APPARATUS AND METHOD FOR FABRICATING NEEDLES VIA CONFORMAL DEPOSITION IN TWO-PIECE MOLDS

Abstract: A method of fabricating a needle via conformal deposition in a two-piece mold includes the step of attaching a top mold member (20) to a bottom mold member (30) such that the top mold member and the bottom mold member define an enclosed, elongated needle trench (34) with a deposition aperture (24, 26). A conformal substance, such as polysilicon (50), is then passed through the deposition aperture such that the conformal substance is deposited within the enclosed, elongated needle trench (34) to form a needle (60). The method is used to form needles with prongs, multiple channels, multiple ports, barbs, strength enhancement features, and circuitry.

Description: APPARATUS AND METHOD FOR FABRICATING NEEDLES VIA CONFORMAL DEPOSITION IN TWO-PIECE MOLDS Brief Description of the Invention This invention relates generally to hypodermic needles. More particularly, this invention relates to a technique for fabricating needles via conformal deposition in two-piece molds. Background of the Invention Traditional machining techniques, such as, tube drawing, grinding, and polishing are used to fabricate needles. While satisfactory for simple needle designs, these techniques cannot be used to fabricate more sophisticated features and geometries that provide extended functionality. For example, a needle with two fluid channels to allow the simultaneous injection of two fluids to the same area is very difficult to fabricate with traditional needle machining techniques. Electronic circuitry, such as, electrodes and amplification circuitry may be used for charge delivery, electric field sensing, or electrophoretic pumping. Biological sensors to provide, for example, biological assay capability, would be extremely useful. Insertion and extraction limiting barbs are also potentially very useful. Additionally, a pump built into the needle and multiple inlet and outlet ports are highly desirable features. A dual prong needle would allow delivery through one prong and sensing in the other. These features are very difficult to implement with traditional machining. Recently, silicon microfabrication techniques have been used to construct hypodermic needles. For example, microfabrication processes to produce needles are described in the work by Chen and Wise (J. Chen et al., "A Multichannel Neural Probe for the Selective Chemical Delivery at the Cellular Level", Solid State Sensor and Actuator Workshop, Hilton Head, South Carolina, 1994) and also by Linn (Liwei L. Linn, et al., "Silicon Processed Microneedles", Technical Digest, 7th International Conference on Solid-State Sensors and Actuators, Transducers '93, Yokohama, Japan, June 7-10, 1993). There are two drawbacks with this early work. First, the disclosed processes are destructive to the wafer from which the needles are produced. Second, the processes do not rely upon a mold. Thus, new wafers must be used each time the process is repeated. This results in considerable added expense. Single moid processes to make needles are known in the art. For example, the HexSil process invented by Chris Keller (Christopher G. Keller et al., "Nickel-Filled HexSil Thermally Actuated Tweezers", Technical Digest, Transducers 95, Stockholm, Sweden, June 25-29, 1995, pp. 376-379) is a single wafer micromolding process. Unfortunately, the Hexsil process can only form relatively short needles (generally less than a millimeter). In view of the foregoing, it would be highly desirable to provide an improved technique for fabricating hypodermic needles. Ideally, the technique would allow the fabrication of needles with extended functionality, such as multiple fluid channels, multiple ports, and integrated circuitry. In addition, the technique would preferably avoid prior art problems of limited needle length. Ideally, the technique would provide a re-usable mold process to reduce fabrication expense. Summary of the Invention A method of fabricating a needle via conformal deposition in a two-piece mold includes the step of attaching a top mold member to a bottom mold member such that the top mold member and the bottom mold member define an enclosed, elongated needle trench with a deposition aperture. A conform substance, such as polysilicon, is then passed through the deposition aperture such that the conformal substance is deposited within the enclosed, elongated needle trench to form a needle. The method is used to form needles with prongs, multiple channels, multiple ports, barbs, strength enhancement features, and circuitry. The invention constitutes .an improved technique for fabricating hypodermic needles. The re-usable mold process reduces fabrication expense. In addition, the mold process of the invention provides for longer needles than available in prior art mold processes. Brief Description of the Drawings For a better understanding of the invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings, in which: FIGURES 1 a- 1 e illustrate the processing of a top mold member in accordance