JP2004524172A - Micro projection array and method of manufacturing micro projection - Google Patents

Abstract

An array of microprojections is formed from a silicon wafer by a plurality of successive plasma and wet isotropic and anisotropic etching steps. The resulting microprojections (14) have a sharp tip (18) or cut edge formed by wet isotropic etching, and each microprojection has a concave side (16). Having a substantially pyramid shape. The tip of each microprojection has a substantially flat upper surface (20) extending parallel to the base (12).

Description

【Technical field】
[0001]
The present invention is directed to microdevices and microprotrusion arrays. The present invention is also directed to a method of manufacturing a microdevice, particularly a microprojection array, for delivering or retrieving a substance through a patient's skin.
[Background Art]
[0002]
Various microdevices that perform various tasks are known in the art. One area of application that has recently attracted attention is in the field of fluid control devices and microvalves. Microvalves have been found to be useful in many industrial applications, including in the field of ink jet printers as well as drug delivery, fuel delivery systems for internal combustion engines, and the like. These devices have been made by many different processes.
[0003]
Many techniques commonly used in the manufacture of electronic devices and integrated circuit chips are suitable for micromachining micromechanical devices. These microdevices are commonly referred to as micro-electrical mechanical systems (MEMS). Devices are extremely small and can be made from many types of materials. A common material is silicon in the form of a silicon wafer as used in the integrated circuit industry. Other materials that can be used include glass and ceramics.
[0004]
An example of a microvalve is disclosed by Johnson et al. The microvalve disclosed therein includes a silicon diaphragm having a valve seat and a flow path. The diaphragm is positioned so that it can contact the valve seat when the diaphragm is deflected. The diaphragm is formed by etching and machining a silicon body. A separate actuation force is applied to the diaphragm to open and close the valve. The actuating device can be a pressurized fluid or a solenoid mechanism to apply a force to one side of the diaphragm.
[0005]
Solenoid actuation of valves in gas chromatography assemblies is known and is disclosed by Terry et al. The valve structure is formed by etching and machining the valve body to form a desired shape. Solenoid-operated devices are expensive to make and some of the devices cannot be manufactured efficiently.
[0006]
Another area of microdevices is in the field of devices for delivering or sampling substances through the skin of a patient. Microdevices are usually small gauge needles or needle-like devices for penetrating the skin to a desired depth. Microneedle devices are desirable in many applications because they can deliver or retrieve substances through the skin with minimal pain or discomfort to the patient.
[0007]
One type of device that has gained attention is a microdevice that can penetrate the outer layers of the skin with less pain or discomfort than a standard cannula. These microdevices typically have needles that are a few microns to a few hundred microns long. Microdevices for delivering drugs through the skin create fine holes or cuts through the stratum corneum. Many drugs can be effectively administered by penetrating the stratum corneum and delivering the drug to the skin in or below the stratum corneum. Devices for penetrating the stratum corneum generally comprise a plurality of micron-sized needles or blades having a length to penetrate the stratum corneum without completely passing through the epidermis. Examples of these devices are disclosed by Godshall et al., Lee et al., Allen et al. (See, for example, US Pat.
[0008]
Various methods have been used to make the microneedle and microblade of a conventional drug delivery device. However, these methods limit the shape and dimensions of the microneedle or microblade. Therefore, there is a continuing need in the manufacturing industry to improve the method of forming microdevices.
[0009]
[Patent Document 1]
U.S. Patent No. 6,056,269
[Patent Document 2]
U.S. Pat. No. 4,582,624
[Patent Document 3]
U.S. Pat. No. 5,879,326
[Patent Document 4]
U.S. Pat. No. 5,250,023
[Patent Document 5]
WO 97/48440 pamphlet
[Patent Document 6]
US Patent No. 6,334,856
DISCLOSURE OF THE INVENTION
[Problems to be solved by the invention]
[0010]
The present invention is directed to microdevices, especially microprojections. The present invention is also directed to a method for forming a microdevice.
[0011]
Accordingly, a primary object of the present invention is to provide a process for forming microdevices, particularly microprojection arrays, in an efficient and economical manner.
[0012]
It is another object of the present invention to provide a process for forming a microprojection array for delivering or retrieving a substance through a patient's skin.
[0013]
Yet another object of the present invention is to provide a process for forming a microprojection array by wet etching of a silicon wafer.
[0014]
It is a further object of the present invention to provide a process for forming a microprojection array by etching a substrate to produce microprojections having a substantially pyramidal shape.
[0015]
It is another object of the present invention to provide an etching process for forming conical microprojections using a wet isotropic etchant.
[0016]
It is a further object of the present invention to provide a process for forming an array of microprojections having an axial passage through the microprojections.
[0017]
It is yet another object of the present invention to provide an etching process for forming an axial passage in a microprojection after forming the microprojection.
[0018]
It is a further object of the present invention to provide a process for forming microprojections by etching a substrate to form microprojections having an annular body and a conical tip.
[0019]
Another object of the present invention is to provide a process for forming an annular microtube having a continuous sharp ridge on the annular surface.
[0020]
It is a further object of the present invention to provide a process for forming an oxide layer on the tip of a microprojection and removing the oxide layer to form a sharp tip.
[0021]
Yet another object of the present invention is to provide a process for forming a microprojection array by forming a ring-shaped masking layer on a substrate and etching the substrate to form annular microprojections. It is to be.
[0022]
It is a further object of the present invention to provide an etching process for forming a microprojection having a beveled tip.
[0023]
Another object of the invention is to provide a process for forming a microprojection array having microprojections having an outer annular surface, wherein the outer annular surface has a plurality of sharp points. It is to be.
[Means for Solving the Problems]
[0024]
These and other objects of the present invention are basically a base having a width and length, a top surface and a bottom surface, and a plurality of micro-projections arranged in an array, extending from a top surface of the base and integral with the base. , Wherein each microprojection comprises a microprojection having at least one surface extending to an outer edge thereof.
[0025]
It is a further object of the present invention to provide a substrate having a top surface and a bottom surface, and to form a patterned masking layer in a plurality of regions on the top surface, wherein the regions of the patterned masking layer are Defining an exposed area on the top surface of the substrate having a predetermined dimension corresponding to the microprojection and surrounding the area of the masking layer; and exposing the exposed area on the upper surface of the substrate to a plurality of microprojections. This is achieved by providing a method of forming a microprojection array that includes the steps of: etching to a desired depth; and removing the masking layer from the substrate to expose the microprojections.
[0026]
It is still another object of the present invention to provide a silicon substrate having a top surface with a masking layer, and removing a portion of the masking layer to expose a plurality of substantially ring-shaped portions of the masking layer on the top surface. Forming a channel extending through the center of each ring-shaped portion and forming an annular column around each ring-shaped portion; and forming a masking layer. Forming a micro-projection array by removing the ring-shaped portion of the micro-projection array.
