Method of patterning a substrate with an atomic mask

Details Method of patterning a substrate with an atomic mask Method of patterning a substrate with an atomic mask

2000-06-23

2001-12-18

Valentine, Donald R. (Department: 1741)

Electrolysis: processes, compositions used therein, and methods

Electrolytic coating

Coating selected area

C216S041000, C205S666000, C427S264000, C427S532000, C427S552000, C427S596000

Reexamination Certificate

active

06331238

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an atomic mask useful for a quantum well semiconductor laser utilizing quantum effects which take place in Bohr's atomic radius or smaller, the formation of a pattern in a ultra-micro device such as a single electron transistor, and the formation of a pattern in a recording medium such as CD-ROM. The invention also relates to a method of patterning a substrate with an atomic mask.
2. Description of the Related Art
As semiconductor devices have been fabricated in smaller and smaller sizes, a metal pattern is designed to have a narrower width, and is sometimes required to have an atomic-sized width on the sub-nanometer or nanometer order. Thus, there is a need for forming a fine pattern having an atomic-sized width.
To this end, there have been suggested many methods employing a scanning tunneling microscope (hereinafter, referred to simply as a “STM”) . One of such methods has been suggested in I-W. Lyo et al., Science 253, pp. 173, 1991. In the suggested method, a probe of a STM is placed close to a substrate at such a distance as a tunnel current could run therebetween with a voltage being applied across the probe and the substrate. Atoms are desorbed out of the substrate because of the field evaporation effect which takes place when a tunneling current is generated.
In another method suggested by H. J. Mamin et al., “Atomic Emission from a Gold Scanning-Tunneling-Microscope Tip”, Physical Review Letters, Vol. 65, No. 19, 1990, pp. 2418-2421, there is used a probe of a STM which is coated with gold atoms by evaporation. The gold atoms are transferred from the probe to a substrate and deposit on the substrate because of the field evaporation effect.
In still another method suggested by M. Baba et al., “Nanostructure Fabrication by Scanning Tunneling Microscope”, Japanese Journal of Applied Physics, Vol. 29, No. 12, 1990, pp. 2854-2857, chlorine or fluorine gas is applied onto a substrate, and etching is carried out just beneath a probe of a STM to thereby pattern the substrate. For instance, a metal gas such as WF
6
gas is flowed onto a substrate, and is decomposed just beneath a probe of a STM and deposited onto the substrate. Thus a pattern is formed on the substrate.
However, the above mentioned conventional methods of forming a fine pattern by employing a STM have to repeatedly carry out the step of moving a probe to align with an atom one by one and applying a voltage across the probe and the atom. Thus, the conventional methods have a problem that it takes too much time to form a pattern.
In addition, the generation of a tunneling current is greatly dependent on the shape of the probe, configuration and defects of a substrate, and contamination on a substrate etc. For instance, if there happens to exist contamination at a place where a probe is positioned, the probe may be destroyed or conditions for making a pattern are significantly varied.
For the above mentioned reasons, the conventional methods would take much time for forming a lot of patterns, and might be quite unstable in forming patterns. Furthermore, a probe of a STM has to be repositioned each time when the same pattern is to be formed in other areas, resulting in a problem that it is impossible to shorten a period of time for forming a lot of patterns.
SUMMARY OF THE INVENTION
In view of the above mentioned problems of the conventional methods of forming a pattern by employing a STM, it is an object of the present invention to provide a method of forming an atomic-sized pattern which method is capable of forming a pattern with simple steps in a shorter period of time than conventional methods, and further capable of repeatedly forming the same patterns. It is also an object of the present invention to provide an atomic mask suitable for the above mentioned method.
In one aspect, there is provided an atomic mask including a mask substrate and atoms adsorbed on the mask substrate, the atoms forming a mask pattern having a one-atomic thickness. For instance, the atoms adsorbed on the mask substrate are noble metal such as tungsten, platinum, gold and palladium.
The atomic mask may further include a device for applying a current to the atomic mask, a heater for heating the atomic mask and/or a device for applying a voltage across the atomic mask and a substrate to be etched by using the atomic mask.
It is preferable that the mask substrate is formed with a raised area in which the mask pattern is formed. The raised area may be formed by etching an area other than the raised area. More specifically, the raised area may be formed by the steps of depositing adatoms over a surface of the mask substrate, putting a probe of a scanning tunneling microscope close to the mask substrate, and scanning the mask substrate with the probe with a voltage being applied across the mask substrate and the probe.
When the above mentioned atomic mask adsorbs adatoms which used to be deposited on a substrate to be patterned, the atomic mask may be recovered by heating in ultra-high vacuum.
In another aspect, there is provided a method of patterning a substrate with an atomic mask having a mask substrate and first atoms adsorbed on the mask substrate, the first atoms forming a mask pattern having a one-atomic thickness, including the steps, in sequence, of (a) depositing adatoms over a surface of a substrate to be patterned, the adatoms having low reactivity with second atoms of which the substrate is composed, and (b) putting the atomic mask close to the substrate in such a distance that the first atoms make a chemical bond with the adatoms, so that adatoms located nearest to the first atoms are desorbed out of the substrate to form a pattern on the substrate, the pattern being defined as an area where none of the adatoms exists.
The above mentioned method is explained in brief hereinbelow with reference to
FIGS. 1A
to
1
F. As illustrated in
FIG. 1A
, there is prepared an atomic mask
4
comprising a mask substrate
1
and a mask pattern
3
composed of atoms
2
and formed on the mask substrate
1
by means of a STM (hereinafter, the atoms
2
are referred to as “mask atoms”). A desired pattern will be formed on a substrate by employing the atomic mask
4
.
First, as illustrated in
FIG. 1B
, first atoms are adsorbed over a surface of the substrate
5
on which a desired pattern is to be formed. Herein, the first atoms are selected from atoms having low reactivity with second atoms of which the substrate
5
is composed (hence, hereinafter the first atoms are referred to as “adatoms”, and the second atoms as “substrate atoms”).
Then, as illustrated in
FIG. 1C
, the atomic mask
4
is placed close to the substrate
5
in such a manner that the atomic mask
4
is kept parallel to the substrate
5
. When the atomic mask
4
is placed close to the substrate
5
in such a distance that the mask atoms
2
form a chemical bonding force such as Coulomb's force and electronegativity with the adatoms
6
, the adatoms
6
located nearest to the mask atoms
2
are desorbed from the substrate
5
because of the chemical bonding force generated therebetween, and are adsorbed to the mask atoms
2
patterned on the atomic mask
4
, as illustrated in FIG.
1
D. Thus, the adatoms
6
are desorbed in a pattern in line with the mask pattern
3
, as illustrated in
FIG. 1F
, and hence, a pattern
8
is formed on the substrate
5
. Herein, the pattern
8
has the same configuration as that of the mask pattern
3
, and is defined as an area in which none of the adatoms
6
exists.
There is further provided a method of patterning a substrate with an atomic mask having a mask substrate and first atoms adsorbed on the mask substrate, the first atoms forming a mask pattern having a one-atomic thickness, including the steps of (a) forming a raised area on the mask substrate, the mask pattern being to be formed within the raised area, (b) depositing adatoms over a surface of a substrate to be patterned, the adatoms having low reactivity with second atoms of which the

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