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https://doi.org/10.29013/ESR-22-1.2-36-39
Utamuradova Sharifa Bekmuradovna, Doctor of Physical and Mathematical Sciences, director of Research Institute of semiconductor physics and microelectronics E-mail: [email protected] Rakhmanov Dilmurod Abdujabbor ugli, PhD student of Research Institute of semiconductor physics and microelectronics E-mail: [email protected]
STUDY OF THE INFLUENCE OF PROTON IRRADIATION ON SILICON STRUCTURES USING RAMAN SPECTROSCOPY
Abstract. In this work, we will study the effect of irradiation with protons on silicon structures using Raman spectroscopy. Usually using Raman spectroscopy we can determine the impurity composition of the samples and their intensities. In the article, we will investigate the change in intensity before and after irradiation with protons.
Keywords: Semiconductor, silicon, proton irradiation, Raman spectroscopy, intensity. Introduction troscopy is a type of spectroscopy, which is based
Irradiation with low-energy protons leads to on the ability of the studied systems (molecules) to a change in the electrophysical, optical and other inelastic (Raman, or Raman) scattering of mono-
properties of the surface region of semiconductor structures, which creates additional possibilities for modifying semiconductor devices [1].
Modification of semiconductor materials, directed change of their properties, by beams of light ions, in particular protons, is one of the most promising and rapidly developing physical and technological methods in recent years. Interest in protons is due to the wide and controllable range of processed material depths (from 0.1 ^m to 1 mm) and the absence of complex radiation complexes with a high annealing temperature after proton irradiation. The main three factors influencing the change in the properties of semiconductors after proton irradiation are: a change in the electrophysical properties of semiconductors, radiation defect formation, and the accumulation of hydrogen atoms [2].
To study the effect of proton irradiation on silicon, we used Raman spectroscopy. Raman spec-
chromatic light. The essence of the method lies in the fact that a beam with a certain wavelength is passed through a sample of the investigated substance, which, upon contact with the sample, is scattered. The resulting rays are collected with a lens in one beam and passed through a light filter that separates weak (0.001% intensity) Raman rays from more intense (99.999%) Rayleigh rays. "Pure" Raman beams are amplified and directed to a detector that records their frequency.
Lasers on such working bodies as Ar + (351.1-514.5 nm), Kr + (337.4-676.4 nm), and He-Ne (632.8 nm) are mainly used as a source of exciting light. In recent years, Nd: YAG lasers, diodes and excimer lasers for UV resonance Raman spectroscopy have also been introduced. From the time of the appearance of spectroscopy to the discovery of the laser (1960 s), the only source of excitation was mercury lamps with an additional light filter. In or-
der to achieve the required power, special amplifiers were included in the set of such lamps [3].
In this work, we will study the effect of irradiation with protons on silicon structures using Raman spectroscopy. Usually using Raman spectroscopy we can determine the impurity composition of the samples and their intensities. In the article, we will investigate the change in intensity before and after investing with protons.
Experimental part
For the experiments, we used n- and p-type silicon, grown by the Czochralski method with a resistivity of 0.5 * 50 Ohm cm. The original silicon was doped with phosphorus (n-Si) or boron (p-Si). In this case, the concentration of dopants was 7.3 • 1013 *
* 7.1 • 1015 cm-3 in n-Si and 4.7 • 1014 * 4.3 • 1016 cm 3 in p-Si [4].
The concentrations of optically active oxygen and carbon in the initial silicon samples of n- and p-type conductivity were, respectively, NOopt ~ 6,2 • 10 17 *
* 1,3 • 10 18 cm-3 and carbon Ncopt = 2 • 10 15 *
* 2 • 10 16 cm-3. The oxygen content NOopt and carbon NCopt were estimated from the IR absorption spectra in the range of wave numbers k = 1100 cm-1 (oxygen band at 9.1 ^m) and k = 610 cm-1 (carbon band at 16.4 ^m), measured on a SpecordIR-75 infrared
spectrophotometer in a two-beam scheme at 300 K [5]. As a control (reference) sample, we used polished oxygen-free silicon of the same thickness as the sample under study, with NOopt < 1016 cm3, NCopt = = 5 • 1015 cm-3.
These samples were initially cut out to dimensions of1.5 x 7 x 13 mm and subjected to mechanical processing, that is, they were ground sequentially with carborundum powders M-17, M-14, M-10, M-7, M-5. After these operations, the samples were defatted in toluene, washed in a stream of deionized water, and etched.
The finished samples were irradiated with a proton with an energy of 300 keV and a current of 1 ^A. The irradiation time was different, that is, 10, 20, 30 minutes (the intensity ofthe beams is 10 12 cm-2s-1).
Irradiation with protons was carried out at the unique object of the SOCOL EG-2 electrostatic accelerator at the Research Institute of Physics Semiconductors and Microelectronics.
Results and its discussion
In the Raman spectrum, the x axis is called the Raman shift and this denotes the wavelength that affects the sample. The y axis denotes the intensity of impurities in the samples. Figure 1. the Raman spectrum of the starting silicon n-Si is shown.
600 000 1000 1200 Raman shift (cm-1)
Figure 1. Raman spectrum of initial n-Si silicon
We can see that there is one large peak (523) and two small peaks (301, 935-990). The peaks located at 301, 523, and 935-990 cm-1 are introduced from the silicon substrate, which is compared with the Raman spectrum of a silicon substrate [6]. Peak 523 is the backbone of the silicon peak. Vibrations of P-O in equivalent tetrahedra [PO4] give the main
Raman band at 972 cm - 1 [7]. That is, these peaks denote the original silicon (doped with nothing) n-Si. In this sample, the value of the intensity of the peak 523 is equal to almost 1400. And now we will discuss the Romanov spectra of silicon samples irradiated with 300 keV energy, 1 ^A current with various doses.
1600 -I 1400 1200 -|
CO
_£> 1000 -
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800 600 -\ 400 200 0
o o
>
2000 -
1500 -
1000 -
500 -
0\ r-o\
M
200 400 S00 800 1000 1200 1400 1600
200 400
600
800 1000 1200 1400 1600
Raman shift(cm-l)
a)
Raman shift(cm-l)
b)
c)
Figure 2. Raman spectrum of silicon n-Si, irradiated with protons: a) irradiated for 10 minutes; b) irradiated for 20 minutes; c) irradiated for 30 minutes (intensity of beams 10 12 cm -2s -1)
After irradiation with protons for 10 minutes, the Raman spectrum did not change along the x axis, because the impurity composition of the sample did not change after irradiation. But the intensity of the 523 peak is increased to 1500 (Fig. 2 a).
After irradiation for 20 and 30 minutes, the location of the peaks along the x axis also did not change due to the unchanged impurity composition (Fig. 2 a, 2 b). But, the intensity of point 523 has increased in large numbers. The intensity of the sample that was
irradiated for 20 minutes is increased to 1979. The intensity of the sample that is irradiated for 30 minutes is increased to 2020. This means that the intensity ofthe beam is directly proportional to the dose of protons.
Conclusion
We know that the intensity is the average power carried by the wave through a unit area located perpendicular to the direction of wave propagation, the energy flux density, that is, the amount of energy
passing per unit of time through a unit of area. We also know that power is always directly proportional to resistance. We have seen that when the dose of irradiation of the sample was increased, the intensity of the beam in Raman spectroscopy also increased. This means that the radiation dose changes the electrical resistance of the silicon samples. How many doses you irradiate, so much the resistivity of silicon samples increases.
References:
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