[0027]
It is a further object of the present invention to provide a substrate having a top surface and a bottom surface, and to form a plurality of recesses in the top surface, the recesses defining a surface inclined with respect to a plane of the top surface; Forming a sloped surface array of sharp tips; removing a portion of the substrate around the sharp tip to form a microprojection array having an outer edge formed by the sharp tips; This is achieved by providing a method for forming a microprojection array comprising:
[0028]
It is still another object of the present invention to provide a substrate having a top surface and a bottom surface, and to form a microprojection array on the top surface of the substrate, wherein the microprojections have a top surface. Forming at least one slope on the top surface of the microprojections.
[0029]
The objects, advantages and other salient features of the present invention will become apparent to those skilled in the art from consideration of the accompanying drawings and the following detailed description of the invention, which form a part of this initial disclosure. It becomes clear to.
BEST MODE FOR CARRYING OUT THE INVENTION
[0030]
The present invention is directed to a microprojection device and a method of forming the microprojection device. More specifically, the present invention is directed to a method of manufacturing an integrated microprojection array and a microdevice from the microprojection array.
[0031]
The microdevice of the invention in a preferred embodiment is a microprojection array for penetrating a patient's skin to a selected depth to deliver or retrieve material through the patient's skin. The term "microprojection" as used herein refers to a structure that can penetrate one or more layers of a patient's skin to a desired depth. The microprojections in a preferred embodiment of the present invention have a sharp tip and can be conical or pyramidal. As the term is used herein, a microprojection, as in some embodiments described herein, has a pointed or sharp tip or a cutting or scraping end. It comprises a protruding member having a square or circular cross section, which may or may not have. The micro-projections also include ring-shaped columns having an axial passage.
[0032]
1 to 3 show one embodiment of the micro device 10 of the present invention. The micro device 10 includes a base 12 and a plurality of micro protrusions 14. In this embodiment, the microprojections 14 are spaced in substantially uniformly spaced rows and columns. The microprojections 14 have a substantially pyramid shape, and each side surface 16 has a concave surface. Side 16 is centered on tip 18. The tip 18 of each microprojection 14 has a substantially flat upper surface 20 that extends parallel to the base 12. As shown in the top view of FIG. 3, the top surface 20 has a substantially square shape.
[0033]
The microdevice 10 has a plurality of projecting members and is primarily used to penetrate a patient's skin to a selected depth for delivering or retrieving a substance from a patient. You. In a preferred embodiment, the microdevice 10 is coupled to a reservoir for delivering a substance, especially a pharmaceutical composition, to a patient. Alternatively, the microdevice 10 comprises a suitable extraction device, an absorbent device or a substance for collecting and storing fluid from the patient. Examples of substances that can be sampled from a patient include drugs, analytes, and glucose.
[0034]
The microprojections 14 of the present invention have a length and width suitable to penetrate into the patient's skin to a desired depth to deliver a substance that the body can absorb and utilize. The length of the microprojections 14 is generally determined by the substance to be delivered and the delivery area on the skin. In embodiments of the present invention, the microprojections 14 can have a length from about 10 μm to about 2 mm. In one embodiment, the microdevice 10 is a delivery device for penetrating the stratum corneum of the skin without penetrating the stratum corneum so as to minimize pain and irritation to the patient. In this embodiment, the microprojections can have a length from about 10 μm to about 100 μm, typically from about 10 μm to about 50 μm. Delivery and sampling devices intended to penetrate selected layers of the skin can have a length from about 100 μm to about 1000 μm. In other embodiments, the microdevice 10 is in a stratum corneum, or in a microabrader for digging or carving grooves through the stratum corneum, to deliver or retrieve material through the skin. Incorporated.
[0035]
The microdevice 10 can be made from a variety of materials, depending on the intended use and the substance to be delivered or sampled. Suitable examples include metals such as gold, polymeric materials such as polycarbonate, and other non-metals. In a preferred embodiment, microdevice 10 is made from silicon. Silicon is a preferred material because silicon wafers are readily available and can be machined and formed using a variety of known processes.
[0036]
The micro device 10 is preferably manufactured from a silicon wafer by MEMS processing (micro electro mechanical system). Silicon is an element that exists in three forms: crystalline, polycrystalline, and amorphous. Silicon is an elastic and strong material that is particularly suitable for the microdevice of the present invention. Ultra-high purity electronic grade silicon wafers available in the electronics industry are suitable for use in the present invention.
[0037]
Polycrystalline silicon (commonly referred to as polysilicon) and amorphous silicon are typically deposited on substrates as thin films with a typical thickness of less than 5 μm. Crystalline silicon substrates are commercially available as circular wafers. These silicon wafers are generally available in 100 mm diameter and about 150 mm diameter. A silicon wafer having a diameter of 100 mm has a thickness of about 525 μm.
[0038]
The mechanical properties of a silicon wafer depend on the crystal orientation of silicon. As will be described in more detail later, the crystal orientation determines the surface selective etching of the silicon wafer. Silicon has a diamond lattice crystal structure that can be considered as a simple cubic shape. Certain directions and planes within the crystal are defined using a three-axis notation enclosed in square brackets, carets, parentheses, and braces, as is known in the art. Is specified for For example, [100] indicates a specific vector direction of the cube, and <100> indicates six directions. Similarly, (111) is a plane perpendicular to the [111] vector. The {111} vector represents all eight equivalent crystal planes. As is known in the art, many etching processes selectively etch {100} planes but do not etch {111} planes, so the angle between {100} and {111} is It is important in micromachining processes. To control the shape of the finished product, some etching processes can etch different surfaces at different rates, while others etch at similar rates. Most of the commercially available silicon wafers have a {100} orientation, indicating that the top surface is a {100} plane.
[0039]
The microdevice 10 in the preferred embodiment is made from a silicon wafer by various successive masking and selective etching steps. In the embodiment of FIGS. 1-3, the microdevice 10 is made by forming a patterned mask on the top surface of a silicon wafer. The mask is formed as an array of spaced dots corresponding to the spacing of the microprojection array and the desired pattern. In the embodiment of FIGS. 1-3, the dots have a substantially square shape to produce a microprojection having a substantially square tip. The size of the dots in the mask material determines the final size of the microprojections. In a preferred embodiment, the mask is a photoresist material applied to the surface of the silicon wafer and exposed to a light source to form a pattern in the photoresist layer.
[0040]
After the photoresist is formed in a desired pattern, the exposed silicon is etched to remove a part of the silicon. In the illustrated embodiment, the silicon is etched to form an inclined surface on the sides of the microprojections. This shape is usually obtained with a wet potassium hydroxide etching solution.
[0041]
The microdevices of the present invention are made by various masking and etching processes, resulting in different shaped microdevices. In one embodiment, the mask is formed by photolithography, resulting in a desired pattern of photoresist. Alternatively, the mask can be formed from a silicon nitride or silicon oxide layer. The etching step can be performed by wet etching, plasma etching, reactive ion etching (RIE), and deep reactive ion etching (DRIE).
[0042]
Lithography is a process commonly used in MEMS manufacturing processes that applies a layer of photoresist on a substrate. Photoresist layers are photosensitive emulsion layers that form soluble and insoluble patterns when exposed to light. The photoresist layer is exposed and an image of a mask is printed on the layer. The mask is an opaque chrome layer patterned on a transparent support such as glass. The pattern of the completed photoresist layer is defined by the mask.
