RU1083842C - Method of creating alloyed regions of semiconducting instruments and integral micro-circuits - Google Patents

Description

 The invention relates to the manufacturing technology of semiconductor devices and integrated circuits.

A known method of ionic doping of boron areas of semiconductor devices into pure silicon or silicon, protected by an oxide film, where with ionic doping of boron areas of semiconductor devices with energies of 50-150 keV and doses in excess of 1.25 ¹⁴ 10 ¹⁴ ion / cm ² (20 µc / cm ² ) the period of the silicon crystal lattice increases due to impurity atoms and silicon atoms knocked out as a result of the bombardment, which are located in the interstices, "bursting" the lattice. Subsequent heat treatments transfer the interstitial atoms to the nodes of the crystal lattice. In this case, the impurity becomes electrically active. Since the atomic radius of boron is smaller than the atomic radius of silicon, the crystal lattice is contracted, which leads to the appearance of defects in the doping regions.

, энергия легирования 200-300 кэВ.Closest to the proposed technical solution is a method of creating doped areas of semiconductor devices and integrated circuits by oxidizing silicon wafers, etching windows in a masking oxide, creating oxide in etched windows and ion implantation of boron, followed by its acceleration. The oxide film in this case is 6000-7000 thick

, doping energy 200-300 keV.

 The disadvantage of this method is that when selecting the ratios of the doping energy and oxide thickness from these intervals, the maximum concentration of implanted boron can lie in silicon, which will lead to defects in the doping regions, especially at high doses of impurities that degrade the electrical parameters of semiconductor devices.

 The purpose of the invention is to improve the electrical characteristics of semiconductor devices and integrated circuits by eliminating defects in areas doped with boron, especially at high doses.

This goal is achieved by the fact that in the method of creating doped areas of semiconductor devices and integrated circuits by oxidizing silicon wafers, etching windows in a masking oxide, creating oxide in etched windows and ion implantation of boron with its subsequent acceleration, an oxide film is grown in etched windows with a thickness determined by ratio:
d = KE, where d is the oxide thickness in nanometers, nm;
E is the ion doping energy in kiloelectron-volts, keV,
K is a coefficient equal to (3.6 - 4.0) nm / keV, after which boron ion implantation is carried out in the oxide with energy from the range of 2-100 keV, corresponding to the selected oxide thickness, and then the boron is transferred by distillation from oxide to silicon by distillation.

 Due to the fact that the energy of boron ions reaching silicon due to the dispersion component of the ion beam is low due to the deceleration of ions in the oxide, and during subsequent heat treatments the p-regions are formed by diffusion of both these ions and impurities from the oxide, defects in doping areas do not arise.

 As a result, breakdown voltages increase and leakages of pn junctions sharply decrease.

 Coefficient K is selected experimentally. The experimental data used to determine the lower boundary of the coefficient K are given in the table.

 At values of K less than 3.6 nm / keV in doped regions, defects can occur.

 The choice of K values greater than 4.0 nm / keV is undesirable, since although there are no defects in the doping regions, due to an increase in the oxide thickness, the maximum impurity concentration after ion implantation will be removed from the oxide-silicon interface, which will lead to a need for an increase in the dose of the implantable impurities.

So, if to obtain a surface resistance of the p-type doped region of 200 Ohm / □ at K equal to 4.0 nm / keV, the dose of the implantable impurity does not exceed 330 μCul / cm ² , then at K more than 4.0 nm / keV the dose also increases at K equal to 4.6 nm / keV will be 520 μCoul / cm ² , and at K more than 5.0 nm / keV, a p-type region is not formed, since the oxide becomes masking.

 To create defect-free doped regions, the necessary oxide thickness can be obtained by choosing any value of the coefficient K from the indicated limits, and the limits of the coefficient K provide for the technological spread of the obtained oxide thicknesses. For example, for a doping energy of 25 keV, the oxide thickness, according to the formula d = KE, can lie in the range of 90-100 nm; for an energy of 100 keV, the oxide thickness is in the range of 360-400 nm.

