CC BY
9
https://doi.org/10.29013/ESR-22-1.2-31-35
Daliev Shakhrukh Kh., leading researcher of Institute of Semiconductor Physics and Microelectronics of National University of Uzbekistan Tashkent, Republic of Uzbekistan E-mail: shakhrukhd@mail.ru Saparov Fayzulla A., junior researcher of Institute of Semiconductor Physics and Microelectronics of National University of Uzbekistan Tashkent, Republic of Uzbekistan E-mail: sfa@inbox.ru
INFLUENCE OF THE INTERFACE ON THE ELECTRICAL CHARACTERISTICS OF MIS STRUCTURES
Abstract. The energy distribution of the surface state density in band gap of Si for metal-insulator-semiconductor structures has been studied. It was show that defects localized at the semiconductor-insulator interface effect on the capasitor-voltage characterestics of the metal-insulator-semiconductor Al-SiO2-n-Si structures.
Keywords: the semiconductor-insulator interface effect, the capasitor-voltage characterestics, MIS structures.
Introduction. An integral part of most innovative semiconductor devices is the metal-insulator-semiconductor (MIS) structure. In devices such as field-effect transistors, surface-barrier varicaps, and charge-coupled devices, the MIS structure is the main working part of the device. In this physical state, which occurs at the semiconductor-insulator interfaces of the MIS structure, it has a significant effect on the functioning characteristics of semiconductor devices.
It is shown in the materials [1-5] of scientific work that the presence of electroactive impurity centers [1-3] or centers of different nature [4; 5] in a semiconductor substrate of an MIS structure (especially in the presence of their concentration distribution profile) affects the density distribution spectra surface states in the band gap of the semiconductor. In works, using the technique of measuring capacitance-voltage (C-V) characteristics [6; 7;14], it was
shown that the presence of electroactive centers localized in dielectric layers adjacent to the interface with a semiconductor changes the C-V characteristic of the metal-insulator-semiconductor structure and, therefore,, affects the distribution of the density of surface states over the semiconductor bandgap, the most commonly used method is the dark, high-frequency C-V characteristics of the MIS [1; 8; 10].
Experimental technique. To clarify the area of applicability of this method, we used the most widely used in microelectronics MIS structures of the Al-SiO -n-Si type, which were prepared by the thermal oxidation of crystalline silicon KEF-5, with crystallographic orientation <100>. The oxygen concentration in the original Si was 3 • 10 17 cm -3. In [4], a typical high-frequency capacitance-voltage characteristic of the structures under study was studied, measured in the dark at a temperature of 21 °C, at a frequency of 150 kHz and normalized to the size
of the oxide layer. The measurement results showed that the measured capacitance of the diodes weakly depends on the magnitude of the applied voltage, and when cooled to -80 °C, it decreases to the value of the geometric capacitance Cg. To determine the effect of the dielectric layer on the distribution of the density of surface states, the structures under study at a temperature of 120 °C for 12 hours were subjected to thermal field treatment, using the procedure of applying an enriching voltage of10 V. The measurement results showed that after thermal field treatments, the C-V characteristics of the structures under study shifted by several units towards more negative voltages, retaining their original shape.
This behavior of the electrophysical characteristics indicates that the dielectric layer is also not responsible for the observed distribution of the density of surface states. However, in practice, an uneven distribution of impurities is often encountered, which can introduce a significant error in the values determined experimentally. When determining the parameters of Schottky diodes by capacitive methods, when the impurity concentration in the semiconductor at the interface with the metal, a - const, x is the coordinate counted from the metal-semiconductor interface deep into the semiconductor.