[0043]
After exposing the photoresist layer to the selected pattern, the layer is immersed in an aqueous developer to dissolve the exposed portions and create a latent image. The positive photoresist is an organic resin material containing a photosensitive agent. Photoresist is often spin-coated on silicon wafers to a thickness of about 0.5 μm to 10 μm. The photosensitizer prevents dissolution of the unexposed photoresist during immersion in the developer. As the photosensitizer is decomposed by exposure to light in the range of 200 to 450 nm, the exposed areas immediately begin to dissolve in the developer. In a negative photoresist, unexposed areas dissolve in the developer, leaving exposed areas.
[0044]
Substrates and coatings can be etched by various etching processes. Since the etching process used determines the final shape of the microdevice, the etching process is selected accordingly. Factors to consider in choosing an etching process include isotropic, etch media, and etch selectivity over other materials.
[0045]
The isotropic etchant etches the substrate at a substantially uniform rate in all directions, creating a rounded cross-sectional feature. In contrast, anisotropic etchants etch mainly in one direction. Usually, an anisotropic etchant etches along a particular crystal plane of a silicon wafer. Some anisotropic etchants etch mainly along one crystallographic plane and, to a lesser extent, other planes to form various shapes. Using the anisotropic etchant, clear deep trenches or cavities are created, outlined by a flat and clear surface. The crystal plane, and thus the etched surface, is not necessarily perpendicular to the surface of the silicon wafer. Wet etchants can be isotropic or anisotropic, and are generally preferred in the present invention because of cost and ease of handling.
[0046]
The isotropic wet etching agent used in the present invention includes hydrofluoric acid (HF) and hydrofluoric acid, nitric acid (HNO_Three), And acetic acid (CH_ThreeCOOH). Nitric acid oxidizes silicon to silicon dioxide. Silicon dioxide is removed by hydrofluoric acid. The silicon etch rate can be varied from 1 μm / min to 5 μm / min by adjusting the rate of acid in the mixture.
[0047]
Wet anisotropic etchants include metal hydroxides such as sodium hydroxide, potassium hydroxide, cesium hydroxide, and the like. Other suitable hydroxides include ammonium hydroxide and tetramethylammonium ((CH_Three)_FourNOH). Other suitable anisotropic etches include an aqueous mixture of ethylenediamine and pyrocatechol (EDP).
[0048]
Potassium hydroxide is the most commonly used anisotropic etchant. Potassium hydroxide etches silicon along the {111} plane at a rate 100 times slower than when etching the {100} plane. As a result, the silicon wafer can be effectively etched with potassium hydroxide to form a V-shaped groove and a deep groove accurately contoured by the {111} crystal plane. The etch rate of potassium hydroxide on silicon is about 0.5 μm to 2 μm per minute, depending on the temperature and concentration of the etchant.
[0049]
Etching silicon with an aqueous anisotropic etchant creates three-dimensional faceted structures formed by intersecting crystal planes. The design of the masking pattern determines the overall shape of the resulting structure.
[0050]
The desired shape of the completed device is determined in part by the crystal orientation of the silicon wafer. For example, in order to form a V-shaped cavity, a {100} oriented wafer is usually used. The forefront of the etch starts at the opening in the mask and proceeds in the vertical direction (<100> direction) to create a cavity with a flat bottom surface and sloping side surfaces. The etch eventually self-limiting to the four intersecting planes, forming an inverted pyramid or V-shaped trough.
[0051]
During the etching, the concave corners bounded by the {111} plane remain intact. However, since the surface other than {111} is exposed due to slight corrosion of the convex corner, the convex corner is immediately attacked by the etching agent. In this manner, the convex corners in the mask layout are undercut during etching, so that the forefront of etching proceeds directly below the mask.
[0052]
A common dry etching process is a plasma-phase etch. Plasma etching basically involves chemically forming reactive neutrals and ions under the action of an electric or magnetic field, and accelerating particles toward a target. The reactive species is SF₆, CF_Four, Cl_Two, CCIF_Three, And NF_ThreeIs included. One type of plasma etching is commonly referred to as reactive ion etching (RIE). Inductively coupled plasma reactive ion etching (ICP-RIE) uses an externally applied RF magnetic field. Deep reactive ion etching (DRIE) is high-speed etching that can anisotropically etch silicon.
[0053]
The masking material of the present invention is selected according to the etching process used to form the finished product. For example, silicon nitride is an excellent masking material that resists etching in potassium hydroxide. Silicon dioxide can be used as a masking layer for short etches in potassium hydroxide. Photoresist materials are easily etched in alkaline solutions and are not suitable for masking silicon etches. Silicon dioxide and silicon nitride are inherently good masking materials for these etchants because they are not etched by tetramethylammonium hydroxide and ethylenediamine pyrocatechol.
[0054]
A silicon dioxide layer on silicon can be made by oxidizing the silicon in dry oxygen or steam at a temperature of 850-1150 ° C. Forming not only silicon dioxide layers but also silicon nitride layers by atmospheric pressure chemical vapor deposition (CVD), reduced pressure chemical vapor deposition (LPCVD), or plasma enhanced chemical vapor deposition (PECVD). Can be. Silicon nitride (Si_ThreeN_Four) Is often silane (SiH_Four) And ammonia (NH_Three) At about 700 ° C. to 900 ° C. to deposit at atmospheric pressure.
[0055]
Silicon dioxide and silicon nitride can be selectively etched with various etchants. For example, hydrofluoric acid is a preferred wet etch for silicon dioxide, but not for silicon nitride. Phosphoric acid (H_ThreePO_Four) Is a preferred etchant for silicon nitride, but not for silicon dioxide. When plasma etching is used, silicon dioxide or silicon nitride can be selectively etched by selecting an etching gas. For example, oxygen and CHF_ThreeCan be used to plasma etch silicon dioxide. Silicon nitride, SF₆Can be used for etching.
[0056]
In the following embodiments, the process of the present invention will be described with reference to the drawings. The drawings schematically illustrate the forming steps and show the resulting structure in cross section. If the figures show only one microprojection, it will be understood that the actual device includes a plurality of microprojections arranged in an array. The various masking materials and etchants used in the present process are selected to obtain the desired etching along the appropriate surface of the silicon substrate. The silicon substrate is typically a silicon wafer selected to have crystal faces oriented to obtain the desired shape of the microprojections. Also, various etching steps are selected to etch the substrate to a desired depth and obtain a desired result. Typically, the finished microprojections are about 50 to 1000 μm in length and about 50 to about 200 μm in width.
