Patent Application
20090011158
The present invention relates to microneedle structures and corresponding production methods and, in particular, it concerns hollow microneedle structures in which a through-bore is formed partially by a dry etching process and partially by a wet etching process.
In MEMS technology, several processing techniques are available for use in fabricating devices, each with its own particular characteristics, advantages and disadvantages. Of particular importance in the context of the present invention are two groups of processing techniques referred to generically as “wet etching processes” and “dry etching processes.” In the dry etching processes category, particular reference will be made to Deep Reactive Ion Etching (DRIE).
In wet etching processes, a wafer with a suitable mask is processed by immersion in an etchant so as to selectively etch away parts of the wafer to form a desired structure. The etching process may be isotropic, i.e., occurring at a constant rate in all directions allowed by the mask, independent of the crystallographic planes of the wafer, or may be anisotropic, i.e., eroding material along specific crystallographic planes. Examples of anisotropic etching processes (such as KOH in silicon on (100) and (110) planes respectively) are illustrated in
In order to manufacture a high aspect ratio structure or hole, DRIE techniques are used. For example, in the field of hollow microneedles, a hole with a high aspect ratio hole (greater then 10:1) is often required. Such holes cannot be formed using conventional wet etching techniques, so a DRIE technique is used instead.
DRIE is typically implemented either using a process known as “the BOSCH® process” (including repeated deposition of a passivation layer) or under cryogenic conditions, thereby inhibiting isotropic etching and limiting the etching process to the direction of direct ion bombardment. This process can form structures perpendicular to a wafer surface, for example a silicon wafer, with high aspect ratio such as holes and wall structures with substantially any desired cross sectional shape.
DRIE processing is a batch process, typically only allowing processing of one wafer at a time, and with limitations on the wafer size. Furthermore, the process itself is relatively slow, optimally performed at a rate of roughly 10 microns per minute, and requires relatively large and expensive equipment. As a result, a DRIE production step is often the limiting factor in rates of production of a MEMS system, and accounts for a relatively large proportion of the production costs.
For these reasons, where possible, it is advantageous to employ wet etching processes in which relatively low costs chemical materials are used to create structure and channels in silicon, and multiple wafers can be etched simultaneously.
In the field of microneedle fabrication, U.S. Pat. No. 6,533,949 to Yeshurun et al. (hereafter “the '949 patent”), which is hereby incorporated by reference in its entirety, discloses fabrication techniques for hollow microneedles in which DRIE processes are used to form upright surfaces of the microneedles and a through-bore while wet etching techniques are used to form an oblique surface, thereby defining various hollow microneedle structures. The structures described therein have been found highly advantageous, combining robustness and sharpness, as well as providing a geometry for a fluid flow bore which does not become blocked during penetration of the skin. The production technique described, however, relies upon dry etching to form the full length of the fluid flow bore passing through the substrate, with the consequent implications for the production processing efficiency and costs.
It would therefore be highly advantageous to provide a structure and corresponding production method which would maintain the advantageous properties of the structures taught by the '949 patent and variants or modifications thereof while employing wet etching techniques to replace at least some of the dry etching steps previously described.
The present invention is a method for forming a hollow microneedle structure and a corresponding microneedle structure.
According to the teachings of the present invention there is provided, a method for forming a hollow microneedle structure comprising the steps of: (a) providing a wafer having a front side and a backside; (b) processing the front side to form at least one microneedle projecting from a substrate and a first part of a through-bore passing through the microneedle and through a part of a thickness of the substrate; and (c) processing the backside to form a second part of the through-bore, wherein the first part of the through-bore is formed by a dry etching process, and wherein the second part of the through-bore is formed by a wet etching process.
According to a further feature of the present invention, the wafer is a silicon wafer.
According to a further feature of the present invention, the second part of the through-bore is formed by an isotropic wet etching process.
According to a further feature of the present invention, the second part of the through-bore is formed by an anisotropic wet etching process.
According to a further feature of the present invention, the first part of the through-bore has an aspect ratio greater than 10:1.
According to a further feature of the present invention, the first part of the through-bore is formed by deep reactive ion etching.
According to a further feature of the present invention, an external shape of the microneedle is formed by at least two intersecting surfaces, at least a first of the surfaces being formed by a dry etching process and at least a second of the surfaces being formed by a wet etching process.
According to a further feature of the present invention, the first surface and the first part of the through-bore are formed concurrently.
According to a further feature of the present invention, the second surface and the second part of the through-bore are formed concurrently.
