Nondestructive Characterization Method Of Processing Damage Layer On Silicon Carbide Substrate Based On Muller Matrix Ellipsometry

As a wide-bandgap semiconductor material,silicon carbide（Si C）single crystal substrate is at the front-end of the semiconductor industry chain and is the core key material for manufacturing devices.It has obvious application advantages in the fields of optoelectronic devices,power devices and radio frequency devices.Qualified substrates need to go through multiple processing stages such as grinding and polishing to achieve ultra-smooth,surface and subsurface damage-free quality to meet the stringent requirements for high-quality epitaxy production.The subsurface damage layer after processing is an important indicator for evaluating the quality of the substrate and the processing technology.However,the non-destructive and high-precision measurement of the nano-scale damage layer is still a big challenge.Aiming at the quantitatively evaluation of the subsurface damage layer,this paper proposes to use Mueller matrix spectroscopic ellipsometry（SE）with 16elements to explore a non-destructive characterization method for the parameters of Si C substrates and subsurface damaged layers,which can not only characterize the thickness of the subsurface damage layer,but also simultaneously characterize the optical characteristic parameters closely related to the optoelectronic properties of the devices.The main research results are as follows:（1）A non-destructive and high-precision measurement and quantitative characterization method of the damaged layer of Si C substrate based on Mueller matrix ellipsometry is proposed.The detection accuracy of ellipsometry reaches sub-nanometer level,and the thickness of damaged layer obtained by ellipsometry modeling analysis is consistent with the thickness measured by transmission electron microscope.At the same time,SE greatly shortens the detection time compared with destructive detection methods.（2）A method to obtain the optical anisotropy of uniaxial crystals from off-axis transmission ellipsometry measurements is proposed.Based on the Mueller matrix differential decomposition theory,the correlation formula between the differential elements of the Mueller matrix and the anisotropy value（birefringence and dichroism）of silicon carbide is deduced.The obtained formula is completely analytical,and does not require the establishment of an optical model and numerical inversion.The method has a solution accuracy of 10^-4,and the numerical error of the calculation is only 0.0006.（3）A solution strategy for the complex optical constants of Si C and the parameters of damaged layer in single-sided polished and double-sided polished Si C substrate is proposed,respectively.Through the established ellipsometry simulation model,the ellipsometry response of the features of the Si C substrate is analyzed.At the same time,combined with the Mueller matrix experimental measurement and fitting analysis,the characterization scheme of polished Si C substrates under fully coherent and partially coherent conditions are explored.For single-sided polished substrate,a characterization strategy is proposed to use multi-incidence angle measurement and oscillator model to fit the refractive index of Si C and damaged layer.For double-sided polished substrate,a characterization strategy is proposed to use multi-incidence angle and multi-rotation angle measurement,point-to-point to fit the complex optical constants of Si C,and oscillator model to fit the refractive index of damaged layer.（4）A substrate analysis strategy based on transmission measurement assisted reflection modeling characterization is constructed,and the characterization scheme of the damaged layer by grinding and polishing process is studied.A measurement scheme considering the texture structure of the substrate surface is established:the Mueller matrix spectrum measurement is performed when the texture direction of the substrate surface is perpendicular to the incident plane,and the maximum spectral response can be obtained from the damage and interface information.The characterization strategy is optimized and the complexity of modeling and fitting is effectively reduced:for double-sided polished substrates,the partially coherent optical model used for ellipsometry fitting can be simplified to a fully coherent model when only the parameters of the damaged layer are fitted,to ignore back reflections.Finally,the Muller element m₃₄is proposed as the evaluation index of damage degree.The damaged layer thickness of Chemical Mechanical Polishing（CMP）Si C substrate analyzed by SE was 2.6±0.1 nm（TEM result was 2.4±0.2 nm）,indicating that the SE has sub-nanometer detection accuracy.SE measurement and analysis of single-point Mueller matrix spectral data takes only tens of seconds.The established Mueller matrix spectral ellipsometry characterization scheme and analysis technique provide a new method for realizing the quality evaluation of the processing damaged layer of Si C substrates.The research results are of importance for optimizing the processing technology of Si C substrates and revealing the influence mechanism of the damaged layer on the epitaxy.