Microneedle manufacturing process with hats

Abstract

Out-of-plane microneedle manufacturing process comprising the simultaneous creation of a network of microneedles and the creation of a polygonal shaped hat (2) above each microneedle (1) under formation, said process comprising the following steps: providing bridges (3) between the hats (3), maintaining the bridges (3) during the remaining microneedle manufacturing steps, removing the bridges (3), together with the hats (2), when the microneedles (1) are formed.

Claims

1. A method of manufacturing a microneedle comprising the steps of: (i) patterning a protective mask to form an etch opening in the protective mask for etching a wafer, the etch openings formed adjacent to an area of the wafer where the microneedle will be formed; (ii) first isotropic etching of an exposed area of the wafer at the etch opening to form a first cavity in the wafer; (iii) first anisotropic etching of the first cavity to define a head of the microneedle; (iv) second isotropic etching to form a shoulder of the microneedle, after the step (iii); (v) second anisotropic etching to form a shaft of the microneedle, after the step (iv); (vi) third isotropic etching to form a tip of the microneedle and to pattern a through hole, such that the tip of the microneedle detaches from the protective mask, after the step (v), and (vii) removing the protective mask after the step (vi).

2. The method of manufacturing the microneedle according to claim 1, wherein the step (vi) removes the wafer material along the entire shaft of the microneedle.

3. The method of manufacturing a microneedle according to claim 1, wherein the steps (ii), (iii), (iv), and (v) are configured such that they do not form a final shape of the tip of the microneedle.

4. The method of manufacturing a microneedle according to claim 1, wherein in the step (iv) of second isotropic etching, the tip of the microneedle does not detach from the hat of the protective mask.

5. The method of manufacturing a microneedle according to claim 1, wherein the step of (i) patterning the protective mask forms a plurality of etch openings in the protective mask, the plurality of etch openings formed adjacent to a hat and traversed by bridges formed by the protective mask.

6. The method of manufacturing a microneedle according to claim 5, wherein the bridges of the protective mask are multi-layered.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The invention is discussed below in a more detailed way with examples illustrated by the following figures:

(2) FIG. 1 shows a microneedle manufacturing process according to the state of the art.

(3) FIG. 2 shows a microneedle manufacturing process according to the invention.

(4) FIG. 3 is an upper view of the element shown in FIG. 2.

(5) FIG. 4 is a picture of an assembly microneedle-hat according to the state of the art (without bridges)

(6) FIG. 5 shows one example of bridges according to the invention.

(7) FIG. 6 shows another example of bridges according to the invention.

(8) FIG. 7 shows another example of bridges according to the invention.

(9) FIG. 8 shows another example of a bridges according to the invention.

(10) FIG. 9 is a picture of the example shown on FIG. 5.

(11) FIG. 10 is a picture of microneedles with hats and bridges before removal (status before FIG. 11)

(12) FIG. 11 is a picture of a microneedle obtained with a process according to the invention.

NUMERICAL REFERENCES USED IN THE FIGURES

(13) 1. Microneedle 2. Hat 3. Bridge 4. Wafer 5. Damaged area 6. Rectilinear segment 7. circle 8. circle 9. Metal layer 10. SiO.sub.2 layer

(14) State of the art MEMS microneedle fabrication process as described in FIG. 1 usually starts with a wafer, preferably a silicon wafer 4. On top of this silicon wafer a silicon dioxide layer is used as a protective mask to pattern the microneedles.

(15) This process aims at obtaining microneedles separated from each others and as a consequence the continuous protective mask in step A becomes discontinue at the start of the structuration of the microneedles step B. The parts of this discontinuous protective mask are called hats 2 and each microneedle is overlooked by a hat, protecting the microneedle and allowing controlled and well defined structuration. FIG. 4 shows an example of a microneedle creation 1 under a hat 2.

(16) This structuration of the microneedles is performed by a sequence of isotropic and anisotropic etches as represented in FIG. 1 steps B to E.

(17) The first isotropic etch as represented in FIG. 1 step B initiates the tip of the microneedle. The first anisotropic etch (FIG. 1, step C) is used to define the head of the microneedle.

(18) The goal of the second isotropic etch as represented in FIG. 1 step D is to initiate the shoulder of the microneedle and to separate the head of the microneedle with the shaft which is obtain thanks to the second anisotropic etch (FIG. 1, step E). Finally comes the last isotropic etch (FIG. 1, step F) which is the most important etch of the process. Thanks to this etch, we pattern the tip of the microneedle, the backside trough holes and the final design of the microneedle,

(19) An oxidation and a silicon oxide etch as represented in FIG. 1, step G are then realized to remove the hats and to polish the silicon surface.

(20) Frequently hats may fall before the end of the process (FIG. 1, step F, Ref. 2): This leads to a situation in which the structuration of the microneedle becomes uncontrolled resulting in malformation and low production yields. In addition the fallen hats provoke a bad surface state as shown in FIG. 1 Ref 5.

(21) The present invention provides a way to hold the hats together so that they won't fall before the end of the process. To this effect the hats are linked together and are linked to the edges as displayed in FIG. 3. These links (FIG. 2, Ref 3), also named bridges in the present text, will stay in place up to the end of the process and guarantee the stability of each hat until the microneedle fabrication is ended (FIG. 2 Step F). When the process has been completed (FIG. 1 step G) the hat and their links are removed revealing perfect microneedles pattern (see e.g. FIG. 11) and chip surface state.

(22) An important advantage of these links is that they do not modify the microneedle structuration parameters. The isotropic and anisotropic etches are the same with or without links.

(23) As described earlier bridges and hats are deeply linked together; as a matter of fact their are made of same materials and have the same thickness.

(24) As far as the design of the bridges is concerned it can take many forms. Simple linear bridge between the hats can be an option as shown schematically in FIG. 5 and on the picture in FIG. 9 which represents microneedle process of step B in FIG. 1.

(25) Curved segments as in FIG. 6 and FIG. 7 or combination of rectilinear and curved segments as in FIG. 8 are also possible.

(26) Another aspect of the design of the bridges is the material. Single layer bridges can be appropriate for many processes but depending on the complexity of the process and also on the cleaning steps multilayer bridges can be a better option. Multilayered bridges improve the characteristics of the bridges (FIG. 10). We may associate metal layers (aluminium, tungsten, nickel . . . ) and no conductive layers (silicon dioxide, silicon nitride . . . ). The metal layers improve the thermal conductivity of the bridges and the non conductive layers improve the mechanical resistance and the high selectivity of the bridges.