Numerical Simulation Of φ300mm CZ Si Crystal Microdefects

The requirement of monocrystalline silicon material is more and more stringent as a result of the rapid growth of ULSI, "Large diameter, free of defects" has become the development trend of silicon materials. Large diameter silicon ingot greatly reduces the production cost of IC manufacturing, but the micro-defects in large diameter CZ Si affect the metal-oxide-semiconductor (MOS) device gate oxide integrity (GOI), thus affecting the electrical properties of semiconductor devices. If micro-defects in silicon can not be effectively controlled, the yield of IC will be badly affected. In particular, as IC feature size continuing to be decreased, this defect has seriously affected the development of the semiconductor industry. So controlling and eliminating CZ Si micro-defects has been the most critical issue for silicon material development.In this paper, the finite element analysis software Femag-CZ is used for numerical analysis of micro-defects concentration and distribution ofφ300mm CZ Si crystal under the conditions of CUSP magnetic field, different crystal growth velocity and different heat shield position. Phenomenon as CUSP magnetic field strength, heat conduction,radiation and gas, melt convection are considered. The finite element analysis method is used, the adopted governing equations for micro-defect calculation are the first law of thermodynamics that energy conservation law, and momentum conservation law.During the process of cp300mm CZ Si crystal growth, the oxygen content of the crystal show a certain regularity with the CUSP magnetic field current coils distance and radius changing. Melt convection has a strong impact on the oxygen content of silicon crystal. Keep the CUSP radial component in the intersection of CUSP and the crucible melt interface constant, adjust CUSP magnetic field current coils distance and radius. With the increase of coils distance and radius, the radial magnetic field strength in melt increases gradually, causing the axial melt convection velocity decreases, the melt containing more oxygen content from the bottom of crucible decreases, so the oxygen concentration in melt crystal interface decreases. Application of CUSP magnetic field, in order to maintain a certain distribution of magnetic field strength in melt, along with current coils distance and radius increase, the applied current is also gradually increased. Compared with the increase of the current coils distance, the increase of coils radius needs a larger current, and then energy consumption is larger, increasing production cost, so the way of increasing coils radius should not be used.CUSP magnetic field coils distance has a significant impact on oxygen concentration in silicon crystal. Keep the applied current constant, with the coils distance increasing, the oxygen concentration in silicon crystal firstly decreases, and then increases, simultaneously, the uniformity of oxygen concentration also show the same variation.The micro-defects distribution in silicon, vacancy type defects are in the central region of crystal, interstitial type defects are near the crystal edge. During the cooling process of silicon crystal, the micro-defects related to vacancy will appear in the center of crystal, such as COPs. With the crystal growth rate increasing, the micro-defects region based on vacancy increases, micro-defects region based on interstitial atoms decreases. At the same time, the concentration of interstitial atoms show decreasing trend. Increasing the speed of crystal growth, the CⅠ-CⅤ=0 region in silicon crystal firstly increased, and then decreased. (CⅠis the concentration of interstitial atoms, CⅤis the concentration of vacancy). This is closely related with the ratio of crystal growth rate Vpul and m-c interface instantaneous axial temperature gradient G. With the increase of crystal pulling rate, V/G value in the critical range, along m-c interface radial distribution show a maximum value and then decrease, so increasing the crystal pulling speed, the CⅠ-CⅤ=0 region in crystal expands and then reduces.With the crystal growth rate increasing, the m-c interface shape is changed significantly, the bending rate increases, the interface is more convex to crystal, melt convection and temperature fluctuation will intensively affect crystal growth. This is not conducive to the crystal growth.Increasing the distance between heat shield and melt free surface properly, m-c interface axial and radial temperature gradient is reduced, so the interface shape becomes flat. Simultaneously, the transformation of V/G value improves the micro-defects distribution in silicon crystal. The vacancy type defect region increases, interstitial type defect region decreases. Increasing the distance between heat shield and melt free surface, the power of graphite heater decreases, thus the temperature of quartz crucible decreases, crucible and molten silicon reaction velocity is reduced, producing less SiO, so the oxygen content in crystal is reduced.