CN116493763A - Laser etching method and system for two-dimensional material - Google Patents
Laser etching method and system for two-dimensional material Download PDFInfo
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- CN116493763A CN116493763A CN202210071305.6A CN202210071305A CN116493763A CN 116493763 A CN116493763 A CN 116493763A CN 202210071305 A CN202210071305 A CN 202210071305A CN 116493763 A CN116493763 A CN 116493763A
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- 238000000034 method Methods 0.000 title claims abstract description 76
- 239000000463 material Substances 0.000 title claims abstract description 53
- 238000010329 laser etching Methods 0.000 title claims abstract description 25
- 238000005530 etching Methods 0.000 claims abstract description 260
- 239000010410 layer Substances 0.000 claims abstract description 90
- 239000002356 single layer Substances 0.000 claims abstract description 42
- 230000008569 process Effects 0.000 claims abstract description 28
- 238000001816 cooling Methods 0.000 claims abstract description 17
- 238000012544 monitoring process Methods 0.000 claims abstract description 10
- 238000011065 in-situ storage Methods 0.000 claims abstract description 8
- 239000000758 substrate Substances 0.000 claims description 40
- 230000001276 controlling effect Effects 0.000 claims description 12
- 238000001069 Raman spectroscopy Methods 0.000 claims description 11
- 230000001105 regulatory effect Effects 0.000 claims description 9
- 238000006073 displacement reaction Methods 0.000 claims description 7
- 239000002344 surface layer Substances 0.000 claims description 7
- 238000009826 distribution Methods 0.000 claims description 5
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- 238000004519 manufacturing process Methods 0.000 abstract description 4
- CWQXQMHSOZUFJS-UHFFFAOYSA-N molybdenum disulfide Chemical compound S=[Mo]=S CWQXQMHSOZUFJS-UHFFFAOYSA-N 0.000 description 17
- 229910052982 molybdenum disulfide Inorganic materials 0.000 description 17
- 239000007789 gas Substances 0.000 description 10
- 238000006243 chemical reaction Methods 0.000 description 8
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 5
- 238000005516 engineering process Methods 0.000 description 5
- 229910052710 silicon Inorganic materials 0.000 description 5
- 239000010703 silicon Substances 0.000 description 5
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 4
- 230000008859 change Effects 0.000 description 4
- 229910052814 silicon oxide Inorganic materials 0.000 description 4
- 238000001237 Raman spectrum Methods 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 230000000630 rising effect Effects 0.000 description 3
- 238000003332 Raman imaging Methods 0.000 description 2
- 238000003486 chemical etching Methods 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 238000013461 design Methods 0.000 description 2
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- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- PQQKPALAQIIWST-UHFFFAOYSA-N oxomolybdenum Chemical group [Mo]=O PQQKPALAQIIWST-UHFFFAOYSA-N 0.000 description 1
- 238000011160 research Methods 0.000 description 1
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- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/36—Removing material
- B23K26/362—Laser etching
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/70—Auxiliary operations or equipment
- B23K26/702—Auxiliary equipment
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Abstract
The invention provides a laser etching method and a laser etching system for a two-dimensional material, wherein in-situ real-time monitoring of etching temperature in a single-point laser etching process is utilized to determine stepped cooling characteristics in the single-point laser etching process, laser power required by layer-by-layer etching in a single-layer controllable etching range is obtained according to the stepped cooling characteristics, and controllable etching of samples with specific layers of the two-dimensional material is realized according to the laser power. The method and the system can provide a single-layer or layer-by-layer etching scheme with higher vertical layer-by-layer etching precision, high controllability and strong universality, can realize the large-scale layer-by-layer etching of the two-dimensional material, can control and quantify the etching process, and has a large-scale automatic production prospect.
Description
Technical Field
The invention belongs to the field of laser etching systems, and particularly relates to a laser etching method and system for a two-dimensional material.