According to a further feature of the present invention, the second part of the through-bore is formed prior to the first part of the through-bore, and wherein the second surface is formed subsequent to the first part of the through bore.
According to a further feature of the present invention, the first part of the through-bore intersects the second surface.
According to a further feature of the present invention, the backside is further processed by a supplementary dry etch process to form a third part of the through-bore within the second part, the third part intersecting the first part to form the through-bore.
According to a further feature of the present invention, a plurality of the microneedles with the through-bores are formed in distinct regions of the wafer for subdivision into chips, and the method further comprises forming, by a wet etching process, dicing channels on at least one of the backside and the front side extending along dicing lines between the distinct regions.
According to a further feature of the present invention, the dicing channels are formed concurrently with the second parts of the through-bores.
According to a further feature of the present invention, the dicing channels are formed on both the front side and the backside.
According to a further feature of the present invention, the dicing channels are formed so as to traverse an entire thickness of the substrate, thereby separating the distinct regions into chips.
According to a further feature of the present invention, a dicing process is performed to sever a remaining thickness of the wafer after formation of the dicing channels so as to separate the distinct regions into chips.
According to a further feature of the present invention, a plurality of the microneedles with the through-bores are formed in distinct regions of the wafer for subdivision along dicing lines into chips, and wherein the method further comprises forming, by a wet etching process, a trench on the backside, the trench substantially circumscribing the through-bore of each distinct region and spaced inwardly from the dicing lines.
According to a further feature of the present invention, at least one trench extension contiguous with the trench and extending to one of the dicing lines is formed on the backside by a wet etching process.
According to a further feature of the present invention, a plurality of non-contiguous recessed features are formed on the backside outside the trench by a wet etching process so as to enhance an available contact surface for receiving an adhesive.
According to a further feature of the present invention: (a) the distinct regions are separated along the dicing lines so as to form chips; (b) adhesive is applied to a peripheral area of the backside of one of the chips outside the trench; and (c) the chip is adhered to a support structure to form a microneedle device, such that any excess adhesive collects within the trench, thereby avoiding clogging of the through-bore.
According to a further feature of the present invention, a plurality of the microneedles with the through-bores are formed in distinct regions of the wafer for subdivision along dicing lines into chips, and the method further comprises forming, by a wet etching process, a plurality of non-contiguous recessed features on the backside so as to enhance an available contact surface for receiving an adhesive.
There is also provided according to the teachings of the present invention, a hollow microneedle structure comprising: (a) a substrate having a front side and a backside; (b) at least one microneedle projecting from the front side of the substrate; and (c) a through-bore passing through the microneedle and through the substrate, wherein a first part of the through-bore extending from the microneedle through a first portion of a thickness of the substrate is formed by a dry etching process, and wherein a second part of the through-bore extending from the backside through a second portion of the thickness of the substrate is formed by a wet etching process.
According to a further feature of the present invention, the substrate and the microneedle are formed from silicon.
According to a further feature of the present invention, the second part of the through-bore is formed by an isotropic wet etching process.
According to a further feature of the present invention, the second part of the through-bore is formed by an anisotropic wet etching process.
According to a further feature of the present invention, the first part of the through-bore has an aspect ratio greater than 10:1.
According to a further feature of the present invention, an external shape of the microneedle is formed by at least two intersecting surfaces, at least a first of the surfaces being an upright surface relative to the front side and at least a second of the surfaces being an oblique surface relative to the front side.
According to a further feature of the present invention, the first part of the through-bore intersects the oblique surface.
According to a further feature of the present invention, the substrate has a boundary, and wherein the backside features a trench substantially circumscribing the through-bore and spaced inwardly from the boundary.
According to a further feature of the present invention, the backside further includes at least one trench extension formed by a wet etching process, the trench extension being contiguous with the trench and extending the boundary.
According to a further feature of the present invention, there is also provided: (a) a support structure for supporting the substrate; and (b) a layer of adhesive applied to a peripheral area of the backside outside the trench, the layer of adhesive attaching the substrate to the support structure.
According to a further feature of the present invention, the backside further includes a plurality of non-contiguous recessed features formed by a wet etching process so as to enhance an available contact surface for receiving an adhesive.
There is also provided according to the teachings of the present invention, a method for forming a hollow microneedle structure comprising the steps of: (a) providing a wafer having a front side and a backside; (b) processing the front side to form: (i) a plurality of microneedles projecting from a substrate in distinct regions of the wafer for subdivision along dicing lines into chips, and (ii) a first part of a through-bore passing through each of the microneedles and through a part of a thickness of the substrate; and (c) processing the backside to form: (i) a second part of the through-bore for each microneedle, and (ii) a trench substantially circumscribing the through-bore of each distinct region and spaced inwardly from the dicing lines.
