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Inductive Type Impedance of Mo/n-Si Barrier Structures Irradiated with Alpha Particles
N.A. Poklonski1, A.I. Kovalev1, K.V. Usenko1, E.A. Ermakova1,2, N.I. Gorbachuk1, S.B. Lastovski2
'Belarusian State University, Nezavisimosti Ave., 4, Minsk 220030, Belarus
2SSPA "Scientific-Practical Materials Research Centre of NAS of Belarus ", P. Brovki str., '9, Minsk 220072, Belarus
Received '0.02.2023
Accepted for publication '4.03.2023
In silicon microelectronics, flat metal spirals are formed to create an integrated inductance. However, the maximum specific inductance of such spirals at low frequencies is limited to a value of the order of tens of microhenries per square centimeter. Gyrators, devices based on operational amplifiers with approximately the same specific inductance as spirals, are also used. Despite the fact that such solutions have been introduced into the production of integrated circuits, the task of searching for new elements with high values of specific inductance is relevant. An alternative to coils and gyrators can be the effect of negative differential capacitance (i.e., inductive type impedance), which is observed in barrier structures based on silicon.
The purpose of the work is to study the low-frequency impedance of Schottky diodes (Mo/n-Si) containing defects induced by a-particles irradiation and determination of the parameters of these defects by methods of low-frequency impedance spectroscopy and DLTS (Deep Level Transient Spectroscopy).
Unpackaged Schottky diodes Mo/n-Si (epitaxial layer of 5.5 ^m thickness and resistivity of 1 Ohm-cm) produced by JSC "Integral" are studied. Inductance measurements were carried out on the as manufactured diodes and on the diodes irradiated with alpha particles (the maximum kinetic energy of an a-particle is 5.147 MeV). The impedance of inductive type of the Schottky diodes at the corresponding DC forward current of 10 ^A were measured in the AC frequency range from 20 Hz to 2 MHz. DLTS spectra were used to determine the parameters of radiation-induced defects. It is shown that irradiation of diodes with alpha particles produces three types of radiation-induced defects: A-centers with thermal activation energy of E1 ~ 190 meV, divacancies with activation energies of E2 ~ 230 meV and E3 ~ 410 meV, and EE-centers with activation energy of E4 ~ 440 meV measured relative to the bottom of c-band of silicon.
Keywords: Schottky diode on silicon, negative differential capacitance, alpha irradiation, A-centers, E-centers, divacancies.
DOI: 10.21122/2220-9506-2023-14-1-38-43
Адрес для переписки: Address for correspondence:
Поклонский Н.А. Poklonski N.A.
Белорусский государственный университет, Belarusian State University,
пр-т Независимости, 4, г. Минск 220030, Беларусь Nezavisimosti Ave., 4, Minsk 220030, Belarus
e-mail: poklonski@bsu. by e-mail: poklonski@bsu. by
Для цитирования: For citation:
N.A. Poklonski, A.I. Kovalev, K. V. Usenko, E.A. Ermakova, N.A. Poklonski, A.I. Kovalev, K.V. Usenko, E.A. Ermakova,
N.I. Gorbachuk, S.B. Lastovski. N.I. Gorbachuk, S.B. Lastovski.
Inductive Type Impedance of Mo/n-Si Barrier Structures Inductive Type Impedance of Mo/n-Si Barrier Structures
Irradiated with Alpha Particles. Irradiated with Alpha Particles.
Приборы и методы измерений. Devices and Methods of Measurements.
2023. - Т. 14, № 1. - С. 38-43. 2023, vol. 14, no. 1, pp. 38-43.