Results and discussion. Using the Poisson equation and the dependence of the space charge density x, we obtain:
d_ en0 1 (l)
dx
ssn
2 , 2 x + a
After integration (1) over the coordinate, we have:
dç dx
x
arctan —
en0 _ a _
SSn
■Q
(2)
To find the constant C1 in equation (2), we use the following boundary conditions
ç = 0;
dç
x = L, d 0, dx
x = 0, d=Vk,
dx '
where cpk - is the contact potential difference between the metal and the semiconductor. Using these boundary conditions, we obtain
C =
L
arctan
en0 _ a _
(3)
ss0 a
substituting expression (3) into equation (2) we obtain
(4)
x L
arctan arctan
en0 _ a _ , en0 _ a
dx ££0 a 880 a
after integration (4) over the coordinate we have:
ç(x )
L x
x ■ arctan — -x■arctan
en0 _ a _ _ a _
ssn
ln
enn
SSn
x
a
(5)
■Q
after finding the constant C2
C 2 =
L
arctan
en0 _ a _
(6)
ssn
a
We find
ç(x ) =
f [ L1 x
x ■ arctan -x ■arctan
en0 V _ a _ _ a _ J
+
ln
+-
enn
1 +
x
- ln
1 +
x
(7)
een
2
and further, we find the depth of penetration of the electric field into the semiconductor.
i . tt\A 1
L = [a •[exp
2ss0 (q>k + U)
en
-1]]2 (8)
From the expression obtained, it can be seen that the dependence of L = L(U) differs significantly from that calculated for a uniform impurity distribution. Considering the metal-conductor contact in the approximation of a flat capacitor
a
1
2
a
a
C (V ) = ^ L
we find the dependence of the capacitance of the Schottky diode on the magnitude of the applied voltage, for various values of the parameter a. Comparative detailed analysis of theoretical and experimental methods showed that the formulation of the density of surface states near the inversion region of the CV characteristic, as well as not far from the region of
strong enrichment. The curves in Figure 1 lead to significant errors. This is due to the need to differentiate the difference between the values of two close quantities. This is due to the need to differentiate the difference of two close values. Several structures were used, each of which was measured using the method of dark high-frequency C-V characteristics 5 times in identical conditions and processed using the same method [10; 11; 12].
Figure 1. Theoretical and experimental capacitance-voltage characteristics of the MIS structure, normalized to the value of the capacitance of the dielectric layer
Figure 2. Sample-averaged distribution of the density of surface states over the band gap of a semiconductor
Figure 2 shows the differential distribution of the density of surface states over the band gap of the structures under study, constructed as a result of averaging all measurements.
It can be seen from the figure that the smallest scatter of the obtained data takes place in the energy range from Ec -0.2 eV to Ec -0.75 eV. It is in this energy range that a good uniformity of the results of all measurements is observed. Meanwhile, a rather large spread in the values ofthe averaged values ofthe density of surface states near the edges of the energy bands is synchronously observed. It is possible that from (Figure 3), in the energy range from Ec to Ec --0.2 eV and from Ec -0.75 eV to EV, this spread reaches 30%. In some cases, this exceeds the permissible error in measuring the distribution of the differential density of surface states over the band gap of a semiconductor. In our opinion, the reason for this scatter of data may be as follows. As the enrichment voltage applied to the structure decreases, the electrons localized on the surface states begin to be ejected into the conduction band due to thermal generation. In this case, the probability of their recapture is high, since the concentration of electrons near the interface is rather high [10]. When the voltage corresponding to the inversion of near-surface conductivity is reached, the process of
capture of generated electrons by the charge of the inversion layer is superimposed on the recharging of surface states [9]. According to the theory of solubility, impurity atoms can be located at lattice sites if the atomic radius of the primary element differs from the atomic radius of the main semiconductor atom (the radius of the Si atom is 1.17 R) by no more than 1.4%. If this condition is also not satisfied, the probability of finding an impurity atom at the sites is significantly limited [14].
On (Figure 1) shows that in the energy region EC - 0.75 eV, a local maximum is observed. In accordance with existing theories, such a distribution of the density of surface states over the band gap of a semiconductor can be associated with the presence of impurity electroactive centers in the semiconductor [3; 5] or in dielectric layers [6; 9] adjacent to the interface with the semiconductor (Fig. 3).