There is also provided according to the teachings of the present invention, a method for forming a hollow microneedle structure comprising the steps of: (a) providing a wafer having a front side and a backside; (b) processing the front side to form: (i) a plurality of microneedles projecting from a substrate in distinct regions of the wafer for subdivision along dicing lines into chips, and (ii) a first part of a through-bore passing through each of the microneedles and through a part of a thickness of the substrate; and (c) processing the backside to form: (i) a second part of the through-bore for each microneedle, and (ii) a plurality of non-contiguous recessed features so as to enhance an available contact surface for receiving an adhesive.
There is also provided according to the teachings of the present invention, a method for forming a hollow microneedle structure comprising the steps of: (a) providing a wafer having a front side and a backside; (b) processing the front side to form: (i) a plurality of microneedles projecting from a substrate in distinct regions of the wafer for subdivision along dicing lines into chips, and (ii) at least part of a through-bore passing through each of the microneedles and a thickness of the substrate; and (c) forming, by a wet etching process, dicing channels on at least one of the backside and the front side extending along dicing lines between the distinct regions.
The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:
The present invention is a method for forming a hollow microneedle structure and correspond microneedle structures.
The principles and operation of production methods and structures according to the present invention may be better understood with reference to the drawings and the accompanying description.
Referring now to the drawings,
The processing of the wafer includes processing the front side to form at least one microneedle projecting from a substrate and a first part of a through-bore passing through the microneedle and through a part of a thickness of the substrate. The processing of the wafer also includes processing the backside to form a second part of the through-bore, the first part and the second part intersecting or being joined by a third part to form the through-bore. It is a feature of certain particularly preferred implementations of the present invention that the first part of the through-bore is formed by a dry etching process, and the second part of the through-bore is formed by a wet etching process. In this manner, the production time and costs are significantly reduced relative to the technique of the aforementioned U.S. Pat. No. 6,533,949 which forms the entirety of the through bore for each microneedle by DRIE techniques. This and other advantages of the present invention will become clearer from the following description.
Before addressing the features of the present invention in more detail, it will be helpful to define certain terminology as used herein in the description and claims. The term “MEMS” is used herein loosely to refer to the field of technology and corresponding production techniques for producing mechanical structures with dimensions in the micron range up to several hundred microns. In most cases, the microneedle structures of the present invention do not include electronic components and could thus be more accurately referred to as “MMS”.
The term “wafer” is used to refer to a block of material from which the microneedle structures of the present invention are produced, primarily by etching techniques. The invention applies primarily to semiconductor wafers, and most preferably to silicon wafers. It should be noted that the structures of the present invention may be referred to as “formed from silicon” despite a surface layer of silicon dioxide which is always present under ambient conditions, and which may be further developed in order to impart desired mechanical or other properties to the final structure, all as is well known in the art.
The term “etching” is used to refer to any process step which selectively removes material from the wafer. “Wet etching” is used to refer to processes in which surfaces of the wafer are selectively covered by a mask and the wafer is then exposed in its entirety, or at least over an entire side, to a chemical etchant, whether by immersion in a bath, by spray application or by any other type of exposure. “Dry etching” is used to refer to processes in which an active species effective to cause etching is applied directionally to the wafer surface, as exemplified by reactive ion etching (RIE). The term “deep reactive ion etching” (DRIE) is used generically to refer to any implementation of RIE or a similar process which is effective to form high aspect ratio features and/or near vertical surfaces. Examples of DRIE include, but are not limited to, cryogenic-DRIE and BOSCH©-process DRIE. Practical implementation details for all of the various etching techniques referred to herein are, per se, well known to those ordinarily skilled in the art, and will not be addressed here in detail.
The term “substrate” is used to refer to the remaining thickness of the substrate which provides an underlying roughly planar surface from which the final microneedles project. Commonly, a single wafer may be processed to fabricate a plurality of microneedle structures at the same time. In such cases, the term “chip” refers to a defined sub-region of the wafer (or substrate) which is to be severed or otherwise separated along “dicing lines” to form a microneedle structure. Unless otherwise specified, the term “dicing” refers to any technique which can be employed to separate a wafer into chips along dicing lines. The term “sever” is used to refer specifically to a cutting operation performed by a saw or other mechanical cutting device.