[0057]
4A-4H embodiment
In this embodiment, the silicon wafer 24 is etched by the various steps shown in FIGS. 4A-4G to produce the microprojection array shown in FIG. 4H. Referring to FIG. 4A, an array is formed using a silicon wafer 24 having a top surface 26 and a bottom surface 28. A silicon oxide layer 30 is formed on top surface 26 and a silicon oxide layer 32 is formed on bottom surface 28 of silicon wafer 24. The silicon oxide layers 32 and 30 can be formed by various processes, for example, a low pressure chemical vapor deposition method. A photoresist layer is formed on the silicon oxide layer 32 and developed to form a plurality of spaced circular open areas 34 in the silicon oxide layer 32. The open areas 34 correspond to the dimensions of the internal passages for each microprojection and are spaced apart by a distance corresponding to the desired spacing of the finished microprojections.
[0058]
As shown in FIG. 4B, the opening region 34 of the silicon oxide layer 32 exposes a part of the silicon substrate 24. As shown in FIG. 4C, a silicon nitride layer 36 is formed on the lower silicon oxide layer 30 and a silicon nitride layer 38 is formed on the upper silicon oxide layer 32 and the opening 34. Silicon nitride layers 36 and 38 can be formed by various processes, including low pressure chemical vapor deposition.
[0059]
A photoresist layer is formed on silicon nitride layer 36 and developed to form a photoresist mask on silicon nitride layer 36 opposite opening area 34. The dimensions of the photoresist layer correspond to the desired shapes and dimensions of the finished microprojections. As shown in FIG. 4D, the exposed portions of silicon nitride layer 36 and silicon oxide layer 30 are etched with a plasma etch to produce nitride mask 40 surrounding exposed surface 42 of silicon substrate 24.
[0060]
A wet isotropic etchant is applied to surface 42 of silicon substrate 24 to etch silicon substrate 24 and oxide layer 30 to produce microprojections 44 having the structure shown in FIG. 4E. As shown in FIG. 4F, nitride layers 40 and 38 are removed by a wet nitride etch. At this stage, the silicon oxide layer 32 defines an exposed area 34 on the underside of the silicon substrate 24.
[0061]
As shown in FIG. 4G, a plasma etch is applied to the lower surface of silicon substrate 24 and exposed area 34 to form an axial passage 46 through microprojections 44. The plasma etch is applied in such a way as to form a substantially smooth walled channel extending perpendicular to the plane of the silicon substrate 24. As shown in FIG. 4G, passages 46 are etched from the bottom surface of silicon substrate 24 and extend to silicon oxide layer 30. As shown in FIG. 4H, the silicon oxide layers 30 and 32 are removed by a silicon oxide etch to obtain a microprojection array 22. Preferably, the silicon oxide layer is removed by a wet etching process.
[0062]
In this embodiment, by forming a masking layer at a selected position on the silicon substrate 24, a plurality of microprojections 44 can be simultaneously formed in the silicon substrate. The shape and length of the microprojections 44 are determined by the etching process, the shape and size of the masking layer, and the time for applying the etching agent. In the illustrated embodiment, the silicon nitride masking layer 40 has a substantially circular shape that creates a conical microprojection 44. In another embodiment, the silicon nitride mask 40 can have a square shape, so that the etching step produces pyramidal shaped microprojections.
[0063]
5A-5I Embodiment
In this embodiment, the microprojection array 48 shown in FIG. 5I is formed from a silicon substrate 50 as shown in FIGS. 5A to 5H. Referring to FIG. 5A, silicon substrate 50 has an upper surface 52 and a bottom surface 54. A silicon nitride layer 56 is deposited on top surface 52 of silicon substrate 50. After a photoresist layer is applied over the silicon nitride layer 56, it is exposed and developed to form a silicon nitride mask 58 on the upper surface 52 of the silicon substrate 50, as shown in FIG. 5B. Silicon nitride mask 58 has a shape and dimensions corresponding to the desired shape of the microprojection tip. Referring to FIG. 5C, an anisotropic wet etch is applied to upper surface 52 of silicon substrate 50, and silicon substrate 50 is etched along the inclined surface to form conical portion 60. Typically, the anisotropic etchant is potassium hydroxide, which etches along the slope as shown in FIG. 5C.
[0064]
As shown in FIG. 5D, the silicon nitride mask 58 is removed by a nitride etch to obtain a conical projection 62 extending from the silicon substrate 50. A silicon oxide layer 64 is applied to the top surface of the silicon substrate 50 to completely cover the conical protrusions 62 and the etched surface 66. A photoresist layer is applied to oxide layer 64. The photoresist layer is exposed and developed to form a photoresist mask overlying the sloped surface 60, and the oxide layer 64 overlying the surface 66 to be etched and the tip 68 of the conical protrusion 62. Expose part. Next, the oxide layer 64 is selectively etched to remove an exposed portion of the oxide layer. The photoresist mask is removed, leaving an oxide mask 70 on the inclined surface 60 of the protruding member 62. As shown in FIG. 5F, a frustoconical shaped oxide mask 70 remains on the inclined surface 60 of the projecting member 62.
[0065]
The oxide layer 70 exposes the upper surface 66 and the tip 68 of the silicon substrate 50. Next, a photoresist layer is applied over the oxide layer 70, the tip 68, and the etched surface 66. Next, the photoresist layer is exposed and developed to form a photoresist mask 72 as shown in FIG. 5G. The photoresist mask 72 substantially covers the oxide layer 70 and the surface 66 of the substrate 50, exposing the tip 68.
[0066]
The axial passage 74 is etched from the top surface through the substrate 50 to form a continuous channel extending through the conical projection 62 to the bottom surface 54 of the substrate 50. As shown in FIG. 5H, the photoresist mask 72 is removed, exposing the surface 66. Preferably, the axial passage 74 is formed by a plasma etch to form the axial passage 74 along a plane substantially perpendicular to the bottom surface 54 of the silicon substrate 50.
[0067]
A plasma etch is then applied to surface 66 and etched along a plane perpendicular to bottom surface 54 to form a substantially annular surface 76 around conical surface 60, as shown in FIG. 5I. As shown in FIG. 5I, the resulting microprojections 48 have a substantially cylindrical sidewall 76 that extends perpendicularly from the substrate 50 and terminates with a conical top surface 60 and a sharp tip 78. An axial passage 74 extends from tip 78 to bottom surface 54.
[0068]
6A-6M Embodiment
In this embodiment, the microprojection array is formed from a silicon substrate 80 having a top surface 82 and a bottom surface 84. An oxide layer 86 is formed on the upper surface 82 of the silicon substrate 80. A photoresist layer is formed on oxide layer 86. The photoresist layer is patterned and developed to form a substantially annular photoresist mask 88 for each microprojection, as shown in FIG. 6B. The photoresist mask 88 defines a central exposed region 90 of the oxide layer 86 and a peripheral exposed region 92. The exposed regions 90 and 92 of the oxide layer 86 are removed by etching, for example, by plasma etching. The oxide etch results in a ring-shaped oxide mask 94 on top surface 82 of silicon substrate 80.
[0069]
The photoresist mask 88 is removed, exposing the oxide mask 94, as shown in FIG. 6C. Oxide mask 94 defines an inner surface 96 and a peripheral surface 97 of upper surface 82 of silicon substrate 80. An isotropic etch is applied to surfaces 96 and 98 to form a curved surface 98 that extends from etched surface 100 to oxide mask 94. As shown in FIG. 6D, the isotropic etch etches a portion of the silicon substrate 80 directly below the oxide mask 94 to define a protrusion 102 below the oxide mask 94. Preferably, the isotropic etch is a wet etch, as known in the art.
