AsGeSeSi-based OTS gate tube material and preparation method thereof

Abstract

The invention provides a preparation method of a GeSe OTS gate tube material introduced with As and Si elements. The amorphous state model of the GeSe OTS gate tube in which As and Si elements are introduced is constructed, the amorphous degree and state density of the material model in which the As and Si elements are introduced are compared, and it is clarified that the amorphous degree of the AsGeSeSi material is larger and the ground state resistance is larger. And then, according to the bonding characteristic, it is clarified that the structure of the GeSe OTS gate tube material after the As and Si elements are selectively introduced is more stable, and guiding significance is provided for optimizing the performance of an OTS threshold device.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor materials, and in particular to an AsGeSeSi-based OTS gating tube material and a preparation method thereof. Background Art

[0002] Phase change memory (PCM) is widely used in new storage applications of three-dimensional integration due to its simple structure, easy expansion, low power consumption, good retention and fast read and write speed. However, with the development of three-dimensional integration technology, the leakage current crosstalk problem faced by PCM has become a major obstacle to its further development. In order to overcome this problem, researchers are committed to exploring and developing gating devices with excellent performance and good integration with PCM.

[0003] Among them, OTS (Ovonic Threshold Switching) devices and PCM functional layer materials are both made of sulfur compounds, and the two are perfectly compatible. Therefore, OTS devices are considered to be the preferred gate tube devices for PCM three-dimensional integration. OTS devices have broad prospects in emerging application fields such as three-dimensional high-density memory and neuromorphic computing, and are expected to be commercially applied. Since OTS devices use an amorphous sulfur compound system, the uncertainty of their internal structure leads to poor stability of OTS gate tube materials, which poses a challenge to the performance regulation of OTS gate tubes.

[0004] At present, the research on OTS material system mainly focuses on selenium (Se) and tellurium (Te) based materials. In particular, GeSe, the representative material of Se-based, performs well in various performance parameters of OTS devices, but still has problems such as large fluctuation of transition voltage, poor consistency and tolerance, which bring difficulties to circuit design. Therefore, the development of an OTS gating tube material with stable performance is of great significance for regulating the performance of OTS devices. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention proposes a method for preparing an OTS gating tube material based on AsGeSeSi, the method comprising the following steps:

[0006] Step S1: cleaning the Si substrate or the Pt substrate;

[0007] Step S2: Install the GeSe target, As target, and Si target to the corresponding RF target positions on the magnetron sputtering equipment, and start the molecular pump and mechanical pump to evacuate the sputtering vacuum chamber to a pressure lower than 2x10 -4 Pa. Turn on the switches of argon, nitrogen, and circulating cooling water. Place the cleaned Si substrate or Pt substrate into the small chamber and wait until the pressure in the small chamber reaches 5x10 -3Pa, transferring the Si substrate or Pt substrate into a vacuum sputtering chamber;

[0008] Step S3: setting sputtering process parameters;

[0009] Step S4: Perform the sputtering process in accordance with the set process parameters, perform pre-sputtering to remove contaminants on the target surface; perform formal sputtering to sputter the two target materials together on the Si substrate or Pt substrate. After the sputtering deposition is completed, the system pressure in the small chamber is restored to atmospheric pressure, the experimental substrate is taken out of the magnetron sputtering instrument, and the RF power supply and the switches of argon, nitrogen, and circulating cooling water are turned off. At this time, a layer of GeSe film containing As and Si is deposited on the experimental substrate, and the AsGeSeSi quaternary compound film with a ratio of As:Si:Ge:Se of 4:1~16:5~20:5~20 is prepared.

[0010] Preferably, in step S2, a target material containing Si and As materials is prepared, a Si wafer with a length, width and height of 0.4-0.8 cm × 0.4-0.8 cm × 0.1-0.4 cm is cleaned and dried, and the Si wafer is attached to the etching ring of the As target with silver glue. The number of Si wafers to be attached is 3-12, and the ratio of As:Si sputtering area in the composite target of As and Si is ensured to be 2:1-16 to meet the content of As:Si of 4:1-16. The composite target is fixed on a copper backing plate with a diameter of 8 cm and installed in the RF target position in the magnetron sputtering equipment.

