A method for controllable doping of two-dimensional molybdenum telluride thin films

Abstract

The present invention discloses a method for controllable doping of two-dimensional semiconductor molybdenum telluride thin films. A Mo thin film doped with impurity elements is deposited on a substrate by means of magnetron sputtering co-evaporation. The doped Mo thin film is placed into a chemical vapor deposition device, and a large-area continuous two-dimensional semiconductor molybdenum telluride thin film doped with impurity elements is grown by controlling the temperature and time. This method can controllably and stably introduce impurity elements during the thin film deposition process, so that the grown doped semiconductor molybdenum telluride thin film can stably adjust the doping concentration, obtaining two-dimensional semiconductor material thin films with different electrical properties, and solving the key problem of applying two-dimensional semiconductor materials to monolithic integrated circuits. This method can also pattern pre-deposited Mo thin films with different doping types through photolithography and etching, and then grow the pre-designed patterned doped molybdenum telluride thin film by the "one-step method", saving material and time costs, and being compatible with mature semiconductor process technologies, having the potential for large-scale applications.

Description

Technical Field

[0001] The present invention relates to the field of semiconductors, and particularly to a method for controllably doping a variety of elements in a two-dimensional semiconductor material to change the physical properties of the two-dimensional semiconductor material. Background Art

[0002] With the rapid development of modern electronic information technology, the silicon-based integrated circuit industry has entered the "post-Moore era". The miniaturization of transistor size and performance improvement face various technical obstacles. Therefore, it is urgent to develop new materials and new processes to promote the further development of the semiconductor industry.

[0003] Two-dimensional (2D) layered semiconductor materials are one of the promising materials for developing next-generation electronic and optoelectronic devices. Due to their atomic-scale thickness, suitable bandgap, high mobility, etc., they have received extensive attention from researchers. However, the research and development of monolithic integrated circuits based on two-dimensional semiconductor materials are very limited. One of the most important problems is that so far, two-dimensional semiconductor materials still cannot be doped with impurity elements stably, controllably, over a large area and in a patterned manner to adjust their conductive properties. Semiconductor doping, which deliberately introduces charged impurities into the semiconductor host lattice to generate free electrons or free holes, is the basis for constructing integrated circuits. In silicon-based integrated circuits, ion implantation into a single-crystalline silicon substrate is a common doping process. However, due to their atomic-scale thickness, two-dimensional semiconductor materials cannot withstand high-energy ion implantation doping.

[0004] Therefore, for two-dimensional semiconductor materials with special electronic and optical properties, due to the lack of regionally controllable doping methods of different types, the construction of monolithic integrated circuits based on two-dimensional semiconductor materials remains challenging. Summary of the Invention

[0005] Aiming at the problems existing in the doping of the above two-dimensional semiconductor materials, the present invention proposes a method for stably, controllably, over a large area and in a patterned manner doping impurity elements into two-dimensional semiconductor materials.

[0006] The present invention studies and discovers that by using the method of magnetron sputtering co-evaporation, a molybdenum (Mo) thin film doped with impurity elements can be deposited on a substrate. The prepared Mo thin film is placed in a chemical vapor deposition (CVD) tube furnace, and by controlling the temperature and time, a large-area continuous two-dimensional semiconductor molybdenum telluride (MoTe2) thin film doped with impurity elements can be grown. Moreover, the doped semiconductor molybdenum telluride thin film grown by this method can stably adjust the doping concentration, and two-dimensional semiconductor material thin films with different electrical properties can be obtained, solving the key problem of applying two-dimensional semiconductor materials to monolithic integrated circuits.

[0007] Based on the above findings, the present invention provides a method for stably, controllably, large-area and patterned doping of a two-dimensional semiconductor molybdenum telluride film, comprising the following steps:

[0008] (1) using a magnetron sputtering device to co-evaporate a 1-10 nm thick Mo film mixed with impurity elements on the surface of the substrate;

[0009] (2) patterning the Mo film mixed with impurity elements according to requirements to obtain a patterned doped Mo film;

[0010] (3) Using tellurium as the Te source, the doped Mo film is treated by chemical vapor deposition to grow a two-dimensional molybdenum telluride film (2H-MoTe2) with a semiconductor phase on the substrate.

[0011] The base in the above step (1) is usually a substrate with a conductive layer at the bottom and an insulating layer at the top, such as a p+-silicon / silicon oxide substrate.