Background
The two-dimensional material generally has obvious quantum confinement effect, and the novel device based on the two-dimensional material has wide application prospect and is also a hot spot for current research. The thickness or the number of layers of the two-dimensional material is an important factor for determining the performance of the device, and the control of the planar structure and the thickness of the two-dimensional material is a key for preparing the device. At present, the planar structure of the two-dimensional material can be obtained by methods such as mask-chemical etching or laser direct writing etching, and the like, and the technology is mature. The control of the thickness of the two-dimensional material, particularly the precise distribution control of the thickness in the same device, is still in the preliminary stage at present. For example, a two-dimensional material (single layer, double layer, or multiple layers) of a particular thickness can be obtained by control of MBE growth conditions, but the thickness or number of layers is substantially single on a wafer scale (wafer scale) or can only form a simple layer-by-layer structure limited by crystal growth. Mask-chemical etching can obtain in-plane control accuracy of submicron or even tens of nanometers, but control of etching thickness is difficult to reach the level of layer-by-layer control, and the layer-by-layer structure preparation process is complex. Laser direct writing etching is one of the possible ways to achieve controlled fabrication of two-dimensional material devices. By adjusting the intensity and wavelength of the laser, the local temperature of the two-dimensional material can be controlled, and the chemical reaction or physical process can be excited to realize point-by-point etching. The method has the advantages that higher etching precision in the vertical direction is obtained in the laser etching process, and the realization of the large-scale layer-by-layer etching of the two-dimensional material is an important target in the field. Recent studies have shown that under suitable laser settings, two-dimensional materials can be etched away layer by layer. However, the reported technology has various defects, which limit the further application, and the symptoms mainly include the following points: 1) Because the laser etching process is sensitive to physical properties of materials, thermal diffusion environment, physicochemical reaction conditions and the like, the time required for etching the materials to a specific layer number, laser power and other parameters can only be given empirically, and no effective etching strategy is formed yet; 2) The range of layer-by-layer etching is smaller. Taking etching of layered molybdenum disulfide materials as an example, it has been reported that the maximum controllable etching range achieved by laser etching technology is, for example, only three layers.
Disclosure of Invention
In order to solve the above-mentioned problems of the prior art, a first aspect of the present invention provides a laser etching method for a sample of a two-dimensional material, the method comprising:
determining the stepped cooling characteristic in the process by utilizing in-situ real-time monitoring of the etching temperature in the single-point laser etching process;
obtaining etching laser power required by etching the sample in a single-layer controllable etching range according to the stepped cooling characteristics;
and realizing controllable etching of the specific layer number of the sample according to the etching laser power.
Preferably, obtaining the single-layer controllable etching range of the sample to be etched includes controlling a temperature distribution of the sample to decrease gradually from layer to layer along the surface layer by adjusting an etching environment, wherein the etching environment includes: the thermal conductivity of the substrate, the contact thermal resistance of the substrate and the sample, the temperature of the substrate and the environment, the atmosphere of etching environment gas, and the control precision and stability of the etching laser power.
Preferably, the adjustment of the thermal conductivity of the substrate in the method includes changing the substrate material and changing the type and thickness of the substrate surface coating.
Preferably, in the method, determining the stepped cooling feature by the in-situ real-time monitoring includes: determining an etching threshold temperature through an etching temperature evolution curve of a sample irradiation center and obtaining the stepped cooling characteristic, wherein the etching threshold temperature is determined through the etching temperature evolution curve of the sample irradiation center
And regulating and controlling the laser power to gradually rise on the premise of no defocus until the temperature of the sample irradiation center is not synchronously risen and is stopped after reverse refraction occurs, and waiting for a sufficient time period on the premise of no defocus and no laser power until the temperature of the sample irradiation center is not changed, wherein the obtained temperature is the etching threshold temperature.
Preferably, the temperature evolution curve in the method is obtained by real-time detection of raman spectra.
Preferably, the method further comprises:
judging whether the initial layer thickness of the sample is within a single-layer controllable etching range by using the temperature evolution curve, if not, etching the sample until the initial layer thickness of the sample is within the single-layer controllable etching range, wherein if the etching laser power cannot enable single-step reduction to occur in the temperature evolution curve, or the temperature of the irradiation center is raised first and then stepped reduction relative to the etching threshold temperature under the etching laser power, or the temperature of the irradiation center is stabilized at a specific temperature higher than the etching threshold temperature, but etching is still continuous by using an instrument, the initial layer thickness of the sample can be determined not to be within the single-layer controllable etching range.
