the Related Art

Electrically erasable programmable read only memory (EEPROM) is a type of non-volatile memory that allows multiple data writing, reading and erasing operations. The stored data will be retained even after power to the device is removed. With these advantages, EEPROM become one of the most widely adopted non-volatile memories for personal computer and electronic equipment.

A typical EEPROM has a floating gate and a control gate fabricated using doped polysilicon. To program data into the memory, electrons injected into the floating gate are distributed evenly within the polysilicon floating gate layer. Obviously, if there are some defects in the tunneling oxide layer underneath the polysilicon floating gate layer, the device may leak and lead to a drop in reliability.

At present, a type of flash memory cell that programs through hot-hole injection nitride electron storage (PHINES) has been developed as shown inFIG. 1.

FIG. 1is a schematic cross-sectional view of a conventional programming through hot-hole injection nitride electron storage (PHINES) type flash memory cell. As shown inFIG. 1, the flash memory cell10typically comprises a substrate100, a control gate120over the substrate100, a source130aand a drain130bwithin the substrate100and an oxide/nitride/oxide (ONO) layer110between the control gate120and the substrate100. The oxide/nitride/oxide (ONO) layer110comprises two silicon oxide layers112and116and a silicon nitride layer114sandwiched between them. In general, the silicon nitride layer114serves as a charge-trapping layer therein.

The PHINES type flash memory cell inFIG. 1utilizes band-to-band tunneling hot-hole (BTBTHH) to program data and utilizes the uniform Fowler-Nordheim (FN) channel to erase data.

Although the advantages of PHINES type flash memory cell includes low power consumption, a low leakage current and a simplified manufacturing method, some unavoidable defects are still present. For example, a PHINES type flash memory cell is designed to store a bit of data near the drain region and another bit of data near the source region. However, if the drain region has already stored up a single data bit, the second bit effect is produced when a reverse reading operation is carried out. The second bit effect often leads to a drop in the threshold voltage (Vt) in reverse reading and hence requires a higher bias voltage for reading. Yet, with a high read-out bias voltage, read-out interference will be intensified. Furthermore, the PHINES type flash memory cell has a relatively slow programming speed. In addition, a typical PHINES flash memory cell needs to incorporate three sets of bit line selection transistors (BLT) for programming. Hence, the overhead area for accommodating the bit line selection transistors is large and the actual packing density of the memory cell array is reduced.

SUMMARY OF THE INVENTION

Accordingly, one aspect of the present invention is to provide a non-volatile memory cell capable of increasing the operating speed and preventing neighboring cell disturb issue.

Further aspect of the present invention is to provide a non-volatile memory capable of increasing the operating speed, avoiding undesirable second bit effect and reducing area occupation of bit line selection transistors.

Another aspect of the present invention is to provide a method of operating a non-volatile memory capable of simplifying operation and reducing the number of bit line selection transistors used in the non-volatile memory.

To achieve these and other advantages, as embodied and broadly described herein, the Invention provides a non-volatile memory cell. The non-volatile memory cell comprises a substrate, a charge-trapping layer over the substrate, a control gate over the charge-trapping layer, a first dielectric layer between the substrate and the charge-trapping layer, a second dielectric layer between the control gate and the charge-trapping layer, a first conductive state of source and drain, a first conductive state of lightly doped region and a second conductive state of pocket-doped region. The source and the drain are disposed in the substrate on each side of the charge-trapping layer. The first conductive state lightly doped region is disposed on the substrate surface between the source and the charge-trapping layer. The second conductive type pocket-doped region is disposed in the substrate between the drain and the charge-trapping layer.

According to a first embodiment of the non-volatile memory cell in the present invention, the charge-trapping layer can be a layer fabricated from silicon nitride or a suitable material.

According to a first embodiment of the non-volatile memory cell in the present invention, the first conductive state is N-type and the second conductive state is P-type.

The present invention also provides a non-volatile memory comprising a substrate, a plurality of first conductive state of buried bit lines within the substrate, a plurality of word lines over the substrate and crossing over the buried bit lines, a charge-trapping layer between the word lines and the substrate that between the buried bit lines, a first dielectric layer between the charge-trapping layer and the substrate, a second dielectric layer between the word lines and the charge-trapping layer, a first conductive state of lightly doped region and a second conductive type pocket-doped region. The lightly doped region is disposed on the substrate surface on one side of the buried bit lines. The pocket-doped region is disposed in the substrate on another side of the buried bit lines.

According to a second embodiment of the non-volatile memory in the present invention, the charge-trapping layer can be a layer fabricated from silicon nitride or a suitable material.

According to a second embodiment of the non-volatile memory in the present invention, the first conductive state is N-type and the second conductive state is P-type.