[0011] Preferably, in step S3, the sputtering process parameters are set as follows: the sputtering temperature is controlled to 25°C, the argon gas flow rate is 40 sccm, the GeSe target sputtering power is 30-60W, the Si target sputtering power is 5-20W, and the As target sputtering power is 5-10W. The pre-sputtering time and the formal sputtering time of the three targets are the same, which are 600s and 1800s, respectively. Next, the corresponding RF power supply is turned on at the same time, and argon gas is introduced into the sputtering vacuum chamber of the magnetron sputtering equipment. The argon gas flow rate is controlled to 40 sccm at room temperature to ensure that the system pressure in the vacuum chamber is 3.7x10 -1 Pa.

[0012] Preferably, in step S3, the sputtering temperature is controlled at 25°C, the argon gas flow rate is 40 sccm, the sputtering power of the GeSe target is 30-60 W, the sputtering power of the Si:As target is 5-10 W, and the pre-sputtering time and the formal sputtering time of the three targets are the same, which are 600 s and 1800 s, respectively. Next, the corresponding RF power supply is turned on at the same time, and argon gas is introduced into the sputtering vacuum chamber of the magnetron sputtering equipment. The argon gas flow rate is controlled to 40 sccm at room temperature to ensure that the system pressure in the vacuum chamber is 3.7x10 -1 Pa.

[0013] The present invention also provides an AsGeSeSi-based OTS gating tube material, which is a material prepared according to the above-mentioned preparation method.

[0014] Compared with the prior art solutions, the present invention has at least the following beneficial effects:

[0015] 1) The present invention proposes a GeSe OTS gating tube material with As and Si elements introduced. By constructing an amorphous model of the GeSe OTS gating tube with As and Si elements introduced, the amorphous degree and state density of the material model after the introduction of As and Si elements are compared, and it is explained that the AsGeSeSi material has a greater amorphous degree and a greater ground state resistance. Then, based on the bonding characteristics, it is explained that the structure of the GeSe OTS gating tube material after the introduction of As and Si elements is more stable.

[0016] 2) In the AsGeSeSi structure provided by the present invention, the As:Si:Ge:Se ratio is preferably 4:1:5:5. Since the As content is higher and the relative content of the 4-membered ring is reduced, the atomic migration speed is reduced, thereby inhibiting the crystallization process, so that the AsGeSeSi structure with this ratio exhibits more stable characteristics than the other two ratios. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a structural diagram of the amorphous GeSe model;

[0018] Figure 2 is the electronic state density of the amorphous GeSe model;

[0019] Figure 3 is the ring number distribution of the amorphous GeSe model;

[0020] Figure 4 It is a schematic diagram of the structure of the AsGeSeSi amorphous model;

[0021] Figure 5 is the electronic state density of the AsGeSeSi amorphous model;

[0022] Figure 6 is the ring number distribution of the AsGeSeSi amorphous model;

[0023] Figure 7 is the distribution function of the bond angle of the AsGeSeSi amorphous model;

[0024] Figure 8 (a) Ring number distribution of AsGeSeSi amorphous model with a ratio of 1:1:2:2;

[0025] Figure 8 (b) Ring number distribution of AsGeSeSi amorphous model with a ratio of 1:4:5:5;

[0026] Figure 8 (c) Ring number distribution of AsGeSeSi amorphous model with a ratio of 4:1:5:5.

[0027] The present invention is further described in detail below. However, the following examples are only simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims. Specific embodiments

[0028] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0029] The invention provides a GeSe OTS gating tube material into which As and Si elements are introduced.

