Sb2Te3 / Sn15Sb85 type superlattice phase change thin film material, phase change memory unit and preparation method of Sb2Te3 / Sn15Sb85 type superlattice phase change thin film material

Abstract

The invention provides a Sb2Te3 / Sn15Sb85 type superlattice phase change thin film material, a phase change memory unit and a preparation method, the chemical expression of the phase change thin film material is [Sb2Te3 (a) / Sn15Sb85 (b)] 5, the total thickness of the thin film is 50 nm, a and b respectively represent the thickness of a Sb2Te3 thin film and the thickness of a Sn15Sb85 thin film in a single period, and 0 lt; a < lt >; 10 nm, 0 lt; blt; 10 nm. According to the invention, the two materials are subjected to nano multi-layer compounding by adopting a magnetron sputtering method to form a similar superlattice structure, and the phase-change film material has higher crystallization temperature, data retention and activation energy, larger amorphous / crystalline resistance ratio and better thermal stability. The phase change film material provided by the invention is applied to the phase change memory, so that the phase change memory has the advantages of high erasing speed, accurate and reliable read-write performance, stable electrical performance and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of phase change storage, in particular to a Sb2Te3 / Sn 15 Sb 85 Superlattice-like phase change thin film material, phase change memory unit and preparation method. Background Art

[0002] With the rapid growth in the diversity and quantity of interactive data in high-performance computing, artificial intelligence (AI) and machine learning applications, traditional storage solutions have shortcomings such as limited capacity and high latency. At the same time, in the traditional von-Neumann system, the difference in operating speed between the processor cache and dynamic random access memory forms a "storage wall". In the era of artificial intelligence computing based on big data and cloud computing, the processor's computing speed and number of cores continue to grow as it follows Moore's Law to improve performance year by year. This structure of separation of storage and computing further highlights the existing storage wall problem, and the limitation of storage on system performance becomes more and more obvious. In order to overcome this bottleneck, storage-class memory (SCM) has become the next-generation memory solution with its advantages of providing large capacity and fast access speed to store large amounts of data. Phase change memory (PCRAM) has gained widespread attention as one of the most promising materials for emerging non-volatile memory (eNVM). PCRAM has become the most competitive candidate product in semiconductor storage technology with its high complementary metal oxide semiconductor (CMOS) compatibility, scalability and good switching efficiency. When programming the memory, the high and low resistance between the crystallized (SET) state and the melt-quenched amorphous state (RESET) of the phase change material in PCRAM are recognized as binary logic "0" and "1". However, PCRAM devices have a series of problems such as large resistance fluctuations in the SET and RESET states, excessive power consumption during operation, low crystallization temperature, and unstable amorphous state. Although research has been conducted to overcome these problems, the reliability and thermal stability defects of the memory remain a challenge.

[0003] The performance of PCRAM devices mainly depends on the performance of phase change storage media. Phase change materials usually use Ge-Sb-Te ternary phase sulfur compounds, such as GST, Sb-Te and Ge-Te. Among them, Ge2Sb2Te5 is widely used as the core material of phase change materials due to its relatively excellent comprehensive performance and as a commercially viable phase change material. However, with the continuous upgrading of market application needs, this material has many shortcomings. For example, the nucleation-dominated crystallization mechanism of Ge2Sb2Te5 phase change material makes the SET speed of PCRAM devices slow, which cannot meet the development requirements of high-speed memory in the future; the high crystalline resistance of Ge2Sb2Te5 phase change material makes the SET resistance of PCRAM devices high, which cannot meet the development requirements of low-power memory in the future; at the same time, the low phase change temperature and crystallization activation energy of Ge2Sb2Te5 phase change material make the thermal stability of PCRAM devices poor, and it cannot meet the development requirements of high reliability and high stability data storage in the future.

[0004] At present, Sb-Te based phase change materials are the most intensively studied, and they exhibit low melting points that help reduce power, as well as high crystallization rates due to growth-dominated mechanisms. However, pure Sb2Te3 materials have poorer thermal stability than GST due to their low crystallization temperature (150°C), and the data storage capability of the PCM devices they fabricate is even weaker than that of traditional GST materials.

[0005] D. Lencer et al. proposed a phase change material optimization method based on hybridization rate and ionization rate in combination with Littlewood theory. When the average number of p orbital electrons is 3, the resonant bond of the phase change material can be determined based on the hybridization rate. Ionization rate The relationship between the ionization rate and the hybridization rate is characterized. A high hybridization rate will cause the material structure to be distorted, resulting in a decrease in saturated covalent bonds, while an increase in the ionization rate will cause an increase in the number of charges near the ion nucleus. The interaction between the two weakens the resonance characteristics of the material. Therefore, only when the ionization rate and the hybridization rate are within a specific range will a resonant bond be generated inside the material, and only then will the material have excellent phase change properties. By calculating the Sn 15 Sb 85 Material With moderate ionization and hybridization rates, it means that Sn 15 Sb 85 The material has good phase change properties.

[0006] Compared with Sb2Te3 phase change materials, Sn-Sb alloy films have a high phase transition temperature and have great application potential in high data retention PCRAM applications (CN 108365090 A). However, thermal stability and phase transition speed are mutually restricted. Sn-Sb alloys with high phase transition temperatures inevitably have the disadvantage of not being fast enough in phase transition speed, and cannot meet the application requirements of reading data at a faster speed.