with an embodiment of the invention. FIGURES 2a-2e illustrate the processing of a bottom mold member in accordance with .an embodiment of the invention. FIGURES 3a-31 illustrate the processing of a combined top mold member and bottom mold member in accordance with .an embodiment of the invention. FIGURE 4 is a perspective view of a needle with multiple fluid ports in accordance with an embodiment of the invention. FIGURE 5 is a perspective view of a needle with insertion and extraction barbs in accordance with an embodiment of the invention. FIGURE 6 is a perspective view of a needle with strength enhancement features in accordance with an embodiment of the invention. FIGURE 7 is an enlarged view of the strength enhancement features of the needle of Figure 6. FIGURE 8 is a perspective view of a dual prong needle in accordance with an embodiment of the invention. FIGURE 9 is a perspective view of a needle with circuitry in accordance with an embodiment of the invention. Like reference numerals refer to corresponding parts throughout the drawings. Detailed Description of the Invention In brief, the invention includes a method of fabricating a needle via conformal deposition in a two-piece mold. The method includes the step of attaching a top mold member to a bottom mold member such that the top mold member and the bottom mold member define .an enclosed, elongated needle trench with a deposition aperture. A conformal substance, such as polysilicon, is then passed through the deposition aperture such that the conformal substance is deposited within the enclosed, elongated needle trench to form a needle. The method is used to form needles with prongs, multiple channels, multiple ports, barbs, strength enhancement features, and circuitry, as demonstrated below. The following processing steps have been used to construct a variety of devices, in accordance with the invention. Those skilled in the art will appreciate that a variety of modifications to the specified steps are feasible, yet still within the scope of the invention. TABLE I -- PREFERRED FABRICATION STEPS A. STANDARD WAFER CLEAN VLSI lab sink Piranha clean (H 2 SO 4 :H 2 O 2 , 5:1) 10 minutes Two, one minute rinses in de-ionized (DI) water Rinse until resistivity of water is > 11 MQ-cm Spin dry Piranha clean (H 2 SO 4 :H 2 O 2 , 5:1) 10 minutes Rinse in DI water for one minute Dip in 25 : 1 HF until hydrophobic Two, one minute rinses in de-ionized (DI) water Rinse until resistivity of water is > 14 MΩ-cm Spin dry B. CLEAN WAFERS WITH MINIMAL OXIDE STRIP VLSI lab sink Piranha clean (H 2 SO 4 :H 2 O 2 , 5:1) 10 minutes Rinse in DI water for one minute Dip in 25:1 HF briefly until native silicon oxide removed Two, one minute rinses in DI water Rinse until resistivity of DI water is >14 MΩ-cm Spin dry C. PARTIAL CLEAN WAFERS VLSI lab sink Piranha clean (H 2 SO 4 :H 2 O 2 , 5:1) 10 minutes Two, one minute rinses in de-ionized (DI) water Rinse until resistivity of water is > 11 MΩ-cm Spin dry D. DEPOSIT LOW-STRESS SILICON NITRIDE Horizontal low pressure chemical vapor deposition reactor Target thickness as specified Conditions = 835°C, 140 mTorr, 100 seem DCS, and 25 seem NH 3 E. DEPOSIT PHOSPHOSILICATE GLASS (PSG) Horizontal low pressure chemical vapor deposition reactor Target thickness as specified Conditions = 450°C, 300 mTorr, 60 seem SiH 4 , 90 seem O 2 , and 10.3 seem PH 3 Step G. - REFLOW PHOSPHOSILICATE GLASS F. DEPOSIT LOW TEMPERATURE OXIDE (LTO) Horizontal low pressure chemical vapor deposition reactor Target thickness as specified Conditions = 450°C, 300 mTorr, 60 seem SiH 4 , 90 seem O 2 , and 10.3 seem PH 3 Step G. - REFLOW PHOSPHOSILICATE GLASS G. REFLOW PHOSPHOSILICATE GLASS Horizontal atmospheric pressure reactor Conditions = 1000°C, N 2 , 1 hour H. PHOTOLITHOGRAPHY I. HMDS prime 2. Photoresist coat Coat 1 μm of Shipley S3813 (thickness may need to be varied depending on topography and thickness of material to be etched) multi-wavelength positive resist 3. Expose resist G-Line wafer stepper Standard exposure time 4. Resist develop Standard develop using Shipley MF 319 5. Hard bake for 30 minutes I. COAT BACKSIDE WITH PHOTORESIST 1. HMDS prime 2. Photoresist coat Coat 1 μm of Shipley S3813 (thickness may need to be varied depending on topography and thickness of material to be etched) multi-wavelength positive resist 3. Resist develop Standard develop using Shipley MF 319 4. Hard bake for 30 minutes J. OXIDE WET ETCHING VLSI lab sink Etch in 5:1 BHF until desired .amount of oxide has been removed Two, one minute rinses in DI water Rinse until resistivity of water is > 11 MΩ-cm Spin dry K. PHOTORESIST STRIP Lab sink PRS-2000, heated to 90 °C, 10 minutes Rinse in three baths of DI water, 2 minutes each Step C. - PARTIAL CLEAN WAFERS L. SILICON NITRIDE ETCH SF 6 +He plasma etch Etch until desired amount of nitride has been removed M. DEPOSIT UNDOPED POLYSILICON Horizontal low pressure chemical vapor deposition reactor Target thickness as specified Conditions = 580°C, 300 mTorr, and 100 seem SiH 4 N. ANISOTROPIC POLYSILICON ETCH Chlorine plasma