Detailed Description
The present application will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present application more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.
The terms "first," "second," "third," "fourth" and the like in the description and in the claims and in the above-described figures, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged under appropriate circumstances, or in other words, the described embodiments may be implemented in other sequences than those illustrated or otherwise described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, may also include other items, such as processes, methods, systems, articles, or apparatus that include a series of steps or elements, are not necessarily limited to only those steps or elements explicitly listed, but may include other steps or elements not explicitly listed or inherent to such processes, methods, articles, or apparatus.
It should be noted that the description of "first", "second", etc. in this disclosure is for descriptive purposes only and is not to be construed as indicating or implying a relative importance or implying an indication of the number of technical features being indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature. In addition, the technical solutions of the embodiments may be combined with each other, but it is necessary to base that the technical solutions can be realized by those skilled in the art, and when the technical solutions are contradictory or cannot be realized, the combination of the technical solutions should be considered to be absent and not within the scope of protection claimed in the present application.
Referring to fig. 1-3, a first embodiment of the present application provides a grating structure 300 that includes a depth-varying grating 100 for the terahertz band. The depth-varying grating 100 comprises successive gratings of different depths. In this embodiment, the depth-variable grating 100 includes a structure in which gaps and gratings are alternately arranged, and the depth of the gratings is not uniform, and the widths of the gaps are the same, and the widths of the gratings are the same. It will be appreciated that in this embodiment, a grating structure 300 is shown that employs a partially depth-varying grating 100 and a partially depth-identical grating structure 200, while in some other possible embodiments, the grating structure 300 may be entirely a depth-varying grating 100. The following describes only the method for fabricating the depth-varying grating 100, and the depth-identical grating structure 200 may be implemented by any conventional fabrication method, and is not described or limited herein.
Referring to fig. 4-5 in combination, the method for fabricating the depth-variable grating 100 includes steps S100-S500.
In step S100, a photoresist layer 2 is coated on the surface of the substrate 1.
Specifically, the substrate 1 is made of silicon, quartz, copper, or the like, and the substrate 1 is used to provide an adhesion platform for the photoresist layer 2. Specifically, before the photoresist layer 2 is coated, the substrate 1 is cleaned to ensure that the surface of the substrate 1 is free of dust and greasy dirt, and then the photoresist is uniformly coated on the cleaned surface of the substrate 1.
Referring again to fig. 2, in this embodiment, the photoresist layer 2 is a negative photoresist. The coating thickness of the photoresist is set according to the depth of the depth-varying grating 100, that is, the thicknesses of the photoresist layer 2 at the positions corresponding to the gratings of different depths are different. Wherein the side of the photoresist layer 2 facing away from the substrate 1 is a flat side. The substrate 1 has different thicknesses according to the different depths of the photoresist layer 2 corresponding to the gratings, thereby obtaining photoresist layers 2 having different thicknesses. In the present embodiment, the depth-variable grating 100 is a graded grating, and therefore, the substrate 1 and the photoresist layer 2 having graded thicknesses are used, that is, the depth of the grating is gradually reduced or increased, the photoresist layer 2 is gradually thinned or thickened, and the substrate 1 is gradually thickened or thinned. The substrate 1 is manufactured by a machining mode and can be milled by a milling machine.
It will be appreciated that in some possible embodiments, the substrate may be provided with the same thickness, while the thickness of the photoresist layer is provided according to the depth of the depth-varying grating 100, in which case the side of the photoresist layer 2 facing away from the substrate 1 is a gradual slope.
In step S200, a mask 5 is provided on the side of the photoresist layer 2 facing away from the substrate 1.
As shown in fig. 2, specifically, the mask 5 includes a mask pattern 51 corresponding to the depth-variable grating, the mask pattern 51 includes a hollowed-out area 510 and a covering area 512 that are disposed at intervals, and the hollowed-out area 510 corresponds to one grating, so that a position corresponding to the photoresist layer 2 and the hollowed-out area 510 is exposed, that is, the photoresist layer 2 is exposed at intervals through the hollowed-out area 510.