[0007] In recent years, in order to achieve higher stability and data retention time, more and more new composite phase change memory materials have been developed. The high cycle life and low power consumption of Sc-Sb2Te3 phase change memory make it possible to replace DRAM. However, Sc-Sb2Te3 itself has some defects, such as the low crystallization temperature of the face-centered cubic phase and the easy oxidation of Sc, which makes the Sc-Sb2Te3 phase change memory material have a slow phase change rate problem. The superlattice phase change memory film is a phase change material that combines two or more films with different phase change properties at the nanoscale, which can effectively utilize the advantages of these two films. It is conducive to improving the heating efficiency, thereby obtaining better phase change performance. TCChong et al. of the Singapore Data Storage Research Institute first proposed in 2006 to apply GeTe / Sb2Te3 multilayer materials to the preparation of PCRAM, and obtained the fastest phase change memory unit in the world at that time. Chinese patent CN 109037439 A discloses Sn for phase change memory. 20 Sb 80 / Si-type superlattice phase change thin film materials, this type of superlattice uses semiconductor Si materials that do not have phase change properties, and the phase change properties need to be further improved. Therefore, how to provide a phase change thin film material with good thermal stability, strong data retention, fast phase change speed, better reliability and compatibility with CMOS technology is a problem that needs to be solved in the current technical field. Summary of the invention

[0008] The object of the present invention is to provide a Sb2Te3 / Sn 15 Sb 85 Superlattice phase change thin film material, phase change memory unit and preparation method, compared with pure Sb2Te3 phase change material, the Sb2Te3 / Sn 15 Sb 85 Superlattice phase change thin film materials have the advantages of good thermal stability, strong data retention ability, faster phase change speed, better programming and reading accuracy and reliability.

[0009] In order to achieve the above technical objectives, the present invention is implemented by the following technical solutions:

[0010] The present invention provides a Sb2Te3 / Sn15 Sb 85 Superlattice phase change thin film material, the chemical expression is [Sb2Te3(a) / Sn 15 Sb 85 (b)]5, the total thickness of the film is 50nm, where a and b represent the Sb2Te3 film and Sn in a single period, respectively. 15 Sb 85 The thickness of the film, and 0 <a<10nm,0<b<10nm。

[0011] The above Sb2Te3 / Sn 15 Sb 85 The preparation method of the superlattice-like phase change thin film material specifically comprises the following steps:

[0012] 1-1) Cleaning the thin film substrate;

[0013] 1-2) Paste the thin film substrate substrate onto the sample stage base, and place one side of the substrate symmetrically with the center of the target;

[0014] 1-3) Install the sputtering targets Sb2Te3 and Sn 15 Sb 85 , start the mechanical pump and molecular pump to evacuate the air;

[0015] 1-4) Set the sputtering gas flow rate, sputtering gas pressure in the chamber, and sputtering power of the target;

[0016] 1-5) Preparation of superlattice-like [Sb2Te3(a) / Sn 15 Sb 85 (b)]5 Phase change storage medium:

[0017] (a) rotating the substrate to the Sb2Te3 target position, turning on the sputtering power of Sb2Te3, and starting to sputter the Sb2Te3 film. After the sputtering of the Sb2Te3 film is completed, turning off the AC sputtering power of Sb2Te3;

[0018] (b) Rotate the substrate to Sn 15 Sb 85 Target position, turn on Sn 15 Sb 85 The sputtering power is set to start sputtering Sn 15 Sb 85 Thin film, Sn 15 Sb 85 After the film sputtering is completed, turn off the Sn 15 Sb 85 DC sputtering power supply;

[0019] (c) Repeat the above steps (a) and (b) until the superlattice [Sb2Te3(a) / Sn 15 Sb 85 (b)]5 The number of cycles set by the phase change storage medium.

[0020] Furthermore, in step 1-1), SiO2 / Si(100), quartz or silicon substrate is used as the substrate material; and / or the specific operation steps of step 1-1) are as follows: the substrate is placed in an acetone solution, cleaned with strong ultrasound for 8 to 10 minutes and then rinsed with deionized water, cleaned with strong ultrasound in an ethanol solution for 8 to 10 minutes and then rinsed with deionized water, the surface and back of the thin film substrate are blown dry with high-purity N2, and placed in a drying oven for complete drying of the water vapor and standby for use.

[0021] Furthermore, the sputtering target in step 1-3) is Sb2Te3 and Sn with a purity of up to 99.999%. 15 Sb 85 ; and / or the vacuum degree after evacuation is less than 2×10 -4 Pa.

[0022] Furthermore, in step 1-4), the DC power sputtering power is set to 25-40W, the AC power sputtering power is set to 25-40W, the sputtering gas is high-purity argon, the flow rate is 30SCCM, and the sputtering pressure is 0.4Pa.

[0023] Furthermore, in step 1-5), Sb2Te3 and Sn 15 Sb 85 The sputtering rates of the thin films are 2.33 s / nm and 2.55 s / nm respectively; and / or the preset rotation speed of the sample stage is 20 rpm.

[0024] The present invention also provides a phase change memory cell, comprising at least a semiconductor substrate, a first metal layer as a bottom electrode, an insulating layer, a heating electrode, a phase change material layer, an adhesion layer and a second metal layer as a top electrode, wherein the phase change material layer comprises the Sb2Te3 / Sn described in any of the above schemes. 15 Sb 85 Superlattice phase change thin film materials.

