Method of forming a conducting structure

Details Method of forming a conducting structure Method of forming a conducting structure

1999-05-21

2001-04-17

Smith, Matthew (Department: 2825)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

To form ohmic contact to semiconductive material

C438S712000, C438S257000

Reexamination Certificate

active

06218278

ABSTRACT:

The present invention relates to the fabrication technique of complicated conducting structure using charged particles.
FIELD OF THE INVENTION
The present invention can find application in microelectronics for lithographic formation of integrated microcircuits, memories, and optic elements having some components of the conducting structure falling within the nanometric range.
BACKGROUND OF THE INVENTION
Up till now the modern microelectronics has been developing by way of successively reducing the microcircuit elements from micron to submicron size range. But ever increasing urgent demands in developing nanometric-size elements leads to search for novel techniques of lithographic formation of a conducting structure that assure high resolution which herein implies a minimum size of the elements of the conducting structure under development, that determines a limiting permissible density of a conducting structure elements per unit length or unit area without a contact therebetween.
One prior-art method of forming a pattern using electron beam (WO 95/26042). The method consists in placing an electron beam focusing system in the reaction chamber, arranging on the electron beam axis the mask and the wafer under processing coated with the layer of a material (photoresist) transformable when exposed to the effect of radiation. Then the wafer is irradiated with an electron beam, with the result that the material of the wafer surface layer undergoes transformation.
However, the aforementioned known method makes use of a widely spread technique of applying a layer of photoresist to the wafer, which technique allows of applying said layer having a thickness on the order of hundreds of nanometers (200 to 500 nm) which makes it impossible to obtain the pattern elements of a conducting structure having linear dimensions on the order of unities of nanometers.
Moreover, according to the known method, the conducting structure elements are formed successively so that whenever necessity arises to provide high density of elements per unit area of the structure being formed, e.g., a microchip, it requires a long period of time running into hundreds and even thousands of hours.
One more heretofore-known method of forming a metal-substrate conducting structure is known (U.S. Pat. No. 5,459,098) to comprise the steps of applying a metal nitride layer to a dielectric substrate and irradiating the latter with a concentrated (focused) laser beam, whereby the metal nitride is decomposed into a solid metallic conducting component which remains on the substrate, and a gaseous nonconducting component which is removed in the course of further carrying out the method. The metal nitride decomposition temperature lies within the range of from 100 to 1000° C. The method is effected in a reaction chamber which is filled with an inert gas or wherein a required vacuum is established. A required pattern is formed from the conducting structure elements due to scanning the substrate surface with a laser beam according to a preset program, which affects adversely the production output of the method.
The method under consideration features but a low resolution because it is deemed impossible to obtain individual elements having linear dimensions on the order of unities and even tenths of nanometers. This is accounted for by the fact that to focus a laser spot to such a smallest size is a very difficult task. Besides, when a laser beam is incident on the layer of metal nitride the laser spot gets blurred due to heat conduction of metal, which results in increased linear dimensions of each individual element of the conducting structure. Therefore the method of photolithography is but of little use for forming conducting structure elements having linear dimensions in the nanometric range.
Moreover, as far as our knowledge goes, the known method in question fails to have found widespread industrial application because to provide long-length conducting structures, e.g., wire conductors in electronic circuits, a very prolonged period of time amounting to hundreds and thousands of hours is required.
Thus, every heretofore-known methods are featured by a multistage and labor-consuming production process; whenever a single-stage process is used it suffers from low production output which places limitation upon the range of practical application of said methods.
SUMMARY OF THE INVENTION
It is a primary object of the present invention to provide individual elements of a conducting structure which have linear dimensions on the order of unities of nanometers.
It is another object of the invention to provide a possibility for establishing a three-dimensional layer-type conducting structure enabling multilayer electronic circuits, e.g., integrated circuits for computer technology.
The foregoing object is accomplished due to the fact that in a method of forming a conducting structure, comprising applying to a substrate a layer of a material transformable into a conducting one when exposed to the effect of radiation and irradiating said layer of said material with a modulated radiation beam, according to the invention, the applied layer of said material is 2 to 20 nm thick and used as the radiation is a beam of charged particles, whereby the material of said layer is transformed, on the irradiated areas, into a conducting component which establishes in said layer a plurality of conducting structure elements, a nonconducting component displaced into the material of the substrate.
The proposed method enables one to form in the layer of said material a conducting structure element having the smallest possible size, this being due to irradiating a layer of a material transformable under the effect of irradiation with a beam of charged particles whose wavelength is less than the wavelength of an optical (in particular, laser) radiation. The fact that the thickness of the layer of said material ranges between 2 and 20 nm contributes to attaining the required resolution, that is, required spatial arrangement of the conducting structure elements with a preset density.
By and large, it is due to said features that the proposed method makes possible forming individual conducting structure elements having linear dimensions on the order of unities of nanometers.
It is beneficial that used as the material of said layer be a single-phase semiconductor or dielectric metalliferous material comprising at least atoms of a first kind and atoms of a second kind which differ in atomic number; used for establishing a charged beam are charged particles each having an energy transferred by said particle upon its interaction with the atoms of the material of said layer in the course of irradiation, which energy is lower than the threshold displacement energy of the first-kind atoms and is higher than the threshold displacement energy of the second-kind atoms; the material of said layer undergoes transformation by displacing second-kind atoms on the irradiated areas of said layer into the substrate material and by transforming first-kind atoms on the irradiated areas of said layer into a plurality of the conducting structure elements.
It is reasonable that the energy transferred by a charged particle upon its interaction with said atoms of said material of said layer be found from the following relationship
E
max
=
4
⁢
E
o
⁢
M
1
·
M
2
(
M
1
+
M
2
)
2
,
where
E
max
is maximum energy transferred by said charged particle to the atoms of each kind;
E
o
is the energy of said charged particle;
M
1
is the mass of said charged particle;
M
2
is the mass of said atom of each kind with which said charged particles collide.
The fact that used as the material applied to the substrate layer is a material having the aforedescribed properties and that the abovedescribed range of energies of charged particles is selected, provides for, in the course of irradiation, conditions for separating said material into a conducting and a nonconducting component of which the nonconducting component is displaced inwards the substrate material and thus does not virtuall

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