etch Etch until desired amount of polysilicon has been removed O. NITROGEN ANNEAL Horizontal atmospheric pressure reactor Conditions = 1000°C, N 2 , 1 hour P. ANISOTROPHIC SILICON WET ETCH Lab sink, heated bath 750 g KOH: 1500 ml H 2 O Temperature: 80 °C Q. OXIDE REMOVAL WET ETCHING Lab sink Etch in diluted HF or buffered HF until desired oxide removed Rinse in deionized water for approximately one hour R. NEAR VERTICAL WALLED TRENCH ETCH Inductively coupled plasma etcher Advanced silicon etch process High plasma density low pressure processing system Fluorine plasma Etch to desired depth S. SACRIFICIAL PSG AND SILICON NITRIDE REMOVAL Lab sink Concentrated HF dip with surfactant if needed, continue until desired sacrificial material has been removed Rinse for 2 minutes in two tanks of DI water Rinse for 120 minutes in third tank of DI water T. SPUTTER GOLD Low pressure chamber Gold target U. GOLD ETCH Lab sink Aqua regent etchant or other commercially available gold etchant V. WET OXIDATION Horizontal atmospheric pressure reactor Conditions = Temperature as specified, water vapor environment W. BORON DIFFUSION Horizontal atmospheric pressure reactor Solid source boron diffusion Conditions = Temperature as specified X. DEPOSIT IN SITU DOPED POLYSELICON Horizontal low pressure chemical vapor deposition reactor Target thickness as specified Conditions = 610°C and 300 mTorr _______________ ______________________^^ Figures la-le illustrate the construction of a top mold member in accordance with an embodiment of the present invention. Figure la illustrates a starting wafer 20, which may be 500 to 500 micron thick, <100> oriented, lightly doped silicon. The wafer is cleaned (Step A) and 4000 A of silicon nitride is deposited (Step D). The resultant silicon nitride layer 22 is illustrated in Figure lb. Photolithography (Step H) is then performed. The silicon nitride is then etched (Step L). Preferably, 5000 A is etched for a 25% over-etch. The photoresist is then stripped (Step K), to produce the device of Figure lc. An anisotropic silicon wet etch (Step P) is then performed through the wafer. Finally, the silicon nitride is removed (Step S). Figure Id provides a side view of the resultant device 20, while Figure le provides a perspective view of the device 20. The top mold member 20 includes deposition apertures 24 and 26. While Figures la-le illustrate a single mold member 20, those skilled in the art will appreciate that typically over a thousand molds are prepared at once. Furthermore, the foregoing steps are only performed once to create the top mold member 20. Thereafter, the top mold member 20 can be reused to construct several batches of needles. Figures 2a-2e illustrate the construction of a bottom mold member in accordance with an embodiment of the invention. Figure 2a illustrates a starting wafer 30, which may be 500 to 500 micron thick, <100> oriented, lightly doped silicon. The wafer is cleaned (Step A). Thereafter, photoresist is spun onto the wafer 30, resulting in photoresist layer 32. Photolithography (Step H) is then performed to define a needle shape, which results in the device of Figure 2b. A deep trench etch (Step R) is then performed to a depth of approximately 100 microns. The resultant needle trench 34 is illustrated in Figure 2c. The photoresist is then stripped (Step K), to produce the device of Figure 2d. Figure 2d provides a side view of the resultant device 30, while Figure 2e provides a perspective view of the device 30. The bottom mold member 30 includes a needle trench 34 defining the shape of a needle. In particular, the mold member 30 defines an elongated needle trench 34. When the top mold member 20 and the bottom mold member 30 .are attached, an enclosed, elongated needle trench results. Deposition of a conformal substance into the trench produces a needle, as described below. While Figures 2a-2e illustrate a single mold member, those skilled in the art will appreciate that typically over a thousand molds are prepared at once. Furthermore, the foregoing steps are only performed once to create the bottom mold member 30. Thereafter, the bottom mold member 30 can be reused to construct several batches of needles. At this juncture, a top mold member 20 and a bottom mold member 30 are available. A perspective view of these elements is shown in Figure 3a, and a side view of the same elements is shown in Figure 3b. The following discussion is directed toward needle fabrication steps using these mold members. The top mold member 20 and the bottom mold member 30 are subjected to a standard wafer clean (Step A). Approximately 2 microns of phosphosilicate glass is then deposited on the top mold member 20 and the bottom mold member 30. Figure 3c illustrates the resultant phosphosilicate glass (PSG) layer 40 on the top mold member 20 and the PSG layer 42 on the bottom mold member 30. The phosphosilicate glass is then reflowed (Step G). Approximately .5 microns of undoped polysilicon is then deposited (Step M) on the bottom mold member 30. The bottom mold member 30 is then subject