The term “microneedle” is used herein to refer to a solid structure protruding from a substrate to a height of between 30 microns and 1000 microns, and most preferably between 250 microns and 800 microns. A microneedle is referred to as “hollow” if it has a bore passing through it to allow supplying or sampling of fluid through the bore. The hole or bore is referred to as a “through-bore” if it passes through to the backside of the substrate. The bore can have any cross-sectional shape.
When reference is made to the “external shape” of the microneedle, this refers to the external surfaces making up the three dimensional shape of the microneedle without reference to the internal surfaces of the bore. Surfaces or directions are referred to as “upright” if they are generally perpendicular to the surface of the wafer or the substrate. For convenience of reference, use may be made of “vertical”, “up”, “down”, “height” or the like to refer to directions or dimensions generally perpendicular to the initial plane of the surface of the wafer, and “horizontal”, “width” or the like to refer to directions or dimensions generally parallel to the initial plane of the surface of the wafer. The work “oblique” is used to refer to a surface which is significantly inclined both to the horizontal and vertical, and typically forming an angle of between 20 degrees and 70 degrees to the upright.
The term “aspect ratio” refers to the ratio of the height to width of a given structure or feature. Particularly in relation to a roughly parallel sided bore, the aspect ratio corresponds to the ratio of the depth of the parallel-sided portion of the bore to the diameter (or otherwise defined maximum width) of the bore.
Channels, trenches or recesses etched into a surface are referred to as “contiguous” if fluid can pass from one to the other without rising above the level of the surrounding surfaces. Conversely, recesses are “non-contiguous” if fluid cannot pass between them without rising above the level of the surrounding surfaces.
The term “concurrently” refers to two operations which occur during coincident or overlapping time periods, either where one begins and ends during the duration of the other, or where a later one starts before the completion of the other. The term “subsequently” refers to a later operation which occurs after completion of the earlier operation. It should be noted that any reference in the description and claims to a plurality of operations or steps should not be taken to define any particular order in which the operations or steps are to be performed unless such temporal relation is explicitly stated.
Turning now to the features of the present invention in more detail,
Turning now to
As mentioned earlier, the order of the various front side and backside processing may be varied without departing from the general scope of the present invention. Certain particular choices of the order of various steps have accompanying advantages and disadvantages. For example, in the sequence as illustrated in
In an alternative approach to the sequence of operations, it is possible to perform front side and backside wet etching processes concurrently, typically preceded by the front side dry etching required to form the upright surfaces of the microneedles and front part of the through-bore. This would reduce the number of process steps, and thus possibly also increase production rates.
The extent of the various wet etching processes may be limited to a required depth by various stopping techniques known in the field of MEMS and microelectronic production methods. By way of example, the processes may be stopped on the basis of elapsed time that the wafer is exposed to the chemical etching agent, or using in situ stopper such as embedded Boron atoms in concentration higher the 1019 per cubic centimeter (which are embedded by diffusion processes or by ion bombardment), or by any other conventional stopping mechanism, all as is known in the art.
In addition to the reduce fabrication time and cost achieved by the use of backside wet etching for part of the through-bore, the resulting structure is believed to provide one or more of a number of additional advantages. Specifically, by shortening the length of the narrow portion of the through-bore, fluid flow impedance is reduced. Furthermore, the shaped rear part of the through-bore serves as a tapered intake, reducing flow impedance for liquids (drugs or other materials) to be delivered to the skin, and rendering the liquid delivery more efficient, for example, allowing delivery of liquid at a given rate by a driving pressure lower than would otherwise be required. The use of reduced liquid pressure in turn reduces the mechanical stress exerted on the mounting of the microneedle array, e.g., adhesive, which holds the array in position.
In summary, it is believed that using wet etching processes to partially etch the silicon wafer back side of the microneedle/pyramid will provide one or more of the following advantages compared to a similar process performed exactly according to the teachings of the '949 patent:
Turning now to the remaining
It should be noted that, although the schematic illustrations of
Referring specifically to
Turning now to
Parenthetically, it is noted that certain applications of the microneedle chips of the present invention have microneedles 30 located in close proximity to one edge of chip 32. In such cases, trench 36 is hereby defined to “substantially circumscribe” microneedles 30 if it extends around the microneedles on the remaining sides on which the microneedles are not in close proximity to the edge.
It will be noted that both the trench features of
It will be appreciated that the above descriptions are intended only to serve as examples, and that many other embodiments are possible within the scope of the present invention as defined in the appended claims.
| Number | Date | Country | |
|---|---|---|---|
| 60895467 | Mar 2007 | US |
