The method of obtaining nuclear-doped silicon, n-type (options)

 

(57) Abstract:

Method for obtaining nuclear-doped silicon, n-type, in which the ingot source of silicon enriched in N stable isotope30Si and irradiated with neutrons. On the basic nuclear reaction (n ) stable isotope30Si contained in the natural mixture of isotopes of silicon, receive the desired concentration of donor impurity31P. Then decontamination of the ingot, it dosimetric control, as well as to remove a substantial part of the radiation defects and stabilize the electrical properties of a material is its thermal annealing. The method can be implemented in two ways. According to the first variant reduces to N times the rate of neutron fluence and, thereby, at the same time the concentration of the complex radiation defects. According to the second variant retain the fluence rate set for the irradiation of silicon with a natural mixture of isotopes, receive N times greater concentration of donor impurity31P and accordingly the concentration of charge carriers. To reduce the number of complex radiation defects in the implementation of the second variant of the method using the moderated neutron spectrum, reduce the share of nectow, not fixed irradiation thermal annealing of irradiated ingot, and the improvement of the electrical properties of silicon. 2 S. p. f-crystals, 1 Il.

The invention relates to the field of nuclear technologies for poly - and monocrystalline silicon of n-type and aims sharp empowering regulatory structure and, through her, " electrical properties of semiconductor silicon and devices based on it.

Currently, nuclear silicon doping n-type is carried out by neutron irradiation of silicon ingot of the desired size and quality in a nuclear reactor or other nuclear installation, when the main nuclear reaction is the reaction on stable isotope30Si contained in the natural mixture of isotopes in the number of 3.12%:

< / BR>
where n is the neutron - gamma radiation due to neutron capture;-beta-particle with an energy of 2.5 MeV, emitted from the half-decay time 157,3 min compound-nucleus 31Si31P - doped impurity is phosphorus, which is the product of nuclear reactions (I. M. Grishkov, S. P. Soloviev, V. A. Kharchenko. "Nuclear doping of semiconductors. Overview" niitekhim, Moscow, 1982, S. 19; C. A. Kharchenko, S. P. Soloviev - Izvestia an SS is their norm of neutron fluence and, therefore, the degree of doping of phosphorus due to the accumulation of complex radiation defects that are not resolved by irradiation thermal annealing of irradiated ingot and significantly reduce electrical properties of silicon. The fluence rate limit due to unavoidable for nuclear technology induced radioactivity of the ingot.

The essence of the proposed method lies in the fact that the original silicon raw material enriched stable isotope 30Si N times, get-rich raw materials in a known manner ingot of the desired size and quality and conducted in a nuclear reactor or other nuclear installation doping ingot according to reaction (1). This may be provided with two variants of the method of obtaining nuclear-doped silicon, n-type, for which irradiation operations - decontamination of the ingot, it dosimetric control, annealing of radiation defects, improving and stabilizing the electrophysical properties of the ingot, conduct as provided by the prototype. At this both ways achieve the same technical result - the reduction of the concentration of the complex radiation defects and, sootvetstvenno is new in comparison with the above prototype, get in svezheubrannom the material is N times lower concentration of residual complex radiation defects and the corresponding improvement of electrical characteristics of silicon.

Option 2.

While maintaining standards fluence limit for a prototype, the increase in N content in silicon isotope30Si leads to an increase in N concentration uniformly distributed in the silicon donor impurity -32P, i.e., the concentration of charge carriers. This method requires the adoption of measures to address the spectrum of neutrons high-energy part, which is associated with education in substance integrated radiation defects. The desired change in the neutron spectrum is achieved by using well-known moderators of beryllium or other materials with low atomic weight; the moderators installed in the irradiation channel. The physical justification of this path are electron microscopy and x-ray diffraction analysis of the complex distribution of radiation defects in crystalline substances, depending on the bombarding energy of nuclear particles (K. Mercle-Report AEPE-R5269, Harwell, 1966; M. L. Jenkins, C. A. English-Journ. Nucl. Mat. 108-109, 46, 1982; centuries Kirsanov "Complexes of point defects is adelene obeys the Rayleigh law:

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where d0- the diameter of the defect - fashion distribution (for fission spectrum neutrons ). Also convincingly shown that reducing energy of bombarding particles fashion distribution dramatically shifted towards smaller defects. Fully carmelitane the integrated neutron radiation defects is practically not create.

Due to appear for enriched isotope 30Si ingot reserve fluency technologist receives the maneuver when the first or second options. The quantitative aspect when determining the tradeoff between the first and second options is provided by a set of graphs or tables according to those or other controlled parameters from the mode of irradiation and annealing.

For both variants (N 1 and N 2) is true: because of the complex radiation defects act on a number of important physical properties of silicon as impurities, the best result in its nuclear doping is provided for a maximum enrichment of stable isotope30Si. The transition from pleistophora composition of silicon (28Si - 92,18%,29Si - 4,71%,30Si - 3,12%) monoisotopic30Si itself, i.e. without neutron oblastey, due to the difference in atomic weights of the isotopes.

Example No. 1.

The proposed option # 1 for the production of nuclear-doped silicon n-type implemented on a pilot channel of a nuclear reactor on a standard silicon ingots with a natural mixture of stable isotopes, obtained by the method of non-crucible melting, and the values of neutron fluence 71020cm-2the resulting concentration of charge carriers 2,51017cm-3; at the same time for 20-gram ingot of silicon with dimensions of approximately h mm, where the content of stable isotope30Si increased from 3,12% to 15%, i.e. about 5 times, received the same concentration of charge carriers after irradiation fluence 1,51020cm-2. A plot of the concentration of charge carriers from the fluence of neutrons, where enriched silicon ingot obtained two experimental points given in the drawing. Thus, the ratio of the values fluences close to the inverse ratio of the content of the above isotopes in irradiated ingots taken for experiment. It proves the correctness of technical solutions and practical value of the proposed method.

Example No. 2.

Option # 2 get aderemi in the drawing. From the dependence of the concentration of charge carriers from the fluence of neutrons (for example, for the same values of fN= 1018cm-2) shows that this concentration is approximately 5 times higher for ingot of silicon-enriched 5-fold isotope 30Si, compared with the ingot with the natural mixture of isotopes. Thus, the enrichment of silicon in the N isotope30Si results after neutron irradiation to a higher (N times) the degree of doping of phosphorus, i.e., option # 2 allows to obtain a high saturation silicon phosphorus with uniform distribution in the crystal. The use in this embodiment of the method of the moderated neutron spectrum allows to reduce the share of high-energy neutrons and, therefore, reduces the number of complex radiation defects.

1. The method of obtaining nuclear-doped silicon, n-type, in which the ingot source of silicon irradiated by neutrons and principal nuclear reaction (n ) stable isotope30Si get the desired concentration of donor impurity31P, decontamination of the ingot, it dosimetric control, as well as to remove a substantial part of the radiation defects and stabilization properties of the material the isotope30Si and decrease in N fluence of neutrons and, thus, the concentration of the complex radiation defects not amenable to thermal annealing.

2. The method of obtaining nuclear-doped silicon, n-type, in which the ingot source of silicon irradiated by neutrons and principal nuclear reaction (n ) stable isotope30Si get the desired concentration of donor impurity31P, decontamination of the ingot, it dosimetric control, as well as to remove a substantial part of the radiation defects and stabilize the material properties of its thermal annealing, characterized in that the starting silicon prior to its irradiation enriched in N stable isotope30Si and the preservation of neutron fluence using moderated neutron spectrum, reduce the share of high-energy neutrons responsible for the formation of complex radiation defects.

 

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