According to a second embodiment of the non-volatile memory in the present invention, the non-volatile memory further comprises two bit line selection transistors connected to the buried bit lines.

The present invention also provides a method of operating a non-volatile memory cell. The non-volatile memory cell comprises a substrate; a first conductive state of first drain, a second drain and a source in the substrate; a word line over the substrate and crossing over the first, the second drain and the source; a charge-trapping layer between the word lines and the substrate that between the first, the second drains and the source; a first dielectric layer between the charge-trapping layer and the substrate; a second dielectric layer between the word lines and the charge-trapping layer; a first conductive state of lightly doped region in the substrate surface on one side of each drain and source; and, a second conductive state of pocket-doped region on the other side of each drain and source. To initiate a programming operation, a first bias voltage is applied to the word line and a second bias voltage is applied to the source, the first drain is connected to a ground and the second drain is set to a floating state. The first bias voltage is lower than the second bias voltage.

The method of operating a non-volatile memory cell according to the present invention further includes an erasing operation. To initiate an erasing operation, a bias voltage for triggering a channel F-N erasing operation is applied to the word line, the first drain and the source are connected to a ground and the second drain is set to a floating state.

The method of operating a non-volatile memory cell according to the present invention further includes a reading operation. To initiate a reading operation, a third bias voltage is applied to the word line, a voltage lower than the third bias voltage is applied to the first drain, the source is connected to a ground and the second drain is set to a floating state.

In the present invention, an implant structure having an asymmetrical configuration and different doped states is applied to a non-volatile memory cell that programs by hot-hole injection nitride electron storage (PHINES). Therefore, programming speed can be increased through increasing the implant dosage while forming the pocket-doped region, and the reading capacity will not be affected. Furthermore, because the lightly doped region in the present invention deploys a low read-out bias voltage, a channel with a higher threshold voltage (Vt) can be used for reading, and the neighboring cell disturb issue is further prevented. In addition, the lightly doped region is able to lower the production of channel hot electrons (CHE) and hence avoids the read-out distribution problem during a reverse reading operation. Moreover, the present invention also disposes of the need to form isolation lines between memory cells so that the programming system and circuits are very much simplified. Additionally, only a single group of bit lines needs to be controlled during a programming operation in the non-volatile memory cell of the present invention so that the area for accommodating the bit line selection transistors can be reduced.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the present invention, a non-volatile memory, a non-volatile memory cell and a method of operating the non-volatile memory cell having a programming by hot-hole injection nitride electron storage (PHINES) is provided.

FIG. 2is a schematic cross-sectional view of a non-volatile memory cell according to a first embodiment of the present invention. As shown inFIG. 2, the non-volatile memory cell20of the present invention comprises a substrate200, a charge-trapping layer214on the substrate200, a control gate220over the charge-trapping layer214, a first dielectric layer212between the substrate200and the charge-trapping layer214, a second dielectric layer216between the control gate220and the charge-trapping layer214, a first conductive state of source230aand drain230b, a first conductive state of lightly doped region202and a second conductive state of pocket-doped region204. In the present invention, the first conductive state is N-type and the second conductive state is P-type, for example. The source230aand the drain230bare disposed in the substrate200on each side of the charge-trapping layer214. A channel region (not shown) is formed in the substrate200between the source230aand the drain230b. The first conductive state of lightly doped region202is disposed close to the top surface of the substrate200between the source230aand the charge-trapping layer214and the second conductive state of pocket-doped region204is disposed in the substrate between the drain230band the charge-trapping layer214. The substrate200can be fabricated from a conventional semiconductor material such as silicon. The charge-trapping layer214can be fabricated using silicon nitride or other suitable material. Both the first dielectric layer212and the second dielectric layer216can be fabricated using a single type of material such as silicon oxide or other suitable material or they are fabricated from different types of materials.

The electron and hole distribution profile in the charge-trapping layer214when the memory cell20is being programmed is shown inFIG. 2. The non-volatile memory20inFIG. 2uses a band-to-band tunneling hot-hole method for a programming operation and a uniform F-N channel for an erasing operation. In addition, the memory cell20of the present embodiment can also be used in a multi-bit-per-cell system. In other words, a multiple level threshold voltage can be established on the right side of the non-volatile memory20through the band-to-band tunneling hot-hole to obtain more memory states. For example, a 4-level threshold voltage (Vt) design can be used to produce a memory state having 2-bit per memory cell storage capacity. However, the left side or right side is a type of usage that refers to the disposition relative to a memory cell. This type of language usage can be changed according to the location of the lightly doped region202and the pocket-doped region204without any effect on the function of the memory cell.