[0025] Preferably, the longitudinal cross-section of the overall structure of the phase change memory unit is T-shaped.

[0026] The present invention further provides a method for preparing the above phase change memory unit, the method at least comprising:

[0027] 2-1) providing a semiconductor substrate, and forming a first metal layer on the semiconductor substrate as a bottom electrode;

[0028] 2-2) a heating electrode, which is located on the upper surface of the bottom electrode, and an insulating layer is formed on the surface of the bottom electrode between the heating electrodes;

[0029] 2-3) depositing a phase change material layer and an adhesion layer successively onto the heating electrode by magnetron sputtering;

[0030] 2-4) depositing a second metal layer as a top electrode onto the surface of the phase change material layer and the adhesion layer;

[0031] 2-5) Forming an extraction electrode on the surface of the top electrode.

[0032] Preferably, the material of the first metal layer and the second metal layer is aluminum or platinum, with a thickness of 50 to 200 nm; and / or the material of the insulating layer is silicon oxide, with a thickness of 50 to 200 nm; and / or the material of the heating electrode is tungsten, which can be a cylindrical heating electrode, the diameter of the cylindrical heating electrode is 190 nm, and the height is 50 to 200 nm.

[0033] Preferably, the phase change material layer has a thickness of 50 nm; and / or the material of the adhesion layer is TiN, with a thickness of 20 nm.

[0034] The present invention is to construct a new phase change memory, analyze and compare the advantages and disadvantages of the existing material Sb2Te3, and find a new material to compound with it to optimize Sb2Te3, overcome the insufficient thermal stability of the existing material Sb2Te3 while retaining its outstanding crystallization speed, and make use of the advantages and disadvantages of Sn with good thermal stability but slow phase change speed. 15 Sb 85 Phase change material and Sb2Te3 material which has high crystallization speed but poor stability due to low crystallization temperature are nano-multilayered to form a superlattice structure by magnetron sputtering.

[0035] Compared with the prior art, the technical solution provided by the present invention has the following advantages:

[0036] The present invention utilizes the interface of the multilayer structure to inhibit the rapid crystallization of the Sb2Te3 material and improve the amorphous thermal stability of the material. Compared with the Sb2Te3 material, the phase transition temperature is increased from 158°C to 189°C, and the activation energy is increased from 1.81eV to 3.54eV, which exceeds the 160°C and 2.24eV of GST. 15 Sb 85 The composite structure can also improve data retention. Traditional GST can retain data for ten years at a temperature of 85°C, while Sb2Te3 / Sn 15 Sb 85 The phase change memory film can be maintained at 116.8°C for ten years, which can meet the usage conditions of automotive electronics.

[0037] The preparation method of the phase change thin film material provided by the present invention has a simple process, is convenient for accurately controlling the material composition and subsequent processes, and is conducive to expanded production and application; Sb2Te3 / Sn 15 Sb 85 The phase change properties of superlattice-like phase change thin film materials, including phase change temperature, phase change speed, material resistivity, etc., can be adjusted by adjusting Sn 15 Sb 85 The thickness ratio of Sb2Te3 and sputtering order is controlled, the control method is simple and the result is highly controllable.

[0038] The method for preparing a phase change memory unit by applying the phase change thin film material provided by the present invention has a simple process, is conducive to reducing heat loss, improving heating efficiency, and reducing device power consumption.

[0039] The Sb2Te3 / Sn 15 Sb 85 The phase change memory unit test performance has lower threshold current (3.1μA) and threshold voltage (1.9V), which are significantly lower than GST (1.5mA, 2.9V), can generate less heat and achieve fast phase change, and can achieve reversible conversion between high resistance and low resistance of no less than three orders of magnitude at a pulse width of 100ns, which can ensure Sb2Te3 / Sn 15 Sb 85 Accuracy and reliability of read and write operations of phase change unit devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 In the embodiment of the present invention, Sb2Te3 / Sn 15 Sb 85 Superlattice-like phase change thin film materials in Sb2Te3 and Sn 15 Sb 85 The relationship curve between the in-situ resistance and temperature under different thickness ratios and different sputtering orders, where Temperature represents temperature and Resistance represents in-situ resistance.

[0041] Figure 2 In the embodiment of the present invention, Sb2Te3 / Sn 15 Sb 85 The activation energy result diagram is calculated from the relationship curves between in-situ resistance and temperature at different heating rates for superlattice phase change thin film materials and Sb2Te3 phase change thin film materials for comparison.

[0042] Figure 3 In the embodiment of the present invention, Sb2Te3 / Sn 15 Sb 85Corresponding relationship curves between failure time and inverse temperature of superlattice-like phase change thin film materials and Sb2Te3 phase change thin film materials used for comparison, where Failure time represents aging time.

[0043] Figure 4 This is a schematic diagram of the structure of a phase change memory unit provided in Embodiment 5 of the present invention.

[0044] Figure 5 The Sb2Te3 / Sn provided by the present invention 15 Sb 85 Voltage-current diagram of a phase-change memory cell.