DOI: 10.21122/2220-9506-2023-14-1-38-43 DOI: 10.21122/2220-9506-2023-14-1-38-43
Импеданс индуктивного типа барьерных структур Mo/w-Si, облученных альфа-частицами
Н.А. Поклонский1, А.И. Ковалев1, К.В. Усенко1, Е.А. Ермакова1,2, 1 2 Н.И. Горбачук , С.Б. Ластовский
'Белорусский государственный университет, пр-т Независимости, 4, г. Минск 220030, Беларусь 2 ГО «НПЦНАНБеларуси по материаловедению», ул. П. Бровки, 4, г. Минск 220072, Беларусь
Поступила '0.02.2023 Принята к печати '4.03.2023
В кремниевой микроэлектронике для создания интегральной индуктивности формируют плоские металлические спирали. Однако максимальная удельная индуктивность таких спиралей на низких частотах ограничена значением порядка десятков микрогенри на квадратный сантиметр. Используются также гираторы - устройства на основе операционных усилителей, примерно с такой же удельной индуктивностью, как и спирали. Несмотря на то, что такие решения внедрены в производство интегральных микросхем, актуальной является задача поиска новых элементов с большими значениями удельной индуктивности. Альтернативой спиралям и гираторам может стать эффект отрицательной дифференциальной емкости (т. е. импеданса индуктивного типа), наблюдаемый в барьерных структурах на кремнии.
Цель работы - исследование низкочастотного импеданса диодов Шоттки (Mo/«-Si), содержащих радиационные дефекты, создаваемые а-частицами, и определение параметров этих дефектов методами низкочастотной импедансной спектроскопии и спектроскопии DLTS (Deep Level Transient Spectroscopy).
Исследованы бескорпусные диоды Шоттки 5.5КЭФ-1 (Mo/«-Si) производства ОАО «Интеграл». Измерения индуктивности проводились на исходных диодах и на диодах, облученных альфа-частицами (максимальная кинетическая энергия а-частицы 5.147 МэВ). В интервале частот переменного тока от 20 Гц до 2 МГц измерен импеданс индуктивного типа диодов при постоянном прямом токе 10 мкА. Для определения параметров радиационных дефектов измерялись спектры DLTS. Показано, что при облучении диодов Шоттки альфа-частицами образуется три типа радиационных дефектов: Л-центры с энергией термической активации E1 ~ 190 мэВ, дивакансии с энергиями активации E2 ~ 230 мэВ и E3 ~ 410 мэВ и E-центры с энергией активации E4 ~ 440 мэВ, отсчитанные от дна с-зоны кремния.
Ключевые слова: диод Шоттки на кремнии, отрицательная дифференциальная емкость, альфа-облучение, Л-центры, E-центры, дивакансии.
DOI: 10.21122/2220-9506-2023-14-1-38-43
Адрес для переписки: Address for correspondence:
Поклонский Н.А. Poklonski N.A.
Белорусский государственный университет, Belarusian State University,
пр-т Независимости, 4, г. Минск 220030, Беларусь Nezavisimosti Ave., 4, Minsk 220030, Belarus
e-mail: poklonski@bsu. by e-mail: poklonski@bsu. by
Для цитирования: For citation:
N.A. Poklonski, A.I. Kovalev, K. V. Usenko, E.A. Ermakova, N.A. Poklonski, A.I. Kovalev, K.V. Usenko, E.A. Ermakova,
N.I. Gorbachuk, S.B. Lastovski. N.I. Gorbachuk, S.B. Lastovski.
Inductive Type Impedance of Mo/n-Si Barrier Structures Inductive Type Impedance of Mo/n-Si Barrier Structures
Irradiated with Alpha Particles. Irradiated with Alpha Particles.
Приборы и методы измерений. Devices and Methods of Measurements.
2023. - Т. 14, № 1. - С. 38-43. 2023, vol. 14, no. 1, pp. 38-43.