Preferably, the initial layer thickness of the sample in the method can be obtained indirectly by growth preparation conditions or directly by spectroscopic or atomic force microscopy.
Preferably, the method further includes obtaining etching laser power required for etching the sample in a single-layer controllable etching range according to the stepped cooling feature:
setting specific etching laser power according to the temperature evolution curve, wherein the number of single etching layers of the specific etching laser power on the sample is equal to the number of steps of the step-shaped cooling feature in the temperature evolution curve corresponding to the specific etching laser power.
Preferably, the determining the number of steps of the stepped cooling feature includes: under the precondition of no defocusing, the etching laser power irradiated on the sample is gradually increased so that the irradiation center temperature of the sample gradually reaches and temporarily exceeds the etching threshold temperature, the laser power is kept unchanged, and the number of steps in the process that the irradiation center temperature of the sample is recovered to the etching threshold temperature is observed.
Preferably, in the method, each point of the etched area of the sample is etched for a sufficient exposure time period by using the specific etching laser power, wherein each point is scanned for a single time, and the exposure time period of the single time is sufficient, wherein the exposure time period is sufficient to perform the etching under the condition of no defocus until the temperature of the irradiation center is lower than the etching threshold temperature in the etching process.
Preferably, in the method, a single point short time exposure is performed on each point and multiple scans accumulate a sufficient total etching time period to achieve sufficient exposure time period, rather than performing a single scan on each point.
The second aspect of the invention provides a two-dimensional material etching system, comprising a controllable power laser source, a temperature detector, a temperature control console, a displacement table and an etching gas atmosphere cavity, wherein
The controllable power laser source is used for providing etching laser with required power; the temperature detector is used for realizing in-situ real-time monitoring of etching temperature; the temperature control console is used for controlling the temperature distribution of the sample to be in a single-layer controllable etching range; the displacement table is used for controlling the etched position of the sample; the etching gas atmosphere cavity is used for forming a gas atmosphere surrounding a sample to be etched; it is characterized in that
Also included is a controller configured to implement the etching method of any of the first aspects above.
Compared with the prior art, the layer-by-layer controllable laser etching method and system provided by the embodiment of the invention have higher vertical layer-by-layer etching precision, realize large-scale layer-by-layer etching of the two-dimensional material, greatly reduce limitation or requirement severity of etching objects and etching environments, and have controllable and quantifiable etching processes and large-scale automatic production prospects.
Drawings
Embodiments of the invention are further described below with reference to the accompanying drawings, in which:
FIG. 1 is a simplified flow chart of a layer-by-layer etching method in accordance with a preferred embodiment of the present invention;
FIG. 2 shows a schematic diagram of a layer-by-layer laser etching system in accordance with a preferred embodiment of the present invention;
FIG. 3 shows the evolution curves of the Raman characteristic peaks of molybdenum disulfide and silicon in the etched sample after Lorentz fitting according to a preferred embodiment of the present invention as a function of laser power;
fig. 4 illustrates optical and raman imaging results of pre-etch and post-etch samples, according to a preferred embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail by the following examples with reference to the accompanying drawings. Structures, proportions, sizes, etc. shown in this description are shown for illustrative purposes only and are not meant to be unduly limiting or limiting, nor to be a technical sense, as will be apparent to those of ordinary skill in the art. Any structural modification, proportional change or size adjustment should be included in the scope of the technical disclosure without affecting the effect and achievement of the object of the present invention.
The invention provides a novel two-dimensional material laser layer-by-layer etching method, which has high applicability to etching materials and etching environments, can obtain optimal etching parameters in situ according to the etching environment conditions, and can effectively realize layer-by-layer etching in a larger range. By taking molybdenum disulfide as an example, in a normal etching environment, the invention can improve the control range of layer-by-layer etching to more than ten layers only by the difference of attaching two-dimensional materials to the substrate, and expands the capability of regulating the physical properties of the materials through the number of layers.