[0045] Figure 6 The Sb2Te3 / Sn provided by the present invention 15 Sb 85 Resistance-voltage diagram of a phase-change memory cell. DETAILED DESCRIPTION

[0046] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0047] The strong ultrasonic cleaning in the following embodiments and comparative examples in acetone solution and ethanol solution is operated under the following parameter conditions: the model of the strong ultrasonic cleaning machine is PS-G60A, its outer dimensions are 360×330×380mm, and the inner tank dimensions are 330×300×200mm; the vibration frequency during operation is 40KHz; and the ultrasonic power is 300W.

[0048] Example 1

[0049] The Sb2Te3 / Sn 15 Sb 85 The superlattice phase change thin film material is a multi-layer composite film structure consisting of Sb2Te3 layers and Sn 15 Sb 85 Layers are alternately deposited and composited, with a layer of Sb2Te3 and a layer of Sn 15 Sb 85 The Sb2Te3 layer of the latter alternating cycle is deposited on the Sn layer of the previous alternating cycle. 15 Sb 85 layer; Sb2Te3 layer and Sn 15 Sb 85 The layer is made of Sb2Te3 target and Sn 15 Sb85 The target material is obtained by magnetron sputtering.

[0050] In this embodiment, Sb2Te3 / Sn 15 Sb 85 The general structure of superlattice phase change thin film materials is [Sb2Te3(1nm) / Sn 15 Sb 85 (9nm)]5, that is, the thickness of a single layer of Sb2Te3 is 1nm, and the thickness of a single layer of Sn 15 Sb 85 The thickness of the layer is 9nm, Sb2Te3 layer and Sn 15 Sb 85 The number of alternating layers is 5, Sb2Te3 / Sn 15 Sb 85 The total thickness of the superlattice-like phase change thin film material is 50nm.

[0051] The Sb2Te3 / Sn 15 Sb 85 The superlattice-like phase change thin film material is obtained by magnetron sputtering, and the specific preparation method includes the following steps:

[0052] (1) Clean the surface and back of the SiO2 / Si (purity of 99.99%) substrate to remove dust particles, organic and inorganic impurities. Place the substrate in an acetone solution, use strong ultrasonic cleaning for 8 to 10 minutes, and then rinse with deionized water. Use strong ultrasonic cleaning in an ethanol solution for 8 to 10 minutes, and then rinse with deionized water. Blow dry the surface and back of the thin film substrate with high-purity N2, place it in a drying oven, and set it aside after the water vapor is completely dried.

[0053] (2) Preparation for magnetron sputtering: Paste the thin film substrate substrate on the sample stage base, and place one side of the substrate symmetrically with the target center. Place the substrate to be sputtered cleaned in step (1) on the base, and install the Sb2Te3 target and Sn 15 Sb 85 The purity of the target material reaches 99.999% (atomic percentage), and the background vacuum is pumped to 1×10 -4 Pa; set the sputtering power to 30W; use high-purity Ar as the sputtering gas (the volume percentage reaches 99.999%), set the Ar gas flow rate to 30SCCM, and adjust the sputtering gas pressure to 0.4Pa.

[0054] (3) Preparation of [Sb2Te3(1nm) / Sn 15 Sb 85 (9nm)] 5 types of superlattice phase change films:

[0055] (a) rotating the substrate to the Sb2Te3 target position, turning on the sputtering power supply of Sb2Te3, sputtering the Sb2Te3 target material at a sputtering rate of 2.33 s / nm, and turning off the AC sputtering power supply of Sb2Te3 after the sputtering of the Sb2Te3 film is completed;

[0056] (b) Rotate the substrate to Sn 15 Sb 85 Target position, turn on Sn 15 Sb 85 The sputtering power supply is based on Sn 15 Sb 85 Effect of sputtering rate of target material 2.55s / nm on Sn 15 Sb 85 The target material is sputtered, Sn 15 Sb 85 After the film sputtering is completed, turn off the Sn 15 Sb 85 DC sputtering power supply;

[0057] (c) Repeat the above steps (a) and (b) until the superlattice [Sb2Te3(a) / Sn 15 Sb 85 (b)]5 The number of cycles set for the phase change film.

[0058] By adjusting the sputtering time to control the thickness ratio of the material, a phase change memory film structure of [Sb2Te3(1nm) / Sn 15 Sb 85 (9nm)]5, abbreviated as ST1 / SS9 or [ST1 / SS9]5.

[0059] Example 2

[0060] In this embodiment, Sb2Te3 / Sn 15 Sb 85 The general structure of superlattice phase change thin film materials [Sb2Te3(2nm) / Sn 15 Sb 85 (8nm)]5, that is, the thickness of a single layer of Sb2Te3 is 2nm, and the thickness of a single layer of Sn 15 Sb 85 The thickness of the layer is 8nm, Sb2Te3 layer and Sn 15 Sb 85 The number of alternating layers is 5, Sb2Te3 / Sn 15 Sb 85 The total thickness of the superlattice-like phase change thin film material is 50nm.

[0061] The preparation method of this embodiment is similar to that of embodiment 1, except that [Sb2Te3(2nm) / Sn15 Sb 85 The thickness of the single-layer Sb2Te3 layer in the (8nm)]5 film is 2nm, and the thickness of the single-layer Sn 15 Sb 85 The thickness of the layer is 8 nm, abbreviated as ST2 / SS8 or [ST2 / SS8]5.