to wet oxidation (Step V) to form an oxide of approximately 1 micron. The resultant silicon dioxide layer 44 is illustrated in Figure 3d. Approximately .5 microns of undoped polysilicon is then deposited (Step M) on the bottom mold member 30 once again. The bottom mold member 30 is then subject to wet oxidation (Step V) to form an oxide of approximately 1 micron. The resultant silicon dioxide layer 46 is illustrated in Figure 3e. The top mold member 20 is then aligned with the bottom mold member 30. Standard techniques, including microscopic viewing techniques and alignment marks may be used in this step. The mold members are then pressure bonded together to produce the device of Figure 3f. 10 At this point, the needle can be formed by depositing a conformal substance into the mold. In particular, the conformal substance is passed through the deposition apertures into the enclosed, elongated needle trench. For example, approximately .3 microns of undoped polysilicon (Step M) may be deposited. Thereafter, a nitrogen anneal (Step O) is performed. The foregoing polysilicon and nitrogen anneal steps are repeated until the desired thickness of polysilicon is achieved. Six to fifteen microns of polysilicon is typical, depending on the strength and stiffness requirements. The resultant device is illustrated in Figure 3g. In particular, the figure shows a polysilicon layer 50. The polysilicon layer 60 within the trench 34 defines a needle. Figure 3h provides a perspective view of the device at this processing juncture. An anisotropic polysilicon etch on the top side of the wafer sandwich of Figures 3g and 3h is then performed (Step N). The polysilicon thickness and a 75% over-etch are preferably performed. This operation results in the device of Figure 3i. An anisotropic polysilicon etch on the bottom side of the wafer sandwich is then performed. The polysilicon thickness and a 25% over-etch are preferably performed, resulting in the device of Figure 3j. The sacrificial phosphosilicate glass layers 42 and 44 are then removed (Step S). The top mold member 20 and the bottom mold member 30 are then separated, and the resultant needle is released. Figure 3k is a side view of the separated top mold member 20, bottom mold member 30, and released needle 60. Figure 31 is a perspective view of the separated top mold member 20, bottom mold member 30, and released needle 60. The released needle and mold members are then rinsed in DI water. The needle may be used at this point and the mold members may be re-used. Figure 4 is a perspective view of a needle 70 constructed in accordance with the disclosed processing steps. The needle 70 includes a fluid input port 72 and a set of fluid outlet ports 74. The operations described in relation to Figure 1 are altered to produce additional deposition apertures in the top mold member so that the additional fluid outlet ports 74 may be provided. Observe that each deposition aperture in the top mold member results in a port in the resultant needle. Figure 5 is a perspective view of another needle 80 constructed in accordance with the processing steps of the invention. The needle 80 includes removal inhibiting 11 barbs 82 and insertion limiting barbs 84. The operations described in relation to Figure 2 are altered to provide a bottom mold member with the configuration corresponding to the barbs 82 and 84. Figure 6 is a perspective view of another needle 90 constructed in accordance with the processing steps of the invention. The needle 90 includes strength enhancement features. In accordance with the invention, strength enhancement features may be in the form of ribs, coatings, or bands. Figure 6 illustrates internal ribs 92 for strength enhancement. Figure 7 is an enlarged view of the region 94 of Figure 6. Figure 7 provides a more detailed view of the internal ribs 92. The operations described in relation to Figure 2 are altered to provide the bottom mold member with ribs. Figure 8 is a perspective view of a dual prong needle 100 constructed in accordance with the processing steps of the invention. The needle 100 includes a first prong 102 and a second prong 104 joined at a hub 106. The operations described in relation to Figure 2 arc altered to provide the bottom mold member with the a trench to form the first prong 102 and a trench to form the second prong 104. Figure 9 is a perspective view of yet another needle 110 constructed in accordance with the processing steps of the invention. The needle 110 includes circuitry 112. The circuitry that may be incorporated into a needle of the invention includes electrodes, amplification circuitry, pumps, and biological sensors. Since the needle 110 is formed of polysilicon, standard processing techniques may be used to add the circuitry 112 to the needle 110. Those skilled in the art will appreciate that various other geometries may be constructed in accordance with the disclosed processing steps. For example, multiple fluid cannulas, pumps, heaters, electrodes, and amplification circuitry may readily be incorporated into the needles of the