FORMATION OF RADIATION-DISTURBED LAYER IN Al/SiO2/n-Si STRUCTURES IRRADIATED WITH HELIUM IONS WITH ENERGY 5 MeV

This paper presents the change in the volt-farad characteristics of the Al/SiO2/n-Si structure irradiated with helium ions with the energy of 5 MeV in the frequencies of 1, 10, 100, and 1000 kHz. The voltage dependence of the capacitance and the frequency dependence of the dissolution angle are measured on an LCR Agilent E4980A and Agilent 4285A meter. The hodograph of the irradiated structure shows that there is a formation of a quasi-continuous radiation-disturbed layer at a fluence of 1012 cm–2 with U < –7 V and 1013 cm–2 with U < –20 V, which enhances the speed of charged particles, thereby increasing the reverse current in the irradiated structure.


Introduction
Over the past decades, the study of metal-oxidesemiconductor (MOS) structures has been of great importance to the development of integrated circuit technologies. The motivation behind the use of silicon dioxide has been the fabrication of stable and high-performance MOS devices and integrated circuits. The silicon dioxide that has an electrically isolated transistor gate from the silicon channel is a key material for the digital revolution with today's GHz microprocessors [1].
However, earlier attempts to fabricate MOS devices were unsuccessful because of the lack of controllable and stable surface [2]. Brown [3] and Garrett and Brattain [4] formulated the theoretical modeling of surface band bending and its consequences. This theoretical background leads to the identification of radiation-induced changes in MOS structures [5] by using capacitive spectroscopy. Especially, the irradiation by helium ions is one of the widely used methods to enhance high-speed semiconductor devices [6].
In this paper, we study the changes of voltfarad characteristics on Al/SiO2/n-Si structures, such as CMOS structures by using the silicon dioxide, irradiated with helium ions that are provided by OAO "INTEGRAL" of Ruhr University (Bochum, Germany).

Experiment
Al/SiO2/n-Si structures are manufactured at OAO

Results and discussion
Fig . 1 shows the volt-farad characteristics of the source structure (vir) and the structures irradiated with helium ions. It can be seen that there is a change not only in the flat bands' voltage but also in the volt-farad characteristic on the irradiated structures. The voltage of the flat regions is shifted to the negative area, which is related to the local charges accumulation in the dielectric [11,12]. The changes in the C-V characteristics can be related to the charge trapping in the bulk of the oxide layer and in the silicon-oxide interface and how the charge trapped can be sensed and actuated [13]. The change in capacitance according to the U voltage of the irradiated structures increases significantly (compared with the source structure). This is due to the influence of local charges on the surface state [5]. Compared with the source structure, the volt-farad characteristics of irradiated structures have a smaller capacitance value in the reverse region.
In Fig. 1 SiO2 [15]. The increase in capacitance via decreasing frequencies is attributed to the existence of the surface states [16]. These capacitance change characteristics could be consistently interpreted by the voltage-driven oxygen ion migration between metal and the semiconductor layers that can alter the dielectric permittivity and induce the gate depletion [17].  Fig. 2a and Fig. 2b). At F = 10 12 cm -2 , the hodograph has two semi-circles ( Fig. 2c) with voltage U < -7 V; similarly, for F = 10 13 cm -2 , the hodograph has two semi-circles ( Fig. 2d) with voltage U < -20 V.
Therefore, we are able to claim that the Al/SiO2/n-Si structure irradiated with ions F = 10 12 ÷10 13 cm -2 at reversed voltage has a multilayer structure. This structure includes a space charge region and a quasi-continuous radiation-disturbed layer. If a circle with low frequency is determined with a space charge region, the remaining circle corresponding to the high frequency forms a highly resistive quasi-continuous radiationdisturbed layer.