[0030] Embodiment 1:

[0031] The method for preparing an AsGeSeSi material having a ratio of As:Si:Ge:Se of 4:1:5:5 comprises the following steps:

[0032] Step S1: Clean the Si substrate or Pt substrate. First, place the prepared 0.8cm×0.8cm Si substrate or Pt substrate in a beaker and pour in an appropriate amount of acetone for cleaning. Since acetone is a volatile solution, it needs to be sealed with plastic wrap and then ultrasonically cleaned for 30 minutes. This step is mainly to remove impurities such as organic matter. After cleaning, take out the substrate with tweezers, place it in another beaker, pour in anhydrous ethanol, clean it twice, seal it, and then ultrasonically clean it for 20 minutes. This step mainly removes acetone and other surface contaminants. Finally, place the substrate in a beaker filled with deionized water for ultrasonic cleaning for 10 minutes. After the ultrasonic cleaning is completed, blow it dry for use.

[0033] Step S2: The present invention adopts a method of co-sputtering GeSe, As, and Si to prepare an AsGeSeSi quaternary compound film. By adjusting the temperature, pressure, argon gas flow rate, and the time and power of each target during sputtering, an AsGeSeSi film with a content ratio of As:Si:Ge:Se of 4:1:5:5 is achieved. First, the GeSe target, As target, and Si target are respectively installed on the corresponding RF target positions on the magnetron sputtering equipment, and the molecular pump and mechanical pump are turned on to evacuate the air so that the pressure of the sputtering vacuum chamber is lower than 2x10 -4 Pa. Turn on the switches of argon, nitrogen, and circulating cooling water. Put the cleaned substrate into the small chamber and wait until the pressure in the small chamber reaches 5x10 -3 Pa, transfer the Si substrate or Pt substrate into a vacuum sputtering chamber.

[0034] Step S3: Set the sputtering process parameters, control the sputtering temperature to 25°C, the argon flow rate to 40 sccm, the GeSe target sputtering power to 60W, the Si target sputtering power to 5W, and the As target sputtering power to 10W. The pre-sputtering time and formal sputtering time of the three targets are the same, which are 600s and 1800s respectively. Next, turn on the corresponding RF power supply at the same time, pass argon into the sputtering vacuum chamber of the magnetron sputtering equipment, control the argon flow rate to 40 sccm at room temperature, and ensure that the system pressure in the vacuum chamber is 3.7x10 -1 Pa.

[0035] Step S4: Perform the sputtering process in sequence according to the set process parameters. Perform pre-sputtering to remove contaminants on the target surface. Perform formal sputtering to sputter the three target materials together on a Si substrate or a Pt substrate. After the sputtering deposition is completed, the system pressure in the small chamber is restored to atmospheric pressure, the experimental substrate is taken out of the magnetron sputtering instrument, and the RF power supply and the switches of argon, nitrogen, and circulating cooling water are turned off. At this time, a layer of GeSe film containing As and Si is deposited on the experimental substrate. The AsGeSeSi quaternary compound film with a ratio of As:Si:Ge:Se of 4:1:5:5 is prepared.

[0036] Embodiment 2

[0037] The method for preparing an AsGeSeSi material having a ratio of As:Si:Ge:Se of 4:1:5:5 comprises the following steps:

[0038] Step S1: Clean the Si substrate or Pt substrate. First, place the prepared 0.8cm×0.8cm Si substrate or Pt substrate in a beaker and pour in an appropriate amount of acetone for cleaning. Since acetone is a volatile solution, it needs to be sealed with plastic wrap and then ultrasonically cleaned for 30 minutes. This step is mainly to remove impurities such as organic matter. After cleaning, take out the substrate with tweezers, place it in another beaker, pour in anhydrous ethanol, clean it twice, seal it, and then ultrasonically clean it for 20 minutes. This step mainly removes acetone and other surface contaminants. Finally, place the substrate in a beaker filled with deionized water for ultrasonic cleaning for 10 minutes. After ultrasonic cleaning, blow it dry for use.

