Photocopying – Projection printing and copying cameras – Focus or magnification control
Reexamination Certificate
1999-09-28
2001-11-06
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Focus or magnification control
C355S053000, C355S067000, C356S399000, C356S400000, C356S401000, C430S005000, C430S020000, C430S022000, C430S030000
Reexamination Certificate
active
06313905
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention is related to an apparatus and method for defining a pattern on a substrate using a shadow masking technique.
2. Prior Art
The shadow masking technique as well as inclined exposure and deposition are well known and allow efficient fabrication of patterns by replacing the conventional lithography cycle comprising deposition, photo and etch process steps by just one single process and machine. A main disadvantage of the traditional shadow masking technique is its limitation to simple low density patterns. Up to now it has not been possible to define more complex patterns, such as ring type patterns, or to produce patterns in close proximity to each other with sub 100 nm dimensions by shadow masking technique. Inclined exposure and deposition allows definition of very small single features, but the close proximity of patterns cannot be achieved by inclination.
V.T. Petrashov, Microelectronic Engineering 35 (1997) p. 357-359 reflects the state of the art. The technique proposed there allows fabrication of more complex patterns and elements with dimensions of less than 50 nm. This is achieved by a lift-off technique using self narrowing of atomic beams and in-situ rotation of the substrate. The lift-off technique is a special form of photo lithography and therefore different from the shadow masking technique. It has not the simplicity of the shadow masking technique because it includes a photo step as well as final removal of photo resist and excess material (the so-called lift-off).
It is an object of the present invention to overcome the disadvantages of prior art systems and to define patterns of complex shape in close proximity to each other with sub 100 nm dimensions.
SUMMARY OF THE INVENTION
The present invention is directed to an apparatus which comprises a flexible member having a mounting base, a movable portion which is movable with respect to said mounting base and at least one aperture in or near said movable portion, said member in operation being positioned above said substrate thereby acting as a shadow mask. The apparatus further comprises an emission source aiming through said aperture at said substrate, distance-controlling means for controlling the distance between said movable portion and said substrate and an actuator for moving said flexible member and said substrate relative to each other parallel to a surface of the substrate.
A unique feature of the described apparatus is that rings and other complex types of patterns can be defined by shadow masking technique. Another unique feature of the invention in comparison with standard shadow masking techniques is that high pattern densities with a spacing of less then 100 nm can be achieved. The ability to move the shadow mask together with the precise positioning relative to previously fabricated patterns allows a high pattern density on the substrate. On the shadow mask, the spacing of the apertures can be much larger. In principle, a shadow mask with one single aperture (e.g. a circular hole) is sufficient to define an arbitrary pattern on the substrate and to repeat it as often as necessary.
Various modifications and improvements of said apparatus are also disclosed. Using the Atomic Force Microscopy (AFM) principle for implementing the described apparatus has additional advantages. The AFM is very powerful at distance regulation on the sub nm scale and at identifying nano-scale features. The current invention concerns a special form of such a device where the cantilever contains one or more apertures and serves as a shadow mask. In the current invention the force interaction between a cantilever with integrated tip, and a surface of a substrate can be used to maintain the cantilever (i.e. the shadow mask) at a constant height with respect to the substrate, to allow precise positioning of the shadow mask in the surface plane relative to previously fabricated or existing patterns, and to validate the defined patterns during/after fabrication. It is important to mention that the cantilever need not resemble a conventional AFM cantilever but could be a larger flexible member. The shadow mask can be moved during patterning and thereby arbitrary patterns can be defined. A plurality of shadow masks may be operated independently or in parallel.
Using a tip integrated in the flexible member proves advantageous because the tip will be able to follow a surface of a substrate very closely when scanning the surface. For certain applications the tip may also be rounded or replaced by a bump or a larger element. A conductive tip may be used for in-situ inspection of electrical properties or in-situ functional testing. It is also possible to have more than one tip on a flexible member. The tip may be used:
as scanning part in the distance-controlling means thus allowing to position the shadow mask in close and at a well defined distance to a surface of a substrate.
for pattern inspection whereby the position of the tip with respect to a pattern can be defined to within
1
nm. The position of an aperture relative to the tip can also be defined within 1 nm. The presence of the aperture on the same movable component (the flexible member) as the tip ensures a precise auto-alignment. The true position of a flexible member could be controlled using optical feedback. This allows e.g. in-situ quality monitoring, identification of existing patterns and subsequent relative positioning of an aperture and the corresponding pattern with nanometer accuracy, and copying and cloning of existing patterns by scanning a master pattern.
for local surface modification on a substrate. This is especially advantageous in repair work where e.g. in-situ interruption of a metal line may be needed.
for inspection of electrical properties. In this case, conductive tips such as diamond tips can be used. In-situ inspection of electric properties allows to define electrical resistance, capacitance, transconductance etc. of devices as they are made, thereby tightening the specification of nanometer electronics. This is particularly a crucial issue in the fabrication of single-electron transistors.
for in-situ functional testing of devices. The test results can be used as input for process control, for yield improvement, for repair or in case of larger devices for activating redundant elements.
The in-situ monitoring of a physical or chemical property can be used to advantage for interactive process control. It is e.g. possible to program the tip to inspect the thickness of a generated pattern and to feed back this information in order to modify the deposition rate or time, or the scan speed at which the aperture is moving.
Locating an aperture in or near a tip proves advantageous because the distance to the surface of a substrate is most accurate at the tip.
Inclined exposure or deposition, where the direction of the emission source, and/or the walls of the apertures in the mask are inclined, can be combined to advantage with an apparatus according to the present invention. Spots and lines thus produced will be smaller and the dimensions of the mask features (i.e. of the apertures in the flexible member) can be much larger than the patterns achieved.
In accordance with the present invention, the emission source can be an electron, light or material source. When an electron source is used, a new form of lithography is possible. The apparatus of the present invention is also compatible with high-resolution e-beam lithography. The creation of a master mask using conventional e-beam lithography compensates for the slow write speed of this technique. In the described apparatus, copies of the master can quickly be generated using a large beam electron source. This removes the need for highly focused expensive electron optics.
When a material source is used, the material deposition in and around an aperture will cause narrowing of the aperture (hole-filling). The hole-filling effect can be used to advantage in enabling single-atom wires to be written. In most cases however it will be necessary
Brugger Juergen P.
Gimzewski James K.
Gueret Pierre L.
Luethi-Oetterli Roland
Schlittler Rato R.
Adams Russell
Brown Khaled
International Business Machines - Corporation
Morris, Esq. Daniel P.
Scully Scott Murphy & Presser
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