CN102592981A - Self-assembly preparation method for floating gate layer of silicon nitride dielectric film with embedded metal tungsten quantum dots - Google Patents

Abstract

The invention discloses a self-assembly preparation method for a floating gate layer of a silicon nitride dielectric film with embedded metal tungsten quantum dots. According to the invention, at a room temperature, a magnetron sputtering method is adopted to prepare the silicon nitride dielectric film with the embedded metal tungsten quantum dots, and the film serves as a floating gate structure of a non-volatile memory; a sputtering target material is formed by small metal tungsten blocks on a silicon nitride target material, and the nano-scale metal tungsten quantum dots, which are uniformly distributed on the silicon nitride dielectric film, can be obtained through cosputtering at the room temperature; and the size and density of the metal tungsten quantum dots can be adjusted through adjusting the amount of the small metal blocks, namely by adjusting the coverage rate of the small metal blocks to the silicon nitride target material. The high-density metal tungsten quantum dots prepared by the invention have favorable thermal stability at the high temperature of 800 DEG C and are easy to compatible with a CMOS (Complementary Metal Oxide Semiconductor) technology. The silicon nitride dielectric film with embedded high-density metal tungsten quantum dots serves as the floating gate layer of the non-volatile memory and has good charge storage characteristics.

Description

A self-assembly method for preparing a floating gate layer of silicon nitride dielectric film embedded with metal tungsten quantum dots

the

technical field

The invention relates to a self-assembly method for preparing a floating gate layer of a silicon nitride dielectric film embedded with metal tungsten quantum dots.

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Background technique

In recent years, the Flash memory market has been expanding day by day, which puts forward higher requirements for its integration and performance. According to ITRS 2010, the Technology node of Flash memory will enter the order of 20nm or below in the near future. However, the miniaturization of traditional flash memory with polysilicon floating gate structure is facing severe challenges. First of all, the miniaturization of flash memory greatly reduces the reliability of data storage and shortens the charge accumulation time. In addition, miniaturization aggravates the short channel effect, increases power consumption and interference between memory units. In order to solve these problems, a breakthrough must be made in the structure and principle of the device. As a new type of non-volatile memory, metal quantum dot floating gate flash memory is considered to be a favorable candidate to replace traditional flash memory. The metal quantum dots are surrounded by an insulating film and become isolated charge storage units, which inhibit the movement of charges in the floating gate, thereby greatly improving the charge storage time. Especially compared with silicon quantum dot non-volatile memory, the use of metal quantum dots with high work function reduces the tunneling probability of charges from quantum dots to the channel, further improving the reliability of charge storage. While maintaining a certain level of reliability, the oxide layer can be thinned to achieve miniaturization of the device. With the miniaturization of quantum dot non-volatile memory, the inhomogeneity of the electrical properties of memory cells brought about by the inhomogeneity of quantum dot density and size distribution is the key problem restricting its miniaturization. The formation of high-density quantum dots will effectively solve the uniformity problem of memory cells and challenge the limit of miniaturization of non-volatile memory.

Metal tungsten has a large work function (4.5eV) and good thermal stability at high temperature. As the floating gate layer of metal quantum dot non-volatile memory, it is a promising metal quantum dot material. The invention introduces a method for preparing a silicon nitride thin film embedded with high-density and high-thermal-stability metal tungsten quantum dots, which is simple to operate and compatible with traditional semiconductor technology.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art, to provide a method suitable for self-assembly of non-volatile memory to prepare a floating gate layer embedded with high-density, high-stability metal tungsten quantum dot silicon nitride dielectric film, which is simple, Easy to operate features.

The present invention is directly obtained by the sputtering method, and the target material adopts a special design, that is, metal tungsten small pieces are placed on the silicon nitride target material. A thin film embedded with metal tungsten quantum dots can be obtained by sputtering at room temperature; the size and density of quantum dots can be adjusted by adjusting the number of small metal blocks.

A method for preparing a floating gate layer of a silicon nitride dielectric film embedded with high-density and high-stability metal tungsten quantum dots by self-assembly, comprising the following steps:

(1) Select a silicon nitride insulating target, and place a metal tungsten block on the insulating target; the coverage of the metal tungsten block on the insulating target is 10% to 30%;

(2) Perform sputtering film formation on the above target material, the sputtering atmosphere is argon, and the substrate is a p-type silicon wafer of thermally oxidized silicon dioxide.

In the above method, the metal tungsten quantum dots prepared by the present invention, when the ratio of the total area of the metal tungsten small pieces to the area of the silicon nitride target material is 16.7%, the density of the obtained metal tungsten quantum dots reaches the highest 1.3×10 ¹³ /cm ² , the size is 1~1.5nm.

In the above method, the size of the insulating target is 2 inches, and the size of the metal block is 5mmx5mmx1.5mm.

In the above method, the conditions for sputtering film formation are as follows: the power is 100W, the body vacuum is < ^10-5 Pa, the working pressure during sputtering is 0.05~1.5Pa, the distance between the target and the substrate is 20cm, and the substrate The bottom was not heated, and the substrate rotation speed was 75 rpm/min.