[0039] Step S2: Prepare a quaternary compound film by sputtering GeSe, As, and Si together, and achieve an AsGeSeSi film with a content ratio of 4:1:5:5 by adjusting the temperature, pressure, argon gas flow rate, and time and power of each target during sputtering. Install the GeSe target and Si:As target to the corresponding RF target position on the magnetron sputtering equipment.

[0040] Among them, a composite target (Si:As target) containing Si and As materials is prepared. The Si wafer with a length, width and height of 0.8cm×0.8cm×0.1~0.4cm is cleaned and blown dry, and the Si wafer is attached to the etching ring of the As target material with silver glue. The number of Si wafers required to be attached is 10, ensuring that the ratio of the As:Si sputtering area in the composite target of As and Si is 2:1 to meet the content of As:Si of 4:1. The composite target is fixed on a copper backing plate with a diameter of 8cm and installed in the RF target position in the magnetron sputtering equipment.

[0041] Step S3: After the target is installed, turn on the molecular pump and mechanical pump to evacuate the sputtering vacuum chamber to a pressure lower than 2x10 -4 Pa. Turn on the switches of argon, nitrogen, and circulating cooling water. Put the cleaned substrate into the small chamber and wait until the pressure in the small chamber reaches 5x10 -3 Pa, transfer the Si substrate or Pt substrate into a vacuum sputtering chamber.

[0042] Step S4: Set the sputtering process parameters, control the sputtering temperature to 25°C, the argon flow rate to 40 sccm, the GeSe target sputtering power to 60W, the Si:As target sputtering power to 10W, and the pre-sputtering time and formal sputtering time of the two targets are the same, which are 600s and 1800s respectively. Next, turn on the corresponding RF power supply at the same time, pass argon into the sputtering vacuum chamber of the magnetron sputtering equipment, control the argon flow rate to 40 sccm at room temperature, and ensure that the system pressure in the vacuum chamber is 3.7x10 -1 Pa. The sputtering process is carried out in sequence according to the set process parameters. Pre-sputtering is performed first to remove contaminants on the target surface. Formal sputtering is performed to sputter the two target materials together on a Si substrate or a Pt substrate. After the sputtering deposition is completed, the system pressure in the small chamber is restored to atmospheric pressure, the experimental substrate is taken out of the magnetron sputtering instrument, and the RF power supply and the switches of argon, nitrogen, and circulating cooling water are turned off. At this time, a layer of GeSe film containing As and Si is deposited on the experimental substrate. The AsGeSeSi quaternary compound film with an As:Si:Ge:Se ratio of 4:1:5:5 is completed.

[0043] Embodiment three:

[0044] The method for preparing an AsGeSeSi material having an As:Si:Ge:Se ratio of 1:4:5:5 comprises the following steps:

[0045] The preparation methods in this embodiment are the same as those in Embodiment 1, except that in this embodiment, the sputtering power of the As target is 5 W, and the sputtering power of the Si target is 20 W.

[0046] Embodiment 4:

[0047] The method for preparing an AsGeSeSi material having an As:Si:Ge:Se ratio of 1:1:2:2 comprises the following steps:

[0048] The preparation methods in this embodiment are the same as those in Embodiment 1, except that in this embodiment, the sputtering power of the As target is 8W, and the sputtering power of the Si target is 15W.

[0049] Based on density functional theory (DFT), the exchange-correlation functional is described using the projection wave augmentation method (PAW) and the functional generalized gradient approximation (GGA-PBE) to describe the molecular dynamics method (AIMD). The AsGeSeSi amorphous model was constructed, and the structural properties, electronic properties, and bonding properties were studied. It was clarified that the As and Si doped OTS gate tube materials have a high degree of amorphousness, a large band gap, a higher ground state resistance, and a more stable material structure.

