EBSD Studies Of Microstructures And Micro-Scale Stresses Of Semiconductor Materials And Devices

Since there is fast development of microelectronic devices and photoelectronic devices to high-speed and high-density, the microstructure character of epitaxial structure in semiconductor and metallic interconnects, and the stress introduced during the preparing and using among multi-layer films, which plays an important role on the reliability, serving life and external quantum efficiency of electronic devices.In this thesis, the integrated analytical system of electron backscatter diffraction (EBSD) equipped in a high resolution TFE-SEM to measure the microstructure, micro-texture and micro-zone stress/strain character of metallic system in microelectronic devices and epitaxial system in semiconductor. The correlations between the microstructure and the preparing technology of semiconductor materials and devices, the influence of failure and reliability of devices were investigated.The analysis and optimization on the collecting parameter and indexing parameter of Kikuchi pattern were also carried out in this research. The spatial resolution of TSL EBSD system was measured and evaluated to be about 30nm⁴0nm. The Al interconnects in VLSI and Cu interconnects in ULSI were investigated with EBSD. The micro-texture and distribution of micro-zone stress in GaN/sapphire system and GaAs/AlGaAs system were studied.The distribution of grains structure, orientation, size and shape in Al interconnects prepared by conventional reactive ion etching technology (RIE) and Cu interconnects prepared by Damascus technology were investigated. Results indicate: the average grain size of 2μm width deposited Al interconnects and Cu interconnects are 120nm and 60⁷0nm, respectively. The grains in Al interconnects increased to 180nm after 2.5hr annealing treatment at 300℃and drived to uniformity.The grains in Cu interconnects increased from 30⁴0nm to 80⁹0nm, while the width increased from 0.5μm to 4μm. After annealing at 350℃, the grains grows up with a bamboo-like structure, which decreases the diffusion of metal ion along the grain boundaries and increases the MTF and Qa of interconnects. There are very strong (111) fiber texture in the 2μm width deposited Al interconnects and gets further developing after annealing. The (111) preferred orientation was weakened by the grains along the side wall of flute in Damascus structure and twin crystals.Σ1 grain boundaries reach 16.4% in Al interconnects and increases to 18.7% with the increasing of annealing temperature.Σ3 grain boundaries reach 79.5% in Cu interconnects. Twin crystal boundaries and low angle grain boundaries, which are low-energy stable boundaries, and they are propitious to enhance the ability to the resist elctromigration of interconnects. In addition, the IQ (Image Quality) of Kikuchi pattern was adopted as the strain sensitive parameters. The average IQ value and the IQ₍₁₁₁₎,IQ(110) and IQ₍₁₀₀₎ of (111), (100) and (110) orientation grains grown after annealing, which indicates that annealing can release the residual stress in Al interconnects. IQ₍₁₁₁₎ is bigger than IQ₍₁₀₀₎ and IQ(110) indicating the difference of elastic ratio among the different crystal orientations. In the epitaxial system of GaN/sapphire and GaAs/AlGaAs, the parameters of IQ value, Hough peak value and low angle misorientation etc. as strain sensitive parameters, were used to characterize the distortion of lattice and the distribution of micro-zone stress. Results indicate that: the sharpness of Kikuchi bands was reduced near the Buffer layer in the GaN structure and the lowest IQ value and Hough peak value were obtained. The sharpness of Kikuchi bands, IQ value and Hough peak value increased gradually with increasing distance from the Buffer layer. The statistic of IQ value and Hough peak value of the distorted region indicate that there is a 200nm⁷00nm elastically distorted region around the Buffer layer. The dislocation density near Buffer layer was calculated to be 8×10¹¹/m². The misorientation and the lattice mismatch between GaN epilayer and sapphire substrate were determined to be 30°and 16%, respectively. With thestress released by 20～30nm Buffer layer, the quality of crystal grown by epitaxial way was enhance and the the external quantum efficiency of light emitting diode in the active region was ensured.In the epitaxial system of Multi-layer increment of GaAs/AlGaAs, the lattice mismatch was measured to be 0.14% and the IQ value in GaAs layer along the epitaxially grown direction decreased gradually 29%. The results indicate that the defects were accumulated in the epitaxial structure. Due to the low diffraction intensity the IQ value can't be obtained, which indicate that IQ value can reflect the difference of diffraction intensity caused by the difference of dispersion factor.The Fast Fourier Transform (FFT) and Inverse Fast Fourier Transform (IFFT) were adopted to calculate the Kikuchi patterns including both distorted region and non-distorted region to obtain the comparison of diffraction intensity. The small crystal lattice shift from the distorted region to non-distorted region can be calculated using the cross-correlation function of Kikuchi pattern, the small shifts in the zone axis position about the distorted region relative to the non-distorted region can be obtained in the GaN/sapphire structure.