飞秒激光表面毛化对单晶氮化镓激光-水射流复合加工性能的影响OA

Objectives:Single-crystal gallium nitride(GaN)is a representative third-generation semiconductor material,and widely used in chip manufacturing.It exhibits high hardness,significant brittleness,and low optical absorptivity,which causes the difficulties in their efficient and micromachining.This paper proposed a novel process method for the micro-machining of single-crystal GaN substrate whereby a femtosecond laser is used first to micro-texture the material surface,then followed by the micromachining using nanosecond laser-waterjet hybrid machining technology to enhance the machining performance.Methods:First,textured surfaces with different surface roughnesses(Ra)of 0.5,1.0,and 1.5 μm,were fabricated using femtosecond laser processing,and the effects of the micro-textures on the light absorptivity were studied.Second,the surface integrity was analyzed in detail,recommendations were made for the selection of process parameters to accommodate different expectations of using this machining process in practice.Third,the effect of textured surface roughness,laser pulse energy,laser pulse overlap and water pressure on the machined microgroove quality,geometric characteristics and material removal rate are then discussed.Results:(1)Laser-induced periodic surface structure(LIPSS)by femtosecond laser can effectively reduce the transmittance and reflectance,thus improve the light absorptivity.After the pre-textured processing,the light absorptivity of single-crystal GaN at a wavelength of 1 066 nm was improved from 3.4%to over 78.3%.(2)When the water pressure was less than 10 MPa,low laser pulse energy of 0.05 mJ and low laser pulse overlap of 99%were used,microgrooves generated by laser-waterjet hybrid micromachining of non-textured single-crystal GaN presented discontinuous features.When the high laser pulse energy of 0.2 mJ and high laser pulse overlap of 99.9%were employed,cracks arise at the edges of microgroove generated by laser-waterjet hybrid micromachining of non-textured single-crystal GaN.Under selected experimental conditions,the microgrooves generated by laser-waterjet hybrid micromachining of pre-textured single-crystal GaN were quite continuous and clean.(3)When the value of process parameters including laser pulse energy,laser pulse overlap and water pressure are too large,the pre-textured processing can not prevent the production of cracks.(4)With the increase of laser pulse energy,the size of microgrooves and material removal rate RMRR both increase.As the laser pulse overlap increasing,the size of the microgrooves increases,but the RMRR efficiency decreases.When the water pressure increases,the top widths of the microgrooves almost remain unchanged,while the depths of the microgrooves and the RMRR decrease.Conclusions:(1)LIPSS by femtosecond laser can effectively improve the light absorptivity,and the light absorptivity of single-crystal GaN at a wavelength of 1 066 nm was improved from 3.4%to over 78.3%.(2)After pre-textured processing,the microgrooves generated by laser-waterjet hybrid micromachining of pre-textured single-crystal GaN were continuous,clean and without cracks,and the processing performance of nanosecond laser-waterjet hybrid micromachining of single-crystal GaN is substantially improved.(3)Under the selected experimental conditions,a good quality microgroove may be achieved with the depth of 154 μm and the aspect ratio of 1.91 by employing a pre-textured surface roughness of 1.0 μm,laser pulse energy of 0.2 mJ,pulse overlap of 99.9%and water pressure of 5 MPa.