Study On The Preparation And Properties Of Plasma Resistant Yttria-based Composite Ceramics

Plasma etching is an indispensable process for selective removal of surface materials in manufacturing integrated circuits,in which microfeatures are created on the patterned locations,on a wafer coated with photoresist,that are exposed to chemical and physical attacks.As the integrated circuit technology advances at an increasingly faster pace,plasma etching process is gradually found much wider applications in manufacture of integrated circuit and micro/nano structures.The fluorine gas plasma,which used to etch silicon wafer,or silicon oxide formed on a silicon wafer,react with the inner ceramic components to form the fluoride particles.The generated particles attached to the wafer surface and cause killing defects on the integrated circuit.Therefore,suppressing the generation of fluoride particles on the chamber wall surface is essential to eliminate particulate contaminations.In short,the plasma etching resistance for the chamber inner wall material is crucial for high quality integrated circuit fabrication,and the research about the plasma resistance materials is of great importance.At present,the most popular chamber inner wall materials is high purity yttrium oxide ceramics,but its mechanical strength is low,while the material cost is high.The fracture toughness and flexural strength of Y2O3 are only 1.1 MPa·m1/2 and 130 MPa,respectively.In contrast,the fracture toughness and flexural strength of 99.9%Al2O3 are as high as 5-6 MPa·m1/2 and 400 MPa,and for ZrO2 it is 4-5 MPa·m1/2 and 1000 MPa,respectively.In this work,a certain proportion of ZrO2 or Al2O3 is mixed into Y2O3 powder to prepare zirconium-toughened or aluminum-toughened yttrium-based composite ceramics(respectively termed as yttria-zirconia composite and yttria-alumina composite),with an equally-important purpose of reducing the fabrication cost.The mass loss rate,surface roughness,surface morphology and electronic binding energy before and after etching are analyzed,and the etching behavior of yttrium-based composite ceramics in plasma environment is intensively studied.The main research contents and important conclusions of this thesis are as follows:(1)Through physical sputtering experiments,the relationships between the mass loss,the surface morphology after etching with the ratio of Y2O3/ZrO2 or Y2O3/Al2O3 were investigated,and the reaction process between Ar plasma with the ceramic surface was studied in details.The non-linear dependence of the mass loss rate after etching on the ratio of Y2O3/ZrO2 or Y2O3/Al2O3 is observed,and the pure physical reaction process between the Ar plasma and the ceramic surface occurs,correspondingly,the particles detached by the sputtering are of composition of the composite ceramic.(2)In-depth analysis,based on the highly recognized sputtering theory proposed by Sigmund,verified the very critical fact that the sputtering resistance of yttrium-based composite ceramics in an Ar plasma environment depends on the surface binding energy of the compound.(3)Through chemical etching experiments,the relationships between the mass loss,the surface morphology after etching with the ratio of Y2O3/ZrO2 or Y2O3/Al2O3 were studied,and the reaction process between the CF4 plasma and the ceramic surface was also discussed in details.The dependence of the mass loss rate after etching on the ratio of Y2O3/ZrO2 or Y2O3/Al2O3 is determined.,The CF4 plasma reacts with the ceramic surface to form reaction byproducts,which is confirmed by the changes in the electron binding energy of the etched surface.The surface sublimation enthalpy and boiling point of the resultant reaction products directly controls the corrosion resistance of the ceramic materials.(4)The percolation concept was applied in understanding the mass loss of yttrium-based composite ceramics under reactive plasma environment.The simulation results show that when the content of ZrO2 or Al2O3 exceeds a certain threshold,the mass loss rate of yttrium-based composite ceramics will undergo abrupt changes.This is consistent with the observed dependence of the mass loss rate on the molar ratio of ZrO2 or Al2O3.