RU2433081C1 - Method of ion-beam treatment - Google Patents

Abstract

FIELD: nanotechnologies. ^ SUBSTANCE: invention relates to micro- and nano-electronics, to the technology of nanostructures manufacturing with size of <30 nm in process of etching through a resistive mask with high aspect ratio. The method of ion-beam treatment includes treatment of dielectric materials by chemically active or inert charged particles, acceleration of which is carried out in the source of ions. Besides, the treatment of dielectric materials is carried out by a beam of ions simultaneously with supply of HF shift to the substrate. ^ EFFECT: neutralisation of positive charge at the whole area of dielectric surface of structures, reduced effect of charged particles at parameters of treated items, increased resolution of minimum sizes of their elements and etching of materials with high aspect ratio. ^ 1 dwg

Description

The invention relates to micro- and nanoelectronics, to a technology for manufacturing nanostructures with a minimum size of <30 nm when etched through a resistive mask with a high aspect ratio, to processes of precision etching in a medium of chemically active or inert gases, deposition of defect-free thin dielectric films, cleaning and polishing surfaces processed products. In the process of treating dielectric surfaces with an ion beam, these surfaces, as shown, for example, in [1], are charged to a positive potential of such a value that the ion current density is equal to the current density of electrons taken from the beam plasma. A Langmuir layer d is formed between the dielectric substrate and the beam plasma, the value of which is determined by the Langmuir law

j _e = j _i = AU ^3/2 / d ² ,

where d is the distance from the boundary of the beam plasma to the surface of the substrate; j _e is the current density of electrons taken from the boundary of the beam plasma onto the substrate; j _i is the ion beam current density; U is the positive potential on the surface of the dielectric substrate; A is constant.

The value of the positive potential can reach from tens to hundreds of volts, depending on the ion energy, beam current, pressure in the region of the processed substrate, the composition of the working substance.

Charging dielectric films deposited on an electrically conductive layer (metal, or semiconductor) can lead to breakdown of the dielectric or to the appearance of a positive space charge in it, which significantly affects the parameters of semiconductor devices. In addition, charging the dielectric mask causes distortion of the ion paths during etching of the functional layers, especially at high aspect ratios (etching depth to the width or diameter of the hole).

Charging the surfaces of dielectrics (for example, resistive masks during etching) during the processing of substrates by non-monoenergetic beams (for example, when using ion sources with a closed electron drift [2, 3]) leads, in particular, to the reflection of slow ions from substrates if their energy is lower energy potential of the substrate and, as a consequence, to reduce the productivity of the processing process.

The value of the positive potential on the dielectric substrate can be controlled by creating an electron stream from a specially organized electron source, for example, a thermionic incandescent cathode, a hollow cathode, and a plasma discharge. The disadvantage of these methods of current neutralization of the ion beam is the lack of neutralization of the positive surface charge at each point of the dielectric surface, even if the currents of ions and electrons on the substrate are equal. This makes it necessary to mechanically move the substrate relative to the ion beam, as, for example, in the Kashtan installation [4], which is not always feasible, in particular, for cluster equipment. In addition, the use of additional electron sources is not always acceptable when working with chemically active gases during reactive ion-beam etching.

The aim of this invention is to achieve a technical result, which consists in neutralizing a positive charge over the entire dielectric surface area of structures, in reducing the influence of charged particles on the parameters of the processed products, in increasing the resolution of the minimum dimensions of their elements and in etching materials with a high aspect ratio.

The problem is solved in a method involving treating a dielectric surface of a substrate with a beam of positive ions of chemically active or inert substances while simultaneously applying an RF potential generating electrons to the substrate that neutralizes the positive charge formed by the ion beam over the entire area of the dielectric surface of the substrate.

