Background

Highly pure semiconductor crystals like silicon, germanium or gallium arsenide are the basis of electronic circuits and microprocessors, light-emitting diodes, lasers and mobile phones. Without these crystals our modern technology simply would not work. Therefore, crystal growth of semiconductor
materials on a large scale and with high quality is an important challenge.

In commercial production, these crystals are usually grown from the melt. In this process, when the semiconducting raw material is melted in a crucible, so-called thermal convections are induced by the melt flow. These convections may lead to defects or inhomogeneities in the grown crystal.

On the other hand, control of the thermal convection allows to enhance homogeneity and to reduce tension in the grown crystal. Therefore, it provides a convenient way to improve the crystalline quality significantly.

Researchers at the IKZ had the idea to change the geometry of the graphite heater used to generate heat for the melting process. This modification allows the simultaneous generation of heat (by direct current) and traveling magnetic fields by using alternating current for magnetic field induction. This heater-magnet module is the key component of the KRISTMAG concept. KRISTMAG is applicable for all materials with electrically conducting melts, since it uses the Lorentz forces induced by the magnetic field.

Variation of the applied alternating currents allows to control the magnetic field and, hence, the induced Lorentz forces. Therefore, it is possible to influence the phase boundary, i.e. to flatten its surface significantly, which leads to a higher structural perfection of the growing crystal. In addition, a more homogenous macroscopic dopant distribution can be achieved, further improving the crystalline quality.

The technical testing of the process has been completed successfully and a transfer of the technology into research and industry has already begun.

Advantages of using KRISTMAG in crystal growth

• Faster removal of heat of crystallisation from the growth phase boundary
• Efficient utilization of the crystal growth equipment by higher growth speed
• Higher homogeneity and structural perfection of the grown crystals
• Energy, cost and space savings due to integrated magnetic field generators into the heaters
• Possibility to retrofit any growth plants with the KRISTMAG-technology
• Adaptation to different growth processes feasible

The IKZ offers the following services

• Process development for growth technologies using traveling magnetic fields
• Equipment development, design and modeling for customer geometries
• Modeling of temperature, tension, Lorentz force density and flow fields
• (2D and 3D) when using traveling magnetic fields
• Control of growth results - real structure investigations of crystal properties grown in magnetic fields

We would be pleased to advice you on the use of the KRISTMAG-technology, also in existing growth plants. On request, we can prepare feasibility studies for technical realization including an estimation of the effort. We also like to offer our expertise for joint research and development projects.

Selected patents

• Verfahren zur gerichteten Kristallisation von Ingots. / DE 102011076860
• Device for producing crystals from electroconductive melts. / DE 102007028547, EP 2162570, WO 2008155138
• Crystallization system and crystallization process for producing a block from a material with an electrically conductive molten mass. / DE 102010041061, WO 2012038432
• Vorrichtung und Verfahren zur Herstellung von Kristallen aus elektrisch leitenden Schmelzen. / DE 102007028548
• Verfahren und Vorrichtung zur gerichteten Kristallisation von Kristallen aus elektrisch leitenden Schmelzen. / DE 102012204313
• Verfahren zur Herstellung von Kristallblöcken hoher Reinheit. / DE 102010028173
• Method for the solidification of a non-metal melt. / DE 102008059521, EP 2370617, US 20110309555, WO 2010060802