In step S300, a mask 3 is disposed on the photoresist layer 2. In the present embodiment, the number of the light shielding plates 3 is 1, and the size is matched with the size of the depth-variable grating 100, so that the light shielding plates 3 completely cover the depth-variable grating 100. The light shielding plate 3 is made of a light shielding material, the depth of the depth-variable grating 100 gradually becomes shallow from right to left, namely, the thickness of the photoresist layer 2 gradually becomes thinner from right to left, the thickness of the substrate 1 gradually becomes thicker from right to left, and the light shielding plate 3 is a plate-shaped object and is arranged on one side, away from the substrate 1, of the photoresist layer 2, namely, above the photoresist layer 2.
Step S400, moving the light shielding plate 3 according to a preset direction and a preset speed, so that the photoresist layer 2 is exposed to obtain an exposure area, wherein the preset direction and the preset speed are set according to the depth of each grating.
Specifically, the preset direction refers to a direction from deep to shallow of the grating depth. The preset speed is to determine the required exposure time according to the depth of each grating, and then determine the corresponding speed according to the exposure time and the distance between each grating. The depth of the grating is proportional to the exposure time, and the grating with a certain depth needs to be exposed at the corresponding position of the photoresist layer 2 for a certain period of time, so that the gratings with different depths need to be exposed for different periods of time. More specifically, taking the example of negative photoresist as the example, the deeper the grating depth, the thicker the photoresist thickness required and the longer the exposure time. It will be appreciated that since the photoresist layer 2 is exposed to light at different thicknesses for different exposure durations, the photoresist layer 2 of different thicknesses is correspondingly formed with the grating 100 of different depths. After the exposure time is determined, the distance to be moved is calculated according to the width of each grating and each gap, and the preset speed is calculated according to the moving distance and time.
In the present embodiment, the movement of the shutter plate 3 is achieved by a driving device (not shown). The driving means may be a motor or a cylinder. It will be appreciated that the preset speed may be calculated according to the structure of the depth-varying grating 100, so that the preset speed is allocated to the driving device, and the driving device moves the movable mask 3 according to the preset speed. For example, when the depth-varying grating 100 is depth-graded, and the width of each grating and the width of each gap are the same, the preset speed is moved at a uniform speed. For another example, in the case where there is a sudden change in the depth of the depth-varying grating 100, the preset speed movement is also sudden, not uniform. That is, the preset speed is set according to the exposure time, width, and width of each grating of the depth-varying grating 100.
In the initial state, the photoresist layer 2 is covered by the light shielding plate 3, and cannot be illuminated in the hollowed-out area 510 and the covering area 512 respectively. When the mask 3 moves, the photoresist layer 2 is gradually illuminated, and when the hollowed-out area 510 is exposed to the illumination, the corresponding photoresist layer 2 undergoes a crosslinking reaction, and forms an insoluble network structure. This network structure makes the photoresist layer 2 more rigid in the exposure environment and the permanent structure of the photoresist layer 2 is better. Further, for better exposure, the present embodiment is to place the substrate 1 provided with the photoresist layer 2 and the light shielding plate 3 in the exposure apparatus 5.
In this embodiment, in the exposure process of the photoresist layer 2, since the depth of the depth-variable grating 100 gradually becomes shallow from right to left, the mask 3 is moved from the right end of the photoresist layer 2 to the left end of the photoresist layer 2 at a constant speed (direction X, speed V), and at the same time, the exposure time is determined according to the depth of each grating, so as to determine the moving speed of the mask 3. That is, the exposure time of the exposed photoresist layer 2 gradually decreases from the right end to the left end, i.e., the exposure amount of the photoresist layer 2 gradually decreases from the right end to the left end. The application realizes the gradual change depth of the photoresist layer 2 by controlling the moving speed of the light shielding plate 3 when the photoresist layer 2 is exposed, thereby manufacturing a complex gradual change grating structure and avoiding complex and expensive machining and electron beam exposure processes.
