Research On Machining High Aspect Ratio Microgrooves On CVD Single Crystal Diamond Substrate By An Ultraviolet Nanosecond Laser

Diamond has excellent properties such as extremely high hardness,good thermal conductivity,excellent optical properties,high chemical stability,and good biocompatibility,making it widely used in precision cutting tools,chip heat dissipation,and optical devices.Some scholars have found that manufacturing high aspect ratio microgrooves on the diamond surface can effectively improve the heat dissipation performance of the diamond radiator.However,due to the great hardness and brittleness,corrosion resistance,and electrical insulation properties of diamond,it brings great challenges to traditional mechanical and chemical processing methods.High-energy beam lasers have an extremely high energy density,which can instantly melt,vaporize,and even sublime the processed materials.Although a large number of scholars have studied nanosecond laser processing of diamond,they mainly explore the material removal mechanism and laser process parameter optimization of laser processing diamond in the visible and infrared bands.Compared with lasers in the visible and infrared wavelengths,the laser photon energy in the ultraviolet wavelength band is higher,and the processing heat affected zone is smaller.Therefore,a UV nanosecond laser is used to process high aspect ratio diamond microgrooves in this paper.At present,no scholars have systematically studied the effect of UV nanosecond laser process parameters on the aspect ratio of diamond microgrooves.Single crystal diamond has anisotropy,so crystal orientation is also an important aspect to be considered in laser processing diamonds.In this paper,the effects of UV nanosecond laser process parameters and crystal orientation on the morphology of diamond microgrooves with high aspect ratio,as well as the width,depth,and aspect ratio of the microgrooves were systematically studied.Finally,in order to further improve the efficiency of laser processing of diamond microgrooves,a new method of gold filmassisted UV nanosecond laser processing of diamond microgrooves is proposed,and a diamond microgroove structure for chip heat dissipation is fabricated on a diamond substrate.The main research contents and experimental conclusions of this thesis are as follows:(1)The influences of parameters such as pulse energy,scan speed,scan times,repetition frequency and defocus amount of the UV nanosecond laser on the morphology of diamond microgrooves,as well as the width,depth,and aspect ratio of the microgrooves were systematically studied.With the increase of laser pulse energy and scan times,the aspect ratio of the microgrooves first increases rapidly and then tends to be stable.As the scanning speed decreases,the aspect ratio of the microgrooves gradually increases.With the increase of the laser repetition frequency,the aspect ratio of the microgroove increases gradually and then tends to be stable.When the defocus amount changes from a negative value to a positive value,the aspect ratio of the microgroove first increases and then decreases.On this basis,the optimal process parameters for machining diamond microgrooves are: pulse energy 200 μJ,scanning speed 5 mm/s,scanning times 25,repetition frequency 60 k Hz,defocus amount-1 mm.The microgroove array structure with good surface quality and aspect ratio of up to 14.5was fabricated on CVD single crystal diamond using the optimized process parameters.(2)The morphology,depth,width,and aspect ratio of diamond microgrooves processed by UV nanosecond laser with <100> and <110> crystal orientations were compared.The ablation rates and material removal rates of the <100> and <110>oriented microgrooves were further calculated.The experimental results show that a large number of graphite particles are attached to the microgrooves with the <100>crystal orientation,while there are almost no particles attached to the microgrooves with the <110> crystal orientation,which are relatively smooth and the graphite layer is thinner.Under the same laser conditions,the ablation rate and material removal rate of <110> microgrooves are always higher than those of <100> microgrooves.The aspect ratio of diamond microgrooves processed along the diamond <110>crystallographic direction is larger than that along the <100> crystallographic direction.Using the preferred laser process parameters along the <110> crystal direction,a microgroove array structure with an aspect ratio of up to 15.7 can be fabricated on CVD single crystal diamond.(3)The effect of gold film on the morphology of diamond microgrooves and the width,depth,and depth ratio of microgrooves processed by UV nanosecond laser was studied.The simulation results show that among the six metal films of gold,titanium,nickel,chromium,copper and silver,the gold film and copper film have the largest depth of diamond micro-holes assisted by a UV nanosecond laser.When the thickness of the gold film reaches 100 nm,the width and depth of the microgrooves both reach the maximum value.The results show that the gold film can improve the ablation rate and material removal rate of laser-processed diamond to a certain extent.Using the previously preferred laser process parameters and along the <110> crystal direction,a microgroove array structure with an aspect ratio of up to 16.6 was fabricated on CVD single crystal diamond coated with a 100 nm thick gold film.In addition,according to the chip heat dissipation requirements,a microgroove array with a surface width of 200μm,an average depth of 1573 μm and an average aspect ratio of about 8.0 was fabricated on a 3 mm thick diamond substrate.