Fig. 1 is a schematic flow chart of a layer-by-layer etching method according to a preferred embodiment of the invention. In this flow, it is first necessary to design the etched structure and design the planned etching path. Specifically, the layer-by-layer etching technology realizes the etching of the material reaching the target residual layer number under the condition of specific laser power saturation duration through the temperature difference between two-dimensional material layers. The realization of which depends on the inter-layer temperature difference existing in the two-dimensional material aimed at by the present invention, which refers to the temperature field formed by the transfer of heat from the sample to the substrate under the laser irradiation condition due to the two-dimensional material transferred or grown on the specific substrate, for example, the substrate on which the sample is arranged may be brought into physical contact with a cold source so as to form a monotonically decreasing temperature field gradient profile from the upper surface of the sample to the contact surface of the sample substrate, and the two-dimensional material structure having this temperature field gradient profile feature, i.e. the etching structure desired in the various embodiments of the present invention, advantageously also needs to be adjusted or maintained substantially unchanged by a temperature console or other means during etching. When the surface layer of the sample does not have the interlayer temperature gradient which monotonically decreases from the upper surface of the sample to the contact surface of the sample substrate, for example, when the temperature of the highest layer of the sample is not very close to the temperature difference of the surface layer or the surface layers (such as the temperature difference of the adjacent layers is within ten degrees celsius) under the irradiation condition of equal laser power, the unsuitable surface layer of the example can be removed by pre-etching until a qualified single-layer controllable etched sample is obtained. And the sample pre-etching is that after the laser power is regulated to be higher than the surface layer etching threshold power, the sample is etched for a sufficient time period until the temperature of the laser irradiation center is reduced to be lower than the etching threshold temperature.
Secondly, the process includes selecting corresponding etching conditions according to the maximum number of layers of the etching material and the structure. In particular, a specific number of layers of etching material is typically disposed on the substrate, the etching conditions including a pre-set of etching laser wavelength, start power, and adjustment of the etching environment, wherein the etching environment includes: the thermal conductivity of the substrate, the contact thermal resistance of the substrate and the multilayer two-dimensional material, the temperature of the substrate and the environment, the gas atmosphere of the etching environment, and the control precision and stability of the etching laser power; wherein, the regulation and control of the heat conductivity of the substrate comprises the replacement of the substrate material and the replacement of the type and thickness of the surface covering layer of the substrate.
The process then further includes transferring a sample to be etched corresponding to the desired maximum layer thickness of the post-etch target onto the selected substrate or by growing thereon. Because the actual etching layer number of the pre-etching is not easy to accurately judge and the etching reaction rate is low, the layer number is preferably controlled to be within the maximum layer-by-layer or single-layer controllable etching layer number when preparing the initial sample.
After this, it is also necessary to determine the power range that satisfies the layer-by-layer laser etching after obtaining a sample suitable for performing layer-by-layer or single-layer controlled etching, which can be obtained by analyzing the laser irradiation center temperature evolution curve characteristics on the sample to be etched. One preferred way is to obtain the temperature evolution curve by measuring the peak position shift of the raman characteristic peak of the material to be etched. However, the technical scheme of the invention can also obtain the temperature evolution curve of the laser irradiation center on the sample to be etched according to other measurement technologies, and the temperature evolution curve does not deviate from the inventive concept of the application. The method specifically comprises the following substeps:
(1) And obtaining a temperature evolution curve by regulating and controlling laser power. One preferred procedure is as follows: the etching laser with a preset specific wavelength (532 nm laser is preferably adopted in the embodiment) is used for irradiating the sample, the laser power is gradually increased on the premise of no defocus, meanwhile, the temperature of the center of a laser spot is monitored in real time by utilizing the Raman peak displacement, the temperature is firstly increased along with the increase of the laser power, and the return reduction caused by the increase of the laser power does not occur after the temperature reaches a certain temperature. This phenomenon indicates that the material starts to undergo an etching reaction at the laser power. Under this condition, the laser power is kept unchanged, the temperature of the sample irradiation center has a step-like cooling feature and the step-like cooling trend is stabilized to be near a certain temperature. The specific temperature is the threshold temperature of laser etching under the condition.