DOI: 10.21122/2220-9506-2023-14-1-38-43 DOI: 10.21122/2220-9506-2023-14-1-38-43
Introduction
In silicon microelectronics, flat film spirals of round or rectangular shape are formed to create an integrated inductance. However, the maximum specific inductance of such spirals at low frequencies is limited to a value of the order of tens of microhenries per square centimeter, while their diameter can be of several millimeters [1]. Another way to create an integrated inductance is gyrators - devices based on operational amplifiers that imitate inductance [2,3]. Despite the fact that such solutions have been introduced into the production of integrated circuits, the task of searching for new elements with inductive impedance is relevant. This will allow more rational use of the useful area of the microcircuits.
An alternative to film coils can be the effect of negative differential capacitance [4,5], which is observed in various semiconductor structures: silicon photodiodes irradiated with neutrons, multilayer hete-rostructures, chalcogenide films, transistor structures, metal-semiconductor interfaces, etc. [6]. Note that, in metal-semiconductor barrier structures, hopping conduction via defects is observed in the forward biased space charge region of semiconductor [7].
The purpose of the work is to study the low-frequency impedance of Schottky diodes (Mo/n-Si) with radiation-induced defects for different fluences of a-particles and determination of the parameters of radiation-induced defects by DLTS spectroscopy.
Studied structures
Al (3.3 цш) Mo (¿Mo) SiO2 (0.4 цш)
——1 /
^ I I I I I
n-Si
T^r
p+-Si
n+-Si
Ti/Ni/Ag (0.1/0.5/0.6 цш)
Layer of radiation-induced Space charge n-Si defects in silicon region layer
b
Figure 1 - Cross section of a Schottky diode (a) and equivalent electrical circuit (b) of an irradiated diode under forward bias Udc = 50-100 mV (Idc = 10 ^A)
initial characteristics, the diodes were irradiated with an uncollimated beam of alpha particles (decay energy of 5.147 MeV) with fluence from 3.6-1011 to 2.1-1014 cm-2. The projective range of a-particles in silicon did not exceed 24 ^m. The surface activity of the source was 2-107 Bq-cm-2. The diode equivalent circuit describing Z(f) dependences at Idc = = 10 ^A is shown in Figure 1b (see also [9]).
d
e
a
Unpackaged Schottky diodes Mo/n-Si (epitaxial 5.5 (m thick layer and resistivity of 1 Ohm-cm) produced by JSC "Integral" were studied [8]. Diodes were fabricated on wafers of monocrystalline silicon of n-type electrical conductivity doped with antimony and grown by the Czochralski method. The resistivity of the wafers was 0.01 Ohm-cm at the laboratory conditions. The thickness of the wafers was 460 (m. An n-type 5.5 (m thick silicon layer was epitaxially grown on the substrate. Then, 0.3 ^m thick molybdenum (Mo) layer was deposited in a vacuum (see Figure 1a and Table). The ohmic contact was formed by deposition of aluminum (Al) 3.3 (m thick layer on molybdenum. On the reverse side, an ohmic contact was formed by deposition of Ti/Ni/Ag (0.1/0.5/0.6 ^m) metal electrode. Then the wafer was cut into chips (un-packaged barrier structures). After measuring the
Measurement results and their discussion
The dependences of the real Z' and imaginary Z" parts of the impedance Z = Z' + i Z" on the AC frequency f (in the range from 20 Hz to 2 MHz) and
Table
The main characteristics of the studied Mo/«-Si Schottky diodes at the laboratory conditions
Parameter Value
Electrical resistivity of the n-type
silicon epitaxial layer doped with 1
phosphorus, Ohm-cm
Epitaxial layer thickness de, ^m 5.5
Molybdenum layer thickness dMo, ^m 0.3
Diode thickness d, ^m 460
Barrier (transition) area, mm2 5.25
Barrier capacitance Cb, nF 0.95 1.25 1.48
DC bias voltage Udc (in the range from 0 to 400 mV) were measured on an Agilent E4980A LCR meter. AC signal amplitude was Uac = 40 mV. When measuring the impedance Z, the diodes were kept in the dark at room temperature. DC forward current Idc through the diodes varied from 0 to 10 mA; the characteristics were chosen at Idc — 10 pA with the highest value of the "inductive type" impedance. The calculation of the diode inductance L was carried out according to the methods [9-11] using a series equivalent LR-circuit (see, e.g., [12]).
