Impact of Carbon-Doped Ｉn-Si-O Channel for Future TFT
Recently, thin-film transistor (TFT) with InOx-based metal oxide semiconductors such as Ga-In-Zn-O (GIZO) , In-Ga-O , In-Sn-O [3, 4], and In-Zn-O [5, 6] have attracted attention as high-speed switches for next-generation flat-panel display. However it remains a big issue of the anomalous oxygen vacancies (VO) formation, which destabilize the electronic properties. We have previously investigated In-Ti-O , In-W-O [7-9], and In-Si-O [7, 10] systems to suppress VObecause of high bond dissociated energies between each element and oxygen such as Ti-O (667 kJ/mol), W-O (720 kJ/mol), and Si-O (799 kJ/mol) .
Although C-O has the highest bond dissociated energies of 1076 kJ/mol , CO and CO2 are gases at standard ambient temperature and pressure. So we tried to fabricate carbon-doped In-Si-O (In1-xSixOC) semiconductor films using co-sputtering method with SiC and In2O3targets.
In this paper, we investigated electrical and physical properties of In1-xSixOC films by the X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy (AFM) and hall measurement.
A 100-nm-thick thermal SiO2 film was formed on a p-type Si substrate. Next, 50-nm-thick In1-xSixOC films were deposited on SiO2 film at room temperature by co-sputtering using In2O3 and SiC target under an Ar/O2 atmosphere at 0.2 Pa with various oxygen partial pressures (PO2 = 0 ~ 0.08 Pa) at room temperature. The Si content (x=0.12 ~ 0.32) in In1-xSixOC films was controlled by changing DC the sputtering power of each target. Then, the post deposition annealing was performed at 250 ~ 600 °C for 1h in air. Finally, Au (100 nm)/ Ti (10 nm) electrodes were deposited by thermal evaporation method for hall measurement.
The carbon content, structure and surface morphology of In1-xSixOC films were examined by XPS, XRD and AFM measurements, respectively.
Results and Discussion
Characteristics of the In1-xSixOC film
Figure 1 shows AFM images of as-grown, 250 °C and 600 °C annealed In0.8Si0.2OC films. The root-mean-square (RMS) values of all samples show small values of 0.43~0.61 nm. We found that the In0.8Si0.2OC films have smooth surface even after annealing at a high temperature (600 °C). We also confirmed that the film was kept to be amorphous structure after annealing at 600 °C by XRD measurement. From the XPS measurement, a large C1s peak was observed due to Si-C bond at around 285 eV in as-grown and 250 °C annealed In0.8Si0.2OC films. This indicates that carbon sufficiently introduced into In-Si-O films using co-sputtering method with SiC target.
Electrical properties of the In1-xSixOC film
Figure 2 shows change of hall mobility and carrier concentration as a function of Si content in the In1-xSixOC films. Two kinds of the In1-xSixOC films were deposited under PO2 0 and 0.08 Pa, and subsequently annealed at 250 °C. The mobility of the In1-xSixO and In1-xSixOC films fabricated under the same PO2 = 0.08 Pa show a similar behavior. On the other hand, the mobility of the In0.88Si0.12OC and In0.8Si0.2OC films fabricated under PO2 = 0 Pa shows about 5 - 8 times smaller than another one, respectively. Furthermore, the mobility and carrier concentration of both In1-xSixOC films decrease as Si content increases. This suggests that the VO formation into the In1-xSixOC films must be strongly influenced by the oxygen pressure during sputtering.
We studied characteristics of the In1-xSixOC films, which fabricated by co-sputtering method using SiC and In2O3 targets. We found that the In1-xSixOC film had an amorphous structure, smooth surface morphology and Si-C bond formation. The In1-xSixOC film is one of promising candidate as metal oxide channel materials because of high hall mobility of about 20.
 K. Nomura et al., Nature 432, 488 (2004).
 K. Ebata et al., Appl. Phys. Express 5, 011102 (2012).
 T. Miyasako et al., Appl. Phys. Lett. 86, 162902 (2005).
 S. Y. Park et al., Appl. Phys. Lett. 100, 162108 (2012).
 N. L. Dehuff et al., J. Appl. Phys. 97, 064505 (2005).
 P. Barquinha et al., J. Non-Cryst. Solids 352, 1749 (2006).
 S. Aikawa et al., Appl. Phys. Lett. 103, 172105 (2013).
 S. Aikawa et al., Appl. Phys. Lett. 102, 102101 (2013).
 T. Kizu et al., Appl. Phys. Lett. 104, 152103 (2014).
 N. Mitoma et al., Appl. Phys. Lett. 104, 102103 (2014).
 Y. R. Luo, “Bond dissociation energies,” in CRC Handbook of Chemistry and Physics, 90th ed.,edited by D. R. Lide (CRC Press/Taylor and Francis, Boca Raton, 2009).