(2) After determining the etch threshold temperature, the laser power range required for single layer etching can be determined by more precisely measuring the temperature evolution curve. The method comprises the steps of on the premise of no defocus, gradually increasing laser power irradiated on a sample to be etched to enable the central temperature of the etched sample to gradually reach the etching threshold temperature, further increasing the laser power stepwise to enable the central temperature of the sample to exceed the threshold temperature in a short time, then keeping the laser power unchanged, and observing the stepwise decrease number (temperature step) in the process of recovering the temperature of an etching area to the threshold temperature. If the number of the temperature steps is 1, the laser power meets the single-layer etching condition of the material; if the number of temperature steps exceeds 1, the laser power is too high, the material single-layer etching condition is not satisfied, and the laser power value should be reduced. The laser power range meeting the single-layer etching requirement can be obtained through multiple tests. Preferably, for molybdenum disulfide two-dimensional materials, the laser power adjustable range can be 0 to 20 milliwatts, and the actual laser power fluctuation and single adjustment accuracy are within 0.1 milliwatts.
(3) After a single-layer etching laser power range is obtained and a single-layer etching laser power of a fixed value is selected, region etching can be realized by fully exposing a specific region. The etching completion determination basis is to ensure that the etching temperature of each point in the area reaches or is lower than the etching threshold temperature. Wherein the sufficient exposure is preferably achieved by a point-wise long exposure. The sufficient exposure time may also be obtained by repeatedly scanning the etched region along the etch path to accumulate the exposure time. The meaning of adopting the single-point short-time long exposure repeated scanning is to reduce the duration of a single scanning etching process so as to weaken the influence of the defocusing of an etching system and avoid the additional exposure time of the etched part aiming at the random fluctuation of the time consumption of the etching reaction process. The single point acquisition duration may not be too short for the purpose of ensuring the signal quality of raman spectrum acquisition. Preferably, the time required for etching the single-point exposure in the atmospheric environment is 2s, so that the single-point exposure time can be 0.1 seconds and the scanning is repeated 20 times.
The initial thickness or number of layers of the sample may be obtained from spectral characteristics, or from the height of the sample directly scanned by an atomic force microscope.
The process further comprises the step of repeatedly executing single-layer etching on the new etching surface after single-layer controllable etching is realized, so that the aim of multi-layer controllable etching can be realized.
The process further comprises the step of etching redundant sample parts except the target etching area in a laser direct writing mode after the layer-by-layer controllable etching is completed, so that a finished product is obtained.
In other preferred embodiments according to the present invention, the temperature evolution curve may also be used to determine whether the sample to be etched is single-layer controllable. Under the condition of single-layer uncontrollable etching, the temperature evolution curve is characterized in that after the laser power is regulated to enable a sample to reach the etching threshold temperature, the laser power is further increased, and after the sample temperature is synchronously and rapidly increased to be higher than the etching threshold temperature along with the change of the laser power, the sample temperature is further increased along with the etching reaction and then is reduced to the etching threshold temperature in a step-like manner; or under the condition that the temperature of the sample is maintained to be higher than the etching threshold value without obvious change, judging that the etching is still continuously performed through other parameters, such as the Raman signal intensity of the sample to be detected; or, the temperature single-stage step cannot be obtained stably by laser power adjustment.
In other preferred embodiments according to the invention, the substrate silicon oxide thickness may also be 2 to 20nm for a conventional silicon oxide covered silicon substrate. The temperature field can also be regulated and controlled by the substrate temperature or the chemical environment of the etching process, taking typical two-dimensional molybdenum disulfide etching as an example, the etching threshold temperature is about 350 ℃ under the atmosphere, the etching process is changed from oxidation evaporation to direct evaporation under the inert gas atmosphere, the temperature required by new etching is about 450 ℃, and the temperature is reduced by 100 ℃ in the equivalent of the substrate temperature.