[0012] In the above step (1), the method for depositing the doped Mo film on the substrate is the "magnetron sputtering co-evaporation" method. By using the targets at different positions in the magnetron sputtering, two or more elements can be sputtered simultaneously. The sputtering material can be selected from the elements included in the periodic table. By setting the corresponding sputtering power for the targets of different elements, the deposition rate (thickness / time) of the different elements can be controlled, thereby regulating the impurity concentration in the Mo film (the higher the sputtering power, the faster the deposition rate). For example, different sputtering powers are applied to the two targets of molybdenum target and niobium target, and a molybdenum film (Nb-Mo) doped with niobium element is obtained by evaporation on the substrate.

[0013] The above step (2) can pattern the doped Mo film by photolithography and etching. If it is necessary to obtain a patterned Mo film doped with different elements, after patterning the first doped Mo film, a layer of Mo film doped with another element with a thickness of 1-10 nm can be deposited by magnetron sputtering, and then the photoresist is stripped to obtain a patterned Mo film doped with different types. The etching method is preferably ion etching, and the etching gas is argon.

[0014] In the above step (3), the patterned doped Mo film sample is placed in a chemical vapor deposition device and a tellurium element (Te source) is added, and a two-dimensional molybdenum telluride film (2H-MoTe2) of a semiconductor phase is grown on the substrate by chemical vapor deposition. At this time, a stable, controllable, large-area and patterned doped semiconductor molybdenum telluride film is grown on the substrate. The chemical vapor deposition device is a normal pressure tube furnace or a box furnace, and the substrate with the doped Mo film deposited on the surface and an appropriate amount of Te source (powder or particles) are placed in a quartz boat, and then the quartz boat is placed in the furnace for chemical vapor deposition.

[0015] In step (3) above, the temperature for chemical vapor deposition is controlled at 550 - 700 °C and the time is 10 - 120 min to obtain a doped molybdenum telluride semiconductor thin film.

[0016] Furthermore, lithography and etching are performed on the thin films of molybdenum telluride with different doping types of semiconductor phases obtained in step (3) above to obtain a homojunction array of patterned doped semiconductor phase molybdenum telluride thin films. Then, metal contact electrodes are prepared by lithography and evaporation (thermal evaporation or electron beam evaporation) to obtain a functional electronic device array.

[0017] The technical advantages of the present invention are mainly reflected in:

[0018] Using a magnetron sputtering device, target elements placed at different positions can be sputter-deposited simultaneously, and impurity elements can be added controllably and stably during the thin film deposition process. The thin film deposited by magnetron sputtering is subjected to CVD growth to obtain a doped two-dimensional semiconductor thin film.

[0019] First of all, since the impurity elements exist in the two-dimensional semiconductor material in the form of "substitutional doping", they can form covalent bonds with surrounding atoms, featuring stability, uniformity, and good repeatability.

[0020] Secondly, through lithography and etching, Mo thin films with different pre-deposited doping types can be patterned, and then a pre-designed patterned doped molybdenum telluride thin film can be grown by a "one-step method", saving material and time costs.

[0021] Finally, the two-dimensional doped semiconductor material prepared by this method has a wafer-level size and is compatible with mature semiconductor process technologies, showing the potential for large-scale applications. Description of the Drawings

[0022] Figure 1 . Schematic diagram of the specific experimental process of step (3) in the embodiment of the present invention.

[0023] Figure 2 . Schematic diagram of growing molybdenum telluride semiconductor phase by chemical vapor deposition method in the embodiment of the present invention, where: 1 - tube furnace, 2 - quartz tube, 3 - quartz boat, 4 - tellurium powder, 5 - thin film sample.

[0024] Figure 3 . Micrographs of patterned planar heterojunction niobium-doped molybdenum telluride thin film (Nb-MoTe2) and rhenium-doped molybdenum telluride thin film (Re-MoTe2) in the embodiment of the present invention.

[0025] Figure 4 . Corresponding Figure 3 Raman spectra of the Nb-MoTe2 and Re-MoTe2 regions in to verify that the grown thin film is molybdenum telluride semiconductor phase.

[0026] Figure 5 .Corresponding Figure 3 The electrical properties of the Nb-MoTe2 and Re-MoTe2 regions (tested after fabricating field effect transistors through semiconductor processes) verify that the grown Nb-MoTe2 thin film is a p-type semiconductor thin film and the Re-MoTe2 thin film is an n-type semiconductor thin film. Specific embodiments

[0027] The present invention will be further described below with reference to the accompanying drawings and through specific embodiments.

[0028] This embodiment prepares a two-dimensional semiconductor molybdenum telluride thin film doped with rhenium element and its field effect transistor device array through the following steps to prove the controllable, large-area, and patternable advantages of this doping technology:

[0029] (1) Provide a substrate, which includes a lower conductive layer and an upper insulating layer. The lower layer is heavily doped p-type Si, and the upper layer is SiO2 with a thickness of 285 nm.

