| The standard Czochralski (CZ) method, used for almost all the silicon crystals grown for microelectronics applications, has reached an evolutionary plateau because of the underlying physics of the problem. As the process is scaled up, the melt height increases and the flow within the melt can become oscillatory and turbulent, creating inhomogenities within the crystal. To overcome many of the shortcomings of the CZ method, a polysilicon pellets-feed continuous CZ (CCZ) process has been proposed and investigated. By reducing the melt height and keeping it fixed, this novel process can suppress many kinds of unsteady kinetics and inhomogenities, and reduce the cost of crystal growth. Impurity build-up, oxygen incorporation and crystal resistivity can also be better controlled by continuously charging the polysilicon and dopants. The key to this process is high purity 1 mm diameter polysilicon spheres fed by a non-vibratory feeder. An analytical and numerical investigation of the melting of both fully and partially submerged spheres show that the highly subcooled pellet feed will melt in approximately one second, suitable for this CCZ method.; Two- and three-dimensional numerical simulations including the effects of buoyancy, surface tension and crucible and crystal rotation have been performed. These simulations show that convection mode changes radically as melt height is reduced, and that varying the crucible shape may be an effective means of reducing and suppressing oscillations. This phenomena is strongly dependent on the boundary condition at the melt free surface and crucible bottom. The influence of the melting pellet heat sink upon the flow has also been investigated, and illustrate that feed placement is critical for this process. The three-dimensional results indicate that the 3D effects are important and must be considered for realistic CZ or CCZ modeling.; Four sets of CCZ experiments were performed in a modified industrial crystal puller. The process is found to be highly dependent on the surface melt temperature and crucible rotation rate. Long-term CCZ growth has been achieved, which indicates that the proposed technique can be successfully used for continuous production of silicon crystals, and is commercially viable. |