Fig. 2 shows a schematic diagram of a layer-by-layer laser etching system according to a preferred embodiment of the invention. The laser etching system 10 comprises a laser module 11, a computer control system 12, a temperature control table 14 on which a substrate 13 is arranged, a displacement table 15 and an etching gas atmosphere cavity 16. Wherein the laser module 11 comprises a laser source, a laser power controller and a raman spectrometer, the substrate 13 facing the top surface of the laser module 11 for arranging a two-dimensional material to be etched. The computer control system 12 at least comprises an etching path planning module, an etching layer number judging module and an etching feedback module. The etching path planning module is used for automatically converting and generating a planning path of the layer-by-layer structure etching according to the target structure; the etching layer number judging module is used for automatically counting the number of temperature steps in the laser spot center temperature detection process; the etching feedback module judges whether etching is finished or not by monitoring whether the temperature of the laser irradiation point (or region) reaches or is lower than the etching threshold temperature.
The temperature control console 14 is in direct thermal contact with the substrate for regulating the temperature of the substrate during etching as required by the etching conditions. In a preferred embodiment, the temperature console 14 includes the following operations: and when the etching laser power reaches the maximum value and the etching of the target layer still cannot be completed, increasing the substrate temperature to promote the etching of the target layer, or reducing the substrate temperature to slow down or prevent the etching of the residual layer when the number of the etching controllable layers is insufficient under the etching environment condition.
The etching gas atmosphere cavity 16 can provide a gas environment with ideal air tightness and simple components, is used for changing the gas atmosphere of the two-dimensional material, changing the material etching physicochemical reaction process and etching product components, and further regulating and controlling the etching conditions of the two-dimensional material. Taking two-dimensional molybdenum disulfide etching as an example, when other etching environment conditions cannot be changed, the equivalent substrate temperature of the gas atmosphere cavity is changed from the atmosphere to the inert gas atmosphere to be reduced by one hundred ℃, meanwhile, the molybdenum oxide part in the etching product residues can be restrained, and the aim of increasing the single-layer controllable etching range is fulfilled.
The etching process of a two-dimensional material according to the laser etching method of the present invention is illustrated in a more specific embodiment.
Example 1:
taking molybdenum disulfide continuous inner multi-level step etching for example, the specific etching flow is as follows: and step 1, setting etching environment conditions. The method specifically comprises the steps of etching laser power fluctuation and power control precision of about 0.1 milliwatt, wherein a substrate required for achieving single-layer controllable etching of more than 13 layers of molybdenum disulfide can be a silicon substrate covered by 2-20 nanometers of silicon oxide under the condition of surrounding room temperature in an atmosphere.
And 2, arranging a sample to be etched. The method specifically comprises the steps of transferring a mechanically stripped molybdenum disulfide layer onto a silicon substrate covered by silicon oxide, for example, 2 nanometers, prepared in the step 1, and searching a sample with a proper layer thickness and area. The AFM is used for characterizing that the height of the selected sample area is 8.5 nanometers, the corresponding molybdenum disulfide thickness is ten three layers, and the requirement of the initial layer number of the etching structure is met; if the actual thickness of the sample is so thick that the thickness of the layer to be etched is larger than the maximum etching range of the layer-by-layer controllable etching, the sample can be pre-etched in advance until the sample meets the etching range of the layer-by-layer controllable etching, and the thickness of the molybdenum disulfide layer can be retested.
And step 3, obtaining a threshold wave number corresponding to controllable etching of the layer to be etched. The method specifically comprises the steps of controlling laser power on a sample to be etched, gradually rising the laser power on the premise of no defocus until the temperature of a sample irradiation center is not synchronously rising any more to generate reverse refraction, recording a single-point temperature evolution curve of the sample irradiation center in the process, taking the evolution of the peak-to-peak position of a Raman characteristic peak as a temperature criterion, and determining A of molybdenum disulfide 1g The threshold wave number of the characteristic peak etching reaction was 405.5cm -1 . Wherein the temperature of the sample irradiation center can be obtained by directly measuring the temperature of the surface to be etched of the sample.
