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13
Section 10. Physics
Daliev Shakhrukh Kh., Institute of semiconductor physics and microelectronics of National University of Uzbekistan Tashkent, Republic of Uzbekistan E-mail: shakhrukhd@mail.ru
THE FORMATION OF DEFECTS IN MIS STRUCTURES BASED ON SILICON WITH MOLYBDENUM IMPURITY
Abstract. By means of methods of capacitance spectroscopy CC-DLTS and is high-frequency capacitance-voltage characteristics processes the formation of defects in the bulk and at the interface Si-SiO2 of MIS-structures based on silicon with molybdenum impurity are investigated. It is revealed, that presence of electro-neutral molybdenum impurity at structures leads to increase Nss, but appreciable change in distribution N on E is not observed. It is established, that presence electroactive
O ss g ' E
molybdenum atoms leads to a further increase Nss of structures and occurrence of the peaks connected with levels molybdenum in silicon. Keywords:
1. Introduction
In connection with the search for semiconductor materials with special properties (increased thermal stability, radiation stability, etc.), recently increased interest in silicon alloyed with refractory elements [1-3]. These specially introduced impurities enter into various interactions with structural defects and different uncontrolled impurities in the process of technological processing, which is accompanied by virtually any route of manufacturing semiconductor devices [4-6]. Among all refractory elements in silicon, molybdenum is the least studied.
In last years, the study of the properties of impurities that create a variety of defective centers in semiconductors has received considerable attention in view of the significant role of refractory impurities in the formation properties of silicon. It is known
that the doping of silicon by refractory elements significantly affects the performance of semiconductor devices [7-8], but data about their electrical activity and interaction with other defects and also about influence on characteristics of silicon structures are inconsistent.. The purpose of this work was to study non-equilibrium processes in the bulk and at the interface Si-SiO2 multilayer structures of the type metal-insulator-semiconductor (MIS) on the basis of silicon, doped with molybdenum.
2. Experimental setup
Below are the results of a complex research CC-DLTS and capacitance-voltage characteristics (C-V characteristics) in MIS-structures with impurity ofMo.
Initial Si it was doped with molybdenum in the process of growing from the melt, and diffusion method. After doping Mo on the Si plates with ori-
entation <100> and a resistivity of 20 Ohm.cm was created by MIS-structures according to the technology described by us earlier [9; 10]. Concentration of possible deep levels (DL) was measured in volume Si by method CC-DLTS on Schottky barriers fabricated on Si after etching of the layer SiO2.
3. Results and discussion
These measurements showed that the introduction of molybdenum in Si the process of growing from the melt does not form any deep levels in a
prohibited area of a silicon substrate. Measuring C-V characteristics of MIS structures based on Si<Mo> (Fig.1, curve 2) showed that they are shifted toward negative displacements in comparison with control samples (Fig.1, curve 1). This suggests that the introduction of molybdenum in Si leads to a change in the generation characteristics of structures: to increase the density of surface states N of
' ss
MIS structures and the formation of positive charge at the interface Si-SiO,.
V, v
-V, V
Figure 1. Capacitance-voltage characteristics of a silicon MIS - structures with an impurity of molybdenum: curves 1, 3 - test MIS - structures without an impurity of Mo, curve 2 - MIS - structure based on Si, doped Mo when growing; curve 4 - MIS -structurebased on Si, the diffusion doped Mo
Measurements of the spectra of CC-DLTS in MIS-structures on the basis of Si<Mo> and test MIS-structures (without an impurity of Mo) showed that their spectra practically coincide, any peaks in the visible concentration not founded (Fig. 2, curve 1). Measurements of distribution N on width of for-
ss
bidden zone E of the semiconductor of structures
g
with impurity molybdenum have shown that the spectrum of distribution of dependence N from E
ss g
has typical U-shaped character.
A different pattern is observed in MIS structures with diffusion introduced molybdenum. Preliminary Si it was doped with Mo by a diffusion method in the
range of temperatures 1000-1200 °C within 2 hours from the layer put on surface Si metal molybdenum. Then, on the wafers n-Si<Mo> with resistivity of p = 5 - 20 Ohm cm made MIS-structures T [9; 10].
Measuring C-V characteristics of MIS structures with diffusion introduced molybdenum (Fig. 1, curve 4) showed that they are even more shifted towards negative offsets relative to control samples (Fig. 1, curve 3). It is known that the shift of C-V characteristics towards negative voltages indicates an increase in the density of surface states (DSS) structures [11]. This suggests that the presence of the electrical active molybdenum
atoms in the silicon substrate of the investigated the formation of positive charge at the interface
structures leads to a further increase of N and Si-SiO-
ss 2
ALT. relative units
1.0
0,5
100
150
200
m
T, K
Figure 2. DLTS spectra of the control (curve 1) and doped molybdenum MIS structures (curves 2 and 3)
Measurements of the spectra of CC-DLTS in the doped (Fig.2, curves 2 and 3) and the control (Fig.2, curve 1) MIS structures showed that the spectra of doped samples are observed 2 peaks with maxima at temperatures of T = 125 K and T = 160 K, and
E max max '
their amplitude increases with increase in the concentration of electroactive molybdenum. In the control samples, these peaks are not detected. Numerical calculations of the parameters of the defects caused by these peaks showed that the peak with a maximum at T = 125 K corresponds to a level with an ionization energy of Ec - 0.20 eV and the peak at T = 160 K - level with an ionization energy of Ec - 0.29 eV.
It was also studied the change of distribution of
N on width of forbidden zone E of the semiconduc-
ss g
tor of MIS structures with impurity of molybdenum and without molybdenum. The spectra of distribution of N on width of the forbidden zone U of the
ss
semiconductor structures with impurity molybdenum are somewhat complicated nature.
It is shown that on the spectrum of distribution of N on width of forbidden zone E , in diffusion-
ss g'
doped structures observed three distinct peak in
the energy values Ec - 0.20 eV, Ec - 0.29 eV and E + 0.36 eV. In the control MIS-structures, this dis-
v 3
tribution as a typical U-shaped character.
To identify the detected defects with certain impurities in the investigated MIS - structures based on n-Si<Mo> etched oxide and on them barriers Schottky were created.
Measurements of spectra CC-DLTS on the received barriers have shown, that in all samples the recharge of two deep levels in the top half of forbidden zone Si with energies of ionization Ec - 0.20 эВ and the Ec - 0.29 эВ is observed. Scanning of all width of the forbidden zone on the same samples by means of photocapacity was shown, that on spectra of the induced photocapacity the recharge near hv ~ 0.36 эВ is observed. The analysis of results shows, that parameters of these deep levels do not differ from parameters of the corresponding DL, observed in silicon doped molybdenum.
4. Conclusions
Thus, the presence of electroneutral impurities molybdenum in the silicon substrate of MIS-structures leads to an increase in N , but a notice-
SS'
able change in the distribution of N in E is not crease of N ,, ,three distinct DLTS peaks
c> ss g ss and the emergence oi
observed. The presence of the electrical active mo- associated with the deep levels of molybdenum in
lybdenum in MIS-structures leads to a further in- silicon.
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