Compared with the prior art, the present invention has the following beneficial effects:

1. The density of the metal tungsten quantum dots of the present invention is adjusted by the number of small pieces of metal tungsten in the target during the sputtering process, which is simple and easy, and can obtain metal tungsten quantum dots with small size and high density;

2. The high-density metal tungsten quantum dots prepared by the present invention have high temperature thermal stability and are easy to be compatible with semiconductor technology;

3. The metal tungsten quantum dots prepared by this method are small in size, with a diameter of about 1-1.5nm, and high density, with the highest density reaching 1.3x10 ¹³ /cm ² ;

4. High-density metal tungsten quantum dots are embedded in silicon nitride film, which can effectively prevent the oxidation of metal tungsten quantum dots;

5. In order to verify the high-temperature thermal stability, the film was vacuum annealed in situ in the sputtering chamber at a temperature of 800 degrees for 1 hour. The metal tungsten quantum dots prepared by the invention still maintain good high-temperature thermal stability and good charge storage characteristics at an annealing temperature of 800 degrees.

Description of drawings

Figure 1 is a graph showing the relationship between the density and size of metal tungsten quantum dots and the target coverage.

Figure 2 is a cross-sectional TEM photo of a silicon nitride film embedded with metal tungsten quantum dots (W-ND) at a coverage rate of 16.7% and an annealing temperature of 800 degrees. The density of metal quantum dots is 1.3x10 ¹³ /cm ² , and the size is 1~1.5nm.

Figure 3 is the CV characteristic curve of the metal tungsten quantum dot floating gate MOS structure (the quantum dot density is 1.3x10 ¹³ /cm ² ), and it is compared with the CV of the MOS structure without the metal quantum dot floating gate layer.

Detailed ways

Further describe the present invention below by embodiment

Example 1:

The target for magnetron sputtering is a 2-inch silicon nitride target, on which 5mmx5mmx1.5mm small metal tungsten pieces are evenly placed, and the coverage of the metal tungsten small pieces on the silicon nitride target is adjusted, and the range is 10%~ 30%. After standard cleaning of P-type (100) silicon wafers, silicon dioxide is grown by thermal oxidation with a thickness of about 5nm. Put the above-mentioned silicon wafer into the magnetron sputtering reaction chamber. The sputtering conditions are: the vacuum degree of the chamber body is 4x10 ^-6 Pa, the flow rate of argon gas is 8 sccm, the power of the RF power supply on the target is 100W, the working pressure is 0.08Pa, the substrate is not heated, and the substrate speed is 75rpm/min , the sputtered film thickness is 5nm. The thin film embedded with metal tungsten quantum dots was vacuum annealed in situ in the sputtering chamber at a temperature of 800 degrees for 1 hour. Figure 1 shows the relationship between the density, size and target coverage of tungsten quantum dots. The sample was annealed in vacuum at 800 degrees for 1 hour. Figure 2 shows the cross-sectional transmission microscope photo of metal tungsten quantum dots when the target coverage rate is 16.7%. The size of the quantum dots is 1~1.5nm and the density is 1.3x10 ¹³ /cm ² .

In this example, a p-type silicon wafer with approximately 5nm thermally oxidized silicon dioxide was selected as the substrate, and the film was sputtered. The target coverage rate was 16.7%, and the thickness of the metal tungsten quantum dot film was 5nm. Vacuum annealing at 800 degrees for a time of 1 hour, and then sputter 40nm HfO2 insulating film on it, annealing temperature is 600 degrees, as a charge blocking layer. Finally, the Al electrode is thermally evaporated to form a MOS structure with a metal quantum dot floating gate layer. Fig. 3 is the C-V hysteresis characteristic curve of this MOS structure. Compared with samples without quantum dot floating gate layer, the metal tungsten quantum dot floating gate MOS structure has a C-V hysteresis window greater than 6V when the voltage is scanned in the range of +/-10V, showing excellent charge storage characteristics.

Claims (4)

1. A kind of self-assembly prepares the method for embedded metal tungsten quantum dot silicon nitride dielectric film floating gate layer, it is characterized in that comprising the steps: (1) Select a silicon nitride insulating target, and place a metal tungsten block on the insulating target; the coverage of the metal tungsten block on the insulating target is 10% to 30%; (2) Perform sputtering film formation on the above target material, the sputtering atmosphere is argon, and the substrate is a p-type silicon wafer of thermally oxidized silicon dioxide. 2. The method according to claim 1, wherein the coverage of the metal tungsten block on the insulating target is 16.7%. 3. The method according to claim 1, wherein the size of the insulating target is 2 inches, and the size of the metal block is 5mmx5mmx1.5mm. 4. The method according to claim 1, wherein the conditions for sputtering to form a film are as follows: the power is 100W, the vacuum degree of the body is < ^10-5 Pa, the working pressure during sputtering is 0.05-1.5Pa, and the target The distance between the material and the substrate is 20cm, the substrate is not heated, and the substrate rotation speed is 75rpm/min.

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