Fig. 3 shows, by way of example, the evolution curves of the raman characteristic peaks of molybdenum disulfide and the raman characteristic peaks of silicon in the etched sample after lorentz fitting according to step 3 as a function of laser power. In the curve, the evolution curve of the molybdenum disulfide Raman characteristic peak along with the change of time and power is arranged on the left side, and the laser power is controlled to rise three times (namely, the temperature in a target area of a sample is risen three times) from the time 0 point on the horizontal axis to the vicinity of about 50 seconds, so that the characteristic peak in the vertical axis is controlled to be from the highest value (about 407cm -1 ) The raman characteristic peak of the sample is obviously stepped after being reduced to the vicinity (namely, the temperature of the sample is increased to the vicinity of the etching threshold temperature, and the abscissa of the graph is about 50 seconds), wherein the wave number is firstly reduced, and then is stepped up to the threshold wave number of 405.5cm in two times -1 In the vicinity, the process corresponds to the sample temperature first rising and then decreasing stepwise twice to about the etching threshold temperature, indicating that there are two layers of the sample surface being etched.
And step 4, determining a single-layer etching power numerical range according to the obtained threshold wave number. The method specifically comprises the steps of observing the displacement of the barycenter of a characteristic peak of molybdenum disulfide A1g in real time at one point on a non-target structural region on a sample to be etched, further improving the laser power after the barycenter is close to a threshold wave number, and controlling the power lifting quantity to ensure that only a single-stage step appears in a molybdenum disulfide temperature evolution curve. Thus, the power range satisfying the above conditions is the power range of the single-layer etching power, and the value is P1.
And 5, performing verification test on another non-target etching area of the sample according to the obtained single-layer etching power, and repeating the step 4 if two or more steps appear in a temperature evolution curve.
And 6, carrying out full-area single-layer etching on the molybdenum disulfide sample according to the single-layer etching laser power determined in the step 4. The method specifically comprises the steps of setting laser power as P1, and realizing full-area etching in a target etching area of a first layer of the surface according to continuous scanning of a path obtained through calculation. The etching single point integration time is 0.1 seconds, the etching point spacing is 0.1 micron, and the etching line spacing is 0.1 micron. And monitoring the etching completion degree in real time through the etching temperature distribution or the uniformity of the signal intensity of the Raman spectrum of the material until the etching is completed.
Step 7, the layer-by-layer etching is continued according to the previous steps 1 to 6 (this step is not necessary in other preferred embodiments where only a single layer etch is desired). Taking single-layer etching power P1 determined by a first layer on the surface as initial power, continuously measuring an etching temperature evolution curve of a second layer after the temperature of an irradiation center is stable, obtaining laser power P2 required by etching the second layer, and further completing etching of an etching region of the second layer; each underlying layer can similarly be etched in turn, ultimately resulting in a target etched structure. Thereafter, the excess sample portion except the target etching region is directly etched by laser light to obtain a finished product. Fig. 4 shows, by way of example, the results of optical and raman imaging of the sample before and after etching.
Technical effects of laser etching systems and methods according to various embodiments of the present invention: according to the laser etching system and the method, higher vertical etching precision can be obtained in the laser etching process, and the two-dimensional material can be etched layer by layer in a large range, wherein key factors such as a temperature field of the material to be etched can be better controlled under a single-layer etching condition by adjusting an etching environment, whether the layer to be detected meets a single-side etching condition or not can be accurately obtained by monitoring the temperature of the center of an etching laser spot in real time, and etching laser power can be accurately adjusted to meet the optimal single-layer etching condition. Meanwhile, the invention aims to form an etching strategy with high universality, and each layer is precisely etched in a single layer by the set external conditions and laser power and the etching method for determining the single-side etching power by using the threshold temperature in the etching process, so that the limitation or the demanding degree of etching objects and etching environments are greatly reduced, and the method has a large-scale automatic production prospect.
While the invention has been described in terms of preferred embodiments, the invention is not limited to the embodiments described herein, but encompasses various changes and modifications that may be made without departing from the scope of the invention.
Claims (12)
1. A method of laser etching a sample of a two-dimensional material, the method comprising:
determining the stepped cooling characteristic in the process by utilizing in-situ real-time monitoring of the etching temperature in the single-point laser etching process;
obtaining etching laser power required by etching the sample in a single-layer controllable etching range according to the stepped cooling characteristics;
and realizing controllable etching of the specific layer number of the sample according to the etching laser power.