Conclusion. From the above results, the following conclusions can be drawn. The use of the method of high-frequency capacitance-voltage characteristics to determine the differential distribution of the density of surface states localized at the semiconductor-insulator interface over the band gap of the semiconductor is limited to an energy range ranging from Ec -0.2 eV to Ec -0.75 eV.
References:
1. Chistov Yu. S., Synorov V. F. Physics of MOS structures. - Voronezh, VSU. 1989.- 224 p.
2. Berman L. S. Capacitive methods of research of parameter semiconductors. L.: Science,. 1981.
3. Daliev Sh. Kh., Saparov F. A. Effect of pressure on the relaxation characteristics of MOS structures "Yarimo'tkazgichlar va polimerlar fizikasining dolzarb muammolari" mavzusidagi Respublika ilmiy-amaliy anjumani - Toshkent. 2022.- P. 33-35.
4. Daliev Sh. Kh., Saparov F. A. and Umarov F. "Influence of thermal field treatments on the volt-farad characteristics of MDS structures". Science and world International scientific journal - No. 10 (98).-Vol 2. 2021.- P. 8-11.
5. Utamuradova Sh. B., Saparov F. A. and Khaydarov Z. "Physical processes at the semiconductor - plasma contact of a gas discharge in a thin gaz-discharge cell". Science and world International scientific journal - No. 9 (97). 2021.- P. 8-10.
6. Utamuradova Sh. B., Daliev H. S., Aliyev Sh. Kh., Fayzullaev K. M. // Applied Physics. - No. 6. 2019.90 p.
7. Daliev Kh.S., Khusanov Z. M., Saparov F. A. Study of temperature effects in structures Silicon with Vanadium "Yarimo'tkazgichlar fizikasi, mikro- va nanoelektronikaning fundamental va amaliy muammolari" mavzusidagi 1-xalqaro anjuman - Toshkent. 2021.- P. 16-17.
8. Utamuradova Sh. B., Daliev Sh. Kh., Saparov F. A. and Turaev R. "Effect of pressure on surface morphology n-Si <Ni>." Actual Problems of Solid State physics. Proceedings of the IX International Scientific conference 22-26 November, 2021.- Minsk, Belarus. Book 2: - P. 162-163.
9. Kuchkarov B. Kh. and Saparov F. A. "To definition of surface state density of semiconductor-dielectric interface; K opredeleniyu plotnosti poverkhnostnykh sostoyanij granitsy razdela poluprovodnik-diehle-ktrik". (2010).
10. Vlasov S. I., Saparov F. A. and Kuchkarov B. Kh. "Effect of the semiconductor-insulator interface on the characteristics of the metal-insulator-semiconductor structures". Uzbekiston Fizika Zhurnali - 11.3.
2009.- P. 203-206.
11. Vlasov S. I., Saparov F. A. and Ismailov K. A. "Effect of pressure on the characteristics of Schottky barrier diodes made of overcompensated semiconductor". Semiconductor physics, quantum electronics & optoelectronics - 13.- No. 4. 2010.- P. 363-365.
12. Vlasov S. I. and Saparov F. A. "Effect of pressure on the electric properties of passivating coatings based on lead borosilicate glasses". Surface Engineering and Applied Electrochemistry - 47.4. 2011.- P. 338-339.
13. Vlasov S. I., Ovsyannikov A. V., Saparov F. A. "Recombination characteristics of Interphase Semiconductor-Dielectric Interfaces." Reports of the Academy of Sciences of the Republic of Uzbekistan.- 2.
2010.- P. 33-35.
14. Zainabidinov S. Z., Daliev Kh. S., Abdurakhmanov K. P., Utamuradova Sh. B., Khomidjonov I. Kh. and Mirzamurodov I. A. // Modern Physics Letters B.- Vol. 11.- No. 20. 1997.- 909 p.