One example of the implementation of the ion beam processing method is shown in the drawing. Technological vacuum chamber 1 is pumped out to a pressure of 5 · 10 ^-4 Pa with a TMN-1500 turbomolecular pump (the drawing shows only flange 5 for connecting the pumping unit) with an effective pumping speed ≥700 l / s in the pressure range (10 ^-2 ÷ 1.3 · 10 ^-4 ) Pa, then through the gas flow regulator 7, the working gas or gas mixture (chemically active or inert) is injected into the ion source 6, and through the gas flow regulator 8, into the substrate region 4 (depending on the process being carried out), and working pressure is set ~ 10 ^-2 Pa

When the power is turned on in the ion source 6, a discharge is ignited and a directed ion beam 9 of the working substance is formed, propagating in the processing chamber to the table 2, on which the processed substrates are fixed 4. At the same time, an RF offset of 20 or more is supplied to the surface of the substrates up to 100 watts.

Experiments on the practical implementation of the invention were carried out on the installation of ion-beam processing "Chestnut" [4].

It was experimentally established by the authors that while etching with the aid of an ion beam and an RF discharge in a CF ₄ medium, for example, materials such as Nb, W, it is possible to significantly (more than 4 times) reduce the working pressure in the process chamber. It was also established that at a pressure of 6.5 · 10 ^-2 Pa, the minimum discharge current was maintained at a voltage of 600 V, which allows etching of film materials with a low-energy ion beam.

For the formation of nanostructures with minimum element sizes (up to 20 nm) for field emission devices, precision etching of Ti by an SF6 ion beam was carried out simultaneously with RF displacement on the substrate through a mask of nanoporous anodic alumina with a thickness of up to 1 μm and aperture diameter (20 ÷ 30) nm (aspect mask structure ratio ~ 50: 1).

Compared with the known technical solutions, the proposed method of ion-beam processing allows you to:

- manage the charge on the surface of the substrate and, for example, when etching through a resistive mask to eliminate breakdowns in it and distortion of the ion trajectories;

- significantly reduce the effect of charged particles on the parameters of the structures being processed due to the fact that their ion beam is processed simultaneously with applying to the substrate an RF potential generating electrons that neutralize the positive charge on the substrate surface formed by the ion beam;

- reduce the working pressure in the region of the substrates by about 4 times, as a result of which the anisotropy of the etching and the resolution of the minimum dimensions of the elements increase;

- to form nanostructures with minimum element sizes (up to 20 nm), for example, for field emission devices;

- carry out the processes of precision etching of nanostructures through a mask up to 1 μm thick and a hole diameter of (20 ÷ 30) nm (the aspect ratio of the mask structure is ~ 50: 1);

- to provide a more uniform treatment (for example, etching) of the entire surface of the substrates;

- independently change the composition of the working substance in the region of the substrates and in the ion beam and carry out etching processes in a single vacuum cycle, for example, of an Al-Cu alloy (HF is etched by plasma-chemical method Al (volatile AlCl compounds), but Cu is not etched (no volatile compounds), and a beam of Ar ions etches Cu).

Literature

1. Valiev K.A., Velikov L.V., Maishev Yu.P. Precise selective etching of SiO ₂ and Si ₃ N ₄ films by ion beams of reactive gases. Proceedings of the FTIAN, Volume 15. “Ion-beam processing of materials in micro- and nanoelectronics”. M., Science-Fizmatlit, 1999. S.3-17.

2. Maishev Y., Ritter J., Terentiev Y., Velikov L. "Cold-cathode ion source with propagation of ions in the electron drift plane". Patent No.6130507, Date of Patent: October 10, 2000.

3. Maishev Yu.P. Ion sources for reactive ion-beam etching and film deposition // Electronic Industry. 1990. No. 5. S.15-18.

4. Maishev Yu.P. Sources of ions and ion-beam equipment for applying and etching materials // Vacuum equipment and technology. 1992. T. 2. No. 4. S.53-58.

Claims (1)

A method of ion beam treatment, which includes treating dielectric materials with chemically active or inert charged particles, the acceleration of which is carried out in an ion source, characterized in that, in order to neutralize the positive charge over the entire dielectric surface of the structures, reduce the effect of charged particles on the parameters of the processed products, increasing the resolution of the minimum sizes of their elements, etching materials with a large aspect ratio, processing dielectric materials The rials are carried out by a beam of positive ions simultaneously with the application of RF bias to the substrate.