 Creating defect-free doped regions is possible at any doping energies by selecting the appropriate oxide thicknesses. However, the energy range of 20-100 keV is the most optimal, since when doping with energies below 20 keV, the ion beam density decreases, the productivity of ion beam systems decreases, and the use of doping energy of more than 100 keV leads to an increase in oxide thickness above 400 nm, which makes reproducible with accuracy determined by the coefficient K = (3.6-4.0) nm / keV, obtaining oxide thicknesses.

 The drawing shows a doped region formed by the proposed method.

 A semiconductor substrate 1 in which a p-type doped region is created, an oxide layer 2 is formed for masking by ion doping, an oxide layer 3 grown in the etched windows of the masking layer, an alloying region 4 for creating semiconductor devices and integrated circuits.

 After creating a masking layer of oxide 2 using photolithography, the windows are etched in it. Then, oxide 3 is grown in the etched windows and ion implantation of boron is carried out with such energy that the maximum concentration of the impurity is in oxide 3 near the oxide-silicon interface. In this case, the p-type region is created due to boron ions having an energy higher than the average beam energy, i.e. due to the dispersion component of the ion beam and due to the redistribution of boron impurities from oxide 3 to silicon during subsequent heat treatments. In this case, the number of defects in silicon is reduced, and all the advantages of creating semiconductor regions by ion doping over other doping methods are preserved.

 The creation of the base areas of the p-type doped with boron by the proposed method, in particular, can be carried out as follows.

In the masking layer of oxide with a thickness of 700-800 nm, windows are etched to create basic areas. Silicon windows oxidized to an oxide thickness of 370-400 nm at a temperature of 1000 ± 1 ^{° C} in dry oxygen for 35 minutes at an oxygen flow of 2 l / min in deionised water vapor - 32 minutes in dry oxygen - 35 min. Then carried out the ion implantation of boron dose of 330 mkKul / cm ² with an energy of 100 keV, after which the plate is subjected to a heat treatment at a temperature of 1120 ± 1 ^{° C} in dry oxygen - 10 minutes at an oxygen flow rate of 1 l / min in deionised water vapor - 25 min , in dry oxygen - 60 minutes

 Other annealing modes are possible both in the oxidizing medium and in the neutral one, while the annealing time and temperature are determined by the required surface concentration and the depth of the transition.

Defects arising from ion doping were detected by processing the plates in the etchant of the following composition:
Cr ₂ O ₃ - 25 g, НF - 60 ml, Н ₂ О - 50 ml.

The density of defects in the areas doped with boron was determined by the proposed method and by the method of doping with boron areas of silicon that are not protected by an oxide film, a dose of 110 μCul / cm ² with an energy of 100 keV.

 Since the proposed method eliminates the occurrence of defects in doped areas and, thereby, improves the main electrical characteristics of pn junctions (increase breakdown voltage and reduce leakage), the use of this method will increase the percentage of suitable products, their quality and reliability.

Claims (1)

METHOD FOR CREATING DOPED AREAS OF SEMICONDUCTOR DEVICES AND INTEGRAL MICROCIRCUITS by oxidizing silicon wafers, etching windows in masking oxide, creating oxide in etched windows and ionic implantation of boron with its subsequent distillation, characterized in that the integrated circuit is equipped with electrical devices for improving electrical characteristics elimination of defects in areas doped with boron, an oxide film is grown in etched windows with a thickness determined by the ratio d = kE,
where d is the thickness of the oxide, nm;
E is the ion doping energy, keV;
K is a coefficient equal to (3.6 - 4.0) nm / keV,
after which ion boron implantation is carried out in an oxide with an energy from the range of 20-100 keV corresponding to the selected thickness of the oxide, and then boron is transferred from the oxide to silicon by distillation.

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