[0062] Example 3

[0063] In this embodiment, Sb2Te3 / Sn 15 Sb 85 The superlattice phase change thin film material is a multi-layer composite film structure composed of Sn 15 Sb 85 The Sn2Te3 layer is alternately deposited and composited. Compared with Example 1, the difference is that 15 Sb 85 A layer of Sn and Sb2Te3 is sputtered sequentially. 15 Sb 85 A layer of Sn and a layer of Sb2Te3 are used as an alternating cycle. The Sb2Te3 layer of the latter alternating cycle is deposited on the Sn 15 Sb 85 layer; Sb2Te3 layer and Sn 15 Sb 85 The layer is made of Sb2Te3 target and Sn 15 Sb 85 The target material is obtained by magnetron sputtering.

[0064] In this embodiment, Sb2Te3 / Sn 15 Sb 85 The general structure of superlattice phase change thin film materials is [Sn 15 Sb 85 (9nm) / Sb2Te3(1nm)]5, i.e. single layer Sn 15 Sb 85 The thickness of the layer is 9nm, the thickness of the single layer Sb2Te3 is 1nm, and the thickness of Sn 15 Sb 85 The number of alternating periods of Sb2Te3 layers is 5, and the Sb2Te3 / Sn 15 Sb 85 The total thickness of the superlattice-like phase change thin film material is 50nm.

[0065] The Sb2Te3 / Sn 15 Sb 85 The superlattice-like phase change thin film material is obtained by magnetron sputtering, and the specific preparation method includes the following steps:

[0066] (1) Clean the surface and back of the SiO2 / Si (purity of 99.99%) substrate to remove dust particles, organic and inorganic impurities. Place the substrate in an acetone solution, use strong ultrasonic cleaning for 8 to 10 minutes, and then rinse with deionized water. Use strong ultrasonic cleaning in an ethanol solution for 8 to 10 minutes, and then rinse with deionized water. Blow dry the surface and back of the thin film substrate with high-purity N2, place it in a drying oven, and set it aside after the water vapor is completely dried.

[0067] (2) Preparation for magnetron sputtering: Paste the thin film substrate substrate onto the sample stage base, and make one side of the substrate symmetrical with the target center. Place the substrate to be sputtered cleaned in step (1) on the base, and install Sn 15 Sb 85 The purity of the target material and Sb2Te3 target material reached 99.999% (atomic percentage), and the background vacuum was pumped to 1×10 -4 Pa; set the sputtering power to 30W; use high-purity Ar as the sputtering gas (the volume percentage reaches 99.999%), set the Ar gas flow rate to 30SCCM, and adjust the sputtering gas pressure to 0.4Pa.

[0068] (3) Preparation of [Sn 15 Sb 85 (9nm) / Sb2Te3(1nm)] 5 types of superlattice structure phase change films:

[0069] (a) Rotate the substrate to Sn 15 Sb 85 Target position, turn on Sn 15 Sb 85 The sputtering power supply is based on Sn 15 Sb 85 Effect of sputtering rate of target material 2.55s / nm on Sn 15 Sb 85 The target material is sputtered, Sn 15 Sb 85 After the film sputtering is completed, turn off the Sn 15 Sb 85 DC sputtering power supply;

[0070] (b) rotating the substrate to the Sb2Te3 target position, turning on the sputtering power of Sb2Te3, sputtering the Sb2Te3 target at a sputtering rate of 2.33 s / nm, and turning off the AC sputtering power of Sb2Te3 after the sputtering of the Sb2Te3 film is completed;

[0071] (c) Repeat the above steps (a) and (b) until the superlattice [Sb2Te3(a) / Sn 15 Sb 85(b)]5 The number of cycles set for the phase change film.

[0072] By adjusting the sputtering time to control the thickness ratio of the material, a phase change memory film structure is prepared: [Sn 15 Sb 85 (9nm) / Sb2Te3(1nm)]5, abbreviated as SS9 / ST1 or [SS9 / ST1]5.

[0073] Example 4

[0074] In this embodiment, Sb2Te3 / Sn 15 Sb 85 The general structure of superlattice-like phase change thin film materials [Sn 15 Sb 85 (5nm) / Sb2Te3(5nm)]5, that is, single-layer Sn 15 Sb 85 The thickness of the layer is 5nm, the thickness of the single layer Sb2Te3 is 5nm, and the thickness of Sn 15 Sb 85 The number of alternating periods of Sb2Te3 layers is 5, and the Sb2Te3 / Sn 15 Sb 85 The total thickness of the superlattice-like phase change thin film material is 50nm.

[0075] The preparation method of this embodiment is similar to that of embodiment 3, except that [Sn 15 Sb 85 Single layer Sn (5nm) / Sb2Te3 (5nm)]5 thin film 15 Sb 85 The thickness of the layer is 5 nm, and the thickness of a single Sb2Te3 layer is 5 nm, abbreviated as SS5 / ST5 or [SS5 / ST5]5.

[0076] The phase change film material of the present invention can also be prepared by other physical vapor deposition methods or chemical vapor deposition methods. The Sb2Te3 / Sn 15 Sb 85 The preparation method of the superlattice-like phase change thin film material is only one of the better preparation methods, to illustrate that the phase change thin film material of the present invention can be successfully prepared, and the prepared phase change thin film material has higher quality and higher purity.

[0077] The present invention also provides a phase change memory unit, the longitudinal cross-section of the overall structure is T-shaped. The phase change memory unit at least comprises a semiconductor substrate, a first metal layer as a bottom electrode, an insulating layer, a heating layer, a phase change material layer, an adhesion layer and a second metal layer as a top electrode. The phase change material layer comprises the Sb2Te3 / Sn 15 Sb85 Superlattice phase change thin film materials.

