Impact of Carbon-Doped Ｉn-Si-O Channel for Future TFT

Introduction

Recently, thin-film transistor (TFT) with InO_x-based metal oxide semiconductors such as Ga-In-Zn-O (GIZO) [1], In-Ga-O [2], 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 (V_O) formation, which destabilize the electronic properties. We have previously investigated In-Ti-O [7], In-W-O [7-9], and In-Si-O [7, 10] systems to suppress V_Obecause 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) [11].

Although C-O has the highest bond dissociated energies of 1076 kJ/mol [11], CO and CO₂ are gases at standard ambient temperature and pressure. So we tried to fabricate carbon-doped In-Si-O (In_1-xSi_xOC) semiconductor films using co-sputtering method with SiC and In₂O₃targets.

In this paper, we investigated electrical and physical properties of In_1-xSi_xOC films by the X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy (AFM) and hall measurement.

Experiment

A 100-nm-thick thermal SiO₂ film was formed on a p-type Si substrate. Next, 50-nm-thick In_1-xSi_xOC 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 (P_O2 = 0 ~ 0.08 Pa) at room temperature. The Si content (x=0.12 ~ 0.32) in In_1-xSi_xOC 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 In_1-xSi_xOC films were examined by XPS, XRD and AFM measurements, respectively.

Results and Discussion

Characteristics of the In_1-xSi_xOC film

Figure 1 shows AFM images of as-grown, 250 °C and 600 °C annealed In_0.8Si_0.2OC films. The root-mean-square (RMS) values of all samples show small values of 0.43~0.61 nm. We found that the In_0.8Si_0.2OC 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 In_0.8Si_0.2OC films. This indicates that carbon sufficiently introduced into In-Si-O films using co-sputtering method with SiC target.

Electrical properties of the In_1-xSi_xOC film

Figure 2 shows change of hall mobility and carrier concentration as a function of Si content in the In_1-xSi_xOC films. Two kinds of the In_1-xSi_xOC films were deposited under P_O2 0 and 0.08 Pa, and subsequently annealed at 250 °C. The mobility of the In_1-xSi_xO and In_1-xSi_xOC films fabricated under the same P_O2 = 0.08 Pa show a similar behavior. On the other hand, the mobility of the In_0.88Si_0.12OC and In_0.8Si_0.2OC films fabricated under P_O2 = 0 Pa shows about 5 - 8 times smaller than another one, respectively. Furthermore, the mobility and carrier concentration of both In_1-xSi_xOC films decrease as Si content increases. This suggests that the V_O formation into the In_1-xSi_xOC films must be strongly influenced by the oxygen pressure during sputtering.

Conclusions

We studied characteristics of the In_1-xSi_xOC films, which fabricated by co-sputtering method using SiC and In₂O₃ targets. We found that the In_1-xSi_xOC film had an amorphous structure, smooth surface morphology and Si-C bond formation. The In_1-xSi_xOC film is one of promising candidate as metal oxide channel materials because of high hall mobility of about 20.

References

[1] K. Nomura et al., Nature 432, 488 (2004).

[2] K. Ebata et al., Appl. Phys. Express 5, 011102 (2012).

[3] T. Miyasako et al., Appl. Phys. Lett. 86, 162902 (2005).

[4] S. Y. Park et al., Appl. Phys. Lett. 100, 162108 (2012).

[5] N. L. Dehuff et al., J. Appl. Phys. 97, 064505 (2005).

[6] P. Barquinha et al., J. Non-Cryst. Solids 352, 1749 (2006).

[7] S. Aikawa et al., Appl. Phys. Lett. 103, 172105 (2013).

[8] S. Aikawa et al., Appl. Phys. Lett. 102, 102101 (2013).

[9] T. Kizu et al., Appl. Phys. Lett. 104, 152103 (2014).

[10] N. Mitoma et al., Appl. Phys. Lett. 104, 102103 (2014).

[11] 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).

[12] S. Parthiban et al., RSC Adv. 4,  21958 (2014).