Selective vapor-liquid-solid growth of needle arrays by hotwire chemical vapor deposition with low substrate temperature

We present the technology for low substrate temperature (∼400°C) growth of high-density, defect-free (without kinks and branches), unidirectional arrays of Si needles with positive profiles and sub-μm tips using selective vapor-liquid-solid (VLS) mechanism. The low substrate temperature allows possible integration with onchip CMOS circuitry or biomaterials with minimal thermal damage. The effect of processing parameters on needle growth modes is analyzed. Needles with similar characteristics have been successfully grown under the optimized conditions on Si〈111〉, Si〈100〉 and polysilicon on insulator substrates. We envision these needle arrays (6–8µm tall, sub-μm tips) as high density electrodes of an integrated retinal implant.