[0070]
The oxide mask 94 is removed by an oxide etch. Preferably, the oxide etch is a wet etch using, for example, hydrofluoric acid. The oxide etch removes oxide mask 94 exposing protruding portions 102 defined by curved surface 97 and top surface 104. As shown in FIG. 6E, the upper surface 104 of the protruding portion 102 has a substantially flat surface corresponding to the original upper surface 82. The protruding portion 102 has a substantially annular shape extending upward from the silicon substrate 80.
[0071]
Next, an oxide layer 106 is formed on the upper surface of the silicon body 80. Oxide layer 106 can be formed using various processes known in the art. In one embodiment, the upper surface of silicon body 80 is heated in an oxygen-containing atmosphere. Preferably, oxide layer 106 is formed in a manner that consumes a portion of the outer surface of silicon body 80. As shown in FIG. 6F, the oxide layer 106 is formed to a thickness such that the opposing curved surfaces 97 of the protrusions 102 are consumed and coalesce to form a sharp tip 108.
[0072]
A photoresist layer is applied over the formed oxide layer 106. The photoresist layer is exposed and developed to form a photoresist mask 110 having an annular shape and overlying the sharp tip 108. The exposed region of the oxide layer 106 is selectively etched to remove the photoresist mask 110. This results in an oxide mask 112 overlying the sharp tip 108, as shown in FIGS. 6G and 6H. As shown in FIG. 6H, oxide mask 112 defines an inner surface 114 and an outer surface 116 of silicon substrate 80.
[0073]
A masking material 118 is applied to the surface 116 of the silicon substrate 80, leaving the central portion 114 exposed. An anisotropic etch, eg, a plasma etch, is applied to the central portion 114 to etch a substantially cylindrical recess 120 in the silicon substrate 80 surrounded by the oxide mask 112, as shown in FIG. 6I. . Next, the masking material 118 is removed, exposing the upper surface 122 of the silicon substrate surrounding the oxide mask 112, as shown in FIG. 6J.
[0074]
Next, an anisotropic etch, eg, a plasma etch, is applied to the top surface 122 and the recess 120 is etched completely through the silicon substrate 80 to form an axial channel 124. The anisotropic etch also etches the upper surface 122 to form an annular microprojection 126 having a substantially cylindrical wall 128 extending perpendicularly from the etched upper surface 130. Next, the oxide mask 112 is removed by selective etching to expose the sharp tip 108. As shown in FIGS. 6L and 6M, the resulting microprojections 126 extend upward from the substrate 80. The sharp tip 108 in this embodiment extends completely around the top surface of the microprojection 126 to form a continuous ridge.
[0075]
7A-7J embodiment
In this embodiment, the microprojection array is formed from a silicon substrate 134 having a top surface 136 and a bottom surface 138. A nitride layer 140 is formed on top surface 136. As shown in FIG. 7A, an oxide layer 142 is formed by a low-temperature formation process so as to cover the nitride layer 140. After a photoresist layer is formed over oxide layer 142, it is exposed and developed to form a photoresist mask. In this embodiment, the photoresist mask has an annular shape that matches the lateral dimensions of the microprojections to be made. The exposed regions of the nitride layer 142 and the oxide layer 140 are etched to form a ring-shaped mask 144. As shown in FIG. 7B, the mask 144 defines a central region 146 and an outer region 148 of the silicon substrate 134.
[0076]
As shown in FIG. 7C, a photoresist layer is applied to the exposed surface 148 and the mask 144. Usually, after applying the photoresist layer 150 as a continuous layer, it is exposed and developed to form a mask. As shown in FIG. 7C, the central portion 146 of the silicon substrate 134 is exposed and not covered by the photoresist layer 150. An anisotropic etch, eg, a plasma etch, is applied to the top surface to etch the central portion 146 to form a cylindrical passage 152 completely through the silicon substrate 134, as shown in FIG. 7D. Preferably, passage 152 is formed by a plasma etch and is etched along a plane substantially perpendicular to upper surface 136 of silicon substrate 134.
[0077]
As shown in FIG. 7E, after removing the photoresist mask 150, a second anisotropic etch is performed to etch the exposed surface of the upper surface 136 of the silicon substrate 134. As shown in FIG. 7F, an anisotropic etch is performed to form an annular column 154 having a substantially cylindrical sidewall 156 that extends perpendicular to the bottom surface 138 of the silicon substrate 134.
[0078]
Referring to FIG. 7G, an oxide layer 158 is formed on the exposed surface of silicon substrate 134. As shown, the oxide layer 158 covers the outer surface 156 of the pillar 154 and the inner surface of the channel 152. A wet nitride etch is applied to etch a portion of the exposed nitride layer of mask 144, as shown in FIG. 7H. The nitride etch etches away a portion of the mask 144 around the edge of the nitride layer, exposing a portion of the top surface of the annular column 154. Since the nitride etch attacks the inner and outer edges of the nitride layer of the mask 144, the resulting nitride layer has dimensions smaller than the dimensions of the top surface of the annular column 154.
[0079]
Next, an isotropic etch is used on the exposed silicon around the mask 144 to form a sharp tip 160 having a concave surface 162. The remaining oxide layer 158 and nitride layer 140 are removed by a selective etch or stripping process known in the art. The resulting microprojection 163, shown in FIG. 7J, is defined by an annular column 158 having a ring-shaped sharp tip 160 extending upward from column 158.
[0080]
8A-8L Embodiment
In this embodiment, the microprojection array is formed from a silicon substrate 164 having a top surface 166 and a bottom surface 168. As shown in FIG. 8A, an oxide layer 170 is formed on top surface 166. As in the previous embodiment, a photoresist layer is formed on oxide layer 170 and then developed to form a photoresist mask having a substantially annular shape corresponding to the desired microprojection dimensions. 172 is manufactured. As shown in FIG. 8B, the oxide layer 170 is selectively etched to form an oxide mask 174. The oxide mask 174 has an annular shape corresponding to the shape of the photoresist mask 172. Next, the photoresist mask 172 is removed.
[0081]
An isotropic etch is applied to the upper surface 166 of the silicon substrate 164 to form an etched surface defined by the lower concave surface 176 of the oxide mask 174. As shown in FIG. 8C, the isotropic etch etches a portion of the silicon below the mask 174 to form a ring-shaped protrusion 178 having dimensions slightly smaller than the width of the mask 174.