[0078] The present invention further provides a method for preparing a phase change memory unit, the method at least comprising:

[0079] 1) providing a semiconductor substrate, and forming a first metal layer on the semiconductor substrate as a bottom electrode;

[0080] 2) a heating layer, located on the upper surface of the bottom electrode, and an insulating layer is formed on the surface of the bottom electrode between the heating layers;

[0081] 3) depositing a phase change material layer and an adhesion layer successively onto the heating layer by magnetron sputtering;

[0082] 4) depositing a second metal layer as a top electrode onto the surface of the phase change material layer and the adhesion layer;

[0083] 5) Forming an extraction electrode on the surface of the top electrode.

[0084] As an example, the bottom electrode, the top electrode and the extraction electrode can be prepared by any one of sputtering, evaporation, chemical vapor deposition, plasma enhanced chemical vapor deposition, low pressure chemical vapor deposition, metal compound vapor deposition, molecular beam epitaxy, atomic vapor deposition or atomic layer deposition. The material of the first metal layer and the second metal layer is aluminum or platinum, and the thickness is 50 to 200 nm.

[0085] As an example, W is prepared by atomic vapor deposition as the heating layer, and the heating layer is a cylindrical heating electrode, and the diameter of the heating electrode can be 190nm and the height is 50-200nm. The material of the insulating layer can be nitride, oxide, oxynitride or carbide, which is used to isolate adjacent heating layers.

[0086] Example 5

[0087] This embodiment provides a phase change memory unit such as Figure 4 As shown, the longitudinal cross-section of the overall structure is T-shaped, including a semiconductor substrate Si with a thickness of 500 μm, a first metal layer Al with a thickness of 100 nm as a bottom electrode, a silicon oxide insulating layer with a thickness of 200 nm, a W heating electrode with a diameter of 190 nm and a height of 200 nm, a phase change material layer, a TiN adhesion layer, and a second metal layer Al with a thickness of 200 nm as a top electrode. The phase change material layer is [Sb2Te3(1 nm) / Sn 15 Sb 85 (9nm)]5, magnetron sputtering was used to utilize Sb2Te3 and Sn 15 Sb 85Alloy target preparation thickness is 50nm Sb2Te3 / Sn 15 Sb 85 The preparation steps and process parameters of the phase change material layer are consistent with those of Example 1. A TiN adhesion layer is prepared on the surface of the phase change material layer by magnetron sputtering, and the process parameters are: the background pressure is 1×10 -4 Pa, the gas pressure during sputtering is 0.4 Pa, the sputtering power is 30 W, the sputtering time is 1000 s, and the TiN thickness is 20 nm.

[0088] Comparative Example 1

[0089] The preparation steps are as follows:

[0090] (1) Clean the surface and back of the SiO2 / Si (purity of 99.99%) substrate to remove dust particles, organic and inorganic impurities. Place the substrate in an acetone solution, use strong ultrasonic cleaning for 8 to 10 minutes, and then rinse with deionized water. Use strong ultrasonic cleaning in an ethanol solution for 8 to 10 minutes, and then rinse with deionized water. Blow dry the surface and back of the thin film substrate with high-purity N2, place it in a drying oven, and set it aside after the water vapor is completely dried.

[0091] (2) Preparation for magnetron sputtering: Paste the thin film substrate substrate onto the sample stage base, and make one side of the substrate symmetrical with the center of the target. Place the substrate to be sputtered cleaned in step (1) on the base, install the Sb2Te3 target material, the purity of the target material reaches 99.999% (atomic percentage), and draw the background vacuum to 1×10 -4 Pa; set the sputtering power to 30W; use high-purity Ar as the sputtering gas (the volume percentage reaches 99.999%), set the Ar gas flow rate to 30SCCM, and adjust the sputtering gas pressure to 0.4Pa.

[0092] (3) Nano-phase change thin film materials were prepared by magnetron sputtering. The empty base was rotated to the target position, the RF power applied to the target was turned on, and the target material was sputtered according to the set sputtering time (116s). After sputtering, the DC sputtering power of the Sb2Te3 target position was turned off to obtain a single-layer Sb2Te3 phase change thin film with a thickness of 50nm.

[0093] Comparative Example 2

[0094] The preparation steps are as follows:

[0095] (1) Clean the surface and back of the SiO2 / Si (purity of 99.99%) substrate to remove dust particles, organic and inorganic impurities. Place the substrate in an acetone solution, use strong ultrasonic cleaning for 8 to 10 minutes, and then rinse with deionized water. Use strong ultrasonic cleaning in an ethanol solution for 8 to 10 minutes, and then rinse with deionized water. Blow dry the surface and back of the thin film substrate with high-purity N2, place it in a drying oven, and set it aside after the water vapor is completely dried.

[0096] (2) Preparation for magnetron sputtering: Paste the thin film substrate substrate onto the sample stage base, and make one side of the substrate symmetrical with the target center. Place the substrate to be sputtered cleaned in step (1) on the base, and install Sn 15 Sb 85 The purity of the target material reaches 99.999% (atomic percentage), and the background vacuum is pumped to 1×10 -4 Pa; set the sputtering power to 30W; use high-purity Ar as the sputtering gas (the volume percentage reaches 99.999%), set the Ar gas flow rate to 30SCCM, and adjust the sputtering gas pressure to 0.4Pa.

