Experimental Study On Nano-mechanical Behavior And Free Abrasive Lapping Of Single Crystal Gallium Oxide

Single crystal gallium oxide??-Ga₂O₃?,as a new generation of semiconductor material,has excellent physical and chemical characteristics such as ultra-wide band gap,high breakdown field strength,excellent conductivity and high transmittance in the deep ultraviolet band,which have broad application prospects in power microelectronic devices and high-voltage equipment.During a series of processing processes such as cutting,lapping,polishing,etc.,surface and subsurface damage will inevitably occur,which severely restricts the subsequent application of the crystal.Therefore,improving the surface quality after processing and reducing subsurface damage have become the key technologies in the process of?-Ga₂O₃ processing.Based on the nano-indentation technology,this paper studies the micro-mechanical behavior of?-Ga₂O₃ and analyzes the surface and sub-surface damage after free abrasive lapping.The main research contents are as follows:?1?The load-controlled quasi-static method was used to perform nano-indentation experiments on?-Ga₂O₃.Based on the Nix-Gao model and the power-law relationship proposed by Manika,the relationship between the hardness and indentation depth of?-Ga₂O₃?100?and?010?planes was fitted,and the indentation size effect on the two crystal planes was studied.The experimental results show that the hardness and elastic modulus of the?-Ga₂O₃?100?and?-Ga₂O₃?010?are decreasing with the increase of the indentation depth and tend to be stable,and both show obvious indentation size effect.The?100?crystal plane of?-Ga₂O₃ has a larger elastic modulus and a smaller hardness than the?010?crystal plane.The hardness of the?100?crystal plane without size effect is 8.238 GPa,the microscopic feature length is 101.196 nm,and the size effect factor is 0.1725;?010?The hardness of the crystal plane without size effect is 9.824 GPa,and the microscopic feature length is 88.033 nm,the size effect factor is 0.1706.The size effect factors of the two crystal planes of?-Ga₂O₃ are between the common metal materials and semiconductor materials,and the indentation size effect of the?100?crystal plane is more obvious.?2?The nanoindentation technique was used to study the creep properties of?-Ga₂O₃ on?100?and?010?planes at room temperature based on constant load method,and the creep stress exponents were obtained by fitting.The experimental results show that nanoindentation method can effectively measure the creep deformation of?-Ga₂O₃ which consists of two stages,primary creep and steady-state creep;?100?plane experiences obvious primary creep and steady-state creep,but the primary creep of?010?plane is not obvious;The creep displacement and average indentation stress of?-Ga₂O₃ are greatly affected by loading,but the creep stress exponents are not.The creep stress exponents of different planes on?-Ga₂O₃ is quite different;The creep stress exponents of?100?plane range from 15.5 to 27.8,and the creep stress exponents of?010?crystal plane range from 46.1 to 63.4,?010?plane has a larger creep stress exponents and stronger creep resistance than the?100?plane.?3?Based on the processing method of free abrasive lapping,?-Ga₂O₃ was subjected to lapping processing experiments,and the influence of the particle size of the abrasive,the material of the grinding disc,and the loading pressure on the surface quality of?-Ga₂O₃ was analyzed,and the three-dimensional topography were used for characterization.The experimental results show that:?-Ga₂O₃?100?plane is prone to cleavage pits,cleavage tongues,and interlayer cleavage in the process of lapping with free abrasives;Reducing the particle size of the abrasive,using a material with a lower hardness grinding disc,and reducing the loading pressure are conducive to suppressing the occurrence of cleavage phenomena during the lapping process of the?-Ga₂O₃?100?plane.A two-step process for rough-grinding and fine-grinding of?-Ga₂O₃?100?was proposed.The rough lapping stage was ground with a W7 diamond abrasive on a cast iron disc at a load pressure of 60 g/cm².The surface roughness Ra after lapping was 173 nm.In the fine lapping stage,W2.5 diamond abrasive was used to grind on the tin-lead alloy disc with a loading pressure of 15 g/cm²,and the surface roughness Ra after grinding was 15 nm.There are a lot of shallow scratches on the surface,the depth of the scratches is about 120¹85 nm,and there is no cleavage.?4?The subsurface damage of the?-Ga₂O₃?100?plane after rough lapping and fine lapping was studied by cross-section microscopy.There are two types of cracks after rough grinding of?-Ga₂O₃?100?,coarse cleavage cracks with a length greater than 30?m and micro cracks with a length less than 10?m.Microcracks are subdivided into median microcracks,oblique microcracks,"T"microcracks,"Herringbone"microcracks,etc.,only median microcracks and oblique microcracks exist after fine lapping,and no oblique cleavage cracks were found.The average depth of the subsurface damage layer after rough lapping and fine lapping of?-Ga₂O₃?100?plane were 22.8 and 4.4?m,respectively,which provided a reference for the machining allowance after rough lapping and fine lapping.