In step S500, after the photoresist layer 2 is exposed, the exposed area is developed to obtain the depth-variable grating 100. Specifically, before the exposure area is subjected to the development treatment, it is necessary to determine whether the exposure of the photoresist layer 2 is completed currently according to the depth of the depth-variable grating 100 and the process parameters. When it is judged that the exposure of the photoresist layer 2 is completed, the photoresist layer 2 is developed with a developing solution to gradually remove the photoresist layer 2 dissolved in the developing solution. Wherein grooves are formed between the areas where the photoresist layer 2 is not dissolved and the areas where the photoresist layer 2 is dissolved, and the depth of the grooves of the photoresist layer 2 is used as the depth of the depth-varying grating 100. The undissolved area of the photoresist layer 2 serves as the top of the groove of the depth-varying grating 100, the dissolved area of the photoresist layer 2 serves as the groove bottom of the groove of the depth-varying grating 100, and the height between the top of the groove and the groove bottom of the groove is the depth of the groove. It will be appreciated that in this embodiment, the photoresist layer 2 is a negative photoresist, and thus, the exposed area (hollowed-out area 510) is an insoluble area, and the non-exposed area (covered area 512) is a dissolved area. It will be appreciated that the photoresist layer 2 provides a structure having greater stability and corrosion resistance after exposure and development processes. The depth-variable grating 100 can remarkably improve the coupling efficiency and the working bandwidth of the grating by matching grooves with different depths with wave vectors of electromagnetic waves, and has wide application prospects in terahertz wave bands. The depth of the photoresist layer 2 after exposure is consistent with the depth of the depth-variable grating 100, and the process parameters (such as the hardness of the exposed area of the photoresist layer 2, the width of the grating, etc.) and the like meet the requirements of preset process parameters.
In this embodiment, after the exposure of the photoresist layer 2 is judged to be completed, the developing solution is contacted with the photoresist layer 2 on the surface of the substrate 1, and the unexposed area of the photoresist layer 2 maintains the original solubility, i.e. the photoresist layer 2 in the unexposed area is gradually dissolved by the developing solution. Since the photoresist layer 2 in the exposure region is insoluble in the developer due to the photo-curing reaction during exposure, the photoresist layer 2 in the exposure region remains as it is, and the depth-variable grating 100 is obtained. It will be appreciated that the solubility of the photoresist layer 2 in the developer is inversely related to the exposure of the photoresist layer 2, i.e., the greater the exposure of the photoresist layer 2, the less the solubility of the photoresist layer 2 in the developer. The developer may be organic solvent such as xylene, n-butyl acetate, or mixed alkane. Development means include, but are not limited to, spin, spray, immersion.
In some possible embodiments, the surface of the depth-varying grating 100 facing away from the substrate 1 is sputtered with a metal such that the depth-varying grating 100 forms a conductive layer. The coupling structure is formed on the surface of the depth-variable grating 100 subjected to metal sputtering treatment, so that efficient coupling between the grooves of the depth-variable grating 100 and the wave vector of the electromagnetic wave can be realized.
In some possible embodiments, the surface of the depth-varying grating 100 facing away from the substrate 1 is sputtered with metal followed by a series of subsequent treatments including, but not limited to, annealing, and surface treatment. The present application can enhance the optical performance and mechanical stability of the depth-varying grating 100 by performing a subsequent treatment of the grating surface.
Please refer to fig. 6, which is a schematic diagram illustrating a fabrication of a depth-variable grating 100a according to a second embodiment. In the present embodiment, the structure of the depth-varying grating 100a is bilaterally symmetrical, and the depth becomes gradually shallower from the middle to the both sides. In the process of manufacturing, first, two identical light shielding plates 3a and 3b are arranged in the middle of the photoresist layer 2 side by side, and the contact position of the two light shielding plates 3a and 3b coincides with the central line 6 of the photoresist layer 2 so as to jointly cover the photoresist layer. In this embodiment, one light shielding plate 3a covers the left side area of the center line 6 of the photoresist layer 2, the other light shielding plate 3b covers the right side area of the center line 6 of the photoresist layer 2, and then the light shielding plates 3a and 3b are respectively moved away from each other in opposite directions X1 and X2 and at the same preset speed V until moving to respective preset end positions, so that the exposure time of each position of the left side area and the right side area of the photoresist layer 2 is the same, thereby making the depth-varying grating 100 in a bilateral symmetry structure. The shape, size, and placement of the light shielding plates 3a and 3b may be designed according to actual needs, and are not limited herein. The above-described moving directions of the light shielding plates 3a and 3b, the preset speed are merely examples, and may be set according to the specific circumstances, and are not limited herein.