[0030] (2) Place the substrate into a magnetron sputtering system, and apply power to two targets simultaneously (10 W DC power for the molybdenum target and 20 W AC power for the niobium target) to deposit a niobium-doped molybdenum thin film (Nb-Mo) on the substrate, with a thickness of about 5 nanometers.

[0031] (3) The patterned Nb-Mo thin film can be obtained by processing the Nb-Mo thin film obtained in step (2) through conventional semiconductor process technologies (lithography and etching). At this time, place the sample into the magnetron sputtering system again, and apply power to two targets (molybdenum target and rhenium target) simultaneously (10 W DC power for the molybdenum target and 50 W AC power for the rhenium target) to deposit a rhenium-doped molybdenum thin film (Re-Mo) on the substrate, with a thickness of about 5 nanometers. Use acetone to remove the photoresist (lift-off) from the sample to obtain the patterned pre-deposited Nb-Mo thin film and Re-Mo thin film. The schematic diagram of this process is as Figure 1 shown.

[0032] (4) Place the thin film samples of the pre-deposited Nb-Mo thin film and Re-Mo thin film into a CVD tube furnace for growth. As Figure 2 shown, put tellurium powder 4 and the thin film sample 5 into quartz boat 3, and then place it into quartz tube 2 of tube furnace 1. After 15 minutes of heating up, the temperature zone of the tube furnace is heated to 620 °C, and after maintaining for 1 hour, it is naturally cooled to room temperature. During this period, maintain a gas flow of 15 sccm hydrogen and 10 sccm argon to obtain a large-area thin-layer p-type doped and n-type doped semiconductor-phase molybdenum telluride thin film. The micrograph after growth is as Figure 3 shown, and the corresponding Raman spectrum ( Figure 4)The p-type doped and n-type doped molybdenum telluride thin films are shown to be in the 2H semiconductor phase.

[0033] (5) The thin film obtained in step (4) is subjected to semiconductor micro-nano processing to fabricate the corresponding field effect transistor, and electrical measurements are performed at room temperature, as Figure 5 shown. It can be seen that the niobium-doped molybdenum telluride field effect transistor exhibits the electrical characteristics of a p-type semiconductor, while the molybdenum telluride device doped with rhenium element has obvious n-type semiconductor characteristics. From the experimental examples, it can be seen that the method for doping impurity elements in two-dimensional semiconductor materials proposed in the present invention has the advantages of stability, controllability, large area and patterning.

[0034] Finally, it should be noted that the purpose of disclosing the embodiments is to help further understand the present invention. However, those skilled in the art can understand that various substitutions and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the content disclosed in the embodiments, and the scope of protection claimed by the present invention shall be defined by the scope defined in the claims.

Claims

1. A method for controllable doping of two-dimensional molybdenum telluride thin film, comprising the following steps: 1) Co-evaporate and deposit a Mo thin film mixed with impurity elements with a thickness of 1-10 nm on the surface of a substrate by using a magnetron sputtering device; 2) Pattern the Mo thin film mixed with impurity elements according to requirements to obtain a patterned doped Mo thin film; specifically: pattern the doped Mo thin film by lithography and etching methods, then deposit another layer of Mo thin film doped with another element with a thickness of 1-10 nm by magnetron sputtering, and then strip the photoresist to obtain a patterned Mo thin film doped with different types; 3) Use tellurium element as the Te source, and treat the doped Mo thin film by chemical vapor deposition to grow a semiconductor-phase two-dimensional molybdenum telluride thin film on the substrate.

2. The method according to claim 1, characterized in that In step 1), the substrate is a substrate with a conductive layer on the lower layer and an insulating layer on the upper layer.

3. The method according to claim 2, wherein In step 1), the substrate is a p+-silicon / silicon oxide substrate.

4. The method according to claim 1, wherein In step 1), the deposition rate of different elements is controlled by setting different sputtering powers for different element targets, so as to regulate the impurity concentration in the Mo thin film.

5. The method according to claim 4, wherein In step 1), different sputtering powers are applied to the molybdenum target and the doped element target.

6. The method according to claim 1, characterized in that In step 2), the etching method is ion etching, and the etching gas is argon.

7. The method according to claim 1, wherein In step 3), put the doped Mo thin film sample into an atmospheric pressure tube furnace or a box furnace and add tellurium element, and treat the sample by chemical vapor deposition to grow a semiconductor-phase two-dimensional molybdenum telluride thin film on the substrate.

8. The method according to claim 1, wherein In step 3), the temperature for chemical vapor deposition is controlled at 550-700 °C, and the time is 10-120 min.

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