Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Forming nonplanar surface
Reexamination Certificate
1999-04-28
2001-09-18
Wu, Shean C. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Forming nonplanar surface
C430S320000, C430S323000, C430S324000, C430S310000, C438S052000
Reexamination Certificate
active
06291140
ABSTRACT:
TECHNICAL FIELD
The present invention concerns cantilevers and a method of making the same. These cantilevers are in particular suited for use in scanning probe systems, such as microscopes.
BACKGROUND OF THE INVENTION
An atomic force microscope (AFM), as well as a scanning force microscope (SFM) or a scanning tunneling microscope (STM), is an instrument in which a flexible cantilever of very small dimension is scanned across a surface. Conventional cantilevers are fabricated by micro machining techniques. Currently, there are two basically different ways to make cantilevers. The first uses thin films deposited onto a silicon substrate. The cantilever is then defined by lithography and etched into the thin film by wet or dry etching, followed by selective removal of the silicon underneath the cantilever. In the second fabrication method, the cantilever is micro machined out of a bulk silicon. This is done by etching through a window in a mask layer from the backside until the thickness equals twice the desired thickness of the cantilever. The cantilever is then defined and patterned by lithography on the front side and consecutively etched into the silicon until both etch fronts meet and the cantilever is released. Operating in reverse order is also possible by adding to the process a deposition step with a masking layer in order to protect the front side during backside thinning. The methods are described, for example, in Journal of Vacuum Science and Technology, Vol. B 9, No 2, March/April 1991, pp. 1353 to 1357.
The tip of a cantilever is the most crucial part. The resolution of a picture of a sample surface depends on the quality of the tip. That requires a well defined tip with known cone angle and sharp top apex.
Tips can also be either prepared as thin film tips using a silicon substrate or etched out of a silicon wafer by the following steps. Starting with a photolithographically patterned circular mask the silicon is etched away in the surroundings of the mask. Simultaneously, the mask is undercut until it is completely under etched. When the mask is released and the etching is stopped a silicon cone remains. An example for the microfabrication of a tip is disclosed in the article “Silicon cantilevers and tips for scanning force microscopy”, J. Brugger et al., Sensor and Actuators A, Vol. 34, 1992, pp. 193-200. Large tips can be made by means of electroplating. To achieve this, a plating base is required to define the position where the tip is to be formed.
A disadvantage of these methods is that there remains residues of the etching. The usual fabrication of cantilevers with integrated tips needs at least three photolithographic steps and several dry and wet etching steps. The labour required for the fabrication is complex and expensive.
It is an object of the present invention to overcome the disadvantages of known approaches.
It is a further object of the present invention to provide a method for cost efficient fabrication of cantilevers with tip.
It is another object of the present invention to provide a simpler method for the fabrication of cantilevers with tip.
SUMMARY OF THE INVENTION
The present invention provides an efficient and easy method for fabricating cantilevers with tip. The method, according to the present invention, comprises the steps of forming a tip-like indent in a substrate to create a master, depositing a photoresist layer which fills said tip-like indent and covers at least a part of the substrate, and photolithographically structuring said photoresist layer to form said cantilever with tip out of said photoresist.
As outlined, the first step concerns the manufacturing of a master. This step is carried out just once. The master is reusable and a lot of cantilevers with tip can be produced using the same master. Only the other steps have to be repeated. There is a photoresist layer which is spin-coated over the master. This first photoresist layer fills also the tip-like indent, covers the master and has a planar surface. Photolithographically structuring means to expose the photoresist layer using a cantilever mask. After that, another photoresist layer together with the first photoresist layer might be deposited, exposed and developed, e.g. to make a body for the attachment. Finally, the cantilever with tip is lifted-off from the master. To improve this step a sacrificial layer might be placed between the master and the photoresist layer. Likewise, the cantilevers with tip might be delivered with the master to guarantee for a safe transport.
The inventive method allows to reduce the cost of manufacturing cantilevers since photoresist, such as SU-
8
, material cost is low and the process sequence is shortened. With the described method are no transfer steps necessary. The method is simple and the fabrication throughput is very high, because the major throughput contributions are only the two exposures and developments. Depending on the substrate and the cantilever size used in production, up to several thousand cantilevers could be fabricated on one substrate (master) with high yield and two exposures only.
The present invention further relates to an apparatus for batch-manufacturing of cantilevers with tip which comprises means for depositing a photoresist layer on a substrate with indent, means for applying and aligning masks, means for illuminating said photoresist layer through openings in said masks, and means for developing said photoresist layer of cantilevers with tip. It might further comprise means for depositing a second photoresist layer, means for illuminating said second photoresist layer through openings in a mask, and means for developing said second photoresist layer, providing a thickened mounting section.
It is an advantage of such an apparatus, that all fabrication steps can be carried out by one apparatus. This apparatus might work automatically and makes the fabrication processes simple and cost-efficient.
REFERENCES:
patent: 4968585 (1990-11-01), Albrecht et al.
patent: 5045439 (1991-09-01), Maner et al.
patent: 5051379 (1991-09-01), Bayer et al.
patent: 5223086 (1993-06-01), Terada et al.
patent: 5272913 (1993-12-01), Toda et al.
Andreoli Cornel
Brugger Jürgen P.
Dreschler Ute
Vettiger Peter
Drumheller Ronald L.
Ohlsson Olaf
Wu Shean C.
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