When the memory cell20of the present invention operates according to the PHINES method of operation, the drain230bhaving a pocket-doped region204can enhance the programming efficiency of band-to-band tunneling hot-hole so that the programming speed is increased. Furthermore, the source230ahaving a lightly doped region202is able to restrict the production of the band-to-band tunneling hot holes. Therefore, there is no need to settle for a conventional bit constraining method in the non-volatile memory cell of the present invention.

In addition, the non-volatile memory cell of the present embodiment has an asymmetrically doped structure. Hence, the implant dosage of the pocket-doped region204can be increased to prevent a punch through of the lightly doped region202and increase the programming speed of the memory cell at the same time.

FIG. 3Ais an equivalent circuit diagram of a non-volatile memory according a second embodiment of the present invention.FIG. 3Bis a schematic cross-sectional view of the labeled section B of the non-volatile memory inFIG. 3A.FIG. 3Cis another schematic cross-sectional view of the labeled section B of the non-volatile memory inFIG. 3A. As shown inFIGS. 3A and 3Bfirst, the non-volatile memory mainly comprises a substrate300, a plurality of first conductive state of buried bit lines330in the substrate300, a plurality of word lines320over the substrate300and crossing over the buried bit lines330, a charge-trapping layer314between the word lines320and the substrate300that between the buried bit lines330, a first dielectric layer312between the charge-trapping layer314and the substrate300, a second dielectric layer316between the word lines320and the charge-trapping layer314, a first conductive state of lightly doped region302and a second conductive state of pocket-doped region304. The first conductive state is N-type and the second conductive state is P-type, for example. The lightly doped region302is disposed near the top surface of the substrate300on one side of the buried bit lines330while the pocket-doped region304is disposed in the substrate300on the other side of the buried bit lines330.

In addition, refer toFIGS. 3B and 3C, a dielectric layer306may completely fill the space between the charge-trapping layer314and each of the word lines320so that they are isolated from each other as shown inFIG. 3B, or the first dielectric layer312, the charge-trapping layer314and the second dielectric layer316are extended over the entire substrate300as shown inFIG. 3C.

Moreover, in order to operate the memory, two bit line selection transistors350are incorporated for electrically connecting with the buried bit lines330with the word lines320.

To initiate a programming operation of the memory cell on the left side of BS (serving as the source of the buried bit line330), a first bias voltage is applied to WL (the word line320), a second bias voltage is applied to BS, the line BDL (serving as the first drain of the buried bit line330) is connected to a ground and the line BDR (serving as the second drain of the buried bit line330) is set to a floating state. The first bias voltage is lower than the second bias voltage. Meanwhile, the bit line on the right side of BS is constrained because of the floating BDR line and the presence of the n-type lightly doped region302. It should be noted that the left side or right side is a type of language usage that refers to the disposition relative to a memory cell. This type of language usage can be changed according to the location of the lightly doped region302and the pocket-doped region304without any effect on the function of the memory.

To erase memory data from the memory cell, a bias voltage capable of triggering an F-N channeling erase operation is applied to the WL line, the BDL and the BS line are connected to a ground and the BDR line is set to a floating state. As a result, electrons are trapped inside the charge-trapping layer324.

To read data from the memory cell, a reverse reading method can be executed. In the reverse reading operation, a third bias voltage is applied to the WL line, a voltage lower than the third bias voltage is applied to the BDL line, the BS line is connected to a ground and the BDR line is set to a floating state.

In table 1 below, the values of the bias voltage for operating the non-volatile memory are shown. According to table 1, only two bit line selection transistors350are required to control a group of word lines WL and a group of bit lines BS in programming the memory of the present embodiment. In addition, a bias voltage smaller than 1.6V applied to the BDL line can be used to carry out a reading operation.

TABLE 1(unit: V)BDLBSBDRWLFN-erase00Floating−20HH-program05Floating−5Read<1.60Floating5
In summary, major aspects of the present invention are as follows.

An implant structure having an asymmetrical configuration and different doped states is applied to a non-volatile memory cell that programs by hot-hole injection nitride electron storage (PHINES). Therefore, programming speed can be increased through increasing the implant dosage while forming the pocket-doped region, and the reading capacity will not be affected. Moreover, the lightly doped region utilized in the present invention can prevent the neighboring cell disturb issue caused by programming.

Because the lightly doped region in the present invention deploys a low read-out bias voltage, a channel with a higher threshold voltage (Vt) can be used for reading. In addition, the lightly doped region is able to lower the production of channel hot electrons (CHE) and hence avoids the read-out distribution problem during a reverse reading operation.

The present invention also disposes of the need to form isolation lines between memory cells so that the programming system and circuits are very much simplified.

Only a single group of bit lines needs to be controlled during a programming operation in the non-volatile memory cell of the present invention so that the area for accommodating the bit line selection transistors can be reduced.