[0050] The specific modeling and calculation process of the AsGeSeSi amorphous atomic structure model with an As:Si:Ge:Se ratio of 4:1:5:5 is as follows:

[0051] 1. Only the Г point is sampled in the Brillouin zone. The amorphous structure modeling uses the typical integration (NVT) method controlled by the Nose-Hoover thermostat to control the temperature, and the time step is set to 3fs. The initial unit cell is a cube containing 150 Ge and Se atoms, of which 27% of the atoms are replaced by As and 7% of the atoms are replaced by Si, and the AsGeSeSi model with an As:Si:Ge:Se ratio of 4:1:5:5 is constructed.

[0052] 2. Use melt quenching process to obtain amorphous model:

[0053] (1) The original AsGeSeSi structure model was kept at 3000K for 9ps to completely melt it to avoid the influence of the initial structure;

[0054] (2) Cool the temperature to 1500 K for 30 ps and equilibrate at 1500 K for another 30 ps to obtain a stable liquid phase structure;

[0055] (3) Rapidly cool the liquid phase structure temperature to 300K at a cooling rate of -40K / ps to simulate the amorphous structure;

[0056] (4) The amorphous model is kept at 300 K for 30 ps, ​​and the trajectories of the atoms are collected. At the same time, the size of the structural unit is adjusted to eliminate the internal pressure of the structure.

[0057] 3. Calculation of the electronic structure of the AsGeSeSi amorphous model: Before calculating the material properties, it is necessary to perform convergence tests on the K-points (K points) and the cutoff energy (Ecut off). The specific details of determining the calculation parameters are as follows: Each atom in the structure is optimized so that the Hellmann-Feynman force is lower than 0.02eV. The K-point sampling density is tested using the Gamma-Center Brillouin zone uniform sampling algorithm. When the K-point value is 2×2×2, the energy of the structure tends to a stable state. Next, the cutoff energy of AsGeSeSi is tested. When Ecut off is equal to 500eV, the energy of the structure is minimal and tends to be stable. Set Ecut off = 500eV, and select the K-point value of 2×2×2 as the convergence condition for the structural calculation.

[0058] like Figure 4 The figure shows the amorphous model structure of AsGeSeSi. In amorphous materials, since the same element is easy to aggregate, the introduction of As and Si will form small clusters of As atoms and small clusters of Si atoms, resulting in localization of electrons. Since the electron localization caused by small clusters of Si atoms is located at deep energy levels, the resistance at deep energy levels is large, so the ground state resistance of the material will increase. Compared with the amorphous GeSe model (such as Figure 1 As shown in the figure, since As and Si atoms are not introduced, small clusters of As and Si atoms will not be formed, and the structure of the amorphous AsGeSeSi material is more stable.

[0059] like Figure 5 As shown, the electronic properties of AsGeSeSi are analyzed and compared with amorphous GeSe (such as Figure 2 The density of states of GeSe and amorphous AsGeSeSi is shown in Figure 1. GeSe has a localized state at the Fermi level, which is conducive to the transition of electrons from the valence band to the conduction band, making it easier to pass through the potential barrier and the resistance is relatively small. The electronic contribution of Si atoms is mainly concentrated at the Fermi level, and obvious localized electrons appear in the forbidden band. The band gap value of AsGeSeSi increases to 0.25eV, and more energy is required for electron excitation. Therefore, AsGeSeSi has a larger resistance.

[0060] like Figure 6 is the ring number distribution of the AsGeSeSi amorphous model. Compared with the ring number distribution of the GeSe amorphous model (such as Figure 3 As shown in the figure, the AsGeSeSi structure is characterized by a higher relative content of 5-membered rings than the GeSe structure, while a lower relative content of 4-membered rings. In addition, a 6-membered ring also appears in the AsGeSeSi structure. The 4-membered ring can make PCM crystallize quickly. Due to the introduction of As and Si in the AsGeSeSi structure, the relative content of the 4-membered ring is reduced, resulting in a decrease in the atomic migration speed, thereby inhibiting the crystallization process and making the structure exhibit more stable characteristics.

