Measurements of Liquid Silicon Resistivity on Silicon Microwires
- PDF / 729,067 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 35 Downloads / 205 Views
1178-AA06-06
Measurements of Liquid Silicon Resistivity on Silicon Microwires Gokhan Bakan, Kadir Cil, Adam Cywar, Helena Silva, Ali Gokirmak Electrical & Computer Engineering, University of Connecticut, 371 Fairfield Way Unit-2157, Storrs, CT 06269, USA E-mail: [email protected], [email protected] ABSTRACT Nanocrystalline silicon microwires are self-heated through microsecond voltage pulses. Nonlinear changes in current level are observed during the voltage pulse, which end with melting of the microwires. Liquid silicon resistivity is extracted as 65.9 ± 6.1 μFPfrom the minimum resistance of the wire during the voltage pulse. The extracted resistivity is in good agreement with previously reported values. INTRODUCTION Interest in achieving high mobility thin-film transistors (TFTs)1 for large area electronics2 has motivated studies on crystallization of amorphous and polycrystalline silicon for several decades. Most of the crystallization techniques such as sequential lateral solidification using an excimer laser3, rapid melting and growth from melt of large patterned-films using YAG laser4 or Joule heating through chromium heaters5, or melting and crystallization of silicon microwires through rapid self-heating6, 7 involve growth from the melt8 which has increased the interest in the properties of molten silicon. Liquid silicon properties such as electrical resistivity, thermopower, density and viscosity have been reported since 1960s. Electrical resistivity measurements have been performed using the electrodeless method in a rotating magnetic field9 or four-point probe method using a macroscopic volume of molten silicon10, 11. Material selection for container and electrical contacts is very important for accuracy and reliability of the measurements in these setups due to the high melting temperature of silicon (1420 C)9. In this work, liquid silicon resistivity is obtained by performing wafer-level measurements on nanocrystalline silicon (nc-Si) microwires with various dimensions through microsecond voltage pulse induced self-heating. Fabrication Microwires are patterned on a nc-Si film which is deposited in a low pressure chemical vapor deposition system at 560 C with high-level in-situ boron doping (~5x1020 cm-3)12 on a thermally oxidized Si substrate. Si wires have design widths (WD) ranging from 300 to 500 nm with 10 nm increments and lengths (L) from 0.5 to 5.5 μm with 0.5 μm increments. Wires are formed using photolithography and reactive ion etching. Wire lengths (L) match well with the design dimensions. Film thickness (t) at the center and the edge of the wafer is measured as 123 and 130 nm, respectively, using optical interferometry and as 128 ± 9 nm on a Si contact pad using atomic force microscopy (AFM). AFM result for t is used to calculate Si resistivity in both solid and liquid phases. Ti/Ni (250/60 nm) electrodes are formed by photolithography, metal
Figure 1. (a) An as-fabricated, 3 ȝP long, p-type, nc-Si wire. (b) Schematic of the experimental setup. RM and RC are resistance of me
Data Loading...