2. The method of claim 1, obtaining the single layer controllable etching range of the sample to be etched comprising controlling a temperature profile of the sample to be decreasingly layer-wise inwardly along a surface layer by adjusting an etching environment, wherein the etching environment comprises: the thermal conductivity of the substrate, the contact thermal resistance of the substrate and the sample, the temperature of the substrate and the environment, the atmosphere of etching environment gas, and the control precision and stability of the etching laser power.
3. The method of claim 2, wherein the adjusting of the substrate thermal conductivity comprises changing substrate material and changing substrate surface coating type and thickness.
4. The method of claim 1, wherein determining the stepped cooling feature by the in situ real-time monitoring comprises: determining an etching threshold temperature through an etching temperature evolution curve of a sample irradiation center and obtaining the stepped cooling characteristic, wherein the etching threshold temperature is determined through the etching temperature evolution curve of the sample irradiation center
And regulating and controlling the laser power to gradually rise on the premise of no defocus until the temperature of the sample irradiation center is not synchronously risen and is stopped after reverse refraction occurs, and waiting for a sufficient time period on the premise of no defocus and no laser power until the temperature of the sample irradiation center is not changed, wherein the obtained temperature is the etching threshold temperature.
5. The method of claim 4, wherein the temperature evolution profile is obtained by raman spectroscopy real-time detection.
6. The method of claim 4, further comprising:
judging whether the initial layer thickness of the sample is within a single-layer controllable etching range by utilizing the temperature evolution curve, if not, etching the sample until the initial layer thickness is within the single-layer controllable etching range,
and if the etching laser power cannot enable the temperature evolution curve to be subjected to single-step reduction, or the temperature of the irradiation center is firstly increased and then is subjected to step reduction relative to the etching threshold temperature under the etching laser power, or the temperature of the irradiation center is stabilized at a specific temperature higher than the etching threshold temperature, but etching is still continuous by using an instrument, the initial layer thickness of the sample can be determined not to be within a single-layer controllable etching range.
7. The method of claim 6, wherein the initial layer thickness of the sample is obtained indirectly by growth preparation conditions or directly by spectroscopic or atomic force microscopy.
8. The method of claim 4, wherein obtaining an etch laser power required to etch the sample within a single layer controllable etch range from the stepped cool down feature further comprises:
setting specific etching laser power according to the temperature evolution curve, wherein the number of single etching layers of the specific etching laser power on the sample is equal to the number of steps of the step-shaped cooling feature in the temperature evolution curve corresponding to the specific etching laser power.
9. The method of claim 8, wherein determining the number of steps of the stepped cooling feature comprises: under the precondition of no defocusing, the etching laser power irradiated on the sample is gradually increased so that the irradiation center temperature of the sample gradually reaches and temporarily exceeds the etching threshold temperature, the laser power is kept unchanged, and the number of steps in the process that the irradiation center temperature of the sample is recovered to the etching threshold temperature is observed.
10. The method of claim 8, wherein each point of the etched area of the sample is etched for a sufficient length of exposure using the particular etching laser power, wherein each point is scanned a single time, and the single scan is exposed for a sufficient length of exposure, wherein the exposure length of exposure is sufficient to refer to performing the etching without defocus until the temperature of the center of irradiation during etching is below the etching threshold temperature.
11. The method of claim 10, wherein a single point short exposure is performed on each spot and multiple scans accumulate a sufficient total etch time to achieve sufficient exposure time, rather than a single scan of each spot.
12. A two-dimensional material etching system, which comprises a controllable power laser source, a temperature detector, a temperature control console, a displacement table and an etching gas atmosphere cavity,
wherein the controllable power laser source is used for providing etching laser with required power; the temperature detector is used for realizing in-situ real-time monitoring of etching temperature; the temperature control console is used for controlling the temperature distribution of the sample to be in a single-layer controllable etching range; the displacement table is used for controlling the etched position of the sample; the etching gas atmosphere cavity is used for forming a gas atmosphere surrounding a sample to be etched; it is characterized in that
Also included is a controller configured to implement the etching method of any one of claims 1 to 11.
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