[0061] The bond angle distribution of GeSe OTS gate tube material after the introduction of As and Si elements is further analyzed. Figure 7 As shown in the figure, from the bond angle distribution function of AsGeSeSi, it can be seen that the bond angle of AsGeSeSi centered on As and Ge atoms is less than 100°, and the bond angle centered on Si and Se atoms is greater than 100°, indicating that the introduction of As and Si makes the structure more amorphous and the structure of the material more stable.

[0062] The specific modeling and calculation process is the same as that of the AsGeSeSi amorphous atomic structure model with an As:Si:Ge:Se ratio of 4:1:5:5, but 7% of the atoms in the initial unit cell are replaced by As and 27% of the atoms are replaced by Si, and the AsGeSeSi amorphous atomic structure model with an As:Si:Ge:Se ratio of 1:4:5:5 is modeled and calculated. 17% of the atoms in the initial unit cell are replaced by As and 17% of the atoms are replaced by Si, and the AsGeSeSi amorphous atomic structure model with an As:Si:Ge:Se ratio of 1:1:2:2 is modeled and calculated.

[0063] The ratio of As:Si:Ge:Se is 4:1-16:5-20:5-20, preferably, the ratio of As:Si:Ge:Se is 4:1:5:5. Figure 8 (a)-8(c) shows the ring number distribution of the AsGeSeSi amorphous model with different element ratios. The As:Si:Ge:Se ratios are 1:1:2:2 (same As and Si content), 4:1:5:5 (more As content) and 1:4:5:5 (more Si content). The AsGeSeSi structure with an As:Si:Ge:Se ratio of 4:1:5:5 is characterized by the highest relative content of 5-membered rings, while the relative content of 4-membered rings is low. In addition, 6-membered rings appear in the AsGeSeSi structure. The AsGeSeSi structures with As:Si:Ge:Se ratios of 1:4:5:5 and 1:1:2:2 have a high relative content of 4-membered rings. The 4-membered ring can make PCM crystallize quickly. In the AsGeSeSi structure with an As:Si:Ge:Se ratio of 4:1:5:5, the As content is higher and the relative content of 4-membered rings is reduced, resulting in a decrease in the atomic migration speed, thereby inhibiting the crystallization process, making the AsGeSeSi structure with this ratio more stable than the other two ratios.

[0064] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0065] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0066] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for preparing an OTS gating tube material based on AsGeSeSi, characterized in that: The method comprises the following steps: Install the GeSe target, As target and Si target respectively to the corresponding RF target positions on the magnetron sputtering equipment; The sputtering process is carried out in sequence according to the set process parameters, and each target material is sputtered together on a Si substrate or a Pt substrate, and a GeSe film containing As and Si is deposited on the substrate. An AsGeSeSi quaternary compound film with an As:Si:Ge:Se ratio of 4:1 to 16:5 to 20:5 to 20 is prepared.

2. The preparation method according to claim 1, characterized in that: The sputtering process parameters are as follows: the sputtering power of the GeSe target is 30-60W, the sputtering power of the Si target is 5-20W, and the sputtering power of the As target is 5-10W.

3. The preparation method according to claim 1, characterized in that: The As target and the Si target use composite targets of As and Si; a Si sheet with a length, width and height of 0.4-0.8 cm×0.4-0.8 cm×0.1-0.4 cm is attached to the etching ring of the As target, and 3-12 Si sheets are required to ensure that the ratio of the As:Si sputtering area in the composite target of As and Si is 2:1-16 to meet the As:Si content of 4:1-16.

4. The preparation method according to claim 1, characterized in that: The sputtering process parameters are as follows: the sputtering power of the GeSe target is 30-60W, and the sputtering power of the Si:As target is 5-10W.

5. An OTS gating tube material based on AsGeSeSi with a specific element ratio, characterized in that: A material prepared according to the preparation method according to any one of claims 1 to 4.

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