Figure 2a,b,c shows the frequency dependences of the inductance for diodes with the concentration of doping impurity (phosphorus) in the epitaxial
layer: 3-10, 4.7-10, 7-1015 cm-3, corresponding to the values of the barrier capacitance: Cb = 0.95, 1.25, 1.48 nF. The barrier capacitance of the diodes and the concentration of phosphorus in the n-Si epitaxial layers were determined from measurements of the capacitance-voltage characteristics at the frequency of 1 MHz under the diode reverse bias of up to 10 V. For the first group of doping (Figure 2a), after irradiation, a significant increase in low-frequency inductance is observed, which then decreases with the fluence of a-particles. For all groups of diodes (Figure 2a,b,c) for fluences O = 1.7-1013 and 3.5-1013 cm-2 there is a decrease in the low-frequency inductance with the transition of the impedance to the capacitive type. When the fluence O = 5.2-1013 cm-2 was reached, all three groups acquired an inductive impedance in the low-frequency region.
The maximum low-frequency inductance in both the virgin and irradiated Schottky diodes was found for the value of stationary current Idc ~ 10 pA excited in them. According to Figure 2a,b,c the dependence of the inductance L on the frequency f of the measuring signal for Idc « 10 pA has two extremes: the first (indicated by the Roman numeral I and marked by a dashed line) in the low-frequency region (75 Hz), the second (indicated by the Roman number II and marked with a dashed line) in the region (1-10 kHz) with capacitive impedance. (The negative inductance of a two-terminal network corresponds to the capacitance.)
So: i) the inductive contribution to the impedance of the diodes (I region) non-monotonically depends on the fluence of a-particles and decreases with the concentration of doping impurity (phosphorus); ii) the capacitive contribution to the impedance of the diodes (II region) increases with the
a 150 100 Я 50 ^ 0 -50 -100
b
100 0
„ -100 -200 -300
с 150 0
_
Cb = 0.98 nF
#4 \ #2
-'■ #3 ;
ii
_____
V
i ; /1 / i
— \ 1 / / ^^ J! 1 """ 1 1
#4 Cb = 1.25 nF
' 'l \ —- #1
: iX \ ^r ч yy #2
#3 \
" ->-•- \ i /1 ч Ai
i "T" 1 1
-150
-300
-450
/ i #4 Cb = 1.48 nF #1
f 1 1 1 1 —1 \ 1 ^N^. » /' #2 -"^v 1 ' \ f \ Ж \ M \ /
\ 1 1 _ #3 ж Г /1
/ \Л ' \ \ / V ii
— 1 T i i
101
102
104
105
103
f Hz
Figure 2 - Frequency dependences of the inductance L of three diodes with different barrier capacitance Cb. Numbers of curves correspond to fluences of a-particles 1013 cm-2: 0 (#1); 1.7 (#2); 3.5 (#3); 5.2 (#4). The concentration of phosphorus atoms in the epitaxial silicon layer, 1015 cm-3: 3 (a); 4.7 (b); 7 (c). Values of L < 0 correspond to the capacitive type of impedance
irradiation fluence and the concentration of phosphorus atoms.
Radiation-induced defects in diodes irradiated with a-particles were studied by DLTS spectroscopy [13-16] on CE-7C capacitance spectrometer in the temperature range from 80 to 300 K. DLTS spectra were recorded for diode irradiated with flu-ence of a-particles O ~ 3.6-1011 cm-2. The spectra were measured at the following setup parameters: filling pulse amplitude +5 V and duration 10 ms, reverse bias voltage -6 V, emission velocity window 19 s-1.
