Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
2001-02-08
2004-11-09
Deo, Duy-Vu (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
C438S719000, C438S745000, C438S753000
Reexamination Certificate
active
06815360
ABSTRACT:
This invention relates to providing a novel micro-machined structure and a method for providing the structure.
Micro-machining of silicon (and other materials) to provide structures which have dimensions of the order of micro-meters is known. This technique is used to provide structures fabricated from bulk material and shares some common features with the techniques used to fabricate integrated circuits. For instance it is disclosed in WO 96/10630 to provide tetrahedral structures, or barbs, which have a base dimension of between 30 micro-meters to 80 micro-meters.
It is disclosed in U.S. Pat. No. 5,591,139 to fabricate a microneedle parallel to the surface of a substrate wherein the walls of the needle are fabricated from SiO
2
deposited by low pressure chemical vapour deposition. To form such a needle a large number of steps are required.
U.S. Pat. No. 5,262,128 discloses micro-projections having ducts therethrough. It is claimed that the micro-projections may be fabricated by the Liga process. The skilled person will appreciate that this process is not a technique for microstructuring silicon and is used for processing metals and polymeric materials. Further, all structures fabricated by the Liga process must have edges which are substantially perpendicular to the surface of the substrate from which they are formed. From the remainder of this document it will be apparent that the Liga process is not suitable for fabricating the micro-projection disclosed herein.
Further, U.S. Pat. No. 5,262,128 states that the structures disclosed therein were fabricated by techniques well-known in the integrated circuit industry. It is disputed that in 1989, the application date of U.S. Pat. No. 5,262,128, silicon processing techniques, were known which could produce the structures disclosed therein. It is even disputed that such techniques were known in 1993, the publication date of U.S. Pat. No. 5,262,128. Techniques for fabricating high aspect ratio ducts have only recently become known. This is no discussion in U.S. Pat. No. 5,262,128 of how to form the structures shown therein, thus the teachings are not enabling.
An alleged Internet disclosure purportedly dated 22 Jun. 1998 by Georgia Tech (www.gtri/gatech/edu/res-news
eedles.htnl) discloses arrays of micro-projections. On the second page of this document it is disclosed that future work includes attempting to fabricate needles which are hollow by some unspecified process. Therefore, the purported Georgia Tech document does not provide an enabling disclosure of hollow micro-projections (since they cannot make them since this is indicated as future work).
Further, the skilled person will appreciate that the fact that other research institutions other than the applicants are working on providing the structures shown in U.S. Pat. No. 5,262,128 points at the non-enabling nature of U.S. Pat. No. 5,262,128.
According to a first aspect of the invention there is provided a method of providing a micro-projection on the surface of a first material, the micro-projection having a base portion adjacent the first material, and a remote, or tip, portion, and a duct at least in a region of the tip portion and the method comprising micro-machining the first material to provide the micro-projection and duct.
The method may comprise forming the duct such that it passes between the tip portion and the base portion.
Indeed, in some embodiments the duct may be formed such that it passes entirely through the micro-projection and may be through the first material supporting the micro-projection. Such a method provides a micro-projection onto the surface of a material through which matter may be passed, possibly a fluid.
The first material may be a semi-conductor, such as silicon material, or other material with a crystal lattice structure. The first material may be glass.
Preferably the base portion has a width of less than approximately 1000 &mgr;m and most preferably less than approximately 100 &mgr;m and possibly below 10 &mgr;m.
The tip portion of the micro-projection may have an apex. The method may fabricate the micro-projection such that the duct is coincident with the apex of the micro-projection. This may provide a needle like structure which has a number of uses.
In one embodiment the method may comprise fabricating the duct in a piece of material and subsequently forming the micro-projection around the duct. If such a method is used the method may comprise fabricating the duct and then fashioning the material such that the tip portion of the micro-projection coincides with the duct. Indeed, the apex of the micro-projection may be fabricated to be coincident with the duct.
The duct may be formed by a number of processes and any one of the following list may be suitable: deep dry etching, laser ablation, light assisted anodisation of n-type silicon in HF acid, focused ion beam milling. Each of these techniques may provide a duct of suitable dimensions for the realisation of the method, and will be known to the person skilled in the art.
A mask layer may be formed on to the surface of the first material. The mask layer may comprise silicon dioxide should the first material be a bulk silicon crystal.
An aperture may be formed into the mask layer using lithographic and etching techniques as will be known to the person skilled in the art.
The first material may be removed from a region underneath the aperture in the mask using an etching technique. This step provides one way of forming the duct.
The duct, or a hole that will become the duct, may be formed in a sheet of planar material. A plurality (e.g. of the order of hundreds of thousands) of ducts may be formed simultaneously.
Once a suitable duct has been formed in, for example, a sheet of material, the micro-projection may be formed from the material by a number of techniques. For example any one of the following list may be suitable: anisotropic wet etching of silicon using liquid alkaline etches, focused ion beam milling, or transferring the pattern to the silicon from a domed resist mask using some form of plasma/ion beam etching.
The mask layer may be removed from the first material. A second masking layer may be created on to the first material which may be silicon dioxide. The second masking layer may be grown (perhaps by a low temperature oxide process LTO) or may be deposited (perhaps by plasma enhanced chemical vapour deposition PECVD). An advantage of removing the first masking layer and creating a second masking layer is that the inside surface of the duct is covered and protected by the second masking layer whereas the first masking layer left this area unprotected. Of course, we may apply the second masking layer without removing the first masking layer (or without removing it completely). The second masking layer may be applied over the hole/duct surfaces.
The second masking layer may be patterned (may be using standard lithographic techniques) and may be subsequently etched.
The second masking layer may be left in the shape of a disc, or a rectangle. In perhaps the preferred embodiment the second masking layer is left with a square remaining. The second masking layer may have its edges aligned with specific crystal planes of the first material. The second masking layer may be silicon dioxide.
In one embodiment the first material (which may be a bulk silicon crystal) may be etched in an anisotropic etch which undercuts the second masking layer. The crystal planes of the first material may have been arranged so that planes having a low etch rate bound the etching process creating the desired micro-projection structure. The second masking layer may then be removed. Such a process results in the micro-projection being formed from the first material.
In an alternative embodiment once the second masking layer has been formed so that it covers the inside surface of the duct, and in this embodiment it also covers the upper surface of the first material, the portion of the masking layer covering the upper surface of the first material may be removed so as to leave the second masking laye
Canham Leigh T
Cox Timothy I
Reeves Christopher L.
Deo Duy-Vu
Nixon & Vanderhye PC
Qinetiq Limited
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