[0097] (3) Prepare nano-phase change thin film materials by magnetron sputtering. Rotate the empty base to the target position, turn on the RF power applied to the target, and start sputtering the target material according to the set sputtering time (127s). After sputtering, turn off the Sn 15 Sb 85 The DC sputtering power supply at the target position produces a single layer of Sn with a thickness of 50nm. 15 Sb 85 Phase change film.

[0098] Related performance tests

[0099] The [Sb2Te3(1nm) / Sn 15 Sb 85 (9nm)]5, [Sb2Te3(2nm) / Sn 15 Sb 85 (8nm)]5, [Sn 15 Sb 85 (9nm) / Sb2Te3(1nm)]5, [Sn 15 Sb 85 (5nm) / Sb2Te3(5nm)]5, Sb2Te3, Sn 15 Sb 85 The phase change memory film is tested to obtain the resistance and temperature relationship curves of each phase change film material. Figure 1 As shown. At low temperatures, all films are in a high-resistance amorphous state. As the temperature continues to rise, the film resistance slowly decreases. When it reaches its phase transition temperature, the film resistance decreases rapidly. After dropping to a certain value, the resistance remains basically unchanged, indicating that the film has undergone a transition from an amorphous state to a crystalline state. Figure 1 Show pure Sb2Te3, Sn 15 Sb 85 The crystallization temperatures of Sb2Te3 / Sn are 159℃ and 232℃ respectively. 15 Sb85 Medium Sn 15 Sb 85 The thickness of [Sb2Te3(1nm) / Sn 15 Sb 85 The crystallization temperature of the Sn (9nm)]5 film gradually increased to 189℃, which indicates that 15 Sb 85 The addition of the layer significantly inhibited the crystallization of the Sb2Te3 material, which may be due to the interface of the multilayer film inhibiting crystallization and improving the amorphous thermal stability of the film. At the same time, we also studied the effect of adjusting the Sb2Te3 layer and Sn 15 Sb 85 The effect of the sputtering sequence of layers on the thermal stability of the film, Figure 1 In [Sn 15 Sb 85 The phase transition temperature of the Sn (9nm) / Sb2Te3 (1nm)]5 film is also significantly higher than that of pure Sb2Te3. 15 Sb 85 The addition of increases the difference between the amorphous resistance and the crystalline resistance of the film from two orders of magnitude to three orders of magnitude. The increase in the high-to-low resistance ratio improves the device's ability to distinguish between logic "0" and logic "1" states when reading and writing.

[0100] For the above Sb2Te3, [Sb2Te3(1nm) / Sn 15 Sb 85 (9nm)]5, [Sb2Te3(2nm) / Sn 15 Sb 85 (8nm)]5 The in-situ resistance of the phase change memory film was measured at different heating rates, and its activation energy was calculated. Figure 2 Represents pure Sb2Te3 and [Sb2Te3(2nm) / Sn 15 Sb 85 (8nm)]5 and [Sb2Te3(1nm) / Sn 15 Sb 85 (9nm)]5 film activation energy E a are 1.18eV, 2.93eV and 3.54eV respectively. 15 Sb 85 Thickness increase, E a This may be due to the 15 Sb 85 There is an interface effect between thin layers. Sn 15 Sb 85 The addition of Sb2Te3 / Sn 15 Sb 85 The film obtains higher Ea It can avoid the thermal crosstalk problem caused by the proximity effect and help improve its thermal stability.

[0101] For the above Sb2Te3, [Sb2Te3(1nm) / Sn 15 Sb 85 (9nm)]5, [Sb2Te3(2nm) / Sn 15 Sb 85 (8nm)]5 phase change memory thin film material was tested for data retention, and the corresponding relationship curve between failure time and temperature inverse was obtained as shown in Figure 3 The data retention capability of the material is judged by the temperature corresponding to when the data is kept for 10 years. The higher the corresponding temperature, the stronger the data retention capability of the material. Figure 3 It can be seen that the single-layer Sb2Te3 phase change thin film material can maintain data for 10 years at 69.8°C, while the [Sb2Te3(2nm) / Sn 15 Sb 85 (8nm)]5 and [Sb2Te3(1nm) / Sn 15 Sb 85 (9nm)] 5 nanometer phase change memory thin film material can keep data for 10 years at temperatures up to 91.5℃ and 116.8℃ respectively. 15 Sb 85 Nano phase change storage thin film materials have better data retention capabilities than traditional Sb2Te3 thin film materials and can be used for high-temperature data storage.

[0102] For the above [Sb2Te3(1nm) / Sn 15 Sb 85 The performance of the (9nm)]5 phase change memory unit was tested, and the device current-voltage and resistance-voltage relationship diagrams were obtained as shown in the figure. Figure 5 , 6 . Figure 5 The curve shows that the PCM voltage drops sharply as the scanning current gradually increases. This indicates that after Joule heating, the device unit undergoes a threshold switch from a high resistance state to a low resistance state. 15 Sb 85 The phase change memory cell device test performance has lower threshold current (3.1μA) and threshold voltage (1.9V) compared to GST (1.5mA, 2.9V), [Sn 15 Sb 85 (9nm) / Sb2Te3(1nm)]5 phase change unit device can generate less heat and achieve fast threshold switching. Figure 6The resistance and voltage curves show that when the PCM device is in the high resistance state, the energy of the initial pulse cannot activate crystallization and the resistance remains unchanged. When the pulse width reaches the critical value, the phase change layer begins to crystallize and the resistance drops suddenly, completing the SET process. The RESET state can be restored by further increasing the voltage, resulting in a sudden increase in resistance. When a pulse width of 100ns is applied, a conversion of no less than three orders of magnitude between high resistance and low resistance can be achieved. This ensures that Sb2Te3 / Sn 15 Sb 85 Accuracy and reliability of read and write operations of phase change memory cells.

