ICMCTF2018 Session F2-3: HiPIMS, Pulsed Plasmas and Energetic Deposition

This study investigates the physical analysis and electrical characteristics for amorphous tungsten and zinc doped indium oxide thin film transistor (a-InWZnO TFT) with a high-k gate insulator, which is applied by fluorine based mixing plasma treatment. Compared with the traditional InGaZnO TFT, the tungsten dopant was proposed as excellent carrier suppressor, which may improve the reliability significantly. However, the carrier mobility was also slightly inhibited by the dopant. In order to achieve good stability and high carrier concentration simultaneously, the fluorine based mixing plasma treatment was introduced in the device process. The fluorine plasma is used as a method to passivate carrier traps within the channel or at the channel/dielectric interface, which can effectively improve the channel conductivity. In addition to that, the oxygen vacancies are also increased in the back channel region by only fluorine plasma treatment. This may result that a extreme high carrier mobility at the back channel surface which can't be control by a reasonable gate bias. With a mixing plasma process, this phenomenon can be suppressed. Furthermore, a high-k gate insulator is applied for improving the ability of gate control. In this report, the devices with CF₄ + N₂O plasma treatment show a high field-effect mobility of ∼ 25 cm²/V.s, a high On/Off current ratio of ∼ 6×10⁶ and a small subthreshold swing of 0.1 V/decade for a best interface quality for all samples. This research proposes that the fluorine based mixing plasma treatment may be an effective approach to improve the interface quality for novel metal oxide TFT fabrication.

Techniques like the intense pulsed electron beams (IPEB) or intense pulsed ion beams (IPIB) generally induce surface melting, evaporation followed by rapid solidification and quenching which are accompanied by the formation of stress waves. As a result, surface/near surface properties such as corrosion and wear resistances can be improved while the generation of structural defects such as vacancies and dislocation loops also affect the depth of the samples and can lead to sub-surface hardening. While the improved wear resistance and corrosion resistance have been attributed to several complementary factors (surface hardening, nanostructure formation) the mechanisms responsible for the deep hardening are much less understood.

In the case of IPEB, the large pulse duration (about 800 ns under High Current Pulsed Electron Beam) and, accordingly, the low rate of energy input, does not provide with the formation of the dynamic stress wave and the increase in dislocation density was entirely provided by the action of the quasi-static thermal stresses. In their modelling approach, Quin et al. [1] suggested that the subsurface initial melting that is associated with the specific energy distribution of the electron beam could create an additional source of plastic deformation via the recoil impulses that are generated as a consequence of crater eruptions.

To the authors knowledge however, there is no experimental work that has been carried so far to undoubtedly verify the electiveness of the formation of craters on hardening the surface and subsurface of HCPEB treated samples. The aim of the present paper is to investigate experimentally the contribution of the potential crater bursts on modifying the deep hardening phenomena. To this end, the HCPEB technique has been applied under similar processing conditions on two stainless steels of very close chemistry but having different potential for crater formation.

[1] Qin, Y ; Dong, C ; Song, ZF; Hao, SZ; Me XX; Li, JA; Wang, XG; Zou, JX; Grosdidier, T, JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A, 27, Pages: 430-435, MAY 2009