| Micro-optical components,as a core of small optoelectronic systems,have lots of advantages of small size,light weight and low cost,which enables various functions such as miniaturization,array,integration,optical imaging,and wavefront conversion.Currently market for emerging micro-optical components is growing rapidly,and has a wide range of application in national economy,science and technology,and national defense sectors such as cell phone,automobile,security,machine vision,medical device,scientific research,military industry,and aerospace exploration et al.With the continuous reduction in feature sizes of micro-optical components,the demand for highly integrated,high-precision,and large-scale fabrication is increasing,posing significant challenges to lithography in terms of resolution,fabrication precision,and yield.To address the demand for high optical performance of micro-optical components,the fabrication of microoptical components with small aperture size,high-precision surface profile,and low surface roughness is a subject for in-depth study worldwide.To address the above issues,in this dissertation a detailed study on a mask-moving-based projection lithography process for fabricating micro-optical components based on the mask moving exposure technique and high resolution of the optical projection lithography technique was carred out:(1)The projection lithography method based on mask movement is proposed to process micro-optical elements: Mask-moving exposure technology,as one of the key technologies in the fabricaiton process of micro-optical elements,is essential to ensure low-cost and mass production.For improving the lithography resolution,further reducing the macro size of micro-optical components,improving their integration degree,and decreasing the difficulty of processing mask feature patterns,this dissertation proposes the projection lithography method based on mask movement.This method is based on the theory of projection optical imaging,combined with mask moving exposure technology,and adopts the principle of micro-slicing to evenly divide the target three-dimensional microstructure feature pattern into a series of thin strip areas,and analyze the microstructure in each strip area.By encoding,in a single one-dimensional moving mask exposure mode,the preparation of more complex three-dimensional micro-optical components can be achieved.(2)A projection lithography system based on mask movement was constructed to address the problem that traditional proximity/contact lithography equipment has low resolution and low yield,resulting in the surface accuracy of processed micro-optical components not meeting the requirements.In view of this,this dissertation constructed a projection lithography system based on mask movement,including core subsystem modules such as a uniform illumination system,a projection objective lens system,a leveling and focusing system,a precision workpiece stage system,and an electrical control system.First,a mercury lamp is used as the illumination source,and the beam is collected and initially collimated through an aspheric lens.The collimated beam enters the building block dislocation fly eye lens group and is subdivided and homogenized.It is completely collimated and imaged through the field lens and condenser lens.On the illumination surface,high optical power density,high uniformity and high collimation illumination of the mask surface are achieved.Secondly,a 0.2 times reduced projection objective lens is used to improve the lithography resolution of the system.The main structure of the objective lens adopts a layered design: the inner lens frame adopts a lowstress clamping method to ensure the surface shape;the middle layer lens barrel is filled with controlled air pressure,to ensure sealing;the outermost layer is an upper and lower series water jacket to control the temperature.The mobile workpiece stage adopts a sixdegree-of-freedom precision air-floating workpiece stage,which includes a two-degreeof-freedom lateral displacement macro-moving stage and a four-degree-of-freedom vertical micro-moving stage to achieve sample loading,focus adjustment and leveling.On this basis,the design and construction of the entire projection lithography equipment based on mask movement was completed.Finally,system integration and machine joint debugging tests were conducted,and photolithography exposure was used to verify that the exposure system has a photolithography resolution of 0.7 μm.(3)Preliminary verification of the projection lithography system based on mask movement: Based on the limitations of traditional mask movement exposure technology for preparing micro-optical components and the advantages of mask movement projection lithography technology,we used the built mask movement projection lithography system platform Experimental trial production,processing and verification of various microoptical components were carried out.The experimental results show that the constructed experimental system platform initially has the ability to prepare micro-optical components,but the surface shape accuracy of the devices still needs to be improved.At the same time,error analysis was conducted on the accuracy of the movement linearity and movement distance of the workpiece stage,and the reasons affecting the surface shape accuracy during the preparation process of micro-optical components were analyzed.(4)Proposed a high-precision surface shape control technology for microlens arrays based on mask movement: For the nonlinear effect of photoresist during the photolithography process,we proposed a high-precision surface shape control technology for microlens arrays based on mask movement.This method utilizes the threshold characteristics of the photoresist development process,combined with pre-exposure technology,to increase its development speed,avoid the impact of the exposure threshold on the surface shape of the microlens,and achieve high-precision control of the surface profile of the microlens.On the other hand,we use an inverted gas bath thermal reflow method to heat the developed photoresist microlens surface to a molten state,reducing irregular burrs on the microlens surface and reducing its surface roughness.At the same time,the experiment also preliminarily verified that this technology can achieve highprecision surface shape control during the preparation process of microlens arrays.(5)Typical micro-optical components were successfully developed: for the application of micro-optical components in optical systems such as beam shaping,optical imaging and focusing,and aberration correction,the relevant parameters affecting the performance of micro-optical components and their geometric structure dimensions were characterized.On this basis,the large-scale preparation of two typical micro-optical components,the Hartmann wavefront detection microlens array and spiral phase plate,was achieved,meeting the practical application needs of the market.Furthermore,in response to the demand for the preparation of random cylindrical lenses with variable sagittal heights and variable pitches,this dissertation has preliminarily carried out exploratory research on random cylindrical lenses.The results show that the projection lithography technology based on mask movement proposed in this dissertation still has the ability to process and prepare variable sagittal heights.and the capability of variable pitch random cylindrical lenses.In summary,this dissertation proposes a method for processing micro-optical elements based on projection lithography based on mask movement,the construction and verification of a projection lithography system based on mask movement,high-precision surface shape control of microlens arrays,and typical micro-optical elements.Detailed research work has been carried out in terms of device development,and the Hartmann wavefront detection microlens array and spiral phase plate for vortex phase imaging have been successfully developed,which has laid a solid foundation for the mass production of micro-optical components for projection lithography based on mask movement. |
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