[0103] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A Sb2Te3 / Sn 15 Sb 85 Superlattice phase change thin film material, the chemical expression is [Sb2Te3(a) / Sn 15 Sb 85 (b)]5, the total thickness of the film is 50nm, where a and b represent the Sb2Te3 film and Sn in a single period, respectively. 15 Sb 85 The thickness of the film, and 0 <a<10nm,0<b<10nm。 2. Sb2Te3 / Sn according to claim 1 15 Sb 85 The preparation method of the superlattice-like phase change thin film material specifically comprises the following steps: 1-1) Cleaning the thin film substrate; 1-2) Paste the thin film substrate substrate onto the sample stage base, and place one side of the substrate symmetrically with the center of the target; 1-3) Install the sputtering targets Sb2Te3 and Sn 15 Sb 85 , start the mechanical pump and molecular pump to evacuate the air; 1-4) Set the sputtering gas flow rate, sputtering gas pressure in the chamber, and sputtering power of the target; 1-5) Preparation of superlattice-like [Sb2Te3(a) / Sn 15 Sb 85 (b)]5 Phase change storage medium: (a) rotating the substrate to the Sb2Te3 target position, turning on the sputtering power of Sb2Te3, and starting to sputter the Sb2Te3 film. After the sputtering of the Sb2Te3 film is completed, turning off the AC sputtering power of Sb2Te3; (b) Rotate the substrate to Sn 15 Sb 85 Target position, turn on Sn 15 Sb 85 The sputtering power is set to start sputtering Sn 15 Sb 85 Thin film, Sn 15 Sb 85 After the film sputtering is completed, turn off the Sn 15 Sb 85 DC sputtering power supply; (c) Repeat the above steps (a) and (b) until the superlattice [Sb2Te3(a) / Sn 15 Sb 85 (b)]5 The number of cycles set by the phase change storage medium.

3. The preparation method according to claim 2, characterized in that:In step 1-1), SiO2 / Si(100), quartz or silicon substrate is used as the substrate material; and / or the specific operation steps of step 1-1) are as follows: the substrate is placed in an acetone solution, and is cleaned with strong ultrasound for 8 to 10 minutes and then rinsed with deionized water, and is cleaned with strong ultrasound in an ethanol solution for 8 to 10 minutes and then rinsed with deionized water, and the surface and back of the thin film substrate are blown dry with high-purity N2, and the substrate is placed in a drying oven and the water vapor is completely dried for standby use.

4. The preparation method according to claim 2, characterized in that: The sputtering target in step 1-3) is Sb2Te3 and Sn with a purity of up to 99.999%. 15 Sb 85 ; and / or the vacuum degree after evacuation is less than 2×10 -4 Pa.

5. The preparation method according to claim 2, characterized in that: The DC power sputtering power set in step 1-4) is 25-40W, the AC power sputtering power is 25-40W, the sputtering gas is high-purity argon, the flow rate is 30SCCM, and the sputtering pressure is 0.4Pa.

6. The preparation method according to claim 2, characterized in that: Step 1-5) Sb2Te3 and Sn 15 Sb 85 The sputtering rates of the thin films are 2.33 s / nm and 2.55 s / nm respectively; and / or the preset rotation speed of the sample stage is 20 rpm.

7. A phase change memory cell, comprising at least a semiconductor substrate, a first metal layer as a bottom electrode, an insulating layer, a heating electrode, a phase change material layer, an adhesion layer and a second metal layer as a top electrode, characterized in that: The phase change material layer comprises the Sb2Te3 / Sn 15 Sb 85 Superlattice phase change thin film materials.

8. The method for preparing a phase change memory cell according to claim 7, the method comprising at least: 2-1) providing a semiconductor substrate, and forming a first metal layer on the semiconductor substrate as a bottom electrode; 2-2) a heating electrode, which is located on the upper surface of the bottom electrode, and an insulating layer is formed on the surface of the bottom electrode between the heating electrodes; 2-3) depositing a phase change material layer and an adhesion layer successively onto the heating electrode by magnetron sputtering; 2-4) depositing a second metal layer as a top electrode onto the surface of the phase change material layer and the adhesion layer; 2-5) Forming an extraction electrode on the surface of the top electrode.

9. The preparation method according to claim 8, characterized in that: The material of the first metal layer and the second metal layer is aluminum or platinum, with a thickness of 50 to 200 nm; and / or the material of the insulating layer is silicon oxide; and / or the material of the heating electrode is tungsten, which is a cylindrical heating electrode with a diameter of 190 nm and a height of 50 to 200 nm.

10. The preparation method according to claim 8, characterized in that: The phase change material layer has a thickness of 50 nm; and / or the material of the adhesion layer is TiN, with a thickness of 20 nm.

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