[0082]
Referring to FIG. 8D, a nitride layer 180 is deposited on the top surface of the silicon substrate 164 and the oxide mask 174. A photoresist mask 182 is formed on the nitride layer 180. As shown in FIG. 8E, photoresist mask 182 has an exposed layer overlying the central opening of oxide mask 174. An isotropic etch is applied to the top surface to etch an axial passage 184 through the exposed nitride layer 180 and through the silicon substrate 164 to the bottom surface 168. Preferably, the anisotropic etch is a plasma etch, which etches along a plane substantially perpendicular to bottom surface 168 of silicon substrate 164. As shown in FIG. 8G, the photoresist layer 182 is removed. An anisotropic etch, preferably a plasma etch, is applied to the top surface to etch nitride layer 180 and silicon substrate 164 to form annular pillars 186, as shown in FIG. 8H. As in the previous embodiment, annular column 186 is defined by a substantially cylindrical outer wall 188 that extends perpendicular to bottom surface 168 of silicon substrate 164.
[0083]
As shown in FIG. 8I, an oxide layer 190 is formed on the exposed surface of the silicon substrate 164 to cover the outer surface of the annular column 186 and the inner surface of the axial passage 184. Applying a nitride etchant, eg, phosphoric acid, removes the remaining portion of nitride layer 180 and exposes concave surface 176 of protrusion 178, as shown in FIG. 8J. Next, an isotropic silicon etch is applied to the exposed concave surface 176 to form a sharp tip 192 on the annular post 186, as shown in FIG. 8K. Next, the remaining oxide layer 190 is removed with an oxide etchant, for example, hydrofluoric acid. As shown in FIG. 8L, the resulting microprojections 194 are defined by an annular column 186 and an annular tip 192.
[0084]
9A-9O embodiment
In this embodiment, the microprojection array is formed from a silicon substrate 196 having a top surface 198 and a bottom surface 200. As in the previous embodiment, an oxide layer 202 is formed on top surface 198, as shown in FIG. 9A. A photoresist mask 204 is formed on oxide layer 202 to define the shape of the resulting microprojections. The photoresist mask 204 has a substantially annular shape and is formed from an exposed and developed photoresist layer, as in the previous embodiment.
[0085]
The exposed region of the oxide layer 202 is selectively etched by, for example, plasma etching to form a ring-shaped oxide mask 206. As shown in FIG. 9C, the photoresist mask 204 is removed, and the upper surface 198 of the silicon substrate 196 is etched with an isotropic etchant. The isotropic etch creates an annular projection 208 defined by a concave outer surface 210 that is concentrated towards the oxide mask 206. As in the previous embodiment, the isotropic etchant removes a portion of the silicon beneath the oxide mask 206, as shown in FIG. 9C.
[0086]
Referring to FIG. 9D, a nitride layer 212 is deposited on the top surface to completely cover the silicon substrate 196 and the oxide mask 206. Referring to FIG. 9E, a photoresist mask 214 is formed on nitride layer 212. Photoresist mask 214 overlies a small area of oxide mask 206. As shown in FIG. 9E, a photoresist mask 214 overlies the outer edge of the oxide mask 206 and covers a small arcuate portion of the oxide mask 206. In a preferred embodiment, photoresist mask 214 covers an arc that is less than about a quarter of the circumference of oxide mask 206. Next, nitride layer 212 is selectively etched to form a nitride mask 216 that matches the shape and dimensions of photoresist mask 214, as shown in FIGS. 9E and 9F. Preferably, the nitride etch acts selectively so that substantially no silicon etching occurs at this stage.
[0087]
Next, as shown in FIG. 9G, the photoresist mask 214 is removed to expose the nitride mask 216. The nitride mask 216 substantially corresponds to the dimensions of the photoresist mask 214 and overlies a small portion of the outer edge of the oxide mask 206, as shown in FIG. 9G. In the illustrated embodiment, nitride mask 214 covers only a portion of the oxide mask. As described below, the dimensions of the nitride mask 214 determine the final shape of the microprojections.
[0088]
A photoresist mask 218 is applied over the top surface of silicon substrate 196, oxide mask 206, and nitride mask 216. A photoresist layer is applied, patterned, and developed to form a photoresist mask 218 that exposes an upper surface 219 of the silicon substrate 196 surrounded by the oxide mask 206, as shown in FIG. 9H.
[0089]
Referring to FIG. 9I, an anisotropic etch is applied to the top surface to etch an axial passage 220 that extends completely through the silicon substrate 196 to the bottom surface 200. Next, as shown in FIG. 9J, the photoresist layer 218 is removed. As shown in FIG. 9K, an anisotropic plasma etch is applied to form an annular column 222 having a cylindrical sidewall 224. As shown in FIG. 9K, the plasma etch etches silicon substrate 196 along a plane substantially perpendicular to bottom wall 200. The plasma etch also removes a portion of nitride mask 216, leaving a portion 226 of nitride mask 216 under oxide mask 206. Next, an oxide layer 228 is formed over the exposed surface of the silicon substrate 196 and the oxide mask 206. As shown in FIG. 9L, the oxide layer 228 is not applied to the nitride mask 216, so that the nitride mask 216 is exposed. A nitride etch solution, such as phosphoric acid, is applied to remove portions 226 of the nitride layer, thereby forming openings to form concave surface 210 formed on annular pillars 222, as shown in FIG. 9M. Expose.
[0090]
Next, an isotropic silicon etch is applied to the exposed surface of the annular pillar 222 through the opening formed by the nitride etch removing the portion 226. The isotropic silicon etch etches the silicon along an interface that extends away from the openings in the oxide layer 228, forming a curved etched outer surface 230, as shown in FIG. 9N. The silicon etch is applied for a time sufficient to etch surface 230 to form sharp tip 232. In one embodiment, the silicon etch is an isotropic etch. In a further embodiment, the silicon etch can be a plasma etch, a wet isotropic etch, or a wet anisotropic etch using potassium hydroxide.
[0091]
Next, the oxide layer 228 is selectively removed with, for example, hydrofluoric acid to expose the microprojections 234. The microprojections 234 generally have a cylindrical shape with an outer surface defined by a curved inner surface 230 and a sharp tip 232.
[0092]
Embodiment of FIG.
In another embodiment of the present invention, a microprojection 236 having a substantially cylindrical sidewall 238 and a base 240 is formed. As in the previous embodiment, microprojections 236 are formed from a silicon wafer by photolithography. That is, after forming a ring-shaped mask, a microprojection having a cylindrical side wall 238 and an axial passage is formed by anisotropic etching. A mask is formed on a silicon wafer to define the dimensions of the microprojections and create a sharp tip 242. In one preferred embodiment, tips 242 are spaced around the circumference of microprojections 236. Each tip 242 is formed concave so that a curved ridge 244 is formed between adjacent tips 242.
[0093]
While several embodiments have been chosen to illustrate the invention, it will be appreciated that various modifications and changes can be made without departing from the scope of the invention as defined in the appended claims. Those skilled in the art will understand.
[Brief description of the drawings]
[0094]
FIG. 1 is a side view showing a micro projection array according to a first embodiment of the present invention.
FIG. 2 is a perspective view showing the microprojection array of the embodiment of FIG. 1;
FIG. 3 is a top view showing the micro projection array of FIG. 2;
FIG. 4A illustrates successive steps of forming a microprojection array according to a second embodiment of the present invention.
FIG. 4B illustrates a sequence of steps for forming a microprojection array according to a second embodiment of the present invention.