T, K
Figure 3 - DLTS spectra of the diode irradiated with a-particles with fluence $ ~ 3.6-1011 cm-2 (Cb = 1.48 nF; see also Table and Figure 2c): after irradiation (spectrum 1); after annealing at 150 °C for 30 min (spectrum 2)
Figure 3 shows DLTS spectrum of diode irradiated with a-particles with fluence $ ~ 3.6-1011 cm-2 (spectrum 1) and DLTS spectrum of the same diode after 30 min annealing at the temperature of 150 °C (spectrum 2).
Spectrum 1 shows DLTS peaks labeled Еl, E2, E3, and Е4. Each peak is associated with the emission of electrons from deep levels of radiation-induced defects. For each peak, from the Arrhenius dependences for deep levels, the values of the activation energy and the electron capture cross section were obtained. Peak E1 corresponds to electron emission from the level Ec - 0.19 eV and capture cross section o„ = 1.4-10-15 cm-2, peak Е2 corresponds to Ec - 0.23 eV and o„ = 1.410-15 cm-2. The overlap of peaks E3 and E4 in spectrum 1 does not allow one to correctly determine the parameters of the corresponding defect levels.
Comparison of the obtained results with the literature data [13,15] allows us to conclude that the Ei peak corresponds to the deep level of the Acenter, which is an "interstitial oxygen - vacancy" pair (O-V)-/0. The E2 peak belongs to the shallow divacancy level (V-V)=/-. The E3 peak is most likely associated with the emission of electrons from the deep divacancy level (V-V)-/0 and corresponds to Ec - 0.41 eV and o„ = 1.7-10-15 cm-2 [13,15,16].
The concentration of phosphorus doping impurity in the n-region of the studied Schottky diode is 4.7-1015 cm-3. At such dopant concentrations, along with the interstitial oxygen atoms, the phosphorus atoms also provide sinks for vacancies generated by alpha particles during irradiation [13,17]. Therefore, the E4 peak most likely corresponds to the
electron emission from the deep level Ec - 0.44 eV and o„ = 1.7-10-15 cm-2 of the phosphorus-vacancy defect (P-V)-/0, i.e. E-center. To test this assumption, the irradiated diode was annealed, since it is known that annealing temperature of the E-center in about 150 °C [17]. Spectrum 2 in Figure 3 was recorded after annealing the irradiated sample at temperature of 150 °C for 30 min. It can be seen from this spectrum that the ЕA peak disappears after the heat treatment and only the E3 peak remains.
Conclusion
It has been established that in the studied range of fluences of irradiation with a-particles (up to $ = 5.2-1013 cm-2) Schottky diodes have a nonmonotonic dependence of the inductance L on the fluence of a-particles. A significant increase in the inductance L for f ~ 75 Hz is observed (e.g., by an order of magnitude at fluence $ ~ 5.2-1013 cm-2 of a-particles). All irradiated diodes have capacitive impedance for f ~ 1 kHz. It is shown that the capacitance and inductance of irradiated Schottky diodes (Mo/n-Si) depend on the concentration of the doping impurity (phosphorus atoms). The maximum specific inductance observed on diodes irradiated with a-particles, measured at frequency f = 75 Hz, is ~ 0.1 H/cm2. This far exceeds the typical value of ~ 10 (iH/cm2 for flat metal film inductors.
It has been shown that three types of radiation-induced defects prevail in the diodes irradiated with a-particles: A-centers (a vacancy of a silicon atom in the crystal matrix and an oxygen atom), divacan-cies, and E-centers (a vacancy and a phosphorus atom). The latter are annealed at 150 °C for 30 min.
Acknowledgments
This work was supported by the Belarusian National Research Program "Materials Science, New Materials and Technologies".
References
1. Zhigal'skii A.A. Proektirovanie i konstruirovanie mikroskhem [Design and construction of microcircuits]. Tomsk, TUSUR Publ., 2007, 195 p.
2. Svirid V.L. Proektirovanie analogovykh mikro-elektronnykh ustroistv [Design of analog microelectronic devices]. Minsk, BSUIR Publ., 2013, 296 p.
