CS252035B1 - A method of curing polymer resists for electron lithography - Google Patents

Abstract

The purpose of curing polymer masks in electron beam lithography is either to increase the resistance of the masks to dry etching processes or to enable direct observation of the masks in scanning electron microscopes. Curing is achieved by bombardment with ions of inert gases in a vacuum. Cured polymer masks achieve the resistance of refractory metal masks in etching processes using ion beams. Cured masks can be used in integrated circuit manufacturing technologies in microelectronics using electron beam lithography.

Description

The invention relates to a method of curing polymer resistors for electron beams. lithography, which enables direct observation of masks in electron scanning microscopes and direct use of masks for etching processes.

Until now, masks for microelectronic applications obtained by the electron-lithographic process could not be directly inspected in electron scanning microscopes. Polymer resist, e.g. polymethyl methacrylate, even after induction, is sensitive to the electron beam of the microscope. The electron dose in microscopy generally exceeds the dose required for mask exposure, so that the resist mask is destroyed by the microscopic beam in a manner resembling mapping, with the formation of bubbles and changes in macroscopic dimensions. Indirect imaging methods, e.g. using a negative replica by a lithographic technique, which does not always provide the necessary information about the shaped resist mask. The known electron resists are also poorly resistant to high-frequency gas plasma and can only sometimes be used for direct shaping of the substrate.

The above mentioned disadvantages are substantially eliminated by sorting option curing polymer resists for electron lithography In accordance with one of the invention, which is characterized in that the polymer mask in vacuum at a pressure below 10 ^_1 Pa cured by ion beam of inert gas in the energy range of 25 eV to 5 keV cartridge dose from 3 to 300 C. cm ^-2 .

The advantage of using cured masks is that in the technological preparation process, an operation in which an additional metal mask of greater resistance to etching processes is formed through the uncured polymer mask is avoided. The use of cured masks brings about an increase in the quality and reproducibility of microcircuit structures, particularly in the field of the implementation of objects of micrometer dimensions. Such hardened resist masks can be observed in electron scanning microscopes, which is of great importance in observing the effect of electron lithographs and optimizing processes. preparation of polymer masks. The cured resist is not electrostatically charged, stable, and provides a good resolution scanning electron microscope image.

The process of curing resist masks by bombarding with inert gas ions is performed in evacuated chambers provided with a source of inert gas ion beam with a maximum ion energy of 5 keV. Of the inert gases, more atomic mass ions, such as xenon, krypton and argon, are more preferably used. Most tone beam sources provide an ion beam in which the ion energies cover a range of energies ranging from a few EVs to some cut-off energy, which is 5 keV for resist curing. The angle of impact of the beam does not matter much. More preferred are angles greater than 45 ° from the plane of the substrate. To cure the resist, a dose of ionic bond up to 300 coulombs per cm ² area is required. The effect of ion bombardment induces a change in the physicochemical properties of the polymer resist, manifested in an increase in etching and electron beam resistance, which is called curing. With resist masks cured in such a way, only minimal dusting of the resist from the front face of the mask occurs during curing, while the surfaces are practically preserved.

Example 1

For the polymer mask a layer of polymethyl methacrylate with an average molecular weight of 5.10 ^{5 and} a thickness of 0.5 µm is used. After the resist is exposed and developed in the electron lithograph, the mask formed is cured by a xenon ion beam, with a maximum energy spectrum of 2.2 keV, in an evacuated chamber with a dry pumping system to eliminate the contaminating effect of residual oil vapors. The ion source gives a beam with a diameter of 500 μΐη and a total current of 700 nA at a pressure of 10 ^-3 Pa. The ion beam is allowed to cure for five minutes. The cured polymer mask enables microscopy without electron scanning in an electron scanning microscope with an electron beam current of 10 nA.

Example 2

A 0.5 m polymer polymer mask from a commercially produced quinondiazide-based resist (SCR 11 from Lachema Brno) is cured in the same manner as in Example 1. The cured polymer mask allows electron scanning microscopy without further treatment.

Example 3

The cured mask of Example 1 is used to form a niobium layer on a silicon substrate by ion etching. The same ion source is used as in Example 1. A time of about 30 minutes is required to etch the 0.5 μΐη niobium layer. The cured polymer mask is also partially etched by the ion beam, but its resistance to the ion beam is greater than that of the niobium layer and considerably greater than that of a 1 'meltable metal mask, e.g. aluminum. The remainder of the cured mask may be removed in effective solvents, e.g. hot glycol.

Example 4

In electronomicroscopic observation of the surface of polypropylene filled with molecularly ground bentonite, we encounter similar instability problems due to the incident electron beam as with biographic masks. To eliminate this instability, use Xe-ion curing of the polymer sample surface in the same manner as in Example 1. The cured surface on the sample surface allows direct observation in a scanning electron microscope without further modification, while retaining the characteristics of the bentonite dispersion in the polypropylene.

The invention can be widely used in technologies for manufacturing integrated circuits with micrometer and submicrometer dimensions using polymer resist masks produced by electron beam lithography techniques.

SUBJECT

Claims (1)

SUBJECT For the curing of polymer resists for electron lithography, characterized in that the polymer mask at a pressure below ¹ Pa p bombarding ion beam inertvynalezu off gas to the energy range of 25 eV to 5 keV of the hub portion 3-300 C. cm “ ² .