FIG. 4C illustrates a sequence of steps for forming a microprojection array according to a second embodiment of the present invention.
FIG. 4D illustrates a sequence of steps for forming a microprojection array according to a second embodiment of the present invention.
FIG. 4E illustrates a sequence of steps for forming a microprojection array according to a second embodiment of the present invention.
FIG. 4F illustrates a sequence of steps for forming a microprojection array according to a second embodiment of the present invention.
FIG. 4G illustrates a sequence of steps for forming a microprojection array according to a second embodiment of the present invention.
FIG. 4H illustrates successive steps of forming a microprojection array according to a second embodiment of the present invention.
FIG. 5A illustrates successive steps of forming a microprojection array according to a third embodiment of the present invention.
FIG. 5B illustrates a sequence of steps for forming a microprojection array according to a third embodiment of the present invention.
FIG. 5C illustrates a sequence of steps for forming a microprojection array according to a third embodiment of the present invention.
FIG. 5D illustrates a sequence of steps for forming a microprojection array according to a third embodiment of the present invention.
FIG. 5E illustrates successive steps of forming a microprojection array according to a third embodiment of the present invention.
FIG. 5F illustrates a sequence of steps for forming a microprojection array according to a third embodiment of the present invention.
FIG. 5G illustrates a sequence of steps for forming a microprojection array according to a third embodiment of the present invention.
FIG. 5H illustrates successive steps of forming a microprojection array according to a third embodiment of the present invention.
FIG. 5I illustrates successive steps of forming a microprojection array according to a third embodiment of the present invention.
FIG. 6A illustrates a sequence of steps for forming a microprojection array according to a fourth embodiment of the present invention.
FIG. 6B illustrates successive steps of forming a microprojection array according to a fourth embodiment of the present invention.
FIG. 6C illustrates a sequence of steps for forming a microprojection array according to a fourth embodiment of the present invention.
FIG. 6D illustrates a sequence of steps for forming a microprojection array according to a fourth embodiment of the present invention.
FIG. 6E illustrates a sequence of steps for forming a microprojection array according to a fourth embodiment of the present invention.
FIG. 6F illustrates a sequence of steps for forming a microprojection array according to a fourth embodiment of the present invention.
FIG. 6G illustrates a sequence of steps for forming a microprojection array according to a fourth embodiment of the present invention.
FIG. 6H illustrates successive steps of forming a microprojection array according to a fourth embodiment of the present invention.
FIG. 6I illustrates a sequence of steps for forming a microprojection array according to a fourth embodiment of the present invention.
FIG. 6J illustrates a sequence of steps for forming a microprojection array according to a fourth embodiment of the present invention.
FIG. 6K illustrates a sequence of steps for forming a microprojection array according to a fourth embodiment of the present invention.
FIG. 6L illustrates successive steps of forming a microprojection array according to a fourth embodiment of the present invention.
FIG. 6M illustrates a sequence of steps for forming a microprojection array according to a fourth embodiment of the present invention.
FIG. 7A illustrates successive steps of forming a microprojection array according to a fifth embodiment of the present invention.
FIG. 7B illustrates a sequence of steps for forming a microprojection array according to a fifth embodiment of the present invention.
FIG. 7C illustrates a sequence of steps for forming a microprojection array according to a fifth embodiment of the present invention.
FIG. 7D illustrates a sequence of steps for forming a microprojection array according to a fifth embodiment of the present invention.
FIG. 7E illustrates successive steps of forming a microprojection array according to a fifth embodiment of the present invention.
FIG. 7F illustrates a sequence of steps for forming a microprojection array according to a fifth embodiment of the present invention.
FIG. 7G illustrates successive steps of forming a microprojection array according to a fifth embodiment of the present invention.
FIG. 7H illustrates a sequence of steps for forming a microprojection array according to a fifth embodiment of the present invention.
FIG. 7I illustrates successive steps of forming a microprojection array according to a fifth embodiment of the present invention.
FIG. 7J illustrates successive steps of forming a microprojection array according to a fifth embodiment of the present invention.
FIG. 8A illustrates successive steps of forming a microprojection array according to a sixth embodiment of the present invention.
FIG. 8B illustrates successive steps of forming a microprojection array according to a sixth embodiment of the present invention.
FIG. 8C illustrates a sequence of steps for forming a microprojection array according to a sixth embodiment of the present invention.
FIG. 8D illustrates a sequence of steps for forming a microprojection array according to a sixth embodiment of the present invention.
FIG. 8E illustrates a sequence of steps for forming a microprojection array according to a sixth embodiment of the present invention.
FIG. 8F illustrates a sequence of steps for forming a microprojection array according to a sixth embodiment of the present invention.
FIG. 8G illustrates a sequence of steps for forming a microprojection array according to a sixth embodiment of the present invention.
FIG. 8H illustrates a sequence of steps for forming a microprojection array according to a sixth embodiment of the present invention.
FIG. 8I illustrates successive steps of forming a microprojection array according to a sixth embodiment of the present invention.
FIG. 8J illustrates successive steps of forming a microprojection array according to a sixth embodiment of the present invention.
FIG. 8K illustrates a sequence of steps for forming a microprojection array according to a sixth embodiment of the present invention.
FIG. 8L illustrates successive steps of forming a microprojection array according to a sixth embodiment of the present invention.
FIG. 9A illustrates successive steps of forming a microprojection array according to a seventh embodiment of the present invention.
FIG. 9B illustrates a sequence of steps for forming a microprojection array according to a seventh embodiment of the present invention.
FIG. 9C illustrates a sequence of steps for forming a microprojection array according to a seventh embodiment of the present invention.
FIG. 9D illustrates a sequence of steps for forming a microprojection array according to a seventh embodiment of the present invention.
FIG. 9E illustrates a sequence of steps for forming a microprojection array according to a seventh embodiment of the present invention.
FIG. 9F illustrates a sequence of steps for forming a microprojection array according to a seventh embodiment of the present invention.
FIG. 9G illustrates a sequence of steps for forming a microprojection array according to a seventh embodiment of the present invention.
FIG. 9H illustrates a sequence of steps for forming a microprojection array according to a seventh embodiment of the present invention.
FIG. 9I illustrates successive steps of forming a microprojection array according to a seventh embodiment of the present invention.
FIG. 9J illustrates a sequence of steps for forming a microprojection array according to a seventh embodiment of the present invention.
FIG. 9K illustrates a sequence of steps for forming a microprojection array according to a seventh embodiment of the present invention.
FIG. 9L illustrates successive steps of forming a microprojection array according to a seventh embodiment of the present invention.
FIG. 9M illustrates a sequence of steps for forming a microprojection array according to a seventh embodiment of the present invention.
FIG. 9N illustrates successive steps of forming a microprojection array according to a seventh embodiment of the present invention.
FIG. 90 illustrates successive steps for forming an array of microprojections according to a seventh embodiment of the present invention.
FIG. 10 is a perspective view showing a micro protrusion in the eighth embodiment of the present invention, showing a plurality of sharp tips on an annular surface.