invention. The simple needle shown in the figures can have any or all of these features added to it by easy modifications of the etch masks of the molds. To fabricate features or components of the needle such as heaters, electrodes, .and amplification circuitry, the release etch must be timed such that the molds are separated, but the needles are still embedded in the mold cavities of the bottom mold wafer. This partial release process step may be aided by using only silicon dioxide as the release layer around the needle, but still using PSG for the wafer 12 to wafer bonding. This change will aid partial release because PSG is etched much faster than silicon dioxide. After this step, further processing can be done to the bottom mold wafer alone to put the features or components mentioned above on the needles. Heaters and/or electrodes can be fabricated by a metal or doped polysilicon deposition and subsequent masking and etching. Amplification circuitry can be added using a CMOS, NMOS, bipolar or FET process. All features that are made of materials other than silicon may be damaged by the concentrated HF release etch, so they should be protected by a layer of polysilicon or other material that is resistant to HF. Needles of the invention have been fabricated on a 100 mm wafer. In particular, over a 1000 needles with lengths of 3 and 6 mm have been fabricated with a 100 mm wafer. Needles up to two inches long may be fabricated in accordance with the invention. For such an embodiment, the deposition apertures in the top mold member 20 must be enlarged. The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the invention. In other instances, well known circuits and devices are shown in block diagram form in order to avoid unnecessary distraction from the underlying invention. Thus, the foregoing descriptions of specific embodiments of the present invention are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, obviously many modifications and variations are possible in view of d e above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following Claims and their equivalents. 13

Claims: IN THE CLAIMS: 1. A method of fabricating a needle via conformal deposition in a two-piece mold, said method comprising the steps of: attaching a top mold member to a bottom mold member such that said top mold member and said bottom mold member define an enclosed, elongated needle trench with a deposition aperture; and passing a conformal substance through said deposition aperture such that said conformal substance is deposited within said enclosed, elongated needle trench. 2. The method of claim 1 wherein said passing step includes the step of passing polysilicon through said deposition aperture. 3. The method of claim 2 wherein said passing step is repeated until said polysilicon is deposited to a desired depth. 4. The method of claim 1 wherein said passing step includes the step of passing said conformal substance through said deposition aperture such that said conformal substance is deposited within said enclosed, elongated needle trench, which defines a dual prong needle. 5. The method of claim 1 wherein said passing step includes the step of passing said conformal substance through said deposition aperture such that said conformal substance is deposited within said enclosed, elongated needle trench, which defines a barb. 6. The method of claim 1 wherein said passing step includes the step of passing said conformal substance through said deposition aperture such that said conformal substance is deposited within said enclosed, elongated needle trench, which defines a a strength enhancement feature. 7. A needle fabricated by the method of claim 1. 14 8. A needle fabricated by the method of claim 2. 9. A needle fabricated by the method of claim 4. 10. A needle fabricated by the method of claim 5. 11. A needle fabricated by the method of claim 6. 12. A two-piece mold for use in conformally constructing a needle, comprising: a top mold member; and a bottom mold member connected to said top mold member, said bottom mold member and said top mold member defining an enclosed elongated needle trench with a deposition aperture. 13. The two-piece mold of claim 12 wherein said top mold member defines said deposition aperture. 14. The two-piece mold of claim 13 wherein said top mold member defines a plurality of deposition apertures. 15. The two-piece mold of claim 14 wherein said deposition aperture allows a conformal substance to enter said enclosed, elongated needle trench such that said conformal substance is deposited within said enclosed, elongated needle trench, except at said deposition aperture where a fluid port aperture results. 16. The two-piece mold of claim 12 wherein said bottom mold member defines said elongated needle trench. 15

Inventors: KELLER CHRISTOPHER G, PISANO ALBERT P, TALBOT NEIL H, KELLER, CHRISTOPHER, G., PISANO, ALBERT, P., TALBOT, NEIL, H.
Applicants: UNIV CALIFORNIA, THE REGENTS OF THE UNIVERSITY OF CALIFORNIA
Application year: 1999
Main classification: B29C67
IPC codes: A61M5, B22C9, B29C33