3. Classic circuits. Electronics (50 Years Special Commemorative Issue), 1980, vol. 50, no. 9, pp. 436-442.
4. Penin N.A. Negative capacitance in semiconductor structures. Semiconductors, 1996, vol. 30, no. 4, pp. 340-343.
5. Poklonski N.A., Shpakovski S.V., Gorbachuk N.I., Lastovskii S.B. Negative capacitance (impedance of the inductive type) of silicon p+-n junctions irradiated with fast electrons. Semiconductors, 2006, vol. 40, no. 7, pp. 803-807. DOI: 10.1134/S1063782606070128
6. Gorbachuk N.I., Poklonski N.A., Marochkina Ya.N., Shpakovski S.V. Effect of hole extraction from the base region of a silicon p-n-p transistor on its reactive impedance. Devices and Methods of Measurements, 2019, vol. 10, no. 4, pp. 322-330 (in Russian).
DOI: 10.21122/2220-9506-2019-10-4-322-330
7. Bochkareva N.I., Voronenkov V.V., Gorbunov R.I., Virko M.V., Kogotkov V.S., Leonidov A.A., Vorontsov-Velyaminov P.N., Sheremet I.A., Shreter Yu.G. Hopping conductivity and dielectric relaxation in Schottky barriers on GaN. Semiconductors, 2017, vol. 51, no. 9, pp. 11861193. DOI: 10.1134/S1063782617090068
8. Poklonski N.A., Gorbachuk N.I., Lapchuk N.M. Fizika elektricheskogo kontakta metall/poluprovodnik [Physics of electrical contact metal/semiconductor]. Minsk, BSU Publ., 2003, 52 p.
9. Poklonski N.A., Gorbachuk N.I., Shpakovski S.V., Lastovskii S.B., Wieck A. Equivalent circuit of silicon diodes subjected to high-fluence electron irradiation. Technical Physics, 2010, vol. 55, no. 10, pp. 1463-1471. DOI: 10.1134/S1063784210100117
10. Tooley M. Electronic Circuits: Fundamentals and Applications. London, Routledge, 2020, xii+510 p. DOI: 10.1201/9780367822651
11. Poklonski N.A., Gorbachuk N.I. Osnovy impe-dansnoi spektroskopii kompozitov [Fundamentals of impedance spectroscopy of composites]. Minsk, BSU Publ., 2005, 130 p.
12. Ng K.K. Complete Guide to Semiconductor Devices. New York, Wiley-IEEE Press, 2002, xxiv+740 p.
13. Lang D.V. Deep-level transient spectroscopy: A new method to characterize traps in semiconductors. J. Appl. Phys, 1974, vol. 45, no. 7, pp. 3023-3032. DOI: 10.1063/1.1663719
14. Vavilov V.S., Kekelidze N.P., Smirnov L.S. Deistvie izluchenii na poluprovodniki [Effect of radiation on semiconductors]. Moscow, Nauka Publ., 1988, 192 p.
15. Bourgoin J., Lannoo M. Point Defects in Semiconductors II. Experimental Aspects. Berlin, Springer, 1983, xvi+295 p. DOI: 10.1007/978-3-642-81832-5
16. Dedovich H.H., Kuzminykh V.A., Lazarchik A.N., Lomako V.M., Pranovich V.I., Romanov A.F. [Digital capacitance spectrometer CE-6]. Materials and Structures of Modern Electronics: Proc. of III Int. Sci. Conf., Minsk, 25-26 Sep., 2008, ed. V.B. Odzhaev (ed.-in-chief) et al., Minsk, BSU Publ., 2008., pp. 16-19 (in Russian).
17. Kozlov V.A., Kozlovskii V.V. Doping of semiconductors using radiation defects produced by irradiation with protons and alpha particles. Semiconductors, 2001, vol. 35, no. 7, pp. 735-761 DOI: 10.1134/1.1385708