Claims (43)

Providing a substrate having a top surface and a bottom surface;
Forming a patterned masking layer in a plurality of regions on the top surface, wherein the region of the patterned masking layer has a predetermined dimension corresponding to a microprojection; Defining an exposed area of the top surface of the substrate around the area of;
Etching the exposed region of the top surface of the substrate to a depth sufficient to form a plurality of microprojections;
Removing the masking layer from the substrate to expose the microprojections;
A method for forming a microprojection array, comprising: The method of claim 1, further comprising forming an oxide layer on the top surface of the substrate. The method of claim 2, wherein the patterned masking layer is a nitride layer. The method of claim 1, wherein the substrate comprises silicon. The method of claim 1, comprising applying a patterned masking layer on the bottom surface of the base to etch a channel through the bottom surface to the top of the microprojections. . Providing an oxide layer on the bottom surface of the substrate;
Etching a region of the oxide layer on the bottom surface of the substrate, located below the microprojections;
Etching a channel extending between the bottom surface and the top surface;
The method of claim 3, further comprising: Before forming the nitride layer,
Etching a plurality of regions in the oxide layer on the bottom surface of the support;
Applying a second continuous nitride layer on the bottom surface to cover the oxide layer and the etched region on the bottom surface;
7. The method according to claim 6, comprising: After the etching of the oxide layer on the bottom surface,
Etching the nitride layer on the bottom surface to expose the etched region in the oxide layer on the bottom surface;
Etching a channel extending through the substrate between the bottom surface and the top surface of the base;
7. The method according to claim 6, comprising: Forming an oxide layer on the top surface and the microprojections,
Etching a portion of the oxide layer on the micro-projections to expose a tip portion of the micro-projections;
Etching the exposed tip portion of the microprojection to form a channel extending between the tip portion of the microprojection and the bottom surface of the base;
The method of claim 1, further comprising: The method of claim 9, further comprising applying a photoresist layer to the microprojections. The method of claim 10, further comprising etching the top surface around the photoresist layer on each of the microprojections to form annular pillars. Providing a silicon substrate having a top surface with a masking layer;
Removing a portion of the masking layer to form a plurality of substantially ring-shaped portions of the masking layer on the top surface;
Etching the top surface of the silicon substrate to form a channel extending through the center of each ring-shaped portion, and forming an annular column around each ring-shaped portion;
Removing the ring-shaped portion of the masking layer to form a microprojection array;
A method for forming a microprojection array, comprising: The method of claim 12, wherein the masking layer is an oxide layer on the substrate. Before removing the ring-shaped portion of the masking layer,
Etching the silicon substrate around the ring-shaped oxide portion to form a sharp tip;
13. The method of claim 12, wherein: Forming a plurality of ring-shaped nitride portions on the oxide layer, and etching the oxide layer around the ring-shaped nitride portions to form the ring-shaped portions from the oxide layer; 14. The method of claim 13, comprising: After removing the ring-shaped oxide portion,
Forming a second oxide layer on the microprojection array to sharpen the microprojections;
Removing the second oxide layer to expose the sharp microprojections;
14. The method of claim 13, further comprising: Applying a photoresist layer to the second oxide layer on the microprojections;
Etching the second oxide layer to form a ring-shaped oxide layer prior to the step of etching the channel and the annular portion;
17. The method according to claim 16, comprising: Applying an oxide layer to the inner and outer surfaces of the annular pillar and then etching the silicon around the ring-shaped oxide portion to form a sharp tip on the pillar ,
14. The method of claim 13, further comprising: 20. The method of claim 18, further comprising applying a nitride layer on the first oxide layer before etching the channel in the microprojections. 20. The method of claim 19, further comprising applying a photoresist layer over the nitride layer and a top surface of the substrate before forming the channel. 21. The method of claim 20, comprising removing the photoresist layer prior to the step of forming the annular pillar. Applying a nitride layer to the top surface and the ring-shaped portion of the substrate before forming the annular pillar;
Applying a photoresist layer to the nitride layer overlying the ring-shaped oxide portion;
Forming the channel and then forming the pillar;
14. The method of claim 13, further comprising: Forming an oxide layer on the outer surface of the pillar and the inner surface of the channel;
Removing the nitride layer from the pillar, and further etching the silicon at the outer edge of the pillar to form a sharp tip;
23. The method of claim 22, further comprising: Before etching the silicon substrate,
Forming an oxide layer on the outer surface of the pillar and the inner surface of the channel, wherein a portion of the upper end of the pillar is free of the oxide layer;
Etching the portion of the upper end of the column to form a beveled tip;
23. The method of claim 22, further comprising: The method of claim 12, further comprising cutting a beveled tip on the post. The method of claim 25, further comprising providing a dicing saw and cutting the beveled tip with the dicing saw. 26. The method of claim 25, further comprising placing the post in a support medium before cutting the slope. The method of claim 27, wherein the support medium is a wax. Providing a substrate having a top surface and a bottom surface;
Forming a plurality of recesses in the top surface, wherein the recesses define a surface inclined relative to a plane of the top surface, the inclined surface forming an array of sharp tips;
Removing a portion of the substrate around the sharp tip to form a microprojection array having an outer edge formed by the sharp tip;
A method for forming a microprojection array, comprising: 30. The method of claim 29, wherein the substrate is a material selected from the group consisting of silicon, silicon oxide, silicon nitride, epoxy resin, nickel, and aluminum. The method of claim 29, wherein the substrate is polysilicon or amorphous silicon. 30. The sloped surface is formed by applying an anisotropic etchant to the top surface of the substrate and forming a sloped surface in a crystal plane of the substrate. The method described in. The anisotropic etchant, potassium hydroxide, ethylene diamine pyrocatechol, ammonium hydroxide, sodium hydroxide, CsOH, and N ₂ The method of claim 32, characterized in that it is selected from the group consisting of H ₄ . 30. The method of claim 29, wherein the sloped surface is formed by applying an isotropic etch to the top surface of the substrate. The method of claim 34, wherein the isotropic etchant comprises a mixture of hydrofluoric acid, acetic acid, and nitric acid. The method of claim 29, wherein the array of microprojections is formed by machining the top surface of the substrate around the sharp tip. Providing a substrate having a top surface and a bottom surface;
Forming a microprojection array on the top surface of the substrate, wherein the microprojections have an upper surface;
Forming at least one slope on the top surface of each of the microprojections;
A method for forming a microprojection array, comprising: The microprojections have an outer surface, and the step of forming the slope comprises:
Forming a non-oxidized layer on the outer surface of the microprojections;
Forming an oxide layer on the top surface of the microprojections;
Etching the non-oxidized layer to form an exposed region on the microprojection;
Etching the microprojections in the exposed area to form the slope;
38. The method of claim 37, comprising: 39. The method of claim 38, further comprising applying a non-etched layer over the non-oxidized layer. The method of claim 38, comprising removing the non-oxidized layer. The method of claim 37, wherein the microprojections are formed by selectively etching the substrate. The method of claim 37, wherein the slope is formed by selectively etching the substrate. The method of claim 37, wherein the slope is formed by selectively etching the microprojections.

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