Referring to fig. 7-8, a depth-varying grating 100b is provided in accordance with a third embodiment. The depth-variable grating 100b provided in the third embodiment includes two depth-variable gratings with the same structure, and the two depth-variable gratings with the same structure are arranged up and down, the substrates 1a and 1b of the two depth-variable gratings with the same structure are arranged in opposite directions, and the photoresist layers 2 of the two depth-variable gratings with the same structure are bonded together after exposure and development. When the mask is manufactured, firstly, the two photoresist layers 2 and the substrates 1a and 1b of the mask 5 are arranged up and down oppositely, the photoresist layers 2 on the substrates 1a and 1b are opposite, then, the photoresist layers 2 on the substrates 1a and 1b are exposed and developed in the same mode, and then, the two depth-variable gratings are fixedly connected in a connecting mode through an adhesive mode, namely, the exposed and developed photoresist layers 2 on the substrates 1a and 1b are attached to form the depth-variable grating 100b with an up-down symmetrical structure. The depth-varying grating 100b of the vertically symmetrical structure can realize a terahertz surface plasmon coupler. The combination of the depth-variable gratings 100b is merely exemplary, and may be arranged according to a specific combination of requirements, which is not limited herein. It is to be understood that, in the present embodiment, in order to improve efficiency, the depth variable grating 100b is manufactured by forming the depth variable grating in a single process. In some possible embodiments, each of the depth-varying gratings 100b may also be fabricated separately in the same manner. It will be appreciated that the light source to which the exposure is applied may be disposed between the masks 5 of the two substrates 1a and 1 b.
Referring to fig. 9, in some other possible embodiments, a positive photoresist is used as the photoresist layer 2', the thickness of the photoresist layer 2 is uniform and the thickness of the substrate 1' is uniform, and the thickness of the photoresist layer 2' is the same as the deepest depth of the grating (as shown in fig. 4), but the exposure time is different.
The photoresist layer 2' contains a sensitizer, which is a dissolution inhibitor. The sensitizer may inhibit the solubility of the photoresist layer 2 'in the dissolution solution before the photoresist layer 2' is exposed. When the photoresist layer 2 'is exposed, the sensitizer will undergo chemical decomposition, and change from dissolution inhibitor to dissolution enhancer, thereby increasing the solubility of the exposed area of the photoresist layer 2' in the dissolution liquid. It will be appreciated that the exposure of the photoresist layer 2 'and the solubility of the photoresist layer 2' in the dissolution liquid are in a positive correlation. The rest of the manufacturing process is the same as that of the first embodiment, and will not be described again here.
It will be appreciated that the selection of the photoresist in the above embodiments is merely exemplary, and one of the positive photoresist and the negative photoresist may be selected as required, or a combination of both may be adopted.
In the above embodiments, the present application can realize a groove structure of gradual depth by controlling the exposure amount of the photoresist. And the terahertz grating structure with high coupling efficiency and broadband performance is prepared by combining a metal sputtering process through a simple mask control exposure and development technology.
It should be noted that, the foregoing reference numerals of the embodiments of the present application are merely for describing the embodiments, and do not represent the advantages and disadvantages of the embodiments. And the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, apparatus, article, or method that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, apparatus, article, or method. Without further limitation, an element defined by the phrase "comprising one does not exclude the presence of other like elements in a process, apparatus, article, or method that comprises the element.
It will be apparent to those skilled in the art that various modifications and variations can be made to the present application without departing from the spirit or scope of the application. Thus, if and when such modifications and variations of the present application fall within the scope of the claims and the equivalents thereof, the present application is intended to encompass such modifications and variations.
The foregoing description is only of the preferred embodiments of the present application, and is not intended to limit the scope of the application, and all equivalent structures or equivalent processes using the descriptions and drawings of the present application or directly or indirectly applied to other related technical fields are included in the scope of the present application.