Semiconductor device manufacturing: process – Radiation or energy treatment modifying properties of...
Reexamination Certificate
2000-05-03
2001-10-23
Zarabian, Amir (Department: 2824)
Semiconductor device manufacturing: process
Radiation or energy treatment modifying properties of...
C438S096000, C438S048000
Reexamination Certificate
active
06306779
ABSTRACT:
BACKGROUND OF THE INVENTION
a) Field of the Invention
The invention relates to the field of production or treatment of semiconductor components or other solid-state components and is directed to a method for nanostructuring of amorphous carbon layers.
The method is advantageously applicable in the production of electronic components in the submicrometer range and in the nanometer range and, in this connection, is suitable particularly for generating nanostructured etch masks whose structure is to be transferred to layers located below them. Further, the method according to the invention can be applied for entering information in amorphous carbon layers for the purpose of storing information.
b) Description of the Related Art
Previously, masks for structure transfer into underlying layers by etching or for application of the lift-off method were produced by photolithography and with electron beam lithography. Further, various possibilities are known for generating structures with structure sizes in the nanometer range by scanning probe microscopes. For example, electron beam sensitive lacquers or resists can be exposed by scanning tunneling microscopes (E. A. Dobisz and C. R. K. Marrian,
Appl. Phys. Lett.
58, 2526 (1991)), and scanning force microscopes are used for mechanical modification of layers (V. Bouchiat and D. Esteve,
Appl. Phys. Lett.
69, 3098 (1996)) or metal conductor paths (R. Rank, H. Brückl, J. Kretz, I. Mönch and G. Reiss,
Vacuum
48, 467 (1997)) and for field-induced local oxidation of silicon (C. Schönenberger, N. Kramer,
Microelectron. Eng.
32, 203 (1996)).
Within the group of inorganic resist materials, amorphous carbon layers hold an important place (K. Kragler, E. Günther, R. Leuschner, G. Falk, A. Hammerschmidt, H. von Seggern and G. Saemann-lschenko,
Appl. Phys. Lett.
67, 1163 (1995)). Among the advantages are that the reactivity of the amorphous carbon with most substrates is negligible, amorphous carbon is resistant to halogen plasma, so that structured carbon films are suitable as etch masks for halogen-plasma etching for structure transfer into underlying layers. Carbon films can easily be removed by means of reactive ion etching with oxygen or hydrogen.
It is known that amorphous carbon layers can be structured in that the structure of a layer lying above the carbon is transferred into the carbon by etching.
Direct structuring of amorphous carbon films by means of etching in the electron beam in a defined oxygen environment is also known. Structure sizes down to 0.5 &mgr;m have been achieved by this method (D. Wang, P. C. Hoyle, J. R. A. Cleaver, G. A. Porkolab and N. C. MacDonald,
J. Vac. Sci. Technol.
B 13, 1984 (1995)). While the reaction products are volatile in an advantageous manner in this case, a substantial disadvantage of this method consists in that structures generated in this manner in the amorphous carbon cannot be transferred into silicon substrates lying below the carbon layer because an etch-resistant layer occurs at the silicon surface during structuring.
Local graphitization of diamond-like carbon films in the focus of a laser and production of masks through the use of the different oxygen plasma etch rates of graphite and diamond-like carbon are also known. In this way, structures with sizes in the range of 5 &mgr;m could be generated (J. Seth, S. V. Babu, V. G. Ralchenko, T. V. Kononenko, V. P. Ageev and V. E. Strelnitsky,
Thin Solid Films,
254, 92 (1995)).
OBJECT AND SUMMARY OF THE INVENTION
It is the primary object of the invention to generate structures with sizes in the nanometer range in amorphous carbon layers by means of a direct structuring.
This object is met by the inventive method described herein for nanostructuring of amorphous carbon layers.
According to the invention, a local field-induced reaction of the carbon is activated by an electrically conductive or semiconducting probe which is located above or guided over the amorphous carbon layer at a distance in which the electric conduction mechanism of the field emission or of tunneling is possible and to which an electric voltage is applied relative to the layer at locations where depressions are introduced in the layer or the layer is to be removed. The reaction products occurring in this way are advantageously volatile, so that the desired structure is formed with an additional technological step.
The electrically conductive or semiconducting probe is advisably located at a distance of up to 10 nm above the amorphous carbon layer or is guided over the latter.
According to the invention, the electric voltage applied to the probe can be a negative DC voltage potential with a minimum voltage in the range of 3 to 8 volts relative to the layer or can be an AC voltage.
Corresponding to an advisable arrangement of the invention, the distance between the electrically conductive or semiconducting probe and the amorphous carbon layer can be defined by an electrically insulating layer with a thickness of up to several nanometers which is located on the surface of the probe.
According to the invention, the reaction can be carried out in an oxygen environment, wherein oxides of the carbon occur as reaction products or the reaction is carried out in a hydrogen environment or a nitrogen environment.
According to an advisable arrangement of the invention, the nanostructuring can be carried out by means of a scanning probe microscope, wherein the electrically conducting or semiconducting probe of the microscope is used for the field-induced reaction of the carbon.
A structured electrode whose structure is formed as the negative of the nanostructure to be achieved in the layer can also be used as electrically conducting probe. An electrode of this kind is then worked into the amorphous carbon layer and, in doing so, transfers its structure.
Corresponding to an arrangement of the invention, the distance between the electrically conductive or semiconducting probe and the amorphous carbon layer can be changed periodically over time during the structuring.
Corresponding to another arrangement of the invention, the negative DC voltage potential can also be changed periodically over time during the structuring.
According to the invention, an electrically conductive or semiconducting probe of silicon can also be used, wherein the polarity of the DC voltage potential is reversed during the structuring at determined intervals for determined times. In this case, a layer of silicon oxide is formed on the surface of the probe by field-induced oxidation or a layer of this kind is reproduced.
Instead of a DC voltage source, a constant current source can also be used according to the invention, wherein the junction resistance or transition resistance between the electrically conductive or semiconducting probe and the amorphous carbon layer is to be adjusted in such a way that a determined minimum voltage is achieved during the structuring.
The invention further provides that the method according to the invention is used for the purpose of storing digital or analog information in that structures representing digital or analog information are introduced into amorphous carbon layers by the nanostructuring according to the invention.
The method according to the invention has several substantial advantages over the prior art. It is particularly advantageous that the structures can be generated in the carbon layers by means of direct structuring since the reaction products of the carbon are volatile in the applied method. It is further advantageous that precise structures can be generated with sizes in the range of nanometers by the method. Further, the method offers arrangement possibilities for the third dimension of the layer to be structured, that is, into the depth of the layer.
In the following, the invention will be described more fully with reference to embodiment examples and accompanying illustrations.
REFERENCES:
patent: 4802951 (1989-02-01), Clark et al.
patent: 4896044 (1990-01-01), Li et al.
patent: 5343042 (1994-08-01), Fuchs et al.
patent: 5504338 (1996-04-01), Marrian
Brueckl Hubert
Muehl Thomas
Reiss Guenter
Institut fuer Festkoerper-und Werkstofforschung Dresden e.V.
Reed Smith LLP
Smith Bradley
Zarabian Amir
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